[feaLib] Imlement special support for feature aalt

Lib/fontTools/feaLib/ast.py

@@ -263,6 +263,16 @@ class CursivePosStatement(Statement):
             self.location, self.glyphclass, self.entryAnchor, self.exitAnchor)
 
 
+class FeatureReferenceStatement(Statement):
+    """Example: feature salt;"""
+    def __init__(self, location, featureName):
+        Statement.__init__(self, location)
+        self.location, self.featureName = (location, featureName)
+
+    def build(self, builder):
+        builder.add_feature_reference(self.location, self.featureName)
+
+
 class LanguageStatement(Statement):
     def __init__(self, location, language, include_default, required):
         Statement.__init__(self, location)

Lib/fontTools/feaLib/builder.py

@@ -28,11 +28,15 @@ 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'
+        self.aalt_location_ = None
+        # for table 'GDEF'
         self.attachPoints_ = {}  # "a" --> {3, 7}
         self.ligatureCaretByIndex_ = {}  # "f_f_i" --> {3, 7}
         self.ligatureCaretByPos_ = {}  # "f_f_i" --> {300, 600}
-        self.parseTree = None
-        self.required_features_ = {}  # ('latn', 'DEU ') --> 'scmp'
         self.glyphClassDefs_ = {}  # "fi" --> (2, (file, line, column))
         self.markAttach_ = {}  # "acute" --> (4, (file, line, column))
         self.markAttachClassID_ = {}  # frozenset({"acute", "grave"}) --> 4
@@ -41,6 +45,7 @@ class Builder(object):
     def build(self):
         self.parseTree = Parser(self.featurefile_path).parse()
         self.parseTree.build(self)
+        self.build_feature_aalt_()
         for tag in ('GPOS', 'GSUB'):
             table = self.makeTable(tag)
             if (table.ScriptList.ScriptCount > 0 or
@@ -93,6 +98,50 @@ class Builder(object):
                                         self.cur_feature_name_)
         return self.cur_lookup_
 
+    def build_feature_aalt_(self):
+        if not self.aalt_features_:
+            return
+        alternates = {}  # glyph --> {glyph.alt1, glyph.alt2, ...}
+        for location, name in self.aalt_features_ + [(None, "aalt")]:
+            feature = [(script, lang, feature, lookups)
+                       for (script, lang, feature), lookups
+                       in self.features_.items()
+                       if feature == name]
+            if not feature:
+                raise FeatureLibError("Feature %s has not been defined" % name,
+                                      location)
+            for script, lang, feature, lookups in feature:
+                for lookup in lookups:
+                    for glyph, alts in lookup.getAlternateGlyphs().items():
+                        alternates.setdefault(glyph, set()).update(alts)
+        single = {glyph: list(repl)[0] for glyph, repl in alternates.items()
+                  if len(repl) == 1}
+        multi = {glyph: sorted(repl, key=self.font.getGlyphID)
+                 for glyph, repl in alternates.items()
+                 if len(repl) > 1}
+        if not single and not multi:
+            return
+        aalt_lookups = []
+        for (script, lang, feature), lookups in self.features_.items():
+            if feature == "aalt":
+                aalt_lookups.extend(lookups)
+        self.features_ = {(script, lang, feature): lookups
+                          for (script, lang, feature), lookups
+                          in self.features_.items()
+                          if feature != "aalt"}
+        old_lookups = self.lookups_
+        self.lookups_ = []
+        self.start_feature(self.aalt_location_, "aalt")
+        if single:
+            self.add_single_subst(
+                self.aalt_location_, prefix=None, suffix=None, mapping=single)
+        for glyph, repl in multi.items():
+            self.add_multiple_subst(
+                self.aalt_location_, prefix=None, glyph=glyph, suffix=None,
+                replacements=repl)
+        self.end_feature()
+        self.lookups_.extend(old_lookups)
+
     def buildGDEF(self):
         gdef = otTables.GDEF()
         gdef.GlyphClassDef = self.buildGDEFGlyphClassDef_()
@@ -331,6 +380,8 @@ class Builder(object):
         self.language_systems = self.get_default_language_systems_()
         self.cur_lookup_ = None
         self.cur_feature_name_ = name
+        if name == "aalt":
+            self.aalt_location_ = location
 
     def end_feature(self):
         assert self.cur_feature_name_ is not None
@@ -482,6 +533,13 @@ class Builder(object):
                 location)
         lookup.alternates[glyph] = replacement
 
