Allow vals in using clauses of givens

Author: odersky

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

@@ -62,7 +62,7 @@ object Parsers {
     case ExtensionFollow // extension clause, following extension parameter
 
     def isClass = // owner is a class
-      this == Class || this == CaseClass
+      this == Class || this == CaseClass || this == Given
     def takesOnlyUsingClauses = // only using clauses allowed for this owner
       this == Given || this == ExtensionFollow
     def acceptsVariance =
@@ -3330,7 +3330,7 @@ object Parsers {
         val isAbstractOwner = paramOwner == ParamOwner.Type || paramOwner == ParamOwner.TypeParam
         val start = in.offset
         var mods = annotsAsMods() | Param
-        if paramOwner == ParamOwner.Class || paramOwner == ParamOwner.CaseClass then
+        if paramOwner.isClass then
           mods |= PrivateLocal
         if isIdent(nme.raw.PLUS) && checkVarianceOK() then
           mods |= Covariant
@@ -4058,6 +4058,14 @@ object Parsers {
       val nameStart = in.offset
       val name = if isIdent && followingIsGivenSig() then ident() else EmptyTermName
 
+      // TODO Change syntax description
+      def adjustDefParams(paramss: List[ParamClause]): List[ParamClause] =
+        paramss.nestedMap: param =>
+          if !param.mods.isAllOf(PrivateLocal) then
+            syntaxError(em"method parameter ${param.name} may not be `a val`", param.span)
+          param.withMods(param.mods &~ (AccessFlags | ParamAccessor | Mutable) | Param)
+        .asInstanceOf[List[ParamClause]]
+
       val gdef =
         val tparams = typeParamClauseOpt(ParamOwner.Given)
         newLineOpt()
@@ -4079,16 +4087,17 @@ object Parsers {
             mods1 |= Lazy
             ValDef(name, parents.head, subExpr())
           else
-            DefDef(name, joinParams(tparams, vparamss), parents.head, subExpr())
+            DefDef(name, adjustDefParams(joinParams(tparams, vparamss)), parents.head, subExpr())
         else if (isStatSep || isStatSeqEnd) && parentsIsType then
           if name.isEmpty then
             syntaxError(em"anonymous given cannot be abstract")
-          DefDef(name, joinParams(tparams, vparamss), parents.head, EmptyTree)
+          DefDef(name, adjustDefParams(joinParams(tparams, vparamss)), parents.head, EmptyTree)
         else
-          val tparams1 = tparams.map(tparam => tparam.withMods(tparam.mods | PrivateLocal))
-          val vparamss1 = vparamss.map(_.map(vparam =>
-            vparam.withMods(vparam.mods &~ Param | ParamAccessor | Protected)))
-          val constr = makeConstructor(tparams1, vparamss1)
+          val vparamss1 = vparamss.nestedMap: vparam =>
+            if vparam.mods.is(Private)
+            then vparam.withMods(vparam.mods &~ PrivateLocal | Protected)
+            else vparam
+          val constr = makeConstructor(tparams, vparamss1)
           val templ =
             if isStatSep || isStatSeqEnd then Template(constr, parents, Nil, EmptyValDef, Nil)
             else withTemplate(constr, parents)