sfx+oob split, shim project refactoring, P2Ps

Split the build of shared framework and out-of-band projects so that
it's possible to just build the shard framework projects, which was
requested by the CLR teams. In the next infrastructure rollout, the
current "libs.ref+libs.src" subsets should be removed. Generate the
targeting pack with an incomplete (without shims) frameworklist as part
of the "libs.sfx" subset.

Build the shim projects after the shared framework and oob projects and
re-generate the targeting pack's frameworklist to include the shims.

Refactor the shims so that they aren't grouped anymore by generated &
manual. Instead group them by "ref" and "src" same as other libraries
in the tree which allows to reference the source project shims and read
from the ReferenceAssembly metadata.

Use ProjectReferences in traversal projects and shim projects instead
of named references that point to binplace directories (see graph below)
This allows to build parts of the product dynamically, i.e. the shim
projects, apicompat.proj, sfx.proj and oob.proj.

14 files changed, 85 insertions, 59 deletions

diff --git a/eng/NoTargetsSdk.BeforeTargets.targets b/eng/NoTargetsSdk.BeforeTargets.targets
index 9afaad0e75e..3b516d31887 100644
--- a/eng/NoTargetsSdk.BeforeTargets.targets
+++ b/eng/NoTargetsSdk.BeforeTargets.targets
@@ -1,9 +1,8 @@
 <Project>
 
   <PropertyGroup>
-    <!-- NoTargets SDK needs a TFM set. Use the latest .NETCoreApp TFM that is supported by the SDK.
-         Only set a default if the project isn't multi-targeting. -->
-    <TargetFramework Condition="'$(TargetFramework)' == '' and '$(TargetFrameworks)' == ''">$(NetCoreAppToolCurrent)</TargetFramework>
+    <!-- NoTargets SDK needs a TFM set. Set a default if the project doesn't multi target. -->
+    <TargetFramework Condition="'$(TargetFramework)' == '' and '$(TargetFrameworks)' == ''">$(NetCoreAppCurrent)</TargetFramework>
   </PropertyGroup>
 
 </Project>
\ No newline at end of file
diff --git a/eng/Subsets.props b/eng/Subsets.props
index 809af20968e..1213b5407e9 100644
--- a/eng/Subsets.props
+++ b/eng/Subsets.props
@@ -71,7 +71,7 @@
     <DefaultLibrariesSubsets Condition="'$(BuildTargetFramework)' == '$(NetCoreAppCurrent)' or
                                         '$(BuildTargetFramework)' == '' or
                                         '$(BuildAllConfigurations)' == 'true'">libs.native+</DefaultLibrariesSubsets>
-    <DefaultLibrariesSubsets>$(DefaultLibrariesSubsets)libs.ref+libs.src</DefaultLibrariesSubsets>
+    <DefaultLibrariesSubsets>$(DefaultLibrariesSubsets)libs.sfx+libs.oob</DefaultLibrariesSubsets>
     <DefaultLibrariesSubsets Condition="'$(DotNetBuildFromSource)' != 'true'">$(DefaultLibrariesSubsets)+libs.pretest</DefaultLibrariesSubsets>
 
     <DefaultHostSubsets>host.native+host.tools</DefaultHostSubsets>
@@ -144,8 +144,10 @@
     <!-- Libs -->
     <SubsetName Include="Libs" Description="The libraries native part, refs and source assemblies, test infra and packages, but NOT the tests (use Libs.Tests to request those explicitly). Equivalent to: $(DefaultLibrariesSubsets)" />
     <SubsetName Include="Libs.Native" Description="The native libraries used in the shared framework." />
-    <SubsetName Include="Libs.Ref" Description="The managed reference libraries." />
-    <SubsetName Include="Libs.Src" Description="The managed implementation libraries." />
+    <SubsetName Include="Libs.Sfx" Description="The managed shared framework libraries." />
+    <SubsetName Include="Libs.Oob" Description="The managed out-of-band libraries." />
+    <SubsetName Include="Libs.Ref" OnDemand="true" Description="The managed reference libraries." />
+    <SubsetName Include="Libs.Src" OnDemand="true" Description="The managed implementation libraries." />
     <SubsetName Include="Libs.PreTest" Description="Test assets which are necessary to run tests." />
     <SubsetName Include="Libs.Packages" Description="The projects that produce NuGet packages from libraries." />
     <SubsetName Include="Libs.Tests" OnDemand="true" Description="The test projects. Note that building this doesn't execute tests: you must also pass the '-test' argument." />
@@ -322,12 +324,20 @@
     <ProjectToBuild Include="$(SharedNativeRoot)libs\build-native.proj" Category="libs" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(_subset.Contains('+libs.ref+'))">
-    <ProjectToBuild Include="$(LibrariesProjectRoot)ref.proj" Category="libs" />
+  <ItemGroup Condition="$(_subset.Contains('+libs.ref+')) or $(_subset.Contains('+libs.src+')) or $(_subset.Contains('+libs.sfx+'))">
+    <ProjectToBuild Include="$(LibrariesProjectRoot)sfx.proj"
+                    Category="libs"
+                    Condition="'$(BuildTargetFramework)' == '$(NetCoreAppCurrent)' or
+                               '$(BuildTargetFramework)' == '' or
+                               '$(BuildAllConfigurations)' == 'true'">
+      <AdditionalProperties Condition="$(_subset.Contains('+libs.ref+'))">%(AdditionalProperties);RefOnly=true</AdditionalProperties>
+    </ProjectToBuild>
   </ItemGroup>
 
