instancer: prune unused name records after instancing

Lib/fontTools/varLib/instancer.py

@@ -21,6 +21,7 @@ from fontTools import varLib
 from fontTools.varLib import builder
 from fontTools.varLib.mvar import MVAR_ENTRIES
 from fontTools.varLib.merger import MutatorMerger
+from contextlib import contextmanager
 import collections
 from copy import deepcopy
 import logging
@@ -540,6 +541,50 @@ def instantiateSTAT(varfont, location):
     stat.DesignAxisCount = len(stat.DesignAxisRecord.Axis)
 
 
+def getVariationNameIDs(varfont):
+    used = []
+    if "fvar" in varfont:
+        fvar = varfont["fvar"]
+        for axis in fvar.axes:
+            used.append(axis.axisNameID)
+        for instance in fvar.instances:
+            used.append(instance.subfamilyNameID)
+            if instance.postscriptNameID != 0xFFFF:
+                used.append(instance.postscriptNameID)
+    if "STAT" in varfont:
+        stat = varfont["STAT"].table
+        for axis in stat.DesignAxisRecord.Axis if stat.DesignAxisRecord else ():
+            used.append(axis.AxisNameID)
+        for value in stat.AxisValueArray.AxisValue if stat.AxisValueArray else ():
+            used.append(value.ValueNameID)
+    # nameIDs <= 255 are reserved by OT spec so we don't touch them
+    return {nameID for nameID in used if nameID > 255}
+
+
+@contextmanager
+def pruningUnusedNames(varfont):
+    origNameIDs = getVariationNameIDs(varfont)
+
+    yield
+
+    log.info("Pruning name table")
+    exclude = origNameIDs - getVariationNameIDs(varfont)
+    varfont["name"].names[:] = [
+        record for record in varfont["name"].names if record.nameID not in exclude
+    ]
+    if "ltag" in varfont:
+        # Drop the whole 'ltag' table if all the language-dependent Unicode name
+        # records that reference it have been dropped.
+        # TODO: Only prune unused ltag tags, renumerating langIDs accordingly.
+        # Note ltag can also be used by feat or morx tables, so check those too.
+        if not any(
+            record
+            for record in varfont["name"].names
+            if record.platformID == 0 and record.langID != 0xFFFF
+        ):
+            del varfont["ltag"]
+
+
 def normalize(value, triple, avar_mapping):
     value = normalizeValue(value, triple)
     if avar_mapping:
@@ -622,10 +667,11 @@ def instantiateVariableFont(varfont, axis_limits, inplace=False, optimize=True):
     if "avar" in varfont:
         instantiateAvar(varfont, normalized_limits)
 
-    if "STAT" in varfont:
+    with pruningUnusedNames(varfont):
-        instantiateSTAT(varfont, axis_limits)
+        if "STAT" in varfont:
+            instantiateSTAT(varfont, axis_limits)
 
-    instantiateFvar(varfont, axis_limits)
+        instantiateFvar(varfont, axis_limits)
 
     return varfont
 

Tests/varLib/data/PartialInstancerTest-VF.ttx

@@ -12,12 +12,12 @@
     <!-- Most of this table will be recalculated by the compiler -->
     <tableVersion value="1.0"/>
     <fontRevision value="2.001"/>
-    <checkSumAdjustment value="0x710b1826"/>
+    <checkSumAdjustment value="0x7815682b"/>
     <magicNumber value="0x5f0f3cf5"/>
     <flags value="00000000 00000011"/>
     <unitsPerEm value="1000"/>
     <created value="Tue Mar  5 00:05:14 2019"/>
-    <modified value="Fri May  3 10:34:01 2019"/>
+    <modified value="Wed May  8 10:35:06 2019"/>
     <xMin value="40"/>
     <yMin value="-200"/>
     <xMax value="450"/>
@@ -186,6 +186,9 @@
   </glyf>
 
   <name>
+    <namerecord nameID="257" platformID="0" platEncID="4" langID="0x0">
+      Bräiti
+    </namerecord>
     <namerecord nameID="256" platformID="1" platEncID="0" langID="0x0" unicode="True">
       Weight
     </namerecord>
@@ -306,6 +309,9 @@
     <namerecord nameID="295" platformID="1" platEncID="0" langID="0x0" unicode="True">
       Upright
     </namerecord>
+    <namerecord nameID="296" platformID="1" platEncID="0" langID="0x0" unicode="True">
+      TestVariableFont-XCdBd
+    </namerecord>
     <namerecord nameID="0" platformID="3" platEncID="1" langID="0x409">
       Copyright 2015 Google Inc. All Rights Reserved.
     </namerecord>
@@ -462,6 +468,9 @@
     <namerecord nameID="295" platformID="3" platEncID="1" langID="0x409">
       Upright
     </namerecord>
+    <namerecord nameID="296" platformID="3" platEncID="1" langID="0x409">
+      TestVariableFont-XCdBd
+    </namerecord>
   </name>
 
   <post>
@@ -1008,7 +1017,8 @@
     </NamedInstance>
 
     <!-- ExtraCondensed ExtraBold -->
-    <NamedInstance flags="0x0" subfamilyNameID="292">
+    <!-- PostScript: TestVariableFont-XCdBd -->
+    <NamedInstance flags="0x0" postscriptNameID="296" subfamilyNameID="292">
       <coord axis="wght" value="800.0"/>
       <coord axis="wdth" value="70.0"/>
     </NamedInstance>
@@ -1076,6 +1086,12 @@
     </glyphVariations>
   </gvar>
 
+  <ltag>
+    <version value="1"/>
+    <flags value="0"/>
+    <LanguageTag tag="gsw-LI"/>
+  </ltag>
+
   <vmtx>
     <mtx name=".notdef" height="1000" tsb="100"/>
     <mtx name="hyphen" height="536" tsb="229"/>

Tests/varLib/instancer_test.py

@@ -966,3 +966,27 @@ class InstantiateSTATTest(object):
         instancer.instantiateSTAT(varfont, {"wght": 100})
 
         assert "STAT" not in varfont
+
+
+def test_pruningUnusedNames(varfont):
+    varNameIDs = instancer.getVariationNameIDs(varfont)
+
+    assert varNameIDs == set(range(256, 296 + 1))
+
+    fvar = varfont["fvar"]
+    stat = varfont["STAT"].table
+
+    with instancer.pruningUnusedNames(varfont):
+        del fvar.axes[0]  # Weight (nameID=256)
+        del fvar.instances[0]  # Thin (nameID=258)
+        del stat.DesignAxisRecord.Axis[0]  # Weight (nameID=256)
+        del stat.AxisValueArray.AxisValue[0]  # Thin (nameID=258)
+
+    assert not any(n for n in varfont["name"].names if n.nameID in {256, 258})
+
+    with instancer.pruningUnusedNames(varfont):
+        del varfont["fvar"]
+        del varfont["STAT"]
+
+    assert not any(n for n in varfont["name"].names if n.nameID in varNameIDs)
+    assert "ltag" not in varfont