Show help text on demand (#49)

CliFx.Tests.Dummy/Commands/ShowErrorMessageThenHelpTextOnErrorCommand.cs

@@ -0,0 +1,20 @@
+using CliFx.Attributes;
+using CliFx.Exceptions;
+using System.Threading.Tasks;
+
+namespace CliFx.Tests.Dummy.Commands
+{
+    /// <summary>
+    /// Demos how to show an error message then help text from an organizational command.
+    /// </summary>
+    [Command("cmd-err", Description = "This is an organizational command. " +
+        "I don't do anything except provide a route to my subcommands. " +
+        "If you use just me, I print an error message then the help text " +
+        "to remind you of my subcommands.")]
+    public class ShowErrorMessageThenHelpTextOnCommandExceptionCommand : ICommand
+    {
+        public ValueTask ExecuteAsync(IConsole console) =>
+            throw new CommandException("It is an error to use me without a subcommand. " +
+                "Please refer to the help text below for guidance.", showHelp: true);
+    }
+}

CliFx.Tests.Dummy/Commands/ShowHelpTextOnErrorCommand.cs

@@ -0,0 +1,18 @@
+using CliFx.Attributes;
+using CliFx.Exceptions;
+using System.Threading.Tasks;
+
+namespace CliFx.Tests.Dummy.Commands
+{
+    /// <summary>
+    /// Demos how to show help text from an organizational command.
+    /// </summary>
+    [Command("cmd", Description = "This is an organizational command. " +
+        "I don't do anything except provide a route to my subcommands. " +
+        "If you use just me, I print the help text to remind you of my subcommands.")]
+    public class ShowHelpTextOnCommandExceptionCommand : ICommand
+    {
+        public ValueTask ExecuteAsync(IConsole console) =>
+            throw new CommandException(null, showHelp: false);
+    }
+}

CliFx.Tests/ErrorReportingSpecs.Commands.cs

@@ -27,5 +27,39 @@ namespace CliFx.Tests
 
             public ValueTask ExecuteAsync(IConsole console) => throw new CommandException(Message, ExitCode);
         }
+
+        [Command("exc")]
+        private class ShowHelpTextOnlyCommand : ICommand
+        {
+            public ValueTask ExecuteAsync(IConsole console) => throw new CommandException(null, showHelp: true);
+        }
+
+        [Command("exc sub")]
+        private class ShowHelpTextOnlySubCommand : ICommand
+        {
+            public ValueTask ExecuteAsync(IConsole console) => default;
+        }
+
+        [Command("exc")]
+        private class ShowErrorMessageThenHelpTextCommand : ICommand
+        {
+            public ValueTask ExecuteAsync(IConsole console) =>
+                throw new CommandException("Error message.", showHelp: true);
+        }
+
+        [Command("exc sub")]
+        private class ShowErrorMessageThenHelpTextSubCommand : ICommand
+        {
+            public ValueTask ExecuteAsync(IConsole console) => default;
+        }
+
+        [Command("exc")]
+        private class StackTraceOnlyCommand : ICommand
+        {
+            [CommandOption("msg", 'm')]
+            public string? Message { get; set; }
+
+            public ValueTask ExecuteAsync(IConsole console) => throw new CommandException(null);
+        }
     }
 }

CliFx.Tests/ErrorReportingSpecs.cs

@@ -9,7 +9,7 @@ namespace CliFx.Tests
     public partial class ErrorReportingSpecs
     {
         [Fact]
-        public async Task Command_may_throw_a_generic_exception_which_exits_and_prints_full_error_details()
+        public async Task Command_may_throw_a_generic_exception_which_exits_and_prints_error_message_and_stack_trace()
         {
             // Arrange
             await using var stdErr = new MemoryStream();
@@ -29,8 +29,10 @@ namespace CliFx.Tests
 
             // Assert
             exitCode.Should().NotBe(0);
-            stdErrData.Should().Contain("Kaput");
-            stdErrData.Length.Should().BeGreaterThan("Kaput".Length);
+            stdErrData.Should().ContainAll(
+                "System.Exception:",
+                "Kaput", "at", 
+                "CliFx.Tests");
         }
 
