bug#32562: 26; `read-char(-exclusive)' and `characterp'

[Eli Zaretskii]

> Date: Tue, 28 Aug 2018 14:24:36 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: 32562@debbugs.gnu.org
> 
> is `read-char' necessarily about chars that satisfy `characterp'?

No.  It returns a character event, not a character.

> The doc string of `text-char-description' says "file-character CHARACTER". 
> What's a "file character"? A character that can appear in a file name?

No, text-char-description accepts only valid character codes, those
which satisfy the 'characterp' test.  This is unlike
single-key-description, which accepts _events_, and thus will happily
process character input events that are not valid character codes,
i.e. fail the 'characterp' test.  I've now made that clear in the
respective doc strings.

> This stuff is not clear more generally, I think - beyond the max value of 
> `max-char'. Do we have or want to have different kinds of "characters" 
> returned from or passed as args to different "character" functions? Why (or 
> why not)?

The basic difference is between a character code and a character input
event.

> Wrt my original problem: taking a value of `M-:' from `read-char' and passing 
> it to `text-char-description', Emacs has a regression of sorts. Older Emacs 
> versions "work", whereas recent versions raise an error. E.g. Emacs 20 
> `read-char' returns -134217670, and passing that to `text-char-description' 
> gives "\272". Whatever `read-char' can read, it seems, 
> `text-char-description' can describe (perhaps imperfectly?).

It's not a regression: text-char-description wants a valid character
code.

I'm closing this bug, as I think this is a documentation issue which
is now fixed.

Thanks.