r/aws_s3_bucket_lifecycle_configuration: preserve transition_default_minimum_object_size when backend omits it

[kayrus]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

No. This change does not alter any access controls, encryption, or logging behavior.

Description

aws_s3_bucket_lifecycle_configuration never stabilized on S3-compatible
backends (e.g. Ceph RADOS Gateway), timing out during create/update.

The resource waits for the applied configuration to be readable back before
returning. That comparison includes transition_default_minimum_object_size,
which the provider defaults to 128k for general purpose buckets. AWS S3
always returns the corresponding x-amz-transition-default-minimum-object-size
field on GetBucketLifecycleConfiguration, but the field is optional and
S3-compatible backends omit it. The observed value therefore came back empty
and never matched the requested 128k, so the stabilization wait
(waitLifecycleConfigEquals) could never reach its target and timed out.
The empty value flattened into state also produced "inconsistent result after
apply" errors and perpetual diffs.

This change:

• Tolerates an empty observed value in lifecycleConfigEqual, so the
  stabilization wait converges when the backend omits the field. The check is
  asymmetric by design — an empty observed value matches any requested value,
  but a non-empty observed value must still match exactly.
• Preserves the planned (Create/Update) or prior (Read) value for
  transition_default_minimum_object_size when the flattened value is empty,
  avoiding the inconsistent-result error and perpetual diff.

On real AWS S3 both behaviors are strict no-ops, because AWS always populates
the field: the observed value is never empty, so the equality guard reduces to
the original comparison and the value is never preserved from an empty result.

Note: the ~3 minute timeout reported in the issue is the create/update
stabilization timeout. With this fix the configuration converges as soon as the
backend reports matching rules, so the operation completes within the default
window rather than timing out.

Relations

Closes #25939

References

• S3 GetBucketLifecycleConfiguration x-amz-transition-default-minimum-object-size is an optional response field: https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetBucketLifecycleConfiguration.html

Output from Acceptance Testing

Unit coverage for the equality guard, which encodes the asymmetric
empty-tolerance behavior:

% go test ./internal/service/s3/ -run '^TestLifecycleConfigEqual$' -v
=== RUN   TestLifecycleConfigEqual
=== RUN   TestLifecycleConfigEqual/observed_empty,_requested_non-empty,_rules_equal
=== RUN   TestLifecycleConfigEqual/observed_empty,_requested_empty,_rules_equal
=== RUN   TestLifecycleConfigEqual/observed_non-empty_differs_from_requested
=== RUN   TestLifecycleConfigEqual/observed_non-empty_equals_requested
=== RUN   TestLifecycleConfigEqual/observed_empty,_rules_differ
=== RUN   TestLifecycleConfigEqual/sizes_equal,_rules_differ
--- PASS: TestLifecycleConfigEqual (0.00s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/s3

[github-actions]

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[kayrus]

@gdavison @jar-b @ewbankkit @YakDriver could you please review this PR?

[justinretzolk]

Similar #48457
Similar #49547

[kayrus]

@justinretzolk Thanks for your attention. The #48457 still doesn't work with the Ceph S3 backend. The flattenBucketLifecycleConfigurationResource helper func modification is still necessary.

the #49547 looks similar to my PR. Would be nice if you pick up one PR and review/merge it.