Re: [PATCH] ls-files: filter pathspec before lstat

[Junio C Hamano <gitster@pobox.com>]

On Sun, Jun 7, 2026 at 11:40, Tamir Duberstein wrote:
> show_files() checks whether each index entry is deleted or modified
> before show_ce() applies the pathspec. prune_index() avoids most of this
> work for pathspecs with a common directory prefix, but a top-level name
> or leading wildcard leaves every entry to be checked.
> 
> Match the pathspec before lstat() for the deleted and modified modes.
> Keep the later match in show_ce() so --error-unmatch is satisfied only
> by entries that are actually shown.

Adding an extra early `match_pathspec()` check before making slow
system calls like `lstat()` makes sense, especially when most of the
index entries need to be skipped.  But if most of them would match,
then we would end up doing the same match_pathspec() calls twice for
each path, and run lstat() anyway, so you may also be able to
construct a perf test that demonstrates a case where this approach
is not a clear win (or even degradation), perhaps?

> diff --git a/builtin/ls-files.c b/builtin/ls-files.c
> index e1a22b41b9..702c607183 100644
> --- a/builtin/ls-files.c
> +++ b/builtin/ls-files.c
> @@ -450,6 +450,13 @@ static void show_files(struct repository *repo, struct dir_struct *dir)
>  			continue;
>  		if (ce_skip_worktree(ce))
>  			continue;
> +		/* Only entries shown by show_ce() satisfy --error-unmatch. */
> +		if (pathspec.nr &&
> +		    !match_pathspec(repo->index, &pathspec, fullname.buf,
> +				    fullname.len, max_prefix_len, NULL,
> +				    S_ISDIR(ce->ce_mode) ||
> +				    S_ISGITLINK(ce->ce_mode)))
> +			continue;
>  		stat_err = lstat(fullname.buf, &st);
>  		if (stat_err && (errno != ENOENT && errno != ENOTDIR))
>  			error_errno("cannot lstat '%s'", fullname.buf);

Hmph.  In the current code, because there is no such pre-filtering,
show_ce() would unconditionally recurse into active submodules when
told to with the "--recurse-submodules" flag, even if your pathspec
coes not match the submodule.  With this change, such a submodule
whose path does not match the pathspec would not even be seen by
show_ce().  Would it cause a change in behaviour?