This does two things:
1. Intersect subsetter glyphset with the table's Coverage before
passing to ClassDef1 for subsetting. Anything that doesn't
get past Coverage wouldn't ever get to ClassDef1,
2. Never reuse class0 of ClassDef2. There's unspoken assumption
that ClassDef2's class0 is never used for actual kerning, since
that's the unbounded "every other glyph" class. Previously our
ClassDef subsetter was reusing class0 if "every other glyph"
happened to become empty because of the subset glyphset. Don't
do that for PairPos's ClassDef2. As a result of this assumption,
don't keep a PairPosClass2 subtable if only ClassDef2's class0
survived subsetting.
Would be good to add tests for both.
Related to https://github.com/harfbuzz/harfbuzz/issues/2703
* Replaced all from ...py23 import * with explicit name imports, or removed completely when possible.
* Replaced tounicode() with tostr()
* Changed all BytesIO ans StringIO imports to from io import ..., replaced all UnicodeIO with StringIO.
* Replaced all unichr() with chr()
* Misc minor tweaks and fixes
Previously otlLib was generating None if the values themselves were
empty even if the value format was non-empty. This happened to work
for compiling to binary since the compiler handles Value=None.
But this was confusing varLib.merger module (as in when building
variable fonts from such otlLib-built master GSUB/GPOS tables, without
roundtripping to OTF/TTF binary first), because in varLib.merger,
a None means "this master doesn't provide that info; skip it"; whereas
in a PairPos table a None as generated by otlLib simply meant "all
values are zero", which is different from "this master doesn't
provide this value".
This fixes that, such that ufo2ft can build variable-font without
saving masters to binary.
Part of https://github.com/googlefonts/ufo2ft/pull/486
See https://github.com/fonttools/fonttools/pull/2214#issuecomment-790742479
Good news: this reverted the one CFF test that needed its expectation to
change when I started this patchset. Bad news: it introduced a couple other
diffs to the same glyph of the same test, which is consistent with changing
the rounding from otRound to round3.
* Revert most of "Use Vector in some places where it improves the clarity of the code (#2206)"
This reverts most of commit 0d3ce2cafc6f604fc46d4d3bfbab34a5bc59e27b.
