Native Terraform/OpenTofu function templatestring() does not work in Terragrunt as a builtin function.

[Jpk518]

Describe the bug

A new function templatestring() was added in Terraform 1.9 and Opentofu 1.7. This New function does not work when attempting to use in terragrunt as a built-in function https://terragrunt.gruntwork.io/docs/reference/built-in-functions/#terraform-built-in-functions, both when using the Terraform binary and the OpenTofu binary.

Steps To Reproduce

Define locals block that uses function templatestring().

example/terragrunt.hcl:

locals {
  template = "$${stage}-test"
  name = templatestring(local.template, { stage = "staging" } )
}

inputs = {
  name = local.name
}

example/main.tf:

variable "name" {}

resource "aws_sqs_queue" "example" {
  name  = var.name
}

Expected behavior

Here is the expected behaviour

$ terragrunt init

OpenTofu has been successfully initialized!

Here is the actual behaviour

$ terragrunt init

ERRO[0000]   on /.../example/terragrunt.hcl line 7, in locals: 
ERRO[0000]    7:   name     = templatestring(local.template, { stage = "staging" }) 
ERRO[0000]                                              
ERRO[0000] with                                         
ERRO[0000] local.template as "${stage}-test"  

ERRO[0000] There is no function named "templatestring".

Versions

• Terragrunt version: v0.59.6
• OpenTofu Version: v1.7.2
• Terraform version: v1.9.2

Additional context

Function works properly when defined directly in .tf file using opentofu/terraform

example/main.tf:

locals {
  template = "$${stage}-test"
  name = templatestring(local.template, { stage = "staging" } )
}

resource "aws_sqs_queue" "test" {
  name = local.name
}

$ terragrunt init

OpenTofu has been successfully initialized!

[begemotik]

@levkohimins would be wonderful to get it supported in Terragrunt. Do you have an estimation?

[yhakbar]

Hey @begemotik , this is a good request, but not a priority right now.

Could you provide any reasons why this should be prioritized higher? I imagine most folks needing this functionality would simply use run_cmd right now.

[Jpk518]

Hey @begemotik , this is a good request, but not a priority right now.

Could you provide any reasons why this should be prioritized higher? I imagine most folks needing this functionality would simply use run_cmd right now.

Is it possible to update the documentation if going forward Terragrunt doesn't plan to support all built in Opentofu/Terraform functions. Can lead to a little confusion https://terragrunt.gruntwork.io/docs/reference/built-in-functions/#opentofuterraform-built-in-functions

[yhakbar]

Is it possible to update the documentation if going forward Terragrunt doesn't plan to support all built in Opentofu/Terraform functions.

Sure thing, I can update that.

To be clear, we're not refusing to support this, we're just trying to prioritize effectively. If there's a use-case that requires this behavior, we can look at prioritizing it.

[begemotik]

Could you provide any reasons why this should be prioritized higher? I imagine most folks needing this functionality would simply use run_cmd right now.

We manage multiple ASGs within one TF state and need to be able to re-use one config template for different cases.
There is another case I can imagine with "generate" block and dynamic providers rendering.

We haven't tried run_cmd, I might be mistaken but it occurs to be that run_cmd would be hard to re-use across many states as it references local file.

run_cmd(command, arg1, arg2…​) runs a shell command and returns the stdout as the result of the interpolation. The command is executed at the same folder as the terragrunt.hcl file