Display show-paren-context-when-offscreen in child frame

* etc/NEWS: Extend section about the new
`show-paren-context-when-offscreen' custom option.
* lisp/paren.el (show-paren-context-when-offscreen): Allow special
value `child-frame'.
(show-paren-function): Handle `child-frame' value of
`show-paren-context-when-offscreen'.
(show-paren--context-child-frame): New defvar.
(show-paren--context-child-frame-redirect-focus): New function.
(show-paren--context-child-frame-buffer): New function.
(show-paren--context-child-frame-parameters): New defvar.
(show-paren--delete-context-child-frame): New function.
(show-paren--show-context-in-child-frame): New function.

diff --git a/etc/NEWS b/etc/NEWS
index 6c5aeacb7bee57956688816e40526e58f5522af1..c3313dc92b683967c805211272031b567dcdaec2 100644 (file)
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -438,6 +438,11 @@ When non-nil, if the point is in a closing delimiter and the opening
 delimiter is offscreen, shows some context around the opening
 delimiter in the echo area.  Default nil.
 
+May also be set to the symbol 'child-frame' in which case the context
+is shown in a child frame at the top left of the current window on
+graphical frames.  On non-graphical frames, the context is shown in
+the echo area.
+
 ** Comint
 
 +++

diff --git a/lisp/paren.el b/lisp/paren.el
index 0065bba72e7158400bb791fbdcbe4b63f809fdd5..b0a2eb8dc5251d7606e8e63ecedafcbb85832f2f 100644 (file)
--- a/lisp/paren.el
+++ b/lisp/paren.el
@@ -89,11 +89,21 @@ its position."
   :type 'boolean)
 
 (defcustom show-paren-context-when-offscreen nil
-  "If non-nil, show context in the echo area when the openparen is offscreen.
+  "If non-nil, show context around the opening paren if it is offscreen.
 The context is usually the line that contains the openparen,
 except if the openparen is on its own line, in which case the
-context includes the previous nonblank line."
-  :type 'boolean
+context includes the previous nonblank line.
+
+By default, the context is shown in the echo area.
+
+If set to the symbol `child-frame', the context is shown in a
+child frame at the top left of the window.  You might want to
+customize the `child-frame-border' face (especially the
+background color) to give the child frame a distinguished border.
+On non-graphical frames, the context is shown in the echo area."
+  :type '(choice (const :tag "Off" nil)
+                 (const :tag "In echo area" t)
+                 (const :tag "Child frame" child-frame))
   :version "29.1")
 
 (defvar show-paren--idle-timer nil)
@@ -260,6 +270,103 @@ It is the default value of `show-paren-data-function'."
                  (if (= dir 1) pos (1+ pos))
                  mismatch)))))))
 
