Allow the user to supply a custom Python function to draw tab bar

docs/changelog.rst

@@ -7,6 +7,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 0.23.2 [future]
 ----------------------
 
+- Allow the user to supply a custom Python function to draw tab bar. See
+  :option:`tab_bar_style`
+
 - Fix a regression that caused :option:`kitty --title` to not work when
   opening new OS windows using :option:`kitty --single-instance` (:iss:`3893`)
 

kitty/options/definition.py

@@ -884,7 +884,7 @@ tab.
 
 
 opt('tab_bar_style', 'fade',
-    choices=('fade', 'hidden', 'powerline', 'separator', 'slant'), ctype='!tab_bar_style',
+    choices=('fade', 'hidden', 'powerline', 'separator', 'slant', 'custom'), ctype='!tab_bar_style',
     long_text='''
 The tab bar style, can be one of:
 
@@ -896,6 +896,10 @@ The tab bar style, can be one of:
     Tabs are separated by a configurable separator (see :opt:`tab_separator`)
 :code:`powerline`
     Tabs are shown as a continuous line with "fancy" separators (see :opt:`tab_powerline_style`)
+:code:`custom`
+    A user-supplied Python function called draw_tab is loaded from the file :file:`tab_bar.py`
+    in the kitty config directory. For examples of how to write such a function see the functions
+    named :code:`draw_tab_with_*` in tab_bar.py in the kitty source code.
 :code:`hidden`
     The tab bar is hidden. If you use this, you might want to create a mapping
     for the :ref:`action-select_tab` action which presents you with a list

kitty/options/parse.py

@@ -1173,7 +1173,7 @@ class Parser:
             raise ValueError(f"The value {val} is not a valid choice for tab_bar_style")
         ans["tab_bar_style"] = val
 
-    choices_for_tab_bar_style = frozenset(('fade', 'hidden', 'powerline', 'separator', 'slant'))
+    choices_for_tab_bar_style = frozenset(('fade', 'hidden', 'powerline', 'separator', 'slant', 'custom'))
 
     def tab_fade(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['tab_fade'] = tab_fade(val)

kitty/options/types.py

@@ -23,7 +23,7 @@ if typing.TYPE_CHECKING:
     choices_for_pointer_shape_when_dragging = typing.Literal['arrow', 'beam', 'hand']
     choices_for_pointer_shape_when_grabbed = typing.Literal['arrow', 'beam', 'hand']
     choices_for_strip_trailing_spaces = typing.Literal['always', 'never', 'smart']
-    choices_for_tab_bar_style = typing.Literal['fade', 'hidden', 'powerline', 'separator', 'slant']
+    choices_for_tab_bar_style = typing.Literal['fade', 'hidden', 'powerline', 'separator', 'slant', 'custom']
     choices_for_tab_powerline_style = typing.Literal['angled', 'round', 'slanted']
     choices_for_tab_switch_strategy = typing.Literal['last', 'left', 'previous', 'right']
 else:

kitty/tab_bar.py

@@ -2,10 +2,14 @@
 # vim:fileencoding=utf-8
 # License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
 
-from functools import lru_cache
+import os
-from typing import Any, Dict, List, NamedTuple, Optional, Sequence, Tuple
+from functools import lru_cache, wraps
+from typing import (
+    Any, Callable, Dict, List, NamedTuple, Optional, Sequence, Tuple
+)
 
 from .config import build_ansi_color_table
+from .constants import config_dir
 from .fast_data_types import (
     DECAWM, Screen, cell_size_for_window, get_options, pt_to_px,
     set_tab_bar_render_data, viewport_for_window
@@ -13,7 +17,7 @@ from .fast_data_types import (
 from .layout.base import Rect
 from .rgb import Color, alpha_blend, color_as_sgr, color_from_int, to_color
 from .types import WindowGeometry, run_once
-from .typing import PowerlineStyle, EdgeLiteral
+from .typing import EdgeLiteral, PowerlineStyle
 from .utils import color_as_int, log_error
 from .window import calculate_gl_geometry
 
@@ -165,6 +169,9 @@ def draw_title(draw_data: DrawData, screen: Screen, tab: TabBarData, index: int)
         screen.draw(title)
 
 
+DrawTabFunc = Callable[[DrawData, Screen, TabBarData, int, int, int, bool], int]
+
+
 def draw_tab_with_slant(draw_data: DrawData, screen: Screen, tab: TabBarData, before: int, max_title_length: int, index: int, is_last: bool) -> int:
     left_sep, right_sep = ('', '') if draw_data.tab_bar_edge == 'top' else ('', '')
     tab_bg = as_rgb(color_as_int(draw_data.active_bg if tab.is_active else draw_data.inactive_bg))
@@ -325,6 +332,29 @@ def draw_tab_with_powerline(draw_data: DrawData, screen: Screen, tab: TabBarData
     return end
 
 
+@run_once
+def load_custom_draw_tab() -> DrawTabFunc:
+    import runpy
+    import traceback
+    try:
+        m = runpy.run_path(os.path.join(config_dir, 'tab_bar.py'))
+        func: DrawTabFunc = m['draw_tab']
+    except Exception as e:
+        traceback.print_exc()
+        log_error(f'Failed to load custom draw_tab function with error: {e}')
+        return draw_tab_with_fade
+
+    @wraps(func)
+    def draw_tab(draw_data: DrawData, screen: Screen, tab: TabBarData, before: int, max_title_length: int, index: int, is_last: bool) -> int:
+        try:
+            return func(draw_data, screen, tab, before, max_title_length, index, is_last)
+        except Exception as e:
+            log_error(f'Custom draw tab function failed with error: {e}')
+            return draw_tab_with_fade(draw_data, screen, tab, before, max_title_length, index, is_last)
+
+    return draw_tab
+
+
 class TabBar:
 
     def __init__(self, os_window_id: int):
@@ -374,12 +404,15 @@ class TabBar:
             opts.tab_powerline_style,
             'top' if opts.tab_bar_edge == 1 else 'bottom'
         )
-        if opts.tab_bar_style == 'separator':
+        ts = opts.tab_bar_style
-            self.draw_func = draw_tab_with_separator
+        if ts == 'separator':
-        elif opts.tab_bar_style == 'powerline':
+            self.draw_func: DrawTabFunc = draw_tab_with_separator
+        elif ts == 'powerline':
             self.draw_func = draw_tab_with_powerline
-        elif opts.tab_bar_style == 'slant':
+        elif ts == 'slant':
             self.draw_func = draw_tab_with_slant
+        elif ts == 'custom':
+            self.draw_func = load_custom_draw_tab()
         else:
             self.draw_func = draw_tab_with_fade