mingw: explicitly specify with which cmd to prefix the cmdline

The main idea of this patch is that even if we have to look up the
absolute path of the script, if only the basename was specified as
argv[0], then we should use that basename on the command line, too, not
the absolute path.

This patch will also help with the upcoming patch where we automatically
substitute "sh ..." by "busybox sh ..." if "sh" is not in the PATH but
"busybox" is: we will do that by substituting the actual executable, but
still keep prepending "sh" to the command line.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/mingw.c

@@ -1838,8 +1838,8 @@ static int is_msys2_sh(const char *cmd)
 }
 
 static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaenv,
-			      const char *dir,
-			      int prepend_cmd, int fhin, int fhout, int fherr)
+			      const char *dir, const char *prepend_cmd,
+			      int fhin, int fhout, int fherr)
 {
 	static int restrict_handle_inheritance = -1;
 	STARTUPINFOEXW si;
@@ -1930,9 +1930,9 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	/* concatenate argv, quoting args as we go */
 	strbuf_init(&args, 0);
 	if (prepend_cmd) {
-		char *quoted = (char *)quote_arg(cmd);
+		char *quoted = (char *)quote_arg(prepend_cmd);
 		strbuf_addstr(&args, quoted);
-		if (quoted != cmd)
+		if (quoted != prepend_cmd)
 			free(quoted);
 	}
 	for (; *argv; argv++) {
@@ -2091,7 +2091,8 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	return (pid_t)pi.dwProcessId;
 }
 
-static pid_t mingw_spawnv(const char *cmd, const char **argv, int prepend_cmd)
+static pid_t mingw_spawnv(const char *cmd, const char **argv,
+			  const char *prepend_cmd)
 {
 	return mingw_spawnve_fd(cmd, argv, NULL, NULL, prepend_cmd, 0, 1, 2);
 }
@@ -2119,14 +2120,14 @@ pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **deltaenv,
 				pid = -1;
 			}
 			else {
-				pid = mingw_spawnve_fd(iprog, argv, deltaenv, dir, 1,
+				pid = mingw_spawnve_fd(iprog, argv, deltaenv, dir, interpr,
 						       fhin, fhout, fherr);
 				free(iprog);
 			}
 			argv[0] = argv0;
 		}
 		else
-			pid = mingw_spawnve_fd(prog, argv, deltaenv, dir, 0,
+			pid = mingw_spawnve_fd(prog, argv, deltaenv, dir, NULL,
 					       fhin, fhout, fherr);
 		free(prog);
 	}
@@ -2154,7 +2155,7 @@ static int try_shell_exec(const char *cmd, char *const *argv)
 		argv2[0] = (char *)cmd;	/* full path to the script file */
 		COPY_ARRAY(&argv2[1], &argv[1], argc);
 		exec_id = trace2_exec(prog, argv2);
-		pid = mingw_spawnv(prog, argv2, 1);
+		pid = mingw_spawnv(prog, argv2, interpr);
 		if (pid >= 0) {
 			int status;
 			if (waitpid(pid, &status, 0) < 0)
@@ -2178,7 +2179,7 @@ int mingw_execv(const char *cmd, char *const *argv)
 		int exec_id;
 
 		exec_id = trace2_exec(cmd, (const char **)argv);
-		pid = mingw_spawnv(cmd, (const char **)argv, 0);
+		pid = mingw_spawnv(cmd, (const char **)argv, NULL);
 		if (pid < 0) {
 			trace2_exec_result(exec_id, -1);
 			return -1;