Remote control: Allow matching tabs by index number in currently active OS Window

Fixes #3708

docs/changelog.rst

@@ -90,6 +90,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
   <https://github.com/be5invis/Iosevka>`_ font (requires Iosevka >= 7.0.4)
   (:iss:`297`)
 
+- Remote control: Allow matching tabs by index number in currently active OS
+  Window (:iss:`3708`)
+
 
 0.20.3 [2021-05-06]
 ----------------------

kitty/boss.py

@@ -299,6 +299,12 @@ class Boss:
                 if q:
                     found = True
                     yield q
+        elif field == 'index':
+            tm = self.active_tab_manager
+            if tm is not None and len(tm.tabs) > 0:
+                idx = (int(pat.pattern) + len(tm.tabs)) % len(tm.tabs)
+                found = True
+                yield tm.tabs[idx]
         if not found:
             tabs = {self.tab_for_window(w) for w in self.match_windows(match)}
             for q in tabs:

kitty/rc/base.py

@@ -90,13 +90,14 @@ MATCH_TAB_OPTION = '''\
 --match -m
 The tab to match. Match specifications are of the form:
 :italic:`field:regexp`. Where field can be one of:
-id, title, window_id, window_title, pid, cwd, env, cmdline.
+id, index, title, window_id, window_title, pid, cwd, env, cmdline.
 You can use the :italic:`ls` command to get a list of tabs. Note that for
-numeric fields such as id and pid the expression is interpreted as a number,
+numeric fields such as id, index and pid the expression is interpreted as a number,
 not a regular expression. When using title or id, first a matching tab is
 looked for and if not found a matching window is looked for, and the tab
 for that window is used. You can also use window_id and window_title to match
-the tab that contains the window with the specified id or title.
+the tab that contains the window with the specified id or title. The index number
+is used to match the nth tab in the currently active OS window.
 '''