SI-5617 Better error message for "x overrides nothing".

"It looks like you're trying to override a method", notes Clippy.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index 26cf246ed7..119bb0852c 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -766,7 +766,16 @@ abstract class RefChecks extends InfoTransform with reflect.internal.transform.R
       for (member <- clazz.info.decls)
         if (member.isAnyOverride && !(clazz.thisType.baseClasses exists (hasMatchingSym(_, member)))) {
           // for (bc <- clazz.info.baseClasses.tail) Console.println("" + bc + " has " + bc.info.decl(member.name) + ":" + bc.info.decl(member.name).tpe);//DEBUG
-          unit.error(member.pos, member.toString() + " overrides nothing");
+
+          val nonMatching: List[Symbol] = clazz.info.member(member.name).alternatives.filterNot(_.owner == clazz).filterNot(_.isFinal)
+          def issueError(suffix: String) = unit.error(member.pos, member.toString() + " overrides nothing" + suffix);
+          nonMatching match {
+            case Nil =>
+              issueError("")
+            case ms =>
+              val superSigs = ms.map(m => m.defStringSeenAs(clazz.tpe memberType m)).mkString("\n")
+              issueError(s".\nNote: the super classes of ${member.owner} contain the following, non final members named ${member.name}:\n${superSigs}")
+          }
           member resetFlag (OVERRIDE | ABSOVERRIDE)  // Any Override
         }
     }