From 04f2037907b8e9335750eafbcaa587e33a92af0c Mon Sep 17 00:00:00 2001
From: Stefan Kangas <stefan@marxist.se>
Date: Mon, 19 Oct 2020 01:03:53 +0200
Subject: [PATCH 1/2] 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 obsolete.
---
 etc/NEWS           | 15 +++++++++++++++
 lisp/face-remap.el | 42 ++++++++++++++++++++++++++++++++----------
 2 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 390cccbff3..b80bcf397c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1314,6 +1314,21 @@ to 'tab-bar-new-tab-choice' for new tabs to show the bookmark list.
 'gomoku-move-sw' and 'gomoku-move-ne' now work correctly, and
 horizontal movements now stop at the edge of the board.
 
+** 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/face-remap.el b/lisp/face-remap.el
index 028269a4b0..4d7be7d65a 100644
--- a/lisp/face-remap.el
+++ b/lisp/face-remap.el
@@ -219,7 +219,10 @@ 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 "no longer used." "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 +232,24 @@ 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 text-scale-mode--remappings)
+    (face-remap-remove-relative remapping))
+  (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 +261,20 @@ 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