Terraform: Resource for_each not working with empty list

[adarobin]

Terraform Version

Terraform v0.12.6
+ provider.google v2.11.0
+ provider.null v2.1.2
+ provider.random v2.1.2

Terraform Configuration Files

variable "datalab_user_list" {
    type = list(string)
    default = []

}
resource "google_service_account" "datalab_service_account" {
    for_each = toset(var.datalab_user_list)
    account_id = "datalab-${split("@", each.key)[0]}"
    project = google_project.hipaa_project.project_id
}

Debug Output

Crash Output

Expected Behavior

Terraform plan and apply are successful and no resources are created

Actual Behavior

Error: Invalid for_each set argument

  on .terraform/modules/hipaa_worker_project1/datalab.tf line 23, in resource "google_service_account" "datalab_service_account":
  23:     for_each = toset(var.datalab_user_list)

The given "for_each" argument value is unsuitable: "for_each" supports maps
and sets of strings, but you have provided a set containing type dynamic.

Steps to Reproduce

Try to use an empty list with for_each on a resource.

Additional Context

As a workaround, this seems to work fine:

variable "datalab_user_list" {
    type = "map"
    default = {}

}
resource "google_service_account" "datalab_service_account" {
    for_each = var.datalab_user_list
    account_id = "datalab-${split("@", each.key)[0]}"
    project = google_project.hipaa_project.project_id
}

However, I don't really need a map and it makes what I pass in to the module a bit more confusing to read.

References

[adarobin]

I also tried:

variable "datalab_user_list" {
    type = list(string)
    default = [ "" ]
}
resource "google_service_account" "datalab_service_account" {
    for_each = toset(compact(var.datalab_user_list))
    account_id = "datalab-${split("@", each.key)[0]}"
    project = google_project.hipaa_project.project_id
}

But that still throws a similar error:

Error: Invalid for_each set argument

  on .terraform/modules/hipaa_worker_project1/datalab.tf line 24, in resource "google_service_account" "datalab_service_account":
  24:     for_each = toset(compact(var.datalab_user_list))

The given "for_each" argument value is unsuitable: "for_each" supports maps
and sets of strings, but you have provided a set containing type dynamic.

[apparentlymart]

Ahh, thanks for reporting this!

Indeed, this is a quirk caused by the fact that in toset([]) there are no elements to hint the function as to what the set element type should be, and so "dynamic" here really means "unknown".

For now I think the most reliable workaround would be to manually convert to a map instead of a set, which shouldn't run into the same problem because map keys are _always_ strings:

  for_each = { for v in var.datalab_user_list : v => v }

A conversion like the above is essentially what Terraform itself does when handling a set of strings, but it checks the set element type first to produce that "Invalid for_each set element" error.

[supergibbs]

This threw me off here too here https://github.com/hashicorp/terraform/issues/22622

I use a resource with count and then for_each those on another resource. If count is 0 it fails.

I think the fix could be for_each checks the length first and aborts when 0. If there are items, then check that they are strings.

[hashibot[bot]]

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