bug#44983: Truncate long lines of grep output

[Juri Linkov]

>> OTOH, ripgrep has the suitable options:
>>    -M, --max-columns NUM
>>        Don’t print lines longer than this limit in bytes. Longer lines are 
>> omitted,
>>        and only the number of matches in that line is printed.
>>    --max-columns-preview
>>        When the --max-columns flag is used, ripgrep will by default 
>> completely
>>        replace any line that is too long with a message indicating that a 
>> matching
>>        line was removed.  When this flag is combined with --max-columns, a 
>> preview
>>        of the line (corresponding to the limit size) is shown instead, where 
>> the
>>        part of the line exceeding the limit is not shown.
>
> You can experiment with these Right Now(tm) by customizing
> xref-search-program-alist (as well as xref-search-program). They'll only
> affect commands that use xref-matches-in-files, though.

You mean adding "-M 200 --max-columns-preview" to xref-search-program-alist?
It works nice, thanks.  Should this be added by default?

>> Wouldn't it be unthinkable to add support of ripgrep to grep.el?
>> This will allow switching to ripgrep when there is a need to
>> search in files with long lines.
>
> I'm fairly sure nothing in terms of politics is stopping us here, but if we
> wanted to update grep.el's abstractions to use different search programs,
> it looks like a bigger job to me.
>
> Though maybe you can get away with customizing a select number of
> variables? Like grep-template, grep-find-template, etc.

I customized grep-find-template to "find <D> <X> -type f <F> -print0 | sort -z |
 xargs -0 -e rg -inH --color always --no-heading -M 200 --max-columns-preview 
-e <R>"

But this also requires customizing grep-match-regexp to the value
"\033\\[[0-9]*m\033\\[[0-9]*1m\033\\[[0-9]*1m\\(.*?\\)\033\\[[0-9]*0m"
provided by Simon in bug#41766.

And also required a small fix in grep.el:

diff --git a/lisp/progmodes/grep.el b/lisp/progmodes/grep.el
index dafba22f77..0a5fd6bf5d 100644
--- a/lisp/progmodes/grep.el
+++ b/lisp/progmodes/grep.el
@@ -412,7 +412,7 @@ grep-regexp-alist
                (- mend beg))))))
      nil nil
      (3 '(face nil display ":")))
-    ("^Binary file \\(.+\\) matches$" 1 nil nil 0 1))
+    ("^Binary file \\(.+\\) matches" 1 nil nil 0 1))
   "Regexp used to match grep hits.
 See `compilation-error-regexp-alist' for format details.")