From: Junio C Hamano <gitster@pobox.com>
Date: Mon, 19 Nov 2012 20:54:45 GMT
Subject: Re: [PATCH 2/4] pathspec: do exact comparison on the leading non-wildcard part
Message-ID: <7vzk2duw3m.fsf@alter.siamese.dyndns.org>
In-Reply-To: <1353229989-13075-3-git-send-email-pclouds@gmail.com>

Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:

> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  dir.c       | 18 +++++++++++++++++-
>  dir.h       |  8 ++++++++
>  tree-walk.c |  6 ++++--
>  3 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/dir.c b/dir.c
> index c391d46..e4e6ca1 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -34,6 +34,21 @@ int fnmatch_icase(const char *pattern, const char *string, int flags)
>  	return fnmatch(pattern, string, flags | (ignore_case ? FNM_CASEFOLD : 0));
>  }
>  
> +inline int git_fnmatch(const char *pattern, const char *string,
> +		       int flags, int prefix)
> +{
> +	int fnm_flags = 0;
> +	if (flags & GF_PATHNAME)
> +		fnm_flags |= FNM_PATHNAME;
> +	if (prefix > 0) {
> +		if (strncmp(pattern, string, prefix))
> +			return FNM_NOMATCH;
> +		pattern += prefix;
> +		string += prefix;
> +	}
> +	return fnmatch(pattern, string, fnm_flags);

How would we protect this optimization from future breakages?

Once we start using FNM_PERIOD, this becomes unsafe, as the simple
part in "foo/bar*baz" would be "foo/bar" with remainder "*baz".

The pattern "foo/bar*baz" should match "foo/bar.baz" with FNM_PERIOD
set.  But with this optimization, fnmatch is fed pattern="*baz",
string=".baz" and they would not match.