Should attributes in ignore_changes list be ignored when comparing TF plans?

[b1az]

Hi. Thanks for everyone's work on this Action. Opening a discussion, as I'm not sure whether the following is an actual issue. Or if you'd also think that the expected behavior, proposed below, would be desired. Or maybe there's already an input that would solve this "issue". A "solution" might be to use auto_approve: true, of course.

Current behavior

When using terraform-apply action with a PR workflow, the action fails if there are differences between the PR plan and the current plan, even for attributes that are explicitly set to be ignored via Terraform's ignore_changes lifecycle rule.

For example, with the following Terraform configuration:

resource "aws_eks_node_group" "example" {
  # ... other configuration ...

  lifecycle {
    ignore_changes = [
      scaling_config[0].desired_size,
    ]
  }
}

If the desired_size changes between plans A) in the PR and B) at apply time (which is common with auto-scaling groups), the action fails with:

Not applying the plan - it has changed from the plan on the PR
The plan on the PR must be up to date. Alternatively, set the auto_approve input to 'true' to apply outdated plans
Performing diff between the pull request plan and the plan generated at execution time.
> are lines from the plan in the pull request
< are lines from the plan generated at execution
Plan differences:
...
< !~          desired_size = 6 -> 1
---
> !~          desired_size = 7 -> 1

Expected behavior?

The action should respect Terraform's ignore_changes settings when comparing plans. If the only differences between plans are attributes listed in ignore_changes, the action should proceed with the apply since Terraform itself would not act on these changes.