bug#61093: Indented file names confuse compilation buffer

[Rudolf Schlatte]

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.