Common.targets support for reference assemblies

Provides an item, `ReferencePathWithInterfaceOnlyAssemblies`, that
consists of the reference (interface-only) versions of assemblies where
available, allowing a consuming task to be incrementally up-to-date
after implementation-only changes have been made to a reference.

When `%(ReferenceAssembly)` metadata is unavailable for a given
reference, the new item contains the implementation assembly directly.

Additionally creates a new output item for the current project's
reference assembly by default when `$(Deterministic)` is `true`. If this
is created, it is copied to the output directory using the new
`CopyRefAssembly` task, which copies only if the ref assembly is
different from the current file. If present, the ref asm is passed to
the project's consumes in metadata.

See #1986, dotnet/roslyn#2184.

src/Tasks/Microsoft.Common.CurrentVersion.targets

@@ -281,6 +281,8 @@ Copyright (C) Microsoft Corporation. All rights reserved.
     <!-- Example, c:\MyProjects\MyProject\bin\debug\MyAssembly.dll -->
     <TargetPath Condition=" '$(TargetPath)' == '' ">$(TargetDir)$(TargetFileName)</TargetPath>
 
+    <TargetRefPath Condition=" '$(TargetRefPath)' == '' and '$(Deterministic)' == 'true' ">$([System.IO.Path]::Combine(`$([System.IO.Path]::GetDirectoryName($([System.IO.Path]::GetFullPath(`$(TargetPath)`))))`, 'ref', `$(TargetFileName)`))</TargetRefPath>
+
     <!-- Example, c:\MyProjects\MyProject\ -->
     <ProjectDir Condition=" '$(ProjectDir)' == '' ">$(MSBuildProjectDirectory)\</ProjectDir>
 
@@ -350,6 +352,13 @@ Copyright (C) Microsoft Corporation. All rights reserved.
     <FinalDocFile Include="@(DocFileItem->'$(OutDir)%(Filename)%(Extension)')"/>
   </ItemGroup>
 
+  <ItemGroup Condition="'$(Deterministic)' == 'true'">
+    <!-- TODO: should this be configurable? Default path obeys conventions. -->
+    <IntermediateRefAssembly Include="$(IntermediateOutputPath)ref\$(TargetName)$(TargetExt)" Condition="'@(IntermediateRefAssembly)' == ''" />
+    <CreateDirectory Include="@(IntermediateRefAssembly->'%(RootDir)%(Directory)')" />
+    <CreateDirectory Include="$(OutDir)ref" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(_DebugSymbolsProduced)' == 'true'">
     <_DebugSymbolsIntermediatePath Include="$(IntermediateOutputPath)$(TargetName).compile.pdb" Condition="'$(OutputType)' == 'winmdobj' and '@(_DebugSymbolsIntermediatePath)' == ''"/>
     <_DebugSymbolsIntermediatePath Include="$(IntermediateOutputPath)$(TargetName).pdb" Condition="'$(OutputType)' != 'winmdobj' and '@(_DebugSymbolsIntermediatePath)' == ''"/>
@@ -771,7 +780,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
       Name="Build"
       Condition=" '$(_InvalidConfigurationWarning)' != 'true' "
       DependsOnTargets="$(BuildDependsOn)"
-      Returns="$(TargetPath)" />
+      Returns="@(TargetPathWithTargetPlatformMoniker)" />
 
   <!--
     ============================================================
@@ -1797,6 +1806,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
       <TargetPathWithTargetPlatformMoniker Include="$(TargetPath)">
         <TargetPlatformMoniker>$(TargetPlatformMoniker)</TargetPlatformMoniker>
         <TargetPlatformIdentifier>$(TargetPlatformIdentifier)</TargetPlatformIdentifier>
+        <ReferenceAssembly Condition="'$(TargetRefPath)' != ''">$(TargetRefPath)</ReferenceAssembly>
       </TargetPathWithTargetPlatformMoniker>
     </ItemGroup>
   </Target>
@@ -2015,8 +2025,18 @@ Copyright (C) Microsoft Corporation. All rights reserved.
       <Output TaskParameter="FilesWritten" ItemName="FileWrites"/>
       <Output TaskParameter="DependsOnSystemRuntime" PropertyName="DependsOnSystemRuntime"/>
     </ResolveAssemblyReference>
+
+    <ItemGroup>
+      <ReferencePathWithInterfaceOnlyAssemblies Include="@(ReferencePath->'%(ReferenceAssembly)')" />
+    </ItemGroup>
   </Target>
 
+  <ItemDefinitionGroup>
+    <ReferencePath>
+      <ReferenceAssembly>%(FullPath)</ReferenceAssembly>
+    </ReferencePath>
+  </ItemDefinitionGroup>
+
   <!--
     ====================================================================================================
 
@@ -4007,6 +4027,17 @@ Copyright (C) Microsoft Corporation. All rights reserved.
 
     </Copy>
 
+    <!-- Copy the build product (.dll or .exe). -->
+    <CopyRefAssembly
+        SourcePath="@(IntermediateRefAssembly)"
+        DestinationPath="$(TargetRefPath)"
+        Condition="'$(CopyBuildOutputToOutputDirectory)' == 'true' and '$(SkipCopyBuildProduct)' != 'true' and Exists('@(IntermediateRefAssembly)')"
+            >
+
+      <Output TaskParameter="DestinationPath" ItemName="ReferenceAssembly"/>
+
+    </CopyRefAssembly>
+
     <Message Importance="High" Text="$(MSBuildProjectName) -&gt; @(MainAssembly->'%(FullPath)')" Condition="'$(CopyBuildOutputToOutputDirectory)' == 'true' and '$(SkipCopyBuildProduct)'!='true'" />
 
     <!-- Copy the additional modules. -->

src/Tasks/Microsoft.Common.tasks

@@ -172,5 +172,6 @@
     <!-- Roslyn tasks are now in an assembly owned and shipped by Roslyn -->
     <UsingTask TaskName="Microsoft.CodeAnalysis.BuildTasks.Csc"                       AssemblyFile="$(RoslynTargetsPath)\Microsoft.Build.Tasks.CodeAnalysis.dll" Condition="'$(MSBuildAssemblyVersion)' != ''" />
     <UsingTask TaskName="Microsoft.CodeAnalysis.BuildTasks.Vbc"                       AssemblyFile="$(RoslynTargetsPath)\Microsoft.Build.Tasks.CodeAnalysis.dll" Condition="'$(MSBuildAssemblyVersion)' != ''" />
+    <UsingTask TaskName="Microsoft.CodeAnalysis.BuildTasks.CopyRefAssembly"           AssemblyFile="$(RoslynTargetsPath)\Microsoft.Build.Tasks.CodeAnalysis.dll" Condition="'$(MSBuildAssemblyVersion)' != ''" />
 </Project>