terraform show doesn't properly output child_modules in certain circumstances - with ready fix

[cube2222]

Hey, I'll try to keep it short.

Let's say you have 3 modules, in the examples that's the root module, the resourceless module, and the lost module.
The resourceless module is a child of the root module.
The lost module is a child of the resourceless module.

The caveat though is that the resourceless module doesn't create any resources itself, it only creates the lost module.

This will break the recurrence in jsonstate/state.go and will never print the contents of the resourceless and lost modules.

I have a simple fix ready, including a regression test, so will create a PR shortly.

Terraform Version

All 0.14.x versions and head of master, the problematic code hasn't been touched for a while though, so it should be reproducible in earlier versions too.

Terraform Configuration Files

# main.tf
module "resourceless-module" {
  source = "./resourceless"
}

# resourceless/main.tf
module "lost-module" {
  source = "./lost"
}

# resourceless/lost/main.tf
resource random_id "lost-id" {
  byte_length = 16
}

Expected Behavior

Running terraform show -json should properly print all the modules in a child_modules hierarchy. Like this (this is the output with my fix):

{
  "format_version": "0.1",
  "terraform_version": "0.15.0",
  "values": {
    "root_module": {
      "child_modules": [
        {
          "address": "module.resourceless-module",
          "child_modules": [
            {
              "address": "module.resourceless-module.module.lost-module",
              "resources": [
                {
                  "address": "module.resourceless-module.module.lost-module.random_id.lost-id",
                  "mode": "managed",
                  "name": "lost-id",
                  "provider_name": "registry.terraform.io/hashicorp/random",
                  "schema_version": 0,
                  "type": "random_id",
                  "values": {
                    "b64_std": "DI0iBocGJYcaeDpQrDYnlg==",
                    "b64_url": "DI0iBocGJYcaeDpQrDYnlg",
                    "byte_length": 16,
                    "dec": "16683539925555807513425851214500079510",
                    "hex": "0c8d2206870625871a783a50ac362796",
                    "id": "DI0iBocGJYcaeDpQrDYnlg",
                    "keepers": null,
                    "prefix": null
                  }
                }
              ]
            }
          ]
        }
      ]
    }
  }
}

Actual Behavior

{"format_version":"0.1","terraform_version":"0.15.0","values":{"root_module":{}}}

Steps to Reproduce

Just apply the above terraform files and run terraform show -json

[danieldreier]

@cube2222 thank you for the report and clear reproduction case! I've reproduced this on 0.14.2 and 0.13.5. Most of the team of off for the holidays, and this looks real but non-urgent to me, so be aware that it probably won't get much more attention until January. Please let me know if I've misunderstood the issue and and it's causing an urgent incident for you.

[cube2222]

Hey, since the Christmas holiday season is over I suppose, could you please take a look at this?
Here's the Pull Request aiming to fix this: #27352

[cube2222]

PR merged, thanks!

[ghost]

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