Unable to use relative path to local Git module

[henrytk]

Context/use case

When operating in an environment with no external network access, I want to use a module accessed via the file system, but still leverage the versioning ability of a Git repository. In other words, I want to use a Terraform module which is inside a Git submodule on the filesystem. This works with an absolute path:

module "a" {
  source = "git::/Users/myusername/repos/repository-name//sub-folder?ref=version-ref"
}

but fails with a relative path (see below).

Terraform Version

$ terraform --version
Terraform v0.12.9

Terraform Configuration Files

I'll give a distilled example.

Say I have a Git repository containing a piece of Terraform intended to be used as a module:

output "value" {
  value = "some value"
}

All it does is output some value.

I then have a repository which includes the above as a Git submodule.:

module "a" {
  # Assume this path correctly traverses to where the Git submodule is located
  source = "git::../terraform-repo/module-path//module-sub-directory"
}

output "a" {
  value = module.a.value
}

Expected Behavior

I expect terraform init to work with absolute or relative file paths.

Actual Behavior

The absolute file paths work, but relative paths always yields:

Error: Failed to download module

Could not download module "a" (main.tf:1) source code from
"git::../../../myusername/dev/test-terraform/test-modules": error downloading
'file:///myusername/dev/test-terraform/test-modules': /usr/bin/git exited with
128: Cloning into '.terraform/modules/a'...
fatal: '/myusername/dev/test-terraform/test-modules' does not appear to be a
git repository
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Steps to Reproduce

Reference a Git repository using a local URL, such as "git::/Users/myusername/repos/repository-name//sub-folder?ref=version-ref", then change it to a relative URL.

Bonus fact

If you use a relative URL which goes up to the root directory it does work:

module "a" {
  source = "git::../../../../Users/myusername/repos/repository-name//sub-folder?ref=version-ref"
}

[henrytk]

@alisdair this was intended as a bug report. Use case only provided for context.

[salewski]

Hi Folks,

I developed a fix for this independently for my own needs in the past couple of days, but am just now seeing this GH issue. I'll write-up my approach and submit a PR for review in the next day or so. I started with the use case of supporting git:: forced local repos for my modules (basically the same as @henrytk's use case), but then generalized it to work with absoulte paths, too (for symmetry).

More soon,
-Al

[salewski]

I'll write-up my approach and submit a PR for review in the next day or so.

That write-up is in hashicorp/go-getter#268, as that's the library that provides the Git repo cloning support for Terraform. The string value of a Terraform module call's source parameter is parsed and handled by the go-getter lib.

Assuming the pull request, hashicorp/go-getter#269, (or something like it) gets merged, then getting the support for this feature in Terraform will require updating the dependency on go-getter to a version that includes the change.