Add a new variable `{num_window_groups}` for tab_title_template

See #3837

docs/changelog.rst

@@ -28,6 +28,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - macOS: Render colors in the sRGB colorspace to match other macOS terminal
   applications (:iss:`2249`)
 
+- Add a new variable ``{num_window_groups}`` for the :opt:`tab_title_template`
+  (:iss:`3837`)
+
 
 0.21.2 [2021-06-28]
 ----------------------

kitty/options/definition.py

@@ -941,8 +941,10 @@ A template to render the tab title. The default just renders the title. If you
 wish to include the tab-index as well, use something like: :code:`{index}:
 {title}`. Useful if you have shortcuts mapped for :code:`goto_tab N`. If you
 prefer to see the index as a superscript, use {sup.index}. In
-addition you can use :code:`{layout_name}` for the current layout name and
-:code:`{num_windows}` for the number of windows in the tab. Note that formatting
+addition you can use :code:`{layout_name}` for the current layout name,
+:code:`{num_windows}` for the number of windows in the tab and
+:code:`{num_window_groups}` for the number of window groups
+(not counting overlay windows) in the tab. Note that formatting
 is done by Python's string formatting machinery, so you can use, for instance,
 :code:`{layout_name[:2].upper()}` to show only the first two letters of the
 layout name, upper-cased. If you want to style the text, you can use styling

kitty/tab_bar.py

@@ -23,6 +23,7 @@ class TabBarData(NamedTuple):
     is_active: bool
     needs_attention: bool
     num_windows: int
+    num_window_groups: int
     layout_name: str
     has_activity_since_last_focus: bool
 
@@ -135,12 +136,14 @@ def draw_title(draw_data: DrawData, screen: Screen, tab: TabBarData, index: int)
             'index': index,
             'layout_name': tab.layout_name,
             'num_windows': tab.num_windows,
+            'num_window_groups': tab.num_window_groups,
             'title': tab.title,
         }
         eval_locals = {
             'index': index,
             'layout_name': tab.layout_name,
             'num_windows': tab.num_windows,
+            'num_window_groups': tab.num_window_groups,
             'title': tab.title,
             'fmt': Formatter,
             'sup': SupSub(data),

kitty/tabs.py

@@ -577,6 +577,10 @@ class Tab:  # {{{
     def __len__(self) -> int:
         return len(self.windows)
 
+    @property
+    def num_window_groups(self) -> int:
+        return self.windows.num_groups
+
     def __contains__(self, window: Window) -> bool:
         return window in self.windows
 
@@ -874,7 +878,7 @@ class TabManager:  # {{{
                     has_activity_since_last_focus = True
             ans.append(TabBarData(
                 title, t is at, needs_attention,
-                len(t), t.current_layout.name or '',
+                len(t), t.num_window_groups, t.current_layout.name or '',
                 has_activity_since_last_focus
             ))
         return ans