code review : removes unnecessary override/types and improves test

Author: Aurélien Richez

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

@@ -1919,9 +1919,9 @@ object messages {
 
   case class PackageNameAlreadyDefined(pkg: Symbol)(implicit ctx: Context) extends Message(PackageNameAlreadyDefinedID) {
 
-    override def msg: String = hl"${pkg} is already defined, cannot be a package"
-    override def kind: String = "Syntax"
-    override def explanation: String =
-      "An object cannot have the same name as an existing package. Rename ${pkg} or the package with the same name."
+    val msg = hl"${pkg} is already defined, cannot be a ${"package"}"
+    val kind = "Syntax"
+    val explanation =
+      hl"An ${"object"} cannot have the same name as an existing ${"package"}. Rename either one of them."
   }
 }

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

@@ -1183,7 +1183,7 @@ class ErrorMessagesTests extends ErrorMessagesTest {
     }.expect { (ictx, messages) =>
       implicit val ctx: Context = ictx
 
-      assertMessageCount(1, messages)
-      assert(messages.head.isInstanceOf[PackageNameAlreadyDefined])
+      val PackageNameAlreadyDefined(pkg) = messages.head
+      assertEquals(pkg.show, "object bar")
     }
 }