Show VMR commit hash under dotnet --info for source-built SDKs

[mateusrodrigues]

Describe the Problem

Currently, a source-built .NET SDK displays the commit hash of the installer repo -- the one in prereqs/git-info/installer.props -- when you run the command dotnet --info, e.g.

.NET SDK:
 Version:   8.0.100-rc.1.23455.1
 Commit:    e14caf947f

Runtime Environment:
 OS Name:     ubuntu
 OS Version:  23.10
 OS Platform: Linux
 RID:         ubuntu.23.10-x64
 Base Path:   /usr/lib/dotnet/sdk/8.0.100-rc.1.23455.1/
...

Describe the Solution

It would probably make more sense to display the VMR repo commit hash equivalent to the source-tree that generated said SDK when the user types in dotnet --info.

Additional Context

This issue was a result of question #3642.

[MichaelSimons]

@omajid - Any interest in picking up this item? This would benefit distro maintainers as well as Microsoft with the unified build effort. All builds coming out of the VMR build should be referencing the VMR's commit hash.

CC @mmitche

[omajid]

Is there some way to get the local commit sha inside the VMR? I know in a git repo we can run git rev-parse HEAD and in a tarball scenario, we can use GIT_DIR/HEAD. Is there some existing generic mechanism that abstracts over these?

[MichaelSimons]

We do fake out some .git files when running in a tarball scenario for source-link. See https://github.com/dotnet/dotnet/blob/main/build.sh#L294.

[omajid]

Thanks, that build.sh trick is what I meant by GIT_DIR/HEAD above. That seems consistent with https://github.com/dotnet/sourcelink/tree/main/docs#minimal-git-repository-metadata, so I was wondering if there's a SourceLink msbuild task to extract that value.