add.c: extract check_path_for_gitlink() from treat_gitlinks() for reuse

Extract the body of the for loop in treat_gitlinks() into a separate
check_path_for_gitlink() function so that it can be reused elsewhere.
This paves the way for a new check-ignore sub-command.

Also document treat_gitlinks().

Signed-off-by: Adam Spiers <git@adamspiers.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/add.c

@@ -121,6 +121,10 @@ static char *prune_directory(struct dir_struct *dir, const char **pathspec, int
 	return seen;
 }
 
+/*
+ * Checks the index to see whether any path in pathspec refers to
+ * something inside a submodule.  If so, dies with an error message.
+ */
 static void treat_gitlinks(const char **pathspec)
 {
 	int i;
@@ -128,24 +132,8 @@ static void treat_gitlinks(const char **pathspec)
 	if (!pathspec || !*pathspec)
 		return;
 
-	for (i = 0; i < active_nr; i++) {
-		struct cache_entry *ce = active_cache[i];
-		if (S_ISGITLINK(ce->ce_mode)) {
-			int len = ce_namelen(ce), j;
-			for (j = 0; pathspec[j]; j++) {
-				int len2 = strlen(pathspec[j]);
-				if (len2 <= len || pathspec[j][len] != '/' ||
-				    memcmp(ce->name, pathspec[j], len))
-					continue;
-				if (len2 == len + 1)
-					/* strip trailing slash */
-					pathspec[j] = xstrndup(ce->name, len);
-				else
-					die (_("Path '%s' is in submodule '%.*s'"),
-						pathspec[j], len, ce->name);
-			}
-		}
-	}
+	for (i = 0; pathspec[i]; i++)
+		pathspec[i] = check_path_for_gitlink(pathspec[i]);
 }
 
 static void refresh(int verbose, const char **pathspec)

pathspec.c

@@ -56,3 +56,34 @@ char *find_pathspecs_matching_against_index(const char **pathspec)
 	add_pathspec_matches_against_index(pathspec, seen, i);
 	return seen;
 }
+
+/*
+ * Check the index to see whether path refers to a submodule, or
+ * something inside a submodule.  If the former, returns the path with
+ * any trailing slash stripped.  If the latter, dies with an error
+ * message.
+ */
+const char *check_path_for_gitlink(const char *path)
+{
+	int i, path_len = strlen(path);
+	for (i = 0; i < active_nr; i++) {
+		struct cache_entry *ce = active_cache[i];
+		if (S_ISGITLINK(ce->ce_mode)) {
+			int ce_len = ce_namelen(ce);
+			if (path_len <= ce_len || path[ce_len] != '/' ||
+			    memcmp(ce->name, path, ce_len))
+				/* path does not refer to this
+				 * submodule or anything inside it */
+				continue;
+			if (path_len == ce_len + 1) {
+				/* path refers to submodule;
+				 * strip trailing slash */
+				return xstrndup(ce->name, ce_len);
+			} else {
+				die (_("Path '%s' is in submodule '%.*s'"),
+				     path, ce_len, ce->name);
+			}
+		}
+	}
+	return path;
+}

pathspec.h

@@ -3,5 +3,6 @@
 
 extern char *find_pathspecs_matching_against_index(const char **pathspec);
 extern void add_pathspec_matches_against_index(const char **pathspec, char *seen, int specs);
+extern const char *check_path_for_gitlink(const char *path);
 
 #endif /* PATHSPEC_H */