Update logging source generator to support generic methods

src/Generators/Microsoft.Gen.Logging/Emission/Emitter.Method.cs

@@ -49,9 +49,13 @@ private void GenLogMethod(LoggingMethod lm)
         OutGeneratedCodeAttribute();
 
         OutIndent();
-        Out($"{lm.Modifiers} void {lm.Name}({extension}");
+        Out($"{lm.Modifiers} void {lm.Name}");
+        GenTypeParameterList(lm);
+        Out($"({extension}");
         GenParameters(lm);
-        Out(")\n");
+        Out(')');
+        GenTypeConstraints(lm);
+        OutLn();
 
         OutOpenBrace();
 

src/Generators/Microsoft.Gen.Logging/Emission/Emitter.Utils.cs

@@ -131,4 +131,42 @@ internal static string PickUniqueName(string baseName, IEnumerable<string> poten
 #pragma warning restore S1643 // Strings should not be concatenated using '+' in a loop
         }
     }
+
+    private void GenTypeParameterList(LoggingMethod lm)
+    {
+        if (lm.TypeParameters.Count == 0)
+        {
+            return;
+        }
+
+        bool firstItem = true;
+        Out('<');
+        foreach (var tp in lm.TypeParameters)
+        {
+            if (firstItem)
+            {
+                firstItem = false;
+            }
+            else
+            {
+                Out(", ");
+            }
+
+            Out(tp.Name);
+        }
+
+        Out('>');
+    }
+
+    private void GenTypeConstraints(LoggingMethod lm)
+    {
+        foreach (var tp in lm.TypeParameters)
+        {
+            if (tp.Constraints is not null)
+            {
+                OutLn();
+                Out($"    where {tp.Name} : {tp.Constraints}");
+            }
+        }
+    }
 }

src/Generators/Microsoft.Gen.Logging/Model/LoggingMethod.cs

@@ -16,6 +16,7 @@ internal sealed class LoggingMethod
 {
     public readonly List<LoggingMethodParameter> Parameters = [];
     public readonly List<string> Templates = [];
+    public readonly List<LoggingMethodTypeParameter> TypeParameters = [];
     public string Name = string.Empty;
     public string Message = string.Empty;
     public int? Level;

src/Generators/Microsoft.Gen.Logging/Model/LoggingMethodTypeParameter.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.Gen.Logging.Model;
+
+/// <summary>
+/// A type parameter of a generic logging method.
+/// </summary>
+internal sealed class LoggingMethodTypeParameter
+{
+    public string Name = string.Empty;
+    public string? Constraints;
+}

src/Generators/Microsoft.Gen.Logging/Parsing/DiagDescriptors.cs

@@ -56,10 +56,10 @@ internal sealed class DiagDescriptors : DiagDescriptorsBase
         messageFormat: Resources.LoggingMethodMustBePartialMessage,
         category: Category);
 
-    public static DiagnosticDescriptor LoggingMethodIsGeneric { get; } = Make(
+    public static DiagnosticDescriptor LoggingMethodHasAllowsRefStructConstraint { get; } = Make(
         id: DiagnosticIds.LoggerMessage.LOGGEN007,
-        title: Resources.LoggingMethodIsGenericTitle,
-        messageFormat: Resources.LoggingMethodIsGenericMessage,
+        title: Resources.LoggingMethodHasAllowsRefStructConstraintTitle,
+        messageFormat: Resources.LoggingMethodHasAllowsRefStructConstraintMessage,
         category: Category);
 
     public static DiagnosticDescriptor RedundantQualifierInMessage { get; } = Make(

src/Generators/Microsoft.Gen.Logging/Parsing/Parser.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
+using System.Reflection;
 using System.Threading;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
@@ -16,6 +17,14 @@ namespace Microsoft.Gen.Logging.Parsing;
 
