Eureka! Figured out why libedit is breaking in prewarm on macOS via launchd

The prewarm zygote imports the world. shell.py had a top level import
for readline. Which means readline was being imported pre-fork. And of
course as is traditional with Apple libedit is not fork safe. Probably
because it initializes its internal IO routines based on the stdio
handles at time of import which are the handles kitty gets from launchd

kittens/ask/main.py

@@ -476,15 +476,6 @@ def main(args: List[str]) -> Response:
         loop.loop(phandler)
         return {'items': items, 'response': phandler.response}
 
-    rd = getattr(sys, 'kitty_run_data')
-    if 'prewarmed' in rd and 'launched_by_launch_services' in rd:
-        # bloody libedit doesnt work in the prewarmed process run from launch
-        # services for reasons I really dont care enough to investigate
-        loop = Loop()
-        phandler = Password(cli_opts, prompt, is_password=False, initial_text=cli_opts.default or '')
-        loop.loop(phandler)
-        return {'items': items, 'response': phandler.response}
-
     import readline as rl
     readline = rl
     from kitty.shell import init_readline

kittens/tui/path_completer.py

@@ -3,7 +3,6 @@
 
 
 import os
-import sys
 from typing import Any, Callable, Dict, Generator, Optional, Sequence, Tuple
 
 from kitty.fast_data_types import wcswidth
@@ -149,9 +148,6 @@ def input(self) -> str:
 
 
 def get_path(prompt: str = '> ') -> str:
-    rd = getattr(sys, 'kitty_run_data')
-    if 'prewarmed' in rd and 'launched_by_launch_services' in rd:
-        return input(prompt)
     return PathCompleter(prompt).input()
 
 

kitty/shell.py

@@ -2,7 +2,6 @@
 # License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
 
 import os
-import readline
 import shlex
 import sys
 import traceback
@@ -39,6 +38,7 @@ def match_commands() -> Tuple[str, ...]:
 
 @run_once
 def init_readline() -> None:
+    import readline
     global is_libedit
     with suppress(OSError):
         readline.read_init_file()
@@ -90,6 +90,7 @@ def __init__(self) -> None:
         self.history_path = os.path.join(ddir, 'shell.history')
 
     def complete(self, text: str, state: int) -> Optional[str]:
+        import readline
         if state == 0:
             line = readline.get_line_buffer()
             cmdline = shlex.split(line)
@@ -102,6 +103,7 @@ def complete(self, text: str, state: int) -> Optional[str]:
         return None
 
     def __enter__(self) -> 'Completer':
+        import readline
         with suppress(Exception):
             readline.read_history_file(self.history_path)
         readline.set_completer(self.complete)
@@ -110,6 +112,7 @@ def __enter__(self) -> 'Completer':
         return self
 
     def __exit__(self, *a: Any) -> None:
+        import readline
         readline.write_history_file(self.history_path)