bug#51899: Odd highlighting in compilation mode

["Kévin Le Gouguec" <kevin.legouguec@gmail.com>]

積丹尼 Dan Jacobson <jidanni@jidanni.org> writes:

> "/tmp/$(basename" is highlighted.

Yup, I guess that's due to this bit this from
compilation-mode-font-lock-keywords:

>      (" --?o\\(?:utfile\\|utput\\)?[= ]\\(\\S +\\)" . 1)

The heuristic, I guess, is "highlight things that look like output
arguments".  Maybe it could do with a smarter font-lock matcher?

I'm not knowledgeable enough with font-lock to see how that could work;
I think we'd want to skip over the --?o\\(?:utfile\\|utput\\)?[= ] part,
then match everything that we find by forward-sexp'ing until
(char-after) matches [ ;&|] (or we hit "no next sexp")?  No idea if
that's expressible with font-lock matchers.

> One $m is highlighted, the others and $i etc. aren't.

compilation-mode mostly expects command outputs, not shell scripts
sources, so I don't know how much shell syntax we want the mode to
highlight by default.

The font-lock rule discussed above does show we expect some shell
commands, but compilation-mode seems more concerned with bits relevant
to the compilation process (i.e. here, the output files) than with shell
syntax in general.

> I have no opinions on what should be highlighted. Just be consistent.

The consistency compilation-mode aims for, IIUC, is "highlight outputs
of the compilation process".