-  <ItemGroup Condition="$(_subset.Contains('+libs.src+'))">
-    <ProjectToBuild Include="$(LibrariesProjectRoot)src.proj" Category="libs" />
+  <ItemGroup Condition="$(_subset.Contains('+libs.ref+')) or $(_subset.Contains('+libs.src+')) or $(_subset.Contains('+libs.oob+'))">
+    <ProjectToBuild Include="$(LibrariesProjectRoot)oob.proj" Category="libs">
+      <AdditionalProperties Condition="$(_subset.Contains('+libs.ref+'))">%(AdditionalProperties);RefOnly=true</AdditionalProperties>
+    </ProjectToBuild>
   </ItemGroup>
 
   <ItemGroup Condition="$(_subset.Contains('+mono.wasmruntime+'))">
diff --git a/eng/TraversalSdk.AfterProps.props b/eng/TraversalSdk.AfterProps.props
deleted file mode 100644
index 9f3f5fdea7a..00000000000
--- a/eng/TraversalSdk.AfterProps.props
+++ /dev/null
@@ -1,8 +0,0 @@
-<Project>
-
-  <PropertyGroup>
-    <!-- Build for NetCoreAppCurrent by default if no BuildTargetFramework is supplied or if not all configurations are built. -->
-    <TraversalGlobalProperties Condition="'$(BuildAllConfigurations)' != 'true'">BuildTargetFramework=$([MSBuild]::ValueOrDefault('$(BuildTargetFramework)', '$(NetCoreAppCurrent)'))</TraversalGlobalProperties>
-  </PropertyGroup>
-
-</Project>
diff --git a/eng/TraversalSdk.AfterTargets.targets b/eng/TraversalSdk.AfterTargets.targets
index f88c48dc867..4eac57bd138 100644
--- a/eng/TraversalSdk.AfterTargets.targets
+++ b/eng/TraversalSdk.AfterTargets.targets
@@ -9,10 +9,17 @@
     <VSTestDependsOn>$(VSTestDependsOn);ResolveP2PReferences</VSTestDependsOn>
     <PackDependsOn>$(PackDependsOn);ResolveP2PReferences</PackDependsOn>
     <PublishDependsOn>$(PublishDependsOn);ResolveP2PReferences</PublishDependsOn>
+    <GetTargetPathDependsOn>ResolveP2PReferences</GetTargetPathDependsOn>
+    <!-- Filter out ProjectReferences which aren't compatible with the project's TargetFramework. -->
+    <OmitIncompatibleProjectReferences>true</OmitIncompatibleProjectReferences>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(FilterTraversalProjectReferences)' == 'true'">
-    <ProjectReference Update="@(ProjectReference)" SkipGetTargetFrameworkProperties="false" />
+    <!-- Override the Traversal SDK setting as filtering relies on the TargetFrameworkProperties being fetched
+         and don't flow the BuildTargetFramework property down. -->
+    <ProjectReference Update="@(ProjectReference)"
+                      SkipGetTargetFrameworkProperties="false"
+                      UndefineProperties="%(UndefineProperties);BuildTargetFramework"  />
   </ItemGroup>
 
