bug#71017: [PATCH] Flow single-paragraph messages

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Sandra Snan <sandra.snan@idiomdrottning.org>
> Date: Sat,  6 Jul 2024 22:49:50 +0200
> From:  Sandra Snan via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> This fixes two bugs when sending RFC 2646–formatted email.

Thanks.  (I also see RFC 3676 mentioned -- what is this about?)

> First, the old code didn't refill or encode the last paragraph at all
> unless there was at least one hard newline EOF.

Isn't this the documented behavior?

> But for months dogfooding those two changes, sometimes a hardwrapped
> email would still be sent. I finally managed to debug and figure it out
> and it took all day. Turns out mml just plain didn't call the
> fill-flowed-encode function if the message doesn't have any hard
> newlines (newlines with the hard text property). Well, of course a
> single-paragraph email isn't gonna have any hard newlines! But it still
> needs reflowing!
> 
> So I've now changed that and updated the documentation to match those
> news semantics. I went all the way, but a possible compromise might be
> to not-flow a message that has \n\n but no hard text props, since that's
> a sign that something is wrong.

The change seems to be an incompatible behavior change, so I wonder
whether we'd need some way for users to get back old behavior.  Eric,
WDYT?

I'll leave it to Eric to comment on the code changes.