bug#30788: 27.0.50; Getting 'char-displayable-p: Invalid hash table rehash size: 1.0' when starting emacs -Q

[Ulrich Mueller]

>>>>> On Tue, 13 Mar 2018, Eli Zaretskii wrote:

> So you are saying that the problems happen when LC_NUMERIC sets a
> locale whose decimal dot is not a period?

I cannot say that this is the reason, only that the problem occurs
with de_DE.UTF-8 (and fr_FR.UTF-8 too) but not with en_US.UTF-8.

> Is this relevant to 25.3 or 27 (or both)?

Both.

> Anyway, what does that have to do with fontconfig?  Emacs arranges
> for LC_NUMERIC to be "C" at startup (see fixup_locale); does this
> new versio0n of fontconfig somehow countermands that?

I believe that this line in function FcConfigEnsure is the culprit
(present in 2.13.0 but not in 2.12.6):
https://cgit.freedesktop.org/fontconfig/tree/src/fccfg.c?h=2.13.0#n52

        setlocale (LC_ALL, "");

Patching that code out fixes the problem here.