[BUG] terramate plan file output not working with terragrunt dependencies

[FabianDohmen]

Describe the bug
Setup: you have two terragrunt modules C and D, where D depends on C. The dependency is marked via wants block. A change in the module C affects its output, which requires D to run, which uses said output. If you run terramate run --changed terragrunt plan -out plan the plan files for both will be created. However the plan file in terragrunt module D does not contain the changes from the terragrunt plan of module C.

To Reproduce

Steps to reproduce the behavior:

1. Scenariao has been described above.

Expected behavior
terramate should transfer the plan output from module C such that the plan of module D does contain the required changes.

[i4ki]

Hi @FabianDohmen

The Terraform plan computes the planned changes based on current stack code and its state, but as you did not apply the changes in C then Terraform cannot plan its change.
If you apply C, then D will pick up the output changes in its plan, as expected.

Does Terragrunt alone shows the correct plan if you do terragrunt run-all plan ?

[FabianDohmen]

You can atleast carry it over via mocked output values. But the core problem here is that the workflow orchestration loses one of the main protective features. I want to write out the plan to a file, review the plan and then apply that plan and nothing that changed between creating the plan and applying. If the plan does not carry over the values to dependencies, then the plan files can not be written properly and therefore its borderline useless in a cicd setting with multiple contributors. The entrie point of the cicd workflow automation is to update the changed module and all the dependent modules in one go.