execv_dashed_external: use child_process struct

When we run a dashed external, we use the one-liner
run_command_v_opt() to do so. Let's switch to using a
child_process struct, which has two advantages:

  1. We can drop all of the allocation and cleanup code for
     building our custom argv array, and just rely on the
     builtin argv_array (at the minor cost of doing a few
     extra mallocs).

  2. We have access to the complete range of child_process
     options, not just the ones that the "_opt()" form can
     forward.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -575,8 +575,7 @@ static void handle_builtin(int argc, const char **argv)
 
 static void execv_dashed_external(const char **argv)
 {
-	struct strbuf cmd = STRBUF_INIT;
-	const char *tmp;
+	struct child_process cmd = CHILD_PROCESS_INIT;
 	int status;
 
 	if (get_super_prefix())
@@ -586,30 +585,20 @@ static void execv_dashed_external(const char **argv)
 		use_pager = check_pager_config(argv[0]);
 	commit_pager_choice();
 
-	strbuf_addf(&cmd, "git-%s", argv[0]);
+	argv_array_pushf(&cmd.args, "git-%s", argv[0]);
+	argv_array_pushv(&cmd.args, argv + 1);
+	cmd.clean_on_exit = 1;
+	cmd.silent_exec_failure = 1;
 
-	/*
-	 * argv[0] must be the git command, but the argv array
-	 * belongs to the caller, and may be reused in
-	 * subsequent loop iterations. Save argv[0] and
-	 * restore it on error.
-	 */
-	tmp = argv[0];
-	argv[0] = cmd.buf;
-
-	trace_argv_printf(argv, "trace: exec:");
+	trace_argv_printf(cmd.args.argv, "trace: exec:");
 
 	/*
 	 * if we fail because the command is not found, it is
 	 * OK to return. Otherwise, we just pass along the status code.
 	 */
-	status = run_command_v_opt(argv, RUN_SILENT_EXEC_FAILURE | RUN_CLEAN_ON_EXIT);
+	status = run_command(&cmd);
 	if (status >= 0 || errno != ENOENT)
 		exit(status);
-
-	argv[0] = tmp;
-
-	strbuf_release(&cmd);
 }
 
 static int run_argv(int *argcp, const char ***argv)