Fix forward_stdio not working on macOS

Author: kovidgoyal

kitty/child.py

@@ -319,12 +319,14 @@ def fork(self) -> Optional[int]:
             if ksi == 'invalid':
                 ksi = 'enabled'
             argv = [kitten_exe(), 'run-shell', '--shell', shlex.join(argv), '--shell-integration', ksi]
-            if is_macos:
+            if is_macos and not self.pass_fds and not opts.forward_stdio:
                 # In addition for getlogin() to work we need to run the shell
                 # via the /usr/bin/login wrapper, sigh.
                 # And login on macOS looks for .hushlogin in CWD instead of
                 # HOME, bloody idiotic so we cant cwd when running it.
                 # https://github.com/kovidgoyal/kitty/issues/6511
+                # login closes inherited file descriptors so dont use it when
+                # forward_stdio or pass_fds are used.
                 import pwd
                 user = pwd.getpwuid(os.geteuid()).pw_name
                 if cwd:

kitty/options/definition.py

@@ -3316,7 +3316,9 @@
 allows child processes to print to kitty's STDOUT directly. For example,
 :code:`echo hello world >&$KITTY_STDIO_FORWARDED` in a shell will print
 to the parent kitty's STDOUT. Sets the :code:`KITTY_STDIO_FORWARDED=fdnum`
-environment variable so child processes know about the forwarding.
+environment variable so child processes know about the forwarding. Note that
+on macOS this prevents the shell from being run via the login utility so getlogin()
+will not work in programs run in this session.
 ''')
 
 opt('+menu_map', '',