Fix error message

The change of Implicit to be a common flag now caused
some breakage, which this commit fixes.

Author: odersky

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

@@ -670,6 +670,10 @@ object desugar {
         ctx.error(TopLevelImplicitClass(cdef), cdef.sourcePos)
         Nil
       }
+      else if (mods.is(Trait)) {
+        ctx.error(TypesAndTraitsCantBeImplicit(), cdef.sourcePos)
+        Nil
+      }
       else if (isCaseClass) {
         ctx.error(ImplicitCaseClass(cdef), cdef.sourcePos)
         Nil
@@ -688,7 +692,7 @@ object desugar {
         // implicit wrapper is typechecked in same scope as constructor, so
         // we can reuse the constructor parameters; no derived params are needed.
         DefDef(className.toTermName, constrTparams, defParamss, classTypeRef, creatorExpr)
-          .withMods(companionMods | mods.flags & ImplicitOrImplied | Synthetic | Final)
+          .withMods(companionMods | mods.flags.toTermFlags & ImplicitOrImplied | Synthetic | Final)
           .withSpan(cdef.span) :: Nil
       }
 

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -1507,8 +1507,7 @@ object messages {
     val explanation: String = ""
   }
 
-  case class TypesAndTraitsCantBeImplicit(sym: Symbol)(
-    implicit ctx: Context)
+  case class TypesAndTraitsCantBeImplicit()(implicit ctx: Context)
     extends Message(TypesAndTraitsCantBeImplicitID) {
     val msg: String = hl"""${"implicit"} modifier cannot be used for types or traits"""
     val kind: String = "Syntax"

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -380,7 +380,7 @@ object Checking {
       if (sym.owner.is(Package))
         fail(TopLevelCantBeImplicit(sym))
       if (sym.isType)
-        fail(TypesAndTraitsCantBeImplicit(sym))
+        fail(TypesAndTraitsCantBeImplicit())
     }
     if (!sym.isClass && sym.is(Abstract))
       fail(OnlyClassesCanBeAbstract(sym))

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -715,8 +715,7 @@ class ErrorMessagesTests extends ErrorMessagesTest {
     .expect { (ictx, messages) =>
       implicit val ctx: Context = ictx
       assertMessageCount(1, messages)
-      val TypesAndTraitsCantBeImplicit(symbol) :: Nil = messages
-      assertEquals("trait S", symbol.show)
+      val TypesAndTraitsCantBeImplicit() :: Nil = messages
     }
 
   @Test def onlyClassesCanBeAbstract =