mingw: demonstrate that all file handles are inherited by child processes

When spawning child processes, we really should be careful which file
handles we let them inherit.

This is doubly important on Windows, where we cannot rename, delete, or
modify files if there is still a file handle open.

Sadly, we have to guard this test inside #ifdef WIN32: we need to use
the value of the HANDLE directly, and that concept does not exist on
Linux/Unix.

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

Author: dscho

t/helper/test-run-command.c

@@ -188,13 +188,58 @@ static int testsuite(int argc, const char **argv)
 	return !!ret;
 }
 
+static int inherit_handle(const char *argv0)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	char path[PATH_MAX];
+	int tmp;
+
+	/* First, open an inheritable handle */
+	sprintf(path, "out-XXXXXX");
+	tmp = xmkstemp(path);
+
+	argv_array_pushl(&cp.args, argv0, "inherited-handle-child", NULL);
+	cp.in = -1;
+	cp.no_stdout = cp.no_stderr = 1;
+	if (start_command(&cp) < 0)
+		die("Could not start child process");
+
+	/* Then close it, and try to delete it. */
+	close(tmp);
+	if (unlink(path))
+		die("Could not delete '%s'", path);
+
+	if (close(cp.in) < 0 || finish_command(&cp) < 0)
+		die("Child did not finish");
+
+	return 0;
+}
+
+static int inherit_handle_child(void)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	if (strbuf_read(&buf, 0, 0) < 0)
+		die("Could not read stdin");
+	printf("Received %s\n", buf.buf);
+	strbuf_release(&buf);
+
+	return 0;
+}
+
 int cmd_main(int argc, const char **argv)
 {
 	struct child_process proc = CHILD_PROCESS_INIT;
 	int jobs;
 
 	if (argc > 1 && !strcmp(argv[1], "testsuite"))
 		exit(testsuite(argc - 1, argv + 1));
+
+	if (!strcmp(argv[1], "inherited-handle"))
+		exit(inherit_handle(argv[0]));
+	if (!strcmp(argv[1], "inherited-handle-child"))
+		exit(inherit_handle_child());
+
 	if (argc < 3)
 		return 1;
 	while (!strcmp(argv[1], "env")) {

t/t0061-run-command.sh

@@ -13,6 +13,10 @@ cat >hello-script <<-EOF
 EOF
 >empty
 
+test_expect_failure MINGW 'subprocess inherits only std handles' '
+	test-run-command inherited-handle
+'
+
 test_expect_success 'start_command reports ENOENT' '
 	test-run-command start-command-ENOENT ./does-not-exist
 '