terraform_empty_list_equality rule does not cover non-trivial expressions

[sergei-ivanov]

Introduction

Thanks for adding this rule, but unfortunately it only picks up the most trivial cases.

For example, it picks up this:

resource "aws_security_group_rule" "outbound_proxy" {
  count =var.proxy_subnets != [] ? 1 : 0

but not this:

resource "aws_security_group_rule" "outbound_proxy" {
  count = var.enabled && var.proxy_subnets != [] ? 1 : 0

nor this:

templatefile("${path.module}/jenkins.yaml.tmpl", {
    JENKINS_INGRESS_ENABLED = var.jenkins_controller_alb_allow_list != []
})

I guess it needs to implement more complex recursion for parsing into expressions.

It may also need to check for comparison with empty maps, e.g. var.peering_connections != {}.

Expected Behavior

All cases of comparison to empty list (or map) are highlighted by the rule.

[bendrucker]

The first example would be worth attempting. Short term, the primary goal should be to support expressions commonly passed to attributes like count.

Recursive evaluation of complex attribute values is a deeper issue than this rule, e.g. see #1257. Providing a helper function that visits each value expression within collection types is its own exercise with potential for use in many rules.

[wata727]

Fixed by #1426