Terraform plan doesn't detect multiple plugins associated to the same route

[ag91]

Thanks for maintaining this module. It is cool to manage kong via text editing.
I got surprised a couple of times by errors not picked up by terraform plan but picked up by terraform apply for this module.
Yesterday I could record the following one.

I suspect the root cause seems to be that on terraform plan this module validates syntax but doesn't do dry-run API calls to test that the new resources respect Kong's rules. (Maybe that could explain also this one?)

Steps to reproduce:

1. define a route
2. add a plugin
3. set plugin's route id to initial route
4. create a new plugin
5. associate to the same route

Actual behavior:
terraform plan succeeds and terraform apply fails with with an error similar to:

"type":"ERROR_TYPE_REFERENCE","messages":["unique-plugin-per-entity
(type: unique) constraint failed for value'acl....'

Expected behavior:
terraform plan fails with the same error

Bonus points:

terraform plan fails with a human friendly explanation, on the lines

Multiple plugins [names&ids] are not allowed for the same route [name&id].

Thanks!

[mheap]

Thanks @ag91. We only provide limited up front validation via terraform plan right now, and I understand that's a pain point.

I don't know when we'll get to implement this feature, but I agree that it would be useful for everyone.