[feaLib] Implement parser for multiple substitutions (GSUB LookupType 2)

Actually building the GSUB table is not implemented yet, since this
will probably need changes to otTables.

Lib/fontTools/feaLib/ast.py

@@ -124,6 +124,15 @@ class LookupReferenceStatement(Statement):
         self.location, self.lookup = (location, lookup)
 
 
+class MultipleSubstitution(Statement):
+    def __init__(self, location, glyph, replacement):
+        Statement.__init__(self, location)
+        self.glyph, self.replacement = glyph, replacement
+
+    def build(self, builder):
+        builder.add_multiple_substitution(self.location, glyph, replacement)
+
+
 class SingleSubstitution(Statement):
     def __init__(self, location, mapping):
         Statement.__init__(self, location)

Lib/fontTools/feaLib/builder.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 from fontTools.feaLib.error import FeatureLibError
 from fontTools.feaLib.parser import Parser
 from fontTools.ttLib.tables import otTables
+import warnings
 
 
 def addOpenTypeFeatures(featurefile_path, font):
@@ -222,6 +223,12 @@ class Builder(object):
         lookup = self.get_lookup_(location, LigatureSubstBuilder)
         lookup.ligatures[glyphs] = replacement
 
+    def add_multiple_substitution(self, location, glyph, replacements):
+        # TODO(sascha): Implement this, possibly via a new class
+        # otTables.MultipleSubst modeled after otTables.SingleSubst.
+        warnings.warn('Multiple substitution (GPOS LookupType 2) '
+                      'is not yet implemented')
+
     def add_single_substitution(self, location, mapping):
         lookup = self.get_lookup_(location, SingleSubstBuilder)
         for (from_glyph, to_glyph) in mapping.items():

Lib/fontTools/feaLib/parser.py

@@ -259,6 +259,15 @@ class Parser(object):
             return ast.SingleSubstitution(location,
                                           dict(zip(glyphs, replacements)))
 
+        # GSUB lookup type 2: Multiple substitution.
+        # Format: "substitute f_f_i by f f i;"
+        if (len(old_prefix) == 0 and len(old_suffix) == 0 and
+                len(old) == 1 and len(old[0]) == 1 and
+                len(new) > 1 and max([len(n) for n in new]) == 1 and
+                num_lookups == 0):
+            return ast.MultipleSubstitution(location, tuple(old[0])[0],
+                                            tuple([list(n)[0] for n in new]))
+
         # GSUB lookup type 4: Ligature substitution.
         # Format: "substitute f f i by f_f_i;"
         if (len(old_prefix) == 0 and len(old_suffix) == 0 and

Lib/fontTools/feaLib/parser_test.py

@@ -310,12 +310,9 @@ class ParserTest(unittest.TestCase):
     def test_substitute_multiple(self):  # GSUB LookupType 2
         doc = self.parse("lookup Look {substitute f_f_i by f f i;} Look;")
         sub = doc.statements[0].statements[0]
-        self.assertEqual(type(sub), ast.SubstitutionRule)
-        self.assertEqual(sub.old_prefix, [])
-        self.assertEqual(sub.old, [{"f_f_i"}])
-        self.assertEqual(sub.old_suffix, [])
-        self.assertEqual(sub.new, [{"f"}, {"f"}, {"i"}])
-        self.assertEqual(sub.lookups, [None])
+        self.assertEqual(type(sub), ast.MultipleSubstitution)
+        self.assertEqual(sub.glyph, "f_f_i")
+        self.assertEqual(sub.replacement, ("f", "f", "i"))
 
     def test_substitute_from(self):  # GSUB LookupType 3
         doc = self.parse("feature test {"