Allow for making more lookups support subtabe breaks. Although AFDKO’s
makeotf supports subtable breaks only in pair pos lookups, I believe
that is an implementation limit that we don’t have to follow; all
OpenType lookups has subtables and it should be possible to code that in
the feature files.
ValueRecord had a makeString() method that takes an optional “vertical”
argument, but no code outside the tests sets this argument. Renamed it
to asFea() and dropped the “vertical”, so that it consistent with the
rest of feaLib.ast classes.
If Coverage is None then the subtable is a noop that does nothing and
there is no point in building it. As a bonus, it makes OTS happy since
it will reject subtables where coverageOffset is NULL (0) and the spec
does not say whether this is allowed or not.
ufo2ft feature writer calls feaLib builder with tables=[GSUB] first, to run closure
over glyph substitutions; if the GSUB features contains 'featureNames' blocks, then
an AssertionError will be raised; in this case, we can simply skip building the
FeatureParams tables as we haven't build the name records they point to.
This would make it easier to construct feaLib AST from code,
where the location is not defined and thus should be None.
Also, we can make other arguments as kwargs with a default
value, now that the first parameter is no longer 'location'.
`tables=None` by default will build all supported tables;
To build only some of these and ignore the others, one can pass a
subset of supported tables tags: .e.g. `tables={'GSUB'}` will only
build the GSUB, even if the feature file may contain e.g. GPOS
related features.
Currently, the feature file parser always resolves included files,
parses their content and inserts it in the resulting AST. The original
`include` statement is lost.
This commit introduces an option to not follow inclusions. Instead, the
output AST will contain an `include` statement. This allows to process a
feature file on its own, and allows to round-trip it.
For example in glyphsLib, when going from a UFO to a .glyphs file, a
UFO feature file will be sliced up into Glyphs.app classes (e.g. a
GSFeaturePrefix with code `include(../family.fea);`) and when going back
from .glyphs to UFO, the feature file will be patched back together.
