Allow exports as toplevel statements

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1033,7 +1033,7 @@ object desugar {
       case stat: TypeDef if stat.mods.is(Opaque) => stat.name
     }
     def needsObject(stat: Tree) = stat match {
-      case _: ValDef | _: PatDef | _: DefDef => true
+      case _: ValDef | _: PatDef | _: DefDef | _: Export => true
       case stat: ModuleDef =>
         stat.mods.is(ImplicitOrImplied) || opaqueNames.contains(stat.name.stripModuleClassSuffix.toTypeName)
       case stat: TypeDef => !stat.isClassDef || stat.mods.is(ImplicitOrImplied)

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

@@ -2778,6 +2778,8 @@ object Parsers {
         }
         else if (in.token == IMPORT)
           stats ++= importClause(IMPORT, Import)
+        else if (in.token == EXPORT)
+          stats ++= importClause(EXPORT, Export.apply)
         else if (in.token == AT || isDefIntro(modifierTokens))
           stats +++= defOrDcl(in.offset, defAnnotsMods(modifierTokens))
         else if (!isStatSep) {

docs/docs/internals/syntax.md

@@ -408,6 +408,7 @@ EnumCase          ::=  ‘case’ (id ClassConstr [‘extends’ ConstrApps]] |
 
 TopStatSeq        ::=  TopStat {semi TopStat}
 TopStat           ::=  Import
+                    |  Export
                     |  {Annotation [nl]} {Modifier} Def
                     |  Packaging
                     |  PackageObject