[feaLib] Implement the ignore substitution statement

https://github.com/behdad/fonttools/issues/503

Lib/fontTools/feaLib/ast.py

@@ -296,12 +296,6 @@ class LanguageSystemStatement(Statement):
         builder.add_language_system(self.location, self.script, self.language)
 
 
-class IgnoreSubstitutionRule(Statement):
-    def __init__(self, location, prefix, glyphs, suffix):
-        Statement.__init__(self, location)
-        self.prefix, self.glyphs, self.suffix = (prefix, glyphs, suffix)
-
-
 class FontRevisionStatement(Statement):
     def __init__(self, location, revision):
         Statement.__init__(self, location)

Lib/fontTools/feaLib/builder_test.py

@@ -49,6 +49,7 @@ class BuilderTest(unittest.TestCase):
         GPOS_1 GPOS_1_zero GPOS_2 GPOS_2b GPOS_3 GPOS_4 GPOS_5 GPOS_6 GPOS_8
         GSUB_2 GSUB_3 GSUB_6 GSUB_8
         spec4h1 spec5d1 spec5d2 spec5fi1 spec5fi2 spec5fi3 spec5fi4
+        spec5f_ii_1
         spec5h1 spec6b_ii spec6d2 spec6e spec6f spec6h_ii spec6h_iii_1 spec8a
         spec9b spec9c1 spec9c2 spec9c3
         bug463 bug501 bug502 bug505

Lib/fontTools/feaLib/parser.py

@@ -295,7 +295,8 @@ class Parser(object):
                 raise FeatureLibError(
                     "No lookups can be specified for \"ignore sub\"",
                     location)
-            return ast.IgnoreSubstitutionRule(location, prefix, glyphs, suffix)
+            return ast.ChainContextSubstStatement(
+                location, prefix, glyphs, suffix, [])
         raise FeatureLibError(
             "Expected \"substitute\"", self.next_token_location_)
 

Lib/fontTools/feaLib/parser_test.py

@@ -291,22 +291,24 @@ class ParserTest(unittest.TestCase):
 
     def test_ignore_sub(self):
         doc = self.parse("feature test {ignore sub e t' c;} test;")
-        s = doc.statements[0].statements[0]
+        sub = doc.statements[0].statements[0]
-        self.assertEqual(type(s), ast.IgnoreSubstitutionRule)
+        self.assertIsInstance(sub, ast.ChainContextSubstStatement)
-        self.assertEqual(glyphstr(s.prefix), "e")
+        self.assertEqual(glyphstr(sub.prefix), "e")
-        self.assertEqual(glyphstr(s.glyphs), "t")
+        self.assertEqual(glyphstr(sub.glyphs), "t")
-        self.assertEqual(glyphstr(s.suffix), "c")
+        self.assertEqual(glyphstr(sub.suffix), "c")
+        self.assertEqual(sub.lookups, [])
 
     def test_ignore_substitute(self):
         doc = self.parse(
             "feature test {"
             "    ignore substitute f [a e] d' [a u]' [e y];"
             "} test;")
-        s = doc.statements[0].statements[0]
+        sub = doc.statements[0].statements[0]
-        self.assertEqual(type(s), ast.IgnoreSubstitutionRule)
+        self.assertIsInstance(sub, ast.ChainContextSubstStatement)
-        self.assertEqual(glyphstr(s.prefix), "f [a e]")
+        self.assertEqual(glyphstr(sub.prefix), "f [a e]")
-        self.assertEqual(glyphstr(s.glyphs), "d [a u]")
+        self.assertEqual(glyphstr(sub.glyphs), "d [a u]")
-        self.assertEqual(glyphstr(s.suffix), "[e y]")
+        self.assertEqual(glyphstr(sub.suffix), "[e y]")
+        self.assertEqual(sub.lookups, [])
 
     def test_language(self):
         doc = self.parse("feature test {language DEU;} test;")