+    def add_feature_reference(self, location, featureName):
+        if self.cur_feature_name_ != "aalt":
+            raise FeatureLibError(
+                'Feature references are only allowed inside "feature aalt"',
+                location)
+        self.aalt_features_.append((location, featureName))
+
     def add_ligature_subst(self, location,
                            prefix, glyphs, suffix, replacement):
         if prefix or suffix:
@@ -732,6 +790,10 @@ class LookupBuilder(object):
         """Infers glyph glasses for the GDEF table, such as {"cedilla":3}."""
         return {}
 
+    def getAlternateGlyphs(self):
+        """Helper for building 'aalt' features."""
+        return {}
+
     def buildCoverage_(self, glyphs, tableClass=otTables.Coverage):
         coverage = tableClass()
         coverage.glyphs = sorted(glyphs, key=self.font.getGlyphID)
@@ -822,6 +884,9 @@ class AlternateSubstBuilder(LookupBuilder):
         subtable.alternates = self.alternates
         return self.buildLookup_([subtable])
 
+    def getAlternateGlyphs(self):
+        return self.alternates
+
 
 class ChainContextPosBuilder(LookupBuilder):
     def __init__(self, font, location):
@@ -882,6 +947,15 @@ class ChainContextSubstBuilder(LookupBuilder):
                     st.SubstLookupRecord.append(rec)
         return self.buildLookup_(subtables)
 
+    def getAlternateGlyphs(self):
+        result = {}
+        for (_prefix, _input, _suffix, lookups) in self.substitutions:
+            for lookup in lookups:
+                alts = lookup.getAlternateGlyphs()
+                for glyph, replacements in alts.items():
+                    result.setdefault(glyph, set()).update(replacements)
+        return result
+
 
 class LigatureSubstBuilder(LookupBuilder):
     def __init__(self, font, location):
@@ -1189,6 +1263,9 @@ class SingleSubstBuilder(LookupBuilder):
         subtable.mapping = self.mapping
         return self.buildLookup_([subtable])
 
+    def getAlternateGlyphs(self):
+        return {glyph: set([repl]) for glyph, repl in self.mapping.items()}
+
 
 class ClassPairPosSubtableBuilder(object):
     def __init__(self, builder, valueFormat1, valueFormat2):

Lib/fontTools/feaLib/builder_test.py

@@ -26,7 +26,8 @@ def makeTTFont():
         "A.sc B.sc C.sc D.sc E.sc F.sc G.sc H.sc I.sc J.sc K.sc L.sc M.sc "
         "N.sc O.sc P.sc Q.sc R.sc S.sc T.sc U.sc V.sc W.sc X.sc Y.sc Z.sc "
         "A.alt1 A.alt2 A.alt3 B.alt1 B.alt2 B.alt3 C.alt1 C.alt2 C.alt3 "
-        "d.alt e.begin n.end s.end "
+        "a.alt1 a.alt2 a.alt3 b.alt c.mid d.alt d.mid e.begin e.mid "
+        "n.end s.end "
         "f_l c_h c_k c_s c_t f_f f_f_i f_f_l f_i o_f_f_i s_t "
         "ydieresis yacute "
         "grave acute dieresis macron circumflex cedilla umlaut ogonek caron "
@@ -167,11 +168,22 @@ class BuilderTest(unittest.TestCase):
 
     def test_spec(self):
         for name in ("4h1 5d1 5d2 5fi1 5fi2 5fi3 5fi4 5h1 "
-                     "6d2 6e 6f 6h_ii 9b").split():
+                     "6d2 6e 6f 6h_ii 8a 9b").split():
             font = makeTTFont()
             addOpenTypeFeatures(self.getpath("spec%s.fea" % name), font)
             self.expect_ttx(font, self.getpath("spec%s.ttx" % name))
 
+    def test_feature_outside_aalt(self):
+        self.assertRaisesRegex(
+            FeatureLibError,
+            'Feature references are only allowed inside "feature aalt"',
+            self.build, "feature test { feature test; } test;")
+
+    def test_feature_undefinedReference(self):
+        self.assertRaisesRegex(
+            FeatureLibError, 'Feature none has not been defined',
+            self.build, "feature aalt { feature none; } aalt;")
+
     def test_GlyphClassDef_conflictingClasses(self):
         self.assertRaisesRegex(
             FeatureLibError, "Glyph X was assigned to a different class",

Lib/fontTools/feaLib/parser.py

@@ -765,6 +765,13 @@ class Parser(object):
         self.parse_block_(block, vertical)
         return block
 
