GNU bug report logs - #3269
23.0.93; C-mode text highlighting

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From: Alan Mackenzie <acm <at> muc.de>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: emacs-pretest-bug <at> gnu.org, Chong Yidong <cyd <at> stupidchicken.com>,
        3269 <at> debbugs.gnu.org,
        Thomas Christensen <thomasc <at> thomaschristensen.org>,
        emacs-devel <at> gnu.org
Subject: bug#3269: 23.0.93; C-mode text highlighting
Date: Tue, 19 May 2009 10:26:19 +0000

Hi, Stefan,

On Mon, May 18, 2009 at 10:24:02PM -0400, Stefan Monnier wrote:
> > The opening string quote (?\" or ?\') gets f-l-warning-face.  The
> > rest of the unclosed string (up to the first EOL which isn't escaped)
> > gets f-l-string-face.

> > Actually, that's not _quite_ "proper".  A string with an even number of
> > backslashes at an EOL is broken at that point, but the font locking
> > doesn't show this (yet).  I don't suppose that will bother you all that
> > much.  ;-)

Whoops!  I was utterly wrong there.  When a string inside a #define has
an even number of backslashes at an EOL, this is perfectly legal; the
last \ escapes the EOL, concatenating the lines, and the second last \
escapes the first character on the next line.  Nice simple language, C.
;-)

> I won't oppose the change, but just to be clear: I think that the
> increased code complexity introduced by your patch is a worse problem
> than the "improper" highlighting it tries to fix.

Well, I don't agree with that, but I'm beginning to think that the
current fontification (ommitting f-l-string-face until the closing " is
there) wasn't perhaps quite so bad after all.

> When code is syntactically incorrect, it's common/normal/expected for
> the highlighting to be "incorrect".

Where "incorrect" here means "different from what it would be if the code
were correct".

> This "incorrect" behavior is actually a good way for the user to notice
> that his code has problems.

Agreed, totally.

> So, from this point of view, there's no need to highlight the opening
> string quote with f-l-warning-face: just looking back in the buffer
> until you find the first char that is not font-locked as expected will
> find the culprit without any need for any extra elisp code, and
> moreover this method will work in many more cases.

> In other words, messed-up highlighting for incorrect code is just as
> good if not better than explicitly recognizing the incorrect code and
> highlighting it with f-l-warning-face.

I was thinking of "compatibility" with unterminated strings in normal
code.  But they're not the same thing.  An open string in a #define is
perfectly valid code, if somewhat unusual outside of the Obfuscated C
competition.

You've persuaded me that the existing fontification is actually better.
So I won't be committing yesterday's patch.  Thanks!

I'll just finish the other patch and commit that.

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).

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