git.c: simplify stripping extension of a file in handle_builtin()

The handle_builtin() starts from stripping of command extension if
STRIP_EXTENSION is enabled. Actually STRIP_EXTENSION does not used
anywhere else.

This patch introduces strip_extension() helper to strip STRIP_EXTENSION
extension from argv[0] with the strip_suffix() instead of manually
stripping.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

diff --git a/git-compat-util.h b/git-compat-util.h
index f649e81..b7fcbd4 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -319,10 +319,6 @@
 #define _PATH_DEFPATH "/usr/local/bin:/usr/bin:/bin"
 #endif
 
-#ifndef STRIP_EXTENSION
-#define STRIP_EXTENSION ""
-#endif
-
 #ifndef has_dos_drive_prefix
 static inline int git_has_dos_drive_prefix(const char *path)
 {

git.c

diff --git a/git.c b/git.c
index 5feba41..a9dc2e8 100644
--- a/git.c
+++ b/git.c
@@ -505,21 +505,25 @@
 	return !!get_builtin(s);
 }
 
+#ifdef STRIP_EXTENSION
+static void strip_extension(const char **argv)
+{
+	size_t len;
+
+	if (strip_suffix(argv[0], STRIP_EXTENSION, &len))
+		argv[0] = xmemdupz(argv[0], len);
+}
+#else
+#define strip_extension(cmd)
+#endif
+
 static void handle_builtin(int argc, const char **argv)
 {
-	const char *cmd = argv[0];
-	int i;
-	static const char ext[] = STRIP_EXTENSION;
+	const char *cmd;
 	struct cmd_struct *builtin;
 
-	if (sizeof(ext) > 1) {
-		i = strlen(argv[0]) - strlen(ext);
-		if (i > 0 && !strcmp(argv[0] + i, ext)) {
-			char *argv0 = xstrdup(argv[0]);
-			argv[0] = cmd = argv0;
-			argv0[i] = '\0';
-		}
-	}
+	strip_extension(argv);
+	cmd = argv[0];
 
 	/* Turn "git cmd --help" into "git help cmd" */
 	if (argc > 1 && !strcmp(argv[1], "--help")) {