bug#41852: 27.0.50; text-scale commands don't scale header of tabulated-list-mode

[Stefan Kangas <stefan@marxist.se>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> > Yes.  Except that now I'm asking whether we need to obsolete the
>> > variable.  is that just because of the name?
>>
>> I guess we could re-use the old name if we really want to.  But it would
>> still be a breaking change, since this is now a list instead of a single
>> value.
>
> That's also easy to handle in a compatible way, right?

OK, here's what I propose.  I still suggest to make the old name into an
obsolete alias in order to mark it as internal, please let me know if
this is acceptable.

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From 419fe81ab759823d43204d706d1e05df4b0e7052 Mon Sep 17 00:00:00 2001
From: Stefan Kangas <stefan@marxist.se>
Date: Thu, 29 Oct 2020 18:27:56 +0100
Subject: [PATCH] Make text-scale-mode optionally adjust header line face

* lisp/face-remap.el (text-scale-remap-header-line-face): New buffer
local variable.
(text-scale-mode): Also adjust header-line face if above new
variable is non-nil.
(face-remap--clear-remappings, face-remap--remap-face): New
functions.
(text-scale-mode--remappings): New variable.
(text-scale-mode-remapping): Make into obsolete variable alias for
above new variable.
* lisp/emacs-lisp/tabulated-list.el (tabulated-list-mode): Use
text-scale-remap-header-line-face.
---
 etc/NEWS                          | 15 +++++++++
 lisp/emacs-lisp/tabulated-list.el |  1 +
 lisp/face-remap.el                | 51 +++++++++++++++++++++++++------
 3 files changed, 57 insertions(+), 10 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 4b1272d18b..f514133680 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1368,6 +1368,21 @@ mouse now pops up a TTY menu by default instead of running the command
 'tmm-menubar'.  To restore the old behavior, set the variable
 'tty-menu-open-use-tmm' to non-nil.
 
+** text-scale-mode
+
+---
+*** text-scale-mode can now adjust font size of the 'header-line' face.
+When the new buffer local variable 'text-scale-mode-header-line' is
+non-nil, 'text-scale-adjust' (bound to 'C-x C-+' and 'C-x C--' by
+default) will also change the text height of the 'header-line' face.
+This will also affect any face that inherits from it.
+
+This feature is intended for use by Emacs Lisp package authors in
+major modes that arrange their display in tabular form below the
+header-line.  It is enabled in 'tabulated-list-mode' and its derived
+modes (such as the modes used by 'list-packages', 'list-buffers' and
+'bookmark-bmenu-list').
+
 ** xwidget-webkit mode
 
 *** New xwidget commands.
diff --git a/lisp/emacs-lisp/tabulated-list.el b/lisp/emacs-lisp/tabulated-list.el
index b13f609f88..18b48edc4f 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -761,6 +761,7 @@ tabulated-list-mode
   (setq-local revert-buffer-function #'tabulated-list-revert)
   (setq-local glyphless-char-display
               (tabulated-list-make-glyphless-char-display-table))
+  (setq-local text-scale-remap-header-line-face t)
   ;; Avoid messing up the entries' display just because the first
   ;; column of the first entry happens to begin with a R2L letter.
   (setq bidi-paragraph-direction 'left-to-right)
diff --git a/lisp/face-remap.el b/lisp/face-remap.el
index 028269a4b0..e61fa4cb4e 100644
--- a/lisp/face-remap.el
+++ b/lisp/face-remap.el
@@ -219,7 +219,11 @@ text-scale-mode-step
 
 ;; current remapping cookie for text-scale-mode
 (defvar text-scale-mode-remapping nil)
-(make-variable-buffer-local 'text-scale-mode-remapping)
+(make-obsolete-variable 'text-scale-mode-remapping
+                        'text-scale-mode--remappings "28.1")
+
+(defvar text-scale-mode--remappings nil
+  "List of current remapping cookies for `text-scale-mode'.")
 
 ;; Lighter displayed for text-scale-mode in mode-line minor-mode list
 (defvar text-scale-mode-lighter "+0")
@@ -229,6 +233,32 @@ text-scale-mode-lighter
 (defvar text-scale-mode-amount 0)
 (make-variable-buffer-local 'text-scale-mode-amount)
 
+(defvar text-scale-remap-header-line-face nil
+  "If non-nil, also change font size of the `header-line' face.
+This will also affect any face that inherits from
+`header-line'.")
+(make-variable-buffer-local 'text-scale-header-line)
+
+(defun face-remap--clear-remappings ()
+  (dolist (remapping
+           ;; This is a bit messy to stay backwards compatible.
+           ;; In the future, this can be simplified to just use
+           ;; `text-scale-mode--remappings'.
+           (if (consp (car-safe text-scale-mode--remappings))
+               text-scale-mode--remappings
+             (cons text-scale-mode-remapping
+                   text-scale-mode--remappings)))
+    (face-remap-remove-relative remapping))
+  (setq text-scale-mode-remapping nil)  ; backwards-compatibility
+  (setq text-scale-mode--remappings nil))
+
+(defun face-remap--remap-face (sym)
+  (push (face-remap-add-relative sym
+                       :height
+                       (expt text-scale-mode-step
+                             text-scale-mode-amount))
+        text-scale-mode--remappings))
+
 (define-minor-mode text-scale-mode
   "Minor mode for displaying buffer text in a larger/smaller font.
 
@@ -240,19 +270,20 @@ text-scale-mode
 The `text-scale-increase', `text-scale-decrease', and
 `text-scale-set' functions may be used to interactively modify
 the variable `text-scale-mode-amount' (they also enable or
-disable `text-scale-mode' as necessary)."
+disable `text-scale-mode' as necessary).
+
+If `text-scale-remap-header-line-face' is non-nil, also change
+the font size of the `header-line' face (and any face that
+inherits from it)."
   :lighter (" " text-scale-mode-lighter)
-  (when text-scale-mode-remapping
-    (face-remap-remove-relative text-scale-mode-remapping))
+  (face-remap--clear-remappings)
   (setq text-scale-mode-lighter
 	(format (if (>= text-scale-mode-amount 0) "+%d" "%d")
 		text-scale-mode-amount))
-  (setq text-scale-mode-remapping
-	(and text-scale-mode
-	     (face-remap-add-relative 'default
-					  :height
-					  (expt text-scale-mode-step
-						text-scale-mode-amount))))
+  (when text-scale-mode
+    (face-remap--remap-face 'default)
+    (when text-scale-remap-header-line-face
+      (face-remap--remap-face 'header-line)))
   (force-window-update (current-buffer)))
 
 (defun text-scale-min-amount ()
-- 
2.28.0