feat!: adds support for description as a templatestring (#43)

## what

- Updates `var.description` to be interpreted as a
[`templatestring`](https://opentofu.org/docs/language/functions/templatestring/).
- Adds `versions.tofu` because `templatestring` is introduced in v1.7 of
tofu and 1.9 of terraform. We now need to manage these pins separately.
  - https://opentofu.org/docs/language/files/#extension-precedence
- [Tofu 1.7 templatestring
introduction](https://opentofu.org/docs/v1.7/intro/whats-new/#built-in-function-changes).
- [Terraform 1.9 templatestring
introduction](https://github.com/hashicorp/terraform/blob/v1.9/CHANGELOG.md#190-june-26-2024)
- Adds tests to cover

## why

- Gives consumers full control over how their Stack descriptions look
across all Stacks created by this module.

## references

- N/A

Author: Gowiem

README.md

@@ -298,7 +298,6 @@ resource "spacelift_stack" "default" {
   before_perform                   = compact(coalesce(try(local.stack_configs[each.key].before_perform, []), var.before_perform))
   before_plan                      = compact(coalesce(try(local.stack_configs[each.key].before_plan, []), var.before_plan))
   branch                           = try(local.stack_configs[each.key].branch, var.branch)
-  description                      = coalesce(try(local.stack_configs[each.key].description, null), var.description)
   enable_local_preview             = try(local.stack_configs[each.key].enable_local_preview, var.enable_local_preview)
   enable_well_known_secret_masking = try(local.stack_configs[each.key].enable_well_known_secret_masking, var.enable_well_known_secret_masking)
   github_action_deploy             = try(local.stack_configs[each.key].github_action_deploy, var.github_action_deploy)
@@ -316,6 +315,13 @@ resource "spacelift_stack" "default" {
   terraform_workspace              = local.configs[each.key].terraform_workspace
   worker_pool_id                   = try(local.stack_configs[each.key].worker_pool_id, var.worker_pool_id)
 
+  # Usage of `templatestring` requires OpenTofu 1.7 and Terraform 1.9 or later.
+  description = coalesce(
+    try(local.stack_configs[each.key].description, null),
+    try(templatestring(var.description, local.configs[each.key]), null),
+    "Managed by spacelift-automation Terraform root module."
+  )
+
   dynamic "github_enterprise" {
     for_each = var.github_enterprise != null ? [var.github_enterprise] : []
     content {

main.tf

@@ -1,6 +1,7 @@
 kind: StackConfigV1
 stack_settings:
   administrative: true
+  description: This is a test of the emergency broadcast system
   before_init:
     - echo 'World'
   labels:

tests/fixtures/multi-instance/root-module-a/stacks/default-example.yaml

@@ -1,4 +1,5 @@
 kind: StackConfigV1
 stack_settings:
+  space_id: 123
   labels:
     - test_label

tests/fixtures/multi-instance/root-module-a/stacks/test.yaml

@@ -55,6 +55,16 @@ run "test_stacks_include_expected" {
   }
 }
 
+# Test that the stack resource is created with the correct name
+run "test_stack_resource_is_created_with_correct_name" {
+  command = plan
+
+  assert {
+    condition = spacelift_stack.default["root-module-a-test"].name == "root-module-a-test"
+    error_message = "Stack resource was not created correctly: ${jsonencode(spacelift_stack.default)}"
+  }
+}
+
 # Test that the folder labels get created with correct format
 run "test_folder_labels_are_correct_format" {
   command = plan
@@ -144,3 +154,35 @@ run "test_before_init_includes_the_default_before_init_and_stack_before_init" {
     error_message = "Before_init was not created correctly: ${jsonencode(local.before_init)}"
   }
 }
+
+# Test that the description is created correctly
+run "test_description_is_created_correctly" {
+  command = plan
+
+  assert {
+    condition = spacelift_stack.default["root-module-a-test"].description == "Root Module: root-module-a\nProject Root: ./tests/fixtures/multi-instance/root-module-a\nWorkspace: test\nManaged by spacelift-automation Terraform root module."
+    error_message = "Description was not created correctly: ${jsonencode(local.configs)}"
+  }
+}
+
+# Test that the description is created correctly when non-default template string is used
+run "test_description_is_created_correctly_when_non_default_template_string_is_used" {
+  command = plan
+  variables {
+    description = "Space ID: $${stack_settings.space_id}"
+  }
+
+  assert {
+    condition = spacelift_stack.default["root-module-a-test"].description == "Space ID: 123"
+    error_message = "Description was not created correctly: ${jsonencode(local.configs)}"
+  }
+}
+
+run "test_description_is_created_correctly_when_passed_from_stack_config" {
+  command = plan
+
+  assert {
+    condition = spacelift_stack.default["root-module-a-default-example"].description == "This is a test of the emergency broadcast system"
+    error_message = "Description was not created correctly: ${jsonencode(local.configs)}"
+  }
+}

tests/main.tftest.hcl

@@ -207,8 +207,12 @@ variable "default_tf_workspace_enabled" {
 
 variable "description" {
   type        = string
-  description = "Description of the stack"
-  default     = "Managed by spacelift-automation Terraform root module."
+  description = <<EOT
+    A description for the created Stacks. This is a template string that will be rendered with the final config object for the stack.
+    See the main.tf for full internals of that object and the documentation on templatestring for usage.
+    https://opentofu.org/docs/language/functions/templatestring/
+  EOT
+  default     = "Root Module: $${root_module}\nProject Root: $${project_root}\nWorkspace: $${terraform_workspace}\nManaged by spacelift-automation Terraform root module."
 }
 
 variable "destructor_enabled" {

variables.tf

@@ -1,5 +1,5 @@
 terraform {
-  required_version = ">= 1.6"
+  required_version = ">= 1.9"
 
   required_providers {
     spacelift = {

versions.tf

@@ -0,0 +1,10 @@
+terraform {
+  required_version = ">= 1.7"
+
+  required_providers {
+    spacelift = {
+      source  = "spacelift-io/spacelift"
+      version = ">= 1.14"
+    }
+  }
+}