bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

[Alan Mackenzie]

Hello, Emacs.

Emacs master branch:

* emacs/lisp/font-lock.el (font-lock-fontify-syntactically-region): At
line 26 of this function, appears:

    (setq state (parse-partial-sexp (point) end nil nil state
                                    'syntax-table))

..  However, there is no goto-char or other way of setting point earlier
in the function (except in one arm of an `if' form).  Neither is point
defined to have a defined setting at the entry to the function.

This is a bug.

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

[Lars Ingebrigtsen]

Alan Mackenzie <acm@muc.de> writes:

> * emacs/lisp/font-lock.el (font-lock-fontify-syntactically-region): At
> line 26 of this function, appears:
>
>     (setq state (parse-partial-sexp (point) end nil nil state
>                                     'syntax-table))
>
> ..  However, there is no goto-char or other way of setting point earlier
> in the function (except in one arm of an `if' form).  Neither is point
> defined to have a defined setting at the entry to the function.

(syntax-ppss start) (called earlier) will skip to start, won't it?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

[Alan Mackenzie]

Hello, Lars.

On Sun, Jun 05, 2022 at 16:23:35 +0200, Lars Ingebrigtsen wrote:
> Alan Mackenzie <acm@muc.de> writes:

> > * emacs/lisp/font-lock.el (font-lock-fontify-syntactically-region): At
> > line 26 of this function, appears:

> >     (setq state (parse-partial-sexp (point) end nil nil state
> >                                     'syntax-table))

> > ..  However, there is no goto-char or other way of setting point earlier
> > in the function (except in one arm of an `if' form).  Neither is point
> > defined to have a defined setting at the entry to the function.

> (syntax-ppss start) (called earlier) will skip to start, won't it?

Er, yes, it will.  Somehow I didn't know that syntax-ppss did that.
Sorry for the false bug report.  I'll close it as notabug (assuming you
haven't done this already.)

> -- 
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

[Lars Ingebrigtsen]

Alan Mackenzie <acm@muc.de> writes:

> Er, yes, it will.  Somehow I didn't know that syntax-ppss did that.

The doc string doesn't mention point movements at all, and perhaps it
should?  Hm...  reading the code now, and I'm not quite sure whether
it's guaranteed to do so or not, really, so perhaps there is a bug here
in some cases.  I've added Stefan to the CCs; perhaps he has a comment
here.

> Sorry for the false bug report.  I'll close it as notabug (assuming you
> haven't done this already.)

No, haven't done so.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Lars Ingebrigtsen [2022-06-05 21:07:30] wrote:
> Alan Mackenzie <acm@muc.de> writes:
>> Er, yes, it will.  Somehow I didn't know that syntax-ppss did that.
> The doc string doesn't mention point movements at all, and perhaps it
> should?

Doesn't it say:

    Point is at POS when this function returns.

?


        Stefan

bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

[Lars Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Doesn't it say:
>
>     Point is at POS when this function returns.
>
> ?

Oh, I interpreted that as meaning...  er...  not a lot.  I think I'll
tweak the doc string.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55798: font-lock-fontify-syntactically-region uses point without initializing it.

[Richard Stallman]

[[[ To any NSA and FBI agents reading my email: please consider    ]]]
[[[ whether defending the US Constitution against all enemies,     ]]]
[[[ foreign or domestic, requires you to follow Snowden's example. ]]]

      > Point is at POS when this function returns.

That way of saying it could be confusing because it doesn't describe
an action.  It sounds like a coincidence.  Would this be clearer?

     This function finishes by moving point to POS.
-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)