fix(dotnet): AnonymousObject fails runtime type checks (#3709)

The `AnonymousObject` class is used when a value is passed from JS to
.NET through a union or `any` typed return point, and there is not
sufficient runtime type information on the value to decisively identify
its dynamic type. The `AnonymousObject` class will be converted by the
jsii runtime to any interface type implicitly (even if that is
technically not correct), and it must hence be allowed through runtime
type-checks for interfaces. Essentially, this is a blind spot of the
runtime type checks, and should not cause valid code to break.



---

By submitting this pull request, I confirm that my contribution is made under the terms of the [Apache 2.0 license].

[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

packages/@jsii/dotnet-runtime-test/test/Amazon.JSII.Runtime.IntegrationTests/TypeCheckingTests.cs

@@ -1,7 +1,9 @@
 
 using System;
 using System.Collections.Generic;
+using Amazon.JSII.Runtime.Deputy;
 using Amazon.JSII.Tests.CalculatorNamespace;
+using Amazon.JSII.Tests.CalculatorNamespace.Anonymous;
 using Xunit;
 
 #pragma warning disable CS0612
@@ -13,17 +15,17 @@ public sealed class TypeCheckingTests : IClassFixture<ServiceContainerFixture>,
         const string Prefix = nameof(TypeCheckingTests) + ".";
 
         private readonly IDisposable _serviceContainerFixture;
-        
+
         public TypeCheckingTests(ServiceContainerFixture serviceContainerFixture)
         {
             _serviceContainerFixture = serviceContainerFixture;
         }
-        
+
         void IDisposable.Dispose()
         {
             _serviceContainerFixture.Dispose();
         }
-        
+
         [Fact(DisplayName = Prefix + nameof(Constructor))]
         public void Constructor()
         {
@@ -39,7 +41,7 @@ public void Constructor()
             );
             Assert.Equal("Expected argument unionProperty[0][\"bad\"] to be one of: Amazon.JSII.Tests.CalculatorNamespace.IStructA, Amazon.JSII.Tests.CalculatorNamespace.IStructB; received System.String (Parameter 'unionProperty')", exception.Message);
         }
-        
+
         [Fact(DisplayName = Prefix + nameof(Setter))]
         public void Setter()
         {
@@ -55,13 +57,21 @@ public void Setter()
                     });
             Assert.Equal("Expected value[0][\"bad\"] to be one of: Amazon.JSII.Tests.CalculatorNamespace.IStructA, Amazon.JSII.Tests.CalculatorNamespace.IStructB; received System.String (Parameter 'value')", exception.Message);
         }
-        
+
         [Fact(DisplayName = Prefix + nameof(StaticMethod))]
         public void StaticMethod()
         {
             var exception = Assert.Throws<System.ArgumentException>(() =>
                 StructUnionConsumer.IsStructA("Not a StructA"));
             Assert.Equal("Expected argument struct to be one of: Amazon.JSII.Tests.CalculatorNamespace.IStructA, Amazon.JSII.Tests.CalculatorNamespace.IStructB; received System.String (Parameter 'struct')", exception.Message);
         }
+
+        [Fact(DisplayName = Prefix + nameof(AnonymousObjectIsValid))]
+        public void AnonymousObjectIsValid()
+        {
+            var anonymousObject = UseOptions.Provide("A");
+            Assert.IsType<AnonymousObject>(anonymousObject);
+            Assert.Equal("A", UseOptions.Consume(anonymousObject));
+        }
     }
-}
+}

packages/@jsii/dotnet-runtime/src/Amazon.JSII.Runtime/Deputy/AnonymousObject.cs

@@ -1,9 +1,9 @@
 namespace Amazon.JSII.Runtime.Deputy
 {
-    internal sealed class AnonymousObject : DeputyBase
+    public sealed class AnonymousObject : DeputyBase
     {
         internal AnonymousObject(ByRefValue byRefValue) : base(byRefValue)
         {
         }
     }
-}
+}

packages/@jsii/python-runtime/tests/test_runtime_type_checking.py

@@ -119,3 +119,10 @@ def test_setter_to_union(self):
     def test_nested_struct(self):
         # None of these should throw...
         NestingClass.NestedStruct(name="Queen B")
+
+    def test_anonymous_object(self):
+        struct = jsii_calc.StructUnionConsumer.provide_struct("A")
+        assert jsii_calc.StructUnionConsumer.is_struct_a(struct)
+
+        iface = jsii_calc.anonymous.UseOptions.provide("A")
+        assert jsii_calc.anonymous.UseOptions.consume(iface) == "A"

packages/jsii-calc/lib/anonymous/index.ts

@@ -0,0 +1,47 @@
+export interface IOptionA {
+  doSomething(): string;
+}
+
+export interface IOptionB {
+  doSomethingElse(): string;
+}
+
+export class UseOptions {
+  public static provide(which: 'A' | 'B'): IOptionA | IOptionB {
+    switch (which) {
+      case 'A':
+        return new OptionA();
+      case 'B':
+        return new OptionB();
+      default:
+        throw new Error(`Unexpected option: ${which as any}`);
+    }
+  }
+
+  public static privideAsAny(which: 'A' | 'B'): any {
+    return this.provide(which);
+  }
+
+  public static consume(option: IOptionA | IOptionB): string {
+    if (option instanceof OptionA) {
+      return option.doSomething();
+    } else if (option instanceof OptionB) {
+      return option.doSomethingElse();
+    }
+    throw new Error(`Unexpected option: ${option as any}`);
+  }
+
+  private constructor() {}
+}
+
+class OptionA implements IOptionA {
+  public doSomething(): string {
+    return 'A';
+  }
+}
+
+class OptionB implements IOptionB {
+  public doSomethingElse(): string {
+    return 'B';
+  }
+}

packages/jsii-calc/lib/compliance.ts

@@ -2358,6 +2358,20 @@ export class StructUnionConsumer {
     }
   }
 
+  public static provideStruct(which: 'A' | 'B'): StructA | StructB {
+    switch (which) {
+      case 'A':
+        return { requiredString: 'required', optionalNumber: 1337 };
+      case 'B':
+        return {
+          requiredString: 'required',
+          optionalStructA: this.provideStruct('A'),
+        };
+      default:
+        throw new Error(`Illegal value for which: ${which as any}`);
+    }
+  }
+
   private constructor() {}
 }
 

packages/jsii-calc/lib/index.ts

@@ -23,3 +23,5 @@ export * as module2700 from './module2700';
 
 export * as cdk16625 from './cdk16625';
 export * as jsii3656 from './jsii3656';
+
+export * as anonymous from './anonymous';