reversion in GIT_COMMON_DIR refs path

Bisecting this test suite failure https://git-annex.branchable.com/git-annex_in_nixpkgs_fails_with_git-2.13.0/ I landed on commit f57f37e2e1bf11ab4cdfd221ad47e961ba9353a0 to git.

It seems that changed resolving refs paths when GIT_DIR and GIT_COMMON_DIR are both set. While before refs were looked for in GIT_COMMON_DIR, now they're not.

Test case:

#!/bin/sh set -e set -x rm -rf testdir git init testdir cd testdir echo 1 > foo git add foo git commit -m add mkdir dummy mkdir dummy/overlay cp .git/index .git/HEAD dummy/overlay #cp .git/refs .git/packed-refs dummy/overlay -a cd dummy export GIT_COMMON_DIR=`pwd`/../.git export GIT_DIR=`pwd`/overlay git rev-parse --git-path refs/heads/master git show refs/heads/master

This script succeeds with git 2.11.0, but with 2.13.0, it fails:

fatal: ambiguous argument 'refs/heads/master': unknown revision or path not in the working tree.

It seems to be failing to look up refs in GIT_COMMON_DIR. Note that uncommenting the commented out line in the script, to copy the refs into GIT_DIR, makes it succeed.

git rev-parse --git-path refs/heads/master shows the GIT_COMMON_DIR/refs path still (as gitrepository-layout documents). So this reversion made different parts of git disagreeing about the refs path.