Look up members at erasure phase for generating static forwarders

Forward-ports scala/scala@b6d7e0c42c

Author: lrytz

compiler/src/dotty/tools/backend/jvm/BCodeHelpers.scala

@@ -607,7 +607,8 @@ trait BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
       val names = tp.memberNames(takeAllFilter).toSeq.sorted
       val buffer = mutable.ListBuffer[Symbol]()
       names.foreach { name =>
-        buffer ++= tp.memberBasedOnFlags(name, required, excluded)
+        // lookup members at erasure: lampepfl/dotty#12753
+        buffer ++= atPhase(erasurePhase)(tp.memberBasedOnFlags(name, required, excluded))
           .alternatives.sortBy(_.signature)(Signature.lexicographicOrdering).map(_.symbol)
       }
       buffer.toList

tests/run/i12753/C.scala

@@ -0,0 +1,16 @@
+trait C[This <: C[This]]
+
+trait COps[This <: C[This]] {
+  def t: This
+  def foo(x: Int): This = t
+  def bar: Object = ""
+}
+
+class D extends C[D] {
+  def x = 1
+}
+object D extends COps[D] {
+  def t = new D
+  override def foo(x: Int): D = super.foo(x)
+  override def bar: String = ""
+}

tests/run/i12753/Test.java

@@ -0,0 +1,6 @@
+public class Test {
+  public static void main(String[] args) {
+    if (D.foo(1).x() != 1 || !D.bar().isEmpty())
+      throw new RuntimeException("");
+  }
+}