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

From: "SZEDER Gábor" <szeder.dev@gmail.com>
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH v3 2/2] git_path(): handle `.lock` files correctly
Date: Mon, 28 Oct 2019 13:32:14 +0100	[thread overview]
Message-ID: <20191028123214.GT4348@szeder.dev> (raw)
In-Reply-To: <nycvar.QRO.7.76.6.1910281225260.46@tvgsbejvaqbjf.bet>

On Mon, Oct 28, 2019 at 01:01:49PM +0100, Johannes Schindelin wrote:
> > > @@ -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,

Do we?  You're right, we do indeed, because in replace_dir(buf, ...)
we call strbuf_splice(buf, ...).
OK, then your suggestion below is even better.

> 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 --