Fix #5083: Fix field references in outer accessors

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -336,7 +336,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       case pre: ThisType =>
         tp.isType ||
         pre.cls.isStaticOwner ||
-        tp.symbol.isParamOrAccessor && !pre.cls.is(Trait) && ctx.owner.enclosingClass == pre.cls
+        tp.symbol.isParamOrAccessor && !tp.symbol.owner.is(Trait) && ctx.owner.enclosingClass == pre.cls
           // was ctx.owner.enclosingClass.derivesFrom(pre.cls) which was not tight enough
           // and was spuriously triggered in case inner class would inherit from outer one
           // eg anonymous TypeMap inside TypeMap.andThen

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

@@ -91,9 +91,19 @@ class ExplicitOuter extends MiniPhase with InfoTransformer { thisPhase =>
         }
       }
 
+      /** Replace `NoPrefix` prefixes of references to symbols in superclasses by `cls.thisType` */
+      def fixPrefix(tp: Type): Type = tp match {
+        case tp @ TermRef(NoPrefix, _) if cls.derivesFrom(tp.symbol.owner) =>
+          tp.derivedSelect(cls.thisType)
+        case tp: NamedType =>
+          tp.derivedSelect(fixPrefix(tp.prefix))
+        case tp =>
+          tp
+      }
+
       for (parentTrait <- cls.mixins) {
         if (needsOuterIfReferenced(parentTrait)) {
-          val parentTp = cls.denot.thisType.baseType(parentTrait)
+          val parentTp = fixPrefix(cls.denot.thisType.baseType(parentTrait))
           val outerAccImpl = newOuterAccessor(cls, parentTrait).enteredAfter(thisPhase)
           newDefs += DefDef(outerAccImpl, singleton(fixThis(outerPrefix(parentTp))))
         }

tests/pos/i5083.scala

@@ -0,0 +1,15 @@
+class A(a: Int) {
+  class X {
+    val x = a
+  }
+
+  trait Y {
+    val y = a
+  }
+
+  trait Z(val o: A) extends o.Y {
+    val z = a
+  }
+
+  class B extends X with Z(new A(4))
+}