Reported by: Daniel Colascione <dan.colascione <at> gmail.com>
Date: Wed, 26 Jan 2011 06:29:02 UTC
Severity: minor
Tags: confirmed, fixed, patch
Found in version 25.2
Fixed in version 26.1
Done: npostavs <at> users.sourceforge.net
Bug is archived. No further changes may be made.
View this message in rfc822 format
From: Alan Mackenzie <acm <at> muc.de> To: Daniel Colascione <dan.colascione <at> gmail.com>, Lars Ingebrigtsen <larsi <at> gnus.org> Cc: 7918 <at> debbugs.gnu.org Subject: bug#7918: [PATCH] cc-mode: only the first clause of a for-loop should be checked for declarations Date: Tue, 1 Mar 2016 18:02:42 +0000
Hello, Daniel and Lars.
On Fri, Feb 26, 2016 at 04:48:13PM +1030, Lars Ingebrigtsen wrote:
> Daniel Colascione <dan.colascione <at> gmail.com> writes:
> > // This code has no variable declarations
> >
> > void foo() {
> > for (; (DWORD) a * b ;)
> > ;
> >
> > for (; a * b ;)
> > ;
> > }
> >
> I can confirm that the Emacs trunk still highlights the "a" in these
> examples wrong, and that Daniel's patch seems to fix the issue.
> However, I'm totally unfamiliar with the cc-mode code, so it would be
> nice if somebody could look at it before it's applied.
OK. I haven't actually tried this patch out, but there are things in it
I find concerning.
> === modified file 'lisp/progmodes/cc-fonts.el'
> --- lisp/progmodes/cc-fonts.el 2010-12-07 12:15:28 +0000
> +++ lisp/progmodes/cc-fonts.el 2011-01-25 11:10:00 +0000
> @@ -1080,7 +1080,8 @@
> ;; o - '<> if the arglist is of angle bracket type;
> ;; o - 'arglist if it's some other arglist;
> ;; o - nil, if not in an arglist at all. This includes the
> - ;; parenthesised condition which follows "if", "while", etc.
> + ;; parenthesised condition which follows "if", "while", etc.,
> + ;; but not "for", which is 'arglist after `;'.
By what logic is `context' set to 'arglist in a "for" statement? The
main function of `context' is to inform `c-forward-decl-or-cast-1' of
the context in which it is being called.
> context
> ;; The position of the next token after the closing paren of
> ;; the last detected cast.
> @@ -1109,7 +1110,7 @@
> ;; `c-forward-decl-or-cast-1' and `c-forward-label' for
> ;; later fontification.
> (c-record-type-identifiers t)
> - label-type
> + label-type paren-state most-enclosing-brace
> c-record-ref-identifiers
> ;; Make `c-forward-type' calls mark up template arglists if
> ;; it finds any. That's necessary so that we later will
> @@ -1171,7 +1172,6 @@
> 'font-lock-function-name-face))))
> (c-font-lock-function-postfix limit))
> -
> (setq start-pos (point))
> (when
> ;; The result of the `if' condition below is true when we don't recognize a
The next hunk attempts to move the detection of a "for" statement here
from later in the function where it previously was. Why?
> @@ -1189,7 +1189,31 @@
> ;; (e.g. "for (").
> (let ((type (and (> match-pos (point-min))
> (c-get-char-property (1- match-pos) 'c-type))))
> - (cond ((not (memq (char-before match-pos) '(?\( ?, ?\[ ?<)))
> + (cond
> + (;; Try to not fontify the second and third clauses of
> + ;; `for' statements as declarations.
> + (and (or (eq (char-before match-pos) ?\;)
> + (save-excursion
> + ;; Catch things like for(; (DWORD)(int) x &
> + ;; y; ) without invoking the full might of
> + ;; c-beginning-of-statement-1.
> + (goto-char match-pos)
> + (while (eq (char-before) ?\))
> + (c-go-list-backward)
> + (c-backward-syntactic-ws))
Here we potentially have an infinite loop when there's an unbalanced ")"
in the code. It's critical to check the return from
`c-go-list-backward' here, too.
> + (eq (char-before) ?\;)))
> +
> + (setq paren-state (c-parse-state))
> + (setq most-enclosing-brace
> + (c-most-enclosing-brace paren-state))
> + (eq (char-after most-enclosing-brace) ?\())
Rather than using `c-parse-state', this could be done more efficiently
with `c-up-list-backward'. There may be the possibility of an error
here if `c-most-enclosing-brace' returns nil, leading to (char-after
nil), but maybe that can't happen. It would certainly be a good idea to
check for it, though.
> +
> + ;; After a ";" in a for-block. A declaration can never
> + ;; begin after a `;' if the most enclosing paren is a
> + ;; `('.
How do we know we're in a "for" block here? There is no `looking-at'
check with the pertinent regexp (c-paren-stmt-key).
> + (setq context 'arglist
> + c-restricted-<>-arglists t))
Again, why is `context' set to 'arglist here? What effect is this
intended to have on `c-forward-decl-or-cast-1'?
> + ((not (memq (char-before match-pos) '(?\( ?, ?\[ ?<)))
> (setq context nil
> c-restricted-<>-arglists nil))
> ;; A control flow expression
> @@ -1252,7 +1276,7 @@
> ;; Are we at a declarator? Try to go back to the declaration
> ;; to check this. Note that `c-beginning-of-decl-1' is slow,
> ;; so we cache its result between calls.
> - (let (paren-state bod-res encl-pos is-typedef)
> + (let (bod-res encl-pos is-typedef)
> (goto-char start-pos)
> (save-excursion
> (unless (and decl-search-lim
> @@ -1318,20 +1342,7 @@
> ;; Back up to the type to fontify the declarator(s).
> (goto-char (car decl-or-cast))
> - (let ((decl-list
> - (if context
> - ;; Should normally not fontify a list of
> - ;; declarators inside an arglist, but the first
> - ;; argument in the ';' separated list of a "for"
> - ;; statement is an exception.
> - (when (eq (char-before match-pos) ?\()
> - (save-excursion
> - (goto-char (1- match-pos))
> - (c-backward-syntactic-ws)
> - (and (c-simple-skip-symbol-backward)
> - (looking-at c-paren-stmt-key))))
> - t)))
> -
> + (let ((decl-list (not context)))
Here the setting of decl-list is changed. Why? `decl-list''s purpose
is to instruct `c-font-lock-declarators' whether to fontify just one
declarator or a whole list of them. The existing logic is to fontify
all the declarators in a "for" block, whereas after the patch only the
first one would be fontified. Again, why?
> ;; Fix the `c-decl-id-start' or `c-decl-type-start' property
> ;; before the first declarator if it's a list.
> ;; `c-font-lock-declarators' handles the rest.
Question (for Daniel): has this patch been run through the CC Mode test
suite, yet?
> --
> (domestic pets only, the antidote for overdose, milk.)
> bloggy blog: http://lars.ingebrigtsen.no
--
Alan Mackenzie (Nuremberg, Germany).
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