-</Project>
\ No newline at end of file
+</Project>
diff --git a/eng/generators.targets b/eng/generators.targets
index f13e56995af..e7835650b04 100644
--- a/eng/generators.targets
+++ b/eng/generators.targets
@@ -13,8 +13,7 @@
          - references System.Runtime.InteropServices -->
     <EnabledGenerators Include="DllImportGenerator"
                        Condition="'$(EnableDllImportGenerator)' == ''
-                        and '$(IsFrameworkSupportFacade)' != 'true'
-                        and '$(IsSourceProject)' == 'true'
+                        and '$(IsRuntimeAssembly)' == 'true'
                         and '$(MSBuildProjectExtension)' == '.csproj'
                         and (
                           ('@(Reference)' != ''
@@ -25,8 +24,7 @@
                             and '$(DisableImplicitAssemblyReferences)' == 'false'))" />
     <EnabledGenerators Include="DllImportGenerator"
                        Condition="'$(EnableDllImportGenerator)' == ''
-                        and '$(IsFrameworkSupportFacade)' != 'true'
-                        and '$(IsSourceProject)' == 'true'
+                        and '$(IsRuntimeAssembly)' == 'true'
                         and '$(MSBuildProjectExtension)' == '.csproj'
                         and ('$(TargetFrameworkIdentifier)' == '.NETStandard' or '$(TargetFrameworkIdentifier)' == '.NETFramework' or ('$(TargetFrameworkIdentifier)' == '.NETCoreApp' and $([MSBuild]::VersionLessThan($(TargetFrameworkVersion), '$(NetCoreAppCurrentVersion)'))))" />
   </ItemGroup>
diff --git a/eng/illink.targets b/eng/illink.targets
index eecd3163559..320d21715ef 100644
--- a/eng/illink.targets
+++ b/eng/illink.targets
@@ -198,14 +198,22 @@
     </ItemGroup>
   </Target>
 
-  <!-- ILLink.Tasks arguments common to runs for both individual libraries and for the entire runtime pack -->
-  <Target Name="SetCommonILLinkArgs">
+  <Target Name="PrepareForAssembliesTrim">
+    <!-- ILLink.Tasks arguments common to runs for both individual libraries and for the entire runtime pack -->
     <PropertyGroup>
       <!-- don't remove attributes after build, our tooling is not ready for that -->
       <ILLinkArgs>$(ILLinkArgs) --ignore-link-attributes true</ILLinkArgs>
       <!-- ignore unresolved references -->
       <ILLinkArgs>$(ILLinkArgs) --skip-unresolved true</ILLinkArgs>
     </PropertyGroup>
+
+    <!-- When running from Desktop MSBuild, DOTNET_HOST_PATH is not set.
+         In this case, explicitly specify the path to the dotnet host. -->
+    <PropertyGroup Condition="'$(DOTNET_HOST_PATH)' == ''">
+      <!-- This is defined when building in Visual Studio. -->
+      <_DotNetHostDirectory>$(NetCoreRoot)</_DotNetHostDirectory>
+      <_DotNetHostFileName>$([System.IO.Path]::GetFileName('$(DotNetTool)'))</_DotNetHostFileName>
+    </PropertyGroup>
   </Target>
 
   <!-- ILLinkTrimAssembly
@@ -215,7 +223,7 @@
   <UsingTask TaskName="ILLink" AssemblyFile="$(ILLinkTasksAssembly)" Condition="'$(ILLinkTasksAssembly)' != ''" />
   <Target Name="ILLinkTrimAssembly"
           Condition="'$(ILLinkTrimAssembly)' == 'true'"
-          DependsOnTargets="SetCommonILLinkArgs">
+          DependsOnTargets="PrepareForAssembliesTrim">
     <PropertyGroup>
       <!-- default action for assemblies with IsTrimmable attribute -->
       <ILLinkArgs>$(ILLinkArgs) --trim-mode skip</ILLinkArgs>
@@ -285,21 +293,12 @@
       <ILLinkArgs Condition="@(_DependencyDirectories->Count()) > 0">$(ILLinkArgs) -d @(_DependencyDirectories->'"%(Identity)"', ' -d ')</ILLinkArgs>
     </PropertyGroup>
 
