Merge master

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.gitattributes

@@ -1,63 +0,0 @@
-###############################################################################
-# Set default behavior to automatically normalize line endings.
-###############################################################################
-* text=auto
-
-###############################################################################
-# Set default behavior for command prompt diff.
-#
-# This is need for earlier builds of msysgit that does not have it on by
-# default for csharp files.
-# Note: This is only used by command line
-###############################################################################
-#*.cs     diff=csharp
-
-###############################################################################
-# Set the merge driver for project and solution files
-#
-# Merging from the command prompt will add diff markers to the files if there
-# are conflicts (Merging from VS is not affected by the settings below, in VS
-# the diff markers are never inserted). Diff markers may cause the following 
-# file extensions to fail to load in VS. An alternative would be to treat
-# these files as binary and thus will always conflict and require user
-# intervention with every merge. To do so, just uncomment the entries below
-###############################################################################
-#*.sln       merge=binary
-#*.csproj    merge=binary
-#*.vbproj    merge=binary
-#*.vcxproj   merge=binary
-#*.vcproj    merge=binary
-#*.dbproj    merge=binary
-#*.fsproj    merge=binary
-#*.lsproj    merge=binary
-#*.wixproj   merge=binary
-#*.modelproj merge=binary
-#*.sqlproj   merge=binary
-#*.wwaproj   merge=binary
-
-###############################################################################
-# behavior for image files
-#
-# image files are treated as binary by default.
-###############################################################################
-#*.jpg   binary
-#*.png   binary
-#*.gif   binary
-
-###############################################################################
-# diff behavior for common document formats
-# 
-# Convert binary document formats to text before diffing them. This feature
-# is only available from the command line. Turn it on by uncommenting the 
-# entries below.
-###############################################################################
-#*.doc   diff=astextplain
-#*.DOC   diff=astextplain
-#*.docx  diff=astextplain
-#*.DOCX  diff=astextplain
-#*.dot   diff=astextplain
-#*.DOT   diff=astextplain
-#*.pdf   diff=astextplain
-#*.PDF   diff=astextplain
-#*.rtf   diff=astextplain
-#*.RTF   diff=astextplain

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -0,0 +1,77 @@
+name: 🐛 Bug report
+description: Report broken functionality.
+labels: [bug]
+
+body:
+  - type: markdown
+    attributes:
+      value: |
+        - Avoid generic or vague titles such as "Something's not working" or "A couple of problems" — be as descriptive as possible.
+        - Keep your issue focused on one single problem. If you have multiple bug reports, please create a separate issue for each of them.
+        - Issues should represent **complete and actionable** work items. If you are unsure about something or have a question, please start a [discussion](https://github.com/Tyrrrz/CliFx/discussions/new) instead.
+        - Remember that **CliFx** is an open-source project funded by the community. If you find it useful, **please consider [donating](https://tyrrrz.me/donate) to support its development**.
+
+        ___
+
+  - type: input
+    attributes:
+      label: Version
+      description: Which version of the package does this bug affect? Make sure you're not using an outdated version.
+      placeholder: v1.0.0
+    validations:
+      required: true
+
+  - type: input
+    attributes:
+      label: Platform
+      description: Which platform do you experience this bug on?
+      placeholder: .NET 7.0 / Windows 11
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: Steps to reproduce
+      description: >
+        Minimum steps required to reproduce the bug, including prerequisites, code snippets, or other relevant items.
+        The information provided in this field must be readily actionable, meaning that anyone should be able to reproduce the bug by following these steps.
+        If the reproduction steps are too complex to fit in this field, please provide a link to a repository instead.
+      placeholder: |
+        - Step 1
+        - Step 2
+        - Step 3
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: Details
+      description: Clear and thorough explanation of the bug, including any additional information you may find relevant.
+      placeholder: |
+        - Expected behavior: ...
+        - Actual behavior: ...
+    validations:
+      required: true
+
+  - type: checkboxes
+    attributes:
+      label: Checklist
+      description: Quick list of checks to ensure that everything is in order.
+      options:
+        - label: I have looked through existing issues to make sure that this bug has not been reported before
+          required: true
+        - label: I have provided a descriptive title for this issue
+          required: true
+        - label: I have made sure that this bug is reproducible on the latest version of the package
+          required: true
+        - label: I have provided all the information needed to reproduce this bug as efficiently as possible
+          required: true
+        - label: I have sponsored this project
+          required: false
+        - label: I have not read any of the above and just checked all the boxes to submit the issue
+          required: false
+
+  - type: markdown
+    attributes:
+      value: |
+        If you are struggling to provide actionable reproduction steps, or if something else is preventing you from creating a complete bug report, please start a [discussion](https://github.com/Tyrrrz/CliFx/discussions/new) instead.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,11 @@
+blank_issues_enabled: false
+contact_links:
+  - name: ⚠ Feature request
+    url: https://github.com/Tyrrrz/.github/blob/master/docs/project-status.md
+    about: Sorry, but this project is in maintenance mode and no longer accepts new feature requests.
+  - name: 🗨 Discussions
+    url: https://github.com/Tyrrrz/CliFx/discussions/new
+    about: Ask and answer questions.
+  - name: 💬 Discord server
+    url: https://discord.gg/2SUWKFnHSm
+    about: Chat with the project community.

.github/dependabot.yml

@@ -0,0 +1,22 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: monthly
+    labels:
+      - enhancement
+    groups:
+      actions:
+        patterns:
+          - "*"
+  - package-ecosystem: nuget
+    directory: "/"
+    schedule:
+      interval: monthly
+    labels:
+      - enhancement
+    groups:
+      nuget:
+        patterns:
+          - "*"

.github/workflows/main.yml

@@ -0,0 +1,34 @@
+name: main
+
+on:
+  workflow_dispatch:
+    inputs:
+      package-version:
+        type: string
+        description: Package version
+        required: false
+      deploy:
+        type: boolean
+        description: Deploy package
+        required: false
+        default: false
+  push:
+    branches:
+      - master
+    tags:
+      - "*"
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  main:
+    uses: Tyrrrz/.github/.github/workflows/nuget.yml@master
+    with:
+      deploy: ${{ inputs.deploy || github.ref_type == 'tag' }}
+      package-version: ${{ inputs.package-version || (github.ref_type == 'tag' && github.ref_name) || format('0.0.0-ci-{0}', github.sha) }}
+      dotnet-version: 9.0.x
+    secrets:
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+      NUGET_TOKEN: ${{ secrets.NUGET_TOKEN }}
+      DISCORD_WEBHOOK: ${{ secrets.DISCORD_WEBHOOK }}

.gitignore

@@ -1,340 +1,12 @@
-## Ignore Visual Studio temporary files, build results, and
-## files generated by popular Visual Studio add-ons.
-##
-## Get latest from https://github.com/github/gitignore/blob/master/VisualStudio.gitignore
-
 # User-specific files
-*.rsuser
+.vs/
+.idea/
 *.suo
 *.user
-*.userosscache
-*.sln.docstates
-
-# User-specific files (MonoDevelop/Xamarin Studio)
-*.userprefs
 
 # Build results
-[Dd]ebug/
-[Dd]ebugPublic/
-[Rr]elease/
-[Rr]eleases/
-x64/
-x86/
-[Aa][Rr][Mm]/
-[Aa][Rr][Mm]64/
-bld/
-[Bb]in/
-[Oo]bj/
-[Ll]og/
+bin/
+obj/
 
-# Visual Studio 2015/2017 cache/options directory
-.vs/
-# Uncomment if you have tasks that create the project's static files in wwwroot
-#wwwroot/
-
-# Visual Studio 2017 auto generated files
-Generated\ Files/
-
-# MSTest test Results
-[Tt]est[Rr]esult*/
-[Bb]uild[Ll]og.*
-
-# NUNIT
-*.VisualState.xml
-TestResult.xml
-
-# Build Results of an ATL Project
-[Dd]ebugPS/
-[Rr]eleasePS/
-dlldata.c
-
-# Benchmark Results
-BenchmarkDotNet.Artifacts/
-
-# .NET Core
-project.lock.json
-project.fragment.lock.json
-artifacts/
-
-# StyleCop
-StyleCopReport.xml
-
-# Files built by Visual Studio
-*_i.c
-*_p.c
-*_h.h
-*.ilk
-*.meta
-*.obj
-*.iobj
-*.pch
-*.pdb
-*.ipdb
-*.pgc
-*.pgd
-*.rsp
-*.sbr
-*.tlb
-*.tli
-*.tlh
-*.tmp
-*.tmp_proj
-*_wpftmp.csproj
-*.log
-*.vspscc
-*.vssscc
-.builds
-*.pidb
-*.svclog
-*.scc
-
-# Chutzpah Test files
-_Chutzpah*
-
-# Visual C++ cache files
-ipch/
-*.aps
-*.ncb
-*.opendb
-*.opensdf
-*.sdf
-*.cachefile
-*.VC.db
-*.VC.VC.opendb
-
-# Visual Studio profiler
-*.psess
-*.vsp
-*.vspx
-*.sap
-
-# Visual Studio Trace Files
-*.e2e
-
-# TFS 2012 Local Workspace
-$tf/
-
-# Guidance Automation Toolkit
-*.gpState
-
-# ReSharper is a .NET coding add-in
-_ReSharper*/
-*.[Rr]e[Ss]harper
-*.DotSettings.user
-
-# JustCode is a .NET coding add-in
-.JustCode
-
-# TeamCity is a build add-in
-_TeamCity*
-
-# DotCover is a Code Coverage Tool
-*.dotCover
-
-# AxoCover is a Code Coverage Tool
-.axoCover/*
-!.axoCover/settings.json
-
-# Visual Studio code coverage results
-*.coverage
-*.coveragexml
-
-# NCrunch
-_NCrunch_*
-.*crunch*.local.xml
-nCrunchTemp_*
-
-# MightyMoose
-*.mm.*
-AutoTest.Net/
-
-# Web workbench (sass)
-.sass-cache/
-
-# Installshield output folder
-[Ee]xpress/
-
-# DocProject is a documentation generator add-in
-DocProject/buildhelp/
-DocProject/Help/*.HxT
-DocProject/Help/*.HxC
-DocProject/Help/*.hhc
-DocProject/Help/*.hhk
-DocProject/Help/*.hhp
-DocProject/Help/Html2
-DocProject/Help/html
-
-# Click-Once directory
-publish/
-
-# Publish Web Output
-*.[Pp]ublish.xml
-*.azurePubxml
-# Note: Comment the next line if you want to checkin your web deploy settings,
-# but database connection strings (with potential passwords) will be unencrypted
-*.pubxml
-*.publishproj
-
-# Microsoft Azure Web App publish settings. Comment the next line if you want to
-# checkin your Azure Web App publish settings, but sensitive information contained
-# in these scripts will be unencrypted
-PublishScripts/
-
-# NuGet Packages
-*.nupkg
-# The packages folder can be ignored because of Package Restore
-**/[Pp]ackages/*
-# except build/, which is used as an MSBuild target.
-!**/[Pp]ackages/build/
-# Uncomment if necessary however generally it will be regenerated when needed
-#!**/[Pp]ackages/repositories.config
-# NuGet v3's project.json files produces more ignorable files
-*.nuget.props
-*.nuget.targets
-
-# Microsoft Azure Build Output
-csx/
-*.build.csdef
-
-# Microsoft Azure Emulator
-ecf/
-rcf/
-
-# Windows Store app package directories and files
-AppPackages/
-BundleArtifacts/
-Package.StoreAssociation.xml
-_pkginfo.txt
-*.appx
-
-# Visual Studio cache files
-# files ending in .cache can be ignored
-*.[Cc]ache
-# but keep track of directories ending in .cache
-!?*.[Cc]ache/
-
-# Others
-ClientBin/
-~$*
-*~
-*.dbmdl
-*.dbproj.schemaview
-*.jfm
-*.pfx
-*.publishsettings
-orleans.codegen.cs
-
-# Including strong name files can present a security risk
-# (https://github.com/github/gitignore/pull/2483#issue-259490424)
-#*.snk
-
-# Since there are multiple workflows, uncomment next line to ignore bower_components
-# (https://github.com/github/gitignore/pull/1529#issuecomment-104372622)
-#bower_components/
-
-# RIA/Silverlight projects
-Generated_Code/
-
-# Backup & report files from converting an old project file
-# to a newer Visual Studio version. Backup files are not needed,
-# because we have git ;-)
-_UpgradeReport_Files/
-Backup*/
-UpgradeLog*.XML
-UpgradeLog*.htm
-ServiceFabricBackup/
-*.rptproj.bak
-
-# SQL Server files
-*.mdf
-*.ldf
-*.ndf
-
-# Business Intelligence projects
-*.rdl.data
-*.bim.layout
-*.bim_*.settings
-*.rptproj.rsuser
-*- Backup*.rdl
-
-# Microsoft Fakes
-FakesAssemblies/
-
-# GhostDoc plugin setting file
-*.GhostDoc.xml
-
-# Node.js Tools for Visual Studio
-.ntvs_analysis.dat
-node_modules/
-
-# Visual Studio 6 build log
-*.plg
-
-# Visual Studio 6 workspace options file
-*.opt
-
-# Visual Studio 6 auto-generated workspace file (contains which files were open etc.)
-*.vbw
-
-# Visual Studio LightSwitch build output
-**/*.HTMLClient/GeneratedArtifacts
-**/*.DesktopClient/GeneratedArtifacts
-**/*.DesktopClient/ModelManifest.xml
-**/*.Server/GeneratedArtifacts
-**/*.Server/ModelManifest.xml
-_Pvt_Extensions
-
-# Paket dependency manager
-.paket/paket.exe
-paket-files/
-
-# FAKE - F# Make
-.fake/
-
-# JetBrains Rider
-.idea/
-*.sln.iml
-
-# CodeRush personal settings
-.cr/personal
-
-# Python Tools for Visual Studio (PTVS)
-__pycache__/
-*.pyc
-
-# Cake - Uncomment if you are using it
-# tools/**
-# !tools/packages.config
-
-# Tabs Studio
-*.tss
-
-# Telerik's JustMock configuration file
-*.jmconfig
-
-# BizTalk build output
-*.btp.cs
-*.btm.cs
-*.odx.cs
-*.xsd.cs
-
-# OpenCover UI analysis results
-OpenCover/
-
-# Azure Stream Analytics local run output
-ASALocalRun/
-
-# MSBuild Binary and Structured Log
-*.binlog
-
-# NVidia Nsight GPU debugger configuration file
-*.nvuser
-
-# MFractors (Xamarin productivity tool) working folder
-.mfractor/
-
-# Local History for Visual Studio
-.localhistory/
-
-# BeatPulse healthcheck temp database
-healthchecksdb
+# Test results
+TestResults/

CliFx.Benchmarks/Benchmarks.CliFx.cs

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Benchmarks;
+
+public partial class Benchmarks
+{
+    [Command]
+    public class CliFxCommand : ICommand
+    {
+        [CommandOption("str", 's')]
+        public string? StrOption { get; set; }
+
+        [CommandOption("int", 'i')]
+        public int IntOption { get; set; }
+
+        [CommandOption("bool", 'b')]
+        public bool BoolOption { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+
+    [Benchmark(Description = "CliFx", Baseline = true)]
+    public async ValueTask<int> ExecuteWithCliFx() =>
+        await new CliApplicationBuilder()
+            .AddCommand<CliFxCommand>()
+            .Build()
+            .RunAsync(Arguments, new Dictionary<string, string>());
+}

CliFx.Benchmarks/Benchmarks.Clipr.cs

@@ -0,0 +1,24 @@
+using BenchmarkDotNet.Attributes;
+using clipr;
+
+namespace CliFx.Benchmarks;
+
+public partial class Benchmarks
+{
+    public class CliprCommand
+    {
+        [NamedArgument('s', "str")]
+        public string? StrOption { get; set; }
+
+        [NamedArgument('i', "int")]
+        public int IntOption { get; set; }
+
+        [NamedArgument('b', "bool", Constraint = NumArgsConstraint.Optional, Const = true)]
+        public bool BoolOption { get; set; }
+
+        public void Execute() { }
+    }
+
+    [Benchmark(Description = "Clipr")]
+    public void ExecuteWithClipr() => CliParser.Parse<CliprCommand>(Arguments).Execute();
+}

CliFx.Benchmarks/Benchmarks.Cocona.cs

@@ -0,0 +1,19 @@
+using BenchmarkDotNet.Attributes;
+using Cocona;
+
+namespace CliFx.Benchmarks;
+
+public partial class Benchmarks
+{
+    public class CoconaCommand
+    {
+        public void Execute(
+            [Option("str", ['s'])] string? strOption,
+            [Option("int", ['i'])] int intOption,
+            [Option("bool", ['b'])] bool boolOption
+        ) { }
+    }
+
+    [Benchmark(Description = "Cocona")]
+    public void ExecuteWithCocona() => CoconaApp.Run<CoconaCommand>(Arguments);
+}

CliFx.Benchmarks/Benchmarks.CommandLineParser.cs

@@ -0,0 +1,27 @@
+using BenchmarkDotNet.Attributes;
+using CommandLine;
+
+namespace CliFx.Benchmarks;
+
+public partial class Benchmarks
+{
+    public class CommandLineParserCommand
+    {
+        [Option('s', "str")]
+        public string? StrOption { get; set; }
+
+        [Option('i', "int")]
+        public int IntOption { get; set; }
+
+        [Option('b', "bool")]
+        public bool BoolOption { get; set; }
+
+        public void Execute() { }
+    }
+
+    [Benchmark(Description = "CommandLineParser")]
+    public void ExecuteWithCommandLineParser() =>
+        new Parser()
+            .ParseArguments(Arguments, typeof(CommandLineParserCommand))
+            .WithParsed<CommandLineParserCommand>(c => c.Execute());
+}

CliFx.Benchmarks/Benchmarks.McMaster.cs

@@ -0,0 +1,24 @@
+using BenchmarkDotNet.Attributes;
+using McMaster.Extensions.CommandLineUtils;
+
+namespace CliFx.Benchmarks;
+
+public partial class Benchmarks
+{
+    public class McMasterCommand
+    {
+        [Option("--str|-s")]
+        public string? StrOption { get; set; }
+
+        [Option("--int|-i")]
+        public int IntOption { get; set; }
+
+        [Option("--bool|-b")]
+        public bool BoolOption { get; set; }
+
+        public int OnExecute() => 0;
+    }
+
+    [Benchmark(Description = "McMaster.Extensions.CommandLineUtils")]
+    public int ExecuteWithMcMaster() => CommandLineApplication.Execute<McMasterCommand>(Arguments);
+}

CliFx.Benchmarks/Benchmarks.PowerArgs.cs

@@ -0,0 +1,24 @@
+using BenchmarkDotNet.Attributes;
+using PowerArgs;
+
+namespace CliFx.Benchmarks;
+
+public partial class Benchmarks
+{
+    public class PowerArgsCommand
+    {
+        [ArgShortcut("--str"), ArgShortcut("-s")]
+        public string? StrOption { get; set; }
+
+        [ArgShortcut("--int"), ArgShortcut("-i")]
+        public int IntOption { get; set; }
+
+        [ArgShortcut("--bool"), ArgShortcut("-b")]
+        public bool BoolOption { get; set; }
+
+        public void Main() { }
+    }
+
+    [Benchmark(Description = "PowerArgs")]
+    public void ExecuteWithPowerArgs() => Args.InvokeMain<PowerArgsCommand>(Arguments);
+}

CliFx.Benchmarks/Benchmarks.SystemCommandLine.cs

@@ -0,0 +1,33 @@
+using System.CommandLine;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+
+namespace CliFx.Benchmarks;
+
+public partial class Benchmarks
+{
+    public class SystemCommandLineCommand
+    {
+        public static void ExecuteHandler(string s, int i, bool b) { }
+
+        public Task<int> ExecuteAsync(string[] args)
+        {
+            var stringOption = new Option<string>(["--str", "-s"]);
+            var intOption = new Option<int>(["--int", "-i"]);
+            var boolOption = new Option<bool>(["--bool", "-b"]);
+
+            var command = new RootCommand();
+            command.AddOption(stringOption);
+            command.AddOption(intOption);
+            command.AddOption(boolOption);
+
+            command.SetHandler(ExecuteHandler, stringOption, intOption, boolOption);
+
+            return command.InvokeAsync(args);
+        }
+    }
+
+    [Benchmark(Description = "System.CommandLine")]
+    public async Task<int> ExecuteWithSystemCommandLine() =>
+        await new SystemCommandLineCommand().ExecuteAsync(Arguments);
+}

