Strange behavior with optional type constraint and variable default values

[seggcsont]

Terraform Version

Terraform v1.3.3
on linux_amd64

Terraform Configuration Files

variable "input" {
  type = list(object({
    a = string                # a required attribute
    b = optional(string)      # an optional attribute
    c = optional(number, 127) # an optional attribute with default value
    d = optional(list(any))
  }))
  default = [
    { a = "a" }, { a = "b", d = [1] }
  ]
}

output "out" {
  value = var.input
}

Debug Output

https://gist.github.com/seggcsont/e7a04c37155e876c4868e9acdc46268b

Expected Behavior

Without variable override it should use default value

Actual Behavior

Error: Invalid default value for module argument

on 1.tf line 1:
1: variable "input" {

The default value for variable "input" is incompatible with its type
constraint: element types must all match for conversion to list.

Steps to Reproduce

1. terraform init
2. terraform plan
3. run command:
   tf plan -var "input=[{a=1},{a=2, d=[]}]"
tf plan -var "input=[{a=1},{a=2, d=[1]}]"
tf plan -var "input=[{a=1},{a=2}]"
tf plan -var "input=[{a=1}]"
tf plan

Additional Context

It works if you apply one of these:

• remove the 1 from the b=[1] so it will be an empty list
• use optional default value d = optional(list(any), [])
• change type any to number like d = optional(list(number))

References

No response

[crw]

Thanks for this report.

[kmoe]

Thanks for the well-written bug report. This shouldn't be happening: a null list should be compatible with a concrete list(number) regardless of initial type constraint. It's interesting to see it works with an empty list - perhaps cty should handle null and empty lists similarly in this case. Will investigate upstream.

@seggcsont, I'm curious as to why you use list(any) here instead of list(number) - could you say more about your use case?

[seggcsont]

@seggcsont, I'm curious as to why you use list(any) here instead of list(number) - could you say more about your use case?

In my real case it is a list complex object and I do not really use any. I wanted to create a small peace of that code to try out something and I faced this issue.

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