-    <!-- When running from Desktop MSBuild, DOTNET_HOST_PATH is not set.
-         In this case, explicitly specify the path to the dotnet host. -->
-    <PropertyGroup Condition=" '$(DOTNET_HOST_PATH)' == '' ">
-      <!-- This is defined when building in Visual Studio. -->
-      <_DotNetHostDirectory>$(NetCoreRoot)</_DotNetHostDirectory>
-      <_DotNetHostFileName>$([System.IO.Path]::GetFileName('$(DotNetTool)'))</_DotNetHostFileName>
-    </PropertyGroup>
-
     <ILLink AssemblyPaths=""
             RootAssemblyNames="@(ILLinkTrimInputAssembly)"
             OutputDirectory="$(ILLinkTrimOutputPath)"
             ExtraArgs="$(ILLinkArgs)"
             ToolExe="$(_DotNetHostFileName)"
             ToolPath="$(_DotNetHostDirectory)" />
-
   </Target>
 
   <!-- ILLink reporting.
diff --git a/eng/pipelines/common/templates/runtimes/build-test-job.yml b/eng/pipelines/common/templates/runtimes/build-test-job.yml
index b05315fc785..0c933647923 100644
--- a/eng/pipelines/common/templates/runtimes/build-test-job.yml
+++ b/eng/pipelines/common/templates/runtimes/build-test-job.yml
@@ -74,7 +74,7 @@ jobs:
       - ${{ each variable in parameters.variables }}:
         - ${{ variable }}
       - name: liveRuntimeBuildParams
-        value: 'libs.ref -c Release -ci'
+        value: 'libs.sfx+libs.oob /p:RefOnly=true -c Release -ci'
       - name: compilerArg
         value: ''
       - ${{ if and(ne(parameters.osGroup, 'windows'), ne(parameters.compilerName, 'gcc')) }}:
diff --git a/eng/pipelines/runtime-official.yml b/eng/pipelines/runtime-official.yml
index 1d404057335..c817f759a30 100644
--- a/eng/pipelines/runtime-official.yml
+++ b/eng/pipelines/runtime-official.yml
@@ -57,7 +57,7 @@ stages:
   - ${{ if eq(variables['Build.SourceBranch'], 'refs/heads/main') }}:
     - template: /eng/common/templates/job/source-index-stage1.yml
       parameters:
-        sourceIndexBuildCommand: build.cmd -subset libs.ref+libs.src -binarylog -os Linux -ci
+        sourceIndexBuildCommand: build.cmd -subset libs.sfx+libs.oob -binarylog -os Linux -ci
 
   #
   # Build CoreCLR
diff --git a/eng/pipelines/runtime-richnav.yml b/eng/pipelines/runtime-richnav.yml
index df7918ee877..341ec115ebf 100644
--- a/eng/pipelines/runtime-richnav.yml
+++ b/eng/pipelines/runtime-richnav.yml
@@ -37,7 +37,7 @@ jobs:
       richCodeNavigationEnvironment: "production"
       richCodeNavigationLanguage: "csharp"
       timeoutInMinutes: 240
-      buildArgs: -s libs.ref+libs.src -c debug -allConfigurations
+      buildArgs: -s libs.sfx+libs.oob -allConfigurations
 
 - template: /eng/pipelines/common/platform-matrix.yml
   parameters:
diff --git a/eng/referenceAssemblies.props b/eng/referenceAssemblies.props
index f61d15a3926..8c986b4475a 100644
--- a/eng/referenceAssemblies.props
+++ b/eng/referenceAssemblies.props
@@ -1,14 +1,9 @@
 <Project>
-  <PropertyGroup Condition="'$(BuildAllProjects)' == 'true' and
-                            !$(BuildTargetFramework.StartsWith('netstandard')) and
-                            !$(BuildTargetFramework.StartsWith('net4'))">
-    <AdditionalBuildTargetFrameworks>$(AdditionalBuildTargetFrameworks);netstandard2.0;netstandard2.1</AdditionalBuildTargetFrameworks>
 
+  <PropertyGroup>
     <!-- Reference assemblies are special and don't initialize fields or have empty finalizers, etc. -->
     <RunAnalyzers>false</RunAnalyzers>
-  </PropertyGroup>
 
-  <PropertyGroup>
     <!-- disable warnings about unused fields -->
     <NoWarn>$(NoWarn);CS0169;CS0649;CS8618</NoWarn>
 
