migrate to `schema.Block` for ordered nested attributes

[sudomateo]

Terraform providers generally use the schema.Block type for ordered nested attributes. Specifically, for ordered nested attributes that are an "array of structs" rather than an array of primitive types like strings, numbers, etc.

Moving to schema.Block allows the code to use typed structs for nested attributes and, more importantly, unlocks our ability to support dynamic blocks.

Here's what setting multiple network interfaces looks like today.

resource "oxide_instance" "example" {
  network_interfaces = [
    {
      subnet_id   = "692b78f6-57e7-4b25-9799-8468481ccb35"
      vpc_id      = "0e463e0e-6dd2-4442-991b-60dc457b421f"
      description = "Primary NIC."
      name        = "primary"
    },
    {
      subnet_id   = "692b78f6-57e7-4b25-9799-8468481ccb35"
      vpc_id      = "0e463e0e-6dd2-4442-991b-60dc457b421f"
      description = "Secondary NIC."
      name        = "secondary"
    },
  ]
}

Here's what it would look like using schema.Block.

resource "oxide_instance" "example" {
  network_interface {
      subnet_id   = "692b78f6-57e7-4b25-9799-8468481ccb35"
      vpc_id      = "0e463e0e-6dd2-4442-991b-60dc457b421f"
      description = "Primary NIC."
      name        = "primary"
  }

  network_interface {
      subnet_id   = "692b78f6-57e7-4b25-9799-8468481ccb35"
      vpc_id      = "0e463e0e-6dd2-4442-991b-60dc457b421f"
      description = "Secondary NIC."
      name        = "secondary"
  }
}

Here's what it would look like using schema.Block and dynamic blocks.

resource "oxide_instance" "example" {
  dynamic "network_interface" {
    for_each = toset(["primary", "secondary"])
    content {
      subnet_id   = "692b78f6-57e7-4b25-9799-8468481ccb35"
      vpc_id      = "0e463e0e-6dd2-4442-991b-60dc457b421f"
      description = "${network_interface.value} NIC."
      name        = network_interface.value
    }
  }
}

[sudomateo]

For some reason I thought schema.Block was the newer method of declaring nested attributes but I was mistaken. schema.*NestedAttribute is the proper way for protocol version 6 according to the HashiCorp documentation.

Use nested attribute types instead of block types for new schema implementations. Block support is mainly for migrating legacy SDK-based providers.