 internal sealed partial class Parser
 {
+    // ITypeParameterSymbol.AllowsRefLikeType was added in Roslyn 4.9 (C# 13). Access via a compiled
+    // delegate so the same source file compiles against all supported Roslyn versions, while
+    // avoiding the per-call overhead of PropertyInfo.GetValue boxing.
+    private static readonly Func<ITypeParameterSymbol, bool>? _getAllowsRefLikeType =
+        (Func<ITypeParameterSymbol, bool>?)typeof(ITypeParameterSymbol)
+            .GetProperty("AllowsRefLikeType")?.GetGetMethod()!
+            .CreateDelegate(typeof(Func<ITypeParameterSymbol, bool>));
+
     private readonly CancellationToken _cancellationToken;
     private readonly Compilation _compilation;
     private readonly Action<Diagnostic> _reportDiagnostic;
@@ -398,11 +407,22 @@ static bool IsAllowedKind(SyntaxKind kind) =>
                 keepMethod = false;
             }
 
-            if (method.Arity > 0)
+            foreach (var tp in methodSymbol.TypeParameters)
             {
-                // we don't currently support generic methods
-                Diag(DiagDescriptors.LoggingMethodIsGeneric, method.TypeParameterList!.GetLocation());
-                keepMethod = false;
+                if (_getAllowsRefLikeType?.Invoke(tp) == true)
+                {
+                    // 'allows ref struct' anti-constraint is not supported because the generated code stores
+                    // parameters in fields and cannot hold ref struct type arguments.
+                    Diag(DiagDescriptors.LoggingMethodHasAllowsRefStructConstraint, method.Identifier.GetLocation());
+                    keepMethod = false;
+                    break;
+                }
+
+                lm.TypeParameters.Add(new LoggingMethodTypeParameter
+                {
+                    Name = tp.Name,
+                    Constraints = GetTypeParameterConstraints(tp),
+                });
             }
 
             bool isPartial = methodSymbol.IsPartialDefinition;
@@ -466,6 +486,45 @@ private static bool HasXmlDocumentation(MethodDeclarationSyntax method)
         return false;
     }
 
+    private static string? GetTypeParameterConstraints(ITypeParameterSymbol typeParameter)
+    {
+        var constraints = new List<string>();
+
+        if (typeParameter.HasReferenceTypeConstraint)
+        {
+            string classConstraint = typeParameter.ReferenceTypeConstraintNullableAnnotation == NullableAnnotation.Annotated ? "class?" : "class";
+            constraints.Add(classConstraint);
+        }
+        else if (typeParameter.HasValueTypeConstraint)
+        {
+            // HasUnmanagedTypeConstraint also implies HasValueTypeConstraint
+            constraints.Add(typeParameter.HasUnmanagedTypeConstraint ? "unmanaged" : "struct");
+        }
+        else if (typeParameter.HasNotNullConstraint)
+        {
+            constraints.Add("notnull");
+        }
+
+        foreach (var constraintType in typeParameter.ConstraintTypes)
+        {
+            if (constraintType is IErrorTypeSymbol)
+            {
+                continue;
+            }
+
+            constraints.Add(constraintType.ToDisplayString(
+                SymbolDisplayFormat.FullyQualifiedFormat.WithMiscellaneousOptions(
+                    SymbolDisplayFormat.FullyQualifiedFormat.MiscellaneousOptions | SymbolDisplayMiscellaneousOptions.IncludeNullableReferenceTypeModifier)));
+        }
+
+        if (typeParameter.HasConstructorConstraint)
+        {
+            constraints.Add("new()");
+        }
+
+        return constraints.Count > 0 ? string.Join(", ", constraints) : null;
+    }
+
     // Returns all the classification attributes attached to a symbol.
     private static List<INamedTypeSymbol> GetDataClassificationAttributes(ISymbol symbol, SymbolHolder symbols)
         => symbol

src/Generators/Microsoft.Gen.Logging/Parsing/Resources.resx

@@ -153,11 +153,11 @@
   <data name="LoggingMethodMustBePartialMessage" xml:space="preserve">
     <value>Logging methods must be partial</value>
   </data>
-  <data name="LoggingMethodIsGenericTitle" xml:space="preserve">
-    <value>Logging methods can't be generic</value>
+  <data name="LoggingMethodHasAllowsRefStructConstraintTitle" xml:space="preserve">
+    <value>Logging methods can't use the 'allows ref struct' constraint</value>
   </data>
-  <data name="LoggingMethodIsGenericMessage" xml:space="preserve">
-    <value>Logging methods can't be generic</value>
+  <data name="LoggingMethodHasAllowsRefStructConstraintMessage" xml:space="preserve">
+    <value>Logging methods can't use the 'allows ref struct' constraint</value>
   </data>
   <data name="ShouldntMentionExceptionInMessageMessage" xml:space="preserve">
     <value>Don't include a template for parameter "{0}" in the logging message, exceptions are automatically delivered without being listed in the logging message</value>

