Terragrunt: Terragrunt after_hook for apply called during output

[WigglesMcMuffin]

When calling terragrunt apply-all on a service (mod1) with a dependency block defined (mod2), the after_hook of mod2 is called twice. Once when it is applied, and then again when terraform output -json is called on it to apply mod1.

[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Detected 1 Hooks
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Executing hook: migrate_tfplan
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Running command: mv /home/tmoss/scratch/tg_bug/envs/mod2/tfplan /home/tmoss/scratch/tg_bug/envs/mod2/$
fplan.success
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Module /home/tmoss/scratch/tg_bug/envs/mod2 has finished successfully!
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod1] 2020/05/08 13:01:04 Dependency /home/tmoss/scratch/tg_bug/envs/mod2 of module /home/tmoss/scratch/tg_bug/envs/mod1 just f$
nished successfully. Module /home/tmoss/scratch/tg_bug/envs/mod1 must wait on 0 more dependencies.
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod1] 2020/05/08 13:01:04 Running module /home/tmoss/scratch/tg_bug/envs/mod1 now
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod1] 2020/05/08 13:01:04 Reading Terragrunt config file at /home/tmoss/scratch/tg_bug/envs/mod1/terragrunt.hcl
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Reading Terragrunt config file at /home/tmoss/scratch/tg_bug/envs/mod2/terragrunt.hcl
...
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Running command: terraform output -json
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Detected 1 Hooks
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Executing hook: migrate_tfplan
[terragrunt] [/home/tmoss/scratch/tg_bug/envs/mod2] 2020/05/08 13:01:04 Running command: mv /home/tmoss/scratch/tg_bug/envs/mod2/tfplan /home/tmoss/scratch/tg_bug/envs/mod2/t
fplan.success
mv: cannot stat '/home/tmoss/scratch/tg_bug/envs/mod2/tfplan': No such file or directory

This are what I think are the useful bits of the apply log. You can see that mod2 is applied, then mod1 reads that it's a dependent, and goes back into mod2 runs the terraform output -json command, at which point the hook fires again, and fails.

the parent hcl files looks like this:

terraform {
  extra_arguments "create_plan_files" {
    commands = [
      "plan",
    ]
    arguments = [
      "-out=${get_terragrunt_dir()}/tfplan",
    ]
  }
  after_hook "migrate_tfplan" {
    commands = ["apply"]
    execute = ["mv", "${get_terragrunt_dir()}/tfplan", "${get_terragrunt_dir()}/tfplan.success"]
    run_on_error = false
  }
}

Can upload the whole test setup to a repo, or somewhere if it helps.

EDIT:
Terraform: 0.12.20
Terragrunt: 0.22.4
I didn't see any issues reported that looked like this, so I assumed it hadn't been patched in the most, most up to date version of terragrunt, but can check if that helps

[brikis98]

This does sound like a bug! I suspect the hooks are running whether a module is being called directly or just being used for outputs as part of a dependency block. If anyone has time to dig into this and submit a PR, we'd probably want (a) to pass some flag along when fetching outputs as part of a dependency block and (b) to update the shouldRunHook method to return false if that flag was passed.