TERRAGRUNT_CONFIG env var not considered?

[cognitiaclaeves]

I have a repo where I need to maintain separate 'tracks' of config for terragrunt.

Running it looks like this:

export TERRAGRUNT_CONFIG=tg-alt.hcl
terragrunt init

And then in tg-alt.hcl:

terragrunt_version_constraint = ">= 0.29.2"
terraform_version_constraint  = ">= 0.15, < 0.15.2"

I had expected tfswitch to have the same behavior as it does when the above version_constraints are found in terragrunt.hcl.

reference: https://terragrunt.gruntwork.io/docs/getting-started/configuration/#terragrunt-configuration-file

[cognitiaclaeves]

Reading back through this, I realized I left out a few important details.

After setting up an AWS profile for automation-examples,

git clone [email protected]:cognitiaclaeves/terragrunt-infrastructure-live-example.git
git checkout tfswitch-json
cd tg-alt/acct1/us-east-1/dev/outputs
export TERRAGRUNT_CONFIG=tg-alt.hcl
AWS_PROFILE=automation-examples terragrunt init --terragrunt-source-update

results in:

INFO[0004] Executing hook: tf_ver_b4_switch              prefix=[.]
Terraform v0.15.3
on darwin_amd64
+ provider registry.terraform.io/hashicorp/aws v3.39.0
INFO[0004] Executing hook: tfswitch                      prefix=[.]
Terragrunt file found: /Users/jason/gitrepo/terragrunt-infrastructure-live-example/tg-alt/acct1/us-east-1/dev/outputs/.terragrunt-cache/zawrRJ_hM_7zIiD8UHSWRzTaxRY/sMSf_E1jGYfdJNHr-4YOZ8AbfM4/outputs-only/terragrunt.hcl
Reading required version from constraint: >= 0.15
Matched version: 0.15.3
Switched terraform to version "0.15.3"

This only works because there is a terragrunt.hcl file for the sole purpose of declaring the TF version constraint.
When this is moved, tfswitch fails to find the constraint:

mv terragrunt.hcl terragrunt.hcl_
AWS_PROFILE=automation-examples terragrunt init --terragrunt-source-update

results in:

INFO[0001] Executing hook: tf_ver_b4_switch              prefix=[.]
Terraform v0.15.3
on darwin_amd64
+ provider registry.terraform.io/hashicorp/aws v3.39.0
INFO[0002] Executing hook: tfswitch                      prefix=[.]
Use the arrow keys to navigate: ↓ ↑ → ←
? Select Terraform version:
  ▸ 0.15.3 *recent
    0.15.2
    0.15.1
    0.15.0
↓   0.14.11

The expected behavior would be that tfswitch would recognize the constraint in the tg-alt.hcl file when the TERRAGRUNT_CONFIG env var is set.

[warrensbox]

@cognitiaclaeves If I am reading this right, TERRAGRUNT_CONFIG is an environment variable of /path/to/terragrunt.hcl?