Make derives a soft keyword

Author: odersky

compiler/src/dotty/tools/dotc/core/StdNames.scala

@@ -397,6 +397,7 @@ object StdNames {
     val definitions: N          = "definitions"
     val delayedInit: N          = "delayedInit"
     val delayedInitArg: N       = "delayedInit$body"
+    val derives: N              = "derives"
     val drop: N                 = "drop"
     val dynamics: N             = "dynamics"
     val elem: N                 = "elem"

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

@@ -2499,7 +2499,7 @@ object Parsers {
         }
         else Nil
       val derived =
-        if (in.token == DERIVES) {
+        if (isIdent(nme.derives)) {
           in.nextToken()
           tokenSeparated(COMMA, qualId)
         }
@@ -2521,7 +2521,7 @@ object Parsers {
      */
     def templateOpt(constr: DefDef, isEnum: Boolean = false): Template = {
       newLineOptWhenFollowedBy(LBRACE)
-      if (in.token == EXTENDS || in.token == DERIVES || in.token == LBRACE)
+      if (in.token == EXTENDS || isIdent(nme.derives) || in.token == LBRACE)
         template(constr, isEnum)
       else
         Template(constr, Nil, EmptyValDef, Nil)

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

@@ -205,8 +205,7 @@ object Scanners {
     private def handleMigration(keyword: Token): Token =
       if (!isScala2Mode) keyword
       else if (  keyword == ENUM
-              || keyword == ERASED
-              || keyword == DERIVES) treatAsIdent()
+              || keyword == ERASED) treatAsIdent()
       else keyword
 
 

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

@@ -94,7 +94,6 @@ abstract class TokensCommon {
   //final val FORSOME = 61;          enter(FORSOME, "forSome") // TODO: deprecate
   //final val ENUM = 62;             enter(ENUM, "enum")
   //final val ERASED = 63;           enter(ERASED, "erased")
-  //final val DERIVES = 64;          enter(DERIVES, "derives")
 
   /** special symbols */
   final val COMMA = 70;            enter(COMMA, "','")
@@ -179,7 +178,6 @@ object Tokens extends TokensCommon {
   final val FORSOME = 61;          enter(FORSOME, "forSome") // TODO: deprecate
   final val ENUM = 62;             enter(ENUM, "enum")
   final val ERASED = 63;           enter(ERASED, "erased")
-  final val DERIVES = 64;          enter(DERIVES, "derives")
 
   /** special symbols */
   final val NEWLINE = 78;          enter(NEWLINE, "end of statement", "new line")
@@ -200,7 +198,7 @@ object Tokens extends TokensCommon {
   /** XML mode */
   final val XMLSTART = 96;         enter(XMLSTART, "$XMLSTART$<") // TODO: deprecate
 
-  final val alphaKeywords: TokenSet = tokenRange(IF, DERIVES)
+  final val alphaKeywords: TokenSet = tokenRange(IF, ERASED)
   final val symbolicKeywords: TokenSet = tokenRange(USCORE, VIEWBOUND)
   final val symbolicTokens: TokenSet = tokenRange(COMMA, VIEWBOUND)
   final val keywords: TokenSet = alphaKeywords | symbolicKeywords