[JUJU-3863] Process region value in cloud models and force it to be computed

[juanmanuel-tirado]

Description

The region parameter in the cloud section from the resource_model should be computed by the provider when empty. In this manner, something like:

resource "juju_model" "terraform" {
  name = "terraform"
  cloud {
    name   = "localhost"
  }
}

will automatically set the region value to be localhost which is the default value returned by the Juju provider.

Fix #209

Type of change

Please mark if proceeds.

• New resource (a new resource in the schema)
• Changed resource (changes in an existing resource)
• Logic changes in resources (the API interaction with Juju has been changed)
• Test changes (one or several tests have been changed)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Other (describe)

Environment

• Juju controller version: 2.9.42
• Terraform version: 1.36

QA steps

Try to apply the plan described in #209 twice. No new values are detected now.

terraform {
  required_providers {
    juju = {
      version = "~> 0.7.0"
      source  = "juju/juju"
    }
  }
}


provider "juju" {}

resource "juju_model" "terraform" {
  name = "terraform"

  cloud {
    name   = "localhost"
  }
}

terraform init
terraform apply --auto-approve
Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the
following symbols:
  + create

Terraform will perform the following actions:

  # juju_model.terraform will be created
  + resource "juju_model" "terraform" {
      + credential = (known after apply)
      + id         = (known after apply)
      + name       = "terraform"
      + type       = (known after apply)

      + cloud {
          + name   = "localhost"
          + region = (known after apply)
        }
    }

Plan: 1 to add, 0 to change, 0 to destroy.
juju_model.terraform: Creating...
juju_model.terraform: Creation complete after 6s [id=77a75e5b-1236-48b5-8564-6c234f36767e]

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
terraform apply --auto-approve
juju_model.terraform: Refreshing state... [id=77a75e5b-1236-48b5-8564-6c234f36767e]

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration and found no differences, so no changes are
needed.

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

[cderici]

LGTM (modulo a possible fix required in code), QA went well 👍

[cderici]

Is this part of the code dead? cloud is set on d below only when the cloudChanged is true, and that happens only when either cloudNameInput == "" or cloudRegionInput == "".

[juanmanuel-tirado]

In this case cloud is obtained from cloud := d.Get("cloud").([]interface{}) and that is basically the value set by the user in the plan. Because it's defined as a list of maps, we have to do all that weird workaround.