add: warn when asked to update SKIP_WORKTREE entries

`git add` already refrains from updating SKIP_WORKTREE entries, but it
silently exits with zero code when it is asked to do so. Instead, let's
warn the user and display a hint on how to update these entries.

Note that we only warn the user whey they give a pathspec item that
matches no eligible path for updating, but it does match one or more
SKIP_WORKTREE entries. A warning was chosen over erroring out right away
to reproduce the same behavior `add` already exhibits with ignored
files. This also allow users to continue their workflow without having
to invoke `add` again with only the eligible paths (as those will have
already been added).

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/pathspec.h b/pathspec.h
index 0feb8e9f67..5b4c6614bf 100644
--- a/pathspec.h
+++ b/pathspec.h
@@ -160,6 +160,14 @@ void add_pathspec_matches_against_index(const struct pathspec *pathspec,
 char *find_pathspecs_matching_against_index(const struct pathspec *pathspec,
 					    const struct index_state *istate,
 					    enum ps_skip_worktree_action sw_action);
+char *find_pathspecs_matching_skip_worktree(const struct pathspec *pathspec);
+static inline int matches_skip_worktree(const struct pathspec *pathspec,
+					int item, char **seen_ptr)
+{
+	if (!*seen_ptr)
+		*seen_ptr = find_pathspecs_matching_skip_worktree(pathspec);
+	return (*seen_ptr)[item];
+}
 int match_pathspec_attrs(const struct index_state *istate,
 			 const char *name, int namelen,
 			 const struct pathspec_item *item);