terraform code to get all GCP shared-vpc service-projects attached to a particular host-project

main.tf

# instructions:
# on the first run you to target apply otherwise terraform will complain with for_each
# 1. terraform apply -target='null_resource.projects'
# 2. terraform apply

terraform {
  required_providers {
    google = {
      source = "hashicorp/google"
    }
  }
}

variable "host_project_id" {
  type    = string
}

variable "projects_json_file" {
  type    = string
  default = "./projects.json"
}

resource "null_resource" "projects" {
  provisioner "local-exec" {
    command = "gcloud compute shared-vpc list-associated-resources ${var.host_project_id} --format='json' > ${var.projects_json_file}"
  }
}

data "local_file" "projects_json" {
  filename = var.projects_json_file
}

data "google_project" "service" {
  for_each   = toset([for k in jsondecode(data.local_file.projects_json.content) : k.id])
  project_id = each.key
}

output "service_projects" {
  value = { for k, v in data.google_project.service : k => v.number }
}