* Introduce a new subclass for chained contextual (sub and pos)
* Rename .substitutions to .rules in subst builders to allow for code reuse
* Make format of subtable break marker tuple common between sub/pos
Note that prior to this patch, add_subtable_break in a Subst builder adds:
(self.SUBTABLE_BREAK_, self.SUBTABLE_BREAK_, self.SUBTABLE_BREAK_, self.SUBTABLE_BREAK_)
while add_subtable_break in a Pos builder adds:
(self.SUBTABLE_BREAK_, self.SUBTABLE_BREAK_, self.SUBTABLE_BREAK_, [self.SUBTABLE_BREAK_])
This is messy. If we read the first element from the tuple instead of the last one to test if a rule is a subtable break, we can make the marker tuple the same.
* And now the subtable break code can be hoisted into superclass
* These helper methods will make the build routine common
* Hoist common build method to superclass
The diff doesn’t show it very clearly because it’s being too clever, but all I’ve done is moved one method. Everything works apart from the error message, which comes next.
* Fix the error message
Refactors feaLib, moving code which builds OpenType lookups into otlLib. Note that this changes feaLib's concept of `location` from a tuple to an object.
[docs] Document feaLib
* Rearrange docs by user intention, highlighting the things you can do with each component.
* Remove reference to lexer and error modules from documentation tree, since they’re not user-facing.
* I’ve added docstrings to the parser even though we only provide access to the user-facing part of the API in the main documentation, just to clarify what some of the more obscure methods do and provide links to the spec.
* AST *is* user-facing if you’re building your own feature files in code, so all classes are documented with the user in mind.
This allows for more than one "lookup ..." chaining statements at each glyph position in a chaining contextual substitution or positioning rule: e.g.
sub a b c' lookup lookup1 lookup lookup2 d;
The corresponding change in the Adobe OpenType Feature File Specification (and implementation in makeotf) happened in adobe-type-tools/afdko#1132.
Support was added in db49f20d6b2629e1ba25c4afd3fb60817387f3d6, but there
was only a parser test and no builder test, fix the build and add a
builder test based on the existing parser one.
Fixes https://github.com/fonttools/fonttools/issues/1901
Raise if lookup_index is None, which would happen only of the lookup
referenced belongs to the wrong table. The error message needs to be less
cryptic, though.
Fixes https://github.com/fonttools/fonttools/issues/1896
Setting script that is the same as current language system should make
no effect. This is not documented in the spec, but it is what makeotf
does. This as the effect of preserving lookupflag when set before such a
script statement.
Fixes https://github.com/fonttools/fonttools/issues/1824
