From 7bd28e4eb1cb15c0e29167164b5f0c2c6eb4940d Mon Sep 17 00:00:00 2001
From: Sergio Pedri <sergio0694@live.com>
Date: Thu, 8 Sep 2022 02:15:41 +0200
Subject: [PATCH 1/4] Enable Roslyn multi-targeting in the MVVM Toolkit
 generator

---
 ...munityToolkit.Mvvm.SourceGenerators.csproj | 22 ++++++++++++++++++-
 .../CommunityToolkit.Mvvm.csproj              | 20 +++++++++++------
 2 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj b/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
index f9e7f71c0..4ae1f4112 100644
--- a/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
+++ b/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
@@ -5,6 +5,26 @@
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
+  <!--
+    The MVVM Toolkit source generators rely on Roslyn multi-targeting to support multiple versions of the Microsoft.CodeAnalysis.CSharp package.
+    This package reference actually needs a matching version of Roslyn to be available for consumers of the source generator, so if we always
+    used the latest version, the MVVM Toolkit would just fail to load for users of eg. an older version of Visual Studio. Thankfully, Roslyn
+    supports analyzers that bundle multiple versions in the same NuGet package, each in a subfolder with a name matching the Roslyn version.
+    To leverage this, this project receives the MvvmToolkitSourceGeneratorRoslynVersion property as input, so that the MVVM Toolkit can build
+    it multiple times with multiple versions during packing, to then extract each .dll and copy it to the right NuGet package folder.
+  -->
+  <PropertyGroup>
+    
+    <!-- When the property is not set (which will not happen when creating a NuGet package anyway), just default to 4.0.1 -->
+    <MvvmToolkitSourceGeneratorRoslynVersion Condition="'$(MvvmToolkitSourceGeneratorRoslynVersion)' == ''">4.0.1</MvvmToolkitSourceGeneratorRoslynVersion>
+    
+    <!-- The output path will end up being eg. "bin\Debug\roslyn4.0\netstandard2.0" (the trailing "netstandard2.0" is added automatically) -->
+    <OutputPath>bin\$(Configuration)\roslyn$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3))</OutputPath>
+    
+    <!-- Also define a "ROSLYN_<MAJOR>_<MINOR>" build constant, so the generator code can multi-target whenever needed and add any required polyfills -->
+    <DefineConstants>$(DefineConstants);ROSLYN_$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3).Replace('.', '_'))</DefineConstants>
+  </PropertyGroup>
+
   <ItemGroup>
     <Compile Remove="EmbeddedResources\INotifyPropertyChanged.cs" />
     <Compile Remove="EmbeddedResources\NotNullAttribute.cs" />
@@ -32,7 +52,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.0.1" PrivateAssets="all" Pack="false" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="$(MvvmToolkitSourceGeneratorRoslynVersion)" PrivateAssets="all" Pack="false" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj b/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj
index 2bfe1cdf1..e7fd2e6b9 100644
--- a/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj
+++ b/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj
@@ -40,9 +40,14 @@
     <IsTrimmable>true</IsTrimmable>
   </PropertyGroup>
 
-  <!-- Source generator project reference for packing -->
+  <!-- Reference the various multi-targeted versions of the source generator project (one per Roslyn version) -->
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" ReferenceOutputAssembly="false" />
+    <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" ReferenceOutputAssembly="false">
+      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=4.0.1</Properties>
+    </ProjectReference>
+    <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" ReferenceOutputAssembly="false">
+      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=4.3.0</Properties>
+    </ProjectReference>
   </ItemGroup>
 
