Fixed nullability attributes generation on .NET Standard 2.0

Author: Sergio0694

Microsoft.Toolkit.Mvvm.SourceGenerators/Attributes/NullabilityAttributesGenerator.cs

@@ -34,7 +34,12 @@ public void Execute(GeneratorExecutionContext context)
         /// </summary>
         private void AddSourceCodeIfTypeIsNotPresent(GeneratorExecutionContext context, string typeFullName)
         {
-            if (context.Compilation.GetTypeByMetadataName(typeFullName) is not null)
+            // Check that the target attributes are not available in the consuming project. To ensure that
+            // this works fine both in .NET (Core) and .NET Standard implementations, we also need to check
+            // that the target types are defined in the reference assemblies for all target runtimes. This
+            // avoids issues on .NET Standard with Roslyn also seeing internal types from referenced assemblies.
+            if (context.Compilation.GetTypeByMetadataName(typeFullName) is
+                { ContainingModule: { MetadataName: "netstandard.dll" or "System.Runtime.dll" } })
             {
                 return;
             }

UnitTests/UnitTests.NetCore/Mvvm/Test_INotifyPropertyChangedAttribute.cs

@@ -107,5 +107,25 @@ public partial class SampleModelWithINPCAndObservableProperties
             [ObservableProperty]
             private int y;
         }
+
+        [TestCategory("Mvvm")]
+        [TestMethod]
+        public void Test_INotifyPropertyChanged_WithGeneratedProperties_ExternalNetStandard20Assembly()
+        {
+            Assert.IsTrue(typeof(INotifyPropertyChanged).IsAssignableFrom(typeof(NetStandard.SampleModelWithINPCAndObservableProperties)));
+            Assert.IsFalse(typeof(INotifyPropertyChanging).IsAssignableFrom(typeof(NetStandard.SampleModelWithINPCAndObservableProperties)));
+
+            NetStandard.SampleModelWithINPCAndObservableProperties model = new();
+            List<PropertyChangedEventArgs> eventArgs = new();
+
+            model.PropertyChanged += (s, e) => eventArgs.Add(e);
+
+            model.X = 42;
+            model.Y = 66;
+
+            Assert.AreEqual(eventArgs.Count, 2);
+            Assert.AreEqual(eventArgs[0].PropertyName, nameof(NetStandard.SampleModelWithINPCAndObservableProperties.X));
+            Assert.AreEqual(eventArgs[1].PropertyName, nameof(NetStandard.SampleModelWithINPCAndObservableProperties.Y));
+        }
     }
 }

UnitTests/UnitTests.NetCore/UnitTests.NetCore.csproj

@@ -10,6 +10,7 @@
     <ProjectReference Include="..\..\Microsoft.Toolkit.Mvvm\Microsoft.Toolkit.Mvvm.csproj" />
     <ProjectReference Include="..\..\Microsoft.Toolkit.Diagnostics\Microsoft.Toolkit.Diagnostics.csproj" />
     <ProjectReference Include="..\..\Microsoft.Toolkit.Mvvm.SourceGenerators\Microsoft.Toolkit.Mvvm.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build" />
+    <ProjectReference Include="..\UnitTests.NetStandard\UnitTests.NetStandard.csproj" />
   </ItemGroup>
 
   <ItemGroup>