@@ -30,4 +25,5 @@
       <_Parameter1_IsLiteral>true</_Parameter1_IsLiteral>
     </AssemblyAttribute>
   </ItemGroup>
+
 </Project>
diff --git a/eng/references.targets b/eng/references.targets
index 4603fb98566..c73b8295397 100644
--- a/eng/references.targets
+++ b/eng/references.targets
@@ -16,19 +16,17 @@
 
   <ItemGroup Condition="'@(ProjectReference)' != ''">
     <_coreLibProjectReference Include="@(ProjectReference->WithMetadataValue('Identity', '$(CoreLibProject)'))" />
-    <ProjectReference Update="@(_coreLibProjectReference)">
-      <!-- Don't flow TargetFramework and Platform to use same inputs and outputs as the CoreLib's build as part of the runtime. -->
-      <UndefineProperties>$(UndefineProperties);TargetFramework;Platform</UndefineProperties>
+    <ProjectReference Update="@(_coreLibProjectReference)"
+                      Private="false">
       <SetConfiguration Condition="'$(RuntimeFlavor)' == 'CoreCLR' and
                                    '$(Configuration)' != '$(CoreCLRConfiguration)'">Configuration=$(CoreCLRConfiguration)</SetConfiguration>
       <SetConfiguration Condition="'$(RuntimeFlavor)' == 'Mono' and
                                    '$(Configuration)' != '$(MonoConfiguration)'">Configuration=$(MonoConfiguration)</SetConfiguration>
-      <Private>false</Private>
     </ProjectReference>
     <!-- If a CoreLib ProjectReference is present, make all P2P assets non transitive. -->
-    <ProjectReference Update="@(ProjectReference)"
+    <ProjectReference Update="@(ProjectReference->WithMetadataValue('PrivateAssets', ''))"
                       PrivateAssets="all"
-                      Condition="'@(_coreLibProjectReference)' != ''" />
+                      Condition="'$(IsSourceProject)' == 'true' and '@(_coreLibProjectReference)' != ''" />
   </ItemGroup>
 
   <!-- Disable TargetArchitectureMismatch warning when we reference CoreLib as it is platform specific. -->
@@ -78,8 +76,19 @@
 
   <Target Name="ValidateReferenceAssemblyProjectReferences"
           AfterTargets="ResolveReferences"
-          Condition="'$(IsReferenceAssembly)' == 'true'">
+          Condition="'$(IsReferenceAssembly)' == 'true' and
+                     '$(SkipValidateReferenceAssemblyProjectReferences)' != 'true'">
     <Error Condition="'%(ReferencePath.ReferenceSourceTarget)' == 'ProjectReference' and '%(ReferencePath.IsReferenceAssembly)' != 'true' and '%(ReferencePath.ReferenceAssembly)' == ''"
            Text="Reference assemblies must only reference other reference assemblies and '%(ReferencePath.ProjectReferenceOriginalItemSpec)' is not a reference assembly project and does not set 'ProduceReferenceAssembly'." />
   </Target>
+
+  <!-- An opt-in target to trim out private assemblies from the ref assembly ReferencePath. -->
+  <Target Name="TrimOutPrivateAssembliesFromReferencePath"
+          Condition="'$(CompileUsingReferenceAssemblies)' == 'true' and '$(TrimOutPrivateAssembliesFromReferencePath)' == 'true'"
+          AfterTargets="FindReferenceAssembliesForReferences">
+    <ItemGroup>
+      <ReferencePathWithRefAssemblies Remove="@(ReferencePathWithRefAssemblies)"
+                                      Condition="$(NetCoreAppLibraryNoReference.Contains('%(Filename);'))" />
+    </ItemGroup>
+  </Target>
 </Project>
diff --git a/eng/resolveContract.targets b/eng/resolveContract.targets
index 327273a100e..0e0cfc05c56 100644
--- a/eng/resolveContract.targets
+++ b/eng/resolveContract.targets
@@ -28,7 +28,10 @@
           DependsOnTargets="ResolveProjectReferences"
           AfterTargets="GetTargetPathWithTargetPlatformMoniker">
     <ItemGroup>
-      <TargetPathWithTargetPlatformMoniker ReferenceAssembly="@(ResolvedMatchingContract)" />
+      <!-- Allow to point to a different reference project than what GenFacades uses to generate the type forwards. -->
+      <TargetPathWithTargetPlatformMoniker ReferenceAssembly="@(ResolvedMatchingContractOverride)" />
+      <TargetPathWithTargetPlatformMoniker ReferenceAssembly="@(ResolvedMatchingContract)"
+                                           Condition="'@(ResolvedMatchingContractOverride)' == ''" />
     </ItemGroup>
   </Target>
 
