path.module and path.root still return absolute paths in terraform console

[rjullman]

Terraform Version

Terraform v0.12.0
+ provider.aws v2.12.0

Terraform Configuration Files

provider "aws" {
  region  = "us-east-1"
  version = "~> 2.12.0"
}

resource "aws_db_instance" "default" {
  identifier     = "${basename(path.module)}-db"
  instance_class = "db.t3.micro"
}

Crash Output

N/A

Expected Behavior

Passes validation.

Actual Behavior

Error: only lowercase alphanumeric characters and hyphens allowed in "identifier"

  on main.tf line 6, in resource "aws_db_instance" "default":
   6: resource "aws_db_instance" "default" {

Error: first character of "identifier" must be a letter

  on main.tf line 6, in resource "aws_db_instance" "default":
   6: resource "aws_db_instance" "default" {

Steps to Reproduce

1. terraform init
2. terraform apply

Additional Context

Replacing the basename function with variables or locals works fine (as long as they do not in turn use basename). I imagine the issue is related to basename not being evaluated before the validation logic applies.

[apparentlymart]

Hi @rjullman! Thanks for reporting this.

The error messages here are coming from the AWS provider itself, but as you said this might be because the basename function is producing an unacceptable result.

In your case I think the situation is that path.module is, as of v0.12.0, a path relative to the current working directory, rather than an absolute path as before. If the module in question is the root module for your configuration and you're running it from its own directory then path.module would be . (current working directory), and thus basename(.) would also be ., which would create:

  identifier = ".-db"

Using the name of the containing directory is not a pattern we expected but we've seen a similar usage (for a different purpose) in #21400. While using the name of the containing directory feels a little "magical" for my tastes, I can see that you were using it to avoid writing the module name again in here, and so I'd like to find a different way to meet that use-case. It's likely that a new abspath function, like proposed in #21400, so you'd be able to write this instead:

identifier     = "${basename(abspath(path.module))}-db"

[rjullman]

Thanks for the help!

I did not realize that the path.module had changed. In terraform console it still prints the absolute path to the module. Does the console work differently than the final interpreter?

I agree that using the directory name in this way is (as you put it) magical. I've been eliminating this construct where possible (I removed all dependencies in the toy example above) and should be able to unblock myself here.

[apparentlymart]

Indeed, I think terraform console is behaving a little differently here, and that's a bug to be fixed. Because terraform console works in a different way than most other Terraform commands (it's evaluating directly against the state, with no plan in progress, etc) some of its behaviors can potentially be different, and I expect we missed updating something in there while we were switching over to using relative paths for these.

[apparentlymart]

Since we already have #21400 open, I think I'm going to repurpose this one to represent the fact that terraform console is behaving differently, since it seems like that was a key cause of you not being able to diagnose the problem here. We'll use #21400 to represent the need for abspath, since it sounds like you've taken a different approach that won't need it for this particular situation.

[jbardin]

Confirmed this is now working as expected in current releases.

Thanks!

[ghost]

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