nightly: use exact branch name in $BUILDVERSION_EXEC

[dancrossnyc]

No description provided.

[dancrossnyc]

I ran into seemingly odd behavior where I was on the stlouis branch, but the branch name in the build was another, different branch that happened to be at that same commit. This was surprising, but seems to be the standard behavior of git describe. Adding the --match argument with the (current) branch name gives the desired behavior, but breaks if one is disconnected from any branch (e.g., one is in "detached HEAD" state as if one checks out some commit that's not associated with a ref head in the current repo), hence the "||" command to revert to the default behavior.

Perhaps there's some simpler way to do this, but if so, I'm not sure what it is.

[citrus-it]

I've seen this before but didn't look too closely, so thanks for investigating.
I had a quick look and couldn't find a better way to do this, which was a bit of a surprise given its clunkiness.

[citrus-it]

Is this being evaluated at the time the .env file is sourced, or when BUILDVERSION_EXEC is used? It should be the latter but this looks like the former, which is a problem if you switch branches while in a bldenv.

[dancrossnyc]

PTAL; it was actually borked (but it takes a while in a build to get the point where one notices). It's evaluated when BUILDVERSION_EXEC is used, but that caused syntax errors, so I've changed it to creating a function that does the branch ... stuff ... and then BUILDVERSION_EXEC invokes that function.

Ugh. Yeah, this feels way uglier than it needs to be.

[jclulow]

I think given how complex this is, that I'd like to get it done in Rust. We should have a new (hidden) subcommand for helios-build that produces the correct value and then use that in the generated environment file.

[dancrossnyc]

I think given how complex this is, that I'd like to get it done in Rust. We should have a new (hidden) subcommand for helios-build that produces the correct value and then use that in the generated environment file.

I agree. This is also hopelessly broken; the issue is that the way that BUILDVERSION_EXEC is actually used is in a Makefile in usr/src/cmd/nsadmin, but it's just expanded as an unevaluated string, which cannot handle the ||. The "fix" would be to eval it in the Makefile, but that's just a bigger change and introduces its own issues. All of my hacky attempts to work around it have come to naught for what are (in retrospect) blindingly obvious reasons.