Add unit test for new diagnostic

Author: Sergio0694

src/CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/Analyzers/WinRTObservablePropertyOnFieldsIsNotAotCompatibleAnalyzer.cs

@@ -46,7 +46,7 @@ public override void Initialize(AnalysisContext context)
             }
 
             // Track whether we produced any diagnostics, for the compilation end scenario
-            bool hasProducedAnyDiagnostics = false;
+            AttributeData? firstObservablePropertyAttribute = null;
 
             context.RegisterSymbolAction(context =>
             {
@@ -57,7 +57,7 @@ public override void Initialize(AnalysisContext context)
                 }
 
                 // Emit a diagnostic if the field is using the [ObservableProperty] attribute
-                if (fieldSymbol.HasAttributeWithType(observablePropertySymbol))
+                if (fieldSymbol.TryGetAttributeWithType(observablePropertySymbol, out AttributeData? observablePropertyAttribute))
                 {
                     context.ReportDiagnostic(Diagnostic.Create(
                         WinRTObservablePropertyOnFieldsIsNotAotCompatible,
@@ -69,7 +69,7 @@ public override void Initialize(AnalysisContext context)
                         fieldSymbol.Name));
 
                     // Notify that we did produce at least one diagnostic
-                    Volatile.Write(ref hasProducedAnyDiagnostics, true);
+                    _ = Interlocked.CompareExchange(ref firstObservablePropertyAttribute, observablePropertyAttribute, null);
                 }
             }, SymbolKind.Field);
 
@@ -83,9 +83,11 @@ public override void Initialize(AnalysisContext context)
             context.RegisterCompilationEndAction(context =>
             {
                 // If we have produced at least one diagnostic, also emit the info message
-                if (Volatile.Read(ref hasProducedAnyDiagnostics))
+                if (Volatile.Read(ref firstObservablePropertyAttribute) is { } observablePropertyAttribute)
                 {
-                    context.ReportDiagnostic(Diagnostic.Create(WinRTObservablePropertyOnFieldsIsNotAotCompatibleCompilationEndInfo, location: null));
+                    context.ReportDiagnostic(Diagnostic.Create(
+                        WinRTObservablePropertyOnFieldsIsNotAotCompatibleCompilationEndInfo,
+                        observablePropertyAttribute.GetLocation()));
                 }
             });
         });

tests/CommunityToolkit.Mvvm.SourceGenerators.Roslyn4110.UnitTests/Test_SourceGeneratorsDiagnostics.cs

@@ -434,6 +434,28 @@ await CSharpAnalyzerWithLanguageVersionTest<WinRTObservablePropertyOnFieldsIsNot
             editorconfig: [("_MvvmToolkitIsUsingWindowsRuntimePack", true), ("CsWinRTAotOptimizerEnabled", "auto")]);
     }
 
+    [TestMethod]
+    public async Task WinRTObservablePropertyOnFieldsIsNotAotCompatibleAnalyzer_TargetingWindows_CsWinRTAotOptimizerEnabled_Auto_NotCSharpPreview_Warns_WithCompilationWarning()
+    {
+        const string source = """
+            using CommunityToolkit.Mvvm.ComponentModel;
+            
+            namespace MyApp
+            {
+                public partial class SampleViewModel : ObservableObject
+                {            
+                    [{|MVVMTK0051:ObservableProperty|}]            
+                    private string {|MVVMTK0045:name|};
+                }
+            }
+            """;
+
+        await CSharpAnalyzerWithLanguageVersionTest<WinRTObservablePropertyOnFieldsIsNotAotCompatibleAnalyzer>.VerifyAnalyzerAsync(
+            source,
+            LanguageVersion.CSharp12,
+            editorconfig: [("_MvvmToolkitIsUsingWindowsRuntimePack", true), ("CsWinRTAotOptimizerEnabled", "auto")]);
+    }
+
     [TestMethod]
     public async Task WinRTObservablePropertyOnFieldsIsNotAotCompatibleAnalyzer_TargetingWindows_CsWinRTAotOptimizerEnabled_True_NoXaml_Level1_DoesNotWarn()
     {