Find CustomHandler or KeySelector methods if they are defined in base types

ServiceScan.SourceGenerator.Tests/CustomHandlerTests.cs

@@ -445,6 +445,57 @@ public partial void ProcessServices()
         Assert.Equal(expected, results.GeneratedTrees[1].ToString());
     }
 
+    [Fact]
+    public void UseInstanceCustomHandlerMethod_FromParentType()
+    {
+        var source = $$"""
+            using ServiceScan.SourceGenerator;
+
+            namespace GeneratorTests;
+
+            public abstract class AbstractServiceProcessor
+            {
+                protected void HandleType<T>() => System.Console.WriteLine(typeof(T).Name);
+            }
+
+            public partial class ServicesProcessor : AbstractServiceProcessor
+            {
+                [GenerateServiceRegistrations(AssignableTo = typeof(IService), CustomHandler = nameof(HandleType))]
+                public partial void ProcessServices();
+            }
+            """;
+
+        var services =
+            """
+            namespace GeneratorTests;
+
+            public interface IService { }
+            public class MyService1 : IService { }
+            public class MyService2 : IService { }
+            """;
+
+        var compilation = CreateCompilation(source, services);
+
+        var results = CSharpGeneratorDriver
+            .Create(_generator)
+            .RunGenerators(compilation)
+            .GetRunResult();
+
+        var expected = $$"""
+            namespace GeneratorTests;
+
+            public partial class ServicesProcessor
+            {
+                public partial void ProcessServices()
+                {
+                    HandleType<global::GeneratorTests.MyService1>();
+                    HandleType<global::GeneratorTests.MyService2>();
+                }
+            }
+            """;
+        Assert.Equal(expected, results.GeneratedTrees[1].ToString());
+    }
+
     [Fact]
     public void UseStaticMethodFromMatchedClassAsCustomHandler_WithoutParameters()
     {

ServiceScan.SourceGenerator/DependencyInjectionGenerator.ParseMethodModel.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using Microsoft.CodeAnalysis;
+using ServiceScan.SourceGenerator.Extensions;
 using ServiceScan.SourceGenerator.Model;
 using static ServiceScan.SourceGenerator.DiagnosticDescriptors;
 
@@ -16,14 +17,12 @@ public partial class DependencyInjectionGenerator
         if (!method.IsPartialDefinition)
             return Diagnostic.Create(NotPartialDefinition, method.Locations[0]);
 
-        var attributeData = context.Attributes.Select(a => AttributeModel.Create(a, method)).ToArray();
+        var position = context.TargetNode.SpanStart;
+        var attributeData = context.Attributes.Select(a => AttributeModel.Create(a, method, context.SemanticModel)).ToArray();
         var hasCustomHandlers = attributeData.Any(a => a.CustomHandler != null);
 
-        for (var i = 0; i < context.Attributes.Length; i++)
+        foreach (var attribute in attributeData)
         {
-            var attribute = AttributeModel.Create(context.Attributes[i], method);
-            attributeData[i] = attribute;
-
             if (!attribute.HasSearchCriteria)
                 return Diagnostic.Create(MissingSearchCriteria, attribute.Location);
 
@@ -35,8 +34,7 @@ public partial class DependencyInjectionGenerator
 
             if (attribute.KeySelector != null)
             {
-                var keySelectorMethod = method.ContainingType.GetMembers().OfType<IMethodSymbol>()
-                    .FirstOrDefault(m => m.IsStatic && m.Name == attribute.KeySelector);
+                var keySelectorMethod = method.ContainingType.GetMethod(attribute.KeySelector, context.SemanticModel, position, isStatic: true);
 
                 if (keySelectorMethod is not null)
                 {
@@ -53,8 +51,7 @@ public partial class DependencyInjectionGenerator
 
             if (attribute.CustomHandler != null)
             {
-                var customHandlerMethod = method.ContainingType.GetMembers().OfType<IMethodSymbol>()
-                    .FirstOrDefault(m => m.Name == attribute.CustomHandler);
+                var customHandlerMethod = method.ContainingType.GetMethod(attribute.CustomHandler, context.SemanticModel, position);
 
                 if (customHandlerMethod != null)
                 {
@@ -80,7 +77,7 @@ public partial class DependencyInjectionGenerator
                 }
             }
 
