How to include file from terraform source module in terragrunt?

Question

I have two repos, one contains terragrunt configuration and the other contains terraform code. I would like to include a file in terragrunt configuration that is present in terraform code.

I guess this is not possible since terragrunt is first processing configuration and then downloads terraform source module code into cache directory.

I this this issue is what I need: https://github.com/gruntwork-io/terragrunt/issues/1070

Did anyone face similar requirement? How did you solve it?

Ideally I need buitin function terraform_module_path() that I can use to include files terraform module cache into terragrunt config. This function would return path to cache directory that contains cloned terraform module source.

Thanks!