handle widened module class in productMirror

Author: bishabosha

compiler/src/dotty/tools/dotc/transform/SymUtils.scala

@@ -94,7 +94,7 @@ object SymUtils:
         && (!ctor.privateWithin.exists || isAccessible(ctor.privateWithin)) // check scope is compatible
 
 
-      val companionMirror = self.useCompanionAsProductMirror
+      def companionMirror = self.useCompanionAsProductMirror
       if (!self.is(CaseClass)) "it is not a case class"
       else if (self.is(Abstract)) "it is an abstract class"
       else if (self.primaryConstructor.info.paramInfoss.length != 1) "it takes more than one parameter list"

compiler/src/dotty/tools/dotc/typer/Synthesizer.scala

@@ -314,9 +314,11 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
       case AndType(tp1, tp2) =>
         orElse(productMirror(tp1, formal, span), productMirror(tp2, formal, span))
       case _ =>
-        if mirroredType.termSymbol.is(CaseVal) then
-          val module = mirroredType.termSymbol
-          val modulePath = pathFor(mirroredType).withSpan(span)
+        val cls = mirroredType.classSymbol
+        if cls.isAllOf(Case | Module) then
+          val module = cls.sourceModule
+          val moduleRef = if mirroredType.termSymbol.exists then mirroredType else module.reachableTermRef
+          val modulePath = pathFor(moduleRef).withSpan(span)
           if module.info.classSymbol.is(Scala2x) then
             val mirrorType = mirrorCore(defn.Mirror_SingletonProxyClass, mirroredType, mirroredType, module.name, formal)
             val mirrorRef = New(defn.Mirror_SingletonProxyClass.typeRef, modulePath :: Nil)
@@ -325,7 +327,6 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
             val mirrorType = mirrorCore(defn.Mirror_SingletonClass, mirroredType, mirroredType, module.name, formal)
             withNoErrors(modulePath.cast(mirrorType))
         else
-          val cls = mirroredType.classSymbol
           val acceptableMsg = whyNotAcceptableType(mirroredType, cls)
           if acceptableMsg.isEmpty then
             if cls.isGenericProduct then makeProductMirror(cls)