+    def parse_feature_reference_(self):
+        assert self.cur_token_ == "feature", self.cur_token_
+        location = self.cur_token_location_
+        featureName = self.expect_tag_()
+        self.expect_symbol_(";")
+        return ast.FeatureReferenceStatement(location, featureName)
+
     def parse_block_(self, block, vertical):
         self.expect_symbol_("{")
         for symtab in self.symbol_tables_:
@@ -779,6 +786,8 @@ class Parser(object):
                 statements.append(self.parse_anchordef_())
             elif self.is_cur_keyword_({"enum", "enumerate"}):
                 statements.append(self.parse_enumerate_(vertical=vertical))
+            elif self.is_cur_keyword_("feature"):
+                statements.append(self.parse_feature_reference_())
             elif self.is_cur_keyword_("ignore"):
                 statements.append(self.parse_ignore_())
             elif self.is_cur_keyword_("language"):

Lib/fontTools/feaLib/parser_test.py

@@ -132,6 +132,12 @@ class ParserTest(unittest.TestCase):
         self.assertEqual(liga.name, "liga")
         self.assertTrue(liga.use_extension)
 
+    def test_feature_reference(self):
+        doc = self.parse("feature aalt { feature salt; } aalt;")
+        ref = doc.statements[0].statements[0]
+        self.assertIsInstance(ref, ast.FeatureReferenceStatement)
+        self.assertEqual(ref.featureName, "salt")
+
     def test_glyphclass(self):
         [gc] = self.parse("@dash = [endash emdash figuredash];").statements
         self.assertEqual(gc.name, "dash")

Lib/fontTools/feaLib/testdata/spec8a.fea

@@ -0,0 +1,21 @@
+languagesystem DFLT dflt;
+languagesystem latn dflt;
+languagesystem latn TRK;
+languagesystem cyrl dflt;
+
+feature aalt {
+    feature salt;
+    feature smcp;
+    substitute d by d.alt;
+} aalt;
+
+feature smcp {
+    sub [a-c] by [A.sc-C.sc];
+    sub f i by f_i;  # not considered for aalt
+} smcp;
+
+feature salt {
+    sub a from [a.alt1 a.alt2 a.alt3];
+    sub e [c d e]' f by [c.mid d.mid e.mid];
+    sub b by b.alt;
+} salt;

