terraform: orphaned grandchild module inherits provider config

[mitchellh]

This fixes an issue where orphaned grandchild modules don't properly
inherit their provider configurations from grandparents. I found this
while working on shadow graphs (the shadow graph actually caught an
inconsistency between runs and exposed this bug!), so I'm unsure if this
affects any pre-existing issues.

To better explain the issue, I'll diagram things.

Here is a hierarchy that works (w/o this PR):

root
|-- child1 (orphan)
|-- child2
    |-- grandchild

All modules in this case will successfully inherit provider
configurations from "root".

Here is a hierarchy that doesn't work without this PR:

root
|-- child1 (orphan)
    |-- grandchild (orphan)

In this case, child1 does successfully inherit the provider from root,
but grandchild will not unless child1 had resources. If child1
has no resources, it wouldn't inherit anything. This PR fixes that.

[jbardin]

You mentioned that this only "periodically" caught the inconsistency. Aren't the transform walk done without any concurrency, via a ReverseDepthFirstWalk? Do you have any idea why the output wasn't deterministic?

[mitchellh]

Yep, because it didn't create a dependece so it'd walk the two providers in paralllel.

The transforms are sequential but the race was in the graph walk (since the edge wasn't made).

[martin-cossy-atwork]

I think this is related, see ticket 8680. There is an example in GitHub which is still failing: terraform-aws-region-prompt. In this example child modules are not properly inheriting the AWS provider, instead terraform tries to use my default profile in ~./aws (!). Running terraform 0.7.6 under Linux 4.7.6-1-ARCH 64 bits (ArchLinux).

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

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