kitty @ ls: Show only environment variables that are different for each window, by default.

Makes the output much less noisy, and env vars that are common across
all windows are useless for selection/identification purposes.

docs/changelog.rst

@@ -46,6 +46,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 
 - Double clicking on empty tab bar area now opens a new tab (:iss:`3201`)
 
+- kitty @ ls: Show only environment variables that are different for each
+  window, by default.
+
 - When passing a directory or a non-executable file as the program to run to
   kitty opens it with the shell or by parsing the shebang, instead of just failing.
 

kitty/rc/ls.py

@@ -3,7 +3,7 @@
 # License: GPLv3 Copyright: 2020, Kovid Goyal <kovid at kovidgoyal.net>
 
 import json
-from typing import Any, Dict, Optional
+from typing import Any, Dict, List, Optional, Set, Tuple
 
 from kitty.constants import appname
 
@@ -15,7 +15,7 @@ from .base import (
 
 class LS(RemoteCommand):
     '''
-    No payload
+    all_env_vars: Whether to send all environment variables for ever window rather than just differing ones
     '''
 
     short_desc = 'List all tabs/windows'
@@ -28,10 +28,16 @@ class LS(RemoteCommand):
         ' running the command inside a kitty window, that window can be identified by the :italic:`is_self` parameter.\n\n'
         'You can use these criteria to select windows/tabs for the other commands.'
     )
+    options_spec = '''\
+--all-env-vars
+type=bool-set
+Show all environment variables in output not just differing ones.
+'''
+
     argspec = ''
 
     def message_to_kitty(self, global_opts: RCOptions, opts: Any, args: ArgsType) -> PayloadType:
-        pass
+        return {'all_env_vars': opts.all_env_vars}
 
     def response_from_kitty(self, boss: Boss, window: Optional[Window], payload_get: PayloadGetType) -> ResponseType:
 
@@ -47,6 +53,24 @@ class LS(RemoteCommand):
         finally:
             if window is not None:
                 window.serialize_callback = orig_callback
+        if not payload_get('all_env_vars'):
+            all_env_blocks: List[Dict[str, str]] = []
+            common_env_vars: Set[Tuple[str, str]] = set()
+            for osw in data:
+                for tab in osw.get('tabs', ()):
+                    for w in tab.get('windows', ()):
+                        env: Dict[str, str] = w.get('env', {})
+                        frozen_env = set(env.items())
+                        if all_env_blocks:
+                            common_env_vars &= frozen_env
+                        else:
+                            common_env_vars = frozen_env
+                        all_env_blocks.append(env)
+            if common_env_vars and len(all_env_blocks) > 1:
+                remove_env_vars = {k for k, v in common_env_vars}
+                for env in all_env_blocks:
+                    for r in remove_env_vars:
+                        env.pop(r, None)
         return json.dumps(data, indent=2, sort_keys=True)