bug#58883: CC Mode 5.35.1 (C/*l); Incorrect fontification of X function

Hello, Po.

Thanks for yet another bug report!

On Sun, Oct 30, 2022 at 09:22:45 +0800, Po Lu via CC-Mode-help wrote:
> Package: cc-mode

> In the following Xlib function:

> Bool XCheckIfEvent (
> 	register Display *dpy,
> 	register XEvent *event,		/* XEvent to be filled in. */
> 	Bool (*predicate)(
> 			  Display*			/* display */,
> 			  XEvent*			/* event */,
> 			  char*				/* arg */
> 			  ),		/* function to call */
> 	char *arg)
> {
> 	register _XQEvent *prev, *qelt;
> 	unsigned long qe_serial = 0;
> 	int n;			/* time through count */

>         LockDisplay(dpy);
> 	prev = NULL;
> 	for (n = 3; --n >= 0;) {
> 	    for (qelt = prev ? prev->next : dpy->head;
> 		 qelt;
> 		 prev = qelt, qelt = qelt->next) {
> 		if(qelt->qserial_num > qe_serial
> 		   && (*predicate)(dpy, &qelt->event, arg)) {
> 		    *event = qelt->event;
> 		    _XDeq(dpy, prev, qelt);
> 		    _XStoreEventCookie(dpy, event);
> 		    UnlockDisplay(dpy);
> 		    return True;
> 		}
> 	    }
> 	    if (prev)
> 		qe_serial = prev->qserial_num;
> 	    switch (n) {
> 	      case 2:
> 		_XEventsQueued(dpy, QueuedAfterReading);
> 		break;
> 	      case 1:
> 		_XFlush(dpy);
> 		break;
> 	    }
> 	    if (prev && prev->qserial_num != qe_serial)
> 		/* another thread has snatched this event */
> 		prev = NULL;
> 	}
> 	UnlockDisplay(dpy);
> 	return False;
> }

> "Display" and "XEvent" are not fontified as types, inside both the
> function prototype and that of the predcate argument.

> "_XQEvent" also fails to be fontified as a type.

Yes.  This was an unwanted consequence of the fix to bug #58537 two
weeks ago.  There, things were being fontified as types and, at the same
time, being wrongly added to c-found-types.  That fix prevented Display,
etc., from being fontified.

The attached patch allows the fontification of these types, but doesn't
add them to c-found-types.  Would you please do the usual with the
patch, and let me know if there are any problems with it.  Thanks!

> Emacs  : GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu)
>  of 2022-10-29
> Package: CC Mode 5.35.1 (C/*l)
> Buffer Style: gnu
> c-emacs-features: (pps-extended-state col-0-paren posix-char-classes gen-string-delim gen-comment-delim syntax-properties category-properties 1-bit)

[ .... ]

-- 
Alan Mackenzie (Nuremberg, Germany).

diff -r 53717eda724c cc-engine.el
--- a/cc-engine.el	Sat Oct 29 09:42:47 2022 +0000
+++ b/cc-engine.el	Sun Oct 30 13:32:23 2022 +0000
@@ -10227,7 +10227,11 @@
 	(save-rec-ref-ids c-record-ref-identifiers)
 	;; Set when we parse a declaration which might also be an expression,
 	;; such as "a *b".  See CASE 16 and CASE 17.
-	maybe-expression)
+	maybe-expression
+	;; Set for the type when `c-forward-type' returned `maybe', and we
+	;; want to fontify it as a type, but aren't confident enough to enter
+	;; it into `c-found-types'.
+	unsafe-maybe)
 
     (save-excursion
       (goto-char preceding-token-end)
@@ -10923,7 +10927,7 @@
 	   ;; a statement beginning with an identifier.
 	   (when (and (eq at-type 'maybe)
 		      (not (eq context 'top)))
-	     (setq c-record-type-identifiers nil))
+	     (setq unsafe-maybe t))
 	   (throw 'at-decl-or-cast t))
 
 	 ;; CASE 11
@@ -11226,7 +11230,8 @@
 		 ;; fontification just because it's "a known type that can't
 		 ;; be a name or other expression".  2013-09-18.
 		 )
-	(let ((c-promote-possible-types t))
+	(let ((c-promote-possible-types
+	       (if unsafe-maybe 'just-one t)))
 	  (save-excursion
 	    (goto-char type-start)
 	    (c-forward-type))))