fix: check function's instance class is a subclass of virtual method (#1985)

Author: Willem Wyndham

src/compiler.ts

@@ -6947,6 +6947,8 @@ export class Compiler extends DiagnosticEmitter {
     // Wouldn't be here if there wasn't at least one overload
     var overloadPrototypes = assert(instance.prototype.overloads);
 
+    assert(instance.parent.kind == ElementKind.CLASS || instance.parent.kind == ElementKind.INTERFACE);
+    var parentClassInstance = <Class>instance.parent;
     var module = this.module;
     var usizeType = this.options.usizeType;
     var sizeTypeRef = usizeType.toRef();
@@ -6992,6 +6994,8 @@ export class Compiler extends DiagnosticEmitter {
       if (classInstances) {
         for (let _values = Map_values(classInstances), j = 0, l = _values.length; j < l; ++j) {
           let classInstance = _values[j];
+          // Chcek if the parent class is a subtype of instance's class
+          if (!classInstance.isAssignableTo(parentClassInstance)) continue;
           let overloadInstance: Function | null;
           if (isProperty) {
             let boundProperty = assert(classInstance.members!.get(unboundOverloadParent.name));

tests/compiler/class-overloading-cast.json

@@ -0,0 +1,5 @@
+{
+  "asc_flags": [
+    "--explicitStart"
+  ]
+}