[feaLib] Test compiling zero values for SinglePos in vertical context

https://github.com/fonttools/fonttools/issues/633

Tests/feaLib/builder_test.py

@@ -65,7 +65,7 @@ class BuilderTest(unittest.TestCase):
         bug453 bug457 bug463 bug501 bug502 bug504 bug505 bug506 bug509
         bug512 bug514 bug568 bug633
         name size size2 multiple_feature_blocks omitted_GlyphClassDef
-        ZeroValue_SinglePos
+        ZeroValue_SinglePos_horizontal ZeroValue_SinglePos_vertical
         ZeroValue_PairPos_horizontal ZeroValue_PairPos_vertical
         ZeroValue_ChainSinglePos_horizontal ZeroValue_ChainSinglePos_vertical
     """.split()

Tests/feaLib/data/ZeroValue_SinglePos_horizontal.fea

@@ -0,0 +1,8 @@
+# For SinglePos statements, zeroes should get compiled to ValueRecord format 0.
+# https://github.com/fonttools/fonttools/issues/633
+
+# Zero value in a horizontal context.
+feature kern {
+    pos A 0;          # format A
+    pos B <0 0 0 0>;  # format B
+} kern;

Tests/feaLib/data/ZeroValue_SinglePos_horizontal.ttx

@@ -20,7 +20,7 @@
     <FeatureList>
       <!-- FeatureCount=1 -->
       <FeatureRecord index="0">
-        <FeatureTag value="TEST"/>
+        <FeatureTag value="kern"/>
         <Feature>
           <!-- LookupCount=1 -->
           <LookupListIndex index="0" value="0"/>

Tests/feaLib/data/ZeroValue_SinglePos_vertical.fea

@@ -1,6 +1,8 @@
 # For SinglePos statements, zeroes should get compiled to ValueRecord format 0.
 # https://github.com/fonttools/fonttools/issues/633
-feature TEST {
+
+# Zero value in a vertical context.
+feature vkrn {
     pos A 0;          # format A
     pos B <0 0 0 0>;  # format B
-} TEST;
+} vkrn;

Tests/feaLib/data/ZeroValue_SinglePos_vertical.ttx

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ttFont sfntVersion="true" ttLibVersion="3.0">
+
+  <GPOS>
+    <Version value="0x00010000"/>
+    <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="vkrn"/>
+        <Feature>
+          <!-- LookupCount=1 -->
+          <LookupListIndex index="0" value="0"/>
+        </Feature>
+      </FeatureRecord>
+    </FeatureList>
+    <LookupList>
+      <!-- LookupCount=1 -->
+      <Lookup index="0">
+        <LookupType value="1"/>
+        <LookupFlag value="0"/>
+        <!-- SubTableCount=1 -->
+        <SinglePos index="0" Format="1">
+          <Coverage>
+            <Glyph value="A"/>
+            <Glyph value="B"/>
+          </Coverage>
+          <ValueFormat value="0"/>
+        </SinglePos>
+      </Lookup>
+    </LookupList>
+  </GPOS>
+
+</ttFont>