[feaLib] Support variable ligature caret position

Allow variable scaler in ligature caret position and build
CaretValueFormat3 with DeviceTable. Does not support non-variable device
table, but can be added if someone really really wants it.

Lib/fontTools/feaLib/builder.py

@@ -1553,7 +1553,26 @@ def add_ligatureCaretByIndex_(self, location, glyphs, carets):
             if glyph not in self.ligCaretPoints_:
                 self.ligCaretPoints_[glyph] = carets
 
+    def build_caret_(self, location, caret, avar):
+        if not isinstance(caret, VariableScalar):
+            return caret
+
+        if not self.varstorebuilder:
+            raise FeatureLibError(
+                "Can't define a variable scalar in a non-variable font", location
+            )
+
+        caret.axes = self.axes
+        default, index = caret.add_to_variation_store(
+            self.varstorebuilder, self.model_cache, avar
+        )
+        if index is not None and index != 0xFFFFFFFF:
+            return (default, buildVarDevTable(index))
+        return default
+
     def add_ligatureCaretByPos_(self, location, glyphs, carets):
+        avar = self.font.get("avar")
+        carets = [self.build_caret_(location, caret, avar) for caret in carets]
         for glyph in glyphs:
             if glyph not in self.ligCaretCoords_:
                 self.ligCaretCoords_[glyph] = carets

Lib/fontTools/feaLib/parser.py

@@ -603,9 +603,9 @@ def parse_ligatureCaretByPos_(self):
         assert self.is_cur_keyword_("LigatureCaretByPos")
         location = self.cur_token_location_
         glyphs = self.parse_glyphclass_(accept_glyphname=True)
-        carets = [self.expect_number_()]
+        carets = [self.expect_number_(variable=True)]
         while self.next_token_ != ";":
-            carets.append(self.expect_number_())
+            carets.append(self.expect_number_(variable=True))
         self.expect_symbol_(";")
         return self.ast.LigatureCaretByPosStatement(glyphs, carets, location=location)
 

Lib/fontTools/otlLib/builder.py

@@ -2509,9 +2509,14 @@ def buildAttachPoint(points):
 
 def buildCaretValueForCoord(coord):
     # 500 --> otTables.CaretValue, format 1
+    # (500, DeviceTable) --> otTables.CaretValue, format 3
     self = ot.CaretValue()
-    self.Format = 1
-    self.Coordinate = coord
+    if isinstance(coord, tuple):
+        self.Format = 3
+        self.Coordinate, self.DeviceTable = coord
+    else:
+        self.Format = 1
+        self.Coordinate = coord
     return self
 
 
@@ -2573,7 +2578,8 @@ def buildLigGlyph(coords, points):
     # ([500], [4]) --> otTables.LigGlyph; None for empty coords/points
     carets = []
     if coords:
-        carets.extend([buildCaretValueForCoord(c) for c in sorted(coords)])
+        coords = sorted(coords, key=lambda c: isinstance(c, tuple) and c[0] or c)
+        carets.extend([buildCaretValueForCoord(c) for c in coords])
     if points:
         carets.extend([buildCaretValueForPoint(p) for p in sorted(points)])
     if not carets:

Tests/feaLib/builder_test.py

@@ -226,6 +226,21 @@ def normal_fea(self, lines):
             output.append(l)
         return output
 
+    def make_mock_vf(self):
+        font = makeTTFont()
+        font["name"] = newTable("name")
+        addFvar(font, self.VARFONT_AXES, [])
+        del font["name"]
+        return font
+
+    @staticmethod
+    def get_region(var_region_axis):
+        return (
+            var_region_axis.StartCoord,
+            var_region_axis.PeakCoord,
+            var_region_axis.EndCoord,
+        )
+
     def test_alternateSubst_multipleSubstitutionsForSameGlyph(self):
         self.assertRaisesRegex(
             FeatureLibError,
@@ -1046,50 +1061,60 @@ def test_variable_scalar_avar(self):
             } kern;
         """
 
-        def make_mock_vf():
-            font = makeTTFont()
-            font["name"] = newTable("name")
-            addFvar(font, self.VARFONT_AXES, [])
-            del font["name"]
-            return font
-
-        def get_region(var_region_axis):
-            return (
-                var_region_axis.StartCoord,
-                var_region_axis.PeakCoord,
-                var_region_axis.EndCoord,
-            )
-
         # Without `avar` (wght=200, wdth=100 is the default location):
-        font = make_mock_vf()
+        font = self.make_mock_vf()
         addOpenTypeFeaturesFromString(font, features)
 
