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Re: Mysterious fontification/C++ context issue

From: Alan Mackenzie
Subject: Re: Mysterious fontification/C++ context issue
Date: 10 Dec 2006 11:56:21 +0100
Date: Sun, 10 Dec 2006 12:06:36 +0000
User-agent: Mutt/1.5.9i

Hi, Richard, hi, Martin!

On Sat, Dec 09, 2006 at 11:24:54PM -0500, Richard Stallman wrote:
>      >     2. That a user's idea of "defun" for her programming
>      >     language does not necessarily coincide with that of
>      >     `beginning-of-defun'.
>      >
>      > The major mode is supposed to try to make them correspond.  It
>      > seems strange to assume that it doesn't succeed.
beginning-of-defun unfortunately conflates (i) "beginning of a function" and
(ii) "outermost level of parens", this arising because they coincide in
the most important language (Lisp).  Having
"beginning-of-defun-function" makes things even worse.

Typically, b-o-d (sense (i)) is going to be calling
foo-beginning-of-defun (the value of b-o-d-function) which is going to
be recursively calling beginning-of-defun (sense (ii)), getting one's
knickers horribly twisted.

Maybe, for Emacs 23, we could disentangle these things.

>     If it really succeeded why should C mode ever bother to provide
>     its own `c-beginning-of-defun'?

c-beginning-of-defun puts point at the beginning of the C function, i.e.
at the "int" in the following, regardless of whether the brace is hung
or at column 0:

int foo (bar)

> Maybe C mode should arrange to use `c-beginning-of-defun'
> as the beginning-of-definition-function.  Is there a reason why
> this would give bad results?


You mean syntax-begin-function?  c-beginning-of-defun is a user level
function, and it's slow.  About 90% of its runtime is spent determining
where point is initially (inside a defun / inside "int foo (bar)" / at
"int foo (bar)"/ ... ) and finally moving from the open brace to the
"int".  Only ~10% is used in finding the outermost open brace, which is
all that's needed for font-locking and so on.

>      > Anyway, this is not the right place to discuss what happens in
>      > specific modes.

>     The current change affects the behavior of `beginning-of-defun' which
>     may affect other modes as well.

> Yes, if they set `open-paren-in-column-0-is-defun-start' to t.

You mean setting it to nil.  ;-)

The behaviour of beginning-of-defun has been changed ONLY for when
opic0ids gets set to nil.  The only other file.el within Emacs which
does this is progmodes/python.el.  Any Python users here?  Dave Love,
are you listening?

There is also this baffling comment in net/tramp.el:

;; Fontification is messed up when
;; `open-paren-in-column-0-is-defun-start' set to t.

Alan Mackenzie (Ittersbach, Germany)

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