Terraform 1.6.0 broke custom Terraform provider using protocol 6

[spkane]

Terraform Version

Terraform v1.6.0
on darwin_arm64
+ provider registry.terraform.io/spkane/todo v2.0.4

Terraform Configuration Files

terraform {
  required_providers {
    todo = {
      source  = "spkane/todo"
      version = "2.0.4"
    }
  }
}

provider "todo" {
  host = "127.0.0.1"
  port = "8080"
  apipath = "/"
  schema = "http"
}

data "todo_todo" "foreign" {
  id = 1
}

resource "todo_todo" "test1" {
  count = 5
  description = "${count.index}-1 ${var.purpose} todo"
  completed = false
}

resource "todo_todo" "test2" {
  count = 5
  description = "${count.index}-2 ${var.purpose} todo (linked to ${data.todo_todo.foreign.description})"
  completed = false
}

output "todo_1_ids" {
  value = todo_todo.test1.*.id
}

output "todo_2_ids" {
  value = todo_todo.test2.*.id
}

variable "purpose" {
    type = string
    description = "Tag the purpose of this todo"
    default = "test"
}

Debug Output

https://gist.github.com/spkane/61273fc4b7bc130d03df7bf1af5c4982

Expected Behavior

The provider spkane/todo v2.0.4 works fine with Terraform 1.5.7. I would expect it to continue to work with Terraform 1.6.0.

• Provider
• Source Code
• API Server

Actual Behavior

$ terraform plan
╷
│ Warning: Provider development overrides are in effect
│
│ The following provider development overrides are set in the CLI configuration:
│  - spkane/todo in /Users/spkane/dev/spkane/terraform-provider-todo
│
│ The behavior may therefore not match any released version of the provider and applying changes may cause the state to become incompatible with published
│ releases.
╵
╷
│ Error: Data Source Type Not Found
│
│   with data.todo_todo.foreign,
│   on main.tf line 17, in data "todo_todo" "foreign":
│   17: data "todo_todo" "foreign" {
│
│ No data source type named "todo_todo" was found in the provider.
╵
╷
│ Error: Resource Type Not Found
│
│   with todo_todo.test1,
│   on main.tf line 21, in resource "todo_todo" "test1":
│   21: resource "todo_todo" "test1" {
│
│ No resource type named "todo_todo" was found in the provider.
╵

From what I can tell this might be due to 1.6.0 no longer asking for the provider schema and the related changes. #33486

I think that I might need to set get_provider_schema_optional via ServerCapabilities, but honestly I wasn't sure how to go about that, or if there was some other issue that was leading to this.

Any pointers would be appreciated if the issue is in the provider.

I could not find any documentation besides the code, on using ServerCapabilities properly.

Steps to Reproduce

1. docker compose up -d # spin up the API server locally.
2. terraform init
3. terraform apply

Additional Context

Not really. The same results occur using provider version 2.0.4 on the registry or using a local dev copy (which I was using when I wrote up this issue).

I also was using a local copy of the simple API, running in a container, to test things.

References

#33486

[jbardin]

Duplicate of #33990

[spkane]

see: hashicorp/terraform-plugin-framework#853

[github-actions]

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