variable validation fails on optional variables

[ChristianRaoulis]

Terraform Version

Terraform v1.6.2
on windows_amd64
+ provider registry.terraform.io/hashicorp/helm v2.11.0
+ provider registry.terraform.io/hashicorp/kubernetes v2.23.0

Terraform Configuration Files

variable "example" {
  type = object({
    test = optional(object({
      val = string
    }))
  })

  validation {
    condition     = var.example.test == null || length(var.example.test.val) > 0
    error_message = "Invalid"
  }
}

example = {}

Debug Output

terraform plan error: This value is null, so it does not have any attributes.

Expected Behavior

The null check of the optional attribute should end the validation successfully

Actual Behavior

It causes an NPE in length(var.example.test.val) > 0 since var.example.test is null

Steps to Reproduce

1. terraform plan

Additional Context

No response

References

No response

[jbardin]

Hi @Skyriis,

Thanks for filing the issue. This appears to only be an instance of #24128, the error is correct that you can't evaluate var.example.test.val because var.example.test is null. The current options would be to define a suitable default value in the type expression, or to change the conditional to use try when indexing attributes might fail.

I'm not sure what you mean by this causing an "NPE" however. Do you have a configuration which causes a panic and stack trace from Terraform?

Thanks!

[apparentlymart]

Here's one way to write that condition with today's Terraform:

  validation {
    condition     = var.example.text != null ? length(var.example.test.val) > 0 : true
    error_message = "Invalid"
  }

The conditional operator only evaluates one of its result "arms" depending on the predicate result, so in the above case if var.example.text is null then Terraform will evaluate only the true result, and not try to evaluate length(var.example.test.val) > 0.

(The unchosen "arm" of the conditional is still subject to static checking, but whether the text is attribute is set to null is a dynamic decision and so will be checked only during full evaluation.)

[jbardin]

Since we have not heard back in a while I'm going to close the issue; updates can be tracked via #24128. If you have any updates regarding the issue, feel free to open a new issue with the requested information. If you have more questions, you can also use the community forum where there are more people ready to help.

Thanks!

[github-actions]

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