bug#47234: 28.0.50; frame-inner-height fails without window system on tab-bar-height

[Basil L. Contovounesios]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: "Basil L. Contovounesios" <contovob@tcd.ie>
>> Date: Thu, 18 Mar 2021 13:41:04 +0000
>> Cc: juri linkov <juri@linkov.net>
>> 
>> The obvious band-aid is to check (fboundp 'tab-bar-height) in
>> frame-inner-height, but shouldn't we count 1 line when tab-bar-mode is
>> enabled even --without-x?  IOW, can/should tab-bar-height or similar be
>> defined regardless of HAVE_WINDOW_SYSTEM?  What's TRT here?
>
> TRT is to teach Emacs to return the tab-bar height on TTY frames as
> well.  But I don't think defining tab-bar-height on TTY frames is the
> right way: the tab-bar is always 1 line high on those frames, so we
> could simply use that hardcoded value instead of signaling an error, I
> think.

I'm not familiar with the tab bar, but I get the impression it's not
that simple.  IIUC no lines should be subtracted if tab-bar-mode is off,
and even if it's on, the tab bar can be hidden subject to tab-bar-show.
That's why I was wondering whether this logic can/should be packed into
a single place (whether Ftab_bar_height or other I don't know).

Is the following close to TRT?

diff --git a/lisp/frame.el b/lisp/frame.el
index b5a8e0ed72..f4b8f1c418 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -1370,7 +1370,9 @@ frame-inner-height
 FRAME defaults to the selected frame."
   (setq frame (window-normalize-frame frame))
   (- (frame-native-height frame)
-     (tab-bar-height frame t)
+     (if (fboundp 'tab-bar-height)
+         (tab-bar-height frame t)
+       (frame-parameter frame 'tab-bar-lines))
      (* 2 (frame-internal-border-width frame))))
 
 (defun frame-outer-width (&optional frame)

Thanks,

-- 
Basil