deal with constant methods in uncurry instead of ctors

Author: adriaanm

src/compiler/scala/tools/nsc/transform/Constructors.scala

@@ -693,10 +693,6 @@ abstract class Constructors extends Statics with Transform with ast.TreeDSL {
     for (stat <- stats) {
       val sym = stat.symbol
       stat match {
-        // TODO what is this doing in Constructors? I'd expect it much earlier -- erasure? uncurry?
-        case dd@ DefDef(_,_,_,_,_,rhs) if sym.info.params.isEmpty && sym.info.resultType.isInstanceOf[ConstantType] =>
-          defBuf += deriveDefDef(dd)(rhs => gen.mkAttributedQualifier(sym.info.resultType) setPos rhs.pos )
-
         // all methods except the primary constructor go into template
         case _: DefDef if sym.isConstructor => if (sym ne primaryConstr.symbol) auxConstructorBuf += stat
 

src/compiler/scala/tools/nsc/transform/UnCurry.scala

@@ -593,11 +593,21 @@ abstract class UnCurry extends InfoTransform
               (vparamss1, rhs0)
             }
 
+          // We know newParamss.length == 1
+          // A no-arg method with ConstantType result type can safely be
+          // reduced to the corresponding Literal (only pure methods are typed as ConstantType).
+          // We could also do this for methods with arguments, after ensuring the arguments are not referenced.
+          val literalRhsIfConst =
+            if (newParamss.head.isEmpty && dd.symbol.info.resultType.isInstanceOf[ConstantType])
+              gen.mkAttributedQualifier(dd.symbol.info.resultType) setPos newRhs.pos
+            else newRhs
+
+
           val flatdd = copyDefDef(dd)(
             vparamss = newParamss,
             rhs = nonLocalReturnKeys get dd.symbol match {
-              case Some(k) => atPos(newRhs.pos)(nonLocalReturnTry(newRhs, k, dd.symbol))
-              case None    => newRhs
+              case Some(k) => atPos(newRhs.pos)(nonLocalReturnTry(literalRhsIfConst, k, dd.symbol))
+              case None    => literalRhsIfConst
             }
           )
           addJavaVarargsForwarders(dd, flatdd)