Add props file to buildMultiTargeting in Microsoft.NET.Test.Sdk nuspec

[natemcmaster]

By adding this property file to buildMultiTargeting, NuGet will import this as a top-level file in test projects with multiple target frameworks. Currently, the properties in from Microsoft.NET.Test.Sdk are only available during the inner build.

Example of the effect:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>netcoreapp1.1;net46</TargetFrameworks>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
  </ItemGroup>
  <Target Name="Peek">
    <Message Text="IsTestProject = $(IsTestProject)" Importance="high" />
  </Target>
</Project>

Before
Executing dotnet msbuild /t:Peek shows:

Microsoft (R) Build Engine version 15.1.548.43366
Copyright (C) Microsoft Corporation. All rights reserved.

  IsTestProject = 

After

Microsoft (R) Build Engine version 15.1.548.43366
Copyright (C) Microsoft Corporation. All rights reserved.

  IsTestProject = true

[msftclas]

@natemcmaster,
Thanks for your contribution as a Microsoft full-time employee or intern. You do not need to sign a CLA.
Thanks,
Microsoft Pull Request Bot

[natemcmaster]

👍 I don't have push rights, so someone will have to merge this for me.

[singhsarab]

Do we need to include the targets file as well ?

[natemcmaster]

You shouldn't need to. NuGet will still import and execute the targets file on the "inner" build. It looks like the current targets file only generates a "Program.cs" file, and which depends on TargetFrameworkIdentifier being set. It probably will work incorrectly when running in the "outer" build.

Btw, if you're not familiar with inner vs outer, here is conceptually what MSBuild is doing in multi-targeting projects:

<!-- this executes when `msbuild.exe /t:Build` runs on the project -->
<Target Name="Build" Condition="'$(TargetFrameworks)' != '' AND '$(TargetFramework)' == ''">
    <!-- import buildMultiTargeting/Microsoft.NET.Test.Sdk.props  -->
    <ItemGroup>
      <_TargetFramework Include="$(TargetFrameworks)" />
    </ItemGroup>
    <!-- starts a new "build" of the project, once per target framework -->
    <MSBuild Projects="$(MSBuildProjectFile)"
             Targets="InnerBuild"
             Properties="TargetFramework=%(_TargetFramework.Identity)" />
</Target>

<Target Name="InnerBuild" Condition="'$(TargetFramework)' != ''">
   <!-- import build/$(TargetFramework)/Microsoft.NET.Test.Sdk.{props, targets} -->
   <!-- gather *.cs files, run compiler, etc. -->
</Target>