Allow to skip all project targets based on a property value

[tmat]

Enable project to set a property during evaluation phase that suppresses all targets, including Restore, Build, Pack, etc.

Use cases:

• when building the .NET Core stack from source we need to skip restoring and building projects and/or specific project target framework for multi-targeting projects that depend on non-OSS libraries.
• when building on non-Windows machine (or machine that doesn't have Visual Studio installed) some projects might need to be skipped since they require Windows or Visual Studio.

Existing workarounds:

• https://github.com/Microsoft/msbuild/blob/master/build/ProducesNoOutput.Imports.props
• https://github.com/dotnet/roslyn-tools/blob/master/sdks/RepoToolset/tools/Empty.targets

[tmat]

@nguerrera @dsplaisted

[rainersigwald]

One option is to filter projects from the solution metaproject: dotnet/msbuild#1730 (comment).

[ericstj]

Agreed we need this sort of feature.

The bit of boilerplate I've used is the following. Properties set might differ depending on what you want it to do. Make sure the name of this is .proj or something that isn't a standard project extension like csproj, vbproj, or fsproj since those all trigger conventions in msbuild. If you want it to have a legitimate

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <!-- don't reference the framework -->
    <DisableImplicitFrameworkReferences>true</DisableImplicitFrameworkReferences>
    <!-- don't copy any build assets -->
    <SkipCopyBuildProduct>true</SkipCopyBuildProduct>    
    <CopyBuildOutputToPublishDirectory>false</CopyBuildOutputToPublishDirectory>
    <!-- don't generate a deps file -->
    <GenerateDependencyFile>false</GenerateDependencyFile>
    <!-- set TargetPath to a bogus value so it doesn't look like we're producing anything -->
    <TargetPath>NOTHING</TargetPath>
  </PropertyGroup>

  <!-- required by common targets, define them but have them do nothing -->
  <Target Name="CreateManifestResourceNames" />
  <Target Name="CoreCompile" />

  <!-- Import design time targets for Roslyn Project System. These are only available if Visual Studio is installed. -->
  <!-- Required for project to load in Visual Studio. -->
  <PropertyGroup>
    <ManagedDesignTimeTargetsPath Condition="'$(ManagedDesignTimeTargetsPath)'==''">$(MSBuildExtensionsPath)\Microsoft\VisualStudio\Managed\Microsoft.Managed.DesignTime.targets</ManagedDesignTimeTargetsPath>
  </PropertyGroup>
  <Import Project="$(ManagedDesignTimeTargetsPath)" Condition="'$(ManagedDesignTimeTargetsPath)' != '' and Exists('$(ManagedDesignTimeTargetsPath)')" />
</Project>