bug#41809: c-context-line-break incorrect after comments: cache issue?

bug#41809: c-context-line-break incorrect after comments: cache issue?

[Daniel Colascione]

c-context-line-break sometimes incorrectly extends a comment when invoked
immediately after the end of a comment. To repro:

emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
(c-context-line-break) (delete-char -2) (end-of-line)
(c-context-line-break))'

The second c-context-line-break occurs when point is *after* the comment,
so the /*foo*/ comment shouldn't be extended --- yet it is. The problem
appears to be some kind of cc-mode cache corruption. This recipe behaves
correctly:

$ emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
(c-context-line-break) (delete-char -2) (end-of-line) (c-before-change
(point-min) (point-max)) (c-after-change (point-min) (point-max) (1-
(point-max))) (c-context-line-break))'

bug#41809: c-context-line-break incorrect after comments: cache issue?

[Alan Mackenzie]

Hello, Daniel.

In article <mailman.1663.1591891807.2541.bug-gnu-emacs@gnu.org> you wrote:
> c-context-line-break sometimes incorrectly extends a comment when invoked
> immediately after the end of a comment. To repro:

> emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
> (c-context-line-break) (delete-char -2) (end-of-line)
> (c-context-line-break))'

> The second c-context-line-break occurs when point is *after* the comment,
> so the /*foo*/ comment shouldn't be extended --- yet it is. The problem
> appears to be some kind of cc-mode cache corruption. This recipe behaves
> correctly:

> $ emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
> (c-context-line-break) (delete-char -2) (end-of-line) (c-before-change
> (point-min) (point-max)) (c-after-change (point-min) (point-max) (1-
> (point-max))) (c-context-line-break))'

Thanks for the report.

After a quick bit of edebugging, it seems to be an off-by-one error in
some cache handling.  It shouldn't be too difficult to sort out.

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#41809: c-context-line-break incorrect after comments: cache issue?

[Alan Mackenzie]

Hello again, Daniel.

On Thu, Jun 11, 2020 at 18:38:29 -0000, Alan Mackenzie wrote:
> In article <mailman.1663.1591891807.2541.bug-gnu-emacs@gnu.org> you wrote:
> > c-context-line-break sometimes incorrectly extends a comment when invoked
> > immediately after the end of a comment. To repro:

> > emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
> > (c-context-line-break) (delete-char -2) (end-of-line)
> > (c-context-line-break))'

> > The second c-context-line-break occurs when point is *after* the comment,
> > so the /*foo*/ comment shouldn't be extended --- yet it is. The problem
> > appears to be some kind of cc-mode cache corruption. This recipe behaves
> > correctly:

> > $ emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
> > (c-context-line-break) (delete-char -2) (end-of-line) (c-before-change
> > (point-min) (point-max)) (c-after-change (point-min) (point-max) (1-
> > (point-max))) (c-context-line-break))'

> Thanks for the report.

> After a quick bit of edebugging, it seems to be an off-by-one error in
> some cache handling.  It shouldn't be too difficult to sort out.

Would you please try out the following patch on your real code where you
found the bug.  It seems to fix your test case.


diff -r fd31432873bd cc-engine.el
--- a/cc-engine.el	Thu Jun 11 10:50:35 2020 +0000
+++ b/cc-engine.el	Fri Jun 12 07:32:38 2020 +0000
@@ -3141,7 +3141,7 @@
 	       (not base)   ; FIXME!!! Compare base and far-base??
 					; (2019-05-21)
 	       (not end)
-	       (> here end))
+	       (>= here end))
 	      (progn
 		(setq far-base-and-state (c-parse-ps-state-below here)
 		      far-base (car far-base-and-state)
@@ -3154,7 +3154,7 @@
 	      (or
 	       (and (> here base) (null end))
 	       (null (nth 8 s))
-	       (and end (> here end))
+	       (and end (>= here end))
 	       (not
 		(or
 		 (and (nth 3 s)		; string


Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#41809: c-context-line-break incorrect after comments: cache issue?

[Alan Mackenzie]

Hello, Daniel.

On Thu, Jun 11, 2020 at 18:38:29 -0000, Alan Mackenzie wrote:
> In article <mailman.1663.1591891807.2541.bug-gnu-emacs@gnu.org> you wrote:
> > c-context-line-break sometimes incorrectly extends a comment when invoked
> > immediately after the end of a comment. To repro:

> > emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
> > (c-context-line-break) (delete-char -2) (end-of-line)
> > (c-context-line-break))'

> > The second c-context-line-break occurs when point is *after* the comment,
> > so the /*foo*/ comment shouldn't be extended --- yet it is. The problem
> > appears to be some kind of cc-mode cache corruption. This recipe behaves
> > correctly:

> > $ emacs -Q --eval '(progn (c-mode) (insert "/*foo*/") (backward-char)
> > (c-context-line-break) (delete-char -2) (end-of-line) (c-before-change
> > (point-min) (point-max)) (c-after-change (point-min) (point-max) (1-
> > (point-max))) (c-context-line-break))'

> Thanks for the report.

> After a quick bit of edebugging, it seems to be an off-by-one error in
> some cache handling.  It shouldn't be too difficult to sort out.

It wasn't.  I've committed a simple patch for this, and I'm closing the
bug.

> -- 
> Alan Mackenzie (Nuremberg, Germany).