bug#51130: 29.0.50; shell completion fails to complete filenames

[Lars Ingebrigtsen <larsi@gnus.org>]

Carlos Pita <carlosjosepita2@gmail.com> writes:

> Now, many usual commands like cp don't have a pcomplete handler so they
> behave very poorly regarding completion, take for example:
>
>      cp <TAB>
>
> this doesn't give me any completion candidate!

[...]

> In shell.el we have:
>
>   ;; Don't use pcomplete's defaulting mechanism, rely on
>   ;; shell-dynamic-complete-functions instead.
>   (setq-local pcomplete-default-completion-function #'ignore)
>
> So pcomplete is falling back to the ignore (no-op) function. If you
> kill the local binding in the shell buffer, then the default of the
> default does complete paths.

This was possibly added by:

commit e17d9003618cef75852a0b88334cea66a5c4b016
Author:     Stefan Monnier <monnier@iro.umontreal.ca>
AuthorDate: Sat Jun 4 09:31:34 2011 -0300

    * lisp/shell.el: Require and use pcomplete.
    (shell-dynamic-complete-functions): Add pcomplete-completions-at-point.
    (shell-completion-vars): Set pcomplete-default-completion-function.

Just leaving pcomplete-default-completion-function alone seems to give
better results in shell-mode (after testing very briefly), so I'm not
sure why that was added.

Perhaps Stefan has some comments; added to the CCs.