tf6to5server: Consider Automatically Handling UpgradeResourceState Legacy Features

[bflad]

terraform-plugin-mux version

v0.5.0

Use cases

While terraform-provider-framework has not actually implemented UpgradeResourceState handling (refer to hashicorp/terraform-plugin-framework#42), there is currently a passthrough implementation there since the RPC is always invoked. When passing a framework provider through terraform-plugin-mux tf6to5server for Terraform CLI 0.12+ compatibility, there should be no errors either.

However, Terraform CLI 0.12 through 0.14 return the following (less than helpful) error:

Error: EOF

This is because those versions of Terraform CLI requires the Msgpack field to be populated. This would require converting from Response JSON (if provided) to MessagePack (if not provided). There may be possibility to also perform some legacy handling with the requests as well (e.g. converting flatmap to JSON), otherwise each wrapped server would also need to handle that data.

Attempted solutions

Considering a terraform-plugin-framework specific implementation, which wouldn't necessarily help the larger ecosystem when using this package with other tf6server implementations.

Proposal

In the tf6to5server implementation for UpgradeResourceState, check if UpgradedState only includes the JSON field. If so, convert it to MessagePack and send in the Msgpack field.

References

• tfsdk: Send UpgradeResourceStateResponse.UpgradedState.Msgpack for Terraform 0.12-0.14 Compatibility terraform-plugin-framework#262

[bflad]

Thinking about this more, we should keep these Go packages as simple as possible and this functionality should be considered out of scope. Having this automatically handled may not be obvious that it exists here and it would be awkward to redirect folks to depending on this.

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