WPF0012 Allow accessor property to be nullable

Fix #293

Author: JohanLarsson

ValidCode/Repro/Issue293.cs

@@ -0,0 +1,22 @@
+namespace ValidCode.Repro;
+
+using System.Drawing;
+using System.Windows;
+
+public class Issue293 : FrameworkElement
+{
+    /// <summary>Identifies the <see cref="Background"/> dependency property.</summary>
+    public static readonly DependencyProperty BackgroundProperty = DependencyProperty.Register(
+        nameof(Background),
+        typeof(Brush),
+        typeof(Issue293),
+        new FrameworkPropertyMetadata(
+            Brushes.Transparent,
+            FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.SubPropertiesDoNotAffectRender));
+
+    public Brush? Background
+    {
+        get => (Brush?)this.GetValue(BackgroundProperty);
+        set => this.SetValue(BackgroundProperty, value);
+    }
+}

WpfAnalyzers.Test/WPF0012ClrPropertyShouldMatchRegisteredTypeTests/Valid.cs

@@ -291,4 +291,34 @@ public enum FooEnum
 }";
         RoslynAssert.Valid(Analyzer, fooCode, code, enumCode);
     }
+
+    [Test]
+    public static void AllowNullableAccessorIssue293()
+    {
+        var code = @"
+namespace N;
+
+using System.Drawing;
+using System.Windows;
+
+public class C : FrameworkElement
+{
+    /// <summary>Identifies the <see cref=""Background""/> dependency property.</summary>
+    public static readonly DependencyProperty BackgroundProperty = DependencyProperty.Register(
+        nameof(Background),
+        typeof(Brush),
+        typeof(C),
+        new FrameworkPropertyMetadata(
+            Brushes.Transparent,
+            FrameworkPropertyMetadataOptions.AffectsRender | FrameworkPropertyMetadataOptions.SubPropertiesDoNotAffectRender));
+
+    public Brush? Background
+    {
+        get => (Brush?)this.GetValue(BackgroundProperty);
+        set => this.SetValue(BackgroundProperty, value);
+    }
+}";
+
+        RoslynAssert.Valid(Analyzer, code);
+    }
 }

WpfAnalyzers/Analyzers/ClrPropertyDeclarationAnalyzer.cs

@@ -36,15 +36,13 @@ context.Node is PropertyDeclarationSyntax propertyDeclaration &&
         {
             if (ClrProperty.Match(property, context.SemanticModel, context.CancellationToken) is { SetValue: { } setValue, BackingSet: { } backingSet, GetValue: { } getValue, BackingGet: { } backingGet })
             {
-                if (getter.Body is { Statements: { } getStatements } &&
-                    getStatements.Count > 1 &&
+                if (getter.Body is { Statements: { Count: > 1 } getStatements } &&
                     getStatements.TryFirst(x => !x.Contains(getValue), out var statement))
                 {
                     context.ReportDiagnostic(Diagnostic.Create(Descriptors.WPF0036AvoidSideEffectsInClrAccessors, statement.GetLocation()));
                 }
 
-                if (setter.Body is { Statements: { } setStatements } &&
-                    setStatements.Count > 1 &&
+                if (setter.Body is { Statements: { Count: > 1 } setStatements } &&
                     setStatements.TryFirst(x => !x.Contains(setValue), out var sideEffect))
                 {
                     context.ReportDiagnostic(Diagnostic.Create(Descriptors.WPF0036AvoidSideEffectsInClrAccessors, sideEffect.GetLocation()));
@@ -73,7 +71,7 @@ context.Node is PropertyDeclarationSyntax propertyDeclaration &&
 
                 if (backingGet.RegisteredType(context.SemanticModel, context.CancellationToken) is { Value: { } registeredType })
                 {
-                    if (!TypeSymbolComparer.Equal(property.Type, registeredType))
+                    if (!MatchesRegisteredType(property.Type, registeredType))
                     {
                         context.ReportDiagnostic(
                             Diagnostic.Create(
@@ -85,7 +83,7 @@ context.Node is PropertyDeclarationSyntax propertyDeclaration &&
                     }
                     else if (getValue is { Parent: CastExpressionSyntax { Type: { } type } } &&
                              context.SemanticModel.GetType(type, context.CancellationToken) is { } castType &&
-                             !TypeSymbolComparer.Equal(registeredType, castType))
+                             !MatchesRegisteredType(castType, registeredType))
                     {
                         context.ReportDiagnostic(
                             Diagnostic.Create(
@@ -95,6 +93,22 @@ context.Node is PropertyDeclarationSyntax propertyDeclaration &&
                                 property,
                                 registeredType));
                     }
+
+                    static bool MatchesRegisteredType(ITypeSymbol candidate, ITypeSymbol registeredType)
+                    {
+                        if (TypeSymbolComparer.Equal(candidate, registeredType))
+                        {
+                            return true;
+                        }
+
+                        if (candidate.NullableAnnotation == NullableAnnotation.Annotated &&
+                            registeredType.NullableAnnotation == NullableAnnotation.NotAnnotated)
+                        {
+                            return TypeSymbolComparer.Equal(candidate.OriginalDefinition, registeredType);
+                        }
+
+                        return false;
+                    }
                 }
 
                 bool IsGettingAndSettingDifferent()