Fix the width of margins for icons in outline-minor-mode (bug#59719)

* doc/lispref/display.texi (Icons): Add :width spec.

* lisp/emacs-lisp/icons.el (icons--create): Handle :width as well.

* lisp/outline.el (outline--margin-width, outline-margin-width):
New variables.
(outline-open-in-margins, outline-close-in-margins)
(outline-close-rtl-in-margins): Don't inherit from parents.
Use `:width font' instead of `:height 10'.
(outline-minor-mode): Calculate the number of columns for margins
to fit the icons.

3 files changed, 41 insertions, 10 deletions

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 60955fd3195..9d929950a7e 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -7124,6 +7124,12 @@ This is only valid for @code{image} icons, and can be either a number
 (which specifies the height in pixels), or the symbol @code{line},
 which will use the default line height in the currently selected
 window.
+
+@item :width
+This is only valid for @code{image} icons, and can be either a number
+(which specifies the width in pixels), or the symbol @code{font},
+which will use the width in pixels of the current buffer’s default
+face font.
 @end table
 
 @var{doc} should be a doc string.
diff --git a/lisp/emacs-lisp/icons.el b/lisp/emacs-lisp/icons.el
index 86c44830308..8ba6d97ea00 100644
--- a/lisp/emacs-lisp/icons.el
+++ b/lisp/emacs-lisp/icons.el
@@ -202,6 +202,10 @@ present if the icon is represented by an image."
                       (list :height (if (eq height 'line)
                                         (window-default-line-height)
                                       height)))
+                  (if-let ((width (plist-get keywords :width)))
+                      (list :width (if (eq width 'font)
+                                       (default-font-width)
+                                     width)))
                   '(:scale 1)
                   (if-let ((rotation (plist-get keywords :rotation)))
                       (list :rotation rotation))
diff --git a/lisp/outline.el b/lisp/outline.el
index 86ac19aa415..2c3f9798ec4 100644
--- a/lisp/outline.el
+++ b/lisp/outline.el
@@ -318,6 +318,12 @@ don't modify the buffer."
 (defvar-local outline--use-rtl nil
   "Non-nil when direction of clickable buttons is right-to-left.")
 
+(defvar-local outline--margin-width nil
+  "Current margin width.")
+
+(defvar-local outline-margin-width nil
+  "Default margin width.")
+
 (define-icon outline-open nil
   '((image "outline-open.svg" "outline-open.pbm" :height (0.8 . em))
     (emoji "🔽")
@@ -344,24 +350,24 @@ don't modify the buffer."
   "Right-to-left icon used for buttons in closed outline sections."
   :version "29.1")
 
-(define-icon outline-open-in-margins outline-open
-  '((image "outline-open.svg" "outline-open.pbm" :height 10)
+(define-icon outline-open-in-margins nil
+  '((image "outline-open.svg" "outline-open.pbm" :width font)
     (emoji "🔽")
     (symbol "▼")
     (text "v"))
   "Icon used for buttons for opened sections in margins."
   :version "29.1")
 
-(define-icon outline-close-in-margins outline-close
-  '((image "outline-open.svg" "outline-open.pbm" :height 10 :rotation -90)
+(define-icon outline-close-in-margins nil
+  '((image "outline-open.svg" "outline-open.pbm" :width font :rotation -90)
     (emoji "▶️")
     (symbol "▶")
     (text ">"))
   "Icon used for buttons for closed sections in margins."
   :version "29.1")
 
-(define-icon outline-close-rtl-in-margins outline-close-rtl
-  '((image "outline-open.svg" "outline-open.pbm" :height 10 :rotation 90)
+(define-icon outline-close-rtl-in-margins nil
+  '((image "outline-open.svg" "outline-open.pbm" :width font :rotation 90)
     (emoji "◀️")
     (symbol "◀")
     (text "<"))
@@ -528,9 +534,22 @@ See the command `outline-mode' for more information on this mode."
           (when (and (eq outline-minor-mode-use-buttons 'in-margins)
                      (> 1 (if outline--use-rtl right-margin-width
                             left-margin-width)))
+            (setq outline--margin-width
+                  (or outline-margin-width
+                      (ceiling
+                       (/ (seq-max
+                           (seq-map #'string-pixel-width
+                                    (seq-map #'icon-string
+                                             `(outline-open-in-margins
+                                               ,(if outline--use-rtl
+                                                    'outline-close-rtl-in-margins
+                                                  'outline-close-in-margins)))))
+                          (* (default-font-width) 1.0)))))
             (if outline--use-rtl
-                (setq-local right-margin-width (1+ right-margin-width))
-              (setq-local left-margin-width (1+ left-margin-width)))
+                (setq-local right-margin-width (+ right-margin-width
+                                                  outline--margin-width))
+              (setq-local left-margin-width (+ left-margin-width
+                                               outline--margin-width)))
             (setq-local fringes-outside-margins t)
             ;; Force display of margins
             (when (eq (current-buffer) (window-buffer))
@@ -566,8 +585,10 @@ See the command `outline-mode' for more information on this mode."
                  (< 0 (if outline--use-rtl right-margin-width
                         left-margin-width)))
         (if outline--use-rtl
-            (setq-local right-margin-width (1- right-margin-width))
-          (setq-local left-margin-width (1- left-margin-width)))
+            (setq-local right-margin-width (- right-margin-width
+                                              outline--margin-width))
+          (setq-local left-margin-width (- left-margin-width
+                                           outline--margin-width)))
         (setq-local fringes-outside-margins nil)
         ;; Force removal of margins
         (when (eq (current-buffer) (window-buffer))