Set CompilerApiVersion in Microsoft.Managed.Core.targets

[eerhardt]

This allows other targets to understand which compiler will be used.
This is useful in the SDK targets that need figure out the version in order to pick the right analyzer assets.

Contributes to #52265

FYI - @dsplaisted. This resolves the feedback from dotnet/sdk#20793 (comment)

[eerhardt]

NOTE: an alternative, simpler approach could be to straight up hard-code roslyn4.0 directly into Microsoft.Managed.Core.targets. And then rely on the test that I added to break whenever we bump the Major/MinorVersion properties in the repo - reminding the person who did the bumping to update the hard-coded version.

I'm open to either approach. I'll let the owners decide which is more preferable (or suggest another alternative).

[chsienki]

That's the exact approach I was concerned about, so I'm definitely in favor of doing it this way.

[jaredpar]

Sorry, I realize I should have brought this up sooner but shoudn't we prefix this property name with Roslyn? Basically RoslynCompilerApiVersion vs. CompilerApiVersion? Reasonable for other compilers to provide similar properties.

[eerhardt]

Reasonable for other compilers to provide similar properties.

The reason I didn't put Roslyn in property name is exactly for that reason - to support other compilers. The CompilerApiVersion version gets piped into the ResolvePackageAssets task in the dotnet/sdk:

https://github.com/dotnet/sdk/blob/500e1f61104f94753d7d84c3941d93fec2814291/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.PackageDependencyResolution.targets#L267-L272

    <ResolvePackageAssets
      ProjectAssetsFile="$(ProjectAssetsFile)"
      ProjectAssetsCacheFile="$(ProjectAssetsCacheFile)"
      ProjectPath="$(MSBuildProjectFullPath)"
      ProjectLanguage="$(Language)"
      CompilerApiVersion="$(CompilerApiVersion)"

I didn't want that task to have to understand compiler-specific properties (for example needing to read both RoslynCompilerApiVersion or FSharpCompilerApiVersion).

Instead, I just made a general CompilerApiVersion which can be set to roslynX.Y or fsharpX.Y or whatever. This way, the task shouldn't need to be updated to support other compilers in the future.

[jaredpar]

Ah ... makes sense