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bug#22256: 25.0.50; multiline font-lock rules broken in C mode
From: |
Alan Mackenzie |
Subject: |
bug#22256: 25.0.50; multiline font-lock rules broken in C mode |
Date: |
29 Dec 2015 21:06:11 -0000 |
User-agent: |
tin/2.3.1-20141224 ("Tallant") (UNIX) (FreeBSD/10.2-RELEASE-p7 (amd64)) |
Hello, Anders.
In article <mailman.1133.1451298006.843.bug-gnu-emacs@gnu.org> you wrote:
> [-- text/plain, encoding 7bit, charset: UTF-8, 143 lines --]
> Hi!
> In C and related modes, multiline font-lock rules no longer work as
> expected. It looks like a few lines are highlighted, but not all of them.
> For example:
> Eval the following:
> (defvar my-multiline-test-keywords
> '(("^X"
> ("^.+$"
> (progn (beginning-of-line)
> (point-max))
> nil
> (0 'highlight)))))
> (defun my-multiline-test-add ()
> (interactive)
> (font-lock-add-keywords nil my-multiline-test-keywords)
> (font-lock-flush))
> Insert the following in a new buffer:
> X START OF A HIGHLIGHTED BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK LONG LINES IN THE BLOCK
> Do:
> M-x c-mode RET
> M-x my-multiline-test-add RET
> I expect the entire buffer to be highlighted. However, only the first eight
> lines are highlighted. When the block is edited, different parts of the
> block is highlighted and unhighlighted.
This is caused by the jit-lock mechanism. The first eight lines are 500
characters (jit-lock-chunk-size) rounded up to a whole number of lines.
What happens is this: when the first jit-lock-chunk (8 lines) is
fontified, the `fontified' property (the one the display engine uses) is
set only on these 8 lines. The `face' property is then set on all the
characters of the file, as requested by the my-multiline-test-keywords
form.
Next thing, jit-lock fontifies the next chunk of ~7 lines starting where
the `fontified' property is nil. The first thing done is to set
`fontified' on these ~7 lines, then the `face' property on them is
erased. There is now no matching font lock pattern to apply any new
faces to these ~7 lines, since the "X" is many lines back. The same
thing happens with the next 500 byte chunk, and so on till the end of the
buffer.
If you set `font-lock-support-mode' to nil and restart font locking, the
problem isn't apparent. (Then set the variable back to 'jit-lock-mode.)
This is a fundamental problem with jit-lock-mode: the assumption that
text to be fontified has no non-trivial context. This is a difficult
problem to solve in general. CC Mode uses some ad-hoc tricks to catch,
for example, long struct declarations.
> As a contrast, when `emacs-lisp-mode' is used, the entire block is
> highlighted, and editing does not change the highlighting.
I do not see this in Emacs 24.5. For me, even in emacs-lisp-mode, I
still see just the 8 lines being fontified. If you could give me a
recipe (starting from emacs-24.5 -Q) to reproduce this, I'd be very
interested.
> This worked as intended in Emacs 24.5.
> -- Anders Lindgren
> In GNU Emacs 25.0.50.60 (x86_64-apple-darwin14.5.0, NS appkit-1348.17
> Version 10.10.5 (Build 14F27))
> of 2015-12-28
> Repository revision: e9916d8880561cc06b6cb73bafe7257b93ffbf4c
> Windowing system distributor 'Apple', version 10.3.1348
> Configured using:
> 'configure --without-dbus'
> Configured features:
> ACL ZLIB TOOLKIT_SCROLL_BARS NS
> Important settings:
> value of $LC_CTYPE: UTF-8
> locale-coding-system: utf-8-unix
> Major mode: C/l
> Minor modes in effect:
> preproc-font-lock-global-mode: t
> preproc-font-lock-mode: t
> tooltip-mode: t
> global-eldoc-mode: t
> electric-indent-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
> abbrev-mode: t
[ .... ]
--
Alan Mackenzie (Nuremberg, Germany).