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bug#5560: 23.1.92; parens matching in c-mode broken
From: |
David Reitter |
Subject: |
bug#5560: 23.1.92; parens matching in c-mode broken |
Date: |
Sun, 21 Feb 2016 16:40:09 -0500 |
Alan,
Your patch works as advertised for my test case. It’s certainly better to
error out than to do the wrong thing.
I think you are catching the right situations, but my confidence is low because
of the readability of the code (what is 4, 5?).
I think the question is whether that fix is appropriate for the 25.1 release.
If you want to apply it there, I would probably test a whole lot of cases in
modes that are derivates of c-mode.
- David
> On Feb 21, 2016, at 7:35 AM, Alan Mackenzie <acm@muc.de> wrote:
>
> Hello again, David and Andrew.
>
> On Sat, Feb 20, 2016 at 10:57:23PM +0000, Alan Mackenzie wrote:
>> On Tue, Feb 16, 2016 at 10:56:34PM -0500, Andrew Hyatt wrote:
>
>>> I can confirm this still doesn't work right in Emacs 25. However, I get
>>> a slightly different experience, with clicking on all 3 left parens
>>> highlighting until the first right paren only. Similarly, that right
>>> paren seems to be the matching paren for all 3 left parens.
>
>>> David Reitter <david.reitter@gmail.com> writes:
>
>>>> Parens matching in C mode is sometimes surprising. In the example
>>>> below, double-clicking on either of the first two opening parentheses
>>>> will mark the text until the " hyper_modifier : 0)", but that is
>>>> correct
>>>> only for the second paren, while the first one is unmatched due to a space
>>>> following the backslash.
>
>>>> #define EV_MODIFIERS(e) \
>>>> ((([e modifierFlags] & NSHelpKeyMask) ? \
>>>> hyper_modifier : 0) \
>>>> ...
>
>
>>>> It would be more useful if an "unmatched parentheses" was shown, or
>>>> if the region up to the end of the scan process (i.e. the
>>>> space+newline) was marked.
>
>> Giving a decent error message here would be difficult. We're down in the
>> depths of the mouse code, but the strategem of giving syntax-table text
>> properties to parentheses is a pure CC Mode one. Signaling an error if
>> a paren has other than paren syntax is liable to have unforseen side
>> effects somewhere, somehow, some time.
>
> After a night's sleep, I've changed my mind about the advisability of
> such a fix. So, here is a fix. It works as indicated last night: if a
> character whose normal syntax is open/close-paren has a different syntax
> due to syntax-table text properties, a 'scan-error error is signaled:
> either "Containing expression ends prematurely" for an open paren, or
> "Unbalanced parentheses" for a close paren.
>
> Here's the patch. Please try it out and let me know if there's anything
> amiss about it. Otherwise, I'll commit it.
>
>
>
> diff --git a/lisp/mouse.el b/lisp/mouse.el
> index 85ffc43..22c5b48 100644
> --- a/lisp/mouse.el
> +++ b/lisp/mouse.el
> @@ -931,20 +931,29 @@ mouse-start-end
> (= start end)
> (char-after start)
> (= (char-syntax (char-after start)) ?\())
> - (list start
> - (save-excursion
> - (goto-char start)
> - (forward-sexp 1)
> - (point))))
> + (if (/= (car (syntax-after start)) 4)
> + ;; This happens in CC Mode when unbalanced parens in CPP
> + ;; constructs are given punctuation syntax with
> + ;; syntax-table text properties. (2016-02-21).
> + (signal 'scan-error (list "Containing expression ends
> prematurely"
> + start start))
> + (list start
> + (save-excursion
> + (goto-char start)
> + (forward-sexp 1)
> + (point)))))
> ((and (= mode 1)
> (= start end)
> (char-after start)
> (= (char-syntax (char-after start)) ?\)))
> - (list (save-excursion
> - (goto-char (1+ start))
> - (backward-sexp 1)
> - (point))
> - (1+ start)))
> + (if (/= (car (syntax-after start)) 5)
> + ;; See above comment about CC Mode.
> + (signal 'scan-error (list "Unbalanced parentheses" start start))
> + (list (save-excursion
> + (goto-char (1+ start))
> + (backward-sexp 1)
> + (point))
> + (1+ start))))
> ((and (= mode 1)
> (= start end)
> (char-after start)
>
>
>
> --
> Alan Mackenzie (Nuremberg, Germany).