Re: Assertion failure in set_iterator_to_next

[Stefan Monnier]

>> > No, it->len should be the length of the multibyte sequence of the
>> > character at IT_CHARPOS (*it).  This is how the basic iteration works,
>> > and if the length is incorrect, we will get garbled display, in
>> > anything but pure 7-bit ASCII buffers.
>> OK, good.  Can you update/complete dispextern.h correspondingly?
> Will do.

Thanks.

>> So the problem now is "why is it->len ==3 rather than ==1"?
> I think it's because it was not yet updated.  It is updated only in
> the next_element_from_* functions.  E.g., for a character from a
> buffer, we have this in next_element_from_buffer:

>       /* Get the next character, maybe multibyte.  */
>       p = BYTE_POS_ADDR (IT_BYTEPOS (*it));
>       if (it->multibyte_p && !ASCII_BYTE_P (*p))
>         it-> c = STRING_CHAR_AND_LENGTH (p, it->len);     <<<<<<<<<
>       else
>         it-> c = *p, it->len = 1;                         <<<<<<<<<

Oh, thank you very much.  I searched for this spot and couldn't find it
(I grepped with a pattern like "->len =", which only caught the second
line which couldn't explain why I was getting it->len==3.
That should help me move forward.

> Since you are saying this is an ASCII buffer, are charpos and bytepos
> at least identical?

Yes, they're identical before the assignment to IT_CHARPOS and
IT_BYTEPOS, but since it->len==3 a discrepancy of 2 appears which then
triggers the subsequent xassert.


        Stefan