         [Fact]
@@ -80,5 +82,95 @@ namespace CliFx.Tests
             exitCode.Should().NotBe(0);
             stdErrData.Should().NotBeEmpty();
         }
+
+        [Fact]
+        public async Task Command_may_throw_a_specialized_exception_which_shows_only_the_help_text()
+        {
+            // Arrange
+            await using var stdOut = new MemoryStream();
+            await using var stdErr = new MemoryStream();
+
+            var console = new VirtualConsole(output: stdOut);
+
+            var application = new CliApplicationBuilder()
+                .AddCommand(typeof(ShowHelpTextOnlyCommand))
+                .AddCommand(typeof(ShowHelpTextOnlySubCommand))
+                .UseConsole(console)
+                .Build();
+
+            // Act
+            await application.RunAsync(new[] { "exc" });
+            var stdOutData = console.Output.Encoding.GetString(stdOut.ToArray()).TrimEnd();
+            var stdErrData = console.Output.Encoding.GetString(stdErr.ToArray()).TrimEnd();
+
+            // Assert
+            stdErrData.Should().BeEmpty();
+            stdOutData.Should().ContainAll(
+                "Usage",
+                "[command]",
+                "Options",
+                "-h|--help", "Shows help text.",
+                "Commands",
+                "sub",
+                "You can run", "to show help on a specific command."
+            );
+        }
+
+        [Fact]
+        public async Task Command_may_throw_specialized_exception_which_shows_the_error_message_then_the_help_text()
+        {
+            // Arrange
+            await using var stdOut = new MemoryStream();
+            await using var stdErr = new MemoryStream();
+            var console = new VirtualConsole(output: stdOut, error: stdErr);
+
+            var application = new CliApplicationBuilder()
+                .AddCommand(typeof(ShowErrorMessageThenHelpTextCommand))
+                .AddCommand(typeof(ShowErrorMessageThenHelpTextSubCommand))
+                .UseConsole(console)
+                .Build();
+
+            // Act
+            await application.RunAsync(new[] { "exc" });
+            var stdErrData = console.Error.Encoding.GetString(stdErr.ToArray()).TrimEnd();
+            var stdOutData = console.Output.Encoding.GetString(stdOut.ToArray()).TrimEnd();
+
+            // Assert
+            stdErrData.Should().Be("Error message.");
+            stdOutData.Should().ContainAll(
+                "Usage",
+                "[command]",
+                "Options",
+                "-h|--help", "Shows help text.",
+                "Commands",
+                "sub",
+                "You can run", "to show help on a specific command."
+            );
+        }
+
+        [Fact]
+        public async Task Command_may_throw_a_specialized_exception_which_shows_only_a_stack_trace_and_no_help_text()
+        {
+            // Arrange
+            await using var stdErr = new MemoryStream();
+            var console = new VirtualConsole(error: stdErr);
+
+            var application = new CliApplicationBuilder()
+                .AddCommand(typeof(GenericExceptionCommand))
+                .UseConsole(console)
+                .Build();
+
+            // Act
+            var exitCode = await application.RunAsync(
+                new[] { "exc", "-m", "Kaput" },
+                new Dictionary<string, string>());
+
+            var stdErrData = console.Error.Encoding.GetString(stdErr.ToArray()).TrimEnd();
+
+            // Assert
+            exitCode.Should().NotBe(0);
+            stdErrData.Should().Contain("Kaput");
+            stdErrData.Length.Should().BeGreaterThan("Kaput".Length);
+        }
     }
 }

