Add analyzer to detect HasFlag() and suggest HasFlagFast() replacement

src/NetEscapades.EnumGenerators/Diagnostics/AnalyzerHelpers.cs

@@ -0,0 +1,60 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace NetEscapades.EnumGenerators.Diagnostics;
+
+public class AnalyzerHelpers
+{
+    public static (INamedTypeSymbol? enumExtensionsAttr, HashSet<INamedTypeSymbol>? externalEnumTypes) GetEnumExtensionAttributes(
+        CompilationStartAnalysisContext ctx)
+    {
+        var enumExtensionsAttr =
+            ctx.Compilation.GetTypeByMetadataName(Attributes.EnumExtensionsAttribute);
+        var externalEnumExtensionsAttr =
+            ctx.Compilation.GetTypeByMetadataName(Attributes.ExternalEnumExtensionsAttribute);
+
+        if (enumExtensionsAttr is null)
+        {
+            return (enumExtensionsAttr, null);
+        }
+
+        // Collect all enum types that have EnumExtensions<T> attributes
+        var externalEnumTypes = new HashSet<INamedTypeSymbol>(SymbolEqualityComparer.Default);
+        if (externalEnumExtensionsAttr is not null)
+        {
+            foreach (var attribute in ctx.Compilation.Assembly.GetAttributes())
+            {
+                if (attribute.AttributeClass is { IsGenericType: true } attrClass &&
+                    SymbolEqualityComparer.Default.Equals(attrClass.ConstructedFrom, externalEnumExtensionsAttr) &&
+                    attrClass.TypeArguments is [INamedTypeSymbol { TypeKind: TypeKind.Enum } enumType])
+                {
+                    externalEnumTypes.Add(enumType);
+                }
+            }
+        }
+
+        return (enumExtensionsAttr, externalEnumTypes);
+    }
+
+    public static bool IsEnumWithExtensions(
+        ITypeSymbol receiverType,
+        INamedTypeSymbol enumExtensionsAttr,
+        HashSet<INamedTypeSymbol> externalEnumTypes)
+    {
+        // Check if the enum has the [EnumExtensions] attribute or is referenced in EnumExtensions<T>
+        // First check if the enum itself has the attribute
+        foreach (var attributeData in receiverType.GetAttributes())
+        {
+            if (SymbolEqualityComparer.Default.Equals(
+                    attributeData.AttributeClass,
+                    enumExtensionsAttr))
+            {
+                return true;
+            }
+        }
+
+        // If not, check if it's in the external enum types (EnumExtensions<T>)
+        return receiverType is INamedTypeSymbol namedType
+               && externalEnumTypes.Contains(namedType);
+    }
+}

src/NetEscapades.EnumGenerators/Diagnostics/HasFlagAnalyzer.cs

@@ -0,0 +1,103 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace NetEscapades.EnumGenerators.Diagnostics;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class HasFlagAnalyzer : DiagnosticAnalyzer
+{
+    public const string DiagnosticId = "NEEG005";
+    public static readonly DiagnosticDescriptor Rule = new(
+#pragma warning disable RS2008 // Enable Analyzer Release Tracking
+        id: DiagnosticId,
+#pragma warning restore RS2008
+        title: "Use HasFlagFast() instead of HasFlag()",
+        messageFormat: "Use HasFlagFast() instead of HasFlag() for better performance on enum '{0}'",
+        category: "Usage",
+        defaultSeverity: DiagnosticSeverity.Info,
+        isEnabledByDefault: true);
+
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics
+        => ImmutableArray.Create(Rule);
+
+    public override void Initialize(AnalysisContext context)
+    {
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+        context.EnableConcurrentExecution();
+        context.RegisterCompilationStartAction(ctx =>
+        {
+            var (enumExtensionsAttr, externalEnumTypes) = AnalyzerHelpers.GetEnumExtensionAttributes(ctx);
+            if (enumExtensionsAttr is null || externalEnumTypes is null)
+            {
+                return;
+            }
+
+            ctx.RegisterSyntaxNodeAction(
+                c => AnalyzeInvocation(c, enumExtensionsAttr, externalEnumTypes),
+                SyntaxKind.InvocationExpression);
+        });
+    }
+
+    private static void AnalyzeInvocation(SyntaxNodeAnalysisContext context, INamedTypeSymbol enumExtensionsAttr, HashSet<INamedTypeSymbol> externalEnumTypes)
+    {
+        var invocation = (InvocationExpressionSyntax)context.Node;
+
+        // Check if this is a member access expression (e.g., value.HasFlag())
+        if (invocation.Expression is not MemberAccessExpressionSyntax memberAccess)
+        {
+            return;
+        }
+
+        // Check if the method name is "HasFlag"
+        if (memberAccess.Name.Identifier.Text != "HasFlag")
+        {
+            return;
+        }
+
+        // Check if there is exactly one argument
+        if (invocation.ArgumentList.Arguments.Count != 1)
+        {
+            return;
+        }
+
+        // Get the symbol information for the invocation
+        var symbolInfo = context.SemanticModel.GetSymbolInfo(invocation);
+        if (symbolInfo.Symbol is not IMethodSymbol methodSymbol)
+        {
+            return;
+        }
+
+        // Verify this is the HasFlag() method from System.Enum
+        if (methodSymbol.Name != "HasFlag" ||
+            methodSymbol.Parameters.Length != 1 ||
+            methodSymbol.ContainingType.SpecialType != SpecialType.System_Enum)
+        {
+            return;
+        }
+
+        // Get the type of the receiver (the thing before .HasFlag())
+        var receiverType = context.SemanticModel.GetTypeInfo(memberAccess.Expression).Type;
+        if (receiverType is null || receiverType.TypeKind != TypeKind.Enum)
+        {
+            return;
+        }
+
+        if (!AnalyzerHelpers.IsEnumWithExtensions(receiverType, enumExtensionsAttr, externalEnumTypes))
+        {
+            return;
+        }
+
+        // Report the diagnostic
+        var diagnostic = Diagnostic.Create(
+            Rule,
+            memberAccess.Name.GetLocation(),
+            receiverType.Name);
+
+        context.ReportDiagnostic(diagnostic);
+    }
+}

