bug#55205: 28.1.50; completion--replace illegally mutates completion candidates

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> I've got an imdb interface where I choose among different movies (some
> with the same name) by putting the movie poster in the completion
> string to disambiguate.  That's the first place I ran into the problem,
> years ago (and it seems like people keep trying to do things like that,
> and then giving up).

I'm a strong proponent of "different completions should be selectable by
different strings", for the kinds of reasons exposed by Daniel: it makes
it possible to use more UI styles than just selection (and it interacts
better with other things like elimination of duplicates).

But FWIW, that is not a reason to force throwing away the text
properties (IOW the act of stripping the text properties is not
a feature of the code).

E.g. I'd recommend you always include the movie's unique ID in the
completions, probably covered/hidden by the movie's poster (so the ugly
ID doesn't show up).  And when the user selects that entry it would make
a lot of sense to keep displaying the poster.

> If I remember correctly, I ended up copying most of the completion
> machinery into the package just to avoid the stripping.

We should fix the code so it's not necessary.


        Stefan