Re: [PATCH 03/13] dir: select directories correctly

["René Scharfe" <l.s.r@web.de>]

Am 24.08.21 um 23:54 schrieb Derrick Stolee via GitGitGadget:
> From: Derrick Stolee <dstolee@microsoft.com>
>
> When matching a path against a list of patterns, the ones that require a
> directory match previously did not work when a filename is specified.
> This was fine when all pattern-matching was done within methods such as
> unpack_trees() that check a directory before recursing into the
> contained files. However, other commands will start matching individual
> files against pattern lists without that recursive approach.
>
> We modify path_matches_dir_pattern() to take a strbuf 'path_parent' that
> is used to store the parent directory of 'pathname' between multiple
> pattern matching tests. This is loaded lazily, only on the first pattern
> it finds that has the PATTERN_FLAG_MUSTBEDIR flag.
>
> If we find that a path has a parent directory, we start by checking to
> see if that parent directory matches the pattern. If so, then we do not
> need to query the index for the type (which can be expensive). If we
> find that the parent does not match, then we still must check the type
> from the index for the given pathname.
>
> Note that this does not affect cone mode pattern matching, but instead
> the more general -- and slower -- full pattern set. Thus, this does not
> affect the sparse index.
>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  dir.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/dir.c b/dir.c
> index 652135df896..fe5ee87bb5f 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -1305,10 +1305,38 @@ int match_pathname(const char *pathname, int pathlen,
>
>  static int path_matches_dir_pattern(const char *pathname,
>  				    int pathlen,
> +				    struct strbuf *path_parent,
>  				    int *dtype,
>  				    struct path_pattern *pattern,
>  				    struct index_state *istate)
>  {
> +	/*
> +	 * Use 'alloc' as an indicator that the string has not been
> +	 * initialized, in case the parent is the root directory.
> +	 */

This means the caller needs to take care to release the strbuf between
calls for files from different directories.  Seems a bit fragile.  The
current caller is only ever passing in the same pathname before throwing
away the strbuf, so it's doing the right thing.

> +	if (!path_parent->alloc) {
> +		char *slash;
> +		strbuf_addstr(path_parent, pathname);
> +		slash = find_last_dir_sep(path_parent->buf);

The caller has pathname, pathlen and basename.  If basename is
guaranteed to be a substring of pathname then the parent directory name
length could be calculated without requiring a string copy or scan.

IIUC if pathname and basename can be pointers to different objects then
just checking if basename is between pathname and pathname + pathlen
would already be undefined behavior.

Using pathname, pathlen and dirlen instead would be safer for such
calculations, as it enforces basename to be a substring.  Seems like
this would require a lot of function signature changes, though, as the
call tree is quite high. :|

> +
> +		if (slash)
> +			*slash = '\0';

This doesn't update path_parent->len...

> +		else
> +			strbuf_setlen(path_parent, 0);
> +	}
> +
> +	/*
> +	 * If the parent directory matches the pattern, then we do not
> +	 * need to check for dtype.
> +	 */
> +	if (path_parent->len &&
> +	    match_pathname(path_parent->buf, path_parent->len,

... so this checks if "<dirname>\0<basename>" matches.  Intended?

> +			   pattern->base,
> +			   pattern->baselen ? pattern->baselen - 1 : 0,
> +			   pattern->pattern, pattern->nowildcardlen,
> +			   pattern->patternlen, pattern->flags))
> +		return 1;
> +
>  	*dtype = resolve_dtype(*dtype, istate, pathname, pathlen);
>  	if (*dtype != DT_DIR)
>  		return 0;
> @@ -1331,6 +1359,7 @@ static struct path_pattern *last_matching_pattern_from_list(const char *pathname
>  {
>  	struct path_pattern *res = NULL; /* undecided */
>  	int i;
> +	struct strbuf path_parent = STRBUF_INIT;
>
>  	if (!pl->nr)
>  		return NULL;	/* undefined */
> @@ -1340,8 +1369,8 @@ static struct path_pattern *last_matching_pattern_from_list(const char *pathname
>  		const char *exclude = pattern->pattern;
>  		int prefix = pattern->nowildcardlen;
>
> -		if ((pattern->flags & PATTERN_FLAG_MUSTBEDIR) &&
> -		    !path_matches_dir_pattern(pathname, pathlen,
> +		if (pattern->flags & PATTERN_FLAG_MUSTBEDIR &&
> +		    !path_matches_dir_pattern(pathname, pathlen, &path_parent,

"a & b && c" is equivalent to "(a & b) && c", but removing the
parentheses here serves no apparent purpose and distracts a bit from
the actual change, i.e. adding a parameter.

>  					      dtype, pattern, istate))
>  			continue;
>
> @@ -1367,6 +1396,7 @@ static struct path_pattern *last_matching_pattern_from_list(const char *pathname
>  			break;
>  		}
>  	}
> +	strbuf_release(&path_parent);
>  	return res;
>  }
>
>