Refactor generated-code checks and helper

Improve detection of generated ICustomPropertyProvider implementations and simplify attribute handling. Make GeneratedCodeAttribute resolution non-nullable and add HasNonGeneratedImplementedMembers helper to centralize logic for checking implemented interface members that were not emitted by this generator. Simplify attribute checks in ISymbolExtensions by using TryGetAttributeWithType and validating the constructor argument, and replace manual loop with LINQ.Any in ITypeSymbolExtensions (added System.Linq). Removes duplicate/nullable checks and streamlines the analyzer to avoid false diagnostics for generator-emitted members.

Author: Sergio0694

src/Authoring/WinRT.SourceGenerator2/Diagnostics/Analyzers/GeneratedCustomPropertyProviderExistingMemberImplementationAnalyzer.cs

@@ -43,7 +43,7 @@ public override void Initialize(AnalysisContext context)
             }
 
             // Resolve the '[GeneratedCode]' attribute type, used to skip generated implementations
-            INamedTypeSymbol? generatedCodeAttributeType = context.Compilation.GetTypeByMetadataName("System.CodeDom.Compiler.GeneratedCodeAttribute");
+            INamedTypeSymbol generatedCodeAttributeType = context.Compilation.GetTypeByMetadataName("System.CodeDom.Compiler.GeneratedCodeAttribute")!;
 
             context.RegisterSymbolAction(context =>
             {
@@ -59,8 +59,20 @@ public override void Initialize(AnalysisContext context)
                     return;
                 }
 
+                // Helper to check whether a symbol has any generated interface members that are not emitted by this generator. his covers
+                // both manually implemented members and those produced by other generators, and explicitly interface implementations too.
+                static bool HasNonGeneratedImplementedMembers(
+                    INamedTypeSymbol typeSymbol,
+                    INamedTypeSymbol? interfaceType,
+                    INamedTypeSymbol generatedCodeAttributeType)
+                {
+                    return
+                        interfaceType is not null &&
+                        !typeSymbol.EnumerateImplementedMembersForInterface(interfaceType).AreAllImplementedByGenerator(generatedCodeAttributeType, nameof(CustomPropertyProviderGenerator));
+                }
+
                 // Check whether the type has or inherits any 'ICustomPropertyProvider' member implementations.
-                // We don't warn if all implementations are generated by CustomPropertyProviderGenerator itself,
+                // We don't warn if all implementations are generated by 'CustomPropertyProviderGenerator' itself,
                 // so that only user-authored implementations trigger this diagnostic.
                 if (HasNonGeneratedImplementedMembers(typeSymbol, windowsUIXamlCustomPropertyProviderType, generatedCodeAttributeType) ||
                     HasNonGeneratedImplementedMembers(typeSymbol, microsoftUIXamlCustomPropertyProviderType, generatedCodeAttributeType))
@@ -70,16 +82,6 @@ public override void Initialize(AnalysisContext context)
                         typeSymbol.Locations.FirstOrDefault(),
                         typeSymbol));
                 }
-
-                static bool HasNonGeneratedImplementedMembers(
-                    INamedTypeSymbol typeSymbol,
-                    INamedTypeSymbol? interfaceType,
-                    INamedTypeSymbol? generatedCodeAttributeType)
-                {
-                    return interfaceType is not null && (generatedCodeAttributeType is not null
-                        ? !typeSymbol.EnumerateImplementedMembersForInterface(interfaceType).AreAllImplementedByGenerator(generatedCodeAttributeType, nameof(CustomPropertyProviderGenerator))
-                        : typeSymbol.HasAnyImplementedMembersForInterface(interfaceType));
-                }
             }, SymbolKind.NamedType);
         });
     }

src/Authoring/WinRT.SourceGenerator2/Extensions/ISymbolExtensions.cs

@@ -92,29 +92,20 @@ public bool AreAllImplementedByGenerator(INamedTypeSymbol generatedCodeAttribute
         {
             foreach (ISymbol symbol in symbols)
             {
-                if (!HasGeneratedCodeAttributeWithName(symbol, generatedCodeAttributeType, generatorName))
+                // Stop if the symbol doesn't have '[GeneratedCode]' on it
+                if (!symbol.TryGetAttributeWithType(generatedCodeAttributeType, out AttributeData? attributeData))
                 {
                     return false;
                 }
-            }
-
-            return true;
 
-            // Checks whether a symbol has a [GeneratedCode] attribute with the specified generator name.
-            static bool HasGeneratedCodeAttributeWithName(ISymbol symbol, INamedTypeSymbol generatedCodeAttributeType, string generatorName)
-            {
-                foreach (AttributeData attribute in symbol.GetAttributes())
+                // Check that the symbol was specifically generated by the target generator
+                if (attributeData.ConstructorArguments is not [{ Value: string name }, ..] || name != generatorName)
                 {
-                    if (SymbolEqualityComparer.Default.Equals(attribute.AttributeClass, generatedCodeAttributeType) &&
-                        attribute.ConstructorArguments is [{ Value: string name }, ..] &&
-                        name == generatorName)
-                    {
-                        return true;
-                    }
+                    return false;
                 }
-
-                return false;
             }
+
+            return true;
         }
     }
 }

src/Authoring/WinRT.SourceGenerator2/Extensions/ITypeSymbolExtensions.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using Microsoft.CodeAnalysis;
 
 #pragma warning disable CS1734, IDE0046
@@ -85,12 +86,7 @@ public IEnumerable<ISymbol> EnumerateImplementedMembersForInterface(INamedTypeSy
         /// <returns>Whether <paramref name="symbol"/> has any implemented members for <paramref name="interfaceType"/>.</returns>
         public bool HasAnyImplementedMembersForInterface(INamedTypeSymbol interfaceType)
         {
-            foreach (ISymbol _ in symbol.EnumerateImplementedMembersForInterface(interfaceType))
-            {
-                return true;
-            }
-
-            return false;
+            return symbol.EnumerateImplementedMembersForInterface(interfaceType).Any();
         }
 
         /// <summary>