A facility to easily have child programs print to kitty stdout

Works better than the kitty-print DCS escape code as that tends to get
interleaved with other writes to the tty since the loop infrastructure
writes in a separate I/O thread.

kitty/options/definition.py

@@ -3082,6 +3082,16 @@ work. Changing this option by reloading the config will only affect newly
 created windows.
 '''
     )
+
+opt('forward_stdio', 'no', option_type='to_bool', long_text='''
+Forward STDOUT and STDERR of the kitty process to child processes
+as file descriptors 3 and 4. This is useful for debugging as it
+allows child processes to print to kitty's STDOUT directly. For example,
+:code:`echo hello world >&3` in a shell will print to the parent kitty's
+STDOUT. When enabled, this also sets the :code:`KITTY_STDIO_FORWARDED=3`
+environment variable so child processes know about the forwarding.
+''')
+
 egr()  # }}}
 
 

kitty/options/parse.py

@@ -990,6 +990,9 @@ class Parser:
     def foreground(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['foreground'] = to_color(val)
 
+    def forward_stdio(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
+        ans['forward_stdio'] = to_bool(val)
+
     def hide_window_decorations(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['hide_window_decorations'] = hide_window_decorations(val)
 

kitty/options/types.py

@@ -365,6 +365,7 @@ option_names = (  # {{{
  'font_size',
  'force_ltr',
  'foreground',
+ 'forward_stdio',
  'hide_window_decorations',
  'inactive_border_color',
  'inactive_tab_background',
@@ -526,6 +527,7 @@ class Options:
     font_size: float = 11.0
     force_ltr: bool = False
     foreground: Color = Color(221, 221, 221)
+    forward_stdio: bool = False
     hide_window_decorations: int = 0
     inactive_border_color: Color = Color(204, 204, 204)
     inactive_tab_background: Color = Color(153, 153, 153)