Well known error for "already exists"

[radeksimko]

It would be nice to have a well known error core expects from providers when a resource already exists so that it can output the required import syntax:

type AlreadyExistsError struct {
  ImportID string
}

etc...

This needs to be raised to core as core is what knows the import syntax and the appropriate naming of the resource itself.

[tombuildsstuff]

Azure has a working example of this: https://github.com/terraform-providers/terraform-provider-azurerm/blob/master/azurerm/helpers/tf/errors.go#L5-L8

Which is implemented in every resource: https://github.com/terraform-providers/terraform-provider-azurerm/blob/master/azurerm/resource_arm_key_vault_secret.go#L104-L115 - that's currently feature-toggled off (but some customers are opting-into)

[bflad]

Proposal for AWS Provider (initially following similar implementation of Azure, but ideally would use this new implementation): hashicorp/terraform-provider-aws#9223

[apparentlymart]

This has a small use-case overlap with hashicorp/terraform#22094, since one of its example use-cases is to detect potential collisions at plan time. It doesn't currently specify any means to check if the planned object conflicts with an object created outside of the current Terraform configuration, but perhaps it could.

That aside, note that in the implementation weeds the provider protocol does not use Go error for errors but rather would require this extra information to be added to ApplyResourceChange.Response as an extra optional field, presumably returned alongside an error diagnostic. No reason this can't be represented as an error type within the SDK itself, though.

[paultyng]

I think in gRPC you can attach arbitrary protobuf to errors, so may not require extending the response as just creating the error messages.

See status.WithDetails