CliFx.Tests/HelpTextSpecs.Commands.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using System.Threading.Tasks;
 using CliFx.Attributes;
+using CliFx.Exceptions;
 
 namespace CliFx.Tests
 {

CliFx/CliApplication.cs

@@ -143,6 +143,50 @@ namespace CliFx
             return 0;
         }
 
+        /// <summary>
+        /// Handle <see cref="CommandException"/>s differently from the rest because we want to
+        /// display it different based on whether we are showing the help text or not.
+        /// </summary>
+        private int HandleCommandException(IReadOnlyList<string> commandLineArguments, CommandException commandException)
+        {
+            var showHelp = commandException.ShowHelp;
+
+            var errorMessage = commandException.HasMessage
+                ? commandException.Message
+                : commandException.ToString();
+               
+            _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(errorMessage));            
+
+            if (showHelp)
+            {
+                var applicationSchema = ApplicationSchema.Resolve(_configuration.CommandTypes);
+                var commandLineInput = CommandLineInput.Parse(commandLineArguments);
+                var commandSchema = applicationSchema.TryFindCommand(commandLineInput) ??
+                    CommandSchema.StubDefaultCommand;
+                _helpTextWriter.Write(applicationSchema, commandSchema);
+            }
+
+            return commandException.ExitCode;
+        }
+
+        /// <summary>
+        /// Handles <see cref="CliFxException"/>s by printing its error message if it has a value.
+        /// Otherwise, it prints the full stack trace from the exception.
+        /// </summary>
+        /// <param name="cliFxException">The exception to handle.</param>
+        /// <returns>The exception's HResult.</returns>
+        private int HandleCliFxException(CliFxException cliFxException)
+        {
+            // Prefer showing message without stack trace on CliFxExceptions.
+            var errorMessage = cliFxException.HasMessage
+                ? cliFxException.Message
+                : cliFxException.ToString();
+
+            _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(errorMessage));
+
+            return cliFxException.HResult;
+        }
+
         /// <summary>
         /// Runs the application with specified command line arguments and environment variables, and returns the exit code.
         /// </summary>
@@ -162,21 +206,23 @@ namespace CliFx
                     HandleHelpOption(applicationSchema, commandLineInput) ??
                     await HandleCommandExecutionAsync(applicationSchema, commandLineInput, environmentVariables);
             }
-            catch (Exception ex)
+            catch (CommandException ce)
             {
                 // We want to catch exceptions in order to print errors and return correct exit codes.
                 // Doing this also gets rid of the annoying Windows troubleshooting dialog that shows up on unhandled exceptions.
-
-                // Prefer showing message without stack trace on exceptions coming from CliFx or on CommandException
-                var errorMessage = !string.IsNullOrWhiteSpace(ex.Message) && (ex is CliFxException || ex is CommandException)
-                    ? ex.Message
-                    : ex.ToString();
-
-                _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(errorMessage));
-
-                return ex is CommandException commandException
-                    ? commandException.ExitCode
-                    : ex.HResult;
+                var exitCode = HandleCommandException(commandLineArguments, ce);
+                return exitCode;
+            }
+            catch (CliFxException cfe)
+            {
+                var hResult = HandleCliFxException(cfe);
+                return hResult;
+            }
+            catch (Exception ex)
+            {
+                // For all other errors, we just write the entire thing to stderr.
+                _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(ex.ToString()));
+                return ex.HResult;
             }
         }
 

CliFx/Exceptions/BaseCliFxException.cs

@@ -0,0 +1,43 @@
+using System;
+
+namespace CliFx.Exceptions
+{
+    /// <summary>
+    /// Provides the base functionality for exceptions thrown within CliFx
+    /// or from one of its commands.
+    /// </summary>
+    public abstract class BaseCliFxException : Exception
+    {
+        /// <summary>
+        /// Whether to show the help text after handling this exception.
+        /// </summary>
+        public bool ShowHelp { get; }
+
+        /// <summary>
+        /// Whether this exception was constructed with a message.
+        /// </summary>
+        /// <remarks>
+        /// We cannot check against the 'Message' property because it will always return 
+        /// a default message if it was constructed with a null value or is currently null.
+        /// </remarks>
+        public bool HasMessage { get; }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="BaseCliFxException"/>.
+        /// </summary>
+        protected BaseCliFxException(string? message, bool showHelp = false)
+            : this(message, null, showHelp)
+        {
+        }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="BaseCliFxException"/>.
+        /// </summary>
+        protected BaseCliFxException(string? message, Exception? innerException, bool showHelp = false)
+            : base(message, innerException)
+        {
+            HasMessage = string.IsNullOrWhiteSpace(message) ? false : true;
+            ShowHelp = showHelp;
+        }
+    }
+}

