execute conditional logic and exit terraform execution - exception

conditional.tf

#
# Filename    : condition.tf
# Date        : 04 Mar 2022
# Author      : Balaji Venkataraman ([email protected])
# Description : terraform script to push updated modules to registry
#     
#     
# case 1:
#     $terraform plan
#     
#     No changes. Your infrastructure matches the configuration.
#     
#     Terraform has compared your real infrastructure against your configuration and found no differences, so no changes are needed.
#
# case 2:
#     $terraform plan -var 'kms=test'
#     
#     No changes. Your infrastructure matches the configuration.
#     
#     Terraform has compared your real infrastructure against your configuration and found no differences, so no changes are needed.
#
# case 3:
#     $terraform plan -var 'env=test'
#     ╷
#     │ Error: External Program Execution Failed
#     │
#     │   with data.external.kmstest[0],
#     │   on condition.tf line 19, in data "external" "kmstest":
#     │   19:   program = ["sh", "-c", ">&2 echo kms has to be with valid env; exit 1"]
#     │
#     │ The data source received an unexpected error while attempting to execute the program.
#     │
#     │ Program: /usr/bin/sh
#     │ Error Message: kms has to be with valid env
#     │
#     │ State: exit status 1
#     ╵
#

variable "kms" {
  default = null
}

variable "env" {
  type = string
  default = null
}

data "external" "kmstest" {
  count = (var.kms == null && var.env != null) ? 1 : 0
  program = ["sh", "-c", ">&2 echo kms has to be with valid env; exit 1"]
}