@@ -38,7 +41,7 @@
           Condition="'@(ProjectReference)' != '' and '@(_ResolvedProjectReferencePaths)' != ''">
     <!-- If we have a ProjectReference to CoreLib, we need to compile against implementation assemblies. -->
     <PropertyGroup Condition="@(_ResolvedProjectReferencePaths->AnyHaveMetadataValue('MSBuildSourceProjectFile', '$(CoreLibProject)'))">
-      <CompileUsingReferenceAssemblies>false</CompileUsingReferenceAssemblies>
+      <CompileUsingReferenceAssemblies Condition="'$(CompileUsingReferenceAssemblies)' == ''">false</CompileUsingReferenceAssemblies>
     </PropertyGroup>
     <!-- Clear the ReferenceAssembly attribute on resolved P2Ps that set SkipUseReferenceAssembly to true. -->
     <ItemGroup>
diff --git a/eng/targetingpacks.targets b/eng/targetingpacks.targets
index 33551569c64..63aa48746ab 100644
--- a/eng/targetingpacks.targets
+++ b/eng/targetingpacks.targets
@@ -146,6 +146,13 @@
       <_targetingPackReferenceExclusion Include="@(DefaultReferenceExclusion)" />
     </ItemGroup>
 
+    <!-- Filter out shims from the targeting pack references as an opt-in. -->
+    <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
+                          '$(SkipTargetingPackShimReferences)' == 'true'">
+      <_targetingPackReferenceExclusion Include="@(NetFxReference)" />
+      <_targetingPackReferenceExclusion Include="netstandard" />
+    </ItemGroup>
+
     <ItemGroup>
       <_targetingPackReferenceWithProjectName Include="@(Reference->WithMetadataValue('ExternallyResolved', 'true')->Metadata('Filename'))"
                                               OriginalIdentity="%(Identity)" />
diff --git a/eng/versioning.targets b/eng/versioning.targets
index 3a40200c173..f31612f41a4 100644
--- a/eng/versioning.targets
+++ b/eng/versioning.targets
@@ -107,7 +107,10 @@
   <Target Name="AddOSPlatformAttributes"
           BeforeTargets="GenerateAssemblyInfo"
           AfterTargets="PrepareForBuild"
-          Condition="'$(TargetPlatformIdentifier)' == '' and '$(IsTestProject)' != 'true' and '$(TargetFrameworkIdentifier)' != '.NETFramework'">
+          Condition="'$(TargetPlatformIdentifier)' == '' and
+                     '$(IsTestProject)' != 'true' and
+                     '$(TargetFrameworkIdentifier)' != '.NETFramework'
+                     and '$(AddOSPlatformAttributes)' != 'false'">
     <!-- Defensively de-dupe the values -->
     <ItemGroup>
       <_unsupportedOSPlatforms Include="$(UnsupportedOSPlatforms)" />
@@ -133,12 +136,15 @@
     </ItemGroup>
   </Target>
 
-  <!-- Removes assembly level attributes from test projects. -->
-  <Target Name="RemoveSupportedOSPlatformAttributeFromTestProjects"
+  <!-- Remove assembly level attributes from certain projects.
+       Use a target for that until https://github.com/dotnet/sdk/issues/14836 is implemented. -->
+  <Target Name="RemoveSupportedOSTargetPlatformAttributeFromProjects"
           AfterTargets="GetAssemblyAttributes"
-          Condition="'$(IsTestProject)' == 'true'">
+          BeforeTargets="CreateGeneratedAssemblyInfoInputsCacheFile">
     <ItemGroup>
-      <AssemblyAttribute Remove="System.Runtime.Versioning.SupportedOSPlatformAttribute" />
+      <AssemblyAttribute Remove="System.Runtime.Versioning.SupportedOSPlatformAttribute"
+                         Condition="'$(IsTestProject)' == 'true' or '$(AddOSPlatformAttributes)' == 'false'" />
+      <!-- Don't include target platform attributes, since we use the target platform to represent RIDs instead. -->
       <AssemblyAttribute Remove="System.Runtime.Versioning.TargetPlatformAttribute" />
     </ItemGroup>
   </Target>