Fixes for handling end marker

 - Only recognize it under indentSyntax
 - But include it as a possible statement start even under Scala 2.
   END might be detected before it can be converted back to IDENTIFIER.
   So it needs to be included in canStartStatement2, just like IDENTIFIER.

Author: odersky

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

@@ -671,7 +671,7 @@ object Scanners {
     }
 
     protected def isEndMarker: Boolean =
-      if isAfterLineEnd then
+      if indentSyntax && isAfterLineEnd then
         val endLine = source.offsetToLine(offset)
         val lookahead = new LookaheadScanner():
           override def isEndMarker = false

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

@@ -255,7 +255,7 @@ object Tokens extends TokensCommon {
   final val mustStartStatTokens: TokenSet = defIntroTokens | modifierTokens | BitSet(IMPORT, EXPORT, PACKAGE)
 
   final val canStartStatTokens2: TokenSet = canStartExprTokens2 | mustStartStatTokens | BitSet(
-    AT, CASE)
+    AT, CASE, END) // END is included since it might be tested before being converted back to IDENTIFIER
   final val canStartStatTokens3: TokenSet = canStartExprTokens3 | mustStartStatTokens | BitSet(
     AT, CASE, END)