CliFx/CliFx.Analyzers/ParameterMustBeSingleIfNonRequiredAnalyzer.cs

using System.Linq;
using CliFx.Analyzers.ObjectModel;
using CliFx.Analyzers.Utils.Extensions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;

namespace CliFx.Analyzers;

[DiagnosticAnalyzer(LanguageNames.CSharp)]
public class ParameterMustBeSingleIfNonRequiredAnalyzer()
    : AnalyzerBase(
        "Parameters marked as non-required are limited to one per command",
        "This parameter is non-required so it must be the only such parameter in the command. "
            + "Property bound to another non-required parameter: `{0}`."
    )
{
    private void Analyze(
        SyntaxNodeAnalysisContext context,
        PropertyDeclarationSyntax propertyDeclaration,
        IPropertySymbol property
    )
    {
        if (property.ContainingType is null)
            return;

        var parameter = CommandParameterSymbol.TryResolve(property);
        if (parameter is null)
            return;

        if (parameter.IsRequired != false)
            return;

        var otherProperties = property
            .ContainingType.GetMembers()
            .OfType<IPropertySymbol>()
            .Where(m => !m.Equals(property))
            .ToArray();

        foreach (var otherProperty in otherProperties)
        {
            var otherParameter = CommandParameterSymbol.TryResolve(otherProperty);
            if (otherParameter is null)
                continue;

            if (otherParameter.IsRequired == false)
            {
                context.ReportDiagnostic(
                    CreateDiagnostic(
                        propertyDeclaration.Identifier.GetLocation(),
                        otherProperty.Name
                    )
                );
            }
        }
    }

    public override void Initialize(AnalysisContext context)
    {
        base.Initialize(context);
        context.HandlePropertyDeclaration(Analyze);
    }
}