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bug#21730: 25.0.50; Random errors in redisplay--pre-redisplay-functions
From: |
Eli Zaretskii |
Subject: |
bug#21730: 25.0.50; Random errors in redisplay--pre-redisplay-functions |
Date: |
Thu, 22 Oct 2015 17:40:19 +0300 |
> From: Michael Welsh Duggan <mwd@md5i.com>
> Date: Thu, 22 Oct 2015 00:04:06 -0400
>
> I don't have a recipe for this. Every now again I get the following in
> my *Messages* buffer:
>
> redisplay--pre-redisplay-functions: (args-out-of-range 0)
>
> I turned on debug-on-error, and got the following backtrace:
>
> Debugger entered--Lisp error: (args-out-of-range 0)
> get-char-property(0 cursor-sensor-functions)
> cursor-sensor--detect(#<window 224 on *Group*>)
> run-hook-with-args(cursor-sensor--detect #<window 224 on *Group*>)
> redisplay--pre-redisplay-functions(t)
> apply(redisplay--pre-redisplay-functions t)
> #[128 "\300\301\"\210\300\302\"\207" [apply
> redisplay--pre-redisplay-functions ignore nil] 4 nil nil](t)
> redisplay_internal\ \(C\ function\)()
>
> This happens infrequently, about a couple of times a day. I cannot make
> this happen on demand, but I can add debugging code if led in the
> correct direction.
Thanks for reporting this. I'll try to help, although Stefan might
have better ideas.
>From the backtrace it is obvious that the immediate reason for the
problem is the call to 'get-char-property' with an invalid 1st argument
of zero (it's a buffer position, so should be at least 1).
Looking at 'cursor-sensor--detect', I see this:
(defun cursor-sensor--detect (window)
(unless cursor-sensor-inhibit
(let* ((point (window-point window))
;; It's often desirable to make the cursor-sensor-functions
property
;; non-sticky on both ends, but that means get-pos-property might
;; never see it.
(new (or (get-char-property point 'cursor-sensor-functions)
(unless (bobp)
(get-char-property (1- point)
'cursor-sensor-functions))))
So my guess is that the value of 'point' (the variable, not the
function) is 1, i.e. beginning of buffer, and subtracting 1 from it
produces that zero. Then the second call to 'get-char-property' barfs
as expected.
The code tries to protect itself against such a calamity by calling
'bobp', but that function looks at the buffer's value of point, which
might be different from what 'window-point' returns.
So my advice would be to replace the call to 'bobp' with an explicit
test of the value of the local variable 'point', and see if that fixes
the problem.