src/NetEscapades.EnumGenerators/Diagnostics/HasFlagCodeFixProvider.cs

@@ -0,0 +1,78 @@
+using System.Collections.Immutable;
+using System.Composition;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace NetEscapades.EnumGenerators.Diagnostics;
+
+[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(HasFlagCodeFixProvider)), Shared]
+public class HasFlagCodeFixProvider : CodeFixProvider
+{
+    private const string Title = "Replace with HasFlagFast()";
+
+    public sealed override ImmutableArray<string> FixableDiagnosticIds
+        => ImmutableArray.Create(HasFlagAnalyzer.DiagnosticId);
+
+    public sealed override FixAllProvider GetFixAllProvider()
+        => WellKnownFixAllProviders.BatchFixer;
+
+    public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
+    {
+        var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+        if (root is null)
+        {
+            return;
+        }
+
+        var diagnostic = context.Diagnostics.First();
+        var diagnosticSpan = diagnostic.Location.SourceSpan;
+
+        // Find the node at the diagnostic location
+        var node = root.FindNode(diagnosticSpan);
+
+        // Check if this is a HasFlag invocation
+        if (node is IdentifierNameSyntax identifierName)
+        {
+            // Register a code action for HasFlag() replacement
+            context.RegisterCodeFix(
+                CodeAction.Create(
+                    title: Title,
+                    createChangedDocument: c => ReplaceHasFlagWithHasFlagFast(context.Document, identifierName, c),
+                    equivalenceKey: Title),
+                context.Diagnostics);
+        }
+    }
+
+    private static async Task<Document> ReplaceHasFlagWithHasFlagFast(
+        Document document,
+        IdentifierNameSyntax identifierName,
+        CancellationToken cancellationToken)
+    {
+        var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+        if (root is null)
+        {
+            return document;
+        }
+
+        // Create the new identifier with "HasFlagFast"
+        var newIdentifier = SyntaxFactory.IdentifierName("HasFlagFast")
+            .WithTriviaFrom(identifierName);
+
+        // Create new member access with the new identifier
+        var memberAccess = identifierName.Parent as MemberAccessExpressionSyntax;
+        if (memberAccess is null)
+        {
+            return document;
+        }
+
+        var newMemberAccess = memberAccess.WithName(newIdentifier);
+
+        // Replace the old member access with the new one
+        var newRoot = root.ReplaceNode(memberAccess, newMemberAccess);
+
+        return document.WithSyntaxRoot(newRoot);
+    }
+}

src/NetEscapades.EnumGenerators/Diagnostics/ToStringAnalyzer.cs

@@ -31,31 +31,12 @@ public override void Initialize(AnalysisContext context)
         context.EnableConcurrentExecution();
         context.RegisterCompilationStartAction(ctx =>
         {
-            var enumExtensionsAttr =
-                ctx.Compilation.GetTypeByMetadataName(Attributes.EnumExtensionsAttribute);
-            var externalEnumExtensionsAttr =
-                ctx.Compilation.GetTypeByMetadataName(Attributes.ExternalEnumExtensionsAttribute);
-
-            if (enumExtensionsAttr is null)
+            var (enumExtensionsAttr, externalEnumTypes) = AnalyzerHelpers.GetEnumExtensionAttributes(ctx);
+            if (enumExtensionsAttr is null || externalEnumTypes is null)
             {
                 return;
             }
 
