bug#23308: 25.0.92; angle brackects in #include breaks syntax-ppss (c-mode)

[Alan Mackenzie]

Hello, Mohammed.

In article <mailman.621.1460994789.7477.bug-gnu-emacs@gnu.org> you wrote:
> In c-mode (may be in other modes too), lines like #include <stdio.h>
> sometimes break (nth 0 (syntax-ppss)), the depth of brackets. This
> happens because angle brackets ('<' and '>') in #include lines are
> considered to be brackets (which is true) in emacs 25.0.92, but not
> in emacs 24.5, where syntax-ppss doesn't break.

Yes, indeed.  Thanks for taking the trouble to report this bug, and
thanks even more for distilling the problem down to a small, easy to work
with test case.

> How to reproduce:

> open a new c file: emacs -Q test.c

> Type the following in the file (where | is the point):

>      #include <>

>      int
>      main (void)
>      {
>        |
>      }

> Now move between the angle brackets (| is the point):
>     #include <|>

>     ...

> Now type some header names:

>     #include <stdio.h|>

>     ...

> Now check the first value of (syntax-ppss). It is zero.

> Now move to some other point (don't press RET). Check the value of
> syntax-ppss.
> The value is negative when outside of any paren,

This was actually quite tricky to track down.  It was caused by an
erroneous fix to a bug in 2010, which has since been properly fixed by
other means.

> In GNU Emacs 25.0.92.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.9)
>  of 2016-04-13 built on fedora.localdomain
> Windowing system distributor 'Fedora Project', version 11.0.11800000
> Configured features:
> XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS NOTIFY ACL LIBSELINUX GNUTLS
> LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

Would you please try out the following patch, and let me know whether it
fixes the bug completely, and if not, what problems still remain.
(cc-engine.el is in directory .../emacs/lisp/progmodes.)  Thanks!


diff -r cf78a1fa7d43 cc-engine.el
--- a/cc-engine.el      Sat Apr 02 17:35:03 2016 +0000
+++ b/cc-engine.el      Wed Apr 20 08:14:02 2016 +0000
@@ -3443,7 +3443,7 @@
                (< c-state-old-cpp-beg here))
           (c-with-all-but-one-cpps-commented-out
            c-state-old-cpp-beg
-           (min c-state-old-cpp-end here)
+           c-state-old-cpp-end
            (c-invalidate-state-cache-1 here))
         (c-with-cpps-commented-out
          (c-invalidate-state-cache-1 here))))


-- 
Alan Mackenzie (Nuremberg, Germany).