Exclude CsWinRT-required partial types from MA0204

docs/Rules/MA0204.md

@@ -9,6 +9,8 @@ The `partial` modifier can be removed when there is no other declaration to merg
 
 Classes inheriting from common WPF XAML base types (`System.Windows.Controls.UserControl`, `System.Windows.Controls.Page`, `System.Windows.Window`, and `System.Windows.Application`) are excluded.
 
+The rule also does not report classes whose `partial` modifier can be required by CsWinRT AOT/WinRT source generation, for instance when CsWinRT support or .NET MAUI types are present in the compilation and a class implements WinRT-mapped interfaces such as `IDisposable`.
+
 ## Non-compliant code
 
 ````csharp

src/Meziantou.Analyzer/Rules/RemoveUnnecessaryPartialModifierAnalyzer.cs

@@ -30,12 +30,35 @@ public override void Initialize(AnalysisContext context)
                 context.Compilation.GetBestTypeByMetadataName("System.Windows.Controls.Page"),
                 context.Compilation.GetBestTypeByMetadataName("System.Windows.Window"),
                 context.Compilation.GetBestTypeByMetadataName("System.Windows.Application"));
+            var csWinRTCustomMappedInterfaces = ImmutableArray.Create(
+                context.Compilation.GetBestTypeByMetadataName("System.IDisposable"),
+                context.Compilation.GetBestTypeByMetadataName("System.IServiceProvider"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.IEnumerable"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.IList"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.Generic.IEnumerable`1"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.Generic.IEnumerator`1"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.Generic.IList`1"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.Generic.IDictionary`2"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.Generic.IReadOnlyList`1"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.Generic.IReadOnlyDictionary`2"),
+                context.Compilation.GetBestTypeByMetadataName("System.Collections.Specialized.INotifyCollectionChanged"),
+                context.Compilation.GetBestTypeByMetadataName("System.ComponentModel.INotifyDataErrorInfo"),
+                context.Compilation.GetBestTypeByMetadataName("System.ComponentModel.INotifyPropertyChanged"),
+                context.Compilation.GetBestTypeByMetadataName("System.Windows.Input.ICommand"));
+            var hasCsWinRTAotSupport =
+                context.Compilation.GetBestTypeByMetadataName("WinRT.WindowsRuntimeTypeAttribute") is not null &&
+                context.Compilation.GetBestTypeByMetadataName("WinRT.GeneratedBindableCustomPropertyAttribute") is not null &&
+                context.Compilation.GetBestTypeByMetadataName("WinRT.GeneratedWinRTExposedTypeAttribute") is not null &&
+                context.Compilation.GetBestTypeByMetadataName("WinRT.WinRTExposedTypeAttribute") is not null;
+            var isMauiCompilation =
+                context.Compilation.GetBestTypeByMetadataName("Microsoft.Maui.Controls.Application") is not null &&
+                context.Compilation.GetBestTypeByMetadataName("Microsoft.Maui.Controls.BindableObject") is not null;
 
-            context.RegisterSymbolAction(context => AnalyzeNamedTypeSymbol(context, excludedBaseTypes), SymbolKind.NamedType);
+            context.RegisterSymbolAction(context => AnalyzeNamedTypeSymbol(context, excludedBaseTypes, csWinRTCustomMappedInterfaces, hasCsWinRTAotSupport, isMauiCompilation), SymbolKind.NamedType);
         });
     }
 
-    private static void AnalyzeNamedTypeSymbol(SymbolAnalysisContext context, ImmutableArray<INamedTypeSymbol?> excludedBaseTypes)
+    private static void AnalyzeNamedTypeSymbol(SymbolAnalysisContext context, ImmutableArray<INamedTypeSymbol?> excludedBaseTypes, ImmutableArray<INamedTypeSymbol?> csWinRTCustomMappedInterfaces, bool hasCsWinRTAotSupport, bool isMauiCompilation)
     {
         var symbol = (INamedTypeSymbol)context.Symbol;
         if (symbol.TypeKind is not (TypeKind.Class or TypeKind.Struct or TypeKind.Interface))
@@ -55,6 +78,9 @@ private static void AnalyzeNamedTypeSymbol(SymbolAnalysisContext context, Immuta
         if (InheritsFromExcludedType(symbol, excludedBaseTypes))
             return;
 
+        if (RequiresPartialForCsWinRT(symbol, csWinRTCustomMappedInterfaces, hasCsWinRTAotSupport, isMauiCompilation))
+            return;
+
         context.ReportDiagnostic(Rule, partialToken.GetLocation());
     }
 
@@ -68,4 +94,54 @@ private static bool InheritsFromExcludedType(INamedTypeSymbol symbol, ImmutableA
 
         return false;
     }
+
