move 'return outside method definition' to error class

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

@@ -98,6 +98,7 @@ public enum ErrorMessageID {
     ExpectedStartOfTopLevelDefinitionID,
     MissingReturnTypeWithReturnStatementID,
     NoReturnFromInlineID,
+    ReturnOutsideMethodDefinitionID,
     ;
 
     public int errorNumber() {

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

@@ -1747,4 +1747,15 @@ object messages {
           |returned from a method.
           |"""
   }
+
+  case class ReturnOutsideMethodDefinition(owner: Symbol)(implicit ctx: Context)
+    extends Message(ReturnOutsideMethodDefinitionID) {
+    val kind = "Syntax"
+    val msg = hl"${"return"} outside method definition"
+    val explanation =
+      hl"""You used ${"return"} in ${owner}.
+          |${"return"} is a keyword and may only be used within method declarations.
+          |"""
+  }
+
 }

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

@@ -980,7 +980,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     def enclMethInfo(cx: Context): (Tree, Type) = {
       val owner = cx.owner
       if (owner.isType) {
-        ctx.error("return outside method definition", tree.pos)
+        ctx.error(ReturnOutsideMethodDefinition(owner), tree.pos)
         (EmptyTree, WildcardType)
       }
       else if (owner != cx.outer.owner && owner.isRealMethod) {

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

@@ -985,4 +985,17 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val NoReturnFromInline(method) :: Nil = messages
       assertEquals("method usesReturn", method.show)
     }
+
+  @Test def returnOutsideMethodDefinition =
+    checkMessagesAfter("frontend") {
+      """object A {
+        |  return 5
+        |}
+      """.stripMargin
+    }.expect { (ictx, messages) =>
+      implicit val ctx: Context = ictx
+      assertMessageCount(1, messages)
+      val ReturnOutsideMethodDefinition(owner) :: Nil = messages
+      assertEquals("object A", owner.show)
+    }
 }