bug#13713: 24.3.50; C indent produces error when narrowing is active

bug#13713: 24.3.50; C indent produces error when narrowing is active

[Dima Kogan]

Hi.

I'm observing an issue with emacs indentation in C mode when narrowing
is enabled. To reproduce, create a tst.c buffer with the following 3
lines:

// 123
// 456
// 789

I select the last 2 lines (456, 789), and narrow-to-region. Then I place
the point at the start of the 789 line, and press 'tab'. I get this:

Debugger entered--Lisp error: (args-out-of-range 1 8)
  parse-partial-sexp(1 8)
  c-determine-limit-get-base(15 1000)
  (let* ((start (or start (point))) (try-size (or try-size (* 2 how-far-back))) (base (c-determine-limit-get-base start try-size)) (pos base) (s (parse-partial-sexp pos pos)) stack elt size (count 0)) (while (< pos start) (setq s (parse-partial-sexp pos start nil nil s (quote syntax-table))) (setq size (- (if (or (nth 4 s) (nth 3 s)) (nth 8 s) (point)) pos)) (if (> size 0) (setq stack (cons (cons pos size) stack))) (if (or (nth 4 s) (nth 3 s)) (setq s (parse-partial-sexp (point) start nil nil s (quote syntax-table)))) (setq pos (point))) (while (and (< count how-far-back) stack) (setq elt (car stack) stack (cdr stack)) (setq count (+ count (cdr elt)))) (cond ((>= count how-far-back) (+ (car elt) (- count how-far-back))) ((eq base (point-min)) (point-min)) (t (c-determine-limit (- how-far-b
 ack count) base try-size))))
  (save-excursion (let* ((start (or start (point))) (try-size (or try-size (* 2 how-far-back))) (base (c-determine-limit-get-base start try-size)) (pos base) (s (parse-partial-sexp pos pos)) stack elt size (count 0)) (while (< pos start) (setq s (parse-partial-sexp pos start nil nil s (quote syntax-table))) (setq size (- (if (or (nth 4 s) (nth 3 s)) (nth 8 s) (point)) pos)) (if (> size 0) (setq stack (cons (cons pos size) stack))) (if (or (nth 4 s) (nth 3 s)) (setq s (parse-partial-sexp (point) start nil nil s (quote syntax-table)))) (setq pos (point))) (while (and (< count how-far-back) stack) (setq elt (car stack) stack (cdr stack)) (setq count (+ count (cdr elt)))) (cond ((>= count how-far-back) (+ (car elt) (- count how-far-back))) ((eq base (point-min)) (point-min)) (t (c-determine-li
 mit (- how-far-back count) base try-size)))))
  c-determine-limit(500)
  c-guess-basic-syntax()
  c-indent-line()
  c-indent-command(nil)
  c-indent-line-or-region(nil nil)
  call-interactively(c-indent-line-or-region nil nil)


As shown above, the failure is in (parse-partial-sexp 1 8). Evaluating
this same for succeeds if the buffer is re-widened.

Thanks

bug#13713: Root cause

[Dima Kogan]

I looked at it some more, and it's pretty clear what's happening. The
indentation command calls (c-determine-limit), which in turn calls
(parse-partial-sexp) in many places. (parse-partial-sexp) fails if asked to look
at the buffer outside of the narrowed region. Thus one way to fix this is to
wrap the definition of c-determine-limit in (save-restriction (widen) ... ).
This is a construct that already appears in many places in cc-engine.el, so
maybe it's appropriate here. This advice makes it work:


(defadvice c-determine-limit (around c-determine-limit-works-with-narrowing
				     (how-far-back &optional start try-size)
				     activate)
  "I lift the restriction around this function to get around emacs bug 13713"
  (save-restriction (widen) ad-do-it))


I don't know enough about the internal design of cc-engine.el to know if this is
an appropriate place to lift the restriction, or if lifting it is the way to go
at all.

Thanks

bug#13713: 24.3.50; C indent produces error when narrowing is active

[Noam Postavsky]

found 13713 25.3
tags 13713 fixed
close 13713 26.1
quit

Dima Kogan <dima@secretsauce.net> writes:

> Hi.
>
> I'm observing an issue with emacs indentation in C mode when narrowing
> is enabled. To reproduce, create a tst.c buffer with the following 3
> lines:
>
> // 123
> // 456
> // 789
>
> I select the last 2 lines (456, 789), and narrow-to-region. Then I place
> the point at the start of the 789 line, and press 'tab'. I get this:
>
> Debugger entered--Lisp error: (args-out-of-range 1 8)

Seems to be fixed in emac-26.