0.12 "dynamic" blocs fail with empty iterator

[ghost]

Terraform Version

Terraform v0.12.0-rc1

Terraform Configuration Files

This is based on the dynamic block example from the 0.12 documentation:

variable "service_ports" {
  type = list(number)
  default = []
}

resource "aws_security_group" "example" {
  name = "example"

  dynamic "ingress" {
    for_each = var.service_ports
    content {
      from_port = ingress.value
      to_port   = ingress.value
      protocol  = "tcp"
    }
  }
}

Actual Behavior

If var.service_ports is an empty list, Terraform fail and return the following error:

Error: Unsupported block type

  on aws.tf line 9, in resource "aws_security_group" "example":
   9:   dynamic "ingress" {

Blocks of type "ingress" are not expected here.

Expected Behavior

If var.service_ports is an empty list, Terraform should not generate any ingress block in the security group and continue successfully instead of failing.

Steps to Reproduce

1. terraform init
2. terraform apply (This will use the default empty list for var.service_ports).

[jbardin]

Hi @xlz-jgoutin,

Thanks filing the issue! Sorry, I initially misunderstood the issue, that syntax does work in this case, but you are correct that does fail only with the empty collection.

[hasheddan]

@jbardin @xlz-jgoutin I am interested in helping out here! Is this a change that we definitely want to make, or is it potentially a feature to fail on an empty collection?

[ghost]

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