CliFx.Benchmarks/Benchmarks.cs

@@ -0,0 +1,18 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Configs;
+using BenchmarkDotNet.Order;
+using BenchmarkDotNet.Running;
+
+namespace CliFx.Benchmarks;
+
+[RankColumn]
+[Orderer(SummaryOrderPolicy.FastestToSlowest)]
+public partial class Benchmarks
+{
+    private static readonly string[] Arguments = ["--str", "hello world", "-i", "13", "-b"];
+
+    public static void Main() =>
+        BenchmarkRunner.Run<Benchmarks>(
+            DefaultConfig.Instance.WithOptions(ConfigOptions.DisableOptimizationsValidator)
+        );
+}

CliFx.Benchmarks/CliFx.Benchmarks.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+    <NuGetAudit>false</NuGetAudit>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="BenchmarkDotNet" Version="0.14.0" />
+    <PackageReference Include="clipr" Version="1.6.1" />
+    <PackageReference Include="Cocona" Version="2.2.0" />
+    <PackageReference Include="CommandLineParser" Version="2.9.1" />
+    <PackageReference Include="CSharpier.MsBuild" Version="0.30.6" PrivateAssets="all" />
+    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="4.1.1" />
+    <PackageReference Include="PowerArgs" Version="4.0.3" />
+    <PackageReference Include="System.CommandLine" Version="2.0.0-beta4.22272.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\CliFx\CliFx.csproj" />
+  </ItemGroup>
+
+</Project>

CliFx.Benchmarks/Readme.md

@@ -0,0 +1,22 @@
+## CliFx.Benchmarks
+
+All benchmarks below were ran with the following configuration:
+
+```ini
+BenchmarkDotNet=v0.12.0, OS=Windows 10.0.14393.3443 (1607/AnniversaryUpdate/Redstone1)
+Intel Core i5-4460 CPU 3.20GHz (Haswell), 1 CPU, 4 logical and 4 physical cores
+Frequency=3124994 Hz, Resolution=320.0006 ns, Timer=TSC
+.NET Core SDK=3.1.100
+  [Host]     : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT
+  DefaultJob : .NET Core 3.1.0 (CoreCLR 4.700.19.56402, CoreFX 4.700.19.56404), X64 RyuJIT
+```
+
+| Method                               |        Mean |     Error |     StdDev | Ratio | RatioSD | Rank |
+| ------------------------------------ | ----------: | --------: | ---------: | ----: | ------: | ---: |
+| CommandLineParser                    |    24.79 us |  0.166 us |   0.155 us |  0.49 |    0.00 |    1 |
+| CliFx                                |    50.27 us |  0.248 us |   0.232 us |  1.00 |    0.00 |    2 |
+| Clipr                                |   160.22 us |  0.817 us |   0.764 us |  3.19 |    0.02 |    3 |
+| McMaster.Extensions.CommandLineUtils |   166.45 us |  1.111 us |   1.039 us |  3.31 |    0.03 |    4 |
+| System.CommandLine                   |   170.27 us |  0.599 us |   0.560 us |  3.39 |    0.02 |    5 |
+| PowerArgs                            |   306.12 us |  1.495 us |   1.398 us |  6.09 |    0.03 |    6 |
+| Cocona                               | 1,856.07 us | 48.727 us | 141.367 us | 37.88 |    2.60 |    7 |

CliFx.Demo/CliFx.Demo.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+    <ApplicationIcon>../favicon.ico</ApplicationIcon>
+    <PublishAot>true</PublishAot>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="CSharpier.MsBuild" Version="0.30.6" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\CliFx\CliFx.csproj" />
+    <ProjectReference Include="..\CliFx.SourceGeneration\CliFx.SourceGeneration.csproj" ReferenceOutputAssembly="false" OutputItemType="analyzer" />
+  </ItemGroup>
+
+</Project>

CliFx.Demo/Commands/BookAddCommand.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Demo.Domain;
+using CliFx.Demo.Utils;
+using CliFx.Exceptions;
+using CliFx.Infrastructure;
+
+namespace CliFx.Demo.Commands;
+
+[Command("book add", Description = "Adds a book to the library.")]
+public class BookAddCommand(LibraryProvider libraryProvider) : ICommand
+{
+    [CommandParameter(0, Name = "title", Description = "Book title.")]
+    public required string Title { get; init; }
+
+    [CommandOption("author", 'a', Description = "Book author.")]
+    public required string Author { get; init; }
+
+    [CommandOption("published", 'p', Description = "Book publish date.")]
+    public DateTimeOffset Published { get; init; } =
+        new(
+            Random.Shared.Next(1800, 2020),
+            Random.Shared.Next(1, 12),
+            Random.Shared.Next(1, 28),
+            Random.Shared.Next(1, 23),
+            Random.Shared.Next(1, 59),
+            Random.Shared.Next(1, 59),
+            TimeSpan.Zero
+        );
+
+    [CommandOption("isbn", 'n', Description = "Book ISBN.")]
+    public Isbn Isbn { get; init; } =
+        new(
+            Random.Shared.Next(0, 999),
+            Random.Shared.Next(0, 99),
+            Random.Shared.Next(0, 99999),
+            Random.Shared.Next(0, 99),
+            Random.Shared.Next(0, 9)
+        );
+
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        if (libraryProvider.TryGetBook(Title) is not null)
+            throw new CommandException($"Book '{Title}' already exists.", 10);
+
+        var book = new Book(Title, Author, Published, Isbn);
+        libraryProvider.AddBook(book);
+
+        console.WriteLine($"Book '{Title}' added.");
+        console.WriteBook(book);
+
+        return default;
+    }
+}

CliFx.Demo/Commands/BookCommand.cs

@@ -0,0 +1,27 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Demo.Domain;
+using CliFx.Demo.Utils;
+using CliFx.Exceptions;
+using CliFx.Infrastructure;
+
+namespace CliFx.Demo.Commands;
+
+[Command("book", Description = "Retrieves a book from the library.")]
+public class BookCommand(LibraryProvider libraryProvider) : ICommand
+{
+    [CommandParameter(0, Name = "title", Description = "Title of the book to retrieve.")]
+    public required string Title { get; init; }
+
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        var book = libraryProvider.TryGetBook(Title);
+
+        if (book is null)
+            throw new CommandException($"Book '{Title}' not found.", 10);
+
+        console.WriteBook(book);
+
+        return default;
+    }
+}

CliFx.Demo/Commands/BookListCommand.cs

@@ -0,0 +1,29 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Demo.Domain;
+using CliFx.Demo.Utils;
+using CliFx.Infrastructure;
+
+namespace CliFx.Demo.Commands;
+
+[Command("book list", Description = "Lists all books in the library.")]
+public class BookListCommand(LibraryProvider libraryProvider) : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        var library = libraryProvider.GetLibrary();
+
+        for (var i = 0; i < library.Books.Count; i++)
+        {
+            // Add margin
+            if (i != 0)
+                console.WriteLine();
+
+            // Render book
+            var book = library.Books[i];
+            console.WriteBook(book);
+        }
+
+        return default;
+    }
+}

CliFx.Demo/Commands/BookRemoveCommand.cs

@@ -0,0 +1,28 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Demo.Domain;
+using CliFx.Exceptions;
+using CliFx.Infrastructure;
+
+namespace CliFx.Demo.Commands;
+
+[Command("book remove", Description = "Removes a book from the library.")]
+public class BookRemoveCommand(LibraryProvider libraryProvider) : ICommand
+{
+    [CommandParameter(0, Name = "title", Description = "Title of the book to remove.")]
+    public required string Title { get; init; }
+
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        var book = libraryProvider.TryGetBook(Title);
+
+        if (book is null)
+            throw new CommandException($"Book '{Title}' not found.", 10);
+
+        libraryProvider.RemoveBook(book);
+
+        console.WriteLine($"Book '{Title}' removed.");
+
+        return default;
+    }
+}

CliFx.Demo/Domain/Book.cs

@@ -0,0 +1,5 @@
+using System;
+
+namespace CliFx.Demo.Domain;
+
+public record Book(string Title, string Author, DateTimeOffset Published, Isbn Isbn);

CliFx.Demo/Domain/Isbn.cs

@@ -0,0 +1,31 @@
+using System;
+
+namespace CliFx.Demo.Domain;
+
+public partial record Isbn(
+    int EanPrefix,
+    int RegistrationGroup,
+    int Registrant,
+    int Publication,
+    int CheckDigit
+)
+{
+    public override string ToString() =>
+        $"{EanPrefix:000}-{RegistrationGroup:00}-{Registrant:00000}-{Publication:00}-{CheckDigit:0}";
+}
+
+public partial record Isbn
+{
+    public static Isbn Parse(string value, IFormatProvider formatProvider)
+    {
+        var components = value.Split('-', 5, StringSplitOptions.RemoveEmptyEntries);
+
+        return new Isbn(
+            int.Parse(components[0], formatProvider),
+            int.Parse(components[1], formatProvider),
+            int.Parse(components[2], formatProvider),
+            int.Parse(components[3], formatProvider),
+            int.Parse(components[4], formatProvider)
+        );
+    }
+}

CliFx.Demo/Domain/Library.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace CliFx.Demo.Domain;
+
+public partial record Library(IReadOnlyList<Book> Books)
+{
+    public Library WithBook(Book book)
+    {
+        var books = Books.ToList();
+        books.Add(book);
+
+        return new Library(books);
+    }
+
+    public Library WithoutBook(Book book)
+    {
+        var books = Books.Where(b => b != book).ToArray();
+
+        return new Library(books);
+    }
+}
+
+public partial record Library
+{
+    public static Library Empty { get; } = new([]);
+}

CliFx.Demo/Domain/LibraryJsonContext.cs

@@ -0,0 +1,6 @@
+using System.Text.Json.Serialization;
+
+namespace CliFx.Demo.Domain;
+
+[JsonSerializable(typeof(Library))]
+public partial class LibraryJsonContext : JsonSerializerContext;

CliFx.Demo/Domain/LibraryProvider.cs

@@ -0,0 +1,43 @@
+using System.IO;
+using System.Linq;
+using System.Text.Json;
+
+namespace CliFx.Demo.Domain;
+
+public class LibraryProvider
+{
+    private static string StorageFilePath { get; } =
+        Path.Combine(Directory.GetCurrentDirectory(), "Library.json");
+
+    private void StoreLibrary(Library library)
+    {
+        var data = JsonSerializer.Serialize(library, LibraryJsonContext.Default.Library);
+        File.WriteAllText(StorageFilePath, data);
+    }
+
+    public Library GetLibrary()
+    {
+        if (!File.Exists(StorageFilePath))
+            return Library.Empty;
+
+        var data = File.ReadAllText(StorageFilePath);
+
+        return JsonSerializer.Deserialize(data, LibraryJsonContext.Default.Library)
+            ?? Library.Empty;
+    }
+
+    public Book? TryGetBook(string title) =>
+        GetLibrary().Books.FirstOrDefault(b => b.Title == title);
+
+    public void AddBook(Book book)
+    {
+        var updatedLibrary = GetLibrary().WithBook(book);
+        StoreLibrary(updatedLibrary);
+    }
+
+    public void RemoveBook(Book book)
+    {
+        var updatedLibrary = GetLibrary().WithoutBook(book);
+        StoreLibrary(updatedLibrary);
+    }
+}

CliFx.Demo/Program.cs

@@ -0,0 +1,18 @@
+using CliFx;
+using CliFx.Demo.Domain;
+using Microsoft.Extensions.DependencyInjection;
+
+// We use Microsoft.Extensions.DependencyInjection for injecting dependencies in commands
+var services = new ServiceCollection();
+services.AddSingleton<LibraryProvider>();
+
+// Register all commands as transient services
+foreach (var commandType in commandTypes)
+    services.AddTransient(commandType);
+
+return await new CliApplicationBuilder()
+    .SetDescription("Demo application showcasing CliFx features.")
+    .AddCommandsFromThisAssembly()
+    .UseTypeActivator(services.BuildServiceProvider())
+    .Build()
+    .RunAsync();

CliFx.Demo/Readme.md

@@ -0,0 +1,5 @@
+# CliFx Demo Project
+
+Sample command-line interface for managing a library of books.
+
+This demo project showcases basic CliFx functionality such as command routing, argument parsing, and autogenerated help text.

CliFx.Demo/Utils/ConsoleExtensions.cs

@@ -0,0 +1,39 @@
+using System;
+using CliFx.Demo.Domain;
+using CliFx.Infrastructure;
+
+namespace CliFx.Demo.Utils;
+
+internal static class ConsoleExtensions
+{
+    public static void WriteBook(this ConsoleWriter writer, Book book)
+    {
+        // Title
+        using (writer.Console.WithForegroundColor(ConsoleColor.White))
+            writer.WriteLine(book.Title);
+
+        // Author
+        writer.Write("  ");
+        writer.Write("Author: ");
+
+        using (writer.Console.WithForegroundColor(ConsoleColor.White))
+            writer.WriteLine(book.Author);
+
+        // Published
+        writer.Write("  ");
+        writer.Write("Published: ");
+
+        using (writer.Console.WithForegroundColor(ConsoleColor.White))
+            writer.WriteLine($"{book.Published:d}");
+
+        // ISBN
+        writer.Write("  ");
+        writer.Write("ISBN: ");
+
+        using (writer.Console.WithForegroundColor(ConsoleColor.White))
+            writer.WriteLine(book.Isbn);
+    }
+
+    public static void WriteBook(this IConsole console, Book book) =>
+        console.Output.WriteBook(book);
+}

CliFx.SourceGeneration/CliFx.SourceGeneration.csproj

@@ -0,0 +1,27 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
+    <GenerateDependencyFile>true</GenerateDependencyFile>
+    <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
+    <NoWarn>$(NoWarn);RS1035</NoWarn>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <!--
+      Because this project only has a single target framework, the condition in
+      Directory.Build.props does not appear to work. This is a workaround for that.
+    -->
+    <Nullable>annotations</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="CSharpier.MsBuild" Version="0.28.2" PrivateAssets="all" />
+    <!-- Make sure to target the lowest possible version of the compiler for wider support -->
+    <PackageReference Include="Microsoft.CodeAnalysis" Version="4.11.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.11.0" PrivateAssets="all" />
+    <PackageReference Include="PolyShim" Version="1.12.0" PrivateAssets="all" />
+  </ItemGroup>
+
+</Project>

CliFx.SourceGeneration/CommandSchemaGenerator.cs

@@ -0,0 +1,130 @@
+using System.Linq;
+using CliFx.SourceGeneration.SemanticModel;
+using CliFx.SourceGeneration.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace CliFx.SourceGeneration;
+
+[Generator]
+public class CommandSchemaGenerator : IIncrementalGenerator
+{
+    public void Initialize(IncrementalGeneratorInitializationContext context)
+    {
+        var values = context.SyntaxProvider.ForAttributeWithMetadataName<(
+            CommandSymbol?,
+            Diagnostic?
+        )>(
+            KnownSymbolNames.CliFxCommandAttribute,
+            (n, _) => n is TypeDeclarationSyntax,
+            (x, _) =>
+            {
+                // Predicate above ensures that these casts are safe
+                var commandTypeSyntax = (TypeDeclarationSyntax)x.TargetNode;
+                var commandTypeSymbol = (INamedTypeSymbol)x.TargetSymbol;
+
+                // Check if the target type and all its containing types are partial
+                if (
+                    commandTypeSyntax
+                        .AncestorsAndSelf()
+                        .Any(a =>
+                            a is TypeDeclarationSyntax t
+                            && !t.Modifiers.Any(m => m.IsKind(SyntaxKind.PartialKeyword))
+                        )
+                )
+                {
+                    return (
+                        null,
+                        Diagnostic.Create(
+                            DiagnosticDescriptors.CommandMustBePartial,
+                            commandTypeSyntax.Identifier.GetLocation()
+                        )
+                    );
+                }
+
+                // Check if the target type implements ICommand
+                var hasCommandInterface = commandTypeSymbol.AllInterfaces.Any(i =>
+                    i.DisplayNameMatches(KnownSymbolNames.CliFxCommandInterface)
+                );
+
+                if (!hasCommandInterface)
+                {
+                    return (
+                        null,
+                        Diagnostic.Create(
+                            DiagnosticDescriptors.CommandMustImplementInterface,
+                            commandTypeSymbol.Locations.First()
+                        )
+                    );
+                }
+
+                // Resolve the command
+                var commandAttribute = x.Attributes.First(a =>
+                    a.AttributeClass?.DisplayNameMatches(KnownSymbolNames.CliFxCommandAttribute)
+                    == true
+                );
+
+                var command = CommandSymbol.FromSymbol(commandTypeSymbol, commandAttribute);
+
+                // TODO: validate command
+
+                return (command, null);
+            }
+        );
+
+        // Report diagnostics
+        var diagnostics = values.Select((v, _) => v.Item2).WhereNotNull();
+        context.RegisterSourceOutput(diagnostics, (x, d) => x.ReportDiagnostic(d));
+
+        // Generate command schemas
+        var symbols = values.Select((v, _) => v.Item1).WhereNotNull();
+        context.RegisterSourceOutput(
+            symbols,
+            (x, c) =>
+                x.AddSource(
+                    $"{c.Type.FullyQualifiedName}.CommandSchema.Generated.cs",
+                    // lang=csharp
+                    $$"""
+                    namespace {{c.Type.Namespace}};
+
+                    partial class {{c.Type.Name}}
+                    {
+                        public static CliFx.Schema.CommandSchema<{{c.Type.FullyQualifiedName}}> Schema { get; } = {{c.GenerateSchemaInitializationCode()}};
+                    }
+                    """
+                )
+        );
+
+        // Generate extension methods
+        var symbolsCollected = symbols.Collect();
+        context.RegisterSourceOutput(
+            symbolsCollected,
+            (x, cs) =>
+                x.AddSource(
+                    "CommandSchemaExtensions.Generated.cs",
+                    // lang=csharp
+                    $$"""
+                  namespace CliFx;
+
+                  static partial class GeneratedExtensions
+                  {
+                      public static CliFx.CliApplicationBuilder AddCommandsFromThisAssembly(this CliFx.CliApplicationBuilder builder)
+                      {
+                          {{
+                              cs.Select(c => c.Type.FullyQualifiedName)
+                                  .Select(t =>
+                                      // lang=csharp
+                                      $"builder.AddCommand({t}.Schema);"
+                                  )
+                                  .JoinToString("\n")
+                          }}
+                          
+                          return builder;
+                      }
+                  }
+                  """
+                )
+        );
+    }
+}

CliFx.SourceGeneration/DiagnosticDescriptors.cs

@@ -0,0 +1,27 @@
+using CliFx.SourceGeneration.SemanticModel;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration;
+
+internal static class DiagnosticDescriptors
+{
+    public static DiagnosticDescriptor CommandMustBePartial { get; } =
+        new(
+            $"{nameof(CliFx)}_{nameof(CommandMustBePartial)}",
+            "Command types must be declared as `partial`",
+            "This type (and all its containing types, if present) must be declared as `partial` in order to be a valid command.",
+            "CliFx",
+            DiagnosticSeverity.Error,
+            true
+        );
+
+    public static DiagnosticDescriptor CommandMustImplementInterface { get; } =
+        new(
+            $"{nameof(CliFx)}_{nameof(CommandMustImplementInterface)}",
+            $"Commands must implement the `{KnownSymbolNames.CliFxCommandInterface}` interface",
+            $"This type must implement the `{KnownSymbolNames.CliFxCommandInterface}` interface in order to be a valid command.",
+            "CliFx",
+            DiagnosticSeverity.Error,
+            true
+        );
+}

