Optional and Computed fields cannot be updated to an empty string

[kayrus]

Terraform Version

Terraform v0.12.7
+ custom provider, which uses the v0.12.7 SDK

Terraform Configuration Files

                        "optional_computed_string": {
                                Type:     schema.TypeString,
                                Optional: true,
                                Computed: true,
                        },
                        "optional_computed_int": {
                                Type:     schema.TypeInt,
                                Optional: true,
                                Computed: true,
                        },

resource "some_resource" "foo" {
  optional_computed_string = ""
  optional_computed_int = 0
}

Debug Output

Crash Output

Expected Behavior

I expect that optional computed field empty string value will be detected as desirable and terraform will try to update this string, as it is done with integer variable being explicitly set to 0.

Actual Behavior

Setting the optional computed field to an empty string is not reflected in a change and terraform doesn't update the computed field to an empty string.

Steps to Reproduce

Additional Context

References

Probably related to hashicorp/terraform#21760

[teamterraform]

Hi @kayrus!

We marked this as an enhancement because the SDK is currently working as designed (it considers empty string equivalent to not being set at all because Terraform 0.11 and earlier do not have null).

However, this is good feedback that will inform future changes to the design of the SDK as we prepare for adopting new Terraform 0.12 features, like the new explicit null. Thanks for creating it!

[kayrus]

I just wonder why zero int is handled correctly. Haven't dig deep into the code.

[kayrus]

Any news on this issue?

[kayrus]

@radeksimko @apparentlymart any news on this issue?

[radeksimko]

Hi @kayrus
Thank you for the report. As it was already mentioned above this is an effect of the way Terraform 0.11 and earlier versions handled types. While 0.12 has first-class support for null, the SDK is still retaining backwards compatibility (which means most providers could be just recompiled without further changes to become 0.12 compatible), hence the SDK and providers still suffer from the same type-related shortcomings, despite being driven by 0.12 with the new type system.

Supporting 0.12 types (which includes null) in SDK is one of our current priorities. We are practically sure though that supporting these in a provider will require deprecation of <0.12 from provider's perspective as only 0.12 uses the new protocol that allows us to carry all the important details about types.

The best you can do in the meantime is to read this blogpost, share it and encourage everyone to upgrade to 0.12.

I'm going to close this as duplicate of #102 since it covers all types and it will allow us to keep discussion in one place.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.