Add supports for type cast and filtering type for field and method owner in global initialization checker

compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -599,6 +599,22 @@ object Objects:
 
           case _ => a
 
+    def filterType(tpe: Type)(using Context): Value =
+      val baseClasses = tpe.baseClasses
+      if baseClasses.isEmpty then a
+      else filterClass(baseClasses.head)
+
+    def filterClass(sym: Symbol)(using Context): Value =
+        if !sym.isClass then a
+        else
+          val klass = sym.asClass
+          a match
+            case Cold => Cold
+            case ref: Ref if ref.klass.isSubClass(klass) => ref
+            case ref: Ref => Bottom
+            case ValueSet(values) => values.map(v => v.filterClass(klass)).join
+            case _ => a // TODO: could be more precise for OfArray; possibly add class information for Fun
+
   extension (value: Ref | Cold.type)
     def widenRefOrCold(height : Int)(using Context) : Ref | Cold.type = value.widen(height).asInstanceOf[ThisValue]
 
@@ -617,7 +633,7 @@ object Objects:
    * @param needResolve  Whether the target of the call needs resolution?
    */
   def call(value: Value, meth: Symbol, args: List[ArgInfo], receiver: Type, superType: Type, needResolve: Boolean = true): Contextual[Value] = log("call " + meth.show + ", this = " + value.show + ", args = " + args.map(_.value.show), printer, (_: Value).show) {
-    value match
+    value.filterClass(meth.owner) match
     case Cold =>
       report.warning("Using cold alias. " + Trace.show, Trace.position)
       Bottom
@@ -733,7 +749,6 @@ object Objects:
    * @param args         Arguments of the constructor call (all parameter blocks flatten to a list).
    */
   def callConstructor(value: Value, ctor: Symbol, args: List[ArgInfo]): Contextual[Value] = log("call " + ctor.show + ", args = " + args.map(_.value.show), printer, (_: Value).show) {
-
     value match
     case ref: Ref =>
       if ctor.hasSource then
@@ -768,7 +783,7 @@ object Objects:
    * @param needResolve  Whether the target of the selection needs resolution?
    */
   def select(value: Value, field: Symbol, receiver: Type, needResolve: Boolean = true): Contextual[Value] = log("select " + field.show + ", this = " + value.show, printer, (_: Value).show) {
-    value match
+    value.filterClass(field.owner) match
     case Cold =>
       report.warning("Using cold alias", Trace.position)
       Bottom
@@ -839,7 +854,7 @@ object Objects:
    * @param rhsTyp      The type of the right-hand side.
    */
   def assign(lhs: Value, field: Symbol, rhs: Value, rhsTyp: Type): Contextual[Value] = log("Assign" + field.show + " of " + lhs.show + ", rhs = " + rhs.show, printer, (_: Value).show) {
-    lhs match
+    lhs.filterClass(field.owner) match
     case fun: Fun =>
       report.warning("[Internal error] unexpected tree in assignment, fun = " + fun.code.show + Trace.show, Trace.position)
 
@@ -876,8 +891,7 @@ object Objects:
    * @param args        The arguments passsed to the constructor.
    */
   def instantiate(outer: Value, klass: ClassSymbol, ctor: Symbol, args: List[ArgInfo]): Contextual[Value] = log("instantiating " + klass.show + ", outer = " + outer + ", args = " + args.map(_.value.show), printer, (_: Value).show) {
-    outer match
-
+    outer.filterClass(klass.owner) match
     case _ : Fun | _: OfArray  =>
       report.warning("[Internal error] unexpected outer in instantiating a class, outer = " + outer.show + ", class = " + klass.show + ", " + Trace.show, Trace.position)
       Bottom
@@ -1091,6 +1105,9 @@ object Objects:
           instantiate(outer, cls, ctor, args)
         }
 
+      case TypeCast(elem, tpe) =>
+        eval(elem, thisV, klass).filterType(tpe)
+
       case Apply(ref, arg :: Nil) if ref.symbol == defn.InitRegionMethod =>
         val regions2 = Regions.extend(expr.sourcePos)
         if Regions.exists(expr.sourcePos) then

compiler/src/dotty/tools/dotc/transform/init/Util.scala

@@ -78,6 +78,13 @@ object Util:
       case _ =>
         None
 
+  object TypeCast:
+    def unapply(tree: Tree)(using Context): Option[(Tree, Type)] =
+      tree match
+        case TypeApply(Select(qual, _), typeArg) if tree.symbol.isTypeCast =>
+          Some(qual, typeArg.head.tpe)
+        case _ => None
+
   def resolve(cls: ClassSymbol, sym: Symbol)(using Context): Symbol = log("resove " + cls + ", " + sym, printer, (_: Symbol).show):
     if sym.isEffectivelyFinal then sym
     else sym.matchingMember(cls.appliedRef)

tests/init-global/neg/TypeCast.scala

@@ -0,0 +1,18 @@
+object A {
+  val f: Int = 10
+  def m() = f
+}
+object B {
+  val f: Int = g()
+  def g(): Int = f // error
+}
+object C {
+  val a: A.type | B.type = if ??? then A else B
+  def cast[T](a: Any): T = a.asInstanceOf[T]
+  val c: A.type = cast[A.type](a) // abstraction for c is {A, B}
+  val d = c.f // treat as c.asInstanceOf[owner of f].f
+  val e = c.m() // treat as c.asInstanceOf[owner of f].m()
+  val c2: B.type = cast[B.type](a)
+  val g = c2.f // no error here
+}
+

tests/init-global/pos/i18882.scala

@@ -0,0 +1,15 @@
+class A:
+  var a = 20
+
+class B:
+  var b = 20
+
+object O:
+  val o: A | B = new A
+  if o.isInstanceOf[A] then
+    o.asInstanceOf[A].a += 1
+  else
+    o.asInstanceOf[B].b += 1 // o.asInstanceOf[B] is treated as bottom
+  o match
+    case o: A => o.a += 1
+    case o: B => o.b += 1