Unsupported Argument gets ignored when using foo_override.tf feature

[pascalwhoop]

@gergelysotidm

Terraform Version

Terraform v0.12.19

Terraform Configuration Files

See example project
https://github.com/pascalwhoop/terraform_module_override_bug_example

See below the unexpected and expected output
https://gist.github.com/pascalwhoop/0c72b73f8f0fbfd7dcdc8f4183a0d671#file-both_runs-log

Debug Output

https://gist.github.com/pascalwhoop/0c72b73f8f0fbfd7dcdc8f4183a0d671

Steps to reproduce

Create a _override.tf file and add an empty module override (or a module override with values in it). Once this is done, the "unsupported argument" check doesn't get executed and any unsupported arguments are simply dropped without error.

[apparentlymart]

Hi @pascalwhoop! Thanks for reporting this odd behavior.

I've marked this as a breaking change because although the behavior you've seen is not what we intended, it doesn't seem that the documentation is explicit about the expected behavior here and so it's possible that others have written configurations that somehow depend on these invalid arguments being ignored. Therefore although we'd like to fix it, we would be required to do so only in a major release.

[pascalwhoop]

@apparentlymart glad to have been of help. In fact, this "bug" would now allow us to build a conditional module enablement hack, by pointing a module source to an empty dummy_module in an override file. This dummy module wouldn't need to define any variables because the variable check is dropped, hence we could have an empty module that serves as a "disable module X if Y" workaround.

I wrote a post about this a while ago but back then, the variables file still had to exist. So it was a "empty module per to-disable module" hack

[mar-pan]

Hi @apparentlymart are you planning to fix it in nearest future? If so would it be possible to put similar behavior (way to not error when unsupported argument is provided under some flag?

[apparentlymart]

Hi @mar-pan,

I no longer work on Terraform at HashiCorp. I don't know what the Terraform team plans to do with this issue. I'm sorry that I cannot answer your question.

[mar-pan]

Hi @teamterraform @crw @bschaatsbergen can you answer my q?