gui-cs.Terminal.Gui/Analyzers/Terminal.Gui.Analyzers.Internal/Analyzers/GenerateEnumExtensionMethodsAttributeAnalyzer.cs

#define JETBRAINS_ANNOTATIONS
using System.Collections.Immutable;
using System.Linq;
using JetBrains.Annotations;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Diagnostics;
using Terminal.Gui.Analyzers.Internal.Attributes;
using Terminal.Gui.Analyzers.Internal.Generators.EnumExtensions;

namespace Terminal.Gui.Analyzers.Internal.Analyzers;

/// <summary>
///     Design-time analyzer that checks for proper use of <see cref="GenerateEnumExtensionMethodsAttribute"/>.
/// </summary>
[DiagnosticAnalyzer (LanguageNames.CSharp)]
[UsedImplicitly]
internal sealed class GenerateEnumExtensionMethodsAttributeAnalyzer : DiagnosticAnalyzer
{
    // ReSharper disable once InconsistentNaming
    private static readonly DiagnosticDescriptor TG0001_GlobalNamespaceNotSupported = new (
                                                                                           // ReSharper restore InconsistentNaming
                                                                                           "TG0001",
                                                                                           $"{nameof (GenerateEnumExtensionMethodsAttribute)} not supported on global enums",
                                                                                           "{0} is in the global namespace, which is not supported by the source generator ({1}) used by {2}. Move the enum to a namespace or remove the attribute.",
                                                                                           "Usage",
                                                                                           DiagnosticSeverity.Error,
                                                                                           true,
                                                                                           null,
                                                                                           null,
                                                                                           WellKnownDiagnosticTags.NotConfigurable,
                                                                                           WellKnownDiagnosticTags.Compiler);

    // ReSharper disable once InconsistentNaming
    private static readonly DiagnosticDescriptor TG0002_UnderlyingTypeNotSupported = new (
                                                                                          "TG0002",
                                                                                          $"{nameof (GenerateEnumExtensionMethodsAttribute)} not supported for this enum type",
                                                                                          "{0} has an underlying type of {1}, which is not supported by the source generator ({2}) used by {3}. Only enums backed by int or uint are supported.",
                                                                                          "Usage",
                                                                                          DiagnosticSeverity.Error,
                                                                                          true,
                                                                                          null,
                                                                                          null,
                                                                                          WellKnownDiagnosticTags.NotConfigurable,
                                                                                          WellKnownDiagnosticTags.Compiler);

    /// <inheritdoc/>
    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } =
        [
            TG0001_GlobalNamespaceNotSupported,
            TG0002_UnderlyingTypeNotSupported
        ];

    /// <inheritdoc/>
    public override void Initialize (AnalysisContext context)
    {
        context.ConfigureGeneratedCodeAnalysis (GeneratedCodeAnalysisFlags.None);
        context.EnableConcurrentExecution ();

        context.RegisterSyntaxNodeAction (CheckAttributeLocations, SyntaxKind.EnumDeclaration);

        return;

        static void CheckAttributeLocations (SyntaxNodeAnalysisContext analysisContext)
        {
            ISymbol? symbol = analysisContext.SemanticModel.GetDeclaredSymbol (analysisContext.Node) as INamedTypeSymbol;

            if (symbol is not INamedTypeSymbol { EnumUnderlyingType: { } } enumSymbol)
            {
                // Somehow not even an enum declaration.
                // Skip it.
                return;
            }

            // Check attributes for those we care about and react accordingly.
            foreach (AttributeData attributeData in enumSymbol.GetAttributes ())
            {
                if (attributeData.AttributeClass?.Name != nameof (GenerateEnumExtensionMethodsAttribute))
                {
                    // Just skip - not an interesting attribute.
                    continue;
                }

                // Check enum underlying type for supported types (int and uint, currently)
                // Report TG0002 if unsupported underlying type.
                if (enumSymbol.EnumUnderlyingType is not { SpecialType: SpecialType.System_Int32 or SpecialType.System_UInt32 })
                {
                    analysisContext.ReportDiagnostic (
                                                      Diagnostic.Create (
                                                                         TG0002_UnderlyingTypeNotSupported,
                                                                         enumSymbol.Locations.FirstOrDefault (),
                                                                         enumSymbol.Name,
                                                                         enumSymbol.EnumUnderlyingType.Name,
                                                                         nameof (EnumExtensionMethodsIncrementalGenerator),
                                                                         nameof (GenerateEnumExtensionMethodsAttribute)
                                                                        )
                                                     );
                }

                // Check enum namespace (only non-global supported, currently)
                // Report TG0001 if in the global namespace.
                if (enumSymbol.ContainingSymbol is not INamespaceSymbol { IsGlobalNamespace: false })
                {
                    analysisContext.ReportDiagnostic (
                                                      Diagnostic.Create (
                                                                         TG0001_GlobalNamespaceNotSupported,
                                                                         enumSymbol.Locations.FirstOrDefault (),
                                                                         enumSymbol.Name,
                                                                         nameof (EnumExtensionMethodsIncrementalGenerator),
                                                                         nameof (GenerateEnumExtensionMethodsAttribute)
                                                                        )
                                                     );
                }
            }
        }
    }
}