org-mode code block parentheses mismatch

Question

Here's some emacs-lisp code in a babel block:

#+begin_src emacs-lisp
(defun factor (number)
  (labels
      ((*factor (divisor number)
        (if (> (* divisor divisor) number)
            (list number)
          (if (= (mod number divisor) 0)
              (cons divisor (*factor divisor (/ number divisor)))
            (*factor (+ divisor 1) number)))))
    (*factor 2 number)))
#+end_src

So in the org buffer I get a parentheses matching problem, i.e., that very last ) at the bottom is flagged as one too many. It flashes red and check-parens flags it as well. Trouble is, this is not an error, i.e., the same code in scratch is perfectly paren-matched, likewise when I bring it up in the Org Source C-c ' window. BTW, this code compiles and runs giving good output. Any ideas what org-mode is doing here? I've got (show-paren-mode 1). When I turn it off, obviously, no problem because no highlighting matching parens.

I don't think this block is the problem. It's evidence of some other syntax problem in your org file. I'd suggest identifying what section of your org file provokes this error. Do this by removing parts of your org file until this matching problem does not occur and adding back what you removed one by one until the error returns. — Aquaactress, Apr 29 '19 at 16:29
I've got this problem in a totally naked file, i.e., just the code block, no headers, saved with an `.org` suffix. I'm on Emacs 26.2 and Org mode version 9.2.3 (9.2.3-11-g42abf5-elpaplus @ /.../.emacs.d/elpa/org-plus-contrib-20190429/) — 147pm, Apr 29 '19 at 19:17
I can run `check-parens` and get the problem. Go into `C-c '` problem disappears. — 147pm, Apr 29 '19 at 20:06

score 4 · Answer 1 · edited May 26 '21 at 09:07

Here is a potential solution:

(defun org-mode-<>-syntax-fix (start end)
  (when (eq major-mode 'org-mode)
    (save-excursion
      (goto-char start)
      (while (re-search-forward "<\\|>" end t)
    (when (get-text-property (point) 'src-block)
      ;; This is a < or > in an org-src block
      (put-text-property (point) (1- (point))
                 'syntax-table (string-to-syntax "_")))))))

(add-hook 'org-mode-hook
      (lambda ()
        (setq syntax-propertize-function 'org-mode-<>-syntax-fix)
        (syntax-propertize (point-max))))

This basically just changes the syntax table for <> inside src blocks I think. It seems to solve the problem.

The code above depends on source blocks already propertized with src-block.

The src-block property is put on source blocks by org-fontify-meta-lines-and-blocks during keyword fontification through font-lock. But, syntax fontification comes before keyword fontification. So maybe the following function is better. For easier copy-paste the full code is given. The main change is the search for source blocks by re-search-backward.

We set syntax-propertize-function as a buffer-local variable to avoid unforeseen consequences outside of our org-mode buffers, such as in cc-mode's check for syntax-table functionality, which otherwise fails and prevents HTML exports of org-mode buffers.

(defun org-mode-<>-syntax-fix (start end)
  "Change syntax of characters ?< and ?> to symbol within source code blocks."
  (let ((case-fold-search t))
    (when (eq major-mode 'org-mode)
      (save-excursion
        (goto-char start)
        (while (re-search-forward "<\\|>" end t)
          (when (save-excursion
                  (and
                   (re-search-backward "[[:space:]]*#\\+\\(begin\\|end\\)_src\\_>" nil t)
                   (string-equal (downcase (match-string 1)) "begin")))
            ;; This is a < or > in an org-src block
            (put-text-property (point) (1- (point))
                               'syntax-table (string-to-syntax "_"))))))))

(defun org-setup-<>-syntax-fix ()
  "Setup for characters ?< and ?> in source code blocks.
Add this function to `org-mode-hook'."
  (make-local-variable 'syntax-propertize-function)
  (setq syntax-propertize-function 'org-mode-<>-syntax-fix)
  (syntax-propertize (point-max)))

(add-hook 'org-mode-hook #'org-setup-<>-syntax-fix)

Dear John, your solution is very nice! I just added a small bugfix. I hope you do not mind. I did not write a new solution since the main idea is yours. — Tobias, Oct 04 '19 at 16:36

score 3 · Answer 2 · answered Aug 18 '19 at 05:04

The reason for the mismatch is the code contains an angled bracket (">") which is treated as a matching paren.

I don't know the solution for how to specify that orgmode emacs-elisp should ignore angled brackets when matching parens (but I would like to know a solution).

Note: I posted this as an "answer" because I don't have enough reputation points to post it as a comment in the OP.

score 2 · Answer 3 · answered Oct 05 '19 at 13:04

2

Since I never use <> as brackets in org mode documents, I have these two lines in my org mode hook function:

(modify-syntax-entry ?< ".")
(modify-syntax-entry ?> ".")

No need to play around with properties etc. Of course, if you use XML or HTML, you may wish to avoid this.

answered Oct 05 '19 at 13:04

éric

420
3
3

Add this to org-mode hook didn't solve it for me. I still get paren mismatch because of < and >. – Sahas Mar 23 '20 at 11:35

score 1 · Answer 4 · answered Aug 30 '21 at 20:52

A small variation of eric's answer that works for me:

(defun org-syntax-table-modify ()
  "Modify `org-mode-syntax-table' for the current org buffer."
  (modify-syntax-entry ?< "." org-mode-syntax-table)
  (modify-syntax-entry ?> "." org-mode-syntax-table))

(add-hook 'org-mode-hook #'org-syntax-table-modify)

org-mode code block parentheses mismatch

4 Answers4