SIP-23 widen LiteralType in result type

Author: adriaanm

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -871,7 +871,8 @@ trait Namers extends MethodSynthesis {
     private def widenIfNecessary(sym: Symbol, tpe: Type, pt: Type): Type = {
       // Are we inferring the result type of a stable symbol, whose type doesn't refer to a hidden symbol?
       // If we refer to an inaccessible symbol, let's hope widening will result in an expressible type.
-      val mayKeepSingletonType = sym.isStable && !refersToSymbolLessAccessibleThan(tpe, sym)
+      // (A LiteralType should be widened because it's too precise for a definition's type.)
+      val mayKeepSingletonType = !tpe.isInstanceOf[LiteralType] && sym.isStable && !refersToSymbolLessAccessibleThan(tpe, sym)
 
       // Only final vals may be constant folded, so deconst inferred type of other members.
       @inline def keepSingleton = if (sym.isFinal) tpe else tpe.deconst