Move check for casting a primitive to a non-primitive type from erasure to refchecks

Author: DarkDimius

src/dotty/tools/dotc/transform/TypeTestsCasts.scala

@@ -47,12 +47,9 @@ trait TypeTestsCasts {
           def argCls = argType.classSymbol
           if (expr.tpe <:< argType)
             Literal(Constant(true)) withPos tree.pos
-          else if (qualCls.isPrimitiveValueClass) {
-            if (argCls.isPrimitiveValueClass) Literal(Constant(qualCls == argCls))
-            else errorTree(tree, "isInstanceOf cannot test if value types are references")
-          }
           else if (argCls.isPrimitiveValueClass)
-            transformIsInstanceOf(expr, defn.boxedClass(argCls).typeRef)
+            if (qualCls.isPrimitiveValueClass) Literal(Constant(qualCls == argCls))
+            else transformIsInstanceOf(expr, defn.boxedClass(argCls).typeRef)
           else argType.dealias match {
             case _: SingletonType =>
               val cmpOp = if (argType derivesFrom defn.AnyValClass) defn.Any_equals else defn.Object_eq

src/dotty/tools/dotc/typer/RefChecks.scala

@@ -814,6 +814,22 @@ class RefChecks extends MiniPhase with SymTransformer { thisTransformer =>
       currentLevel.enterReference(tree.tpe.typeSymbol, tree.pos)
       tree
     }
+
+    override def transformTypeApply(tree: tpd.TypeApply)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
+      tree.fun match {
+        case fun@Select(qual, selector) =>
+          val sym = tree.symbol
+
+          if (sym == defn.Any_isInstanceOf) {
+            val argType = tree.args.head.tpe
+            val qualCls = qual.tpe.widen.classSymbol
+            val argCls = argType.classSymbol
+            if (qualCls.isPrimitiveValueClass && !argCls.isPrimitiveValueClass) ctx.error("isInstanceOf cannot test if value types are references", tree.pos)
+          }
+        case _ =>
+      }
+      tree
+    }
   }
 }