local-path modules nested more than 1 layer deep fail terraform get (and also ${path.module} makes no sense)

[bitglue]

Say I have a project with three modules, a, b, and c.

a is a module that does nothing.

$ mkdir a b c
$ cd a
$ touch a.tf
$ terraform plan
Refreshing Terraform state prior to plan...


No changes. Infrastructure is up-to-date. This means that Terraform
could not detect any differences between your configuration and
the real physical resources that exist. As a result, Terraform
doesn't need to do anything.

So far, so good. Now, b uses a:

$ cd ../b
$ cat > b.tf
module "a" {
    source = "../a"
}
$ terraform get
Get: file:///terraform-test/a
$ terraform plan
Refreshing Terraform state prior to plan...


No changes. Infrastructure is up-to-date. This means that Terraform
could not detect any differences between your configuration and
the real physical resources that exist. As a result, Terraform
doesn't need to do anything.

Awesome carrots. Now c uses b:

$ cd ../c
$ cat > c.tf
module "b" {
    source = "../b"
}
$ terraform get
Get: file:///terraform-test/b
Get: file:///terraform-test/c/.terraform/modules/a
Error loading Terraform: Error downloading modules: error downloading module 'file:///terraform-test/c/.terraform/modules/a': source path error: stat /terraform-test/c/.terraform/modules/a: no such file or directory

💥 💥 💥

Using ${path.module} just makes things even more confusing.

$ cd ../b
$ cat > b.tf
module "a" {
    source = "${path.module}/../a"
}
$ terraform get
Get: file:///terraform-test/b/a
Error loading Terraform: Error downloading modules: error downloading module 'file:///terraform-test/b/a': source path error: stat /terraform-test/b/a: no such file or directory

Did you not see the .. in the path? What if I omit it?

$ cat > b.tf 
module "a" {
    source = "${path.module}/a"
}
$ terraform get
Get: file:///terraform-test/b/${path.module}/a
Error loading Terraform: Error downloading modules: error downloading module 'file:///terraform-test/b/${path.module}/a': source path error: stat /terraform-test/b/${path.module}/a: no such file or directory

Now the variable just isn't expanded at all? 😕 If no .. is worse, how about more ..?

$ cat > b.tf
module "a" {
    source = "${path.module}/../../a"
}
$ terraform get
Get: file:///terraform-test/a

I have no logical explanation for why this works. Does it solve my problem?

$ cd ../c
$ cat > c.tf 
module "b" {
    source = "${path.module}/../../b"
}
$ terraform get
Get: file:///terraform-test/b
Get: file:///terraform-test/c/.terraform/modules/a
Error loading Terraform: Error downloading modules: error downloading module 'file:///terraform-test/c/.terraform/modules/a': source path error: stat /terraform-test/c/.terraform/modules/a: no such file or directory

Apparently not. 😞

[mitchellh]

Interpolations don't work at all in source. We should add validation for that. For the others, I'll take a look here.

[mitchellh]

Found the bug, looking into it further.

[mitchellh]

Fixed in linked PR.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.