   <ItemGroup Label="Package">
@@ -53,11 +58,12 @@
     <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" />
+    <!--
+      Pack the source generator to the right package folders (each matching the target Roslyn version).
+      Roslyn will automatically load the highest version compatible with Roslyn's version in the SDK.
+    -->
+    <None Include="..\CommunityToolkit.Mvvm.SourceGenerators\bin\$(Configuration)\roslyn4.0\netstandard2.0\CommunityToolkit.Mvvm.SourceGenerators.dll" PackagePath="analyzers\dotnet\roslyn4.0\cs" Pack="true" Visible="false" />
+    <None Include="..\CommunityToolkit.Mvvm.SourceGenerators\bin\$(Configuration)\roslyn4.3\netstandard2.0\CommunityToolkit.Mvvm.SourceGenerators.dll" PackagePath="analyzers\dotnet\roslyn4.3\cs" Pack="true" Visible="false" />
   </ItemGroup>
 
 </Project>
\ No newline at end of file

From b661cb7f91a19806875a2801a7c72355748be0ed Mon Sep 17 00:00:00 2001
From: Sergio Pedri <sergio0694@live.com>
Date: Thu, 8 Sep 2022 02:28:24 +0200
Subject: [PATCH 2/4] Enable multi-targeting Roslyn for unit test projects

---
 .../CommunityToolkit.Mvvm.SourceGenerators.csproj   |  2 +-
 .../CommunityToolkit.Mvvm.ExternalAssembly.csproj   |  8 +++++++-
 ...tyToolkit.Mvvm.SourceGenerators.UnitTests.csproj | 10 ++++++++--
 .../CommunityToolkit.Mvvm.UnitTests.csproj          | 13 +++++++++++--
 4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj b/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
index 4ae1f4112..03db2e91e 100644
--- a/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
+++ b/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
@@ -19,7 +19,7 @@
     <MvvmToolkitSourceGeneratorRoslynVersion Condition="'$(MvvmToolkitSourceGeneratorRoslynVersion)' == ''">4.0.1</MvvmToolkitSourceGeneratorRoslynVersion>
     
     <!-- The output path will end up being eg. "bin\Debug\roslyn4.0\netstandard2.0" (the trailing "netstandard2.0" is added automatically) -->
-    <OutputPath>bin\$(Configuration)\roslyn$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3))</OutputPath>
+    <OutputPath>bin\$(Configuration)\roslyn$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3))\</OutputPath>
     
     <!-- Also define a "ROSLYN_<MAJOR>_<MINOR>" build constant, so the generator code can multi-target whenever needed and add any required polyfills -->
     <DefineConstants>$(DefineConstants);ROSLYN_$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3).Replace('.', '_'))</DefineConstants>
diff --git a/tests/CommunityToolkit.Mvvm.ExternalAssembly/CommunityToolkit.Mvvm.ExternalAssembly.csproj b/tests/CommunityToolkit.Mvvm.ExternalAssembly/CommunityToolkit.Mvvm.ExternalAssembly.csproj
index d0d39011b..d2a95ec41 100644
--- a/tests/CommunityToolkit.Mvvm.ExternalAssembly/CommunityToolkit.Mvvm.ExternalAssembly.csproj
+++ b/tests/CommunityToolkit.Mvvm.ExternalAssembly/CommunityToolkit.Mvvm.ExternalAssembly.csproj
@@ -12,9 +12,15 @@
     <NoWarn>$(NoWarn);CS8002;SA0001</NoWarn>
   </PropertyGroup>
 
+  <!-- See comments in CommunityToolkit.MvvmUnitTests -->
+  <PropertyGroup>
+    <MvvmToolkitSourceGeneratorRoslynVersion Condition="'$(MvvmToolkitSourceGeneratorRoslynVersion)' == ''">4.3.0</MvvmToolkitSourceGeneratorRoslynVersion>
+  </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\CommunityToolkit.Mvvm\CommunityToolkit.Mvvm.csproj" />
-    <ProjectReference Include="..\..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build" />
+    <ProjectReference Include="..\..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build">
+      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=$(MvvmToolkitSourceGeneratorRoslynVersion)</Properties>
+    </ProjectReference>
   </ItemGroup>
 
