From e92a8d062cca54152bd816bdf88dad0bade87120 Mon Sep 17 00:00:00 2001
From: Tassilo Horn <tsdh@gnu.org>
Date: Mon, 7 Feb 2022 15:05:14 +0100
Subject: [PATCH] Show show-paren context in overlay or header-line

---
 lisp/paren.el | 66 ++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 60 insertions(+), 6 deletions(-)

diff --git a/lisp/paren.el b/lisp/paren.el
index 6de4364b4f..e0a8d6fc24 100644
--- a/lisp/paren.el
+++ b/lisp/paren.el
@@ -368,6 +368,51 @@ show-paren--show-context-in-child-frame
       (add-hook 'post-command-hook
                 #'show-paren--delete-context-child-frame))))
 
+(defvar-local show-paren--context-overlay nil)
+
+(defun show-paren--delete-context-overlay ()
+  (when show-paren--context-overlay
+    (delete-overlay show-paren--context-overlay)
+    (setq show-paren--context-overlay nil))
+  (remove-hook 'post-command-hook #'show-paren--delete-overlays
+               'local))
+
+(defun show-paren--show-context-in-overlay (text)
+  "Show TEXT in an overlay at the top-left of the current window."
+  ;; FIXME: This works pretty well but the overlay text is not
+  ;; outstanding at all.  It's good that it's the font-locked string
+  ;; but it would be good if we could place a :box or :background face
+  ;; attribute, too.
+  (setq text (replace-regexp-in-string "\n" " " text))
+  (show-paren--delete-context-overlay)
+  (let* ((beg (window-start))
+         (end (save-excursion
+                (goto-char beg)
+                (line-end-position))))
+    (setq show-paren--context-overlay (make-overlay beg end)))
+  (overlay-put show-paren--context-overlay 'display text)
+  (add-hook 'post-command-hook #'show-paren--delete-context-overlay
+            nil 'local))
+
+(defvar-local show-paren--orig-header-line-format nil)
+
+(defun show-paren--restore-orig-header-line-format ()
+  (setq header-line-format show-paren--orig-header-line-format)
+  (remove-hook 'post-command-hook
+               #'show-paren--restore-orig-header-line-format
+               'local))
+
+(defun show-paren--show-context-in-header-line (text)
+  "Show TEXT in the header-line."
+  ;; FIXME: This bounces the buffer one line down which is a bit
+  ;; annoying.  Can we do anything about it?
+  (setq text (replace-regexp-in-string "\n" " " text))
+  (setq show-paren--orig-header-line-format header-line-format)
+  (setq header-line-format text)
+  (add-hook 'post-command-hook
+            #'show-paren--restore-orig-header-line-format
+            nil 'local))
+
 (defun show-paren-function ()
   "Highlight the parentheses until the next input arrives."
   (let ((data (and show-paren-mode (funcall show-paren-data-function))))
@@ -438,12 +483,21 @@ show-paren-function
                 (let ((open-paren-line-string
                        (blink-paren-open-paren-line-string openparen))
                       (message-log-max nil))
-                  (if (and (eq show-paren-context-when-offscreen
-                               'child-frame)
-                           (display-graphic-p))
-                      (show-paren--show-context-in-child-frame
-                       open-paren-line-string)
-                    (minibuffer-message "Matches %s" open-paren-line-string)))))
+                  (cond ((and (eq show-paren-context-when-offscreen
+                                  'child-frame)
+                              (display-graphic-p))
+                         (show-paren--show-context-in-child-frame
+                          open-paren-line-string))
+                        ((eq show-paren-context-when-offscreen
+                             'overlay)
+                         (show-paren--show-context-in-overlay
+                          open-paren-line-string))
+                        ((eq show-paren-context-when-offscreen
+                             'header-line)
+                         (show-paren--show-context-in-header-line
+                          open-paren-line-string))
+                        (show-paren-context-when-offscreen
+                         (minibuffer-message "Matches %s" open-paren-line-string))))))
           ;; Always set the overlay face, since it varies.
           (overlay-put show-paren--overlay 'priority show-paren-priority)
           (overlay-put show-paren--overlay 'face face))))))
-- 
2.35.1