bug#52566: 29.0.50; Wishlist: There should be a print-unreadable-function variable

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sat, 22 Jan 2022 15:14:03 +0100
> 
> Lars Ingebrigtsen <larsi@gnus.org> writes:
> 
> > It should be called from print_vectorlike (and any other places that
> > print unreadable objects, but I'm not sure there are any other places),
> > and should probably have a signature like
> >
> > OBJECT PRINTCHARFUN ESCAPEFLAG
> >
> > If it returns nil, the object should be printed as normal.
> >
> > This can then be used to implement a `readablep' function (that would
> > bind this to a function that signals an error, and then catch that
> > error), and also to possibly make an alternative version of prin1 that
> > returns whether it printed something unprintable.
> 
> This has now been implemented in Emacs 29.  The function interface was
> changed a bit, though.

The doc string of print-unreadable-function and its documentation in
the manual seem to contradict each other.