bug#50207: 28.0.50; ansi-color-compilation-filter and rgrep

[Augusto Stoffel <arstoffel@gmail.com>]

On Fri, 27 Aug 2021 at 09:06, Juri Linkov wrote:

>>> - (add-hook 'compilation-filter-hook #'ansi-color-compilation-filter)
>>
>> I encountered this a bit ago, and did a bit of diagnosis, but it ended up
>> on my back-burner. I think the issue is due to how the
>> compilation-filter-hooks for grep and ansi-color interact. `grep-filter' is
>> fairly simple and wants to see both the start and end of an ANSI-colorized
>> region, so it "rewinds" to the beginning of a line every time it's
>> called. `ansi-color-compilation-filter', on the other hand, is smart enough
>> to handle the case where it only sees the start of a colorized region in
>> one call, and the end in the next call (see `ansi-color-context' for
>> details).
>
> Would it be possible to solve the problem by adding a new buffer-local
> variable (disabled by default) that will enable line mode for
> `ansi-color-compilation-filter' so that it will handle only complete lines
> like grep mode does?

To complement this a bit, my hunch is that the problem is due to
`compilation-filter-start' being a number and not a marker (bug?).  When
`grep-filter' deletes some characters between `compilation-filter-start'
and the beginning of its line, it causes `ansi-color-compilation-filter'
to skip treating a portion of the buffer.

Or at least I was having this kind of issue in the `grep-heading-mode'
suggested in a recent ticket. :-)