Merge a variable List of Maps in Terraform 0.12

terraform.tf

# This gist mimics the supposed behavior of
# variable = merge(someListOfMaps[*].parameters...)
# or
# policy_parameters = merge(data.azurerm_policy_definition.d_policy_definitions[*].parameters...)

locals {
  policy_parameters = [
    for key,value in data.azurerm_policy_definition.d_policy_definitions:
      {
        parameters = jsondecode(value.parameters)
      }
  ]
  ph_parameters = local.policy_parameters[*].parameters
  input_parameter = [for item in local.ph_parameters: merge(item,local.ph_parameters...)]
  
  usage = local.input_parameter[0]
}