Windows: start_command: Support non-NULL dir in struct child_process

A caller of start_command can set the member 'dir' to a directory to
request that the child process starts with that directory as CWD. The first
user of this feature was added recently in eee49b6 (Teach diff --submodule
and status to handle .git files in submodules).

On Windows, we have been lazy and had not implemented support for this
feature, yet. This fixes the shortcoming.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -618,6 +618,7 @@ static int env_compare(const void *a, const void *b)
 }
 
 static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
+			      const char *dir,
 			      int prepend_cmd, int fhin, int fhout, int fherr)
 {
 	STARTUPINFO si;
@@ -697,7 +698,7 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
 
 	memset(&pi, 0, sizeof(pi));
 	ret = CreateProcess(cmd, args.buf, NULL, NULL, TRUE, flags,
-		env ? envblk.buf : NULL, NULL, &si, &pi);
+		env ? envblk.buf : NULL, dir, &si, &pi);
 
 	if (env)
 		strbuf_release(&envblk);
@@ -714,10 +715,11 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
 static pid_t mingw_spawnve(const char *cmd, const char **argv, char **env,
 			   int prepend_cmd)
 {
-	return mingw_spawnve_fd(cmd, argv, env, prepend_cmd, 0, 1, 2);
+	return mingw_spawnve_fd(cmd, argv, env, NULL, prepend_cmd, 0, 1, 2);
 }
 
 pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **env,
+		     const char *dir,
 		     int fhin, int fhout, int fherr)
 {
 	pid_t pid;
@@ -740,14 +742,14 @@ pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **env,
 				pid = -1;
 			}
 			else {
-				pid = mingw_spawnve_fd(iprog, argv, env, 1,
+				pid = mingw_spawnve_fd(iprog, argv, env, dir, 1,
 						       fhin, fhout, fherr);
 				free(iprog);
 			}
 			argv[0] = argv0;
 		}
 		else
-			pid = mingw_spawnve_fd(prog, argv, env, 0,
+			pid = mingw_spawnve_fd(prog, argv, env, dir, 0,
 					       fhin, fhout, fherr);
 		free(prog);
 	}

compat/mingw.h

@@ -223,6 +223,7 @@ int mingw_utime(const char *file_name, const struct utimbuf *times);
 #define utime mingw_utime
 
 pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **env,
+		     const char *dir,
 		     int fhin, int fhout, int fherr);
 void mingw_execvp(const char *cmd, char *const *argv);
 #define execvp mingw_execvp

run-command.c

@@ -335,8 +335,6 @@ fail_pipe:
 	else if (cmd->out > 1)
 		fhout = dup(cmd->out);
 
-	if (cmd->dir)
-		die("chdir in start_command() not implemented");
 	if (cmd->env)
 		env = make_augmented_environ(cmd->env);
 
@@ -346,7 +344,7 @@ fail_pipe:
 		cmd->argv = prepare_shell_cmd(cmd->argv);
 	}
 
-	cmd->pid = mingw_spawnvpe(cmd->argv[0], cmd->argv, env,
+	cmd->pid = mingw_spawnvpe(cmd->argv[0], cmd->argv, env, cmd->dir,
 				  fhin, fhout, fherr);
 	failed_errno = errno;
 	if (cmd->pid < 0 && (!cmd->silent_exec_failure || errno != ENOENT))