Interpolation issue for multi-dimensonal/nested lists

[vancluever]

Possibly HIL/HCL related, might be known, couldn't find an issue in my <5min sanity check. Logging to track.

EDIT: Related: #8047

The Variable

variable "public_subnet_addresses" {
  type = "map"

  default = {
    production = ["10.0.0.0/25", "10.0.0.128/25"]
    staging    = ["10.0.1.0/25", "10.0.1.128/25"]
  }
}

Good

output "element_from_list_from_map_func" {
  value = "${element(var.public_subnet_addresses["production"], 0)}"
}               

Gives:

element_from_list_from_map_func = 10.0.0.0/25

Bad

output "element_from_list_from_map" {
  value = "${var.public_subnet_addresses["production"][0]}"
}

Gives:

Error loading config: Error loading variables.tf: Error reading config for output element_from_list_from_map: parse error at 1:48: expected "}" but found "["

[apparentlymart]

Hi @vancluever,

You're right that this is a HIL issue rather than directly a Terraform issue, and indeed I've been working on it over in hashicorp/hil#42 though I stalled a bit over the holidays.

I don't remember there being a Terraform issue about this yet, so I'm going to leave this here to represent the need to update the vendored HIL and make the required changes to Terraform's interpolation functions once that issue is resolved.

[jlsjonas]

The same issue (but, as far as I could see, no workaround) occurs when trying to do the invers (having a map inside a list)

example:

locals {
  test = [{
    a = "a1"
    b = "b1"
  },{
    a= "a2"
    b = "b2"
  }]
}

There's no way to actually get the vars, only the entire object

(one of my attempts, errors out)

//output "test" {
//  value = "${element(local.test[0], "timeSpan")}"
//}
``

[sadpirit]

locals { test = [{ a = "a1" b = "b1" },{ a= "a2" b = "b2" }] }

Try:
${lookup(local.test[0], "a")}

[joariasl]

For nested maps, for example, for configure it based on the Terraform workspace, you can use:

variable "nested_map_name" {
  default = {
    default    = {
      value1 = 10
      value2 = false
    }
    staging    = {
      value1 = 20
      value2 = false
    }
    production = {
      value1 = 50
      value2 = true
    }
  }
}

resource "resource_where_use_nested_map" "resource_name" {
  resouce_param1 = "${lookup(var.nested_map_name[terraform.workspace], "value1")}"
  resouce_param2 = "${lookup(var.nested_map_name[terraform.workspace], "value2")}"
}

(Remember that you don't have to add interpolation on Terraform variables)

[apparentlymart]

I've just tried a variant of the original non-working example on Terraform v0.12.0-alpha1:

variable "public_subnet_addresses" {
  type = "map"

  default = {
    production = ["10.0.0.0/25", "10.0.0.128/25"]
    staging    = ["10.0.1.0/25", "10.0.1.128/25"]
  }
}

output "element_from_list_from_map" {
  value = var.public_subnet_addresses["production"][0]
}

And now it works as expected!

$ terraform apply

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

element_from_list_from_map = 10.0.0.0/25

In the end this has been resolved not by a change in HIL but by moving Terraform over to HCL 2.0, which incorporates HIL-like expression functionality but has full support for chaining attribute and index syntax after any expression.

Thanks for reporting this!

[ozbillwang]

this blog is helpful, it gives full solution with real example you can reference.

https://salekseev.com/posts/nested-maps-in-terraform-variables/

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.