Add a new state_mv method

[karajan1001]

fix #12

1. Add a new rename method to TerraformBackend
2. Add a test for rename method

[codecov-commenter]

Codecov Report

Merging #13 (19abda5) into master (fc779c4) will increase coverage by 0.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
+ Coverage   79.25%   79.58%   +0.32%     
==========================================
  Files           5        5              
  Lines         188      191       +3     
==========================================
+ Hits          149      152       +3     
  Misses         39       39              

Impacted Files	Coverage Δ
tpi/terraform.py	93.67% <100.00%> (+0.24%)	⬆️

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[karajan1001]

One problems. I hadn't found a way to modify the name inside the instance's attribute , in terraform.tfstate

  "resources": [
    {
      "type": "iterative_machine",
      "name": "new_name",
      "provider": "provider[\"registry.terraform.io/iterative/iterative\"]",
      "instances": [
        {
          "attributes": {
            "name": "still_old_name",
            }
}
}

[0x2b3bfa0]

[...] modify the name inside the instance's attribute , in terraform.tfstate

Terraform state files are intended to represent already existing infrastructure, not as a replacement or alternative representation for .tf or .tf.json files. Modifying an attribute would require performing the change in the latter and running terraform apply again.

Even if you did so, our Terraform provider doesn't support renaming instances. If you change its name you would also have to destroy/create it again.

This doesn't have an easy solution, because we're using the Terraform provider just to run a bunch of cloud API calls sequentially and don't have granular resources nor Read/Update methods for any of them. 🙈 🙊 🙉

Deeply related to iterative/terraform-provider-iterative#175 (comment)

[pmrowla]

@karajan1001 Modifying the instance attributes isn't really part of the requirement from the DVC side. Renaming the resource itself via terraform state mv is good enough since we can still access the resource (to destroy it when needed) by the new name, even if some of the instance attributes don't match up exactly. In DVC we don't actually use the name instance attribute at all, we only look things up by the resource name.

[casperdcl]

what about setting a timeout exclusion for just this test?

[pmrowla]

Thinking about this some more, it's non-intuitive that most of the TPI functions depend on per-iterative-machine workspace directories created in make_tf (meaning that source and destination here should always be iterative-machine.<...> names), it makes more sense for TPI to be generic, but that doesn't have to be handled in this PR

see: #15

[casperdcl]

minor comment

[casperdcl]

great 😅 thanks to #17 doesn't this function now become unnecessary?

@pmrowla WDYT?

[pmrowla]

We'll still need the wrapper for terraform state mv in DVC

[casperdcl]

lgtm apart from minor utility comment/query

[casperdcl]

/tag v2.1.0 b80ed24