Allow using VS to run host tests when libraries use different config

Directory.Build.props

@@ -11,6 +11,9 @@
          all cases, rather than ordinarily where we build them during mobile or wasm
          build legs. This makes the manifests available on source-only builds. -->
     <ForceBuildMobileManifests Condition="'$(DotNetBuildSourceOnly)' == 'true'">true</ForceBuildMobileManifests>
+    <!-- Propagate the configuration and platform to project references. When building in VS, this defaults to true.
+         Explicitly setting it to false ensures projects are built in the corresponding configuration both in VS and on the command line. -->
+    <ShouldUnsetParentConfigurationAndPlatform>false</ShouldUnsetParentConfigurationAndPlatform>
   </PropertyGroup>
 
   <PropertyGroup Label="CalculateTargetOS">

docs/workflow/testing/host/testing.md

@@ -77,6 +77,11 @@ The `category!=failing` is to respect the [filtering traits](../libraries/filter
 ### Visual Studio
 
 The [Microsoft.DotNet.CoreSetup.sln](/src/installer/Microsoft.DotNet.CoreSetup.sln) can be used to run and debug host tests through Visual Studio. When using the solution, the product should have already been [built](#building-tests) and the [test context](#test-context) set up.
+If you built the runtime or libraries with a different configuration from the host, you have to specify this when starting visual studio:
+
+```console
+build.cmd -vs Microsoft.DotNet.CoreSetup -rc Release -lc Release
+```
 
 ### Preserving test artifacts
 

eng/build.ps1

@@ -261,6 +261,12 @@ if ($vs) {
     $env:RUNTIMECONFIGURATION=$runtimeConfiguration
   }
 
+  if ($librariesConfiguration)
+  {
+    # Respect the LibrariesConfiguration variable for building inside VS with different libraries configurations
+    $env:LIBRARIESCONFIGURATION=$librariesConfiguration
+  }
+
   # Respect the RuntimeFlavor variable for building inside VS with a different CoreLib and runtime
   if ($runtimeFlavor)
   {

src/libraries/Directory.Build.props

@@ -16,7 +16,6 @@
 
   <PropertyGroup>
     <BeforeTargetFrameworkInferenceTargets>$(RepositoryEngineeringDir)BeforeTargetFrameworkInference.targets</BeforeTargetFrameworkInferenceTargets>
-    <ShouldUnsetParentConfigurationAndPlatform>false</ShouldUnsetParentConfigurationAndPlatform>
     <GeneratePlatformNotSupportedAssemblyHeaderFile>$(RepositoryEngineeringDir)LicenseHeader.txt</GeneratePlatformNotSupportedAssemblyHeaderFile>
   </PropertyGroup>