Subject: bug#63285: 30.0.50; CC Mode: K&R argument declaration misdetection after parenthesized type

From: Alan Mackenzie <[email-masked]>
Date: Fri, 6 Oct 2023 13:18:01 +0000

Hello, Olivier and Stefan.

On Thu, Oct 05, 2023 at 20:43:24 +0000, Stefan Kangas wrote:
> Olivier Certner <[email-masked]> writes:

> > Sorry, I had clobbered the "(+ (point) 1000)" part in the previous patch.
> >
> > Please use this one instead.

Olivier, thanks for taking the trouble to submit this bug report.  Sorry
it's taken me so long to getting around to looking at it.

> Alan, could you please take a look at the below patch?

> Thanks in advance.

> > From 0515de23d84a48c57b456c6730f826c5d783b965 Mon Sep 17 00:00:00 2001
> > From: Olivier Certner <[email-masked]>
> > Date: Wed, 3 May 2023 11:44:43 +0200
> > Subject: [PATCH] CC Mode: Fix K&R argument declaration misdetection after
> >  parenthesized type
> >
> > * lisp/progmodes/cc-engine.el (c-in-knr-argdecl): When trying to loop
> > over candidate declarations (between the function declaration's
> > identifier list's end and point) to check whether the names of their
> > identifiers correspond with that of the identifier list, actually fail
> > as soon as stumbling on something other than a declaration instead of
> > silently succeeding, which causes some constructs to be erroneously
> > recognized as K&R argument declarations.

I don't think this would be quite the right way to go.  It would be too
rigorous in rejecting partially written K&R constructs which might cause
them to be excessively reindented as commas and or semicolons get typed.

It seems that (throw 'knr nil) when the c-forward-decl-or-cast-1 form
fails is sufficient to prevent the wrong recognition of your test file's
line 2 as a K&R declaration.  Please feel free to try out my (simpler)
patch below on your real C code.

Also, I propose adopting your 2-line test file, reindented, as a new
test in the CC Mode test suite.  Please let me know if you'd prefer that
not to happen.

> > (Bug#63285)
> > ---
> >  lisp/progmodes/cc-engine.el | 29 ++++++++++++++++++-----------
> >  1 file changed, 18 insertions(+), 11 deletions(-)
> >
> > diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
> > index 8b34daf03c2..27740b4903c 100644
> > --- a/lisp/progmodes/cc-engine.el
> > +++ b/lisp/progmodes/cc-engine.el
> > @@ -12039,17 +12039,24 @@ c-in-knr-argdecl
> >  		       ;; Each time around the following checks one
> >  		       ;; declaration (which may contain several identifiers).
> >  		       (while (and
> > -			       (consp (setq decl-or-cast
> > -					    (c-forward-decl-or-cast-1
> > -					     after-prec-token
> > -					     nil ; Or 'arglist ???
> > -					     nil)))
> > -			       (memq (char-after) '(?\; ?\,))
> > -			       (goto-char (car decl-or-cast))
> > -			       (save-excursion
> > -				 (setq semi-position+1
> > -				       (c-syntactic-re-search-forward
> > -					";" (+ (point) 1000) t)))
> > +			       (or
> > +				(and
> > +				 (consp (setq decl-or-cast
> > +					      (c-forward-decl-or-cast-1
> > +					       after-prec-token
> > +					       nil ; Or 'arglist ???
> > +					       nil)))
> > +				 (memq (char-after) '(?\; ?\,))
> > +				 (goto-char (car decl-or-cast))
> > +				 (save-excursion
> > +				   (setq semi-position+1
> > +					 (1+ (or
> > +					      (c-syntactic-re-search-forward
> > +					       ";" (+ (point) 1000) t)
> > +					      (1- (point-max)))))))
> > +				;; Can't parse declarations correctly,
> > +				;; bail out.
> > +				(throw 'knr nil))
> >  			       (c-do-declarators
> >  				semi-position+1 t nil nil
> >  				(lambda (id-start id-end _next _not-top
> > --
> > 2.39.2

Here's my amended patch:

diff -r b680bbba3141 cc-engine.el
--- a/cc-engine.el	Fri Sep 29 11:15:58 2023 +0000
+++ b/cc-engine.el	Fri Oct 06 11:22:31 2023 +0000
@@ -12285,11 +12285,14 @@
 		       ;; Each time around the following checks one
 		       ;; declaration (which may contain several identifiers).
 		       (while (and
-			       (consp (setq decl-or-cast
-					    (c-forward-decl-or-cast-1
-					     after-prec-token
-					     nil ; Or 'arglist ???
-					     nil)))
+			       (not (eq (char-after) ?{))
+			       (or
+				(consp (setq decl-or-cast
+					     (c-forward-decl-or-cast-1
+					      after-prec-token
+					      nil ; Or 'arglist ???
+					      nil)))
+				(throw 'knr nil))
 			       (memq (char-after) '(?\; ?\,))
 			       (goto-char (car decl-or-cast))
 			       (save-excursion

-- 
Alan Mackenzie (Nuremberg, Germany).