CliFx.SourceGeneration/SemanticModel/CommandInputSymbol.cs

@@ -0,0 +1,66 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration.SemanticModel;
+
+internal abstract partial class CommandInputSymbol(
+    PropertyDescriptor property,
+    bool isSequence,
+    string? description,
+    TypeDescriptor? converterType,
+    IReadOnlyList<TypeDescriptor> validatorTypes
+)
+{
+    public PropertyDescriptor Property { get; } = property;
+
+    public bool IsSequence { get; } = isSequence;
+
+    public string? Description { get; } = description;
+
+    public TypeDescriptor? ConverterType { get; } = converterType;
+
+    public IReadOnlyList<TypeDescriptor> ValidatorTypes { get; } = validatorTypes;
+}
+
+internal partial class CommandInputSymbol : IEquatable<CommandInputSymbol>
+{
+    public bool Equals(CommandInputSymbol? other)
+    {
+        if (ReferenceEquals(null, other))
+            return false;
+        if (ReferenceEquals(this, other))
+            return true;
+
+        return Property.Equals(other.Property)
+            && IsSequence == other.IsSequence
+            && Description == other.Description
+            && Equals(ConverterType, other.ConverterType)
+            && ValidatorTypes.SequenceEqual(other.ValidatorTypes);
+    }
+
+    public override bool Equals(object? obj)
+    {
+        if (ReferenceEquals(null, obj))
+            return false;
+        if (ReferenceEquals(this, obj))
+            return true;
+        if (obj.GetType() != GetType())
+            return false;
+
+        return Equals((CommandInputSymbol)obj);
+    }
+
+    public override int GetHashCode() =>
+        HashCode.Combine(Property, IsSequence, Description, ConverterType, ValidatorTypes);
+}
+
+internal partial class CommandInputSymbol
+{
+    public static bool IsSequenceType(ITypeSymbol type) =>
+        type.AllInterfaces.Any(i =>
+            i.SpecialType == SpecialType.System_Collections_Generic_IEnumerable_T
+        )
+        && type.SpecialType != SpecialType.System_String;
+}

CliFx.SourceGeneration/SemanticModel/CommandOptionSymbol.cs

@@ -0,0 +1,90 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using CliFx.SourceGeneration.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration.SemanticModel;
+
+internal partial class CommandOptionSymbol(
+    PropertyDescriptor property,
+    bool isSequence,
+    string? name,
+    char? shortName,
+    string? environmentVariable,
+    bool isRequired,
+    string? description,
+    TypeDescriptor? converterType,
+    IReadOnlyList<TypeDescriptor> validatorTypes
+) : CommandInputSymbol(property, isSequence, description, converterType, validatorTypes)
+{
+    public string? Name { get; } = name;
+
+    public char? ShortName { get; } = shortName;
+
+    public string? EnvironmentVariable { get; } = environmentVariable;
+
+    public bool IsRequired { get; } = isRequired;
+}
+
+internal partial class CommandOptionSymbol : IEquatable<CommandOptionSymbol>
+{
+    public bool Equals(CommandOptionSymbol? other)
+    {
+        if (ReferenceEquals(null, other))
+            return false;
+        if (ReferenceEquals(this, other))
+            return true;
+
+        return base.Equals(other)
+            && Name == other.Name
+            && ShortName == other.ShortName
+            && EnvironmentVariable == other.EnvironmentVariable
+            && IsRequired == other.IsRequired;
+    }
+
+    public override bool Equals(object? obj)
+    {
+        if (ReferenceEquals(null, obj))
+            return false;
+        if (ReferenceEquals(this, obj))
+            return true;
+        if (obj.GetType() != GetType())
+            return false;
+
+        return Equals((CommandOptionSymbol)obj);
+    }
+
+    public override int GetHashCode() =>
+        HashCode.Combine(base.GetHashCode(), Name, ShortName, EnvironmentVariable, IsRequired);
+}
+
+internal partial class CommandOptionSymbol
+{
+    public static CommandOptionSymbol FromSymbol(
+        IPropertySymbol property,
+        AttributeData attribute
+    ) =>
+        new(
+            PropertyDescriptor.FromSymbol(property),
+            IsSequenceType(property.Type),
+            attribute
+                .ConstructorArguments.FirstOrDefault(a =>
+                    a.Type?.SpecialType == SpecialType.System_String
+                )
+                .Value as string,
+            attribute
+                .ConstructorArguments.FirstOrDefault(a =>
+                    a.Type?.SpecialType == SpecialType.System_Char
+                )
+                .Value as char?,
+            attribute.GetNamedArgumentValue("EnvironmentVariable", default(string)),
+            attribute.GetNamedArgumentValue("IsRequired", property.IsRequired),
+            attribute.GetNamedArgumentValue("Description", default(string)),
+            TypeDescriptor.FromSymbol(attribute.GetNamedArgumentValue<ITypeSymbol?>("Converter")),
+            attribute
+                .GetNamedArgumentValues<ITypeSymbol>("Validators")
+                .Select(TypeDescriptor.FromSymbol)
+                .ToArray()
+        );
+}

CliFx.SourceGeneration/SemanticModel/CommandParameterSymbol.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using CliFx.SourceGeneration.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration.SemanticModel;
+
+internal partial class CommandParameterSymbol(
+    PropertyDescriptor property,
+    bool isSequence,
+    int order,
+    string name,
+    bool isRequired,
+    string? description,
+    TypeDescriptor? converterType,
+    IReadOnlyList<TypeDescriptor> validatorTypes
+) : CommandInputSymbol(property, isSequence, description, converterType, validatorTypes)
+{
+    public int Order { get; } = order;
+
+    public string Name { get; } = name;
+
+    public bool IsRequired { get; } = isRequired;
+}
+
+internal partial class CommandParameterSymbol : IEquatable<CommandParameterSymbol>
+{
+    public bool Equals(CommandParameterSymbol? other)
+    {
+        if (ReferenceEquals(null, other))
+            return false;
+        if (ReferenceEquals(this, other))
+            return true;
+
+        return base.Equals(other)
+            && Order == other.Order
+            && Name == other.Name
+            && IsRequired == other.IsRequired;
+    }
+
+    public override bool Equals(object? obj)
+    {
+        if (ReferenceEquals(null, obj))
+            return false;
+        if (ReferenceEquals(this, obj))
+            return true;
+        if (obj.GetType() != GetType())
+            return false;
+
+        return Equals((CommandParameterSymbol)obj);
+    }
+
+    public override int GetHashCode() =>
+        HashCode.Combine(base.GetHashCode(), Order, Name, IsRequired);
+}
+
+internal partial class CommandParameterSymbol
+{
+    public static CommandParameterSymbol FromSymbol(
+        IPropertySymbol property,
+        AttributeData attribute
+    ) =>
+        new(
+            PropertyDescriptor.FromSymbol(property),
+            IsSequenceType(property.Type),
+            (int)attribute.ConstructorArguments.First().Value!,
+            attribute.GetNamedArgumentValue("Name", default(string)),
+            attribute.GetNamedArgumentValue("IsRequired", true),
+            attribute.GetNamedArgumentValue("Description", default(string)),
+            TypeDescriptor.FromSymbol(attribute.GetNamedArgumentValue<ITypeSymbol>("Converter")),
+            attribute
+                .GetNamedArgumentValues<ITypeSymbol>("Validators")
+                .Select(TypeDescriptor.FromSymbol)
+                .ToArray()
+        );
+}

CliFx.SourceGeneration/SemanticModel/CommandSymbol.cs

@@ -0,0 +1,167 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using CliFx.SourceGeneration.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration.SemanticModel;
+
+internal partial class CommandSymbol(
+    TypeDescriptor type,
+    string? name,
+    string? description,
+    IReadOnlyList<CommandInputSymbol> inputs
+)
+{
+    public TypeDescriptor Type { get; } = type;
+
+    public string? Name { get; } = name;
+
+    public string? Description { get; } = description;
+
+    public IReadOnlyList<CommandInputSymbol> Inputs { get; } = inputs;
+
+    public IReadOnlyList<CommandParameterSymbol> Parameters =>
+        Inputs.OfType<CommandParameterSymbol>().ToArray();
+
+    public IReadOnlyList<CommandOptionSymbol> Options =>
+        Inputs.OfType<CommandOptionSymbol>().ToArray();
+
+    private string GeneratePropertyBindingInitializationCode(PropertyDescriptor property) =>
+        // lang=csharp
+        $$"""
+            new CliFx.Schema.PropertyBinding<{{Type.FullyQualifiedName}}, {{property
+                .Type
+                .FullyQualifiedName}}>(
+                (obj) => obj.{{property.Name}},
+                (obj, value) => obj.{{property.Name}} = value
+            )
+            """;
+
+    private string GenerateSchemaInitializationCode(CommandInputSymbol input) =>
+        input switch
+        {
+            CommandParameterSymbol parameter
+                =>
+                // lang=csharp
+                $$"""
+                    new CliFx.Schema.CommandParameterSchema<{{Type.FullyQualifiedName}}, {{parameter
+                        .Property
+                        .Type
+                        .FullyQualifiedName}}>(
+                        {{GeneratePropertyBindingInitializationCode(parameter.Property)}},
+                        {{parameter.IsSequence}},
+                        {{parameter.Order}},
+                        "{{parameter.Name}}",
+                        {{parameter.IsRequired}},
+                        "{{parameter.Description}}",
+                        // TODO,
+                        // TODO
+                    );
+                    """,
+            CommandOptionSymbol option
+                =>
+                // lang=csharp
+                $$"""
+                    new CliFx.Schema.CommandOptionSchema<{{Type.FullyQualifiedName}}, {{option
+                        .Property
+                        .Type
+                        .FullyQualifiedName}}>(
+                        {{GeneratePropertyBindingInitializationCode(option.Property)}},
+                        {{option.IsSequence}},
+                        "{{option.Name}}",
+                        '{{option.ShortName}}',
+                        "{{option.EnvironmentVariable}}",
+                        {{option.IsRequired}},
+                        "{{option.Description}}",
+                        // TODO,
+                        // TODO
+                    );
+                    """,
+            _ => throw new ArgumentOutOfRangeException(nameof(input), input, null)
+        };
+
+    public string GenerateSchemaInitializationCode() =>
+            // lang=csharp
+            $$"""
+            new CliFx.Schema.CommandSchema<{{Type.FullyQualifiedName}}>(
+                "{{Name}}",
+                "{{Description}}",
+                new CliFx.Schema.CommandInputSchema[]
+                {
+                    {{Inputs.Select(GenerateSchemaInitializationCode).JoinToString(",\n")}}
+                }
+            )
+            """;
+}
+
+internal partial class CommandSymbol : IEquatable<CommandSymbol>
+{
+    public bool Equals(CommandSymbol? other)
+    {
+        if (ReferenceEquals(null, other))
+            return false;
+        if (ReferenceEquals(this, other))
+            return true;
+
+        return Type.Equals(other.Type)
+            && Name == other.Name
+            && Description == other.Description
+            && Inputs.SequenceEqual(other.Inputs);
+    }
+
+    public override bool Equals(object? obj)
+    {
+        if (ReferenceEquals(null, obj))
+            return false;
+        if (ReferenceEquals(this, obj))
+            return true;
+        if (obj.GetType() != GetType())
+            return false;
+
+        return Equals((CommandSymbol)obj);
+    }
+
+    public override int GetHashCode() => HashCode.Combine(Type, Name, Description, Inputs);
+}
+
+internal partial class CommandSymbol
+{
+    public static CommandSymbol FromSymbol(INamedTypeSymbol symbol, AttributeData attribute)
+    {
+        var inputs = new List<CommandInputSymbol>();
+        foreach (var property in symbol.GetMembers().OfType<IPropertySymbol>())
+        {
+            var parameterAttribute = property
+                .GetAttributes()
+                .FirstOrDefault(a =>
+                    a.AttributeClass?.Name == KnownSymbolNames.CliFxCommandParameterAttribute
+                );
+
+            if (parameterAttribute is not null)
+            {
+                inputs.Add(CommandParameterSymbol.FromSymbol(property, parameterAttribute));
+                continue;
+            }
+
+            var optionAttribute = property
+                .GetAttributes()
+                .FirstOrDefault(a =>
+                    a.AttributeClass?.Name == KnownSymbolNames.CliFxCommandOptionAttribute
+                );
+
+            if (optionAttribute is not null)
+            {
+                inputs.Add(CommandOptionSymbol.FromSymbol(property, optionAttribute));
+                continue;
+            }
+        }
+
+        return new CommandSymbol(
+            TypeDescriptor.FromSymbol(symbol),
+            attribute.ConstructorArguments.FirstOrDefault().Value as string,
+            attribute.GetNamedArgumentValue("Description", default(string)),
+            inputs
+        );
+    }
+}

CliFx.SourceGeneration/SemanticModel/KnownSymbolNames.cs

@@ -0,0 +1,10 @@
+namespace CliFx.SourceGeneration.SemanticModel;
+
+internal static class KnownSymbolNames
+{
+    public const string CliFxCommandInterface = "CliFx.ICommand";
+    public const string CliFxCommandAttribute = "CliFx.Attributes.CommandAttribute";
+    public const string CliFxCommandParameterAttribute =
+        "CliFx.Attributes.CommandParameterAttribute";
+    public const string CliFxCommandOptionAttribute = "CliFx.Attributes.CommandOptionAttribute";
+}

CliFx.SourceGeneration/SemanticModel/PropertyDescriptor.cs

@@ -0,0 +1,44 @@
+using System;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration.SemanticModel;
+
+internal partial class PropertyDescriptor(TypeDescriptor type, string name)
+{
+    public TypeDescriptor Type { get; } = type;
+
+    public string Name { get; } = name;
+}
+
+internal partial class PropertyDescriptor : IEquatable<PropertyDescriptor>
+{
+    public bool Equals(PropertyDescriptor? other)
+    {
+        if (ReferenceEquals(null, other))
+            return false;
+        if (ReferenceEquals(this, other))
+            return true;
+
+        return Type.Equals(other.Type) && Name == other.Name;
+    }
+
+    public override bool Equals(object? obj)
+    {
+        if (ReferenceEquals(null, obj))
+            return false;
+        if (ReferenceEquals(this, obj))
+            return true;
+        if (obj.GetType() != GetType())
+            return false;
+
+        return Equals((PropertyDescriptor)obj);
+    }
+
+    public override int GetHashCode() => HashCode.Combine(Type, Name);
+}
+
+internal partial class PropertyDescriptor
+{
+    public static PropertyDescriptor FromSymbol(IPropertySymbol symbol) =>
+        new(TypeDescriptor.FromSymbol(symbol.Type), symbol.Name);
+}

CliFx.SourceGeneration/SemanticModel/TypeDescriptor.cs

@@ -0,0 +1,47 @@
+using System;
+using CliFx.SourceGeneration.Utils.Extensions;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration.SemanticModel;
+
+internal partial class TypeDescriptor(string fullyQualifiedName)
+{
+    public string FullyQualifiedName { get; } = fullyQualifiedName;
+
+    public string Namespace { get; } = fullyQualifiedName.SubstringUntilLast(".");
+
+    public string Name { get; } = fullyQualifiedName.SubstringAfterLast(".");
+}
+
+internal partial class TypeDescriptor : IEquatable<TypeDescriptor>
+{
+    public bool Equals(TypeDescriptor? other)
+    {
+        if (ReferenceEquals(null, other))
+            return false;
+        if (ReferenceEquals(this, other))
+            return true;
+
+        return FullyQualifiedName == other.FullyQualifiedName;
+    }
+
+    public override bool Equals(object? obj)
+    {
+        if (ReferenceEquals(null, obj))
+            return false;
+        if (ReferenceEquals(this, obj))
+            return true;
+        if (obj.GetType() != GetType())
+            return false;
+
+        return Equals((TypeDescriptor)obj);
+    }
+
+    public override int GetHashCode() => FullyQualifiedName.GetHashCode();
+}
+
+internal partial class TypeDescriptor
+{
+    public static TypeDescriptor FromSymbol(ITypeSymbol symbol) =>
+        new(symbol.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat));
+}

CliFx.SourceGeneration/Utils/Extensions/CollectionExtensions.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+
+namespace CliFx.SourceGeneration.Utils.Extensions;
+
+internal static class CollectionExtensions
+{
+    public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T?> source)
+        where T : class
+    {
+        foreach (var i in source)
+        {
+            if (i is not null)
+                yield return i;
+        }
+    }
+}

CliFx.SourceGeneration/Utils/Extensions/GenericExtensions.cs

@@ -0,0 +1,9 @@
+using System;
+
+namespace CliFx.SourceGeneration.Utils.Extensions;
+
+internal static class GenericExtensions
+{
+    public static TOut Pipe<TIn, TOut>(this TIn input, Func<TIn, TOut> transform) =>
+        transform(input);
+}

CliFx.SourceGeneration/Utils/Extensions/RoslynExtensions.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+
+namespace CliFx.SourceGeneration.Utils.Extensions;
+
+internal static class RoslynExtensions
+{
+    public static bool DisplayNameMatches(this ISymbol symbol, string name) =>
+        string.Equals(
+            // Fully qualified name, without `global::`
+            symbol.ToDisplayString(SymbolDisplayFormat.CSharpErrorMessageFormat),
+            name,
+            StringComparison.Ordinal
+        );
+
+    public static T GetNamedArgumentValue<T>(
+        this AttributeData attribute,
+        string name,
+        T defaultValue = default
+    ) =>
+        attribute.NamedArguments.FirstOrDefault(i => i.Key == name).Value.Value is T valueAsT
+            ? valueAsT
+            : defaultValue;
+
+    public static IReadOnlyList<T> GetNamedArgumentValues<T>(
+        this AttributeData attribute,
+        string name
+    )
+        where T : class =>
+        attribute.NamedArguments.FirstOrDefault(i => i.Key == name).Value.Values.CastArray<T>();
+
+    public static IncrementalValuesProvider<T> WhereNotNull<T>(
+        this IncrementalValuesProvider<T?> values
+    )
+        where T : class => values.Where(i => i is not null);
+}

CliFx.SourceGeneration/Utils/Extensions/StringExtensions.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+
+namespace CliFx.SourceGeneration.Utils.Extensions;
+
+internal static class StringExtensions
+{
+    public static string SubstringUntilLast(
+        this string str,
+        string sub,
+        StringComparison comparison = StringComparison.Ordinal
+    )
+    {
+        var index = str.LastIndexOf(sub, comparison);
+        return index < 0 ? str : str[..index];
+    }
+
+    public static string SubstringAfterLast(
+        this string str,
+        string sub,
+        StringComparison comparison = StringComparison.Ordinal
+    )
+    {
+        var index = str.LastIndexOf(sub, comparison);
+        return index >= 0 ? str.Substring(index + sub.Length, str.Length - index - sub.Length) : "";
+    }
+
+    public static string JoinToString<T>(this IEnumerable<T> source, string separator) =>
+        string.Join(separator, source);
+}

CliFx.Tests.Dummy/CliFx.Tests.Dummy.csproj

@@ -2,12 +2,17 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net45</TargetFramework>
-    <LangVersion>latest</LangVersion>
+    <TargetFramework>net9.0</TargetFramework>
+    <ApplicationIcon>../favicon.ico</ApplicationIcon>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="CSharpier.MsBuild" Version="0.30.6" PrivateAssets="all" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\CliFx\CliFx.csproj" />
+    <ProjectReference Include="..\CliFx.SourceGeneration\CliFx.SourceGeneration.csproj" ReferenceOutputAssembly="false" OutputItemType="analyzer" />
   </ItemGroup>
 
