Improve type of getClass

The new assumed signature is

    def getClass[A >: this.type](): Class[? <: A]

This matches what scalac does, without requiring special machinery in
the type checker and inferencer.

Author: odersky

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -153,10 +153,12 @@ class Definitions {
       tl => op(tl.paramRefs(0), tl.paramRefs(1))))
 
   private def enterPolyMethod(cls: ClassSymbol, name: TermName, typeParamCount: Int,
-                    resultTypeFn: PolyType => Type, flags: FlagSet = EmptyFlags,
+                    resultTypeFn: PolyType => Type,
+                    flags: FlagSet = EmptyFlags,
+                    bounds: TypeBounds = TypeBounds.empty,
                     useCompleter: Boolean = false) = {
     val tparamNames = PolyType.syntheticParamNames(typeParamCount)
-    val tparamInfos = tparamNames map (_ => TypeBounds.empty)
+    val tparamInfos = tparamNames map (_ => bounds)
     def ptype = PolyType(tparamNames)(_ => tparamInfos, resultTypeFn)
     val info =
       if (useCompleter)
@@ -261,19 +263,26 @@ class Definitions {
   @tu lazy val AnyValClass: ClassSymbol = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.AnyVal, Abstract, List(AnyClass.typeRef)))
   def AnyValType: TypeRef = AnyValClass.typeRef
 
-    @tu lazy val Any_== : TermSymbol       = enterMethod(AnyClass, nme.EQ, methOfAny(BooleanType), Final)
-    @tu lazy val Any_!= : TermSymbol       = enterMethod(AnyClass, nme.NE, methOfAny(BooleanType), Final)
-    @tu lazy val Any_equals: TermSymbol   = enterMethod(AnyClass, nme.equals_, methOfAny(BooleanType))
-    @tu lazy val Any_hashCode: TermSymbol = enterMethod(AnyClass, nme.hashCode_, MethodType(Nil, IntType))
-    @tu lazy val Any_toString: TermSymbol = enterMethod(AnyClass, nme.toString_, MethodType(Nil, StringType))
-    @tu lazy val Any_## : TermSymbol       = enterMethod(AnyClass, nme.HASHHASH, ExprType(IntType), Final)
-    @tu lazy val Any_getClass: TermSymbol = enterMethod(AnyClass, nme.getClass_, MethodType(Nil, ClassClass.typeRef.appliedTo(TypeBounds.empty)), Final)
+    @tu lazy val Any_== : TermSymbol           = enterMethod(AnyClass, nme.EQ, methOfAny(BooleanType), Final)
+    @tu lazy val Any_!= : TermSymbol          = enterMethod(AnyClass, nme.NE, methOfAny(BooleanType), Final)
+    @tu lazy val Any_equals: TermSymbol       = enterMethod(AnyClass, nme.equals_, methOfAny(BooleanType))
+    @tu lazy val Any_hashCode: TermSymbol     = enterMethod(AnyClass, nme.hashCode_, MethodType(Nil, IntType))
+    @tu lazy val Any_toString: TermSymbol     = enterMethod(AnyClass, nme.toString_, MethodType(Nil, StringType))
+    @tu lazy val Any_## : TermSymbol          = enterMethod(AnyClass, nme.HASHHASH, ExprType(IntType), Final)
     @tu lazy val Any_isInstanceOf: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOf_, _ => BooleanType, Final)
     @tu lazy val Any_asInstanceOf: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.asInstanceOf_, _.paramRefs(0), Final)
-    @tu lazy val Any_typeTest: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOfPM, _ => BooleanType, Final | Synthetic | Artifact)
-    @tu lazy val Any_typeCast: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.asInstanceOfPM, _.paramRefs(0), Final | Synthetic | Artifact | StableRealizable)
+    @tu lazy val Any_typeTest: TermSymbol     = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOfPM, _ => BooleanType, Final | Synthetic | Artifact)
+    @tu lazy val Any_typeCast: TermSymbol     = enterT1ParameterlessMethod(AnyClass, nme.asInstanceOfPM, _.paramRefs(0), Final | Synthetic | Artifact | StableRealizable)
       // generated by pattern matcher, eliminated by erasure
 
+    // def getClass[A >: this.type](): Class[? <: A]
+    @tu lazy val Any_getClass: TermSymbol =
+        enterPolyMethod(
+          AnyClass, nme.getClass_, 1,
+          pt => MethodType(Nil, ClassClass.typeRef.appliedTo(TypeBounds.upper(pt.paramRefs(0)))),
+          Final,
+          bounds = TypeBounds.lower(AnyClass.thisType))
+
     def AnyMethods: List[TermSymbol] = List(Any_==, Any_!=, Any_equals, Any_hashCode,
       Any_toString, Any_##, Any_getClass, Any_isInstanceOf, Any_asInstanceOf, Any_typeTest, Any_typeCast)
 

tests/pos/i3495.scala

@@ -0,0 +1,13 @@
+class A
+
+object Test {
+  val x: A = new A()
+
+  def y = x.getClass
+
+  val z: Class[? <: A] = y
+
+  1.getClass
+
+}
+

tests/pos/t1107b/T.scala

@@ -2,6 +2,6 @@ sealed trait Top
 sealed trait Sub extends Top
 trait C {
   private object P extends Sub
-  def bob() = P.getClass
+  def bob(): Class[_] = P.getClass
   def bob2() = O.d(P)
 }