Pass value from validation block condition to error_message

[drewmullen]

Current Terraform Version

$ Terraform v1.1.6
on darwin_amd64
+ provider registry.terraform.io/hashicorp/aws v4.4.0

Your version of Terraform is out of date! The latest version
is 1.1.7. You can update by downloading from https://www.terraform.io/downloads.html```

Use-cases

I often use nested maps as variables and perform validation for complex situations. It would be great if i could provider extra context to the error_message a users sees by passing output from the condition check

Proposal

change condition to fail if non-true, meaning false or a string. the output of condition can be used as part of the error:

In the example below i want to make sure the keys listed in var.subnets contain only one key cidrs or netmask. private would error and be passed to error message:

> var.subnets
{
  "private" = {
    "cidrs" = ["10.0.0.0/16"]
    "netmask" = 24
  }
  "public" = {
    "netmask" = 24
  }
}

validation propsal

validation {
  error_message = "Each subnet type must contain only 1 key: `cidrs` or `netmask`. Subnet type ${condition_output} violated."
  condition     = [for subnet_type, v in var.subnets: subnet_type if length(setintersection(keys(v), ["cidrs", "netmask"])) != 1]
}

error proposal:

│ Error: Invalid value for variable
│ 
│   on variables.tf line 64:
│   64: variable "subnets" {
│ 
│ Each subnet type must contain only 1 key: `cidrs` or `netmask`. Subnet type ["private"] violated.

References

[jbardin]

Hi @drewmullen,

This seems very similar to the proposal made in #24160, which was recently closed via #30613. I'm not sure if making the condition value "truthy" wold be acceptable, but perhaps the ability to use expressions there would suffice for your needs?

[drewmullen]

Hi @jbardin!

Wow. What a coincidence. Yes i do think that provides a solution to my use case. It doesnt however help with DRYness. My suggestion for "truthy" is certainly more pythonic than gopher-ic 😅 Ill close this for now... I'm going to keep thinking on this to see if i can come up with another suggestion to help with DRY

Either way I'm really looking forward to when this new experiment is available

[github-actions]

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