bug#39595: #39595: M-x compile still very line-length weak

[Mattias Engdegård]

Dan, in your example you used a long line of spaces. Presumably that is 
representative for your particular use, but different message parsers are 
sensitive to different kinds of long lines:

* 'omake' in compilation-error-regexp-alist is indeed what makes Emacs unusably 
slow with long lines of spaces.

* 'msft' and 'watcom' are both expensive with long lines of spaces, but not as 
bad as 'omake'. Maybe these regexps can be tuned further.

* 'msft' occurs twice by mistake; the last one should be removed. This helps a 
bit.

* 'maven' is still expensive for long lines of non-spaces; see bug#3441. 
Anchoring the match at line-start would fix it:

(rx bol
    (? "["
       (or "ERROR" (group "WARNING") (group "INFO"))
       "]"
       (+ " "))
    (group
     (not (in "\n "))
     (* (or (not (in "\n :"))
            (: " "
               (not (in "\n/-")))
            (: ":"
               (not (in "\n ["))))))
    ":["
    (group (+ digit))
    ","
    (group (+ digit))
    "] ")

Is that correct? (CC:ing Paul Pogonyshev, who worked on that regexp in 
bug#20556.)

I suggest we disable omake by default --- although a nice tool, it was never 
widely used, and OCaml programmers tend to use Dune (or plain Make) these days. 
The omake rule will still be there for those who need it, but the majority 
shouldn't bear the cost.