 </Project>

CliFx.Tests.Dummy/Commands/AddCommand.cs

@@ -1,25 +0,0 @@
-using System;
-using System.Globalization;
-using CliFx.Attributes;
-using CliFx.Models;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command("add")]
-    public class AddCommand : Command
-    {
-        [CommandOption("a", IsRequired = true, Description = "Left operand.")]
-        public double A { get; set; }
-
-        [CommandOption("b", IsRequired = true, Description = "Right operand.")]
-        public double B { get; set; }
-
-        public override ExitCode Execute()
-        {
-            var result = A + B;
-            Console.WriteLine(result.ToString(CultureInfo.InvariantCulture));
-
-            return ExitCode.Success;
-        }
-    }
-}

CliFx.Tests.Dummy/Commands/CancellationTestCommand.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Tests.Dummy.Commands;
+
+[Command("cancel-test")]
+public class CancellationTestCommand : ICommand
+{
+    public async ValueTask ExecuteAsync(IConsole console)
+    {
+        try
+        {
+            console.WriteLine("Started.");
+
+            await Task.Delay(TimeSpan.FromSeconds(3), console.RegisterCancellationHandler());
+
+            console.WriteLine("Completed.");
+        }
+        catch (OperationCanceledException)
+        {
+            console.WriteLine("Cancelled.");
+            throw;
+        }
+    }
+}

CliFx.Tests.Dummy/Commands/ConsoleTestCommand.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Tests.Dummy.Commands;
+
+[Command("console-test")]
+public class ConsoleTestCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        var input = console.Input.ReadToEnd();
+
+        using (console.WithColors(ConsoleColor.Black, ConsoleColor.White))
+        {
+            console.Output.WriteLine(input);
+            console.Error.WriteLine(input);
+        }
+
+        return default;
+    }
+}

CliFx.Tests.Dummy/Commands/DefaultCommand.cs

@@ -1,31 +0,0 @@
-using System;
-using System.Text;
-using CliFx.Attributes;
-using CliFx.Models;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [DefaultCommand]
-    public class DefaultCommand : Command
-    {
-        [CommandOption("target", ShortName = 't', Description = "Greeting target.")]
-        public string Target { get; set; } = "world";
-
-        [CommandOption("enthusiastic", ShortName = 'e', Description = "Whether the greeting should be enthusiastic.")]
-        public bool IsEnthusiastic { get; set; }
-
-        public override ExitCode Execute()
-        {
-            var buffer = new StringBuilder();
-
-            buffer.Append("Hello ").Append(Target);
-
-            if (IsEnthusiastic)
-                buffer.Append("!!!");
-
-            Console.WriteLine(buffer.ToString());
-
-            return ExitCode.Success;
-        }
-    }
-}

CliFx.Tests.Dummy/Commands/EnvironmentTestCommand.cs

@@ -0,0 +1,18 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Tests.Dummy.Commands;
+
+[Command("env-test")]
+public class EnvironmentTestCommand : ICommand
+{
+    [CommandOption("target", EnvironmentVariable = "ENV_TARGET")]
+    public string GreetingTarget { get; init; } = "World";
+
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        console.WriteLine($"Hello {GreetingTarget}!");
+        return default;
+    }
+}

CliFx.Tests.Dummy/Commands/LogCommand.cs

@@ -1,25 +0,0 @@
-using System;
-using System.Globalization;
-using CliFx.Attributes;
-using CliFx.Models;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command("log")]
-    public class LogCommand : Command
-    {
-        [CommandOption("value", IsRequired = true, Description = "Value whose logarithm is to be found.")]
-        public double Value { get; set; }
-
-        [CommandOption("base", Description = "Logarithm base.")]
-        public double Base { get; set; } = 10;
-
-        public override ExitCode Execute()
-        {
-            var result = Math.Log(Value, Base);
-            Console.WriteLine(result.ToString(CultureInfo.InvariantCulture));
-
-            return ExitCode.Success;
-        }
-    }
-}

CliFx.Tests.Dummy/Program.cs

@@ -1,9 +1,28 @@
-using System.Threading.Tasks;
+using System;
+using System.IO;
+using System.Reflection;
+using System.Threading.Tasks;
 
-namespace CliFx.Tests.Dummy
+namespace CliFx.Tests.Dummy;
+
+// This dummy application is used in tests for scenarios that require an external process to properly verify
+public static class Program
 {
-    public static class Program
+    // Path to the apphost
+    public static string FilePath { get; } =
+        Path.ChangeExtension(
+            Assembly.GetExecutingAssembly().Location,
+            OperatingSystem.IsWindows() ? "exe" : null
+        );
+
+    public static async Task Main()
     {
-        public static Task<int> Main(string[] args) => new CliApplication().RunAsync(args);
+        // Make sure color codes are not produced because we rely on the output in tests
+        Environment.SetEnvironmentVariable(
+            "DOTNET_SYSTEM_CONSOLE_ALLOW_ANSI_COLOR_REDIRECTION",
+            "false"
+        );
+
+        await new CliApplicationBuilder().AddCommandsFromThisAssembly().Build().RunAsync();
     }
-}
+}

CliFx.Tests/ApplicationSpecs.cs

@@ -0,0 +1,71 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class ApplicationSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_create_an_application_with_the_default_configuration()
+    {
+        // Act
+        var app = new CliApplicationBuilder()
+            .AddCommandsFromThisAssembly()
+            .UseConsole(FakeConsole)
+            .Build();
+
+        var exitCode = await app.RunAsync([], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+    }
+
+    [Fact]
+    public async Task I_can_create_an_application_with_a_custom_configuration()
+    {
+        // Act
+        var app = new CliApplicationBuilder()
+            .AddCommand<NoOpCommand>()
+            .AddCommandsFrom(typeof(NoOpCommand).Assembly)
+            .AddCommands([typeof(NoOpCommand)])
+            .AddCommandsFrom([typeof(NoOpCommand).Assembly])
+            .AddCommandsFromThisAssembly()
+            .AllowDebugMode()
+            .AllowPreviewMode()
+            .SetTitle("test")
+            .SetExecutableName("test")
+            .SetVersion("test")
+            .SetDescription("test")
+            .UseConsole(FakeConsole)
+            .UseTypeActivator(Activator.CreateInstance!)
+            .Build();
+
+        var exitCode = await app.RunAsync([], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+    }
+
+    [Fact]
+    public async Task I_can_try_to_create_an_application_and_get_an_error_if_it_has_invalid_commands()
+    {
+        // Act
+        var app = new CliApplicationBuilder()
+            .AddCommand(typeof(ApplicationSpecs))
+            .UseConsole(FakeConsole)
+            .Build();
+
+        var exitCode = await app.RunAsync([], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("not a valid command");
+    }
+}

CliFx.Tests/CancellationSpecs.cs

@@ -0,0 +1,107 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using CliWrap;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class CancellationSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact(Timeout = 15000)]
+    public async Task I_can_configure_the_command_to_listen_to_the_interrupt_signal()
+    {
+        // Arrange
+        using var cts = new CancellationTokenSource();
+
+        // We need to send the cancellation request right after the process has registered
+        // a handler for the interrupt signal, otherwise the default handler will trigger
+        // and just kill the process.
+        void HandleStdOut(string line)
+        {
+            if (string.Equals(line, "Started.", StringComparison.OrdinalIgnoreCase))
+                cts.CancelAfter(TimeSpan.FromSeconds(0.2));
+        }
+
+        var stdOutBuffer = new StringBuilder();
+
+        var pipeTarget = PipeTarget.Merge(
+            PipeTarget.ToDelegate(HandleStdOut),
+            PipeTarget.ToStringBuilder(stdOutBuffer)
+        );
+
+        var command = Cli.Wrap(Dummy.Program.FilePath).WithArguments("cancel-test") | pipeTarget;
+
+        // Act & assert
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(
+            async () =>
+                await command.ExecuteAsync(
+                    // Forceful cancellation (not required because we have a timeout)
+                    CancellationToken.None,
+                    // Graceful cancellation
+                    cts.Token
+                )
+        );
+
+        stdOutBuffer.ToString().Trim().Should().ConsistOfLines("Started.", "Cancelled.");
+    }
+
+    [Fact]
+    public async Task I_can_configure_the_command_to_listen_to_the_interrupt_signal_when_running_in_isolation()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public async ValueTask ExecuteAsync(IConsole console)
+                {
+                    try
+                    {
+                        console.WriteLine("Started.");
+
+                        await Task.Delay(
+                            TimeSpan.FromSeconds(3),
+                            console.RegisterCancellationHandler()
+                        );
+
+                        console.WriteLine("Completed.");
+                    }
+                    catch (OperationCanceledException)
+                    {
+                        console.WriteLine("Cancelled.");
+                        throw;
+                    }
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        FakeConsole.RequestCancellation(TimeSpan.FromSeconds(0.2));
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().ConsistOfLines("Started.", "Cancelled.");
+    }
+}

CliFx.Tests/CliApplicationTests.cs

@@ -1,33 +0,0 @@
-using System.Collections.Generic;
-using System.Threading.Tasks;
-using CliFx.Services;
-using CliFx.Tests.TestObjects;
-using Moq;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class CliApplicationTests
-    {
-        [Test]
-        public async Task RunAsync_Test()
-        {
-            // Arrange
-            var command = new TestCommand();
-            var expectedExitCode = await command.ExecuteAsync();
-
-            var commandResolverMock = new Mock<ICommandResolver>();
-            commandResolverMock.Setup(m => m.ResolveCommand(It.IsAny<IReadOnlyList<string>>())).Returns(command);
-            var commandResolver = commandResolverMock.Object;
-
-            var application = new CliApplication(commandResolver);
-
-            // Act
-            var exitCodeValue = await application.RunAsync();
-
-            // Assert
-            Assert.That(exitCodeValue, Is.EqualTo(expectedExitCode.Value));
-        }
-    }
-}

CliFx.Tests/CliFx.Tests.csproj

@@ -1,18 +1,26 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net45</TargetFramework>
-    <IsPackable>false</IsPackable>
-    <IsTestProject>true</IsTestProject>
-    <LangVersion>latest</LangVersion>
+    <TargetFramework>net9.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.0.1" />
-    <PackageReference Include="NUnit" Version="3.11.0" />
-    <PackageReference Include="NUnit3TestAdapter" Version="3.11.0" />
-    <PackageReference Include="Moq" Version="4.11.0" />
-    <PackageReference Include="CliWrap" Version="2.3.0" />
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Basic.Reference.Assemblies.Net80" Version="1.8.0" />
+    <PackageReference Include="CliWrap" Version="3.7.1" />
+    <PackageReference Include="coverlet.collector" Version="6.0.4" PrivateAssets="all" />
+    <PackageReference Include="CSharpier.MsBuild" Version="0.30.6" PrivateAssets="all" />
+    <PackageReference Include="FluentAssertions" Version="8.0.1" />
+    <PackageReference Include="GitHubActionsTestLogger" Version="2.4.1" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.11.0" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="PolyShim" Version="1.14.0" PrivateAssets="all" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.1" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Tests/CommandOptionConverterTests.cs

@@ -1,83 +0,0 @@
-using System;
-using System.Collections.Generic;
-using CliFx.Services;
-using CliFx.Tests.TestObjects;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class CommandOptionConverterTests
-    {
-        private static IEnumerable<TestCaseData> GetData_ConvertOption()
-        {
-            yield return new TestCaseData("value", typeof(string), "value")
-                .SetName("To string");
-
-            yield return new TestCaseData("value", typeof(object), "value")
-                .SetName("To object");
-
-            yield return new TestCaseData("true", typeof(bool), true)
-                .SetName("To bool (true)");
-
-            yield return new TestCaseData("false", typeof(bool), false)
-                .SetName("To bool (false)");
-
-            yield return new TestCaseData(null, typeof(bool), true)
-                .SetName("To bool (switch)");
-
-            yield return new TestCaseData("123", typeof(int), 123)
-                .SetName("To int");
-
-            yield return new TestCaseData("123.45", typeof(double), 123.45)
-                .SetName("To double");
-
-            yield return new TestCaseData("28 Apr 1995", typeof(DateTime), new DateTime(1995, 04, 28))
-                .SetName("To DateTime");
-
-            yield return new TestCaseData("28 Apr 1995", typeof(DateTimeOffset), new DateTimeOffset(new DateTime(1995, 04, 28)))
-                .SetName("To DateTimeOffset");
-
-            yield return new TestCaseData("00:14:59", typeof(TimeSpan), new TimeSpan(00, 14, 59))
-                .SetName("To TimeSpan");
-
-            yield return new TestCaseData("value2", typeof(TestEnum), TestEnum.Value2)
-                .SetName("To enum");
-
-            yield return new TestCaseData("666", typeof(int?), 666)
-                .SetName("To int? (with value)");
-
-            yield return new TestCaseData(null, typeof(int?), null)
-                .SetName("To int? (no value)");
-
-            yield return new TestCaseData("value3", typeof(TestEnum?), TestEnum.Value3)
-                .SetName("To enum? (with value)");
-
-            yield return new TestCaseData(null, typeof(TestEnum?), null)
-                .SetName("To enum? (no value)");
-
-            yield return new TestCaseData("01:00:00", typeof(TimeSpan?), new TimeSpan(01, 00, 00))
-                .SetName("To TimeSpan? (with value)");
-
-            yield return new TestCaseData(null, typeof(TimeSpan?), null)
-                .SetName("To TimeSpan? (no value)");
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetData_ConvertOption))]
-        public void ConvertOption_Test(string value, Type targetType, object expectedConvertedValue)
-        {
-            // Arrange
-            var converter = new CommandOptionConverter();
-
-            // Act
-            var convertedValue = converter.ConvertOption(value, targetType);
-
-            // Assert
-            Assert.That(convertedValue, Is.EqualTo(expectedConvertedValue));
-
-            if (convertedValue != null)
-                Assert.That(convertedValue, Is.AssignableTo(targetType));
-        }
-    }
-}

CliFx.Tests/CommandOptionParserTests.cs

@@ -1,139 +0,0 @@
-using System.Collections.Generic;
-using CliFx.Models;
-using CliFx.Services;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class CommandOptionParserTests
-    {
-        private static IEnumerable<TestCaseData> GetData_ParseOptions()
-        {
-            yield return new TestCaseData(
-                new string[0],
-                CommandOptionSet.Empty
-            ).SetName("No arguments");
-
-            yield return new TestCaseData(
-                new[] {"--argument", "value"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"argument", "value"}
-                })
-            ).SetName("Single argument");
-
-            yield return new TestCaseData(
-                new[] {"--argument1", "value1", "--argument2", "value2", "--argument3", "value3"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"argument1", "value1"},
-                    {"argument2", "value2"},
-                    {"argument3", "value3"}
-                })
-            ).SetName("Multiple arguments");
-
-            yield return new TestCaseData(
-                new[] {"-a", "value"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"a", "value"}
-                })
-            ).SetName("Single short argument");
-
-            yield return new TestCaseData(
-                new[] {"-a", "value1", "-b", "value2", "-c", "value3"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"a", "value1"},
-                    {"b", "value2"},
-                    {"c", "value3"}
-                })
-            ).SetName("Multiple short arguments");
-
-            yield return new TestCaseData(
-                new[] {"--argument1", "value1", "-b", "value2", "--argument3", "value3"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"argument1", "value1"},
-                    {"b", "value2"},
-                    {"argument3", "value3"}
-                })
-            ).SetName("Multiple mixed arguments");
-
-            yield return new TestCaseData(
-                new[] {"--switch"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"switch", null}
-                })
-            ).SetName("Single switch");
-
-            yield return new TestCaseData(
-                new[] {"--switch1", "--switch2", "--switch3"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"switch1", null},
-                    {"switch2", null},
-                    {"switch3", null}
-                })
-            ).SetName("Multiple switches");
-
-            yield return new TestCaseData(
-                new[] {"-s"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"s", null}
-                })
-            ).SetName("Single short switch");
-
-            yield return new TestCaseData(
-                new[] {"-a", "-b", "-c"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"a", null},
-                    {"b", null},
-                    {"c", null}
-                })
-            ).SetName("Multiple short switches");
-
-            yield return new TestCaseData(
-                new[] {"-abc"},
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"a", null},
-                    {"b", null},
-                    {"c", null}
-                })
-            ).SetName("Multiple stacked short switches");
-
-            yield return new TestCaseData(
-                new[] {"command"},
-                new CommandOptionSet("command")
-            ).SetName("No arguments (with command name)");
-
-            yield return new TestCaseData(
-                new[] {"command", "--argument", "value"},
-                new CommandOptionSet("command", new Dictionary<string, string>
-                {
-                    {"argument", "value"}
-                })
-            ).SetName("Single argument (with command name)");
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetData_ParseOptions))]
-        public void ParseOptions_Test(IReadOnlyList<string> commandLineArguments, CommandOptionSet expectedCommandOptionSet)
-        {
-            // Arrange
-            var parser = new CommandOptionParser();
-
-            // Act
-            var optionSet = parser.ParseOptions(commandLineArguments);
-
-            // Assert
-            Assert.That(optionSet.CommandName, Is.EqualTo(expectedCommandOptionSet.CommandName));
-            Assert.That(optionSet.Options, Is.EqualTo(expectedCommandOptionSet.Options));
-        }
-    }
-}

CliFx.Tests/CommandResolverTests.cs

@@ -1,116 +0,0 @@
-using System;
-using System.Collections.Generic;
-using CliFx.Exceptions;
-using CliFx.Models;
-using CliFx.Services;
-using CliFx.Tests.TestObjects;
-using Moq;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class CommandResolverTests
-    {
-        private static IEnumerable<TestCaseData> GetData_ResolveCommand()
-        {
-            yield return new TestCaseData(
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"int", "13"}
-                }),
-                new TestCommand {IntOption = 13}
-            ).SetName("Single option");
-
-            yield return new TestCaseData(
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"int", "13"},
-                    {"str", "hello world" }
-                }),
-                new TestCommand { IntOption = 13, StringOption = "hello world"}
-            ).SetName("Multiple options");
-
-            yield return new TestCaseData(
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"i", "13"}
-                }),
-                new TestCommand { IntOption = 13 }
-            ).SetName("Single short option");
-
-            yield return new TestCaseData(
-                new CommandOptionSet("command", new Dictionary<string, string>
-                {
-                    {"int", "13"}
-                }),
-                new TestCommand { IntOption = 13 }
-            ).SetName("Single option (with command name)");
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetData_ResolveCommand))]
-        public void ResolveCommand_Test(CommandOptionSet commandOptionSet, TestCommand expectedCommand)
-        {
-            // Arrange
-            var commandTypes = new[] {typeof(TestCommand)};
-
-            var typeProviderMock = new Mock<ITypeProvider>();
-            typeProviderMock.Setup(m => m.GetTypes()).Returns(commandTypes);
-            var typeProvider = typeProviderMock.Object;
-
-            var optionParserMock = new Mock<ICommandOptionParser>();
-            optionParserMock.Setup(m => m.ParseOptions(It.IsAny<IReadOnlyList<string>>())).Returns(commandOptionSet);
-            var optionParser = optionParserMock.Object;
-
-            var optionConverter = new CommandOptionConverter();
-
-            var resolver = new CommandResolver(typeProvider, optionParser, optionConverter);
-
-            // Act
-            var command = resolver.ResolveCommand() as TestCommand;
-
-            // Assert
-            Assert.That(command, Is.Not.Null);
-            Assert.That(command.StringOption, Is.EqualTo(expectedCommand.StringOption), nameof(command.StringOption));
-            Assert.That(command.IntOption, Is.EqualTo(expectedCommand.IntOption), nameof(command.IntOption));
-        }
-
-        private static IEnumerable<TestCaseData> GetData_ResolveCommand_IsRequired()
-        {
-            yield return new TestCaseData(
-                CommandOptionSet.Empty
-            ).SetName("No options");
-
-            yield return new TestCaseData(
-                new CommandOptionSet(new Dictionary<string, string>
-                {
-                    {"str", "hello world"}
-                })
-            ).SetName("Required option is not set");
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetData_ResolveCommand_IsRequired))]
-        public void ResolveCommand_IsRequired_Test(CommandOptionSet commandOptionSet)
-        {
-            // Arrange
-            var commandTypes = new[] { typeof(TestCommand) };
-
-            var typeProviderMock = new Mock<ITypeProvider>();
-            typeProviderMock.Setup(m => m.GetTypes()).Returns(commandTypes);
-            var typeProvider = typeProviderMock.Object;
-
-            var optionParserMock = new Mock<ICommandOptionParser>();
-            optionParserMock.Setup(m => m.ParseOptions(It.IsAny<IReadOnlyList<string>>())).Returns(commandOptionSet);
-            var optionParser = optionParserMock.Object;
-
-            var optionConverter = new CommandOptionConverter();
-
-            var resolver = new CommandResolver(typeProvider, optionParser, optionConverter);
-
-            // Act & Assert
-            Assert.Throws<CommandResolveException>(() => resolver.ResolveCommand());
-        }
-    }
-}

