bug#31938: followup

[Paul Eggert]

On 06/23/2018 04:46 AM, Eli Zaretskii wrote:
> > From: Paul Pogonyshev <pogonyshev@gmail.com>
> > Date: Sat, 23 Jun 2018 12:21:00 +0200
> >
> > Another difference. In Emacs 24-26:
> >
> >      (format "%d" 0.9) => "0"
> >
> > In Emacs 27:
> >
> >      (format "%d" 0.9) => "1"
> This looks like the (unintended?) result of 80e145fc9.

I vaguely recall relying on the Elisp manual, which says that %d must be 
applied only to integers, and I guess I figured the semantics didn't 
matter so that the simplest implementation (thought that rounding and 
keeping -0) would satisfy the doc and anyway would be more helpful than 
truncating and discarding the sign of -0. But now that I reread the 
manual I see that it says %d must signal an error when given a float, 
which is obviously not the behavior, so the manual is wrong. And now 
that this issue has come up I notice that 80e145fc9 caused %d to behave 
inconsistently with %x; the latter truncates and converts -0 to 0 
whereas the former rounds and keeps -0. This inconsistency is not good.

To try to improve this, I installed the attached into master to change 
'format' to be more compatible with Emacs 26 etc. and am boldly closing 
the bug report.

0001-format-d-F-now-truncates-floating-F.patch
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