Disallow toplevel statements other than definitions

Have tests for other sorts of definitions

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2620,7 +2620,7 @@ object Parsers {
           if (in.token == CASE)
             syntaxErrorOrIncomplete(OnlyCaseClassOrCaseObjectAllowed())
           else
-            syntaxErrorOrIncomplete(ExpectedClassOrObjectDef())
+            syntaxErrorOrIncomplete(ExpectedToplevelDef())
         }
         acceptStatSepUnlessAtEnd()
       }

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

@@ -88,7 +88,7 @@ public enum ErrorMessageID {
     ValueClassParameterMayNotBeAVarID,
     ValueClassNeedsExactlyOneValParamID,
     OnlyCaseClassOrCaseObjectAllowedID,
-    ExpectedClassOrObjectDefID,
+    ExpectedTopLevelDefID,
     AnonymousFunctionMissingParamTypeID,
     SuperCallsNotAllowedInlineableID,
     ModifiersNotAllowedID,

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

@@ -1670,10 +1670,10 @@ object messages {
     val explanation: String = ""
   }
 
-  case class ExpectedClassOrObjectDef()(implicit ctx: Context)
-    extends Message(ExpectedClassOrObjectDefID) {
+  case class ExpectedToplevelDef()(implicit ctx: Context)
+    extends Message(ExpectedTopLevelDefID) {
     val kind: String = "Syntax"
-    val msg: String = "Expected class or object definition"
+    val msg: String = "Expected a toplevel definition"
     val explanation: String = ""
   }
 

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

@@ -966,7 +966,7 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       implicit val ctx: Context = ictx
       assertMessageCount(1, messages)
       val err :: Nil = messages
-      assertEquals(err, ExpectedClassOrObjectDef())
+      assertEquals(err, ExpectedToplevelDef())
     }
 
   @Test def implicitClassPrimaryConstructorArity =

docs/docs/reference/dropped-features/package-objects.md

@@ -12,11 +12,18 @@ Package objects
 ```
 will be dropped. They are still available in Scala 3.0, but will be deprecated and removed afterwards.
 
-Package objects are no longer needed since all kinds of definitions and statements can now be written at the top-level. E.g.
+Package objects are no longer needed since all kinds of definitions can now be written at the top-level. E.g.
 ```scala
     package p
-    val a = ...
-    def b = ...
+    type Labelled[T] = (String, T)
+    val a: Labelled[Int] = ("count", 1)
+    def b = a._2
+
+    case class C()
+
+    implicit object Cops {
+      def (x: C) pair (y: C) = (x, y)
+    }
 ```
 There may be several source files in a package containing such toplevel definitions, and source files can freely mix toplevel value, method, and tyoe definitions with classes and objects.
 

tests/neg/toplevel.scala

@@ -0,0 +1 @@
+println("hello")   // error: Expected a toplevel definition

tests/neg/validate.scala

@@ -4,7 +4,7 @@ trait X {
   abstract def y: Y // error: abstract term
 }
 
-implicit object Z { // error: implicit at toplevel
+implicit object Z { // now ok: implicit at top level
   implicit case class C() // error: implicit classes may not be case classes
   implicit type T = Int // error: implicit modifier cannot be used for types or traits
   implicit trait U // error: implicit modifier cannot be used for types or traits

tests/run/toplevel-defs.check

@@ -1,2 +1,5 @@
+...
 hello, Bill
 hello, Bob
+hello, Eve
+total : 3

tests/run/toplevel-defs/Test_2.scala

@@ -1,4 +1,8 @@
 object Test extends App {
   println(hello("Bill"))
   println(O.hi)
+  println(hello(her))
+
+  val x: Labelled[Int] = ("total", 3)
+  println(showLabelled(x))
 }

tests/run/toplevel-defs/defs_1.scala

@@ -1,5 +1,14 @@
 def hello(name: String) = s"hello, $name"
 
+val her = {
+  println("...")
+  "Eve"
+}
+
+type Labelled[T] = (String, T)
+
+def showLabelled[T](x: Labelled[T]) = s"${x(0)} : ${x(1)}"
+
 object O {
   def hi = hello("Bob")
 }