bug#3418: Issue with compile.el and compilation-parse-errors-filename-function

[npostavs]

Gary Oberbrunner <garyo@genarts.com> writes:

> If a user (such as myself) has an implementation of this function in his 
> .emacs today, like so:
>
> (defun process-error-filename (filename)
>   ;;; do stuff with filename
>   filename)
> (setq compilation-parse-errors-filename-function 'process-error-filename)
>
> and we add a new argument that gets passed to that function, it'll throw an 
> error. *Users* will have to add 
>   &optional spec-dir 
> to their implementations of it to avoid the error.

We could do something like

    (condition-case err
        (funcall compilation-parse-errors-filename-function filename spec-dir)
      (wrong-number-of-arguments
       ;; Try again with single arg for backwards compatibility.
       (funcall compilation-parse-errors-filename-function filename)))