CliFx.Tests/ConsoleSpecs.cs

@@ -0,0 +1,204 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
+using CliFx.Infrastructure;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using CliWrap;
+using CliWrap.Buffered;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class ConsoleSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact(Timeout = 15000)]
+    public async Task I_can_run_the_application_with_the_default_console_implementation_to_interact_with_the_system_console()
+    {
+        // Can't verify our own console output, so using an external process for this test
+
+        // Arrange
+        var command =
+            "Hello world" | Cli.Wrap(Dummy.Program.FilePath).WithArguments("console-test");
+
+        // Act
+        var result = await command.ExecuteBufferedAsync();
+
+        // Assert
+        result.StandardOutput.Trim().Should().Be("Hello world");
+        result.StandardError.Trim().Should().Be("Hello world");
+    }
+
+    [Fact]
+    public void I_can_run_the_application_on_a_system_with_a_custom_console_encoding_and_not_get_corrupted_output()
+    {
+        // Arrange
+        using var buffer = new MemoryStream();
+        using var consoleWriter = new ConsoleWriter(FakeConsole, buffer, Encoding.UTF8);
+
+        // Act
+        consoleWriter.Write("Hello world");
+        consoleWriter.Flush();
+
+        // Assert
+        var outputBytes = buffer.ToArray();
+        outputBytes.Should().NotContain(Encoding.UTF8.GetPreamble());
+
+        var output = consoleWriter.Encoding.GetString(outputBytes);
+        output.Should().Be("Hello world");
+    }
+
+    [Fact]
+    public async Task I_can_run_the_application_with_the_fake_console_implementation_to_isolate_console_interactions()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.ResetColor();
+                    console.ForegroundColor = ConsoleColor.DarkMagenta;
+                    console.BackgroundColor = ConsoleColor.DarkMagenta;
+                    console.WindowWidth = 100;
+                    console.WindowHeight = 25;
+                    console.CursorLeft = 42;
+                    console.CursorTop = 24;
+
+                    console.Output.WriteLine("Hello ");
+                    console.Error.WriteLine("world!");
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        Console.OpenStandardInput().Should().NotBeSameAs(FakeConsole.Input.BaseStream);
+        Console.OpenStandardOutput().Should().NotBeSameAs(FakeConsole.Output.BaseStream);
+        Console.OpenStandardError().Should().NotBeSameAs(FakeConsole.Error.BaseStream);
+
+        Console.ForegroundColor.Should().NotBe(ConsoleColor.DarkMagenta);
+        Console.BackgroundColor.Should().NotBe(ConsoleColor.DarkMagenta);
+
+        // This fails because tests don't spawn a console window
+        //Console.WindowWidth.Should().Be(100);
+        //Console.WindowHeight.Should().Be(25);
+        //Console.CursorLeft.Should().NotBe(42);
+        //Console.CursorTop.Should().NotBe(24);
+
+        FakeConsole.IsInputRedirected.Should().BeTrue();
+        FakeConsole.IsOutputRedirected.Should().BeTrue();
+        FakeConsole.IsErrorRedirected.Should().BeTrue();
+    }
+
+    [Fact]
+    public async Task I_can_run_the_application_with_the_fake_console_implementation_and_simulate_stream_interactions()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    var input = console.Input.ReadToEnd();
+                    console.Output.WriteLine(input);
+                    console.Error.WriteLine(input);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        FakeConsole.WriteInput("Hello world");
+
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("Hello world");
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Trim().Should().Be("Hello world");
+    }
+
+    [Fact]
+    public async Task I_can_run_the_application_with_the_fake_console_implementation_and_simulate_key_presses()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(console.ReadKey().Key);
+                    console.WriteLine(console.ReadKey().Key);
+                    console.WriteLine(console.ReadKey().Key);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        FakeConsole.EnqueueKey(new ConsoleKeyInfo('0', ConsoleKey.D0, false, false, false));
+        FakeConsole.EnqueueKey(new ConsoleKeyInfo('a', ConsoleKey.A, false, false, false));
+        FakeConsole.EnqueueKey(new ConsoleKeyInfo('\0', ConsoleKey.Backspace, false, false, false));
+
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().ConsistOfLines("D0", "A", "Backspace");
+    }
+}

CliFx.Tests/ConversionSpecs.cs

@@ -0,0 +1,941 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class ConversionSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_string_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "xyz"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("xyz");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_an_object_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public object? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "xyz"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("xyz");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_boolean_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public bool Foo { get; init; }
+
+                [CommandOption('b')]
+                public bool Bar { get; init; }
+
+                [CommandOption('c')]
+                public bool Baz { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+                    console.WriteLine("Baz = " + Baz);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "true", "-b", "false", "-c"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = True", "Bar = False", "Baz = True");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_an_integer_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public int Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "32"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("32");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_double_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public double Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo.ToString(CultureInfo.InvariantCulture));
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "32.14"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("32.14");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_DateTimeOffset_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public DateTimeOffset Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo.ToString("u", CultureInfo.InvariantCulture));
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "1995-04-28Z"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("1995-04-28 00:00:00Z");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_TimeSpan_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public TimeSpan Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo.ToString(null, CultureInfo.InvariantCulture));
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "12:34:56"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("12:34:56");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_an_enum_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public enum CustomEnum { One = 1, Two = 2, Three = 3 }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public CustomEnum Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine((int) Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "two"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("2");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_nullable_integer_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public int? Foo { get; init; }
+
+                [CommandOption('b')]
+                public int? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-b", "123"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = ", "Bar = 123");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_nullable_enum_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public enum CustomEnum { One = 1, Two = 2, Three = 3 }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public CustomEnum? Foo { get; init; }
+
+                [CommandOption('b')]
+                public CustomEnum? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + (int?) Foo);
+                    console.WriteLine("Bar = " + (int?) Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-b", "two"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = ", "Bar = 2");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_string_constructable_object_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public class CustomType
+            {
+                public string Value { get; }
+
+                public CustomType(string value) => Value = value;
+            }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public CustomType? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo.Value);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "xyz"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("xyz");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_string_parsable_object_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public class CustomTypeA
+            {
+                public string Value { get; }
+
+                private CustomTypeA(string value) => Value = value;
+
+                public static CustomTypeA Parse(string value) =>
+                    new CustomTypeA(value);
+            }
+
+            public class CustomTypeB
+            {
+                public string Value { get; }
+
+                private CustomTypeB(string value) => Value = value;
+
+                public static CustomTypeB Parse(string value, IFormatProvider formatProvider) =>
+                    new CustomTypeB(value);
+            }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public CustomTypeA? Foo { get; init; }
+
+                [CommandOption('b')]
+                public CustomTypeB? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo.Value);
+                    console.WriteLine("Bar = " + Bar.Value);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "hello", "-b", "world"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = hello", "Bar = world");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_property_with_a_custom_converter()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public class CustomConverter : BindingConverter<int>
+            {
+                public override int Convert(string rawValue) =>
+                    rawValue.Length;
+            }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f', Converter = typeof(CustomConverter))]
+                public int Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "hello world"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("11");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_string_array_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public string[]? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "one", "two", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_read_only_list_of_strings_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public IReadOnlyList<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "one", "two", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_a_string_list_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public List<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "one", "two", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_or_an_option_to_an_integer_array_property()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public int[]? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "1", "13", "27"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("1", "13", "27");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_or_an_option_to_a_property_and_get_an_error_if_it_is_of_an_unsupported_type()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public class CustomType
+            {
+            }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public CustomType? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "xyz"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("has an unsupported underlying property type");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_or_an_option_to_a_non_scalar_property_and_get_an_error_if_it_is_of_an_unsupported_type()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public class CustomType : IEnumerable<object>
+            {
+                public IEnumerator<object> GetEnumerator() => Enumerable.Empty<object>().GetEnumerator();
+
+                IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+            }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public CustomType? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "one", "two"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("has an unsupported underlying property type");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_or_an_option_to_a_property_and_get_an_error_if_the_user_provides_an_invalid_value()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public int Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "12.34"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().NotBeNullOrWhiteSpace();
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_or_an_option_to_a_property_and_get_an_error_if_a_custom_validator_fails()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public class ValidatorA : BindingValidator<int>
+            {
+                public override BindingValidationError Validate(int value) => Ok();
+            }
+
+            public class ValidatorB : BindingValidator<int>
+            {
+                public override BindingValidationError Validate(int value) => Error("Hello world");
+            }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f', Validators = [typeof(ValidatorA), typeof(ValidatorB)])]
+                public int Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "12"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Hello world");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_or_an_option_to_a_string_parsable_property_and_get_an_error_if_the_parsing_fails()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public class CustomType
+            {
+                public string Value { get; }
+
+                private CustomType(string value) => Value = value;
+
+                public static CustomType Parse(string value) => throw new Exception("Hello world");
+            }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public CustomType? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f", "bar"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Hello world");
+    }
+}

CliFx.Tests/DirectivesSpecs.cs

@@ -0,0 +1,91 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using CliWrap;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class DirectivesSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact(Timeout = 15000)]
+    public async Task I_can_use_the_debug_directive_to_make_the_application_wait_for_the_debugger_to_attach()
+    {
+        // Arrange
+        using var cts = new CancellationTokenSource();
+
+        // We can't actually attach a debugger, but we can ensure that the process is waiting for one
+        void HandleStdOut(string line)
+        {
+            // Kill the process once it writes the output we expect
+            if (line.Contains("Attach the debugger to", StringComparison.OrdinalIgnoreCase))
+                cts.Cancel();
+        }
+
+        var command = Cli.Wrap(Dummy.Program.FilePath).WithArguments("[debug]") | HandleStdOut;
+
+        // Act & assert
+        try
+        {
+            await command.ExecuteAsync(cts.Token);
+        }
+        catch (OperationCanceledException ex) when (ex.CancellationToken == cts.Token)
+        {
+            // This means that the process was killed after it wrote the expected output
+        }
+    }
+
+    [Fact]
+    public async Task I_can_use_the_preview_directive_to_make_the_application_print_the_parsed_command_input()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command("cmd")]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .AllowPreviewMode()
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["[preview]", "cmd", "param", "-abc", "--option", "foo"],
+            new Dictionary<string, string> { ["ENV_QOP"] = "hello", ["ENV_KIL"] = "world" }
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "cmd",
+                "<param>",
+                "[-a]",
+                "[-b]",
+                "[-c]",
+                "[--option \"foo\"]",
+                "ENV_QOP",
+                "=",
+                "\"hello\"",
+                "ENV_KIL",
+                "=",
+                "\"world\""
+            );
+    }
+}

CliFx.Tests/DummyTests.cs

@@ -1,32 +0,0 @@
-using System.IO;
-using System.Threading.Tasks;
-using CliWrap;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class DummyTests
-    {
-        private string DummyFilePath => Path.Combine(TestContext.CurrentContext.TestDirectory, "CliFx.Tests.Dummy.exe");
-
-        [Test]
-        [TestCase("", "Hello world")]
-        [TestCase("-t .NET", "Hello .NET")]
-        [TestCase("-e", "Hello world!!!")]
-        [TestCase("add --a 1 --b 2", "3")]
-        [TestCase("add --a 2.75 --b 3.6", "6.35")]
-        [TestCase("log --value 100", "2")]
-        [TestCase("log --value 256 --base 2", "8")]
-        public async Task Execute_Test(string arguments, string expectedOutput)
-        {
-            // Act
-            var result = await Cli.Wrap(DummyFilePath).SetArguments(arguments).ExecuteAsync();
-
-            // Assert
-            Assert.That(result.ExitCode, Is.Zero);
-            Assert.That(result.StandardOutput.Trim(), Is.EqualTo(expectedOutput));
-            Assert.That(result.StandardError.Trim(), Is.Empty);
-        }
-    }
-}

CliFx.Tests/EnvironmentSpecs.cs

@@ -0,0 +1,160 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using CliWrap;
+using CliWrap.Buffered;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class EnvironmentSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_configure_an_option_to_fall_back_to_an_environment_variable_if_the_user_does_not_provide_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo", EnvironmentVariable = "ENV_FOO")]
+                public string? Foo { get; init; }
+
+                [CommandOption("bar", EnvironmentVariable = "ENV_BAR")]
+                public string? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    console.WriteLine(Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "42"],
+            new Dictionary<string, string> { ["ENV_FOO"] = "100", ["ENV_BAR"] = "200" }
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().ConsistOfLines("42", "200");
+    }
+
+    [Fact]
+    public async Task I_can_configure_an_option_bound_to_a_non_scalar_property_to_fall_back_to_an_environment_variable_if_the_user_does_not_provide_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo", EnvironmentVariable = "ENV_FOO")]
+                public IReadOnlyList<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string> { ["ENV_FOO"] = $"bar{Path.PathSeparator}baz" }
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("bar", "baz");
+    }
+
+    [Fact]
+    public async Task I_can_configure_an_option_bound_to_a_scalar_property_to_fall_back_to_an_environment_variable_while_ignoring_path_separators()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo", EnvironmentVariable = "ENV_FOO")]
+                public string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string> { ["ENV_FOO"] = $"bar{Path.PathSeparator}baz" }
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be($"bar{Path.PathSeparator}baz");
+    }
+
+    [Fact(Timeout = 15000)]
+    public async Task I_can_run_the_application_and_it_will_resolve_all_required_environment_variables_automatically()
+    {
+        // Ensures that the environment variables are properly obtained from
+        // System.Environment when they are not provided explicitly to CliApplication.
+
+        // Arrange
+        var command = Cli.Wrap(Dummy.Program.FilePath)
+            .WithArguments("env-test")
+            .WithEnvironmentVariables(e => e.Set("ENV_TARGET", "Mars"));
+
+        // Act
+        var result = await command.ExecuteBufferedAsync();
+
+        // Assert
+        result.StandardOutput.Trim().Should().Be("Hello Mars!");
+    }
+}

CliFx.Tests/ErrorReportingSpecs.cs

@@ -0,0 +1,209 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class ErrorReportingSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_throw_an_exception_in_a_command_to_report_an_error_with_a_stacktrace()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) =>
+                    throw new Exception("Something went wrong");
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().BeEmpty();
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr
+            .Should()
+            .ContainAllInOrder("System.Exception", "Something went wrong", "at", "CliFx.");
+    }
+
+    [Fact]
+    public async Task I_can_throw_an_exception_with_an_inner_exception_in_a_command_to_report_an_error_with_a_stacktrace()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) =>
+                    throw new Exception("Something went wrong", new Exception("Another exception"));
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().BeEmpty();
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr
+            .Should()
+            .ContainAllInOrder(
+                "System.Exception",
+                "Something went wrong",
+                "System.Exception",
+                "Another exception",
+                "at",
+                "CliFx."
+            );
+    }
+
+    [Fact]
+    public async Task I_can_throw_an_exception_in_a_command_to_report_an_error_and_exit_with_the_specified_code()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) =>
+                    throw new CommandException("Something went wrong", 69);
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(69);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().BeEmpty();
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Trim().Should().Be("Something went wrong");
+    }
+
+    [Fact]
+    public async Task I_can_throw_an_exception_without_a_message_in_a_command_to_report_an_error_with_a_stacktrace()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) =>
+                    throw new CommandException("", 69);
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(69);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().BeEmpty();
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().ContainAllInOrder("CliFx.Exceptions.CommandException", "at", "CliFx.");
+    }
+
+    [Fact]
+    public async Task I_can_throw_an_exception_in_a_command_to_report_an_error_and_print_the_help_text()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) =>
+                    throw new CommandException("Something went wrong", 69, true);
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .SetDescription("This will be in help text")
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(69);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().Contain("This will be in help text");
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Trim().Should().Be("Something went wrong");
+    }
+}

