bug#38049: closed (C mode fontification broken with reposition-window)

[GNU bug Tracking System]

Your message dated Sat, 9 Nov 2019 14:45:17 +0000
with message-id <20191109144517.GB5546@ACM>
and subject line Re: bug#38049: C mode fontification broken with 
reposition-window
has caused the debbugs.gnu.org bug report #38049,
regarding C mode fontification broken with reposition-window
to be marked as done.

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-- 
38049: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=38049
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> --- Begin Message ---
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>
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> Subject: 
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> C mode fontification broken with reposition-window
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>
>
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> Date: 
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> Sun, 03 Nov 2019 22:28:05 +0200
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> User-agent: 
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> Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (x86_64-pc-linux-gnu)
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>
>
>
> Version: 27.0.50
>
> This is a reproducible test case:
>
> 0. emacs -Q
> 1. C-x C-f emacs/lib-src/emacsclient.c
> 2. M-: (progn (search-forward "create-frame" nil t) (reposition-window))
>
> Then half screen displays unfontified lines.
>
> Fontification doesn't fail in other modes, only in C mode.
>
> This has something to do with interaction between c-font-lock
> and buffer navigation in reposition-window.
>
>
>
> --- End Message ---
> --- Begin Message ---
>
>
>
> Subject: 
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> Re: bug#38049: C mode fontification broken with reposition-window
>
>
>
>
> Date: 
>
> Sat, 9 Nov 2019 14:45:17 +0000
>
>
>
>
> User-agent: 
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> Mutt/1.10.1 (2018-07-13)
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>
>
>
> Hello, Juri.
>
> On Tue, Nov 05, 2019 at 21:07:37 +0000, Alan Mackenzie wrote:
> > On Sun, Nov 03, 2019 at 22:28:05 +0200, Juri Linkov wrote:
> > > Version: 27.0.50
>
> > > This is a reproducible test case:
>
> > > 0. emacs -Q
> > > 1. C-x C-f emacs/lib-src/emacsclient.c
> > > 2. M-: (progn (search-forward "create-frame" nil t) (reposition-window))
>
> > > Then half screen displays unfontified lines.
>
> > > Fontification doesn't fail in other modes, only in C mode.
>
> > > This has something to do with interaction between c-font-lock
> > > and buffer navigation in reposition-window.
>
> > Indeed it does.
>
> > Briefly,
> > (i) reposition-window narrows to (2758 3940) in
> > repos-count-screen-lines.
> > (ii) This latter function uses vertical-motion to count the lines.
> > (iii) vertical-motion triggers jit-lock fontification.
> > (iv) This calls (eventually) c-font-lock-fontify-region.
> > (v) c-font-lock-fontify-region attempts to examine buffer text before
> >   the start of the jit-lock chunk to find syntactic context.
> > (vi) This is outside the visible region, so Emacs raises an exception.
> > (vii) The exception is caught and discarded by an unwind-protect in
> >   c-font-lock-fontify-region.
> > (viii) The jit-lock chunk remains unfontified.
>
> [ .... ]
>
> I have fixed this bug by widening around c-font-lock-fontify-region.  I
> am closing the bug with this post.
>
> -- 
> Alan Mackenzie (Nuremberg, Germany).
>
>
> --- End Message ---