+(defvar show-paren--context-child-frame nil)
+
+(defun show-paren--context-child-frame-redirect-focus ()
+  "Redirect focus from child frame."
+  (redirect-frame-focus
+   show-paren--context-child-frame
+   (frame-parent corfu--frame)))
+
+(defun show-paren--context-child-frame-buffer (text)
+  (with-current-buffer
+      (get-buffer-create " *show-paren context*")
+    ;; Redirect focus to parent.
+    (add-hook 'pre-command-hook
+              #'show-paren--delete-context-child-frame
+              nil t)
+    ;; Use an empty keymap.
+    (use-local-map (make-keymap))
+    (dolist (var '((mode-line-format . nil)
+                   (header-line-format . nil)
+                   (tab-line-format . nil)
+                   (tab-bar-format . nil) ;; Emacs 28 tab-bar-format
+                   (frame-title-format . "")
+                   (truncate-lines . t)
+                   (cursor-in-non-selected-windows . nil)
+                   (cursor-type . nil)
+                   (show-trailing-whitespace . nil)
+                   (display-line-numbers . nil)
+                   (left-fringe-width . nil)
+                   (right-fringe-width . nil)
+                   (left-margin-width . 0)
+                   (right-margin-width . 0)
+                   (fringes-outside-margins . 0)
+                   (buffer-read-only . t)))
+      (set (make-local-variable (car var)) (cdr var)))
+    (let ((inhibit-modification-hooks t)
+          (inhibit-read-only t))
+      (erase-buffer)
+      (insert text)
+      (goto-char (point-min)))
+    (current-buffer)))
+
+(defvar show-paren--context-child-frame-parameters
+  `((visibility . nil)
+    (width . 0) (height . 0)
+    (min-width . t) (min-height . t)
+    (no-accept-focus . t)
+    (no-focus-on-map . t)
+    (border-width . 0)
+    (child-frame-border-width . 1)
+    (left-fringe . 0)
+    (right-fringe . 0)
+    (vertical-scroll-bars . nil)
+    (horizontal-scroll-bars . nil)
+    (menu-bar-lines . 0)
+    (tool-bar-lines . 0)
+    (tab-bar-lines . 0)
+    (no-other-frame . t)
+    (no-other-window . t)
+    (no-delete-other-windows . t)
+    (unsplittable . t)
+    (undecorated . t)
+    (cursor-type . nil)
+    (no-special-glyphs . t)
+    (desktop-dont-save . t)))
+
+(defun show-paren--delete-context-child-frame ()
+  (when show-paren--context-child-frame
+    (delete-frame show-paren--context-child-frame))
+  (remove-hook 'post-command-hook
+               #'show-paren--delete-context-child-frame))
+
+(defun show-paren--show-context-in-child-frame (text)
+  "Show TEXT in a child-frame at the top-left of the current window."
+  (let ((minibuffer (minibuffer-window (window-frame)))
+        (buffer (show-paren--context-child-frame-buffer text))
+        (x (window-pixel-left))
+        (y (window-pixel-top))
+        (window-min-height 1)
+        (window-min-width 1)
+        after-make-frame-functions)
+    (show-paren--delete-context-child-frame)
+    (setq show-paren--context-child-frame
+          (make-frame
+           `((parent-frame . ,(window-frame))
+             (minibuffer . ,minibuffer)
+             ,@show-paren--context-child-frame-parameters)))
+    (let ((win (frame-root-window show-paren--context-child-frame)))
+      (set-window-buffer win buffer)
+      (set-window-dedicated-p win t)
+      (set-frame-size show-paren--context-child-frame
+                      (string-width text)
+                      (length (string-lines text)))
+      (set-frame-position show-paren--context-child-frame x y)
+      (make-frame-visible show-paren--context-child-frame)
+      (add-hook 'post-command-hook
+                #'show-paren--delete-context-child-frame))))
+
 (defun show-paren-function ()
   "Highlight the parentheses until the next input arrives."
   (let ((data (and show-paren-mode (funcall show-paren-data-function))))
@@ -299,8 +406,8 @@ It is the default value of `show-paren-data-function'."
         ;; Otherwise, turn off any such highlighting.
         (if (or (not here-beg)
                 (and (not show-paren-highlight-openparen)
-                    (> here-end (point))
-                    (<= here-beg (point))
+                     (> here-end (point))
+                     (<= here-beg (point))
                      (integerp there-beg)))
             (delete-overlay show-paren--overlay-1)
           (move-overlay show-paren--overlay-1
@@ -315,7 +422,7 @@ It is the default value of `show-paren-data-function'."
             (delete-overlay show-paren--overlay)
           (if highlight-expression
               (move-overlay show-paren--overlay
-                           (if (< there-beg here-beg) here-end here-beg)
+                            (if (< there-beg here-beg) here-end here-beg)
                             (if (< there-beg here-beg) there-beg there-end)
                             (current-buffer))
             (move-overlay show-paren--overlay
@@ -330,7 +437,12 @@ It is the default value of `show-paren-data-function'."
                 (let ((open-paren-line-string
                        (blink-paren-open-paren-line-string openparen))
                       (message-log-max nil))
-                  (minibuffer-message "Matches %s" open-paren-line-string))))
+                  (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)))))
           ;; Always set the overlay face, since it varies.
           (overlay-put show-paren--overlay 'priority show-paren-priority)
           (overlay-put show-paren--overlay 'face face))))))