Need way to detect Common targets

[clairernovotny]

We have a need to detect if the specified LanguageTargets file was successfully imported (because it existed).

We had been doing something like this:

  <PropertyGroup>
    <MSBuildAllProjects Condition=" '$(MSBuildVersion)' == '' Or '$(MSBuildVersion)' &lt; '16.0' ">$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
  </PropertyGroup>

  <!-- Need to detect if the expected targets where actually imported and reset to common if not -->
  <PropertyGroup>
    <_SdkLanguageTargetsMissing Condition="$(MSBuildAllProjects.Contains('Microsoft.Common.targets')) ">false</_SdkLanguageTargetsMissing>
    <_SdkLanguageTargetsMissing Condition="'$(_SdkLanguageTargetsMissing)' == ''">true</_SdkLanguageTargetsMissing>
  </PropertyGroup>

However, that no longer works since MSBuildAllProjects isn’t set anymore. We was simply looking to see if Common targets was in the list. I can’t do a simple Exists() check earlier on because of the fallback location on Mono/MacOS. That special exists check only works in an Import block, so we can’t do a regular conditional on it to set the variable. Either the import succeeds or its skipped.