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

[Alan Mackenzie <acm@muc.de>]

Hello, Stefan.

On Sat, Dec 30, 2017 at 23:26:24 -0500, Stefan Monnier wrote:
> > +      (if (nth 3 ppss)                  ; in a string
> > +          start
> > +        (when (nth 4 ppss)              ; in a comment
> > +          (setq ppss
> > +                (parse-partial-sexp (point) eol nil nil ppss 'syntax-table)))
> > +        (catch 'got-it
> > +          (while (< (point) eol)
> > +            (setq start (point))
> > +            (setq ppss (parse-partial-sexp (point) eol nil nil ppss t))
> > +            (setq end (if (nth 4 ppss) (nth 8 ppss) eol))
> > +            (goto-char start)
> > +            (skip-syntax-forward "-" end)
> > +            (when (< (point) end)
> > +              (throw 'got-it (point)))
> > +            (unless (forward-comment 1) ; comment straddles line break.
> > +              (throw 'got-it nil))
> > +            (setq ppss (syntax-ppss))))))))

> Why not use something like

>    (>= (forward-comment (point-max)) (line-end-position))

> ?

Indeed.  Why not just use beginning-of-defun--in-emptyish-line-p, which
is in the same file, in the same place as I coded
non-syntactic-ws-in-line, yet I failed to notice it?  It is also
somewhat more elegantly coded than my new function.

However, beginning-of-defun--in-emptyish-line-p isn't quite right, in
that it fails to check whether BOL is inside a string.  Something like
the following (untested) should fix it:

(defun beginning-of-defun--in-emptyish-line-p ()
  "Return non-nil if the point is in an \"emptyish\" line.
This means a line that consists entirely of comments and/or
whitespace."
;; See https://lists.gnu.org/r/help-gnu-emacs/2016-08/msg00141.html
  (save-excursion
    (forward-line 0)
    (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)))))))

Happy New Year!

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).