-            // Collect all enum types that have EnumExtensions<T> attributes
-            var externalEnumTypes = new HashSet<INamedTypeSymbol>(SymbolEqualityComparer.Default);
-            if (externalEnumExtensionsAttr is not null)
-            {
-                foreach (var attribute in ctx.Compilation.Assembly.GetAttributes())
-                {
-                    if (attribute.AttributeClass is { IsGenericType: true } attrClass &&
-                        SymbolEqualityComparer.Default.Equals(attrClass.ConstructedFrom, externalEnumExtensionsAttr) &&
-                        attrClass.TypeArguments is [INamedTypeSymbol { TypeKind: TypeKind.Enum } enumType])
-                    {
-                        externalEnumTypes.Add(enumType);
-                    }
-                }
-            }
-
             ctx.RegisterSyntaxNodeAction(
                 c => AnalyzeInvocation(c, enumExtensionsAttr, externalEnumTypes),
                 SyntaxKind.InvocationExpression);
@@ -136,7 +117,7 @@ private static void AnalyzeInvocation(SyntaxNodeAnalysisContext context, INamedT
             return;
         }
 
-        if (!IsEnumWithExtensions(receiverType, enumExtensionsAttr, externalEnumTypes))
+        if (!AnalyzerHelpers.IsEnumWithExtensions(receiverType, enumExtensionsAttr, externalEnumTypes))
         {
             return;
         }
@@ -190,7 +171,7 @@ private static void AnalyzeInterpolation(SyntaxNodeAnalysisContext context, INam
             }
         }
 
-        if (!IsEnumWithExtensions(expressionType, enumExtensionsAttr, externalEnumTypes))
+        if (!AnalyzerHelpers.IsEnumWithExtensions(expressionType, enumExtensionsAttr, externalEnumTypes))
         {
             return;
         }
@@ -203,27 +184,4 @@ private static void AnalyzeInterpolation(SyntaxNodeAnalysisContext context, INam
 
         context.ReportDiagnostic(diagnostic);
     }
-
-    private static bool IsEnumWithExtensions(
-        ITypeSymbol receiverType,
-        INamedTypeSymbol enumExtensionsAttr,
-        HashSet<INamedTypeSymbol> externalEnumTypes)
-    {
-        // Check if the enum has the [EnumExtensions] attribute or is referenced in EnumExtensions<T>
-        // First check if the enum itself has the attribute
-        foreach (var attributeData in receiverType.GetAttributes())
-        {
-            if (SymbolEqualityComparer.Default.Equals(
-                    attributeData.AttributeClass,
-                    enumExtensionsAttr))
-            {
-                return true;
-            }
-        }
-
-        // If not, check if it's in the external enum types (EnumExtensions<T>)
-        return receiverType is INamedTypeSymbol namedType
-               && externalEnumTypes.Contains(namedType);
-    }
-
 }

tests/NetEscapades.EnumGenerators.IntegrationTests/.editorconfig

@@ -4,4 +4,5 @@
 dotnet_diagnostic.NEEG001.severity = error
 dotnet_diagnostic.NEEG002.severity = error
 dotnet_diagnostic.NEEG003.severity = error
-dotnet_diagnostic.NEEG004.severity = error
+dotnet_diagnostic.NEEG004.severity = error
+dotnet_diagnostic.NEEG005.severity = error

tests/NetEscapades.EnumGenerators.IntegrationTests/AnalyzerTests.cs

@@ -1,4 +1,5 @@
 using System;
+using NetEscapades.EnumGenerators.IntegrationTests;
 using Xunit;
 
 namespace NetEscapades.EnumGenerators.Benchmarks;
@@ -24,4 +25,14 @@ public void Neeg004Testing()
         _ = $"Some value: {EnumInSystem.First:G} <-";
 #pragma warning restore NEEG004
     }
+
+    [Fact]
+    public void Neeg005Testing()
+    {
+#pragma warning disable NEEG005
+        var test = FlagsEnum.First;
+        _ = test.HasFlag(FlagsEnum.Second);
+        _ = $"Some value: {test.HasFlag(FlagsEnum.Second)} <-";
+#pragma warning restore NEEG005
+    }
 }