CliFx/Exceptions/CliFxException.cs

@@ -9,21 +9,21 @@ namespace CliFx.Exceptions
     /// <summary>
     /// Domain exception thrown within CliFx.
     /// </summary>
-    public partial class CliFxException : Exception
+    public partial class CliFxException : BaseCliFxException
     {
         /// <summary>
         /// Initializes an instance of <see cref="CliFxException"/>.
         /// </summary>
-        public CliFxException(string? message)
-            : base(message)
+        public CliFxException(string? message, bool showHelp = false) 
+            : base(message, showHelp)
         {
         }
 
         /// <summary>
         /// Initializes an instance of <see cref="CliFxException"/>.
         /// </summary>
-        public CliFxException(string? message, Exception? innerException)
-            : base(message, innerException)
+        public CliFxException(string? message, Exception? innerException, bool showHelp = false) 
+            : base(message, innerException, showHelp)
         {
         }
     }

CliFx/Exceptions/CommandException.cs

@@ -7,7 +7,7 @@ namespace CliFx.Exceptions
     /// Use this exception if you want to report an error that occured during execution of a command.
     /// This exception also allows specifying exit code which will be returned to the calling process.
     /// </summary>
-    public class CommandException : Exception
+    public class CommandException : BaseCliFxException
     {
         private const int DefaultExitCode = -100;
 
@@ -19,8 +19,9 @@ namespace CliFx.Exceptions
         /// <summary>
         /// Initializes an instance of <see cref="CommandException"/>.
         /// </summary>
-        public CommandException(string? message, Exception? innerException, int exitCode = DefaultExitCode)
-            : base(message, innerException)
+        public CommandException(string? message, Exception? innerException, 
+            int exitCode = DefaultExitCode, bool showHelp = false)
+                : base(message, innerException, showHelp)
         {
             ExitCode = exitCode != 0
                 ? exitCode
@@ -30,16 +31,16 @@ namespace CliFx.Exceptions
         /// <summary>
         /// Initializes an instance of <see cref="CommandException"/>.
         /// </summary>
-        public CommandException(string? message, int exitCode = DefaultExitCode)
-            : this(message, null, exitCode)
+        public CommandException(string? message, int exitCode = DefaultExitCode, bool showHelp = false)
+                : this(message, null, exitCode, showHelp)
         {
         }
 
         /// <summary>
         /// Initializes an instance of <see cref="CommandException"/>.
         /// </summary>
-        public CommandException(int exitCode = DefaultExitCode)
-            : this(null, exitCode)
+        public CommandException(int exitCode = DefaultExitCode, bool showHelp = false)
+            : this(null, exitCode, showHelp)
         {
         }
     }

Readme.md

@@ -430,6 +430,32 @@ Division by zero is not supported.
 1337
 ```
 
+You can use the `showHelp` parameter to choose whether to show the help text after handling an exception. For example, you can tell CliFx to show `ExampleCommand`'s help text upon an error like this:
+
+```c#
+[Command]
+public class ExampleCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        throw new CommandException(showHelp: true);
+    }
+}
+```
+
+To display an error message before the help text, throw the `CommandException` like this:
+
+```c#
+[Command]
+public class ExampleCommand : ICommand
+{
+    public ValueTask ExecuteAsync(IConsole console)
+    {
+        throw new CommandException("My custom error message.", showHelp: true);
+    }
+}
+```
+
 ### Graceful cancellation
 
 It is possible to gracefully cancel execution of a command and preform any necessary cleanup. By default an app gets forcefully killed when it receives an interrupt signal (Ctrl+C or Ctrl+Break), but you can easily override this behavior.