test/Generators/Microsoft.Gen.Logging/TestClasses/GenericTestExtensions.cs

@@ -0,0 +1,31 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using Microsoft.Extensions.Logging;
+
+namespace TestClasses
+{
+    internal static partial class GenericTestExtensions
+    {
+        // generic method with single type parameter
+        [LoggerMessage(0, LogLevel.Debug, "M1 {value}")]
+        internal static partial void M1<T>(ILogger logger, T value);
+
+        // generic method with struct+Enum constraint
+        [LoggerMessage(1, LogLevel.Debug, "M2 {code}")]
+        internal static partial void M2<TCode>(ILogger logger, TCode code)
+            where TCode : struct, Enum;
+
+        // generic method with multiple type parameters
+        [LoggerMessage(2, LogLevel.Debug, "M3 {p1} {p2}")]
+        internal static partial void M3<T1, T2>(ILogger logger, T1 p1, T2 p2)
+            where T1 : class
+            where T2 : notnull;
+
+        // generic method with new() constraint
+        [LoggerMessage(3, LogLevel.Debug, "M4 {value}")]
+        internal static partial void M4<T>(ILogger logger, T value)
+            where T : new();
+    }
+}

test/Generators/Microsoft.Gen.Logging/Unit/ParserTests.LogMethod.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
 using Microsoft.Gen.Logging.Parsing;
 using Xunit;
 
@@ -273,15 +274,67 @@ partial class C
     [Fact]
     public async Task MethodGeneric()
     {
+        const string Source = @"
+                partial class C
+                {
+                    [LoggerMessage(0, LogLevel.Debug, ""M1 {value}"")]
+                    static partial void M1<T>(ILogger logger, T value);
+                }
+            ";
+
+        await RunGenerator(Source);
+    }
+
+    [Fact]
+    public async Task MethodGenericWithConstraints()
+    {
+        const string Source = @"
+                partial class C
+                {
+                    [LoggerMessage(0, LogLevel.Debug, ""M1 {code}"")]
+                    static partial void M1<TCode>(ILogger logger, TCode code)
+                        where TCode : struct, System.Enum;
+                }
+            ";
+
+        await RunGenerator(Source);
+    }
+
+    [Fact]
+    public async Task MethodGenericMultipleTypeParams()
+    {
+        const string Source = @"
+                partial class C
+                {
+                    [LoggerMessage(0, LogLevel.Debug, ""M1 {p1} {p2}"")]
+                    static partial void M1<T1, T2>(ILogger logger, T1 p1, T2 p2)
+                        where T1 : class
+                        where T2 : notnull;
+                }
+            ";
+
+        await RunGenerator(Source);
+    }
+
+    [Fact]
+    public async Task MethodGenericWithAllowsRefStructConstraint()
+    {
+        // The 'allows ref struct' detection requires Roslyn 4.9+ (ITypeParameterSymbol.AllowsRefLikeType).
+        // Skip gracefully on older Roslyn versions where the property and syntax are unavailable.
+        if (typeof(ITypeParameterSymbol).GetProperty("AllowsRefLikeType") is null)
+        {
+            return;
+        }
+
         const string Source = @"
                 partial class C
                 {
                     [LoggerMessage(0, LogLevel.Debug, ""M1"")]
-                    static partial void M1/*0+*/<T>/*-0*/(ILogger logger);
+                    static partial void /*0+*/M1/*-0*/<T>(ILogger logger) where T : allows ref struct;
                 }
             ";
 
-        await RunGenerator(Source, DiagDescriptors.LoggingMethodIsGeneric);
+        await RunGenerator(Source, DiagDescriptors.LoggingMethodHasAllowsRefStructConstraint);
     }
 
     [Theory]