[feaLib] allow to build from pre-parsed ast.FeatureFile object

Lib/fontTools/feaLib/builder.py

@@ -5,6 +5,7 @@ from fontTools.misc import sstruct
 from fontTools.misc.textTools import binary2num, safeEval
 from fontTools.feaLib.error import FeatureLibError
 from fontTools.feaLib.parser import Parser
+from fontTools.feaLib.ast import FeatureFile
 from fontTools.otlLib import builder as otl
 from fontTools.ttLib import newTable, getTableModule
 from fontTools.ttLib.tables import otBase, otTables
@@ -45,7 +46,12 @@ class Builder(object):
 
     def __init__(self, font, featurefile):
         self.font = font
-        self.file = featurefile
+        # 'featurefile' can be either a path or file object (in which case we
+        # parse it into an AST), or a pre-parsed AST instance
+        if isinstance(featurefile, FeatureFile):
+            self.parseTree, self.file = featurefile, None
+        else:
+            self.parseTree, self.file = None, featurefile
         self.glyphMap = font.getReverseGlyphMap()
         self.default_language_systems_ = set()
         self.script_ = None
@@ -58,7 +64,6 @@ class Builder(object):
         self.cur_feature_name_ = None
         self.lookups_ = []
         self.features_ = {}  # ('latn', 'DEU ', 'smcp') --> [LookupBuilder*]
-        self.parseTree = None
         self.required_features_ = {}  # ('latn', 'DEU ') --> 'scmp'
         # for feature 'aalt'
         self.aalt_features_ = []  # [(location, featureName)*], for 'aalt'
@@ -92,7 +97,8 @@ class Builder(object):
         self.vhea_ = {}
 
     def build(self, tables=None):
-        self.parseTree = Parser(self.file, self.glyphMap).parse()
+        if self.parseTree is None:
+            self.parseTree = Parser(self.file, self.glyphMap).parse()
         self.parseTree.build(self)
         # by default, build all the supported tables
         if tables is None:

Tests/feaLib/builder_test.py

@@ -495,6 +495,13 @@ class BuilderTest(unittest.TestCase):
     def test_build_unsupported_tables(self):
         self.assertRaises(AssertionError, self.build, "", tables={"FOO"})
 
+    def test_build_pre_parsed_ast_featurefile(self):
+        f = UnicodeIO("feature liga {sub f i by f_i;} liga;")
+        tree = Parser(f).parse()
+        font = makeTTFont()
+        addOpenTypeFeatures(font, tree)
+        assert "GSUB" in font
+
 
 def generate_feature_file_test(name):
     return lambda self: self.check_feature_file(name)