Refactor MarkFeatureWriter._makeContextualAttachments

Make attachments for mark2base and mark2liga in the same pass
Coerce numberless liga anchors to mark2base

Lib/ufo2ft/featureWriters/markFeatureWriter.py

@@ -2,6 +2,7 @@
 import re
 from collections import OrderedDict, defaultdict
 from functools import partial
+from typing import Dict, Set, Tuple
 
 from ufo2ft.constants import INDIC_SCRIPTS, OBJECT_LIBS_KEY, USE_SCRIPTS
 from ufo2ft.featureWriters import BaseFeatureWriter, ast
@@ -725,25 +726,31 @@ def _makeMarkToLigaAttachments(self):
             result.append(MarkToLigaPos(glyphName, ligatureMarks))
         return result
 
-    def _makeContextualAttachments(self, glyphClass, liga=False):
-        ctx = self.context
-        result = defaultdict(list)
-        markGlyphNames = ctx.markGlyphNames
-        for glyphName, anchors in sorted(ctx.anchorLists.items()):
-            if glyphName in markGlyphNames:
+    def _makeContextualAttachments(
+        self, baseClass: Set[str], ligatureClass: Set[str]
+    ) -> Tuple[Dict[str, Tuple[str, NamedAnchor]], Dict[str, Tuple[str, NamedAnchor]]]:
+        baseResult = defaultdict(list)
+        ligatureResult = defaultdict(list)
+
+        for glyphName, anchors in sorted(self.context.anchorLists.items()):
+            if glyphName in self.context.markGlyphNames:
                 continue
-            if glyphClass and glyphName not in glyphClass:
+            if glyphName not in baseClass and glyphName not in ligatureClass:
+                # TODO: should this be a warning everything should be one group or another?
                 continue
             for anchor in anchors:
                 # Skip non-contextual anchors
                 if not anchor.isContextual:
                     continue
-                # If we are building the mark2liga lookup, skip anchors without a number
-                if liga and anchor.number is None:
-                    continue
-                # If we are building the mark2base lookup, skip anchors with a number
-                if not liga and anchor.number is not None:
+                if glyphName in ligatureClass and anchor.number:
+                    dest = ligatureResult
+                elif glyphName in baseClass and anchor.number:
+                    # Skip mark2base where anchor has a number
                     continue
+                else:
+                    # Note: this catch-all treats ligas without anchor numbers
+                    # as mark2base
+                    dest = baseResult
                 anchor_context = anchor.libData.get("GPOS_Context", "").strip()
                 if not anchor_context:
                     self.log.warning(
@@ -752,8 +759,8 @@ def _makeContextualAttachments(self, glyphClass, liga=False):
                         glyphName,
                     )
                     continue
-                result[anchor_context].append((glyphName, anchor))
-        return result
+                dest[anchor_context].append((glyphName, anchor))
+        return baseResult, ligatureResult
 
     @staticmethod
     def _iterAttachments(attachments, include=None, marksFilter=None):
@@ -1031,12 +1038,9 @@ def _makeFeatures(self):
         ctx.markToMarkAttachments = self._makeMarkToMarkAttachments()
 
         baseClass = self.context.gdefClasses.base
-        ctx.contextualMarkToBaseAnchors = self._makeContextualAttachments(baseClass)
-
         ligatureClass = self.context.gdefClasses.ligature
-        ctx.contextualMarkToLigaAnchors = self._makeContextualAttachments(
-            ligatureClass,
-            True,
+        ctx.contextualMarkToBaseAnchors, ctx.contextualMarkToLigaAnchors = (
+            self._makeContextualAttachments(baseClass, ligatureClass)
         )
 
         abvmGlyphs, notAbvmGlyphs = self._getAbvmGlyphs()