[WIP] backend/enhanced: start with absolute configuration path

[mildwonkey]

We recently started normalizing the config path before all "command"
operations, which was necessary for consistency but had unexpected
consequences for remote backend operations, specifically when a vcs root
with a working directory are configured.

This PR de-normalizes the path back to an absolute path.

I am still contemplating tests - this issue only occurs when a TFC user has a workspace with both a VCS root and a working directory configured, not something we can cover in unit tests. Any suggestions are appreciated.

[apparentlymart]

Looks good so far!

From a testing standpoint, the only thing that springs to mind is a rather heavyweight solution of having this run against a mock API server in the test and verifying that a suitable result gets submitted. Ideally it'd be nice if we could make that call to b.client.ConfigurationVersions.Upload below instead point to a mock implementation, and thus avoid the need to start up a server at all, but I believe b.client is a concrete struct from the Terraform Cloud client library and thus not something we can mock without some considerable refactoring. 😖

[svanharmelen]

but I believe b.client is a concrete struct from the Terraform Cloud client library and thus not something we can mock without some considerable refactoring

That is not entirely true. Have a look at the testBackend function defined here. It creates a new client and then mocks endpoints that are used by the remote backend (using the code defined in backend_mock.go).

As I was running into this issue myself, I was going to take a stab at fixing the problem. But since that seems to be done already, let me take a stab at adding a test for the fix instead.

[svanharmelen]

@mildwonkey I added a single commit on your branch that adds an error check and a test for this use case.

It turned out that the mock and existing tests we used already worked as expected, but since they always use a specific configuration directory, the problem didn't show itself. So I added an additional test that simulates doing a plan from the current working directory which fails when running without the fix you added in this PR.

[mildwonkey]

@svanharmelen thank you so much!! 🎉 I woke up annoyed that I hadn't had any brilliant ideas, and here you are 😀 I greatly appreciate the assist and I will learn from your test.

[svanharmelen]

Your welcome 😄

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