Re: beginning-of-defun-comments bug [was: Re: 26.0.90: mark-defun problem in c-mode]

[Alan Mackenzie]

Hello, Marcin.

On Wed, Jan 03, 2018 at 05:51:35 +0100, Marcin Borkowski wrote:

> On 2017-12-30, at 14:05, Alan Mackenzie <address@hidden> wrote:
> > On Sat, Dec 30, 2017 at 14:53:27 +0200, Eli Zaretskii wrote:
> >> > Date: Sat, 30 Dec 2017 12:01:36 +0000
> >> > Cc: address@hidden, zhang cc <address@hidden>,
> >> >   Noam Postavsky <address@hidden>
> >> > From: Alan Mackenzie <address@hidden>

> >> > > I see the error, with point anywhere in the body of the second 
> >> > > function.
> >> > > Critical seems to be there being no blank line between the functions.

> >> > > I think there's a bug in beginning-of-defun-comments, which I'm in the
> >> > > middle of edebugging.  It moves point into the first function.

> >> > beginning-of-defun-comments has a bug.  On doing M-x
> >> > beginning-of-defun-comments from the inside of a function, when there's
> >> > no blank lines between it and the previous function, point ends up
> >> > inside that previous function, not at the comments which may separate
> >> > them.

> >> > Perhaps this bug should be fixed before the next Emacs-26 pretest.

> >> How old is this problem?  It looks like it's new in Emacs 26?  If so,
> >> we should try fixing it on the release branch.

> > beginning-of-defun-comments came into existence on 2017-03-31, so this
> > problem is definitely new in Emacs 26.

> Yep, it was committed by me.  Sorry for the mess.  And I thought I had
> tested that thoroughly...

These things are tricky to test properly.  ;-)

> > I've diagnosed the bug.  At one place, it is necessary to scan a line of
> > text from BOL to detect any non-comment/non-space character.  The
> > current code tries to do this by using parse-partial-sexp with the
> > fourth argument STOPBEFORE non-nil.

> > This STOPBEFORE causes the scanning to stop at any character which
> > begins a sexp.  A closing brace doesn't fit into this category.  The
> > scan therefore reaches EOL, and the code therefore falsely assumes there
> > are no non-syntactic-ws characters on that line.

> > I'm sure I can fix this today.

> Any success?  If not, can I help in any way?  (At the very least,
> I could write some more tests to cover this case.)

Sorry, I got distracted by the turn of the year, and one or two other
things.  Please try this:



diff --git a/lisp/emacs-lisp/lisp.el b/lisp/emacs-lisp/lisp.el
index 6952ef4cf4..28605cd35c 100644
--- a/lisp/emacs-lisp/lisp.el
+++ b/lisp/emacs-lisp/lisp.el
@@ -405,12 +405,13 @@ beginning-of-defun--in-emptyish-line-p
 ;; See https://lists.gnu.org/r/help-gnu-emacs/2016-08/msg00141.html
   (save-excursion
     (forward-line 0)
-    (< (line-end-position)
-       (let ((ppss (syntax-ppss)))
-         (when (nth 4 ppss)
-           (goto-char (nth 8 ppss)))
-         (forward-comment (point-max))
-         (point)))))
+    (let ((ppss (syntax-ppss)))
+      (and (null (nth 3 ppss))
+           (< (line-end-position)
+              (progn (when (nth 4 ppss)
+                       (goto-char (nth 8 ppss)))
+                     (forward-comment (point-max))
+                     (point)))))))
 
 (defun beginning-of-defun-comments (&optional arg)
   "Move to the beginning of ARGth defun, including comments."
@@ -428,10 +429,7 @@ beginning-of-defun-comments
                   (progn (skip-syntax-backward
                           "-" (line-beginning-position))
                          (not (bolp))) ; Check for blank line.
-                  (progn (parse-partial-sexp
-                          (line-beginning-position) (line-end-position)
-                          nil t (syntax-ppss (line-beginning-position)))
-                         (eolp))))) ; Check for non-comment text.
+                  (beginning-of-defun--in-emptyish-line-p)))) ; Check for 
non-comment text.
     (forward-line (if first-line-p 0 1))))
 
 (defvar end-of-defun-function


> Best,

> -- 
> Marcin Borkowski

-- 
Alan Mackenzie (Nuremberg, Germany).