bug#44983: Truncate long lines of grep output

[Juri Linkov <juri@linkov.net>]

>>> Is the same problem exhibited by commands using the Xref UI? I don't
>>> remember seeing it, but of course our projects can be very different.
>> No difference from grep, Xref output has the same problem.
>
> Perhaps (setq truncate-lines t) could help in that case?

I customized truncate-lines to t long ago, and still this doesn't help
to improve performance on long lines in grep output.

> Then the lines would be cut at the window width, as you suggest below.
>
>> This will avoid the need of using such workarounds as in bug#44941:
>> grep -a "$@" | cut -c -200
>
> That might cut filenames unnecessary. Even when those a long, we need them
> in their entirety.
>
> The Grep results parsing code could be changed to only take the first XY
> characters of each line, though.

The proposed patch doesn't cut filenames, it hides only endings of long lines.
But still performance is not much better on very long lines.