Add .targets file to disable source generators on Roslyn 3.x

Still a bit experimental, needs more testing and validation

Author: Sergio0694

CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj

@@ -18,7 +18,6 @@
       - Ioc: a helper class to configure dependency injection service containers.
     </Description>
     <PackageTags>MVVM;Toolkit;MVVMToolkit;INotifyPropertyChanged;Observable;IOC;DI;Dependency Injection;Object Messaging;Extensions;Helpers</PackageTags>
-    <TargetsForTfmSpecificContentInPackage>$(TargetsForTfmSpecificContentInPackage);CopyAnalyzerProjectReferencesToPackage</TargetsForTfmSpecificContentInPackage>
   </PropertyGroup>
 
   <!-- .NET Standard 2.0 doesn't have the Span<T> and IAsyncEnumerable<T> types -->
@@ -36,22 +35,23 @@
   </ItemGroup>
 
   <!-- Source generator project reference for packing -->
-  <ItemGroup>
-    <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" PrivateAssets="all" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" ReferenceOutputAssembly="false" />
   </ItemGroup>
 
-  <!--
-      Target to pack the source generator into the "analyzers\dotnet\cs" package folder.
-      The condition is set to .NET Standard 2.0 so that the analyzer is only added to the package
-      when that target is being built, instead of once for all three targets, which would fail.
-      It will still be available for all targets anyway though, as analyzers don't have a target.
-  -->
-  <Target Name="CopyAnalyzerProjectReferencesToPackage" DependsOnTargets="BuildOnlySettings;ResolveReferences" Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
-    <ItemGroup>
-      <TfmSpecificPackageFile Include="@(ReferenceCopyLocalPaths->WithMetadataValue('ReferenceSourceTarget', 'ProjectReference')->WithMetadataValue('PrivateAssets', 'All'))">
-        <PackagePath>analyzers\dotnet\cs</PackagePath>
-      </TfmSpecificPackageFile>
-    </ItemGroup>
-  </Target>
+  <ItemGroup Label="Package">
+    
+    <!-- Include the custom .targets file to check the source generator (.NET 6 is not needed as it guarantees Roslyn 4.x) -->
+    <None Include="CommunityToolkit.Mvvm.targets" PackagePath="buildTransitive\netstandard2.0" Pack="true" />
+    <None Include="CommunityToolkit.Mvvm.targets" PackagePath="buildTransitive\netstandard2.1" Pack="true" />
+    <None Include="CommunityToolkit.Mvvm.targets" PackagePath="build\netstandard2.0" Pack="true" />
+    <None Include="CommunityToolkit.Mvvm.targets" PackagePath="build\netstandard2.1" Pack="true" />
+
+    <!-- Pack the source generator to the right package folder -->
+    <None Include="..\CommunityToolkit.Mvvm.SourceGenerators\bin\$(Configuration)\netstandard2.0\CommunityToolkit.Mvvm.SourceGenerators.dll"
+          PackagePath="analyzers\dotnet\roslyn4.0\cs"
+          Pack="true"
+          Visible="false" />
+  </ItemGroup>
 
 </Project>

CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.targets

@@ -0,0 +1,21 @@
+<Project>
+
+  <!-- Get the analyzer from the CommunityToolkit.Mvvm NuGet package -->
+  <Target Name="_MVVMToolkitGatherAnalyzers">
+    <ItemGroup>
+      <_MVVMToolkitAnalyzer Include="@(Analyzer)" Condition="'%(Analyzer.NuGetPackageId)' == 'CommunityToolkit.Mvvm'" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Remove the analyzer if using Roslyn 3.x (incremental generators require Roslyn 4.x) -->
+  <Target Name="_MVVMToolkitRemoveAnalyzersForRoslyn3"
+          Condition="'$(SupportsRoslynComponentVersioning)' != 'true'"
+          AfterTargets="ResolvePackageDependenciesForBuild;ResolveNuGetPackageAssets"
+          DependsOnTargets="_MVVMToolkitGatherAnalyzers">
+    <ItemGroup>
+      <Analyzer Remove="@(_MVVMToolkitAnalyzer)"/>
+    </ItemGroup>
+    <Warning Text="The MVVM Toolkit source generators have been disabled on the current configuration, as they need Roslyn 4.x in order to work. The MVVM Toolkit will work just fine, but features relying on the source generators will not be available."/>
+  </Target>
+
+</Project>