Fix ConstantFold folding constant funcs without calling them

Author: gan74

compiler/src/dotty/tools/dotc/transform/localopt/ConstantFold.scala

@@ -139,16 +139,16 @@ import Simplify.desugarIdent
         //   Block(List(lhs),
         //     ref(defn.throwMethod).appliedTo(New(defn.ArithmeticExceptionClass.typeRef, defn.ArithmeticExceptionClass_stringConstructor, Literal(Constant("/ by zero")) :: Nil)))
 
-        case _ =>
-          val lhType = lhs.tpe.widenTermRefExpr
-          val rhType = rhs.tpe.widenTermRefExpr
-          (lhType, rhType) match {
+        case (l: Literal, r: Literal)  =>
+          (l.tpe.widenTermRefExpr, r.tpe.widenTermRefExpr) match {
             case (ConstantType(_), ConstantType(_)) => 
               val s = ConstFold.apply(t)
               if ((s ne null) && s.tpe.isInstanceOf[ConstantType]) Literal(s.tpe.asInstanceOf[ConstantType].value)
               else t
             case _ => t
           }
+
+        case _ => t
       }
 
     // This case can only be triggered when running Simplify before pattern matching:

compiler/test/dotty/tools/dotc/SimplifyTests.scala

@@ -152,7 +152,7 @@ abstract class SimplifyTests(val optimise: Boolean) extends DottyBytecodeTest {
         |print(4)
       """)
 
-  @Test def TwoValConstantFold =
+  @Test def twoValConstantFold =
     check(
       """
         |val i = 3