[Java] Re-rendering a stack template after a modification returns the same result

[osdrv]

Hey all,

I'm trying to make some sense out of the assertions.Template behavior I'm observing. What I'm trying to do is to build a headless Java application that is supposed to render a stack YAML template, do some modifications to the stack and then re-render it again. The second YAML render turns out to be completely identical to the first one, even though the changes seems to be applied to the stack successfully.

I'm using Java lib software.amazon.awscdk.aws-cdk-lib of version 2.65.0.

Here is a sample of the app I'm running:

import software.amazon.awscdk.assertions.Template;
...
public class Main {

    final private static StackProps NO_BOOTSTRAP_RULE = StackProps.builder()
            .synthesizer(
                    DefaultStackSynthesizer.Builder.create().generateBootstrapVersionRule(false).build()
            ).build();

    final private static ObjectMapper mapper = new ObjectMapper(new YAMLFactory());

    public static void main(String[] args) throws IOException {
        App app = new App();
        TestStack stack = new TestStack(app, "test-stack", NO_BOOTSTRAP_RULE);

        stack.addMetadata("version", 1);
        System.out.println(renderTemplate(Template.fromStack(stack)));

        stack.addMetadata("version", 2);
        System.out.println(renderTemplate(Template.fromStack(stack)));
    }

    private static String renderTemplate(final Template template) throws IOException {
        final ByteArrayOutputStream buf = new ByteArrayOutputStream();
        mapper.writeValue(buf, template.toJSON());
        return buf.toString();
    }

    static class TestStack extends Stack {
        public TestStack(Construct scope, String id, StackProps props) {
            super(scope, id, props);
            Bucket.Builder.create(this, "S3Bucket")
                    .bucketName("test-bucket")
                    .build();
        }
    }
}

This program would output 2 identical YAML renders:

---
Metadata:
  version: 1
Resources:
  S3Bucket07682993:
    Type: "AWS::S3::Bucket"
    Properties:
      BucketName: "test-bucket"
    UpdateReplacePolicy: "Retain"
    DeletionPolicy: "Retain"

My expectation is that the second render should contain version: 2. I narrowed it down to the invocation of Kernel in Template.java class:

software.amazon.jsii.Kernel.call(this, "toJSON", ...)

The Kernel seems to be returning identical JSONs for an alternated stack if it was already traversed and resolved before the modification.

Hence my question: is the expectation to get 2 distinct renders fair? If so, is there a way to instruct the Kernel to flush whatever has been resolved for this stack and return a new render?