bug#61093: Indented file names confuse compilation buffer

[Rudolf Schlatte <rudi@constantly.at>]

Mattias Engdegård <mattias.engdegard@gmail.com> writes:

>> I think it might be ok to ignore leading whitespace, because file
>> names do not start very often with whitespace.
>
> The story goes like this: a tool uses a modification of the GNU message format and its users then expect Emacs to conform to that variant.
>
> The problem with doing that is that each little tweak makes the compilation message rules less robust and more likely to collide with one another and become slower. There are about 60 regexps now, most of which are used by very few people, and we keep adding. Build logs can become quite long so performance is not unimportant.
>
> Maybe it's safe to accept and ignore not arbitrary leading whitespace but a single tab, which your tool seems to emit. Or you could ask those making it to cease emitting the tab.
>
> You could also put your own rule in compilation-regexp-alist. It might look like this:
>
> ;; Message pattern for ancillary locations (notes) from the Go compiler
> (let ((rule
>        `(go-note
>          ,(rx bol "\t"
>               (group                    ; 1: hyperlink
>                (group                    ; 2: file
>                 (not (in " \t\n:"))
>                 (* (not (in "\t\n"))))
>                ":"
>                (group (+ digit))         ; 3: line
>                ":"
>                (group (+ digit))         ; 4: column
>                ":")
>               " "
>               (+ nonl))                ; message
>           2 3 4 0 1)))
>   (setq compilation-error-regexp-alist-alist
>         (remq (assq 'go-note compilation-error-regexp-alist-alist)
>               compilation-error-regexp-alist-alist))
>   (push rule compilation-error-regexp-alist-alist)
>   (setq compilation-error-regexp-alist
>         (remq 'go-note compilation-error-regexp-alist))
>   (push 'go-note compilation-error-regexp-alist))

Is there a way for an emacs mode to add mode-specific values to
compilation-error-regexp-alist(-alist)?  If a major mode starts
compilation, presumably it knows the error message format and could set
up that one compilation buffer accordingly without having to add to
global error message parsing.