widenIfNecessary: we have bootstrap

Author: adriaanm

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

@@ -871,15 +871,16 @@ trait Namers extends MethodSynthesis {
         //  - We don't need to call dropIllegalStarTypes on a ref to a module class, do we? Where would the stars be? In the prefix?
 
         // We're inferring the result type of a stable symbol, and the type doesn't refer to a hidden symbol
-        val mayKeepSingletonType = sym.isStable && !refersToSymbolLessAccessibleThan(tpe, sym)
-
+        // Also widen constant/literal return types of non-final definitions
+        val mayKeepSingletonType = (sym.isStable &&
+            (sym.isFinal || !(tpe.isInstanceOf[ConstantType] || tpe.isInstanceOf[LiteralType])) &&
+            !refersToSymbolLessAccessibleThan(tpe, sym))
+
+        // on't change the type if the definition can keep its inferred singleton type,
+        // or widening would mean no longer conforming to the expected type.
+        // Otherwise, widen.
         // (OPT: 99.99% of the time, pt will be WildcardType)
-        @inline def cannotWiden  = (pt ne WildcardType) && !(tpe.widen <:< pt)
-
-        // If the definition can keep its inferred singleton type,
-        // or widening would mean no longer conforming to the expected type,
-        // we must still deconst unless it's a final val. Otherwise, widen.
-        if (mayKeepSingletonType || cannotWiden) { if (sym.isFinal) tpe else tpe.deconst }
+        if (mayKeepSingletonType || (pt ne WildcardType) && !(tpe.widen <:< pt)) tpe
         else tpe.widen
       } else {
         val shouldWiden = (