bug#73363: 30.0.91; CJK Font Rendering Behavior Changed

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

> Po Lu, why does it make sense to reject iso10646-1 in these cases?  I
> could perhaps understand why reject gb2312.1980-0 when we request
> something like jisx0208*-*, but iso10646-1 is supposed to support all
> the characters, so I don't understand the rationale for rejecting
> that.  And the same for unicode-bmp and unicode-sip, I think (although
> those are rarely used).

Because such font objects that are cached are subsequently rejected,
once Emacs detects that their registries do not agree with the font
specs'.  I don't recall where this rejection is implemented,
unfortunately.

> And what if the requested registry is ascii-0?  That one should match
> any registry, IMO.  If not, why not?

See above.

> More generally, what were the examples where you saw problems in
> accepting registries different from the requested one?  Also, if those
> problems are specific to certain platforms, how about making this test
> only on those platforms?  Font selection machinery in Emacs is
> delicate enough to try to "do no harm" first and foremost.

I tested my original reproducer, and it appears that the problem has
resolved of itself, probably because the performance of the sfnt font
driver has since improved.  Therefore I will disable this change
elsewhere than Android on the release branch, and remove it entirely on
master.