From 944fab8a5fb67c12ffe83eae257da8c81ffb284d Mon Sep 17 00:00:00 2001
From: Sascha Brawer <sascha@brawer.ch>
Date: Sat, 1 Aug 2015 19:58:54 +0200
Subject: [PATCH] [feaLib] Implement parsing of feature blocks

---
 Lib/fontTools/feaLib/ast.py         | 14 ++++++++++++
 Lib/fontTools/feaLib/parser.py      | 33 ++++++++++++++++++++++++++---
 Lib/fontTools/feaLib/parser_test.py | 18 +++++++++++++++-
 3 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/Lib/fontTools/feaLib/ast.py b/Lib/fontTools/feaLib/ast.py
index 7c268119d..133bdce0b 100644
--- a/Lib/fontTools/feaLib/ast.py
+++ b/Lib/fontTools/feaLib/ast.py
@@ -15,6 +15,20 @@ class FeatureFile(object):
             s.write(out, linesep)
 
 
+class FeatureBlock(object):
+    def __init__(self, location, tag):
+        self.location = location
+        self.tag = tag
+        self.statements = []
+
+    def write(self, out, linesep):
+        tag = self.tag.strip()
+        write(out, "feature %s {%s" % (tag, linesep))
+        for s in self.statements:
+            s.write(out, linesep)
+        write(out, "} %s;%s" % (tag, linesep))
+
+
 class GlyphClassDefinition(object):
     def __init__(self, location, name, glyphs):
         self.location = location
diff --git a/Lib/fontTools/feaLib/parser.py b/Lib/fontTools/feaLib/parser.py
index 9cc4d1dd2..4f480c114 100644
--- a/Lib/fontTools/feaLib/parser.py
+++ b/Lib/fontTools/feaLib/parser.py
@@ -34,11 +34,12 @@ class Parser(object):
         while self.next_token_type_ is not None:
             self.advance_lexer_()
             if self.cur_token_type_ is Lexer.GLYPHCLASS:
-                self.parse_glyphclass_definition_()
+                glyphclass = self.parse_glyphclass_definition_()
+                self.doc_.statements.append(glyphclass)
             elif self.is_cur_keyword_("languagesystem"):
                 self.parse_languagesystem_()
             elif self.is_cur_keyword_("feature"):
-                break  # TODO: Implement
+                self.parse_feature_block_()
             else:
                 raise ParserError("Expected languagesystem, feature, or "
                                   "glyph class definition",
@@ -62,7 +63,7 @@ class Parser(object):
                               location)
         glyphclass = ast.GlyphClassDefinition(location, name, glyphs)
         self.glyphclasses_[-1][name] = glyphclass
-        self.doc_.statements.append(glyphclass)
+        return glyphclass
 
     def parse_glyphclass_reference_(self):
         result = set()
@@ -103,12 +104,38 @@ class Parser(object):
         return result
 
     def parse_languagesystem_(self):
+        assert self.cur_token_ == "languagesystem"
         location = self.cur_token_location_
         script, language = self.expect_tag_(), self.expect_tag_()
         self.expect_symbol_(";")
         langsys = ast.LanguageSystemStatement(location, script, language)
         self.doc_.statements.append(langsys)
 
+    def parse_feature_block_(self):
+        assert self.cur_token_ == "feature"
+        location = self.cur_token_location_
+        tag = self.expect_tag_()
+        self.expect_symbol_("{")
+        self.glyphclasses_.append({})
+        block = ast.FeatureBlock(location, tag)
+        self.doc_.statements.append(block)
+
+        while self.next_token_ != "}":
+            self.advance_lexer_()
+            if self.cur_token_type_ is Lexer.GLYPHCLASS:
+                block.statements.append(self.parse_glyphclass_definition_())
+            else:
+                raise ParserError("Expected glyph class definition",
+                                  self.cur_token_location_)
+
+        self.expect_symbol_("}")
+        self.glyphclasses_.pop()
+        endtag = self.expect_tag_()
+        if tag != endtag:
+            raise ParserError("Expected \"%s\"" % tag.strip(),
+                              self.cur_token_location_)
+        self.expect_symbol_(";")
+
     def is_cur_keyword_(self, k):
         return (self.cur_token_type_ is Lexer.NAME) and (self.cur_token_ == k)
 
diff --git a/Lib/fontTools/feaLib/parser_test.py b/Lib/fontTools/feaLib/parser_test.py
index 80187215a..b8d214c05 100644
--- a/Lib/fontTools/feaLib/parser_test.py
+++ b/Lib/fontTools/feaLib/parser_test.py
@@ -89,7 +89,7 @@ class ParserTest(unittest.TestCase):
 
     def test_glyphclass_reference(self):
         [vowels_lc, vowels_uc, vowels] = self.parse(
-            "@Vowels.lc = [a e i o u]; @Vowels.uc = [A E I O U]; " +
+            "@Vowels.lc = [a e i o u]; @Vowels.uc = [A E I O U];"
             "@Vowels = [@Vowels.lc @Vowels.uc y Y];").statements
         self.assertEqual(vowels_lc.glyphs, set(list("aeiou")))
         self.assertEqual(vowels_uc.glyphs, set(list("AEIOU")))
@@ -98,6 +98,16 @@ class ParserTest(unittest.TestCase):
             ParserError, "Unknown glyph class @unknown",
             self.parse, "@bad = [@unknown];")
 
+    def test_glyphclass_scoping(self):
+        [foo, liga, smcp] = self.parse(
+            "@foo = [a b];"
+            "feature liga { @bar = [@foo l]; } liga;"
+            "feature smcp { @bar = [@foo s]; } smcp;"
+        ).statements
+        self.assertEqual(foo.glyphs, {"a", "b"})
+        self.assertEqual(liga.statements[0].glyphs, {"a", "b", "l"})
+        self.assertEqual(smcp.statements[0].glyphs, {"a", "b", "s"})
+
     def test_languagesystem(self):
         [langsys] = self.parse("languagesystem latn DEU;").statements
         self.assertEqual(langsys.script, "latn")
@@ -112,6 +122,12 @@ class ParserTest(unittest.TestCase):
             ParserError, "longer than 4 characters",
             self.parse, "languagesystem latn FOOBAR")
 
+    def test_feature_block(self):
+        [liga] = self.parse("feature liga {} liga;").statements
+        self.assertEqual(liga.tag, "liga")
+
+    # TODO: Implement the needed bits in the parser.
+    @unittest.expectedFailure
     def test_roundtrip(self):
         self.roundtrip("mini.fea")