remove prefix argument from pathspec_prefix

Passing a prefix to a function that is supposed to find the prefix is
strange. And it's really only used if the pathspec is NULL. Make the
callers handle this case instead.

As we are always returning a fresh copy of a string (or NULL), change the
type of the returned value to non-const "char *".

Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -257,8 +257,9 @@ static int list_paths(struct string_list *list, const char *with_tree,
 	m = xcalloc(1, i);
 
 	if (with_tree) {
-		const char *max_prefix = pathspec_prefix(prefix, pattern);
-		overlay_tree_on_cache(with_tree, max_prefix);
+		char *max_prefix = pathspec_prefix(pattern);
+		overlay_tree_on_cache(with_tree, max_prefix ? max_prefix : prefix);
+		free(max_prefix);
 	}
 
 	for (i = 0; i < active_nr; i++) {

builtin/ls-files.c

@@ -541,7 +541,7 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 		strip_trailing_slash_from_submodules();
 
 	/* Find common prefix for all pathspec's */
-	max_prefix = pathspec_prefix(prefix, pathspec);
+	max_prefix = pathspec_prefix(pathspec);
 	max_prefix_len = max_prefix ? strlen(max_prefix) : 0;
 
 	/* Treat unmatching pathspec elements as errors */

cache.h

@@ -426,7 +426,7 @@ extern void set_git_work_tree(const char *tree);
 #define ALTERNATE_DB_ENVIRONMENT "GIT_ALTERNATE_OBJECT_DIRECTORIES"
 
 extern const char **get_pathspec(const char *prefix, const char **pathspec);
-extern const char *pathspec_prefix(const char *prefix, const char **pathspec);
+extern char *pathspec_prefix(const char **pathspec);
 extern void setup_work_tree(void);
 extern const char *setup_git_directory_gently(int *);
 extern const char *setup_git_directory(void);

setup.c

@@ -264,13 +264,13 @@ const char **get_pathspec(const char *prefix, const char **pathspec)
 	return pathspec;
 }
 
-const char *pathspec_prefix(const char *prefix, const char **pathspec)
+char *pathspec_prefix(const char **pathspec)
 {
 	const char **p, *n, *prev;
 	unsigned long max;
 
 	if (!pathspec)
-		return prefix ? xmemdupz(prefix, strlen(prefix)) : NULL;
+		return NULL;
 
 	prev = NULL;
 	max = PATH_MAX;