Re: [PATCH v3 2/2] git_path(): handle `.lock` files correctly

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi,

On Tue, 22 Oct 2019, SZEDER Gábor wrote:

> On Mon, Oct 21, 2019 at 09:54:42PM +0000, Johannes Schindelin via GitGitGadget wrote:
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > Ever since worktrees were introduced, the `git_path()` function _really_
> > needed to be called e.g. to get at the path to `logs/HEAD` (`HEAD` is
> > specific to the worktree, and therefore so is its reflog). However, the
> > wrong path is returned for `logs/HEAD.lock`.
> >
> > This does not matter as long as the Git executable is doing the asking,
> > as the path for that `logs/HEAD.lock` file is constructed from
> > `git_path("logs/HEAD")` by appending the `.lock` suffix.
> >
> > However, Git GUI just learned to use `--git-path` instead of appending
> > relative paths to what `git rev-parse --git-dir` returns (and as a
> > consequence not only using the correct hooks directory, but also using
> > the correct paths in worktrees other than the main one). While it does
> > not seem as if Git GUI in particular is asking for `logs/HEAD.lock`,
> > let's be safe rather than sorry.
> >
> > Side note: Git GUI _does_ ask for `index.lock`, but that is already
> > resolved correctly, due to `update_common_dir()` preferring to leave
> > unknown paths in the (worktree-specific) git directory.
> >
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> >  path.c               |  8 +++++++-
> >  t/t1500-rev-parse.sh | 15 +++++++++++++++
> >  2 files changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/path.c b/path.c
> > index e3da1f3c4e..5ff64e7a8a 100644
> > --- a/path.c
> > +++ b/path.c
> > @@ -349,10 +349,16 @@ static int check_common(const char *unmatched, void *value, void *baton)
> >  static void update_common_dir(struct strbuf *buf, int git_dir_len,
> >  			      const char *common_dir)
> >  {
> > -	char *base = buf->buf + git_dir_len;
> > +	char *base = buf->buf + git_dir_len, *base2 = NULL;
> > +
> > +	if (ends_with(base, ".lock"))
> > +		base = base2 = xstrndup(base, strlen(base) - 5);
>
> Hm, this adds the magic number 5 and calls strlen(base) twice, because
> ends_with() calls strip_suffix(), which calls strlen().  Calling
> strip_suffix() directly would allow us to avoid the magic number and
> the second strlen():
>
>   size_t len;
>   if (strip_suffix(base, ".lock", &len))
>           base = base2 = xstrndup(base, len);

Actually, we should probably avoid the extra allocation. Earlier, I was
concerned about multi-threading issues when attempting to modify the
`strbuf`. But then, we modify that `strbuf` a couple of lines later
anyway, so my fears were totally unfounded. Therefore, my current
version reads like this:

-- snip --
	int has_lock_suffix = strbuf_strip_suffix(buf, LOCK_SUFFIX);

	init_common_trie();
	if (trie_find(&common_trie, base, check_common, NULL) > 0)
		replace_dir(buf, git_dir_len, common_dir);

	if (has_lock_suffix)
		strbuf_addstr(buf, LOCK_SUFFIX);
-- snap --


>
> >  	init_common_trie();
> >  	if (trie_find(&common_trie, base, check_common, NULL) > 0)
> >  		replace_dir(buf, git_dir_len, common_dir);
> > +
> > +	free(base2);
> >  }
> >
> >  void report_linked_checkout_garbage(void)
> > diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
> > index 01abee533d..d318a1eeef 100755
> > --- a/t/t1500-rev-parse.sh
> > +++ b/t/t1500-rev-parse.sh
> > @@ -116,6 +116,21 @@ test_expect_success 'git-path inside sub-dir' '
> >  	test_cmp expect actual
> >  '
> >
> > +test_expect_success 'git-path in worktree' '
> > +	test_tick &&
> > +	git commit --allow-empty -m empty &&
> > +	git worktree add --detach wt &&
> > +	test_write_lines >expect \
> > +		"$(pwd)/.git/worktrees/wt/logs/HEAD" \
> > +		"$(pwd)/.git/worktrees/wt/logs/HEAD.lock" \
> > +		"$(pwd)/.git/worktrees/wt/index" \
> > +		"$(pwd)/.git/worktrees/wt/index.lock" &&
> > +	git -C wt rev-parse >actual \
> > +		--git-path logs/HEAD --git-path logs/HEAD.lock \
> > +		--git-path index --git-path index.lock &&
> > +	test_cmp expect actual
> > +'
>
> I think this test better fits into 't0060-path-utils.sh': it already
> checks 'logs/HEAD' and 'index' in a different working tree (well, with
> GIT_COMMON_DIR set, but that's the same), and it has a helper function
> to make each of the two new .lock tests a one-liner.

Excellent point. Thank you for helping me improve the patch!

Ciao,
Dscho

>
> >  test_expect_success 'rev-parse --is-shallow-repository in shallow repo' '
> >  	test_commit test_commit &&
> >  	echo true >expect &&
> > --
> > gitgitgadget
>