compute: fix omission of explicit 0 values in BackendService cdn_policy TTLs

[burczyk]

This PR fixes a bug where explicitly setting default_ttl, max_ttl, or client_ttl to 0 inside the cdn_policy block of google_compute_backend_service or google_compute_region_backend_service resulted in the value being omitted from the JSON payload sent to the API (zero-value omission), causing the API to apply its own defaults instead of the requested 0.

Changes:

1. Added send_empty_value: true to defaultTtl, maxTtl, and clientTtl fields in both BackendService.yaml and RegionBackendService.yaml. This ensures that explicit 0 values are preserved in the JSON payload instead of being skipped by tpgresource.IsEmptyValue.

2. Added two new acceptance tests to verify this behavior:

• backend_service_cache_zero_ttl: Verifies explicit 0 values are sent and preserved.
• backend_service_cache_omitted_ttl: Verifies that omitting the fields (complimentary behavior) still works as expected (omitted from payload, allowing API defaults).

Linked Issues:
Fixes https://issuetracker.google.com/issues/498433517

Release Note Template for Downstream PRs (will be copied)

compute: fixed omission of explicit `0` values for `default_ttl`, `max_ttl`, and `client_ttl` in `cdn_policy` for `google_compute_backend_service` and `google_compute_region_backend_service`

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit 5218a37:

Diff report

Your PR generated the following diffs in downstream repositories:

Repository	Diff Link	Changes
google provider	View Diff	4 files changed, 178 insertions(+), 6 deletions(-)
google-beta provider	View Diff	4 files changed, 178 insertions(+), 6 deletions(-)
terraform-google-conversion	View Diff	5 files changed, 18 insertions(+), 12 deletions(-)
Open in Cloud Shell	View Diff	8 files changed, 238 insertions(+)

Test report

Analytics

Total Tests	Passed	Skipped	Affected
1509	1409	94	6

Affected Service Packages

• compute

Learn how VCR tests work

---

Step 1: Replaying Mode

Action taken

Found 6 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit.

Click here to see the affected tests

• TestAccComputeBackendService_backendServiceCacheIncludeHttpHeadersExample
• TestAccComputeBackendService_backendServiceCacheOmittedTtlExample
• TestAccComputeBackendService_backendServiceCacheSimpleExample
• TestAccComputeBackendService_backendServiceCacheZeroTtlExample
• TestAccComputeBackendService_withCdnPolicy
• TestAccComputeRouterPeer_UpdateMd5AuthenticationKey

View the replaying VCR build log

---

Step 2: Recording Mode

Recording Mode	Replaying Rerun	Test Name
✅ Log	✅	TestAccComputeBackendService_backendServiceCacheOmittedTtlExample
✅ Log	✅	TestAccComputeBackendService_backendServiceCacheSimpleExample
✅ Log	✅	TestAccComputeBackendService_backendServiceCacheZeroTtlExample
✅ Log	✅	TestAccComputeBackendService_withCdnPolicy
✅ Log	✅	TestAccComputeRouterPeer_UpdateMd5AuthenticationKey
❌ Error · Log	-	TestAccComputeBackendService_backendServiceCacheIncludeHttpHeadersExample

Caution

Issues requiring attention before PR completion

🔴 Initial Recording Failed: Some tests failed during the recording step. See the table above for details.

Please address these issues to complete your PR. If you believe these detections are incorrect or unrelated to your change, please raise the concern with your reviewer.

View the recording VCR build log or the debug logs folder for detailed results.

@burczyk VCR tests complete for 5218a37!