CliFx.Tests/HelpTextSpecs.cs

@@ -0,0 +1,994 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class HelpTextSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_request_the_help_text_by_running_the_application_without_arguments_if_the_default_command_is_not_defined()
+    {
+        // Arrange
+        var application = new CliApplicationBuilder()
+            .UseConsole(FakeConsole)
+            .SetDescription("This will be in help text")
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().Contain("This will be in help text");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_by_running_the_application_with_the_help_option()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .SetDescription("This will be in help text")
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().Contain("This will be in help text");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_by_running_the_application_with_the_help_option_even_if_the_default_command_is_not_defined()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command("cmd")]
+            public class NamedCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd child")]
+            public class NamedChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .SetDescription("This will be in help text")
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().Contain("This will be in help text");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_for_a_specific_command_by_running_the_application_and_specifying_its_name_with_the_help_option()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd", Description = "Description of a named command.")]
+            public class NamedCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd child")]
+            public class NamedChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["cmd", "--help"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().Contain("Description of a named command.");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_for_a_specific_nested_command_by_running_the_application_and_specifying_its_name_with_the_help_option()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd")]
+            public class NamedCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd child", Description = "Description of a named child command.")]
+            public class NamedChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["cmd", "sub", "--help"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().Contain("Description of a named child command.");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_by_running_the_application_with_invalid_arguments()
+    {
+        // Arrange
+        var application = new CliApplicationBuilder()
+            .AddCommand<NoOpCommand>()
+            .UseConsole(FakeConsole)
+            .SetDescription("This will be in help text")
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["invalid-command", "--invalid-option"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().Contain("This will be in help text");
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().NotBeNullOrWhiteSpace();
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_application_title_description_and_version()
+    {
+        // Arrange
+        var application = new CliApplicationBuilder()
+            .UseConsole(FakeConsole)
+            .SetTitle("App title")
+            .SetDescription("App description")
+            .SetVersion("App version")
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ContainAll("App title", "App description", "App version");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_command_description()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command(Description = "Description of the default command.")]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ContainAllInOrder("DESCRIPTION", "Description of the default command.");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_usage_format_for_a_named_command()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd")]
+            public class NamedCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ContainAllInOrder("USAGE", "[command]", "[...]");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_usage_format_for_all_parameters()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
+
+                [CommandParameter(2)]
+                public required IReadOnlyList<string> Baz { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ContainAllInOrder("USAGE", "<foo>", "<bar>", "<baz...>");
+    }
+
+    // https://github.com/Tyrrrz/CliFx/issues/117
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_usage_format_for_all_parameters_in_the_correct_order()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            // Base members appear last in reflection order
+            public abstract class CommandBase : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                public abstract ValueTask ExecuteAsync(IConsole console);
+            }
+
+            [Command]
+            public class Command : CommandBase
+            {
+                [CommandParameter(2)]
+                public required IReadOnlyList<string> Baz { get; init; }
+
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
+
+                public override ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ContainAllInOrder("USAGE", "<foo>", "<bar>", "<baz...>");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_usage_format_for_all_required_options()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public required string Foo { get; init; }
+
+                [CommandOption("bar")]
+                public string? Bar { get; init; }
+
+                [CommandOption("baz")]
+                public required IReadOnlyList<string> Baz { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder("USAGE", "--foo <value>", "--baz <values...>", "[options]");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_list_of_all_parameters_and_options()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0, Name = "foo", Description = "Description of foo.")]
+                public string? Foo { get; init; }
+
+                [CommandOption("bar", Description = "Description of bar.")]
+                public string? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "PARAMETERS",
+                "foo",
+                "Description of foo.",
+                "OPTIONS",
+                "--bar",
+                "Description of bar."
+            );
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_help_and_version_options()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "OPTIONS",
+                "-h",
+                "--help",
+                "Shows help text",
+                "--version",
+                "Shows version information"
+            );
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_on_a_named_command_to_see_the_help_option()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command("cmd")]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["cmd", "--help"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+
+        stdOut.Should().ContainAllInOrder("OPTIONS", "-h", "--help", "Shows help text");
+
+        stdOut.Should().NotContainAny("--version", "Shows version information");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_list_of_valid_values_for_all_parameters_and_options_bound_to_enum_properties()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public enum CustomEnum { One, Two, Three }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public CustomEnum Foo { get; init; }
+
+                [CommandOption("bar")]
+                public CustomEnum Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "PARAMETERS",
+                "foo",
+                "Choices:",
+                "One",
+                "Two",
+                "Three",
+                "OPTIONS",
+                "--bar",
+                "Choices:",
+                "One",
+                "Two",
+                "Three"
+            );
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_list_of_valid_values_for_all_parameters_and_options_bound_to_non_scalar_enum_properties()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public enum CustomEnum { One, Two, Three }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required IReadOnlyList<CustomEnum> Foo { get; init; }
+
+                [CommandOption("bar")]
+                public required IReadOnlyList<CustomEnum> Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "PARAMETERS",
+                "foo",
+                "Choices:",
+                "One",
+                "Two",
+                "Three",
+                "OPTIONS",
+                "--bar",
+                "Choices:",
+                "One",
+                "Two",
+                "Three"
+            );
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_list_of_valid_values_for_all_parameters_and_options_bound_to_nullable_enum_properties()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public enum CustomEnum { One, Two, Three }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public CustomEnum? Foo { get; init; }
+
+                [CommandOption("bar")]
+                public IReadOnlyList<CustomEnum?>? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "PARAMETERS",
+                "foo",
+                "Choices:",
+                "One",
+                "Two",
+                "Three",
+                "OPTIONS",
+                "--bar",
+                "Choices:",
+                "One",
+                "Two",
+                "Three"
+            );
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_environment_variables_of_options_that_use_them_as_fallback()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public enum CustomEnum { One, Two, Three }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo", EnvironmentVariable = "ENV_FOO")]
+                public CustomEnum Foo { get; init; }
+
+                [CommandOption("bar", EnvironmentVariable = "ENV_BAR")]
+                public CustomEnum Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "OPTIONS",
+                "--foo",
+                "Environment variable:",
+                "ENV_FOO",
+                "--bar",
+                "Environment variable:",
+                "ENV_BAR"
+            );
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_default_values_of_non_required_options()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public enum CustomEnum { One, Two, Three }
+
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public object? Foo { get; init; } = 42;
+
+                [CommandOption("bar")]
+                public string? Bar { get; init; } = "hello";
+
+                [CommandOption("baz")]
+                public IReadOnlyList<string>? Baz { get; init; } = new[] {"one", "two", "three"};
+
+                [CommandOption("qwe")]
+                public bool Qwe { get; init; } = true;
+
+                [CommandOption("qop")]
+                public int? Qop { get; init; } = 1337;
+
+                [CommandOption("zor")]
+                public TimeSpan Zor { get; init; } = TimeSpan.FromMinutes(123);
+
+                [CommandOption("lol")]
+                public CustomEnum Lol { get; init; } = CustomEnum.Two;
+
+                [CommandOption("hmm")]
+                public required string Hmm { get; init; } = "not printed";
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "OPTIONS",
+                "--foo",
+                "Default:",
+                "42",
+                "--bar",
+                "Default:",
+                "hello",
+                "--baz",
+                "Default:",
+                "one",
+                "two",
+                "three",
+                "--qwe",
+                "Default:",
+                "True",
+                "--qop",
+                "Default:",
+                "1337",
+                "--zor",
+                "Default:",
+                "02:03:00",
+                "--lol",
+                "Default:",
+                "Two"
+            );
+
+        stdOut.Should().NotContain("not printed");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_list_of_all_immediate_child_commands()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command("cmd1", Description = "Description of one command.")]
+            public class FirstCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd2", Description = "Description of another command.")]
+            public class SecondCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd2 child", Description = "Description of another command's child command.")]
+            public class SecondCommandChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd3 child", Description = "Description of an orphaned command.")]
+            public class ThirdCommandChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "COMMANDS",
+                "cmd1",
+                "Description of one command.",
+                "cmd2",
+                "Description of another command.",
+                // `cmd2 child` will appear as an immediate command because it does not
+                // have a more specific parent.
+                "cmd3 child",
+                "Description of an orphaned command."
+            );
+
+        // `cmd2 child` will still appear in the list of `cmd2` subcommands,
+        // but its description will not be visible.
+        stdOut.Should().NotContain("Description of another command's child command.");
+    }
+
+    [Fact]
+    public async Task I_can_request_the_help_text_to_see_the_list_of_all_immediate_grand_child_commands()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command("cmd1")]
+            public class FirstCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd1 child1")]
+            public class FirstCommandFirstChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd2")]
+            public class SecondCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd2 child11")]
+            public class SecondCommandFirstChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+
+            [Command("cmd2 child2")]
+            public class SecondCommandSecondChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--help"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ContainAllInOrder(
+                "COMMANDS",
+                "cmd1",
+                "Subcommands:",
+                "cmd1 child1",
+                "cmd2",
+                "Subcommands:",
+                "cmd2 child1",
+                "cmd2 child2"
+            );
+    }
+
+    [Fact]
+    public async Task I_can_request_the_version_text_by_running_the_application_with_the_version_option()
+    {
+        // Arrange
+        var application = new CliApplicationBuilder()
+            .AddCommand<NoOpCommand>()
+            .SetVersion("v6.9")
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--version"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("v6.9");
+    }
+}

CliFx.Tests/OptionBindingSpecs.cs

@@ -0,0 +1,762 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class OptionBindingSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_by_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public bool Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--foo"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("True");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_by_short_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public bool Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["-f"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("True");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_set_by_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
+
+                [CommandOption("bar")]
+                public string? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "one", "--bar", "two"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = two");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_set_by_short_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public string? Foo { get; init; }
+
+                [CommandOption('b')]
+                public string? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "one", "-b", "two"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = two");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_value_from_the_corresponding_argument_stack_by_short_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public string? Foo { get; init; }
+
+                [CommandOption('b')]
+                public string? Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-fb", "value"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = ", "Bar = value");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_arguments_by_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("Foo")]
+                public IReadOnlyList<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "one", "two", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_arguments_by_short_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public IReadOnlyList<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "one", "two", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_argument_sets_by_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public IReadOnlyList<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "one", "--foo", "two", "--foo", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_argument_sets_by_short_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption('f')]
+                public IReadOnlyList<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["-f", "one", "-f", "two", "-f", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_non_scalar_property_and_get_the_values_from_the_corresponding_argument_sets_by_name_or_short_name()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo", 'f')]
+                public IReadOnlyList<string>? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    foreach (var i in Foo)
+                        console.WriteLine(i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "one", "-f", "two", "--foo", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("one", "two", "three");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_and_get_no_value_if_the_user_does_not_provide_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
+
+                [CommandOption("bar")]
+                public string? Bar { get; init; } = "hello";
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "one"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = hello");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_through_multiple_inheritance()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            public static class SharedContext
+            {
+                public static int Foo { get; set; }
+
+                public static bool Bar { get; set; }
+            }
+
+            public interface IHasFoo : ICommand
+            {
+                [CommandOption("foo")]
+                public int Foo
+                {
+                    get => SharedContext.Foo;
+                    init => SharedContext.Foo = value;
+                }
+            }
+
+            public interface IHasBar : ICommand
+            {
+                [CommandOption("bar")]
+                public bool Bar
+                {
+                    get => SharedContext.Bar;
+                    init => SharedContext.Bar = value;
+                }
+            }
+
+            public interface IHasBaz : ICommand
+            {
+                public string? Baz { get; init; }
+            }
+
+            [Command]
+            public class Command : IHasFoo, IHasBar, IHasBaz
+            {
+                [CommandOption("baz")]
+                public string? Baz { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + SharedContext.Foo);
+                    console.WriteLine("Bar = " + SharedContext.Bar);
+                    console.WriteLine("Baz = " + Baz);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--foo", "42", "--bar", "--baz", "xyz"]);
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = 42", "Bar = True", "Baz = xyz");
+    }
+
+    [Fact]
+    public async Task I_can_bind_an_option_to_a_property_and_get_the_correct_value_if_the_user_provides_an_argument_containing_a_negative_number()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(Foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "-13"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("-13");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_required_option_to_a_property_and_get_an_error_if_the_user_does_not_provide_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Missing required option(s)");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_required_option_to_a_property_and_get_an_error_if_the_user_provides_an_empty_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public required string Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--foo"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Missing required option(s)");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_an_option_to_a_non_scalar_property_and_get_an_error_if_the_user_does_not_provide_at_least_one_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public required IReadOnlyList<string> Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["--foo"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Missing required option(s)");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_options_and_get_an_error_if_the_user_provides_unrecognized_arguments()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "one", "--bar", "two"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Unrecognized option(s)");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_an_option_to_a_scalar_property_and_get_an_error_if_the_user_provides_too_many_arguments()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandOption("foo")]
+                public string? Foo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["--foo", "one", "two", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("expects a single argument, but provided with multiple");
+    }
+}

CliFx.Tests/ParameterBindingSpecs.cs

@@ -0,0 +1,263 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using CliFx.Tests.Utils.Extensions;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class ParameterBindingSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_bind_a_parameter_to_a_property_and_get_the_value_from_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["one", "two"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = one", "Bar = two");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_parameter_to_a_non_scalar_property_and_get_values_from_the_remaining_non_option_arguments()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
+
+                [CommandParameter(2)]
+                public required IReadOnlyList<string> Baz { get; init; }
+
+                [CommandOption("boo")]
+                public string? Boo { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    foreach (var i in Baz)
+                        console.WriteLine("Baz = " + i);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["one", "two", "three", "four", "five", "--boo", "xxx"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut
+            .Should()
+            .ConsistOfLines("Foo = one", "Bar = two", "Baz = three", "Baz = four", "Baz = five");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_to_a_property_and_get_an_error_if_the_user_does_not_provide_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["one"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Missing required parameter(s)");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_a_parameter_to_a_non_scalar_property_and_get_an_error_if_the_user_does_not_provide_at_least_one_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required IReadOnlyList<string> Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["one"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Missing required parameter(s)");
+    }
+
+    [Fact]
+    public async Task I_can_bind_a_non_required_parameter_to_a_property_and_get_no_value_if_the_user_does_not_provide_the_corresponding_argument()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1, IsRequired = false)]
+                public string? Bar { get; init; } = "xyz";
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("Foo = " + Foo);
+                    console.WriteLine("Bar = " + Bar);
+
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["abc"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Should().ConsistOfLines("Foo = abc", "Bar = xyz");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_bind_parameters_and_get_an_error_if_the_user_provides_too_many_arguments()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                [CommandParameter(0)]
+                public required string Foo { get; init; }
+
+                [CommandParameter(1)]
+                public required string Bar { get; init; }
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["one", "two", "three"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Unexpected parameter(s)");
+    }
+}

CliFx.Tests/RoutingSpecs.cs

@@ -0,0 +1,179 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Tests.Utils;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class RoutingSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_configure_a_command_to_be_executed_by_default_when_the_user_does_not_specify_a_command_name()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("default");
+                    return default;
+                }
+            }
+
+            [Command("cmd")]
+            public class NamedCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("cmd");
+                    return default;
+                }
+            }
+
+            [Command("cmd child")]
+            public class NamedChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("cmd child");
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("default");
+    }
+
+    [Fact]
+    public async Task I_can_configure_a_command_to_be_executed_when_the_user_specifies_its_name()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("default");
+                    return default;
+                }
+            }
+
+            [Command("cmd")]
+            public class NamedCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("cmd");
+                    return default;
+                }
+            }
+
+            [Command("cmd child")]
+            public class NamedChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("cmd child");
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(["cmd"], new Dictionary<string, string>());
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("cmd");
+    }
+
+    [Fact]
+    public async Task I_can_configure_a_nested_command_to_be_executed_when_the_user_specifies_its_name()
+    {
+        // Arrange
+        var commandTypes = DynamicCommandBuilder.CompileMany(
+            // lang=csharp
+            """
+            [Command]
+            public class DefaultCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("default");
+                    return default;
+                }
+            }
+
+            [Command("cmd")]
+            public class NamedCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("cmd");
+                    return default;
+                }
+            }
+
+            [Command("cmd child")]
+            public class NamedChildCommand : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("cmd child");
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommands(commandTypes)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            ["cmd", "child"],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("cmd child");
+    }
+}

CliFx.Tests/SpecsBase.cs

@@ -0,0 +1,19 @@
+using System;
+using CliFx.Infrastructure;
+using CliFx.Tests.Utils.Extensions;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public abstract class SpecsBase(ITestOutputHelper testOutput) : IDisposable
+{
+    public ITestOutputHelper TestOutput { get; } = testOutput;
+
+    public FakeInMemoryConsole FakeConsole { get; } = new();
+
+    public void Dispose()
+    {
+        FakeConsole.DumpToTestOutput(TestOutput);
+        FakeConsole.Dispose();
+    }
+}

CliFx.Tests/TestObjects/TestCommand.cs

@@ -1,18 +0,0 @@
-using CliFx.Attributes;
-using CliFx.Models;
-
-namespace CliFx.Tests.TestObjects
-{
-    [DefaultCommand]
-    [Command("command")]
-    public class TestCommand : Command
-    {
-        [CommandOption("int", ShortName = 'i', IsRequired = true)]
-        public int IntOption { get; set; } = 24;
-
-        [CommandOption("str", ShortName = 's')]
-        public string StringOption { get; set; } = "foo bar";
-
-        public override ExitCode Execute() => new ExitCode(IntOption, StringOption);
-    }
-}

CliFx.Tests/TestObjects/TestEnum.cs

@@ -1,9 +0,0 @@
-namespace CliFx.Tests.TestObjects
-{
-    public enum TestEnum
-    {
-        Value1,
-        Value2,
-        Value3
-    }
-}

CliFx.Tests/TypeActivationSpecs.cs

@@ -0,0 +1,223 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Infrastructure;
+using CliFx.Tests.Utils;
+using FluentAssertions;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests;
+
+public class TypeActivationSpecs(ITestOutputHelper testOutput) : SpecsBase(testOutput)
+{
+    [Fact]
+    public async Task I_can_configure_the_application_to_use_the_default_type_activator_to_initialize_types_through_parameterless_constructors()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("foo");
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .UseTypeActivator(new DefaultTypeActivator())
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("foo");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_configure_the_application_to_use_the_default_type_activator_and_get_an_error_if_the_requested_type_does_not_have_a_parameterless_constructor()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public Command(string foo) {}
+
+                public ValueTask ExecuteAsync(IConsole console) => default;
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .UseTypeActivator(new DefaultTypeActivator())
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Failed to create an instance of type");
+    }
+
+    [Fact]
+    public async Task I_can_configure_the_application_to_use_a_custom_type_activator_to_initialize_types_using_a_delegate()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                private readonly string _foo;
+
+                public Command(string foo) => _foo = foo;
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(_foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .UseTypeActivator(type => Activator.CreateInstance(type, "Hello world")!)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("Hello world");
+    }
+
+    [Fact]
+    public async Task I_can_configure_the_application_to_use_a_custom_type_activator_to_initialize_types_using_a_service_provider()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                private readonly string _foo;
+
+                public Command(string foo) => _foo = foo;
+
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine(_foo);
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .UseTypeActivator(commandTypes =>
+            {
+                var services = new ServiceCollection();
+
+                foreach (var serviceType in commandTypes)
+                {
+                    services.AddSingleton(
+                        serviceType,
+                        Activator.CreateInstance(serviceType, "Hello world")!
+                    );
+                }
+
+                return services.BuildServiceProvider();
+            })
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().Be(0);
+
+        var stdOut = FakeConsole.ReadOutputString();
+        stdOut.Trim().Should().Be("Hello world");
+    }
+
+    [Fact]
+    public async Task I_can_try_to_configure_the_application_to_use_a_custom_type_activator_and_get_an_error_if_the_requested_type_cannot_be_initialized()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // lang=csharp
+            """
+            [Command]
+            public class Command : ICommand
+            {
+                public ValueTask ExecuteAsync(IConsole console)
+                {
+                    console.WriteLine("foo");
+                    return default;
+                }
+            }
+            """
+        );
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .UseTypeActivator((Type _) => null!)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            [],
+            new Dictionary<string, string>()
+        );
+
+        // Assert
+        exitCode.Should().NotBe(0);
+
+        var stdErr = FakeConsole.ReadErrorString();
+        stdErr.Should().Contain("Failed to create an instance of type");
+    }
+}

CliFx.Tests/Utils/DynamicCommandBuilder.cs

@@ -0,0 +1,135 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using Basic.Reference.Assemblies;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Text;
+
+namespace CliFx.Tests.Utils;
+
+// This class uses Roslyn to compile commands dynamically.
+// It allows us to collocate commands with tests more easily, which helps a lot when reasoning about them.
+// Unfortunately, this comes at a cost of static typing, but this is still a worthwhile trade off.
+// Maybe one day C# will allow declaring classes inside methods and doing this will no longer be necessary.
+// Language proposal: https://github.com/dotnet/csharplang/discussions/130
+internal static class DynamicCommandBuilder
+{
+    public static IReadOnlyList<Type> CompileMany(string sourceCode)
+    {
+        // Get default system namespaces
+        var defaultSystemNamespaces = new[]
+        {
+            "System",
+            "System.Collections",
+            "System.Collections.Generic",
+            "System.Linq",
+            "System.Threading.Tasks",
+            "System.Globalization",
+        };
+
+        // Get default CliFx namespaces
+        var defaultCliFxNamespaces = typeof(ICommand)
+            .Assembly.GetTypes()
+            .Where(t => t.IsPublic)
+            .Select(t => t.Namespace)
+            .Distinct()
+            .ToArray();
+
+        // Append default imports to the source code
+        var sourceCodeWithUsings =
+            string.Join(Environment.NewLine, defaultSystemNamespaces.Select(n => $"using {n};"))
+            + string.Join(Environment.NewLine, defaultCliFxNamespaces.Select(n => $"using {n};"))
+            + Environment.NewLine
+            + sourceCode;
+
+        // Parse the source code
+        var ast = SyntaxFactory.ParseSyntaxTree(
+            SourceText.From(sourceCodeWithUsings),
+            CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.Preview)
+        );
+
+        // Compile the code to IL
+        var compilation = CSharpCompilation.Create(
+            "CliFxTests_DynamicAssembly_" + Guid.NewGuid(),
+            [ast],
+            Net80
+                .References.All.Append(
+                    MetadataReference.CreateFromFile(typeof(ICommand).Assembly.Location)
+                )
+                .Append(
+                    MetadataReference.CreateFromFile(
+                        typeof(DynamicCommandBuilder).Assembly.Location
+                    )
+                ),
+            // DLL to avoid having to define the Main() method
+            new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)
+        );
+
+        var compilationErrors = compilation
+            .GetDiagnostics()
+            .Where(d => d.Severity >= DiagnosticSeverity.Error)
+            .ToArray();
+
+        if (compilationErrors.Any())
+        {
+            throw new InvalidOperationException(
+                $"""
+                Failed to compile code.
+                {string.Join(Environment.NewLine, compilationErrors.Select(e => e.ToString()))}
+                """
+            );
+        }
+
+        // Emit the code to an in-memory buffer
+        using var buffer = new MemoryStream();
+        var emit = compilation.Emit(buffer);
+
+        var emitErrors = emit
+            .Diagnostics.Where(d => d.Severity >= DiagnosticSeverity.Error)
+            .ToArray();
+
+        if (emitErrors.Any())
+        {
+            throw new InvalidOperationException(
+                $"""
+                Failed to emit code.
+                {string.Join(Environment.NewLine, emitErrors.Select(e => e.ToString()))}
+                """
+            );
+        }
+
+        // Load the generated assembly
+        var generatedAssembly = Assembly.Load(buffer.ToArray());
+
+        // Return all defined commands
+        var commandTypes = generatedAssembly
+            .GetTypes()
+            .Where(t => t.IsAssignableTo(typeof(ICommand)) && !t.IsAbstract)
+            .ToArray();
+
+        if (commandTypes.Length <= 0)
+        {
+            throw new InvalidOperationException(
+                "There are no command definitions in the provided source code."
+            );
+        }
+
+        return commandTypes;
+    }
+
+    public static Type Compile(string sourceCode)
+    {
+        var commandTypes = CompileMany(sourceCode);
+        if (commandTypes.Count > 1)
+        {
+            throw new InvalidOperationException(
+                "There are more than one command definitions in the provided source code."
+            );
+        }
+
+        return commandTypes.Single();
+    }
+}

