* lisp/outline.el (outline-search-function): New variable (bug#53981).

(outline-font-lock-keywords, outline-font-lock-face)
(outline-minor-mode-highlight-buffer, outline-next-preface)
(outline-next-heading, outline-previous-heading)
(outline-back-to-heading, outline-on-heading-p, outline-demote)
(outline-map-region, outline-next-visible-heading)
(outline-hide-sublevels, outline-up-heading): Use outline-search-function
when it's non-nil as an alternative to searching outline-regexp.
(outline-search-level, outline-search-text-property): New functions.

* lisp/apropos.el (apropos-mode): Set outline-search-function
instead of unreliable outline-regexp.
(apropos-print): Add text property outline-level.

* lisp/emacs-lisp/shortdoc.el (shortdoc-display-group):
Add text property outline-level on text separate from final newlines.
(shortdoc-display-group): Add a narrow newline to not show
text properties of the final line when the outline is hidden.
(shortdoc--display-function): Add text property outline-level.
(shortdoc-mode): Set buffer-local outline-search-function and outline-level.

1 files changed, 14 insertions, 4 deletions

diff --git a/lisp/emacs-lisp/shortdoc.el b/lisp/emacs-lisp/shortdoc.el
index 022bf1e7360..83283247150 100644
--- a/lisp/emacs-lisp/shortdoc.el
+++ b/lisp/emacs-lisp/shortdoc.el
@@ -1374,13 +1374,20 @@ If SAME-WINDOW, don't pop to a new window."
          (unless (bobp)
            (insert "\n"))
          (insert (propertize
-                  (concat (substitute-command-keys data) "\n\n")
+                  (substitute-command-keys data)
+                  'face 'shortdoc-heading
+                  'shortdoc-section t
+                  'outline-level 1))
+         (insert (propertize
+                  "\n\n"
                   'face 'shortdoc-heading
                   'shortdoc-section t)))
         ;; There may be functions not yet defined in the data.
         ((fboundp (car data))
          (when prev
-           (insert (make-separator-line)))
+           (insert (make-separator-line)
+                   ;; This helps with hidden outlines (bug#53981)
+                   (propertize "\n" 'face '(:height 0))))
          (setq prev t)
          (shortdoc--display-function data))))
      (cdr (assq group shortdoc--groups))))
@@ -1397,7 +1404,7 @@ If SAME-WINDOW, don't pop to a new window."
         (start-section (point))
         arglist-start)
     ;; Function calling convention.
-    (insert (propertize "(" 'shortdoc-function function))
+    (insert (propertize "(" 'shortdoc-function function 'outline-level 2))
     (if (plist-get data :no-manual)
         (insert-text-button
          (symbol-name function)
@@ -1531,7 +1538,10 @@ Example:
 
 (define-derived-mode shortdoc-mode special-mode "shortdoc"
   "Mode for shortdoc."
-  :interactive nil)
+  :interactive nil
+  (setq-local outline-search-function #'outline-search-level
+              outline-level (lambda ()
+                              (get-text-property (point) 'outline-level))))
 
 (defun shortdoc--goto-section (arg sym &optional reverse)
   (unless (natnump arg)