Lib/fontTools/feaLib/testdata/spec8a.ttx

@@ -0,0 +1,194 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ttFont>
+
+  <GSUB>
+    <Version value="1.0"/>
+    <ScriptList>
+      <!-- ScriptCount=3 -->
+      <ScriptRecord index="0">
+        <ScriptTag value="DFLT"/>
+        <Script>
+          <DefaultLangSys>
+            <ReqFeatureIndex value="65535"/>
+            <!-- FeatureCount=3 -->
+            <FeatureIndex index="0" value="0"/>
+            <FeatureIndex index="1" value="1"/>
+            <FeatureIndex index="2" value="2"/>
+          </DefaultLangSys>
+          <!-- LangSysCount=0 -->
+        </Script>
+      </ScriptRecord>
+      <ScriptRecord index="1">
+        <ScriptTag value="cyrl"/>
+        <Script>
+          <DefaultLangSys>
+            <ReqFeatureIndex value="65535"/>
+            <!-- FeatureCount=3 -->
+            <FeatureIndex index="0" value="0"/>
+            <FeatureIndex index="1" value="1"/>
+            <FeatureIndex index="2" value="2"/>
+          </DefaultLangSys>
+          <!-- LangSysCount=0 -->
+        </Script>
+      </ScriptRecord>
+      <ScriptRecord index="2">
+        <ScriptTag value="latn"/>
+        <Script>
+          <DefaultLangSys>
+            <ReqFeatureIndex value="65535"/>
+            <!-- FeatureCount=3 -->
+            <FeatureIndex index="0" value="0"/>
+            <FeatureIndex index="1" value="1"/>
+            <FeatureIndex index="2" value="2"/>
+          </DefaultLangSys>
+          <!-- LangSysCount=1 -->
+          <LangSysRecord index="0">
+            <LangSysTag value="TRK "/>
+            <LangSys>
+              <ReqFeatureIndex value="65535"/>
+              <!-- FeatureCount=3 -->
+              <FeatureIndex index="0" value="0"/>
+              <FeatureIndex index="1" value="1"/>
+              <FeatureIndex index="2" value="2"/>
+            </LangSys>
+          </LangSysRecord>
+        </Script>
+      </ScriptRecord>
+    </ScriptList>
+    <FeatureList>
+      <!-- FeatureCount=3 -->
+      <FeatureRecord index="0">
+        <FeatureTag value="aalt"/>
+        <Feature>
+          <!-- LookupCount=2 -->
+          <LookupListIndex index="0" value="0"/>
+          <LookupListIndex index="1" value="1"/>
+        </Feature>
+      </FeatureRecord>
+      <FeatureRecord index="1">
+        <FeatureTag value="salt"/>
+        <Feature>
+          <!-- LookupCount=3 -->
+          <LookupListIndex index="0" value="5"/>
+          <LookupListIndex index="1" value="7"/>
+          <LookupListIndex index="2" value="8"/>
+        </Feature>
+      </FeatureRecord>
+      <FeatureRecord index="2">
+        <FeatureTag value="smcp"/>
+        <Feature>
+          <!-- LookupCount=2 -->
+          <LookupListIndex index="0" value="3"/>
+          <LookupListIndex index="1" value="4"/>
+        </Feature>
+      </FeatureRecord>
+    </FeatureList>
+    <LookupList>
+      <!-- LookupCount=9 -->
+      <Lookup index="0">
+        <!-- LookupType=1 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SingleSubst index="0">
+          <Substitution in="e" out="e.mid"/>
+        </SingleSubst>
+      </Lookup>
+      <Lookup index="1">
+        <!-- LookupType=2 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <MultipleSubst index="0">
+          <Substitution in="a" out="A.sc,a.alt1,a.alt2,a.alt3"/>
+          <Substitution in="b" out="B.sc,b.alt"/>
+          <Substitution in="c" out="C.sc,c.mid"/>
+          <Substitution in="d" out="d.alt,d.mid"/>
+        </MultipleSubst>
+      </Lookup>
+      <Lookup index="2">
+        <!-- LookupType=1 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SingleSubst index="0">
+          <Substitution in="d" out="d.alt"/>
+        </SingleSubst>
+      </Lookup>
+      <Lookup index="3">
+        <!-- LookupType=1 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SingleSubst index="0">
+          <Substitution in="a" out="A.sc"/>
+          <Substitution in="b" out="B.sc"/>
+          <Substitution in="c" out="C.sc"/>
+        </SingleSubst>
+      </Lookup>
+      <Lookup index="4">
+        <!-- LookupType=4 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <LigatureSubst index="0" Format="1">
+          <LigatureSet glyph="f">
+            <Ligature components="i" glyph="f_i"/>
+          </LigatureSet>
+        </LigatureSubst>
+      </Lookup>
+      <Lookup index="5">
+        <!-- LookupType=3 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <AlternateSubst index="0" Format="1">
+          <AlternateSet glyph="a">
+            <Alternate glyph="a.alt1"/>
+            <Alternate glyph="a.alt2"/>
+            <Alternate glyph="a.alt3"/>
+          </AlternateSet>
+        </AlternateSubst>
+      </Lookup>
+      <Lookup index="6">
+        <!-- LookupType=1 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SingleSubst index="0">
+          <Substitution in="c" out="c.mid"/>
+          <Substitution in="d" out="d.mid"/>
+          <Substitution in="e" out="e.mid"/>
+        </SingleSubst>
+      </Lookup>
+      <Lookup index="7">
+        <!-- LookupType=6 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <ChainContextSubst index="0" Format="3">
+          <!-- BacktrackGlyphCount=1 -->
+          <BacktrackCoverage index="0">
+            <Glyph value="e"/>
+          </BacktrackCoverage>
+          <!-- InputGlyphCount=1 -->
+          <InputCoverage index="0">
+            <Glyph value="c"/>
+            <Glyph value="d"/>
+            <Glyph value="e"/>
+          </InputCoverage>
+          <!-- LookAheadGlyphCount=1 -->
+          <LookAheadCoverage index="0">
+            <Glyph value="f"/>
+          </LookAheadCoverage>
+          <!-- SubstCount=1 -->
+          <SubstLookupRecord index="0">
+            <SequenceIndex value="0"/>
+            <LookupListIndex value="6"/>
+          </SubstLookupRecord>
+        </ChainContextSubst>
+      </Lookup>
+      <Lookup index="8">
+        <!-- LookupType=1 -->
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SingleSubst index="0">
+          <Substitution in="b" out="b.alt"/>
+        </SingleSubst>
+      </Lookup>
+    </LookupList>
+  </GSUB>
+
+</ttFont>