[varLib] Allow feature variations to be active across the entire space (

#1957)

* Allow feature variations to be active across the entire space

* Add test with empty condition set

* Skip initial box instead of removing it

* Correct comment

Lib/fontTools/varLib/featureVars.py

@@ -82,6 +82,7 @@ def overlayFeatureVariations(conditionalSubstitutions):
     ...     ([{"wght": (0.5, 1.0)}], {"dollar": "dollar.rvrn"}),
     ...     ([{"wght": (0.5, 1.0)}], {"dollar": "dollar.rvrn"}),
     ...     ([{"wdth": (0.5, 1.0)}], {"cent": "cent.rvrn"}),
+    ...     ([{"wght": (0.5, 1.0), "wdth": (-1, 1.0)}], {"dollar": "dollar.rvrn"}),
     ... ]
     >>> from pprint import pprint
     >>> pprint(overlayFeatureVariations(condSubst))
@@ -136,12 +137,14 @@ def overlayFeatureVariations(conditionalSubstitutions):
                     remainder = hashdict(remainder)
                     newMap[remainder] = newMap.get(remainder, 0) | rank
         boxMap = newMap
-    del boxMap[hashdict()]
 
     # Generate output
     items = []
     for box,rank in sorted(boxMap.items(),
                            key=(lambda BoxAndRank: -popCount(BoxAndRank[1]))):
+        # Skip any box that doesn't have any substitution.
+        if rank == 0:
+            continue
         substsList = []
         i = 0
         while rank:

Tests/varLib/data/FeatureVarsWholeRange.designspace

@@ -0,0 +1,34 @@
+<?xml version='1.0' encoding='utf-8'?>
+<designspace format="3">
+    <axes>
+        <axis default="368.0" maximum="1000.0" minimum="0.0" name="weight" tag="wght" />
+    </axes>
+    <rules processing="last">
+        <rule name="always">
+            <conditionset>
+                <condition name="weight" minimum="0" maximum="1000" />
+            </conditionset>
+            <sub name="uni0024" with="uni0024.nostroke" />
+        </rule>
+    </rules>
+    <sources>
+        <source familyname="Test Family" filename="master_ufo/TestFamily-Master0.ufo" name="master_0" stylename="Master0">
+            <location>
+                <dimension name="weight" xvalue="0" />
+            </location>
+        </source>
+        <source familyname="Test Family" filename="master_ufo/TestFamily-Master1.ufo" name="master_1" stylename="Master1">
+            <lib copy="1" />
+            <groups copy="1" />
+            <info copy="1" />
+            <location>
+                <dimension name="weight" xvalue="368" />
+            </location>
+        </source>
+        <source familyname="Test Family" filename="master_ufo/TestFamily-Master3.ufo" name="master_3" stylename="Master3">
+            <location>
+                <dimension name="weight" xvalue="1000" />
+            </location>
+        </source>
+    </sources>
+</designspace>

Tests/varLib/data/FeatureVarsWholeRangeEmpty.designspace

@@ -0,0 +1,33 @@
+<?xml version='1.0' encoding='utf-8'?>
+<designspace format="3">
+    <axes>
+        <axis default="368.0" maximum="1000.0" minimum="0.0" name="weight" tag="wght" />
+    </axes>
+    <rules processing="last">
+        <rule name="always">
+            <conditionset>
+            </conditionset>
+            <sub name="uni0024" with="uni0024.nostroke" />
+        </rule>
+    </rules>
+    <sources>
+        <source familyname="Test Family" filename="master_ufo/TestFamily-Master0.ufo" name="master_0" stylename="Master0">
+            <location>
+                <dimension name="weight" xvalue="0" />
+            </location>
+        </source>
+        <source familyname="Test Family" filename="master_ufo/TestFamily-Master1.ufo" name="master_1" stylename="Master1">
+            <lib copy="1" />
+            <groups copy="1" />
+            <info copy="1" />
+            <location>
+                <dimension name="weight" xvalue="368" />
+            </location>
+        </source>
+        <source familyname="Test Family" filename="master_ufo/TestFamily-Master3.ufo" name="master_3" stylename="Master3">
+            <location>
+                <dimension name="weight" xvalue="1000" />
+            </location>
+        </source>
+    </sources>
+</designspace>

Tests/varLib/data/test_results/FeatureVarsWholeRange.ttx

@@ -0,0 +1,75 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ttFont sfntVersion="\x00\x01\x00\x00" ttLibVersion="4.9">
+
+  <fvar>
+
+    <!-- Weight -->
+    <Axis>
+      <AxisTag>wght</AxisTag>
+      <Flags>0x0</Flags>
+      <MinValue>0.0</MinValue>
+      <DefaultValue>368.0</DefaultValue>
+      <MaxValue>1000.0</MaxValue>
+      <AxisNameID>256</AxisNameID>
+    </Axis>
+  </fvar>
+
+  <GSUB>
+    <Version value="0x00010001"/>
+    <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="rclt"/>
+        <Feature>
+          <!-- LookupCount=0 -->
+        </Feature>
+      </FeatureRecord>
+    </FeatureList>
+    <LookupList>
+      <!-- LookupCount=1 -->
+      <Lookup index="0">
+        <LookupType value="1"/>
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SingleSubst index="0" Format="1">
+          <Substitution in="uni0024" out="uni0024.nostroke"/>
+        </SingleSubst>
+      </Lookup>
+    </LookupList>
+    <FeatureVariations>
+      <Version value="0x00010000"/>
+      <!-- FeatureVariationCount=1 -->
+      <FeatureVariationRecord index="0">
+        <ConditionSet>
+          <!-- ConditionCount=0 -->
+        </ConditionSet>
+        <FeatureTableSubstitution>
+          <Version value="0x00010000"/>
+          <!-- SubstitutionCount=1 -->
+          <SubstitutionRecord index="0">
+            <FeatureIndex value="0"/>
+            <Feature>
+              <!-- LookupCount=1 -->
+              <LookupListIndex index="0" value="0"/>
+            </Feature>
+          </SubstitutionRecord>
+        </FeatureTableSubstitution>
+      </FeatureVariationRecord>
+    </FeatureVariations>
+  </GSUB>
+
+</ttFont>

Tests/varLib/varLib_test.py

@@ -218,6 +218,30 @@ def test_varlib_build_feature_variations(self):
             save_before_dump=True,
         )
 
+    def test_varlib_build_feature_variations_whole_range(self):
+        """Designspace file contains <rules> element specifying the entire design
+        space, used to build GSUB FeatureVariations table.
+        """
+        self._run_varlib_build_test(
+            designspace_name="FeatureVarsWholeRange",
+            font_name="TestFamily",
+            tables=["fvar", "GSUB"],
+            expected_ttx_name="FeatureVarsWholeRange",
+            save_before_dump=True,
+        )
+
+    def test_varlib_build_feature_variations_whole_range_empty(self):
+        """Designspace file contains <rules> element without a condition, specifying
+        the entire design space, used to build GSUB FeatureVariations table.
+        """
+        self._run_varlib_build_test(
+            designspace_name="FeatureVarsWholeRangeEmpty",
+            font_name="TestFamily",
+            tables=["fvar", "GSUB"],
+            expected_ttx_name="FeatureVarsWholeRange",
+            save_before_dump=True,
+        )
+
     def test_varlib_build_feature_variations_with_existing_rclt(self):
         """Designspace file contains <rules> element, used to build GSUB
         FeatureVariations table. <rules> is specified to do its OT processing