Using variables for a charm resource results in a Value Conversion Error

[wyattrees]

Description

When trying to use a variable for a charm resource as below, a Value Conversion Error is thrown.

Resource definition:

resource juju_application "temporal_worker" {
  name = "temporal-worker-k8s"
  for_each = juju_model.temporal_worker
  model = each.value.name
  units = 1
  charm {
    name = "temporal-worker-k8s"
    channel = var.temporal_worker_channel
    revision = var.temporal_worker_revision
  }
  resources = {
    temporal-worker-image = var.temporal_worker_resource
  }
}

Variable definition:

variable temporal_worker_resource {
  description = "OCI Image resource for temporal worker"
  type        = string
  default     = "ghcr.io/canonical/msm-temporal-worker:1.0"
}

Error thrown:

╷
│ Error: Value Conversion Error
│ 
│   with juju_application.temporal_worker,
│   on main.tf line 319, in resource "juju_application" "temporal_worker":
│  319: resource juju_application "temporal_worker" {
│ 
│ An unexpected error was encountered trying to build a value. This is always an error in the provider. Please report the following to
│ the provider developer:
│ 
│ Received unknown value, however the target type cannot handle unknown values. Use the corresponding `types` package type or a custom
│ type that handles unknown values.
│ 
│ Path: ["temporal-worker-image"]
│ Target Type: string
│ Suggested Type: basetypes.StringValue

Workaround

Defining the variable as a map will remove the error:

variable temporal_worker_resources {
  description = "OCI Image resource version for temporal worker"
  type        = map
  default     = {temporal-worker-resource:"ghcr.io/canonical/msm-temporal-worker:1.0"}
}

resources = var.temporal_worker_resources

Urgency

Casually reporting

Terraform Juju Provider version

0.21.0

Terraform version

1.12.2

Juju version

3.6.8

Terraform Configuration(s)

#variables.tf
variable temporal_worker_resource {
  description = "OCI Image resource for temporal worker"
  type        = string
  default     = "ghcr.io/canonical/msm-temporal-worker:1.0"
}


#main.tf
terraform {
  required_providers {
    juju = {
      version = "~> 0.21.0"
      source  = "juju/juju"
    }
  }
}

resource "juju_model" "temporal_worker" {
  name = "temporal-worker"
  cloud {
    name = "microk8s"
  }
}


resource juju_application "temporal_worker" {
  name = "temporal-worker-k8s"
  model = juju_model.temporal_worker.name
  units = 1
  charm {
    name = "temporal-worker-k8s"
    channel = "latest/stable"
  }
  resources = {
    temporal-worker-image = var.temporal_worker_resource
  }
}

Reproduce / Test

terraform init
terraform validate

Debug/Panic Output

╷
│ Error: Value Conversion Error
│ 
│   with juju_application.temporal_worker,
│   on main.tf line 319, in resource "juju_application" "temporal_worker":
│  319: resource juju_application "temporal_worker" {
│ 
│ An unexpected error was encountered trying to build a value. This is always an error in the provider. Please report the following to
│ the provider developer:
│ 
│ Received unknown value, however the target type cannot handle unknown values. Use the corresponding `types` package type or a custom
│ type that handles unknown values.
│ 
│ Path: ["temporal-worker-image"]
│ Target Type: string
│ Suggested Type: basetypes.StringValue

Notes & References

No response

[skatsaounis]

@SimoneDutto this is similar to that: #534. I guess the fix is likewise trivial