bug#42052: 28.0.50; tab-bar-mode should be frame-local

[James N. V. Cash <james.nvc@gmail.com>]

James N. V. Cash <james.nvc@gmail.com> writes:

> Juri Linkov <juri@linkov.net> writes:
>
>>> When setting tab-bar-show to `1`, I expect the tab bar to only show if
>>> there is more than one tab in the frame.
>>>
>> If someone will point out an example of frame-local modes,
>> this could help in implementing the same for tab-bar-mode.
>
> Looking at how the tab-bar-mode currently works, the thing that seems
> simplest to me would be to change the various functions that
> conditionally turn tab-bar-mode on/off (e.g. in tab-bar-new-tab-to)
> to have an additional check if (natnump tab-bar-show), in which case
> instead of calling (tab-bar-mode 1) or -1, setting the frame parameter
> tab-bar-lines for that particular frame to be 1 or 0, as appropriate.
>
> The wrinkle would be, I suppose, having to remove all the frame-local
> settings if tab-bar-show changes, but presumably that wouldn't be
> happening too often.
>
> A frame-local toggling of the tab bar could work the same way.
>
> If that makes sense (i.e. having the setting be frame local only when
> tab-bar-show is 1), I can try submitting a patch later today.

Here's a simple patch I made that seems to act more like I expect

--- /home/james/src/emacs/lisp/tab-bar.el 2020-06-20 10:16:57.177037735 -0400
+++ tab-bar.el  2020-06-28 15:40:38.711147160 -0400
@@ -799,11 +799,16 @@
       (run-hook-with-args 'tab-bar-tab-post-open-functions
                           (nth to-index tabs)))

-    (when (and (not tab-bar-mode)
-               (or (eq tab-bar-show t)
-                   (and (natnump tab-bar-show)
-                        (> (length tabs) tab-bar-show))))
+    (cond
+     (tab-bar-mode)
+     ((eq tab-bar-show t)
       (tab-bar-mode 1))
+     ((and (natnump tab-bar-show)
+           (> (length tabs) tab-bar-show)
+           (zerop (frame-parameter nil 'tab-bar-lines)))
+      (progn
+        (message "show")
+        (set-frame-parameter nil 'tab-bar-lines 1))))

     (force-mode-line-update)
     (unless tab-bar-mode
@@ -936,10 +941,10 @@
                 tab-bar-closed-tabs)
           (set-frame-parameter nil 'tabs (delq close-tab tabs)))

-        (when (and tab-bar-mode
+        (when (and (not (zerop (frame-parameter nil 'tab-bar-lines)))
                    (and (natnump tab-bar-show)
                         (<= (length tabs) tab-bar-show)))
-          (tab-bar-mode -1))
+          (set-frame-parameter nil 'tab-bar-lines 0))

         (force-mode-line-update)
         (unless tab-bar-mode
@@ -975,10 +980,12 @@
           (run-hook-with-args 'tab-bar-tab-pre-close-functions (nth index tabs) nil)))
       (set-frame-parameter nil 'tabs (list (nth current-index tabs)))

-      (when (and tab-bar-mode
-                 (and (natnump tab-bar-show)
-                      (<= 1 tab-bar-show)))
-        (tab-bar-mode -1))
+      (when (and (not (zerop (frame-parameter nil 'tab-bar-lines)))
+                   (and (natnump tab-bar-show)
+                        (<= (length tabs) tab-bar-show)))
+          (modify-frame-parameters
+           nil
+           (assq-delete-all 'tab-bar-lines (frame-parameters nil))))

       (force-mode-line-update)
       (unless tab-bar-mode