bug#50459: 28.0.50; Python shell completion is incompatible with flex, orderless, etc.

[Gregory Heytings]

> > You shouldn't use (setq completion-styles '(flex)), you should use 
> > (add-to-list 'completion-styles 'flex).  Otherwise the default 
> > completion styles are not used anymore.
>
> This doesn't change the issue described in the subject line.  I would 
> still not see any flex completions if I did what you suggest.

Because the flex completion mechanism returns no completions, and the next 
completion mechanism is called.  What kind of flex completions would you 
expect to see after x.t TAB in your example?

> Granted, completion wouldn't be totally broken.  But I don't mind 
> letting the brokenness manifest itself.  Therefore I use (setq 
> completion-styles '(orderless)).

It's not broken, it works as designed.  Instead of asking each user of the 
completion mechanism to implement a specific function for substring / flex 
completion, these mechanisms tell them "please return all possible 
completions, I'll do the filtering job for you".