core: Do not create "delete" changes for nonexistent outputs

[kmoe]

If there are outputs in configuration, a destroy plan will always contain a "delete" change for each of these outputs.

If an output was not present in state to begin with, the change will look like this:

 "output_changes": {
    "foo": {
      "actions": [
        "delete"
      ],
      "before": null,
      "after": null,
      "after_unknown": false,
      "before_sensitive": false,
      "after_sensitive": false
    }
  },

Since there is a change in the plan, this plan will be considered applyable, and the user will be presented with text instructing them to apply a plan in which there are no actual changes.

Applying the destroy plan will not actually do anything, since the output was not in state to begin with.

This commit stops the above from happening in the case of root module outputs.

A simple example follows. For a more realistic example and the issue that motivated this change, please see #23387 (comment).

Example

Configuration

output "foo" {
  value = null
}

Steps

1. terraform init
2. terraform plan -detailed-exitcode -destroy

Result prior to change

Exit code 2.

Changes to Outputs:

You can apply this plan to save these new output values to the
Terraform state, without changing any real infrastructure.

───────────────────────────────────────────────────────────────────

Plan prior to change

{
  "format_version": "1.1",
  "terraform_version": "1.3.0-dev",
  "planned_values": {
    "root_module": {}
  },
  "output_changes": {
    "foo": {
      "actions": [
        "delete"
      ],
      "before": null,
      "after": null,
      "after_unknown": false,
      "before_sensitive": false,
      "after_sensitive": false
    }
  },
  "configuration": {
    "root_module": {
      "outputs": {
        "foo": {
          "expression": {
            "constant_value": null
          }
        }
      }
    }
  }
}

Result after change

Exit code 0.

No changes. No objects need to be destroyed.

Either you have not created any objects yet or the existing objects were already deleted outside of Terraform.

Plan after change

{
  "format_version": "1.1",
  "terraform_version": "1.3.0-dev",
  "planned_values": {
    "root_module": {}
  },
  "configuration": {
    "root_module": {
      "outputs": {
        "foo": {
          "expression": {
            "constant_value": null
          }
        }
      }
    }
  }
}

[jbardin]

LGTM! These were never in there for any particular reason. Since outputs are always re-calculated during a plan, they were always added to the changes regardless of what that change was.

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

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