No need for a method, just use a function

src/fontra_rcjk/backend_fs.py

@@ -122,59 +122,13 @@ def _populateGlyphCache(self, glyphName):
         for layerName, glifData in layerGLIFData:
             layerGlyphs[layerName] = GLIFGlyph.fromGLIFData(glifData)
 
-        layerGlyphs = self._fudgeLayerNames(glyphName, layerGlyphs)
+        layerGlyphs = _fudgeLayerNames(glyphName, layerGlyphs)
 
         self._tempGlyphCache[glyphName] = layerGlyphs
 
         for compoName in layerGlyphs["foreground"].getComponentNames():
             self._populateGlyphCache(compoName)
 
-    def _fudgeLayerNames(self, glyphName, layerGlyphs):
-        #
-        # The rcjk format does not play well with case-insensitive file systems:
-        # layer names become folder names, and to read layer names we read folder
-        # names. Since layer names are global per font, case differences in layer
-        # names can cause ambiguities. For example, if a layer "s2" exists, a
-        # folder named "s2" will be written. If "S2" (cap S!) *also* exists, its
-        # data will be happily written to the "s2" folder on a case-insensitive
-        # file system. When reading back the project, we find "s2", but not "S2".
-        # The code below tries to detect that situation and work around it. This
-        # works as long as the layer names *within a single glyph* are not
-        # ambiguous: "S1" and "s1" should not co-exist in the same glyph.
-        #
-        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:
@@ -347,3 +301,48 @@ def deleteGlyph(self, glyphName):
             layerPath.unlink()
             self.registerWrittenPath(layerPath, deleted=True)
         del self.glyphMap[glyphName]
+
+
+def _fudgeLayerNames(glyphName, layerGlyphs):
+    #
+    # The rcjk format does not play well with case-insensitive file systems:
+    # layer names become folder names, and to read layer names we read folder
+    # names. Since layer names are global per font, case differences in layer
+    # names can cause ambiguities. For example, if a layer "s2" exists, a
+    # folder named "s2" will be written. If "S2" (cap S!) *also* exists, its
+    # data will be happily written to the "s2" folder on a case-insensitive
+    # file system. When reading back the project, we find "s2", but not "S2".
+    # The code below tries to detect that situation and work around it. This
+    # works as long as the layer names *within a single glyph* are not
+    # ambiguous: "S1" and "s1" should not co-exist in the same glyph.
+    #
+    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