Lib/fontTools/feaLib/testdata/spec5f_ii_1.fea

@@ -0,0 +1,9 @@
+# OpenType Feature File specification, section 5.f.ii, example 1
+# "Specifying exceptions to the Chain Sub rule"
+# http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html
+
+feature test {
+    ignore substitute f [a e] d';
+    ignore substitute a d' d;
+    substitute [a e n] d' by d.alt;
+} test;

Lib/fontTools/feaLib/testdata/spec5f_ii_1.ttx

@@ -0,0 +1,97 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ttFont sfntVersion="true" ttLibVersion="3.0">
+
+  <GSUB>
+    <Version value="1.0"/>
+    <ScriptList>
+      <!-- ScriptCount=1 -->
+      <ScriptRecord index="0">
+        <ScriptTag value="DFLT"/>
+        <Script>
+          <DefaultLangSys>
+            <ReqFeatureIndex value="65535"/>
+            <!-- FeatureCount=1 -->
+            <FeatureIndex index="0" value="0"/>
+          </DefaultLangSys>
+          <!-- LangSysCount=0 -->
+        </Script>
+      </ScriptRecord>
+    </ScriptList>
+    <FeatureList>
+      <!-- FeatureCount=1 -->
+      <FeatureRecord index="0">
+        <FeatureTag value="test"/>
+        <Feature>
+          <!-- LookupCount=1 -->
+          <LookupListIndex index="0" value="0"/>
+        </Feature>
+      </FeatureRecord>
+    </FeatureList>
+    <LookupList>
+      <!-- LookupCount=2 -->
+      <Lookup index="0">
+        <!-- LookupType=6 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=3 -->
+        <ChainContextSubst index="0" Format="3">
+          <!-- BacktrackGlyphCount=2 -->
+          <BacktrackCoverage index="0">
+            <Glyph value="a"/>
+            <Glyph value="e"/>
+          </BacktrackCoverage>
+          <BacktrackCoverage index="1">
+            <Glyph value="f"/>
+          </BacktrackCoverage>
+          <!-- InputGlyphCount=1 -->
+          <InputCoverage index="0">
+            <Glyph value="d"/>
+          </InputCoverage>
+          <!-- LookAheadGlyphCount=0 -->
+          <!-- SubstCount=0 -->
+        </ChainContextSubst>
+        <ChainContextSubst index="1" Format="3">
+          <!-- BacktrackGlyphCount=1 -->
+          <BacktrackCoverage index="0">
+            <Glyph value="a"/>
+          </BacktrackCoverage>
+          <!-- InputGlyphCount=1 -->
+          <InputCoverage index="0">
+            <Glyph value="d"/>
+          </InputCoverage>
+          <!-- LookAheadGlyphCount=1 -->
+          <LookAheadCoverage index="0">
+            <Glyph value="d"/>
+          </LookAheadCoverage>
+          <!-- SubstCount=0 -->
+        </ChainContextSubst>
+        <ChainContextSubst index="2" Format="3">
+          <!-- BacktrackGlyphCount=1 -->
+          <BacktrackCoverage index="0">
+            <Glyph value="a"/>
+            <Glyph value="e"/>
+            <Glyph value="n"/>
+          </BacktrackCoverage>
+          <!-- InputGlyphCount=1 -->
+          <InputCoverage index="0">
+            <Glyph value="d"/>
+          </InputCoverage>
+          <!-- LookAheadGlyphCount=0 -->
+          <!-- SubstCount=1 -->
+          <SubstLookupRecord index="0">
+            <SequenceIndex value="0"/>
+            <LookupListIndex value="1"/>
+          </SubstLookupRecord>
+        </ChainContextSubst>
+      </Lookup>
+      <Lookup index="1">
+        <!-- LookupType=1 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SingleSubst index="0">
+          <Substitution in="d" out="d.alt"/>
+        </SingleSubst>
+      </Lookup>
+    </LookupList>
+  </GSUB>
+
+</ttFont>