Support deleting Firestore databases

Due to backwards compatibility concerns, the default behavior remains to
abandon the database upon destroy rather than to actually delete it.

To actually delete the database, you must set deletion_policy to DELETE,
and apply if necessary, before running `terraform destroy`.

This also cleans up some related deletion-related docs and bugs:

* Updates the delete protection docs
* Either delete protection or deletion policy being set prevents destroy

Fixes hashicorp/terraform-provider-google#16488
Fixes hashicorp/terraform-provider-google#16404
Fixes hashicorp/terraform-provider-google#16325

mmv1/products/firestore/Database.yaml

@@ -47,7 +47,6 @@ async: !ruby/object:Api::OpAsync
   error: !ruby/object:Api::OpAsync::Error
     path: 'error'
     message: 'message'
-skip_delete: true
 autogen_async: true
 id_format: 'projects/{{project}}/databases/{{name}}'
 import_format:
@@ -105,6 +104,32 @@ examples:
     test_env_vars:
       project_id: :PROJECT_NAME
     skip_test: true
+  - !ruby/object:Provider::Terraform::Examples
+    name: 'firestore_database_with_deletion_policy'
+    primary_resource_id: 'database'
+    pull_external: true
+    vars:
+      name: "example-database-id"
+    test_env_vars:
+      project_id: :PROJECT_NAME
+    ignore_read_extra:
+      - project
+      - etag
+virtual_fields:
+  - !ruby/object:Api::Type::Enum
+    name: 'deletion_policy'
+    description: |
+      Deletion behavior for this database.
+      If the deletion policy is ABANDON, the database will be removed from Terraform state but not deleted from Google Cloud upon destruction.
+      If the deletion policy is DELETE, the database will both be removed from Terraform state and deleted from Google Cloud upon destruction.
+      The default value is ABANDON.
+      See also delete_protection.
+    values:
+      - :DELETE
+      - :ABANDON
+    default_value: :ABANDON
+custom_code: !ruby/object:Provider::Terraform::CustomCode
+  pre_delete: templates/terraform/pre_delete/firestore_database.go.erb
 properties:
   - !ruby/object:Api::Type::String
     name: name
@@ -177,8 +202,10 @@ properties:
     name: deleteProtectionState
     description: |
       State of delete protection for the database.
+      When delete protection is enabled, this database cannot be deleted.
+      The default value is DELETE_PROTECTION_DISABLED.
+      Note: Additionally, to delete this database using `terraform destroy`, deletion_policy must be set to DELETE.
     values:
-      - :DELETE_PROTECTION_STATE_UNSPECIFIED
       - :DELETE_PROTECTION_ENABLED
       - :DELETE_PROTECTION_DISABLED
     default_from_api: true

mmv1/templates/terraform/examples/firestore_database_with_deletion_policy.tf.erb

@@ -0,0 +1,10 @@
+resource "google_firestore_database" "<%= ctx[:primary_resource_id] %>" {
+  project     = "<%= ctx[:test_env_vars]['project_id'] %>"
+  name        = "<%= ctx[:vars]['name']%>"
+  location_id = "nam5"
+  type        = "FIRESTORE_NATIVE"
+
+  # Required to allow deleting the database with Terraform
+  # Also ensure that delete_protection_state is set to DELETE_PROTECTION_DISABLED (the default)
+  deletion_policy = "DELETE"
+}

mmv1/templates/terraform/pre_delete/firestore_database.go.erb

@@ -0,0 +1,7 @@
+if deletionPolicy := d.Get("deletion_policy"); deletionPolicy == "ABANDON" {
+    log.Printf("[WARN] Firestore database %q deletion_policy is set to 'ABANDON', skipping deletion", d.Get("name").(string))
+    return nil
+}
+if d.Get("deletion_protection").(bool) {
+    return fmt.Errorf("Cannot delete Firestore database %s:  Delete Protection is enabled. Set delete_protection_state to DELETE_PROTECTION_DISABLED for this resource and run \"terraform apply\" before attempting to delete it.", d.Get("name").(string))
+}