Diagnostics Handling with helper/schema.ResourceImporter

[bflad]

SDK version

v2.0.0

Use-cases

Version 2 of the Terraform Plugin SDK added some awesome diagnostics handling to many of the core provider resource handling functions. It appears that resource import handling didn't receive the same love however.

https://github.com/hashicorp/terraform-plugin-sdk/blob/b8c88233915352e876c277b19992dc3ebfea7d94/helper/schema/resource_importer.go#L50

It would be great if resource import functions could implement warnings in addition to errors. For example, a provider today cannot signal a deprecation of import syntax or provide other informational messages to the Terraform user interface.

Attempted Solutions

• Returning informational/warning log messages, which are not very visible to operators.

Proposal

Support the return type of diag.Diagnostic from a schema.ResourceImporter function field. When presented with:

• Informational diagnostic: the message is shown in the Terraform user interface after import
• Warning diagnostic: the message is shown in the Terraform user interface after import and returns an appropriate exit code
• Error diagnostic: fail the resource import and show the error message

References

• https://www.terraform.io/docs/extend/guides/v2-upgrade-guide.html#support-for-diagnostics
• https://registry.terraform.io/providers/hashicorp/aws/latest/docs/guides/version-3-upgrade#resource-aws_lambda_alias

[bflad]

Bummer, in investigating https://github.com/hashicorp/terraform-plugin-sdk/issues/877, it appears that helper/schema.Provider.ImportState is unfortunately an exported method signature, therefore it is protected by major version compatibility guarantees. Creating a separate method, that then calls a new diagnostics compatible field on ResourceImporter, would introduce its own oddities and could be confusing for anyone building on this API, so therefore wouldn't likely be a good path forward here here either.

Rather than keeping this open, I think the best recommendation then is convert resources over to terraform-plugin-framework, which properly allows diagnostics during resource import logic. Very soon we will support muxing terraform-plugin-sdk/v2 and terraform-plugin-framework providers together without requiring Terraform CLI 1.0 or later, so there will be a migration path to getting this functionality without introducing breaking changes.

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