Show matching lines when parentheses go off-screen
This posts will describe how I display lines matching off-screen parentheses at the top of the window:
The variable blink-matching-paren can be used to configure the display of
matching parentheses. If you look at the source, you will see that
blink-paren-post-self-insert-function is added to post-self-insert-hook to
do the job.
There are two things I would like to change about the way it works:
-
When the matching paren goes off-screen, I usually look at the top of the window. Thus, this is the place where I would like to display the match information.
-
The matching information should be displayed after movement commands as well.
First let’s take care of blink-matching-paren:
;; we will call `blink-matching-open` ourselves...
(remove-hook 'post-self-insert-hook
#'blink-paren-post-self-insert-function)
;; this still needs to be set for `blink-matching-open` to work
(setq blink-matching-paren 'show)As I already use show-paren-mode to visualize matching parentheses it makes
sense to look for a way to hook into it. Because of that I decided to advice
show-paren-function:
(let ((ov nil)) ; keep track of the overlay
(advice-add
#'show-paren-function
:after
(defun show-paren--off-screen+ (&rest _args)
"Display matching line for off-screen paren."
(when (overlayp ov)
(delete-overlay ov))
;; check if it's appropriate to show match info,
;; see `blink-paren-post-self-insert-function'
(when (and (overlay-buffer show-paren--overlay)
(not (or cursor-in-echo-area
executing-kbd-macro
noninteractive
(minibufferp)
this-command))
(and (not (bobp))
(memq (char-syntax (char-before)) '(?\) ?\$)))
(= 1 (logand 1 (- (point)
(save-excursion
(forward-char -1)
(skip-syntax-backward "/\\")
(point))))))
;; rebind `minibuffer-message' called by
;; `blink-matching-open' to handle the overlay display
(cl-letf (((symbol-function #'minibuffer-message)
(lambda (msg &rest args)
(let ((msg (apply #'format-message msg args)))
(setq ov (display-line-overlay+
(window-start) msg ))))))
(blink-matching-open))))))To create the overlay I have written the following helper function:
(defun display-line-overlay+ (pos str &optional face)
"Display line at POS as STR with FACE.
FACE defaults to inheriting from default and highlight."
(let ((ol (save-excursion
(goto-char pos)
(make-overlay (line-beginning-position)
(line-end-position)))))
(overlay-put ol 'display str)
(overlay-put ol 'face
(or face '(:inherit default :inherit highlight)))
ol))All that is left is to activate show-paren-mode with the settings you like:
(setq show-paren-style 'paren
show-paren-delay 0.03
show-paren-highlight-openparen t
show-paren-when-point-inside-paren nil
show-paren-when-point-in-periphery t)
(show-paren-mode 1)To use the code of this post make sure to evaluate the code with lexical-scope.