Fix #2202: Check bridge clash in super classes.

Author: nicolasstucki

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

@@ -626,17 +626,20 @@ object Erasure extends TypeTestsCasts{
 
                     if (isRequired) {
                       // check for clashes
-                      val clash: Option[Symbol] = oldSymbol.owner.info.decls.lookupAll(bridge.name).find {
-                        sym =>
-                          (sym.name eq bridge.name) && sym.info.widen =:= bridge.info.widen
-                      }.orElse(
-                        emittedBridges.find(stat => (stat.name == bridge.name) && stat.tpe.widen =:= bridge.info.widen)
+                      val clash: Option[Symbol] = oldSymbol.owner.info.memberExcluding(bridge.name, Flags.Bridge).alternatives.find {
+                        denot => {
+                          !denot.symbol.owner.is(Flags.Trait) && // ignore traits, the clash will happen on their bridges.
+                          (denot.symbol ne defn.Object_clone) && // TODO: remove, only needed for legacy test: compileStdLib
+                          !denot.symbol.owner.derivesFrom(bridge.owner) && denot.symbol.info.widen =:= bridge.info.widen
+                        }
+                      }.map(_.symbol).orElse(
+                        emittedBridges.find(stat => (stat.name eq bridge.name) && stat.tpe.widen =:= bridge.info.widen)
                           .map(_.symbol))
                       clash match {
                         case Some(cl) =>
                           ctx.error(i"bridge for method ${newSymbol.showLocated(beforeCtx)} of type ${newSymbol.info(beforeCtx)}\n" +
                             i"clashes with ${cl.symbol.showLocated(beforeCtx)} of type ${cl.symbol.info(beforeCtx)}\n" +
-                            i"both have same type after erasure: ${bridge.symbol.info}")
+                            i"both have same type after erasure: ${bridge.symbol.info}", newSymbol.pos)
                         case None => minimalSet += bridge
                       }
                     }

tests/neg/i2202.scala

@@ -0,0 +1,12 @@
+
+class A {
+  def compareTo(o: Any): Int = 0
+}
+class B extends A with Comparable[B] {
+  def compareTo(b: B): Int = 0 // error
+}
+object C {
+  def main(args: Array[String]): Unit = {
+    println(new B().compareTo(new Object()))
+  }
+}