Fixes for turning erased into a soft modifier

Author: odersky

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

@@ -186,7 +186,9 @@ object Scanners {
         error(s"illegal combination of -rewrite targets: ${enabled(0).name} and ${enabled(1).name}")
     }
 
-    var languageImportContext: Context = ctx
+    private var myLanguageImportContext: Context = ctx
+    def languageImportContext = myLanguageImportContext
+    final def languageImportContext_=(c: Context) = myLanguageImportContext = c
 
     def featureEnabled(name: TermName) = Feature.enabled(name)(using languageImportContext)
     def erasedEnabled = featureEnabled(Feature.erasedTerms) || ctx.settings.YerasedTerms.value
@@ -912,7 +914,9 @@ object Scanners {
         reset()
       next
 
-    class LookaheadScanner() extends Scanner(source, offset)
+    class LookaheadScanner() extends Scanner(source, offset) {
+      override def languageImportContext = Scanner.this.languageImportContext
+    }
 
     /** Skip matching pairs of `(...)` or `[...]` parentheses.
      *  @pre  The current token is `(` or `[`

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

@@ -248,7 +248,7 @@ object Tokens extends TokensCommon {
 
   final val modifierTokensOrCase: TokenSet = modifierTokens | BitSet(CASE)
 
-  final val modifierFollowers = modifierTokens | defIntroTokens
+  final val modifierFollowers = modifierTokensOrCase | defIntroTokens
 
   /** Is token only legal as start of statement (eof also included)? */
   final val mustStartStatTokens: TokenSet = defIntroTokens | modifierTokens | BitSet(IMPORT, EXPORT, PACKAGE)

tests/neg/i5525.scala

@@ -29,6 +29,6 @@ enum Foo11 {
   protected case C9  // ok
 }
 
-enum Foo12 {  // error: enums must contain at least one case
-  inline    case C10() // error // error (inline treated as ident here)
+enum Foo12 {
+  inline    case C10() // error: only access modifiers allowed
 }