[feaLib] Parse Mark-to-mark attachment positioning statements

No output is produced yet; this will come in an upcoming change.

Lib/fontTools/feaLib/ast.py

@@ -198,6 +198,17 @@ class MarkLigPosStatement(Statement):
         builder.add_mark_lig_pos(self.location, self.ligatures, self.marks)
 
 
+class MarkMarkPosStatement(Statement):
+    def __init__(self, location, baseMarks, marks):
+        Statement.__init__(self, location)
+        self.baseMarks, self.marks = baseMarks, marks
+
+    def build(self, builder):
+        # TODO: Implement this.
+        # builder.add_mark_mark_pos(self.location, self.baseMarks, self.marks)
+        pass
+
+
 class MultipleSubstStatement(Statement):
     def __init__(self, location, glyph, replacement):
         Statement.__init__(self, location)

Lib/fontTools/feaLib/parser.py

@@ -286,6 +286,8 @@ class Parser(object):
             return self.parse_position_base_(enumerated, vertical)
         elif self.next_token_ == "ligature":   # GPOS type 5
             return self.parse_position_ligature_(enumerated, vertical)
+        elif self.next_token_ == "mark":   # GPOS type 6
+            return self.parse_position_mark_(enumerated, vertical)
 
         location = self.cur_token_location_
         gc2, value2 = None, None
@@ -353,6 +355,19 @@ class Parser(object):
         self.expect_symbol_(";")
         return ast.MarkLigPosStatement(location, ligatures, marks)
 
+    def parse_position_mark_(self, enumerated, vertical):
+        location = self.cur_token_location_
+        self.expect_keyword_("mark")
+        if enumerated:
+            raise FeatureLibError(
+                '"enumerate" is not allowed with '
+                'mark-to-mark attachment positioning',
+                location)
+        baseMarks = self.parse_glyphclass_(accept_glyphname=True)
+        marks = self.parse_anchor_marks_()
+        self.expect_symbol_(";")
+        return ast.MarkMarkPosStatement(location, baseMarks, marks)
+
     def parse_script_(self):
         assert self.is_cur_keyword_("script")
         location, script = self.cur_token_location_, self.expect_script_tag_()

Lib/fontTools/feaLib/parser_test.py

@@ -456,10 +456,8 @@ class ParserTest(unittest.TestCase):
         self.assertEqual(type(pos), ast.MarkBasePosStatement)
         self.assertEqual(pos.base, {"a", "e", "o", "u"})
         (a1, m1), (a2, m2) = pos.marks
-        self.assertEqual((a1.x, a1.y), (250, 450))
+        self.assertEqual((a1.x, a1.y, m1.name), (250, 450, "TOP_MARKS"))
-        self.assertEqual(m1.name, "TOP_MARKS")
+        self.assertEqual((a2.x, a2.y, m2.name), (210, -10, "BOTTOM_MARKS"))
-        self.assertEqual((a2.x, a2.y), (210, -10))
-        self.assertEqual(m2.name, "BOTTOM_MARKS")
 
     def test_gpos_type_4_enumerated(self):
         self.assertRaisesRegex(
@@ -510,6 +508,29 @@ class ParserTest(unittest.TestCase):
             "        ligComponent <anchor NULL>;"
             "} test;")
 
+    def test_gpos_type_6(self):
+        doc = self.parse(
+            "markClass damma <anchor 189 -103> @MARK_CLASS_1;"
+            "feature test {"
+            "    position mark hamza <anchor 221 301> mark @MARK_CLASS_1;"
+            "} test;")
+        pos = doc.statements[-1].statements[0]
+        self.assertEqual(type(pos), ast.MarkMarkPosStatement)
+        self.assertEqual(pos.baseMarks, {"hamza"})
+        [(a1, m1)] = pos.marks
+        self.assertEqual((a1.x, a1.y, m1.name), (221, 301, "MARK_CLASS_1"))
+
+    def test_gpos_type_6_enumerated(self):
+        self.assertRaisesRegex(
+            FeatureLibError,
+            '"enumerate" is not allowed with '
+            'mark-to-mark attachment positioning',
+            self.parse,
+            "markClass damma <anchor 189 -103> @MARK_CLASS_1;"
+            "feature test {"
+            "    enum pos mark hamza <anchor 221 301> mark @MARK_CLASS_1;"
+            "} test;")
+
     def test_markClass(self):
         doc = self.parse("markClass [acute grave] <anchor 350 3> @MARKS;"
                          "feature test {"