don't provide custom class names (#114)

* i knew better

* add test case

* remove half comment

swiftwinrt/Resources/Support/WinRTProtocols.swift

@@ -41,14 +41,10 @@ extension WinRTClass {
   }
 
   public func GetRuntimeClassName() -> HString {
-    if type(of: self) != Self.self {
-      // Aggregated, get a string describing the type of the Swift class instead.
-      // Use String(reflecting:) instead of NSStringFromClass because that doesn't
-      // crash on nested classes
-      let string = String(reflecting: type(of: self))
-      return try! HString(string)
-    } else {
-      return try! _inner.GetRuntimeClassName()
-    }
+    // always use the runtime class name of the inner WinRT object. the winui runtime will query for
+    // class names and if it isn't recognized, it will call out to IXamlMetadataProvider (IXMP)
+    // to get the associated XamlType. We aren't using Xaml for swift, so we don't actually
+    // need or want the framework to think it's dealing with custom types.
+    return try! _inner.GetRuntimeClassName()
   }
 }

tests/test_app/AggregationTests.swift

@@ -1,6 +1,6 @@
 import WinSDK
 import XCTest
-import test_component
+@_spi(WinRTInternal) import test_component
 import Ctest_component
 import Foundation
 
@@ -91,11 +91,29 @@ class AggregationTests : XCTestCase {
     let derived = UnsealedDerived(32)
     XCTAssertEqual(derived.prop, 32)
   }
+
+  public func runtimeClassName(_ base: Base) -> String {
+    return String(hString: base.GetRuntimeClassName())
+  }
+
+  public func testGetRuntimeClassNameReturnsBase() throws {
+    // WinUI calls GetRuntimeClassName when types are being constructed,
+    // so we need to return something that the runtime understands. Without an
+    // IXamlMetadataProvider implementation, returning custom type names will
+    // break the app.
+    let appDerived = AppDerived()
+
+    // In order to validate the test, we have to call GetRuntimeClassName on the base
+    // type. This will make the type check we had think we're being aggregated, where
+    // calling it directly on the AppDerived type won't
+    XCTAssertEqual(runtimeClassName(appDerived), "test_component.Base")
+  }
 }
 
 var aggregationTests: [XCTestCaseEntry] = [
   testCase([
     ("testAggregation", AggregationTests.testAggregation),
     ("testCustomConstructorOnUnsealedType", AggregationTests.testCustomConstructorOnUnsealedType),
+    ("testGetRuntimeClassNameReturnsBase", AggregationTests.testGetRuntimeClassNameReturnsBase)
   ])
 ]