-            if (attributeData[i].HasErrors)
+            if (attribute.HasErrors)
                 return null;
         }
 

ServiceScan.SourceGenerator/Extensions/TypeSymbolExtensions.cs

@@ -0,0 +1,36 @@
+using System.Linq;
+using Microsoft.CodeAnalysis;
+
+namespace ServiceScan.SourceGenerator.Extensions;
+
+internal static class TypeSymbolExtensions
+{
+    /// <summary>
+    /// Retrieves a method symbol from the specified type by name, considering accessibility, static context, and
+    /// inheritance.
+    /// </summary>
+    /// <remarks>This method searches the specified type and its base types for a method with the given name
+    /// that matches the specified accessibility and static context. If no matching method is found, the method returns
+    /// <see langword="null"/>.</remarks>
+    public static IMethodSymbol? GetMethod(this ITypeSymbol type, string methodName, SemanticModel semanticModel, int position, bool? isStatic = null)
+    {
+        var currentType = type;
+
+        while (currentType != null)
+        {
+            var method = currentType.GetMembers()
+                .OfType<IMethodSymbol>()
+                .Where(m => m.Name == methodName
+                    && (isStatic == null || m.IsStatic == isStatic)
+                    && semanticModel.IsAccessible(position, m))
+                .FirstOrDefault();
+
+            if (method != null)
+                return method;
+
+            currentType = currentType.BaseType;
+        }
+
+        return null;
+    }
+}

ServiceScan.SourceGenerator/Model/AttributeModel.cs

@@ -1,5 +1,6 @@
 using System.Linq;
 using Microsoft.CodeAnalysis;
+using ServiceScan.SourceGenerator.Extensions;
 
 namespace ServiceScan.SourceGenerator.Model;
 
@@ -31,8 +32,10 @@ record AttributeModel(
 {
     public bool HasSearchCriteria => TypeNameFilter != null || AssignableToTypeName != null || AttributeFilterTypeName != null;
 
-    public static AttributeModel Create(AttributeData attribute, IMethodSymbol method)
+    public static AttributeModel Create(AttributeData attribute, IMethodSymbol method, SemanticModel semanticModel)
     {
+        var position = attribute.ApplicationSyntaxReference?.Span.Start ?? 0;
+
         var assemblyType = attribute.NamedArguments.FirstOrDefault(a => a.Key == "FromAssemblyOf").Value.Value as INamedTypeSymbol;
         var assemblyNameFilter = attribute.NamedArguments.FirstOrDefault(a => a.Key == "AssemblyNameFilter").Value.Value as string;
         var assignableTo = attribute.NamedArguments.FirstOrDefault(a => a.Key == "AssignableTo").Value.Value as INamedTypeSymbol;
@@ -51,9 +54,7 @@ public static AttributeModel Create(AttributeData attribute, IMethodSymbol metho
         KeySelectorType? keySelectorType = null;
         if (keySelector != null)
         {
-            var keySelectorMethod = method.ContainingType.GetMembers()
-                .OfType<IMethodSymbol>()
-                .FirstOrDefault(m => m.IsStatic && m.Name == keySelector);
+            var keySelectorMethod = method.ContainingType.GetMethod(keySelector, semanticModel, position, isStatic: true);
 
             if (keySelectorMethod != null)
             {
@@ -69,9 +70,7 @@ public static AttributeModel Create(AttributeData attribute, IMethodSymbol metho
         var customHandlerGenericParameters = 0;
         if (customHandler != null)
         {
-            var customHandlerMethod = method.ContainingType.GetMembers()
-                .OfType<IMethodSymbol>()
-                .FirstOrDefault(m => m.Name == customHandler);
+            var customHandlerMethod = method.ContainingType.GetMethod(customHandler, semanticModel, position);
 
             customHandlerType = customHandlerMethod != null ? Model.CustomHandlerType.Method : Model.CustomHandlerType.TypeMethod;
             customHandlerGenericParameters = customHandlerMethod?.TypeParameters.Length ?? 0;