bug#23117: 25.0.92; Having pcomplete-ignore-case different from completion-ignore-case can lead to an error

[Stefan Monnier]

>> 1. (setq pcomplete-ignore-case t)
>> 2. Keep completion-ignore-case at its default nil value.
>> 3. M-x shell
>> 3. Type 'cd /Usr/', press C-M-i.
>> 4. See the below error.
>>
>> Should the former variable just be made into an alias for the latter one?
>>
>> Debugger entered--Lisp error: (error "Internal error: usr/games/ doesn’t 
>> match \\`Usr\\(.*?\\)/")
>
> This is still the case in Emacs 28, so the question remains, I guess --
> should one of them be made into an alias for the other,

That would be nice, yes.

> and in that case, which one should be the alias?

`pcomplete-ignore-case` fundamentally belongs to the pcomplete UI which
is considered obsolete, so I'd make that an alias for the
core variable `completion-ignore-case`.


        Stefan