bug#42383: 28.0.50; Two bugs with M-x compile

[Stefan Monnier <monnier@iro.umontreal.ca>]

>>         * lisp/shell.el (shell-dynamic-complete-functions): Move
>>         pcomplete-completions-at-point down the list so that filename
>>         completion has a chance to complete before pcompletion.
>>         
>>         Fixes bug#34330
>>
>> yet, `pcomplete-completions-at-point` is supposed to perform filename
>> completion also (via `pcomplete-default-completion-function`), so
>> I think `pcomplete-completions-at-point` should come first and I suspect
>> that the problem in bug#34330 is internal to pcomplete and the above
>> commit just worked around it.
>
> I find pcomplete really confusing (why is it that there's a whole second
> kind of completion framework outside completion-at-point?).

They are not competing nor redundant: pcomplete.el is a system that lets
one explain how to split a line into fields and which completion table
applies to which field (i.e. explain that in a shell command the first
element should be an executable, while the rest will depend on which
executable was used in the first element, ...).

There is sadly some redundancy here in that originally pcomplete.el also
provided a completion UI (under the command `pcomplete`) and this one is
indeed competing with the `completion-at-point` command.
But this part is now obsolete.


        Stefan