Fix #5486: Constant-fold types in TypeAssigner

Instead of doing it in Typer, sometimes losing it in PostTyper or when
unpickling, then recovering it in FirstTransform. We still need a
special case in TreeUnpickler because we don't use TypeAssigner when
unpickling Select nodes.

Author: smarter

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -16,6 +16,7 @@ import Flags._
 import Constants._
 import Annotations._
 import NameKinds._
+import typer.ConstFold
 import typer.Checking.checkNonCyclic
 import util.Positions._
 import ast.{TreeTypeMap, Trees, tpd, untpd}
@@ -996,7 +997,7 @@ class TreeUnpickler(reader: TastyReader,
         val localCtx =
           if (name == nme.CONSTRUCTOR) ctx.addMode(Mode.InSuperCall) else ctx
         val qual = readTerm()(localCtx)
-        untpd.Select(qual, name).withType(tpf(qual.tpe.widenIfUnstable))
+        ConstFold(untpd.Select(qual, name).withType(tpf(qual.tpe.widenIfUnstable)))
       }
 
       def readQualId(): (untpd.Ident, TypeRef) = {

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -588,15 +588,6 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       // add type to term nodes; replace type nodes with their types unless -Yprint-pos is also set.
       def tp = tree.typeOpt match {
         case tp: TermRef if tree.isInstanceOf[RefTree] && !tp.denot.isOverloaded => tp.underlying
-        case tp: ConstantType if homogenizedView =>
-          // constant folded types are forgotten in Tasty, are reconstituted subsequently in FirstTransform.
-          // Therefore we have to gloss over this when comparing before/after pickling by widening to
-          // underlying type `T`, or, if expression is a unary primitive operation, to `=> T`.
-          tree match {
-            case Select(qual, _) if qual.typeOpt.widen.typeSymbol.isPrimitiveValueClass =>
-              ExprType(tp.widen)
-            case _ => tp.widen
-          }
         case tp => tp
       }
       if (!suppressTypes)

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

@@ -769,7 +769,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
                 new ApplyToTyped(tree, fun1, funRef, proto.typedArgs, pt)
               else
                 new ApplyToUntyped(tree, fun1, funRef, proto, pt)(argCtx(tree))
-            convertNewGenericArray(ConstFold(app.result))
+            convertNewGenericArray(app.result)
           case _ =>
             handleUnexpectedFunType(tree, fun1)
         }

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

@@ -17,7 +17,7 @@ object ConstFold {
   import tpd._
 
   /** If tree is a constant operation, replace with result. */
-  def apply(tree: Tree)(implicit ctx: Context): Tree = finish(tree) {
+  def apply[T <: Tree](tree: T)(implicit ctx: Context): T = finish(tree) {
     tree match {
       case Apply(Select(xt, op), yt :: Nil) =>
         xt.tpe.widenTermRefExpr match {
@@ -40,18 +40,18 @@ object ConstFold {
   /** If tree is a constant value that can be converted to type `pt`, perform
    *  the conversion.
    */
-  def apply(tree: Tree, pt: Type)(implicit ctx: Context): Tree =
+  def apply[T <: Tree](tree: T, pt: Type)(implicit ctx: Context): T =
     finish(apply(tree)) {
       tree.tpe.widenTermRefExpr match {
         case ConstantType(x) => x convertTo pt
         case _ => null
       }
     }
 
-  private def finish(tree: Tree)(compX: => Constant)(implicit ctx: Context): Tree =
+  private def finish[T <: Tree](tree: T)(compX: => Constant)(implicit ctx: Context): T =
     try {
       val x = compX
-      if (x ne null) tree withType ConstantType(x)
+      if (x ne null) tree.withType(ConstantType(x)).asInstanceOf[T]
       else tree
     } catch {
       case _: ArithmeticException => tree   // the code will crash at runtime,

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

@@ -291,7 +291,7 @@ trait TypeAssigner {
 
       case _ => accessibleSelectionType(tree, qual)
     }
-    tree.withType(tp)
+    ConstFold(tree.withType(tp))
   }
 
   def assignType(tree: untpd.New, tpt: Tree)(implicit ctx: Context): New =
@@ -372,7 +372,7 @@ trait TypeAssigner {
       case t =>
         errorType(err.takesNoParamsStr(fn, ""), tree.pos)
     }
-    tree.withType(ownType)
+    ConstFold(tree.withType(ownType))
   }
 
   def assignType(tree: untpd.TypeApply, fn: Tree, args: List[Tree])(implicit ctx: Context): TypeApply = {

tests/pos/constfold.scala

@@ -1,8 +1,12 @@
 object A {
-  val x = 2;
-  val y = x.asInstanceOf[Byte];
-  val z = 1.0 / 2;
-  val s = "z is " + z;
+  val x = 2
+  val y = x.asInstanceOf[Byte]
+  val z = 1.0 / 2
+  val s = "z is " + z
+
+  val a = 1 + 1
+  val b = -(1:1)
+  val c = -(1:1 & Any)
 }
 
 object Test extends App {