+    private static bool RequiresPartialForCsWinRT(INamedTypeSymbol symbol, ImmutableArray<INamedTypeSymbol?> csWinRTCustomMappedInterfaces, bool hasCsWinRTAotSupport, bool isMauiCompilation)
+    {
+        if (!hasCsWinRTAotSupport && !isMauiCompilation)
+            return false;
+
+        return ContainsTypeRequiringCsWinRTPartial(symbol, csWinRTCustomMappedInterfaces);
+    }
+
+    private static bool ContainsTypeRequiringCsWinRTPartial(INamedTypeSymbol symbol, ImmutableArray<INamedTypeSymbol?> csWinRTCustomMappedInterfaces)
+    {
+        if (IsTypeRequiringCsWinRTPartial(symbol, csWinRTCustomMappedInterfaces))
+            return true;
+
+        foreach (var nestedType in symbol.GetTypeMembers())
+        {
+            if (ContainsTypeRequiringCsWinRTPartial(nestedType, csWinRTCustomMappedInterfaces))
+                return true;
+        }
+
+        return false;
+    }
+
+    private static bool IsTypeRequiringCsWinRTPartial(INamedTypeSymbol symbol, ImmutableArray<INamedTypeSymbol?> csWinRTCustomMappedInterfaces)
+    {
+        if (symbol.TypeKind != TypeKind.Class || symbol.IsAbstract || symbol.IsStatic)
+            return false;
+
+        foreach (var interfaceType in symbol.AllInterfaces)
+        {
+            if (IsCsWinRTCustomMappedInterface(interfaceType, csWinRTCustomMappedInterfaces))
+                return true;
+        }
+
+        return false;
+    }
+
+    private static bool IsCsWinRTCustomMappedInterface(INamedTypeSymbol interfaceType, ImmutableArray<INamedTypeSymbol?> csWinRTCustomMappedInterfaces)
+    {
+        foreach (var csWinRTCustomMappedInterface in csWinRTCustomMappedInterfaces)
+        {
+            if (csWinRTCustomMappedInterface is not null &&
+                SymbolEqualityComparer.Default.Equals(interfaceType.OriginalDefinition, csWinRTCustomMappedInterface))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
 }

tests/Meziantou.Analyzer.Test/Rules/RemoveUnnecessaryPartialModifierAnalyzerTests.cs

@@ -196,6 +196,109 @@ partial class Nested
         return test.RunAsync();
     }
 
+    [Fact]
+    public Task PartialClass_ImplementingDisposable_WithCsWinRTSupport_NoDiagnostic()
+    {
+        var test = CreateTest();
+        test.TestCode = """
+            using System;
+
+            namespace WinRT
+            {
+                sealed class WindowsRuntimeTypeAttribute : Attribute
+                {
+                }
+
+                sealed class GeneratedBindableCustomPropertyAttribute : Attribute
+                {
+                }
+
+                sealed class GeneratedWinRTExposedTypeAttribute : Attribute
+                {
+                }
+
+                sealed class WinRTExposedTypeAttribute : Attribute
+                {
+                }
+            }
+
+            partial class Sample : IDisposable
+            {
+                public void Dispose()
+                {
+                }
+            }
+            """;
+
+        return test.RunAsync();
+    }
+
+    [Fact]
+    public Task PartialClass_ImplementingDisposable_WithoutCsWinRTOrMauiSupport_ReportsDiagnostic()
+    {
+        var test = CreateTest();
+        test.TestCode = """
+            using System;
+
+            {|MA0204:partial|} class Sample : IDisposable
+            {
+                public void Dispose()
+                {
+                }
+            }
+            """;
+        test.FixedCode = """
+            using System;
+            class Sample : IDisposable
+            {
+                public void Dispose()
+                {
+                }
+            }
+            """;
+
+        return test.RunAsync();
+    }
+
+    [Fact]
+    public Task PartialContainingClass_WithNestedDisposableType_InMauiCompilation_NoDiagnostic()
+    {
+        var test = CreateTest();
+        test.TestCode = """
+            using System;
+
+            namespace Microsoft.Maui.Controls
+            {
+                class BindableObject
+                {
+                }
+
+                class Application : BindableObject
+                {
+                }
+            }
+
+            partial class Sample
+            {
+                partial class Nested : IDisposable
+                {
+                    public void Dispose()
+                    {
+                    }
+                }
+            }
+
+            partial class Sample
+            {
+                partial class Nested
+                {
+                }
+            }
+            """;
+
+        return test.RunAsync();
+    }
+
     [Fact]
     public Task PartialClass_InheritingFromWpfUserControl_NoDiagnostic()
     {