First concept

node_modules/postcss-import/lib/assign-layer-names.js

@@ -0,0 +1,17 @@
+"use strict"
+
+module.exports = function (layer, node, state, options) {
+  layer.forEach((layerPart, i) => {
+    if (layerPart.trim() === "") {
+      if (options.nameLayer) {
+        layer[i] = options
+          .nameLayer(state.anonymousLayerCounter++, state.rootFilename)
+          .toString()
+      } else {
+        throw node.error(
+          `When using anonymous layers in @import you must also set the "nameLayer" plugin option`
+        )
+      }
+    }
+  })
+}