tag checkout action overwrites tag with pointed-to commit

[Joshua Wise]

I have an action that does some stuff that reads the output of git tag -l --format=%(contents) to generate a version file.

On my laptop, I get the tag message if I do something like:

git commit -a -m 'Commit message!'
git tag -a -m 'Tag message!' mytags/v1.0
git tag -l mytags/v1.0 '--format=%(contents)'

But if I do that very same git tag command in CI in a push action that is

 on:
  push:
    branches: [ "master" ]
    tags: [ "mytags/*" ]

then the git tag command returns the commit message, instead!

After an hour of hunting, I tracked it down to this logic:

checkout/src/git-source-provider.ts

Lines 177 to 182 in b32f140

 // When all history is fetched, the ref we're interested in may have moved to a different 
 // commit (push or force push). If so, fetch again with a targeted refspec. 
 if (!(await refHelper.testRef(git, settings.ref, settings.commit))) { 
   refSpec = refHelper.getRefSpec(settings.ref, settings.commit) 
   await git.fetch(refSpec, fetchOptions) 
 } 

Roughly, what's happening here is that CI first does:

/usr/bin/git -c protocol.version=2 fetch --prune --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/tags/*:refs/tags/*

And then it immediately after does this:

/usr/bin/git -c protocol.version=2 fetch --no-tags --prune --no-recurse-submodules origin +[the pointed to tag commit]:refs/tags/mytags/v1.0

as a result of the above logic. But this is wrong: it should not fetch the pointed to tag commit! It should fetch the tag object itself!