Need help with json.patch built-in

[cmorinupgrade]

Hi folks,

I am having a hard time getting the json.patch built-in to work with my rule.

Let's say I got this object:

required_approvals := {
    "approvals": [{
        "users": [],
        "files": [],
    }]
}

As part of a comprehension, I'd like to dynamically patch that object. For the sake of simplicity, I'm trying to go with a very simple example to get to a working solution. However, I did not have much success so far.

patch := {
    "users": [
        "user1",
        "user2",
    ],
    "files": [
        "file1",
        "file2",
     ],
}

then I'm trying with this:

required_approvals = json.patch(required_approvals, [{ "op": "add", "path": "/approvals/0", "value": patch } ])

However, when printing required_approvals after the patch, I got this, which suggests it's not working as I am thinking it should work:
{"approvals": [{"files": [], "users": []}]}

Looking at the output of json.patch, it seems to work. However, it does not seem to actually change the initial required_approvals object I defined, which is what I would like. I tried doing required_approvals = output, but nothing changes.

I do not get any error messages.

Am I missing something?

Thank you in advance for help.

[anderseknert]

Hi there! 👋 Variables in Rego are immutable, so you can't change the value of required_approvals. You can however assign the result of the patch operation to a new var. I'm surprised you did not see an error message about that. If you can share your policy in full, I'd be happy to take a look.

See example of working policy here: https://play.openpolicyagent.org/p/vQQQopNORc