t/perf: avoid copying worktree files from test repo

When running the perf suite, we copy files from an existing $GIT_DIR to
a scratch repository to give us a realistic setup on which to operate.
Since the perf scripts themselves may modify the scratch repository, we
want to make sure we've scrubbed any references back to the original.

One existing example is that we avoid copying the file "commondir" at
the top-level of the repository. In a worktree git-dir (e.g.,
.git/worktrees/foo), that file contains the path to the parent
repository; copying it could mean ref updates in the scratch repository
affect the original.

But there are other files we should cover, too:

  - "gitdir" in a worktree git-dir contains the path to the actual .git
    file in the working tree. We _shouldn't_ end up looking at it at
    all, since the lack of a "commondir" file means Git won't consider
    this to be a worktree git-dir. But it's best to err on the safe
    side.

  - in a parent repository that contains worktrees, the
    "$GIT_DIR/worktrees" directory will contain the git dirs for the
    individual worktrees. Which will themselves contain commondir and
    gitdir files that may reference the original repository. We should
    likewise remove them.

    Note that this does mean that the perf suite's scratch repositories
    will never have any worktrees. That's OK; we don't have any perf tests
    that are influenced by their presence. If we add any, they'd
    probably want to create the worktrees themselves anyway.

This patch adds both paths to the set of omissions in
test_perf_copy_repo_contents(). Note that we won't get confused here by
matching arbitrary names like refs/heads/commondir. This list is always
matching top-level entries in $GIT_DIR (we rely on "cp -R" to do the
actual recursion).

Suggested-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/perf/perf-lib.sh

@@ -74,7 +74,7 @@ test_perf_copy_repo_contents () {
 	for stuff in "$1"/*
 	do
 		case "$stuff" in
-		*/objects|*/hooks|*/config|*/commondir)
+		*/objects|*/hooks|*/config|*/commondir|*/gitdir|*/worktrees)
 			;;
 		*)
 			cp -R "$stuff" "$repo/.git/" || exit 1