Although this feels like a hack, it fixes the issue without impact much of the code. Otherwise, we would get regression issues. Someone from git community, please check this once.
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On Tuesday, October 14th, 2025 at 6:04 AM, Jeff King <peff@peff.net> wrote:
Show 126 quoted lines
> On Fri, Oct 10, 2025 at 02:57:07PM +0000, Sruteesh Kumar wrote:
>
> > Look at the first scenario in the above link. Git is matching the path
> > foobar with the pattern foo**/bar which is against the git's official
> > documentation (Look at the last point in the double asterisk section
> > at the URL https://git-scm.com/docs/gitignore#_pattern_format).
> >
> > Is this an issue with the code or the documentation?
>
>
> I think the code is buggy. Here's a patch which would fix it, but I've
> marked it as RFC because:
>
> 1. I haven't entirely convinced myself that there aren't more
> complicated variants of the same problem.
>
> 2. It's kind of a disgusting hack.
>
> -- >8 --
>
> Subject: match_pathname(): give fnmatch one char of prefix context
>
> In match_pathname(), which we use for matching .gitignore and
> .gitattribute patterns, we are comparing paths with with fnmatch
> patterns (actually our extended wildmatch, which will be important).
> There's an extra optimization there: we pre-compute the number of
> non-wildcard characters at the beginning of the pattern and do an
> fspathncmp() on that prefix.
>
> That lets us avoid fnmatch entirely on patterns without wildcards, and
> shrinks the amount of work we hand off to fnmatch. For a pattern like
> "foo*.txt" and a path "foobar.txt", we'd cut away the matching "foo"
> prefix and just pass "*.txt" and "bar.txt" to fnmatch().
>
> But this misses a subtle corner case. In fnmatch(), we'll think
> "bar.txt" is the start of the path, but it's not. This doesn't matter
> for the pattern above, but consider the wildmatch pattern "foo**/bar"
> and the path "foobar". These two should not match, because there is no
> file named "bar", and the "" applies only to the containing directory
> name. But after removing the "foo" prefix, fnmatch will get "/bar" and
> "bar", which it does consider a match, because "/" can match zero
> directories.
>
> We can solve this by giving fnmatch a bit more context. As long as it
> has one byte of the matched prefix, then it will know that "bar" is not
> the start of the path. In this example it would get "o/bar" and
> "obar", and realize that they cannot match.
>
> In the case that there are no wildcards at all (i.e., the whole prefix
> matches), we'll continue to return without running fnmatch at all. We
> just need to account for the extra byte in our adjusted lengths.
>
> Signed-off-by: Jeff King peff@peff.net
>
> ---
> I wonder how much this prefix-matching buys us in practice. There are
> two cases that are helped:
>
> 1. When there is no wildcard in the pattern at all, we skip fnmatch
> entirely.
>
> 2. We do a raw match of the prefix chars, shrinking the size of what
> is passed to fnmatch.
>
> My suspicion is that most of the improvement comes from (1), and it
> would be very easy to retain that case and get rid of (2). But I haven't
> done any measuring.
>
> dir.c | 9 ++++++++-
> t/t0008-ignores.sh | 11 +++++++++++
> 2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/dir.c b/dir.c
> index 0a67a99cb3..764400d9c5 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -1360,6 +1360,13 @@ int match_pathname(const char pathname, int pathlen,
>
> if (fspathncmp(pattern, name, prefix))
> return 0;
> +
> + /
> + * Retain one character of the prefix to
> + * pass to fnmatch, which lets it distinguish
> + * the start of a directory component correctly.
> + */
> + prefix--;
> pattern += prefix;
> patternlen -= prefix;
> name += prefix;
> @@ -1370,7 +1377,7 @@ int match_pathname(const char pathname, int pathlen,
> * then our prefix match is all we need; we
> * do not need to call fnmatch at all.
> /
> - if (!patternlen && !namelen)
> + if (patternlen == 1 && namelen == 1)
> return 1;
> }
>
> diff --git a/t/t0008-ignores.sh b/t/t0008-ignores.sh
> index 273d71411f..db8bde280e 100755
> --- a/t/t0008-ignores.sh
> +++ b/t/t0008-ignores.sh
> @@ -847,6 +847,17 @@ test_expect_success 'directories and ** matches' '
> test_cmp expect actual
> '
>
> +test_expect_success ' not confused by matching leading prefix' '
> + cat >.gitignore <<-\EOF &&
>
> + foo**/bar
> + EOF
> + git check-ignore foobar foo/bar >actual &&
>
> + cat >expect <<-\EOF &&
>
> + foo/bar
> + EOF
> + test_cmp expect actual
> +'
> +
> ############################################################################
> #
> # test whitespace handling
> --
> 2.51.0.754.gd4f5ded95f