 </Project>
\ No newline at end of file
diff --git a/tests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests.csproj b/tests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests.csproj
index c0e0b2a21..eba05a8ab 100644
--- a/tests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests.csproj
+++ b/tests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFrameworks>net472;netcoreapp3.1;net6.0</TargetFrameworks>
@@ -11,9 +11,15 @@
     <PackageReference Include="MSTest.TestFramework" Version="2.2.8" />
   </ItemGroup>
 
+  <!-- See comments in CommunityToolkit.MvvmUnitTests -->
+  <PropertyGroup>
+    <MvvmToolkitSourceGeneratorRoslynVersion Condition="'$(MvvmToolkitSourceGeneratorRoslynVersion)' == ''">4.3.0</MvvmToolkitSourceGeneratorRoslynVersion>
+  </PropertyGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" />
     <ProjectReference Include="..\..\CommunityToolkit.Mvvm\CommunityToolkit.Mvvm.csproj" />
+    <ProjectReference Include="..\..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj">
+      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=$(MvvmToolkitSourceGeneratorRoslynVersion)</Properties>
+    </ProjectReference>
   </ItemGroup>
 
 </Project>
\ No newline at end of file
diff --git a/tests/CommunityToolkit.Mvvm.UnitTests/CommunityToolkit.Mvvm.UnitTests.csproj b/tests/CommunityToolkit.Mvvm.UnitTests/CommunityToolkit.Mvvm.UnitTests.csproj
index fff3b5625..d033b5323 100644
--- a/tests/CommunityToolkit.Mvvm.UnitTests/CommunityToolkit.Mvvm.UnitTests.csproj
+++ b/tests/CommunityToolkit.Mvvm.UnitTests/CommunityToolkit.Mvvm.UnitTests.csproj
@@ -12,9 +12,18 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\..\CommunityToolkit.Mvvm\CommunityToolkit.Mvvm.csproj" />
-    <ProjectReference Include="..\..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build" />
     <ProjectReference Include="..\CommunityToolkit.Mvvm.ExternalAssembly\CommunityToolkit.Mvvm.ExternalAssembly.csproj" />
   </ItemGroup>
 
+  <!-- Since the MVVM Toolkit generator uses multi-targeting for Roslyn versions, we also want to test all of them here -->
+  <PropertyGroup>
+    <MvvmToolkitSourceGeneratorRoslynVersion Condition="'$(MvvmToolkitSourceGeneratorRoslynVersion)' == ''">4.3.0</MvvmToolkitSourceGeneratorRoslynVersion>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\CommunityToolkit.Mvvm\CommunityToolkit.Mvvm.csproj" />
+    <ProjectReference Include="..\..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build">
+      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=$(MvvmToolkitSourceGeneratorRoslynVersion)</Properties>
+    </ProjectReference>
+  </ItemGroup>
+
 </Project>
\ No newline at end of file

From 514710b1119c4c8a55e20be0770363aae8eb3225 Mon Sep 17 00:00:00 2001
From: Sergio Pedri <sergio0694@live.com>
Date: Thu, 8 Sep 2022 02:28:35 +0200
Subject: [PATCH 3/4] Run multi-targeted Roslyn projects in CI

---
 azure-pipelines.yml | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 3287eb2df..3259edb40 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -46,6 +46,14 @@ jobs:
   - script: dotnet test -c Release -f net6.0 -l "trx;LogFileName=VSTestResults_net6.0.trx"
     displayName: Run .NET 6 unit tests
 
