Emit all bridge methods non-final

src/compiler/scala/tools/nsc/transform/Erasure.scala

@@ -565,7 +565,7 @@ abstract class Erasure extends InfoTransform
       if (!bridgeNeeded)
         return
 
-      var newFlags = (member.flags | BRIDGE | ARTIFACT) & ~(ACCESSOR | DEFERRED | LAZY)
+      var newFlags = (member.flags | BRIDGE | ARTIFACT) & ~(ACCESSOR | DEFERRED | LAZY | FINAL)
       // If `member` is a ModuleSymbol, the bridge should not also be a ModuleSymbol. Otherwise we
       // end up with two module symbols with the same name in the same scope, which is surprising
       // when implementing later phases.

test/files/run/t12532.scala

@@ -0,0 +1,27 @@
+class Sync
+
+class Async extends Sync { def x = 1 }
+
+trait Base {
+  def foo: Sync
+}
+
+trait BaseSync extends Base {
+  override def foo: Sync
+}
+
+trait BaseAsync extends Base  {
+  override def foo: Async
+}
+
+abstract class ImplAsync extends BaseAsync {
+  final override def foo: Async = new Async
+}
+
+final class StrangeClass extends ImplAsync with BaseSync
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert((new StrangeClass).foo.x == 1)
+  }
+}

test/files/run/t6028.check

@@ -33,7 +33,7 @@ package <empty> {
       <specialized> def apply$mcI$sp(): Int = $anonfun$foo$1.this.$outer.classParam.+($anonfun$foo$1.this.$outer.field()).+($anonfun$foo$1.this.methodParam$1).+($anonfun$foo$1.this.methodLocal$1);
       <synthetic> <paramaccessor> <artifact> private[this] val $outer: T = _;
       <synthetic> <stable> <artifact> def $outer(): T = $anonfun$foo$1.this.$outer;
-      final <bridge> <artifact> def apply(): Object = scala.Int.box($anonfun$foo$1.this.apply());
+      <bridge> <artifact> def apply(): Object = scala.Int.box($anonfun$foo$1.this.apply());
       <synthetic> <paramaccessor> private[this] val methodParam$1: Int = _;
       <synthetic> <paramaccessor> private[this] val methodLocal$1: Int = _
     };
@@ -73,7 +73,7 @@ package <empty> {
       } finally ();
       <synthetic> <paramaccessor> <artifact> private[this] val $outer: T = _;
       <synthetic> <stable> <artifact> def $outer(): T = $anonfun$tryy$1.this.$outer;
-      final <bridge> <artifact> def apply(): Object = {
+      <bridge> <artifact> def apply(): Object = {
         $anonfun$tryy$1.this.apply();
         scala.runtime.BoxedUnit.UNIT
       };