bug#56393: Actually fix the long lines display bug

[Lars Ingebrigtsen]

Gregory Heytings <gregory@heytings.org> writes:

> +  When a file with extremely long lines is opened or inserted in a
> +buffer, Emacs automatically enters auto-narrow mode, and the word
> +@samp{Auto-Narrow} appears in the mode line.  This means that Emacs
> +restricts display, but not editing, to a portion of the buffer above
> +and below point.  All editing commands, including narrowing commands,
> +remain available, and they act on the whole buffer.  For example,
> +@kbd{M->} moves point to the end of the buffer, and not, as would
> +happen with ordinary narrowing, to the end of the portion of the
> +buffer to which display is currently restricted.

Oh, that's an interesting approach.  I haven't tried your patch, but it
sounds like it'd do the trick.

> +      if (!noninteractive && !NILP (Vauto_narrow_long_line_threshold))
> +     {
> +       ptrdiff_t cur, next, found, max = 0;
> +       for (cur = PT; cur < PT + inserted; cur = next)
> +         {
> +           next = find_newline1 (cur, CHAR_TO_BYTE (cur), 0, -1, 1,
> +                                 &found, NULL, true);

You could also use Fbuffer_line_statistics here, which I think should be
faster.

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   bloggy blog: http://lars.ingebrigtsen.no