Terraform: Invalid Terraform version constraint in module gives confusing error

[dennyx]

Terraform Version

Terraform v0.12.0

Terraform Configuration Files

module "kafka_agents" {
  source  = "../terraform-azurerm-private-agents"

  providers = {
    azurerm = "azurerm"
  }

  hostname_format           = "${var.kafka_hostname_format}"

}

Expected Behavior

work as version 0.11.13 that no need to specify version for local modules

Actual Behavior

Error: Invalid provider version constraint
Invalid version core constraint "" in dcos.dcos-infrastructure.kafka_agents.

Steps to Reproduce

# change terraform version to 0.12
terraform init

Additional Context

1. tried to add version while encountered issue https://github.com/hashicorp/terraform/issues/21328

Thanks for any kindly help

[mildwonkey]

Hi @dennyx !
Thanks for reporting this. Can you share the rest of the configuration, including the module, or a smaller example that we can use to reproduce this issue?

[dennyx]

hi @mildwonkey
Thanks for the kindly feeback.
Add sample repository https://github.com/dennyx/terraform-21424 for reproduce.

git clone https://github.com/dennyx/terraform-21424.git
cd terraform-21424/terraform-main
terraform init

Appreciate if any kindly help on this, thanks~

ps: add terraform v0.12 download link
https://releases.hashicorp.com/terraform/0.12.0/terraform_0.12.0_linux_amd64.zip

[mildwonkey]

Thanks @dennyx!
There error is caused by this block (I found it in at least two files):

terraform {
  required_version = ""
}

You cannot have an empty string "" in the version constraint.

[dennyx]

hi @mildwonkey ,
Thanks for the kindly help, it works now~
And I will close this issue

[krystian-kulgawczuk]

Hi @mildwonkey,
Doesn't the error message sound a little confusing? Isn't there some way to propagate to this error message the exact name of the variable that violates the constraint?

[mildwonkey]

I agree! The message could certainly be clearer, and it should include the file name (like the other error messages try to do). I'm going to reopen this as an enhancement.