Work around layername issues on case-insensitive file systems

src/fontra_rcjk/backend_fs.py

@@ -1,4 +1,5 @@
 import json
+import logging
 import os
 import pathlib
 
@@ -16,6 +17,8 @@
     unpackAxes,
 )
 
+logger = logging.getLogger(__name__)
+
 glyphSetNames = ["characterGlyph", "deepComponent", "atomicElement"]
 
 
@@ -118,11 +121,48 @@ def _populateGlyphCache(self, glyphName):
         layerGlyphs = {}
         for layerName, glifData in layerGLIFData:
             layerGlyphs[layerName] = GLIFGlyph.fromGLIFData(glifData)
+
+        layerGlyphs = self._fudgeLayerNames(glyphName, layerGlyphs)
+
         self._tempGlyphCache[glyphName] = layerGlyphs
 
         for compoName in layerGlyphs["foreground"].getComponentNames():
             self._populateGlyphCache(compoName)
 
+    def _fudgeLayerNames(self, glyphName, layerGlyphs):
+        usedLayerNames = set()
+        for varData in layerGlyphs["foreground"].lib.get("robocjk.variationGlyphs", []):
+            layerName = varData.get("layerName")
+            if layerName:
+                usedLayerNames.add(layerName)
+        missingLayerNames = usedLayerNames - set(layerGlyphs)
+
+        if not missingLayerNames:
+            return layerGlyphs
+
+        if len(usedLayerNames) != len(
+            {layerName.casefold() for layerName in usedLayerNames}
+        ):
+            logger.warn(
+                f"Possible layer name conflict on case-insensitive file system ({glyphName})"
+            )
+            return layerGlyphs
+
+        renameMap = {}
+        availableLayerNames = {
+            layerName.casefold(): layerName for layerName in layerGlyphs
+        }
+        for missingLayerName in missingLayerNames:
+            folded = missingLayerName.casefold()
+            fudged = availableLayerNames.get(folded)
+            if fudged:
+                renameMap[fudged] = missingLayerName
+        if renameMap:
+            logger.warn(f"fudging layer names for {glyphName}: {renameMap}")
+            layerGlyphs = {renameMap.get(k, k): v for k, v in layerGlyphs.items()}
+
+        return layerGlyphs
+
     def _getLayerGLIFData(self, glyphName):
         for gs, _ in self._iterGlyphSets():
             if glyphName in gs: