Merge pull request #2070 from dotty-staging/fix/erasedLub

Fix bug in erasedLub leading to incorrect signatures

Author: odersky

compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -246,10 +246,14 @@ object TypeErasure {
           val cls2 = tp2.classSymbol
           def loop(bcs: List[ClassSymbol], bestSoFar: ClassSymbol): ClassSymbol = bcs match {
             case bc :: bcs1 =>
-              if (cls2.derivesFrom(bc))
-                if (!bc.is(Trait) && bc != defn.AnyClass) bc
-                else loop(bcs1, if (bestSoFar.derivesFrom(bc)) bestSoFar else bc)
-              else
+              if (cls2.derivesFrom(bc)) {
+                val newBest = if (bestSoFar.derivesFrom(bc)) bestSoFar else bc
+
+                if (!bc.is(Trait) && bc != defn.AnyClass)
+                  newBest
+                else
+                  loop(bcs1, newBest)
+              } else
                 loop(bcs1, bestSoFar)
             case nil =>
               bestSoFar

tests/pos/erased-lub-2.scala

@@ -0,0 +1,15 @@
+trait Foo
+
+trait PF[A, +B] {
+  def apply(x: A): B
+}
+
+object Test {
+  def orElse2[A1, B1 >: Foo](that: PF[A1, B1]): PF[A1, B1] = ???
+
+  def identity[E]: PF[E, E] = ???
+
+  def foo: PF[Foo, Foo] = ???
+
+  def bla(foo: Foo) = orElse2(identity).apply(foo)
+}