Fix perma-diff in google_container_cluster when cluster_dns_scope is unspecified

[Michcioperz]

Terraform defaults this field to DNS_SCOPE_UNSPECIFIED, but the API
corrects this to an empty value.

Following https://googlecloudplatform.github.io/magic-modules/develop/diffs/#default_if_empty
to tackle this issue.

To make writing DNS tests faster, I refactored the helper function testAccContainerCluster_autopilot_withDNSConfig I added previously into testAccContainerCluster_withAdvancedDNSConfig.

Fixes hashicorp/terraform-provider-google#20285

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container: fixed perma-diff in `google_container_cluster` when `cluster_dns_scope` is unspecified

[github-actions]

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[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 2 files changed, 54 insertions(+), 14 deletions(-))
google-beta provider: Diff ( 2 files changed, 54 insertions(+), 14 deletions(-))

[modular-magician]

Tests analytics

Total tests: 226
Passed tests: 214
Skipped tests: 11
Affected tests: 1

Click here to see the affected service packages

• container

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

• TestAccContainerCluster_cloudDns_nil_scope

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[modular-magician]

🔴 Tests failed during RECORDING mode:
TestAccContainerCluster_cloudDns_nil_scope [Error message] [Debug log]

🔴 Errors occurred during RECORDING mode. Please fix them to complete your PR.

View the build log or the debug log for each test

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 2 files changed, 54 insertions(+), 14 deletions(-))
google-beta provider: Diff ( 2 files changed, 54 insertions(+), 14 deletions(-))

[modular-magician]

Tests analytics

Total tests: 226
Passed tests: 214
Skipped tests: 11
Affected tests: 1

Click here to see the affected service packages

• container

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

• TestAccContainerCluster_cloudDns_nil_scope

Get to know how VCR tests work

[modular-magician]

🟢 Tests passed during RECORDING mode:
TestAccContainerCluster_cloudDns_nil_scope [Debug log]

🟢 No issues found for passed tests after REPLAYING rerun.

---

🟢 All tests passed!

View the build log or the debug log for each test

[melinath]

We usually don't include UNSPECIFIED values in enums because they're the equivalent of the empty string.

Changing default values or making validation stricter is a breaking change; however, given that users are experiencing a bug (this permadiff) I think it would fall under the fixing a bug exemption and be allowed in a minor release.

In particular, I would recommend:

1. Remove the default (which would be the same as changing to Default: "").
2. Remove DNS_SCOPE_UNSPECIFIED from the ValidateFunc for the field so that it is no longer an allowed value.

What would you think of that? Any objection?

[Michcioperz]

Remove DNS_SCOPE_UNSPECIFIED from the ValidateFunc for the field so that it is no longer an allowed value.

@melinath Ah, so the idea here would be that, since setting this value is always causing permadiff right now, it's okay if we disallow it and force people change it to empty? Is that the rationale more or less?