[aws-stepfunctions] recurseObject skips repeated object references even when they're not causing a cycle

[marciocarmona]

While writing a StepFunction (LambdaInvoke) I noticed part of my input was just missing from the StateMachine step definition.

Reproduction Steps

For example, if I do this:

        let x = {
            foo: "Hello world"
        }
        let input = {
            value1: x,
            value2: x
        }
        console.log(FieldUtils.renderObject(input))

I get this output:

{ value1: { foo: 'Hello world' }, value2: {} }

What did you expect to happen?

It should have returned:

{ value1: { foo: 'Hello world' }, value2: { foo: 'Hello world' } }

What actually happened?

It returned:

{ value1: { foo: 'Hello world' }, value2: {} }

Environment

• CDK CLI Version : 1.98.0 (build 79f4512)
• Framework Version: ?
• Node.js Version: v12.22.1
• OS : Linux Red Hat 7.2.1-2
• Language (Version): TypeScript (4.0.5)

Other

After doing some investigation I found that the issue happens in the FieldUtils.renderObject call, more specifically when it calls the recurseObject function.

The problem seems to happen because the recurseObject pushes all nodes to a visited list as it traverses them to avoid any cycles, however, it doesn't pop them afterwards, so repeated objects are skipped even if they're not in the same subtree, i.e. there's no circular reference.

Code reference:

aws-cdk/packages/@aws-cdk/aws-stepfunctions/lib/json-path.ts

Line 89 in 7966f8d

visited.push(obj);

As a fix the recurseObject should either pop the visited array before returning, or actually send a copy of the visited nodes in the recursive calls, like [...visited, obj].

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This is 🐛 Bug Report

[github-actions]

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