New format for trait redefined final method from AnyRef error message…

compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java

@@ -112,6 +112,7 @@ public enum ErrorMessageID {
     UndefinedNamedTypeParameterID,
     IllegalStartOfStatementID,
     TraitIsExpectedID,
+    TraitRedefinedFinalMethodFromAnyRefID,
     ;
 
     public int errorNumber() {

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -1916,4 +1916,10 @@ object messages {
           |"""
     }
   }
+
+  case class TraitRedefinedFinalMethodFromAnyRef(method: Symbol)(implicit ctx: Context) extends Message(TraitRedefinedFinalMethodFromAnyRefID) {
+    val kind = "Syntax"
+    val msg = hl"Traits cannot redefine final $method from ${"class AnyRef"}."
+    val explanation = ""
+  }
 }

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -116,7 +116,7 @@ object RefChecks {
     if (!cls.owner.is(ModuleClass)) {
       def clashes(sym: Symbol) =
         sym.isClass &&
-        sym.name.stripModuleClassSuffix == cls.name.stripModuleClassSuffix        
+        sym.name.stripModuleClassSuffix == cls.name.stripModuleClassSuffix
 
       val others = cls.owner.linkedClass.info.decls.filter(clashes)
       others.foreach { other =>
@@ -606,7 +606,7 @@ object RefChecks {
         // override a concrete method in Object. The jvm, however, does not.
         val overridden = decl.matchingDecl(defn.ObjectClass, defn.ObjectType)
         if (overridden.is(Final))
-          ctx.error("trait cannot redefine final method from class AnyRef", decl.pos)
+          ctx.error(TraitRedefinedFinalMethodFromAnyRef(overridden), decl.pos)
       }
     }
 

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -1172,4 +1172,21 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val TraitIsExpected(symbol) :: Nil = messages
       assertEquals("class B", symbol.show)
     }
+
+  @Test def traitRedefinedFinalMethodFromAnyRef =
+    checkMessagesAfter("refchecks") {
+      """
+        |trait C {
+        |  def wait (): Unit
+        |}
+      """.stripMargin
+    }
+    .expect { (ictx, messages) =>
+      implicit val ctx: Context = ictx
+
+      assertMessageCount(1, messages)
+      val TraitRedefinedFinalMethodFromAnyRef(method) = messages.head
+      assertEquals("method wait", method.show)
+    }
+
 }