https://github.com/behdad/harfbuzz/commit/e1d4d0f1dbd8518b5672245c05d73f22a9ed03ea#commitcomment-15006653

Fixes https://github.com/behdad/harfbuzz/issues/187

Funcs implementations that have a non-zero horizontal origin must
implement the glyph_h_origin() callback, nothing new here.

Other implementations (all I know of!) can simply not set
glyph_h_origin() now.  I did that for hb-ot and hb-ft in
44f82750, though that broke the
fallback shaper because the default was returning false...

To avoid triggering -Wmissing-braces; see https://bugzilla.mozilla.org/show_bug.cgi?id=1226175#c8

Hopefully makes clang build happy

Hopefully this wouldn't break any compiler.  There was some magic
moments to getting this to compile...

In anticipation of further changes.  No functional changes.

API change: all fonts created with hb_font_create() now inherit from
(ie have parent) hb_font_get_empty().

No reason to not have it.  Makes life easier later.
We (hb-ft, hb-ot-font, etc) can use this API to inject new
parent into a font...

Makes for a better default and avoids nasty inheritance issues.
See mailing list thread "Default hb_font_t scale".

We don't rely on that.  However, whenever hb_font_make_immutable()
is called, it makes its parenting chain immutable.

A while back we marked every API as version:1.0.  We should fix them all
to reflect real version they were introduced.  This is a start.

Patch from Nikolay Sivov.

Based on data from http://upstream-tracker.org/versions/harfbuzz.html
Resolves #103

Previously, when creating an object from inert inputs (eg:
"hb_font_create(hb_face_get_empty())") we returned the inert
empty object.  This is not helpful as there are legitimate
usecases to do that.

We now never return the inert object unless allocation failed.

Tests are revised to reflect.

Without the element-type they will be getting garbage, at least with
Python.

Ouch!

Should move these out of the public header...

We're "clean" of introspection warnings now.  Remaining ones are about
graphite2 / freetype types not being introspectable.

Since our types are not associated with their methods, marking
constructors makes them inaccessible from bindings.  Undo for now.

Makes documentation / introspection easier.

Avoids USHORT, SHORT, ULONG, LONG clashes with Windows API.

We already set recount to INVALID when destroying.
This block was not necessary.

Should give us some performance boost.

Add global shape_plan.  Unused so far.

To be used for cmap and advance caching if desired.