+  # Run the .NET 6 MVVM Toolkit tests targeting Roslyn 4.0.1
+  - script: dotnet test tests\CommunityToolkit.Mvvm.UnitTests\CommunityToolkit.Mvvm.UnitTests.csproj -c Release -f net6.0 -l "trx;LogFileName=VSTestResults_net6.0_mvvmtoolkit_roslyn401.trx"
+    displayName: Run CommunityToolkit.Mvvm.UnitTests unit tests with Roslyn 4.0.1
+
+  # Run the .NET 6 MVVM Toolkit source generator tests targeting Roslyn 4.0.1
+  - script: dotnet test tests\CommunityToolkit.Mvvm.SourceGenerators.UnitTests\CommunityToolkit.Mvvm.SourceGenerators.UnitTests.csproj -c Release -f net6.0 -l "trx;LogFileName=VSTestResults_net6.0_mvvmtoolkit_generators_roslyn401.trx"
+    displayName: Run CommunityToolkit.Mvvm.UnitTests unit tests with Roslyn 4.0.1
+
   # Run .NET Core 3.1 tests
   - script: dotnet test -c Release -f netcoreapp3.1 -l "trx;LogFileName=VSTestResults_netcoreapp3.1.trx"
     displayName: Run .NET Core 3.1 unit tests

From f577ec03478e7884debb9b1e581b6eba230c1d9f Mon Sep 17 00:00:00 2001
From: Sergio Pedri <sergio0694@live.com>
Date: Thu, 8 Sep 2022 19:28:20 +0200
Subject: [PATCH 4/4] Only set OutputPath in generators during packing

---
 .../CommunityToolkit.Mvvm.SourceGenerators.csproj          | 7 +++++--
 CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj         | 4 ++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj b/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
index 03db2e91e..18e81311f 100644
--- a/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
+++ b/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.csproj
@@ -18,8 +18,11 @@
     <!-- When the property is not set (which will not happen when creating a NuGet package anyway), just default to 4.0.1 -->
     <MvvmToolkitSourceGeneratorRoslynVersion Condition="'$(MvvmToolkitSourceGeneratorRoslynVersion)' == ''">4.0.1</MvvmToolkitSourceGeneratorRoslynVersion>
     
-    <!-- The output path will end up being eg. "bin\Debug\roslyn4.0\netstandard2.0" (the trailing "netstandard2.0" is added automatically) -->
-    <OutputPath>bin\$(Configuration)\roslyn$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3))\</OutputPath>
+    <!--
+      The output path will end up being eg. "bin\Debug\roslyn4.0\netstandard2.0" (the trailing "netstandard2.0" is added automatically).
+      This is only set when $(MvvmToolkitIsGeneratingNuGetPackage) is set (when packing CommunityToolkit.Mvvm). This avoids unit test issues.
+    -->
+    <OutputPath Condition="'$(MvvmToolkitIsGeneratingNuGetPackage)' == 'true'">bin\$(Configuration)\roslyn$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3))\</OutputPath>
     
     <!-- Also define a "ROSLYN_<MAJOR>_<MINOR>" build constant, so the generator code can multi-target whenever needed and add any required polyfills -->
     <DefineConstants>$(DefineConstants);ROSLYN_$(MvvmToolkitSourceGeneratorRoslynVersion.Substring(0, 3).Replace('.', '_'))</DefineConstants>
diff --git a/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj b/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj
index e7fd2e6b9..2160f590d 100644
--- a/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj
+++ b/CommunityToolkit.Mvvm/CommunityToolkit.Mvvm.csproj
@@ -43,10 +43,10 @@
   <!-- Reference the various multi-targeted versions of the source generator project (one per Roslyn version) -->
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" ReferenceOutputAssembly="false">
-      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=4.0.1</Properties>
+      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=4.0.1;MvvmToolkitIsGeneratingNuGetPackage=true</Properties>
     </ProjectReference>
     <ProjectReference Include="..\CommunityToolkit.Mvvm.SourceGenerators\CommunityToolkit.Mvvm.SourceGenerators.csproj" ReferenceOutputAssembly="false">
-      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=4.3.0</Properties>
+      <Properties>MvvmToolkitSourceGeneratorRoslynVersion=4.3.0;MvvmToolkitIsGeneratingNuGetPackage=true</Properties>
     </ProjectReference>
   </ItemGroup>