Subject: 24.1.50; (Contains ERT Test) show-paren-mode doesn't work in C comments if there's a quote between the parenthesis (affects c-mode and modes derived from it)

From: Rolando Pereira <[email-masked]>
Date: Wed, 18 Jul 2012 21:16:17 +0100

In c-mode if you type the following comment with M-x show-paren-mode
activated, the closing parenthesis is highlighted correctly:

// Lorem ipsum (dolor sit amet)

However, if the ' character appears inside the parenthesis, then
show-paren-mode won't match them.

For example, when typing the following comment, show-paren-mode highlights
the closing parenthesis using show-paren-mismatch:

// Comments are good (aren't they?)

I tried to make an ERT test that would check if the parenthesis was
highlighted correctly, but I couldn't get the overlay that
show-paren-mode uses.

However I found out that forward-sexp also doesn't work when the '
character appears between parenthesis, which makes me think the problem
may be somewhere in the syntax-table used by c-mode.

Here's the ERT test:

(ert-deftest cc-mode-should-forward-sexp-with-quotes-inside ()
  "Check if `forward-sexp' works in c-mode when the cursor is
inside a comment and there's a ' character inside the
parenthesis"
  (with-temp-buffer
    (c-mode)
    (insert "// Comments are good (aren't they?)")
    (goto-char (point-min))
    (search-forward "(")
    (backward-char 1)
    (forward-sexp)
    (ert-should (= (point) 36))))

Also, the reason I think that the problem only affects c-mode and modes that
derive from it is because this problem doesn't show up in
emacs-lisp-mode or lisp-mode.

Here's how to see the problem when starting emacs with the -Q flag:

1. Create the temporary buffer "temp-buffer" with C-x b temp-buffer RET
2. Activate c-mode with M-x c-mode
3. Activate show-paren-mode with M-x show-paren-mode
4. Write "// Comments are good (aren't they?)"
5. When typing the closing parenthesis, notice that it's highlighted
with the face show-paren-mismatch

Another test that can be used that doesn't use show-paren-mode but still
shows wrong behaviour is the following:

1. Create the temporary buffer as before
2. Activate c-mode as before
2. Write "// Comments are good (aren't they?)"
3. When typing the closing parenthesis, notice that the minibuffer shows
the message "No matching parenthesis found".

In GNU Emacs 24.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2012-07-15 on rolando-desktop
Bzr revision: 109096 [email-masked]
Windowing system distributor `The X.Org Foundation', version 11.0.10706000
Important settings:
  value of $LANG: pt_PT.utf8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
M-x r e p o r <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Starting new Ispell process [/usr/bin/aspell::default] ...
Checking spelling of PARENTHESIS...
byte-code: Window #<window 4 on  *Minibuf-1*> too small for splitting

Load-path shadows:
None found.

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