bug#44983: Truncate long lines of grep output

[Dmitry Gutov]

On 01.12.2020 10:45, Juri Linkov wrote:
> [New bug report from emacs-devel]
> > > > > For grep output a bigger problem is that grep on binary data
> > > > > might output too long lines before the terminating newline.
> > > >
> > > > (*) We already have this kind of problem with "normal" files which contain
> > > > minified assets (JS or CSS). The file contents are usually normal ASCII,
> > > > but it's just one line which can reach several MBs in length.
> > > >
> > > > The usual way to deal with that is with project-ignores and
> > > > grep-find-ignored-files. That works for both cases.
> > > This is a bug problem - often grep output lines are so long
> > > that Emacs freezes, so need to kill the process.  Updating
> > > manually ignored-files every time a new file causes freeze
> > > is very unreliable and time-consuming workaround.
> >
> > And a non-obvious one (for an average user).
> >
> > 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?

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.