"panic: inconsistent list element types" when using optional object attributes across multiple modules

[hanneshayashi]

Terraform Version

Terraform v1.3.0
on darwin_arm64

Terraform Configuration Files

Root module:

module "my_module" {
  source = "./my_module"
  permissions = [
    {
      role = "foo"
      service_accounts = [
        "bar"
      ]
    },
    {
      role          = "roles/servicenetworking.networksAdmin"
      create_groups = true
    },
  ]
}

my_module:

variable "permissions" {
  type = list(object({
    role             = string
    create_groups    = optional(bool)
    service_accounts = optional(set(string))
    condition = optional(object({
      title       = string
      description = optional(string)
      expression  = string
    }))
  }))
  default = []
}

module "my_submodule" {
  source      = "./my_submodule"
  permissions = var.permissions
}

my_submodule:

variable "permissions" {
  type = list(object({
    role             = string
    create_groups    = optional(bool, false)
    service_accounts = optional(set(string), [])
    condition = optional(object({
      title       = string
      description = optional(string)
      expression  = string
    }))
  }))
  default = []
}

Debug Output

https://gist.github.com/hanneshayashi/fe9e91f2254f733a3cd3e57239bec856

Expected Behavior

Terraform doesn't crash.

Actual Behavior

Terraform crashes.

Steps to Reproduce

1. terraform init
2. terraform plan

Additional Context

It seems like Terraform 1.3.0 has a problem with optional attributes in lists of objects. We have multiple nested modules and we were using the experimental feature until now.
Since I can no longer use the default() function, I need to declare my variable in the "lowest" submodule like so:

variable "permissions" {
  type = list(object({
    role             = string
    create_groups    = optional(bool, false)     # Defaults here
    service_accounts = optional(set(string), []) # Defaults here
    condition = optional(object({
      title       = string
      description = optional(string)
      expression  = string
    }))
  }))
  default = []
}

Since I don't want to declare the defaults in all modules that use the submodule I declare the variable like so:

  type = list(object({
    role             = string
    create_groups    = optional(bool)        # No defaults here
    service_accounts = optional(set(string)) # No defaults here
    condition = optional(object({
      title       = string
      description = optional(string)
      expression  = string
    }))
  }))
  default = []}

When I then call the first module with two differently constructed objects Terraform crashes:

module "my_module" {
  source = "./my_module"
  permissions = [
    {
      role = "foo"
      service_accounts = [
        "bar"
      ]
    },
    {
      role          = "roles/servicenetworking.networksAdmin"
      create_groups = true
    },
  ]
}

Removing either of the objects prevents the crash.

References

No response

[alisdair]

Thanks for the report! I'm able to reproduce the crash, and I'm looking into the cause.

[alisdair]

A smaller reproduction:

main.tf:

variable "configs" {
  type = list(object({
    a = optional(set(string))
  }))
  default = [
    { a = ["boop"] },
    {},
  ]
}

module "child" {
  source  = "./child"
  configs = var.configs
}

child/main.tf:

variable "configs" {
  type = list(object({
    a = optional(set(string), [])
  }))
}

Same crash:

inconsistent list element types (cty.Object(map[string]cty.Type{"a":cty.Set(cty.String)})
then cty.Object(map[string]cty.Type{"a":cty.EmptyTuple}))