builtin/commit.c: remove the PATH_MAX limitation via dynamic allocation

Remove the PATH_MAX limitation from the environment setting that
points to a filename by switching to dynamic allocation.

As a side effect of this change, we also reduce the snprintf()
calls, that may silently truncate results if the programmer is not
careful.

Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -960,15 +960,15 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		return 0;
 
 	if (use_editor) {
-		char index[PATH_MAX];
-		const char *env[2] = { NULL };
-		env[0] =  index;
-		snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
-		if (launch_editor(git_path_commit_editmsg(), NULL, env)) {
+		struct argv_array env = ARGV_ARRAY_INIT;
+
+		argv_array_pushf(&env, "GIT_INDEX_FILE=%s", index_file);
+		if (launch_editor(git_path_commit_editmsg(), NULL, env.argv)) {
 			fprintf(stderr,
 			_("Please supply the message using either -m or -F option.\n"));
 			exit(1);
 		}
+		argv_array_clear(&env);
 	}
 
 	if (!no_verify &&
@@ -1557,23 +1557,22 @@ static int run_rewrite_hook(const unsigned char *oldsha1,
 
 int run_commit_hook(int editor_is_used, const char *index_file, const char *name, ...)
 {
-	const char *hook_env[3] =  { NULL };
-	char index[PATH_MAX];
+	struct argv_array hook_env = ARGV_ARRAY_INIT;
 	va_list args;
 	int ret;
 
-	snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
-	hook_env[0] = index;
+	argv_array_pushf(&hook_env, "GIT_INDEX_FILE=%s", index_file);
 
 	/*
 	 * Let the hook know that no editor will be launched.
 	 */
 	if (!editor_is_used)
-		hook_env[1] = "GIT_EDITOR=:";
+		argv_array_push(&hook_env, "GIT_EDITOR=:");
 
 	va_start(args, name);
-	ret = run_hook_ve(hook_env, name, args);
+	ret = run_hook_ve(hook_env.argv,name, args);
 	va_end(args);
+	argv_array_clear(&hook_env);
 
 	return ret;
 }