CliFx.Tests/Utils/Extensions/AssertionExtensions.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using FluentAssertions;
+using FluentAssertions.Primitives;
+
+namespace CliFx.Tests.Utils.Extensions;
+
+internal static class AssertionExtensions
+{
+    public static void ConsistOfLines(
+        this StringAssertions assertions,
+        params IEnumerable<string> lines
+    ) =>
+        assertions
+            .Subject.Split(['\n', '\r'], StringSplitOptions.RemoveEmptyEntries)
+            .Should()
+            .Equal(lines);
+
+    public static AndConstraint<StringAssertions> ContainAllInOrder(
+        this StringAssertions assertions,
+        IEnumerable<string> values
+    )
+    {
+        var lastIndex = 0;
+
+        foreach (var value in values)
+        {
+            var index = assertions.Subject.IndexOf(value, lastIndex, StringComparison.Ordinal);
+
+            if (index < 0)
+            {
+                assertions.CurrentAssertionChain.FailWith(
+                    $"Expected string '{assertions.Subject}' to contain '{value}' after position {lastIndex}."
+                );
+            }
+
+            lastIndex = index;
+        }
+
+        return new AndConstraint<StringAssertions>(assertions);
+    }
+
+    public static AndConstraint<StringAssertions> ContainAllInOrder(
+        this StringAssertions assertions,
+        params string[] values
+    ) => assertions.ContainAllInOrder((IEnumerable<string>)values);
+}

CliFx.Tests/Utils/Extensions/ConsoleExtensions.cs

@@ -0,0 +1,19 @@
+using CliFx.Infrastructure;
+using Xunit.Abstractions;
+
+namespace CliFx.Tests.Utils.Extensions;
+
+internal static class ConsoleExtensions
+{
+    public static void DumpToTestOutput(
+        this FakeInMemoryConsole console,
+        ITestOutputHelper testOutput
+    )
+    {
+        testOutput.WriteLine("[*] Captured standard output:");
+        testOutput.WriteLine(console.ReadOutputString());
+
+        testOutput.WriteLine("[*] Captured standard error:");
+        testOutput.WriteLine(console.ReadErrorString());
+    }
+}

CliFx.Tests/Utils/NoOpCommand.cs

@@ -0,0 +1,11 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+
+namespace CliFx.Tests.Utils;
+
+[Command]
+internal class NoOpCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console) => default;
+}

CliFx.Tests/xunit.runner.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "methodDisplayOptions": "all",
+  "methodDisplay": "method"
+}

CliFx.sln

@@ -7,15 +7,21 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx", "CliFx\CliFx.csproj
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Tests", "CliFx.Tests\CliFx.Tests.csproj", "{268CF863-65A5-49BB-93CF-08972B7756DC}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Tests.Dummy", "CliFx.Tests.Dummy\CliFx.Tests.Dummy.csproj", "{4904B3EB-3286-4F1B-8B74-6FF051C8E787}"
-EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{3AAE8166-BB8E-49DA-844C-3A0EE6BD40A0}"
 	ProjectSection(SolutionItems) = preProject
-		Changelog.md = Changelog.md
+		Directory.Build.props = Directory.Build.props
 		License.txt = License.txt
 		Readme.md = Readme.md
 	EndProjectSection
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Benchmarks", "CliFx.Benchmarks\CliFx.Benchmarks.csproj", "{8ACD6DC2-D768-4850-9223-5B7C83A78513}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Demo", "CliFx.Demo\CliFx.Demo.csproj", "{AAB6844C-BF71-448F-A11B-89AEE459AB15}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Tests.Dummy", "CliFx.Tests.Dummy\CliFx.Tests.Dummy.csproj", "{F717347D-8656-44DA-A4A2-BE515E8C4655}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.SourceGeneration", "CliFx.SourceGeneration\CliFx.SourceGeneration.csproj", "{F8460D69-F8CF-405C-A6ED-BED02A21DB42}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -50,18 +56,54 @@ Global
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x64.Build.0 = Release|Any CPU
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x86.ActiveCfg = Release|Any CPU
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x86.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x64.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x64.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x86.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x86.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|Any CPU.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x64.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x64.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x86.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x86.Build.0 = Release|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|x64.Build.0 = Debug|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|x86.Build.0 = Debug|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Release|Any CPU.Build.0 = Release|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Release|x64.ActiveCfg = Release|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Release|x64.Build.0 = Release|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Release|x86.ActiveCfg = Release|Any CPU
+		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Release|x86.Build.0 = Release|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Debug|x64.Build.0 = Debug|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Debug|x86.Build.0 = Debug|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|Any CPU.Build.0 = Release|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|x64.ActiveCfg = Release|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|x64.Build.0 = Release|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|x86.ActiveCfg = Release|Any CPU
+		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|x86.Build.0 = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x64.Build.0 = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x86.Build.0 = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x64.ActiveCfg = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x64.Build.0 = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x86.ActiveCfg = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x86.Build.0 = Release|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Debug|x64.Build.0 = Debug|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Debug|x86.Build.0 = Debug|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Release|x64.ActiveCfg = Release|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Release|x64.Build.0 = Release|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Release|x86.ActiveCfg = Release|Any CPU
+		{F8460D69-F8CF-405C-A6ED-BED02A21DB42}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

CliFx/ApplicationConfiguration.cs

@@ -0,0 +1,28 @@
+using CliFx.Schema;
+
+namespace CliFx;
+
+/// <summary>
+/// Configuration of an application.
+/// </summary>
+public class ApplicationConfiguration(
+    ApplicationSchema schema,
+    bool isDebugModeAllowed,
+    bool isPreviewModeAllowed
+)
+{
+    /// <summary>
+    /// Application schema.
+    /// </summary>
+    public ApplicationSchema Schema { get; } = schema;
+
+    /// <summary>
+    /// Whether debug mode is allowed in the application.
+    /// </summary>
+    public bool IsDebugModeAllowed { get; } = isDebugModeAllowed;
+
+    /// <summary>
+    /// Whether preview mode is allowed in the application.
+    /// </summary>
+    public bool IsPreviewModeAllowed { get; } = isPreviewModeAllowed;
+}

CliFx/ApplicationMetadata.cs

@@ -0,0 +1,32 @@
+namespace CliFx;
+
+/// <summary>
+/// Metadata associated with an application.
+/// </summary>
+public class ApplicationMetadata(
+    string title,
+    string executableName,
+    string version,
+    string? description
+)
+{
+    /// <summary>
+    /// Application title.
+    /// </summary>
+    public string Title { get; } = title;
+
+    /// <summary>
+    /// Application executable name.
+    /// </summary>
+    public string ExecutableName { get; } = executableName;
+
+    /// <summary>
+    /// Application version.
+    /// </summary>
+    public string Version { get; } = version;
+
+    /// <summary>
+    /// Application description.
+    /// </summary>
+    public string? Description { get; } = description;
+}

CliFx/Attributes/CommandAttribute.cs

@@ -1,15 +1,29 @@
 using System;
 
-namespace CliFx.Attributes
-{
-    [AttributeUsage(AttributeTargets.Class, Inherited = false)]
-    public class CommandAttribute : Attribute
-    {
-        public string Name { get; }
+namespace CliFx.Attributes;
 
-        public CommandAttribute(string name)
-        {
-            Name = name;
-        }
-    }
-}
+/// <summary>
+/// Annotates a type that defines a command.
+/// If the command is named, then the user must provide its name through the
+/// command-line arguments in order to execute it.
+/// If the command is not named, then it is treated as the application's
+/// default command and is executed whenever the user does not provide a command name.
+/// </summary>
+/// <remarks>
+/// Only one default command is allowed per application.
+/// All commands registered in an application must have unique names (comparison IS NOT case-sensitive).
+/// </remarks>
+[AttributeUsage(AttributeTargets.Class, Inherited = false)]
+public class CommandAttribute(string? name = null) : Attribute
+{
+    /// <summary>
+    /// Command name.
+    /// </summary>
+    public string? Name { get; } = name;
+
+    /// <summary>
+    /// Command description.
+    /// This is shown to the user in the help text.
+    /// </summary>
+    public string? Description { get; set; }
+}

CliFx/Attributes/CommandHelpOptionAttribute.cs

@@ -0,0 +1,19 @@
+namespace CliFx.Attributes;
+
+/// <summary>
+/// Binds a property to the help option of a command.
+/// </summary>
+/// <remarks>
+/// This attribute is applied automatically by the framework and should not need to be used explicitly.
+/// </remarks>
+public class CommandHelpOptionAttribute : CommandOptionAttribute
+{
+    /// <summary>
+    /// Initializes an instance of <see cref="CommandHelpOptionAttribute" />.
+    /// </summary>
+    public CommandHelpOptionAttribute()
+        : base("help", 'h')
+    {
+        Description = "Show help for this command.";
+    }
+}

CliFx/Attributes/CommandInputAttribute.cs

@@ -0,0 +1,34 @@
+using System;
+using CliFx.Extensibility;
+
+namespace CliFx.Attributes;
+
+/// <summary>
+/// Binds a property to a command-line input.
+/// </summary>
+[AttributeUsage(AttributeTargets.Property)]
+public abstract class CommandInputAttribute : Attribute
+{
+    /// <summary>
+    /// Input description, as shown in the help text.
+    /// </summary>
+    public string? Description { get; set; }
+
+    /// <summary>
+    /// Custom converter used for mapping the raw command-line argument into
+    /// the type and shape expected by the underlying property.
+    /// </summary>
+    /// <remarks>
+    /// Converter must derive from <see cref="BindingConverter{T}" />.
+    /// </remarks>
+    public Type? Converter { get; set; }
+
+    /// <summary>
+    /// Custom validators used for verifying the value of the underlying
+    /// property, after it has been set.
+    /// </summary>
+    /// <remarks>
+    /// Validators must derive from <see cref="BindingValidator{T}" />.
+    /// </remarks>
+    public Type[] Validators { get; set; } = [];
+}

CliFx/Attributes/CommandOptionAttribute.cs

@@ -1,21 +1,67 @@
 using System;
 
-namespace CliFx.Attributes
+namespace CliFx.Attributes;
+
+/// <summary>
+/// Binds a property to a command option — a command-line input that is identified by a name and/or a short name.
+/// </summary>
+/// <remarks>
+/// All options in a command must have unique names (comparison IS NOT case-sensitive)
+/// and short names (comparison IS case-sensitive).
+/// </remarks>
+[AttributeUsage(AttributeTargets.Property)]
+public class CommandOptionAttribute : CommandInputAttribute
 {
-    [AttributeUsage(AttributeTargets.Property)]
-    public class CommandOptionAttribute : Attribute
+    /// <summary>
+    /// Initializes an instance of <see cref="CommandOptionAttribute" />.
+    /// </summary>
+    private CommandOptionAttribute(string? name, char? shortName)
     {
-        public string Name { get; }
-
-        public char ShortName { get; set; }
-
-        public bool IsRequired { get; set; }
-
-        public string Description { get; set; }
-
-        public CommandOptionAttribute(string name)
-        {
-            Name = name;
-        }
+        Name = name;
+        ShortName = shortName;
     }
-}
+
+    /// <summary>
+    /// Initializes an instance of <see cref="CommandOptionAttribute" />.
+    /// </summary>
+    public CommandOptionAttribute(string name, char shortName)
+        : this(name, (char?)shortName) { }
+
+    /// <summary>
+    /// Initializes an instance of <see cref="CommandOptionAttribute" />.
+    /// </summary>
+    public CommandOptionAttribute(string name)
+        : this(name, null) { }
+
+    /// <summary>
+    /// Initializes an instance of <see cref="CommandOptionAttribute" />.
+    /// </summary>
+    public CommandOptionAttribute(char shortName)
+        : this(null, (char?)shortName) { }
+
+    /// <summary>
+    /// Option name.
+    /// </summary>
+    public string? Name { get; }
+
+    /// <summary>
+    /// Option short name.
+    /// </summary>
+    public char? ShortName { get; }
+
+    /// <summary>
+    /// Whether this option is required (default: <c>false</c>).
+    /// If an option is required, the user will get an error when they don't set it.
+    /// </summary>
+    /// <remarks>
+    /// You can use the <c>required</c> keyword on the property (introduced in C# 11) to implicitly
+    /// set <see cref="IsRequired" /> to <c>true</c>.
+    /// </remarks>
+    public bool IsRequired { get; set; }
+
+    /// <summary>
+    /// Environment variable whose value will be used as a fallback if the option
+    /// has not been explicitly set through command-line arguments.
+    /// </summary>
+    public string? EnvironmentVariable { get; set; }
+}

CliFx/Attributes/CommandParameterAttribute.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+
+namespace CliFx.Attributes;
+
+/// <summary>
+/// Binds a property to a command parameter — a command-line input that is identified by its relative position (order).
+/// Higher order means that the parameter appears later, lower order means that it appears earlier.
+/// </summary>
+/// <remarks>
+/// All parameters in a command must have unique order values.
+/// If a parameter is bound to a property whose type is a sequence (i.e. implements <see cref="IEnumerable{T}"/>; except <see cref="string" />),
+/// then it must have the highest order in the command.
+/// Only one sequential parameter is allowed per command.
+/// </remarks>
+[AttributeUsage(AttributeTargets.Property)]
+public class CommandParameterAttribute(int order) : CommandInputAttribute
+{
+    /// <summary>
+    /// Parameter order.
+    /// </summary>
+    public int Order { get; } = order;
+
+    /// <summary>
+    /// Whether this parameter is required (default: <c>true</c>).
+    /// If a parameter is required, the user will get an error when they don't set it.
+    /// </summary>
+    /// <remarks>
+    /// Parameter marked as non-required must have the highest order in the command.
+    /// Only one non-required parameter is allowed per command.
+    /// </remarks>
+    public bool IsRequired { get; set; } = true;
+
+    /// <summary>
+    /// Parameter name, as shown in the help text.
+    /// </summary>
+    /// <remarks>
+    /// If this isn't specified, parameter name is inferred from the property name.
+    /// </remarks>
+    public string? Name { get; set; }
+}

CliFx/Attributes/CommandVersionOptionAttribute.cs

@@ -0,0 +1,19 @@
+namespace CliFx.Attributes;
+
+/// <summary>
+/// Binds a property to the version option of a command.
+/// </summary>
+/// <remarks>
+/// This attribute is applied automatically by the framework and should not need to be used explicitly.
+/// </remarks>
+public class CommandVersionOptionAttribute : CommandOptionAttribute
+{
+    /// <summary>
+    /// Initializes an instance of <see cref="CommandVersionOptionAttribute" />.
+    /// </summary>
+    public CommandVersionOptionAttribute()
+        : base("version")
+    {
+        Description = "Show application version.";
+    }
+}

CliFx/Attributes/DefaultCommandAttribute.cs

@@ -1,9 +0,0 @@
-using System;
-
-namespace CliFx.Attributes
-{
-    [AttributeUsage(AttributeTargets.Class, Inherited = false)]
-    public class DefaultCommandAttribute : Attribute
-    {
-    }
-}

CliFx/CliApplication.cs

@@ -1,45 +1,226 @@
-using System.Collections.Generic;
-using System.Reflection;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
 using System.Threading.Tasks;
-using CliFx.Services;
+using CliFx.Exceptions;
+using CliFx.Formatting;
+using CliFx.Infrastructure;
+using CliFx.Parsing;
+using CliFx.Schema;
+using CliFx.Utils;
+using CliFx.Utils.Extensions;
 
-namespace CliFx
+namespace CliFx;
+
+/// <summary>
+/// Command-line application facade.
+/// </summary>
+public class CliApplication(
+    ApplicationMetadata metadata,
+    ApplicationConfiguration configuration,
+    IConsole console,
+    ITypeActivator typeActivator
+)
 {
-    public partial class CliApplication : ICliApplication
+    /// <summary>
+    /// Application metadata.
+    /// </summary>
+    public ApplicationMetadata Metadata { get; } = metadata;
+
+    /// <summary>
+    /// Application configuration.
+    /// </summary>
+    public ApplicationConfiguration Configuration { get; } = configuration;
+
+    private bool IsDebugModeEnabled(CommandArguments commandArguments) =>
+        Configuration.IsDebugModeAllowed && commandArguments.IsDebugDirectiveSpecified;
+
+    private bool IsPreviewModeEnabled(CommandArguments commandArguments) =>
+        Configuration.IsPreviewModeAllowed && commandArguments.IsPreviewDirectiveSpecified;
+
+    private async ValueTask PromptDebuggerAsync()
     {
-        private readonly ICommandResolver _commandResolver;
-
-        public CliApplication(ICommandResolver commandResolver)
+        using (console.WithForegroundColor(ConsoleColor.Green))
         {
-            _commandResolver = commandResolver;
+            console.Output.WriteLine(
+                $"Attach the debugger to process with ID {ProcessEx.GetCurrentProcessId()} to continue."
+            );
         }
 
-        public CliApplication()
-            : this(GetDefaultCommandResolver(Assembly.GetCallingAssembly()))
+        // Try to also launch the debugger ourselves (only works with Visual Studio)
+        Debugger.Launch();
+
+        while (!Debugger.IsAttached)
+            await Task.Delay(100);
+    }
+
+    private async ValueTask<int> RunAsync(
+        ApplicationSchema applicationSchema,
+        CommandArguments commandArguments,
+        IReadOnlyDictionary<string, string?> environmentVariables
+    )
+    {
+        // Console colors may have already been overridden by the parent process,
+        // so we need to reset it to make sure that everything we write looks properly.
+        console.ResetColor();
+
+        // Handle the debug directive
+        if (IsDebugModeEnabled(commandArguments))
         {
+            await PromptDebuggerAsync();
         }
 
-        public async Task<int> RunAsync(IReadOnlyList<string> commandLineArguments)
+        // Handle the preview directive
+        if (IsPreviewModeEnabled(commandArguments))
         {
-            // Resolve and execute command
-            var command = _commandResolver.ResolveCommand(commandLineArguments);
-            var exitCode = await command.ExecuteAsync();
+            console.WriteCommandInput(commandArguments);
+            return 0;
+        }
 
-            // TODO: print message if error?
+        // Try to get the command schema that matches the input
+        var command =
+            (
+                !string.IsNullOrWhiteSpace(commandArguments.CommandName)
+                    // If the command name is specified, try to find the command by name.
+                    // This should always succeed, because the input parsing relies on
+                    // the list of available command names.
+                    ? applicationSchema.TryFindCommand(commandArguments.CommandName)
+                    // Otherwise, try to find the default command
+                    : applicationSchema.TryFindDefaultCommand()
+            )
+            ??
+            // If a valid command was not found, use the fallback default command.
+            // This is only used as a stub to show the help text.
+            FallbackDefaultCommand.Schema;
 
