Re: [PATCH 02/18] t9300: check ref existence using git-rev-parse rather than FS check

On Mon, Apr 19 2021, Han-Wen Nienhuys via GitGitGadget wrote:

It seems to me that this breaks the test, to the extent that it's
testing something we care about at all.

I.e. reading ea08a6fd19 (Actually allow TAG_FIXUP branches in
fast-import, 2007-08-02) the whole point is to test that a "TEMP_TAG"
ref is accepted by fast-import, as opposed to "refs/heads/TEMP_TAG".

So we're trying to check that the refstore accepts a concept of a name
like HEAD called BLAHBLAH or whatever, that lives at the "top-level".

For something unrelated I was trying to figure out how to detect that
the other day and couldn't come up with anything I was happy with,
e.g. this seems to work:

    # Rely on for-each-ref not listing it...
    git for-each-ref >gfe &&
    ! grep TEMP_TAG gfe &&
    # ... but rev-parse grokking it
    git rev-parse TEMP_TAG

Or, rely on rev-parse emitting a warning about it:

    $ git update-ref refs/heads/TEMP_TAG HEAD
    # A bug? We emit both an error and a warning with
    # --symbolic-full-name?
    $ git rev-parse --symbolic-full-name TEMP_TAG
    warning: refname 'TEMP_TAG' is ambiguous.
    error: refname 'TEMP_TAG' is ambiguous
    $ echo $?
    0

IOW re my
https://lore.kernel.org/git/87wnt2th1v.fsf@evledraar.gmail.com/ (local) this
seems like exactly the sort of edge case where we want to dig a bit more
and assert that we support (or explicitly don't support) this "mode"
under reftable.

In any case, if we're not testing for .git/TEMP_TAG anymore I think your
addition of "git rev-parse TEMP_TAG" is entirely redundant to the ad-hoc
"test_cmp" that comes after it, when would we not be able to rev-parse
FOO, but succeed with FOO^ ?