Compute instance missing external IPv6 address output attribute

[espes]

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Terraform Version

Terraform v1.2.3
on darwin_arm64
+ provider registry.terraform.io/hashicorp/google v4.25.0

Affected Resource(s)

• google_compute_instance

Terraform Configuration Files

provider "google" {
  region  = "europe-west2"
}

resource "google_compute_network" "network" {
  name = "demo-net"
  auto_create_subnetworks = false
}

resource "google_compute_subnetwork" "subnet" {
  name = "demo-subnet"
  network = google_compute_network.network.id
  ip_cidr_range = "10.1.0.0/20"
  stack_type = "IPV4_IPV6"
  ipv6_access_type = "EXTERNAL"
}

resource "google_compute_instance" "instance" {
  name         = "server"
  machine_type = "f1-micro"
  zone         = "europe-west2-a"

  boot_disk {
    initialize_params {
      image = "debian-cloud/debian-9"
    }
  }

  network_interface {
    network = google_compute_network.network.id
    subnetwork = google_compute_subnetwork.subnet.id
    access_config {
      network_tier = "PREMIUM"
    }
    stack_type = "IPV4_IPV6"
    ipv6_access_config {
      network_tier = "PREMIUM"
    }
  }
}

Debug Output

https://gist.github.com/espes/71be84b987f04421398c968c1459434a

Expected Behavior

The network_interface.0.ipv6_access_config.0.external_ipv6 property is populated with the IPv6 address of the instance

Actual Behavior

external_ipv6 is not populated. Notably, the ipv6 address is visible in networkInterfaces.ipv6AccessConfigs when running gcloud compute instances describe server, and in the API output in the debug log

Steps to Reproduce

1. terraform apply
2. terraform state show google_compute_instance.instance
3. Observe the ipv6_access_config block does not contain the external_ipv6 field

I'm not an expert on provider internals, but comparing the flattenIpv6AccessConfigs method to the equivalent flattenAccessConfigs method seems suspect: https://github.com/hashicorp/terraform-provider-google/blob/main/google/compute_instance_helpers.go#L171

[github-actions]

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