path: add a function to check for path suffix

We have a function to strip the path suffix from a commit, but we don't
have one to check for a path suffix. For a plain filename, we can use
basename, but that requires an allocation, since POSIX allows it to
modify its argument. Refactor strip_path_suffix into a helper function
and a new function, ends_with_path_components, to meet this need.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

diff --git a/path.c b/path.c
index 25e97b8..e3da1f3 100644
--- a/path.c
+++ b/path.c
@@ -1221,31 +1221,52 @@ static inline int chomp_trailing_dir_sep(const char *path, int len)
 }
 
 /*
+ * If path ends with suffix (complete path components), returns the offset of
+ * the last character in the path before the suffix (sans trailing directory
+ * separators), and -1 otherwise.
+ */
+static ssize_t stripped_path_suffix_offset(const char *path, const char *suffix)
+{
+	int path_len = strlen(path), suffix_len = strlen(suffix);
+
+	while (suffix_len) {
+		if (!path_len)
+			return -1;
+
+		if (is_dir_sep(path[path_len - 1])) {
+			if (!is_dir_sep(suffix[suffix_len - 1]))
+				return -1;
+			path_len = chomp_trailing_dir_sep(path, path_len);
+			suffix_len = chomp_trailing_dir_sep(suffix, suffix_len);
+		}
+		else if (path[--path_len] != suffix[--suffix_len])
+			return -1;
+	}
+
+	if (path_len && !is_dir_sep(path[path_len - 1]))
+		return -1;
+	return chomp_trailing_dir_sep(path, path_len);
+}
+
+/*
+ * Returns true if the path ends with components, considering only complete path
+ * components, and false otherwise.
+ */
+int ends_with_path_components(const char *path, const char *components)
+{
+	return stripped_path_suffix_offset(path, components) != -1;
+}
+
+/*
  * If path ends with suffix (complete path components), returns the
  * part before suffix (sans trailing directory separators).
  * Otherwise returns NULL.
  */
 char *strip_path_suffix(const char *path, const char *suffix)
 {
-	int path_len = strlen(path), suffix_len = strlen(suffix);
+	ssize_t offset = stripped_path_suffix_offset(path, suffix);
 
-	while (suffix_len) {
-		if (!path_len)
-			return NULL;
-
-		if (is_dir_sep(path[path_len - 1])) {
-			if (!is_dir_sep(suffix[suffix_len - 1]))
-				return NULL;
-			path_len = chomp_trailing_dir_sep(path, path_len);
-			suffix_len = chomp_trailing_dir_sep(suffix, suffix_len);
-		}
-		else if (path[--path_len] != suffix[--suffix_len])
-			return NULL;
-	}
-
-	if (path_len && !is_dir_sep(path[path_len - 1]))
-		return NULL;
-	return xstrndup(path, chomp_trailing_dir_sep(path, path_len));
+	return offset == -1 ? NULL : xstrndup(path, offset);
 }
 
 int daemon_avoid_alias(const char *p)

path.h

diff --git a/path.h b/path.h
index 2ba6ca5..14d6dca 100644
--- a/path.h
+++ b/path.h
@@ -193,4 +193,7 @@ const char *git_path_merge_head(struct repository *r);
 const char *git_path_fetch_head(struct repository *r);
 const char *git_path_shallow(struct repository *r);
 
+
+int ends_with_path_components(const char *path, const char *components);
+
 #endif /* PATH_H */