go: unable to reuse instances between child/parent interfaces

[iliapolo]

🐛 Bug Report

When a TS child instance is first returned to the guest as a parent interface, the same instance cannot be returned as the child interface.

Affected Languages

• TypeScript or Javascript
• Python
• Java
• .NET (C#, F#, ...)
• Golang

General Information

• JSII Version: ALL
• Platform: ALL

What is the problem?

Consider the following TS code:

jsii/packages/jsii-calc/lib/compliance.ts

Lines 2214 to 2225 in 45b527c

	export class AnonymousImplementationProvider
	implements IAnonymousImplementationProvider {
	private readonly instance = new PrivateType();
	public provideAsClass(): Implementation {
	return this.instance;
	}
	public provideAsInterface(): IAnonymouslyImplementMe {
	return this.instance;
	}
	}

Where:

jsii/packages/jsii-calc/lib/compliance.ts

Line 2233 in 45b527c

class PrivateType extends Implementation implements IAnonymouslyImplementMe {

The following Golang code will work:

provider := calc.NewAnonymousImplementationProvider();
provider.ProvideAsClass(); // works - returning in instance of `Implementation`

But this subsequent invocation will fail:

provider.ProvideAsInterface(); // fails - trying to assign the same instance of `Implementation` to `IAnonymouslyImplementMe`

test panicked: reflect.Set: value of type *jsiicalc.jsiiProxy_Implementation is not assignable to type jsiicalc.IAnonymouslyImplementMe

Note that if the invocation order is reverse, it works. Because its now trying to assign a child to a parent, and not vise-versa.
Also, if the TS implementation returns a new instance on each Provide call, it will also work and since it won't reuse the previous instance.

Verbose Log

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