-            return exitCode.Value;
+        // Initialize an instance of the command type
+        var commandInstance =
+            command == FallbackDefaultCommand.Schema
+                ? new FallbackDefaultCommand() // bypass the activator
+                : typeActivator.CreateInstance<ICommand>(command.Type);
+
+        // Assemble the help context
+        var helpContext = new HelpContext(
+            Metadata,
+            applicationSchema,
+            command,
+            command.GetValues(commandInstance)
+        );
+
+        // Starting from this point, we may produce exceptions that are meant for the
+        // end-user of the application (i.e. invalid input, command exception, etc).
+        // Catch these exceptions here, print them to the console, and don't let them
+        // propagate further.
+        try
+        {
+            // Activate the command instance with the provided user input
+            command.Activate(commandInstance, commandArguments, environmentVariables);
+
+            // Handle the version option
+            if (commandInstance is ICommandWithVersionOption { IsVersionRequested: true })
+            {
+                console.WriteLine(Metadata.Version);
+                return 0;
+            }
+
+            // Handle the help option
+            if (
+                commandInstance
+                is ICommandWithHelpOption { IsHelpRequested: true }
+                    // Fallback default command always shows help, even if the option is not specified
+                    or FallbackDefaultCommand
+            )
+            {
+                console.WriteHelpText(helpContext);
+                return 0;
+            }
+
+            // Execute the command
+            await commandInstance.ExecuteAsync(console);
+            return 0;
+        }
+        catch (CliFxException ex)
+        {
+            console.WriteException(ex);
+
+            if (ex.ShowHelp)
+            {
+                console.WriteLine();
+                console.WriteHelpText(helpContext);
+            }
+
+            return ex.ExitCode;
         }
     }
 
-    public partial class CliApplication
+    /// <summary>
+    /// Runs the application with the specified command-line arguments and environment variables.
+    /// Returns the exit code which indicates whether the application completed successfully.
+    /// </summary>
+    /// <remarks>
+    /// When running WITHOUT the debugger attached (i.e. in production), this method swallows
+    /// all exceptions and reports them to the console.
+    /// </remarks>
+    public async ValueTask<int> RunAsync(
+        IReadOnlyList<string> commandLineArguments,
+        IReadOnlyDictionary<string, string?> environmentVariables
+    )
     {
-        private static ICommandResolver GetDefaultCommandResolver(Assembly assembly)
+        try
         {
-            var typeProvider = TypeProvider.FromAssembly(assembly);
-            var commandOptionParser = new CommandOptionParser();
-            var commandOptionConverter = new CommandOptionConverter();
-
-            return new CommandResolver(typeProvider, commandOptionParser, commandOptionConverter);
+            return await RunAsync(
+                Configuration.Schema,
+                CommandArguments.Parse(
+                    commandLineArguments,
+                    Configuration.Schema.GetCommandNames()
+                ),
+                environmentVariables
+            );
+        }
+        // To prevent the app from showing the annoying troubleshooting dialog on Windows,
+        // we handle all exceptions ourselves and print them to the console.
+        // We only want to do that if the app is running in production, which we infer
+        // based on whether the debugger is attached to the process.
+        // When not running in production, we want the IDE to show exceptions to the
+        // developer, so we don't swallow them in that case.
+        catch (Exception ex) when (!Debugger.IsAttached)
+        {
+            console.WriteException(ex);
+            return 1;
         }
     }
-}
+
+    /// <summary>
+    /// Runs the application with the specified command-line arguments.
+    /// Returns the exit code which indicates whether the application completed successfully.
+    /// </summary>
+    /// <remarks>
+    /// When running WITHOUT the debugger attached (i.e. in production), this method swallows
+    /// all exceptions and reports them to the console.
+    /// </remarks>
+    public async ValueTask<int> RunAsync(IReadOnlyList<string> commandLineArguments) =>
+        await RunAsync(
+            commandLineArguments,
+            Environment
+                .GetEnvironmentVariables()
+                .ToDictionary<string, string?>(StringComparer.Ordinal)
+        );
+
+    /// <summary>
+    /// Runs the application.
+    /// Command-line arguments and environment variables are resolved automatically.
+    /// Returns the exit code which indicates whether the application completed successfully.
+    /// </summary>
+    /// <remarks>
+    /// When running WITHOUT the debugger attached (i.e. in production), this method swallows
+    /// all exceptions and reports them to the console.
+    /// </remarks>
+    public async ValueTask<int> RunAsync() =>
+        await RunAsync(
+            Environment
+                .GetCommandLineArgs()
+                .Skip(1) // first element is the file path
+                .ToArray()
+        );
+}

CliFx/CliApplicationBuilder.cs

@@ -0,0 +1,252 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
+using System.Linq;
+using CliFx.Infrastructure;
+using CliFx.Schema;
+using CliFx.Utils;
+using CliFx.Utils.Extensions;
+
+namespace CliFx;
+
+/// <summary>
+/// Builder for <see cref="CliApplication" />.
+/// </summary>
+public partial class CliApplicationBuilder
+{
+    private readonly HashSet<CommandSchema> _commands = [];
+
+    private bool _isDebugModeAllowed = true;
+    private bool _isPreviewModeAllowed = true;
+    private string? _title;
+    private string? _executableName;
+    private string? _version;
+    private string? _description;
+    private IConsole? _console;
+    private ITypeActivator? _typeActivator;
+
+    // TODO:
+    // The source generator should generate an internal extension method for the builder called
+    // AddCommandsFromThisAssembly() that would add all command types from the assembly where the builder is used.
+
+    /// <summary>
+    /// Adds a command to the application.
+    /// </summary>
+    public CliApplicationBuilder AddCommand(CommandSchema command)
+    {
+        _commands.Add(command);
+        return this;
+    }
+
+    /// <summary>
+    /// Adds multiple commands to the application.
+    /// </summary>
+    public CliApplicationBuilder AddCommands(IReadOnlyList<CommandSchema> commands)
+    {
+        foreach (var command in commands)
+            AddCommand(command);
+
+        return this;
+    }
+
+    /// <summary>
+    /// Specifies whether debug mode (enabled with the [debug] directive) is allowed in the application.
+    /// </summary>
+    public CliApplicationBuilder AllowDebugMode(bool isAllowed = true)
+    {
+        _isDebugModeAllowed = isAllowed;
+        return this;
+    }
+
+    /// <summary>
+    /// Specifies whether preview mode (enabled with the [preview] directive) is allowed in the application.
+    /// </summary>
+    public CliApplicationBuilder AllowPreviewMode(bool isAllowed = true)
+    {
+        _isPreviewModeAllowed = isAllowed;
+        return this;
+    }
+
+    /// <summary>
+    /// Sets the application title, which is shown in the help text.
+    /// </summary>
+    /// <remarks>
+    /// By default, application title is inferred from the assembly name.
+    /// </remarks>
+    public CliApplicationBuilder SetTitle(string title)
+    {
+        _title = title;
+        return this;
+    }
+
+    /// <summary>
+    /// Sets the application executable name, which is shown in the help text.
+    /// </summary>
+    /// <remarks>
+    /// By default, application executable name is inferred from the assembly file name.
+    /// </remarks>
+    public CliApplicationBuilder SetExecutableName(string executableName)
+    {
+        _executableName = executableName;
+        return this;
+    }
+
+    /// <summary>
+    /// Sets the application version, which is shown in the help text or when the user specifies the version option.
+    /// </summary>
+    /// <remarks>
+    /// By default, application version is inferred from the assembly version.
+    /// </remarks>
+    public CliApplicationBuilder SetVersion(string version)
+    {
+        _version = version;
+        return this;
+    }
+
+    /// <summary>
+    /// Sets the application description, which is shown in the help text.
+    /// </summary>
+    public CliApplicationBuilder SetDescription(string? description)
+    {
+        _description = description;
+        return this;
+    }
+
+    /// <summary>
+    /// Configures the application to use the specified implementation of <see cref="IConsole" />.
+    /// </summary>
+    public CliApplicationBuilder UseConsole(IConsole console)
+    {
+        _console = console;
+        return this;
+    }
+
+    /// <summary>
+    /// Configures the application to use the specified implementation of <see cref="ITypeActivator" />.
+    /// </summary>
+    public CliApplicationBuilder UseTypeActivator(ITypeActivator typeActivator)
+    {
+        _typeActivator = typeActivator;
+        return this;
+    }
+
+    /// <summary>
+    /// Configures the application to use the specified delegate for activating types.
+    /// </summary>
+    public CliApplicationBuilder UseTypeActivator(Func<Type, object> createInstance) =>
+        UseTypeActivator(new DelegateTypeActivator(createInstance));
+
+    /// <summary>
+    /// Configures the application to use the specified service provider for activating types.
+    /// </summary>
+    public CliApplicationBuilder UseTypeActivator(IServiceProvider serviceProvider) =>
+        // Null returns are handled by DelegateTypeActivator
+        UseTypeActivator(serviceProvider.GetService!);
+
+    /// <summary>
+    /// Creates a configured instance of <see cref="CliApplication" />.
+    /// </summary>
+    public CliApplication Build()
+    {
+        var metadata = new ApplicationMetadata(
+            _title ?? GetDefaultTitle(),
+            _executableName ?? GetDefaultExecutableName(),
+            _version ?? GetDefaultVersionText(),
+            _description
+        );
+
+        var configuration = new ApplicationConfiguration(
+            new ApplicationSchema(_commands.ToArray()),
+            _isDebugModeAllowed,
+            _isPreviewModeAllowed
+        );
+
+        return new CliApplication(
+            metadata,
+            configuration,
+            _console ?? new SystemConsole(),
+            _typeActivator ?? new DefaultTypeActivator()
+        );
+    }
+}
+
+public partial class CliApplicationBuilder
+{
+    private static string GetDefaultTitle()
+    {
+        var entryAssemblyName = EnvironmentEx.EntryAssembly?.GetName().Name;
+        if (string.IsNullOrWhiteSpace(entryAssemblyName))
+        {
+            throw new InvalidOperationException(
+                "Failed to infer the default application title. "
+                    + $"Please specify it explicitly using `{nameof(SetTitle)}()`."
+            );
+        }
+
+        return entryAssemblyName;
+    }
+
+    [UnconditionalSuppressMessage(
+        "SingleFile",
+        "IL3000:Avoid accessing Assembly file path when publishing as a single file",
+        Justification = "The file path is checked to ensure the assembly location is available."
+    )]
+    private static string GetDefaultExecutableName()
+    {
+        var processFilePath = EnvironmentEx.ProcessPath;
+
+        // Process file path should generally always be available
+        if (string.IsNullOrWhiteSpace(processFilePath))
+        {
+            throw new InvalidOperationException(
+                "Failed to infer the default application executable name. "
+                    + $"Please specify it explicitly using `{nameof(SetExecutableName)}()`."
+            );
+        }
+
+        var entryAssemblyFilePath = EnvironmentEx.EntryAssembly?.Location;
+
+        // Single file application: entry assembly is not on disk and doesn't have a file path
+        if (string.IsNullOrWhiteSpace(entryAssemblyFilePath))
+        {
+            return Path.GetFileNameWithoutExtension(processFilePath);
+        }
+
+        // Legacy .NET Framework application: entry assembly has the same file path as the process
+        if (PathEx.AreEqual(entryAssemblyFilePath, processFilePath))
+        {
+            return Path.GetFileNameWithoutExtension(entryAssemblyFilePath);
+        }
+
+        // .NET Core application launched through the native application host:
+        // entry assembly has the same file path as the process, but with a different extension.
+        if (
+            PathEx.AreEqual(Path.ChangeExtension(entryAssemblyFilePath, "exe"), processFilePath)
+            || PathEx.AreEqual(
+                Path.GetFileNameWithoutExtension(entryAssemblyFilePath),
+                processFilePath
+            )
+        )
+        {
+            return Path.GetFileNameWithoutExtension(entryAssemblyFilePath);
+        }
+
+        // .NET Core application launched through the .NET CLI
+        return "dotnet " + Path.GetFileName(entryAssemblyFilePath);
+    }
+
+    private static string GetDefaultVersionText()
+    {
+        var entryAssemblyVersion = EnvironmentEx.EntryAssembly?.GetName().Version;
+        if (entryAssemblyVersion is null)
+        {
+            throw new InvalidOperationException(
+                "Failed to infer the default application version. "
+                    + $"Please specify it explicitly using `{nameof(SetVersion)}()`."
+            );
+        }
+
+        return "v" + entryAssemblyVersion.ToSemanticString();
+    }
+}

CliFx/CliFx.csproj

@@ -1,23 +1,37 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net45;netstandard2.0</TargetFrameworks>
-    <LangVersion>latest</LangVersion>
-    <Version>0.0.1</Version>
-    <Company>Tyrrrz</Company>
-    <Authors>$(Company)</Authors>
-    <Copyright>Copyright (C) Alexey Golub</Copyright>
-    <Description>Declarative framework for CLI applications</Description>
-    <PackageTags>command line executable interface framework parser arguments net core</PackageTags>
-    <PackageProjectUrl>https://github.com/Tyrrrz/CliFx</PackageProjectUrl>
-    <PackageReleaseNotes>https://github.com/Tyrrrz/CliFx/blob/master/Changelog.md</PackageReleaseNotes>
-    <PackageIconUrl>https://raw.githubusercontent.com/Tyrrrz/CliFx/master/favicon.png</PackageIconUrl>
-    <PackageLicenseExpression>LGPL-3.0-only</PackageLicenseExpression>
-    <RepositoryUrl>https://github.com/Tyrrrz/CliFx</RepositoryUrl>
-    <RepositoryType>git</RepositoryType>
-    <PackageRequireLicenseAcceptance>True</PackageRequireLicenseAcceptance>
-    <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
-    <DocumentationFile>bin\$(Configuration)\$(TargetFramework)\$(AssemblyName).xml</DocumentationFile>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net8.0;net9.0</TargetFrameworks>
+    <IsPackable>true</IsPackable>
+    <IsTrimmable Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net6.0'))">true</IsTrimmable>
+    <IsAotCompatible Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net7.0'))">true</IsAotCompatible>
   </PropertyGroup>
 
+  <PropertyGroup>
+    <Authors>$(Company)</Authors>
+    <Description>Class-first framework for building command-line interfaces</Description>
+    <PackageTags>command line executable interface framework parser arguments cli app application net core</PackageTags>
+    <PackageProjectUrl>https://github.com/Tyrrrz/CliFx</PackageProjectUrl>
+    <PackageReleaseNotes>https://github.com/Tyrrrz/CliFx/releases</PackageReleaseNotes>
+    <PackageIcon>favicon.png</PackageIcon>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <None Include="../favicon.png" Pack="true" PackagePath="" Visible="false" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="CSharpier.MsBuild" Version="0.30.6" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="all" />
+    <PackageReference Include="PolyShim" Version="1.14.0" PrivateAssets="all" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.6.0" Condition="'$(TargetFramework)' == 'netstandard2.0'" />
+  </ItemGroup>
+
+  <!-- Embed the analyzer inside the package -->
+  <ItemGroup>
+    <ProjectReference Include="..\CliFx.SourceGeneration\CliFx.SourceGeneration.csproj" ReferenceOutputAssembly="false" OutputItemType="analyzer" />
+  </ItemGroup>
+
 </Project>

CliFx/Command.cs

@@ -1,15 +0,0 @@
-using System;
-using System.Threading.Tasks;
-using CliFx.Models;
-
-namespace CliFx
-{
-    public abstract class Command
-    {
-        public virtual ExitCode Execute() => throw new InvalidOperationException(
-            "Can't execute command because its execution method is not defined. " +
-            $"Override Execute or ExecuteAsync on {GetType().Name} in order to make it executable.");
-
-        public virtual Task<ExitCode> ExecuteAsync() => Task.FromResult(Execute());
-    }
-}

CliFx/Exceptions/CliFxException.cs

@@ -0,0 +1,47 @@
+using System;
+
+namespace CliFx.Exceptions;
+
+/// <summary>
+/// Exception thrown within <see cref="CliFx" />.
+/// </summary>
+public partial class CliFxException(
+    string message,
+    int exitCode = CliFxException.DefaultExitCode,
+    bool showHelp = false,
+    Exception? innerException = null
+) : Exception(message, innerException)
+{
+    internal const int DefaultExitCode = 1;
+
+    // When an exception is created without a message, the base Exception class
+    // provides a default message that is not very useful.
+    // This property is used to identify whether this instance was created with
+    // a custom message, so that we can avoid printing the default message.
+    internal bool HasCustomMessage { get; } = !string.IsNullOrWhiteSpace(message);
+
+    /// <summary>
+    /// Returned exit code.
+    /// </summary>
+    public int ExitCode { get; } = exitCode;
+
+    /// <summary>
+    /// Whether to show the help text before exiting.
+    /// </summary>
+    public bool ShowHelp { get; } = showHelp;
+}
+
+public partial class CliFxException
+{
+    // Internal errors don't show help because they're meant for the developer and
+    // not the end-user of the application.
+    internal static CliFxException InternalError(
+        string message,
+        Exception? innerException = null
+    ) => new(message, DefaultExitCode, false, innerException);
+
+    // User errors are typically caused by invalid input and are meant for the end-user,
+    // so we want to show help.
+    internal static CliFxException UserError(string message, Exception? innerException = null) =>
+        new(message, DefaultExitCode, true, innerException);
+}

CliFx/Exceptions/CommandException.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace CliFx.Exceptions;
+
+/// <summary>
+/// Exception thrown when a command cannot proceed with its normal execution due to an error.
+/// Use this exception to report an error to the console and return a specific exit code.
+/// </summary>
+public class CommandException(
+    string message,
+    int exitCode = CliFxException.DefaultExitCode,
+    bool showHelp = false,
+    Exception? innerException = null
+) : CliFxException(message, exitCode, showHelp, innerException);

CliFx/Exceptions/CommandResolveException.cs

@@ -1,21 +0,0 @@
-using System;
-
-namespace CliFx.Exceptions
-{
-    public class CommandResolveException : Exception
-    {
-        public CommandResolveException()
-        {
-        }
-
-        public CommandResolveException(string message)
-            : base(message)
-        {
-        }
-
-        public CommandResolveException(string message, Exception innerException)
-            : base(message, innerException)
-        {
-        }
-    }
-}

CliFx/Extensibility/BindingConverter.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace CliFx.Extensibility;
+
+/// <summary>
+/// Defines custom conversion logic for activating command inputs from the corresponding raw command-line arguments.
+/// </summary>
+public abstract class BindingConverter<T> : IBindingConverter
+{
+    /// <inheritdoc cref="IBindingConverter.Convert" />
+    public abstract T? Convert(string? rawValue, IFormatProvider? formatProvider);
+
+    object? IBindingConverter.Convert(string? rawValue, IFormatProvider? formatProvider) =>
+        Convert(rawValue, formatProvider);
+}

CliFx/Extensibility/BindingValidationError.cs

@@ -0,0 +1,12 @@
+namespace CliFx.Extensibility;
+
+/// <summary>
+/// Represents a validation error.
+/// </summary>
+public class BindingValidationError(string message)
+{
+    /// <summary>
+    /// Error message shown to the user.
+    /// </summary>
+    public string Message { get; } = message;
+}

CliFx/Extensibility/BindingValidator.cs

@@ -0,0 +1,26 @@
+namespace CliFx.Extensibility;
+
+/// <summary>
+/// Defines custom validation logic for activated command inputs.
+/// </summary>
+public abstract class BindingValidator<T> : IBindingValidator
+{
+    /// <summary>
+    /// Returns a successful validation result.
+    /// </summary>
+    protected BindingValidationError? Ok() => null;
+
+    /// <summary>
+    /// Returns a non-successful validation result.
+    /// </summary>
+    protected BindingValidationError Error(string message) => new(message);
+
+    /// <inheritdoc cref="IBindingValidator.Validate" />
+    /// <remarks>
+    /// You can use the utility methods <see cref="Ok" /> and <see cref="Error" /> to
+    /// create an appropriate result.
+    /// </remarks>
+    public abstract BindingValidationError? Validate(T? value);
+
+    BindingValidationError? IBindingValidator.Validate(object? value) => Validate((T?)value);
+}

CliFx/Extensibility/BoolBindingConverter.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace CliFx.Extensibility;
+
+/// <summary>
+/// Converter for activating command inputs bound to properties of type <see cref="bool" />.
+/// </summary>
+public class BoolBindingConverter : BindingConverter<bool>
+{
+    /// <inheritdoc />
+    public override bool Convert(string? rawValue, IFormatProvider? formatProvider) =>
+        string.IsNullOrWhiteSpace(rawValue) || bool.Parse(rawValue);
+}