[PATCH 3/4] Fix diff regression for submodules not checked out

[Ping Yin <pkufranky@gmail.com>]

This regression is introduced by f58dbf23c3, which calls
check_work_tree_entity in run_diff_files. While check_work_tree_entity
treats submodule not checked out as non stagable which causes that
diff-files shows these submodules as deleted.

check_work_tree_entity considers a worktree entity having two statuses:
stagable and inexistent. Actually, there is a 3rd status: a submodule
entity can be existent but not stagable (for example, empty directory for
non-checked-out submodule)

This patch redesigns the return value of check_work_tree_entity to
consider both the 3 statuses.

Signed-off-by: Ping Yin <pkufranky@gmail.com>
---
 diff-lib.c |   22 +++++++++++++---------
 1 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/diff-lib.c b/diff-lib.c
index cfd629d..72c2a7b 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -337,25 +337,29 @@ int run_diff_files_cmd(struct rev_info *revs, int argc, const char **argv)
 	}
 	return run_diff_files(revs, options);
 }
+
+#define ENT_STAGABLE 1
+#define ENT_INEXISTENT 2
+#define ENT_NOTGITDIR 3		/* Existent but not stagable (not a git dir) */
 /*
- * See if work tree has an entity that can be staged.  Return 0 if so,
- * return 1 if not and return -1 if error.
+ * Check the status of a work tree entity
+ * Return ENT_{STAGABLE,INEXISTENT,NOTGITDIR} or -1 if error
  */
 static int check_work_tree_entity(const struct cache_entry *ce, struct stat *st, char *symcache)
 {
 	if (lstat(ce->name, st) < 0) {
 		if (errno != ENOENT && errno != ENOTDIR)
 			return -1;
-		return 1;
+		return ENT_INEXISTENT;
 	}
 	if (has_symlink_leading_path(ce->name, symcache))
-		return 1;
+		return ENT_INEXISTENT;
 	if (S_ISDIR(st->st_mode)) {
 		unsigned char sub[20];
 		if (resolve_gitlink_ref(ce->name, "HEAD", sub))
-			return 1;
+			return ENT_NOTGITDIR;
 	}
-	return 0;
+	return ENT_STAGABLE;
 }
 
 int run_diff_files(struct rev_info *revs, unsigned int option)
@@ -403,7 +407,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 			       sizeof(struct combine_diff_parent)*5);
 
 			changed = check_work_tree_entity(ce, &st, symcache);
-			if (!changed)
+			if (changed != ENT_INEXISTENT)
 				dpath->mode = ce_mode_from_stat(ce, st.st_mode);
 			else {
 				if (changed < 0) {
@@ -467,7 +471,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 			continue;
 
 		changed = check_work_tree_entity(ce, &st, symcache);
-		if (changed) {
+		if (changed == ENT_INEXISTENT) {
 			if (changed < 0) {
 				perror(ce->name);
 				continue;
@@ -527,7 +531,7 @@ static int get_stat_data(struct cache_entry *ce,
 		changed = check_work_tree_entity(ce, &st, cbdata->symcache);
 		if (changed < 0)
 			return -1;
-		else if (changed) {
+		else if (changed == ENT_INEXISTENT) {
 			if (match_missing) {
 				*sha1p = sha1;
 				*modep = mode;
-- 
1.5.5.1.116.ge4b9c.dirty