         var_region_list = font.tables["GDEF"].table.VarStore.VarRegionList
         var_region_axis_wght = var_region_list.Region[0].VarRegionAxis[0]
         var_region_axis_wdth = var_region_list.Region[0].VarRegionAxis[1]
-        assert get_region(var_region_axis_wght) == (0.0, 0.875, 0.875)
-        assert get_region(var_region_axis_wdth) == (0.0, 0.0, 0.0)
+        assert self.get_region(var_region_axis_wght) == (0.0, 0.875, 0.875)
+        assert self.get_region(var_region_axis_wdth) == (0.0, 0.0, 0.0)
         var_region_axis_wght = var_region_list.Region[1].VarRegionAxis[0]
         var_region_axis_wdth = var_region_list.Region[1].VarRegionAxis[1]
-        assert get_region(var_region_axis_wght) == (0.0, 0.875, 0.875)
-        assert get_region(var_region_axis_wdth) == (0.0, 0.5, 0.5)
+        assert self.get_region(var_region_axis_wght) == (0.0, 0.875, 0.875)
+        assert self.get_region(var_region_axis_wdth) == (0.0, 0.5, 0.5)
 
         # With `avar`, shifting the wght axis' positive midpoint 0.5 a bit to
         # the right, but leaving the wdth axis alone:
-        font = make_mock_vf()
+        font = self.make_mock_vf()
         font["avar"] = newTable("avar")
         font["avar"].segments = {"wght": {-1.0: -1.0, 0.0: 0.0, 0.5: 0.625, 1.0: 1.0}}
         addOpenTypeFeaturesFromString(font, features)
 
         var_region_list = font.tables["GDEF"].table.VarStore.VarRegionList
         var_region_axis_wght = var_region_list.Region[0].VarRegionAxis[0]
         var_region_axis_wdth = var_region_list.Region[0].VarRegionAxis[1]
-        assert get_region(var_region_axis_wght) == (0.0, 0.90625, 0.90625)
-        assert get_region(var_region_axis_wdth) == (0.0, 0.0, 0.0)
+        assert self.get_region(var_region_axis_wght) == (0.0, 0.90625, 0.90625)
+        assert self.get_region(var_region_axis_wdth) == (0.0, 0.0, 0.0)
         var_region_axis_wght = var_region_list.Region[1].VarRegionAxis[0]
         var_region_axis_wdth = var_region_list.Region[1].VarRegionAxis[1]
-        assert get_region(var_region_axis_wght) == (0.0, 0.90625, 0.90625)
-        assert get_region(var_region_axis_wdth) == (0.0, 0.5, 0.5)
+        assert self.get_region(var_region_axis_wght) == (0.0, 0.90625, 0.90625)
+        assert self.get_region(var_region_axis_wdth) == (0.0, 0.5, 0.5)
+
+    def test_ligatureCaretByPos_variable_scalar(self):
+        """Test that the `avar` table is consulted when normalizing user-space
+        values."""
+
+        features = """
+            table GDEF {
+                LigatureCaretByPos f_i (wght=200:400 wght=900:1000) 380;
+            } GDEF;
+        """
+
+        font = self.make_mock_vf()
+        addOpenTypeFeaturesFromString(font, features)
+
+        table = font["GDEF"].table
+        lig_glyph = table.LigCaretList.LigGlyph[0]
+        assert lig_glyph.CaretValue[0].Format == 1
+        assert lig_glyph.CaretValue[0].Coordinate == 380
+        assert lig_glyph.CaretValue[1].Format == 3
+        assert lig_glyph.CaretValue[1].Coordinate == 400
+
+        var_region_list = table.VarStore.VarRegionList
+        var_region_axis = var_region_list.Region[0].VarRegionAxis[0]
+        assert self.get_region(var_region_axis) == (0.0, 0.875, 0.875)
 
 
 def generate_feature_file_test(name):

Tests/feaLib/parser_test.py

@@ -707,6 +707,17 @@ def test_ligatureCaretByPos_singleGlyph(self):
         self.assertEqual(glyphstr([s.glyphs]), "f_i")
         self.assertEqual(s.carets, [400, 380])
 
+    def test_ligatureCaretByPos_variable_scalar(self):
+        doc = self.parse(
+            "table GDEF {LigatureCaretByPos f_i (wght=200:400 wght=900:1000) 380;} GDEF;"
+        )
+        s = doc.statements[0].statements[0]
+        self.assertIsInstance(s, ast.LigatureCaretByPosStatement)
+        self.assertEqual(glyphstr([s.glyphs]), "f_i")
+        self.assertEqual(len(s.carets), 2)
+        self.assertEqual(str(s.carets[0]), "(wght=200:400 wght=900:1000)")
+        self.assertEqual(s.carets[1], 380)
+
     def test_lookup_block(self):
         [lookup] = self.parse("lookup Ligatures {} Ligatures;").statements
         self.assertEqual(lookup.name, "Ligatures")