cloudbuild: suppress comment_control permadiff on pull_request blocks (#19853)

[jbbqqf]

Summary

Suppress the permanent diff on comment_control in google_cloudbuild_trigger's pull-request filters. When users explicitly set comment_control = "COMMENTS_DISABLED" (the API's semantic default), the API stores/returns an empty value because the field is omitempty in the proto, and Terraform shows a forever-pending update to add COMMENTS_DISABLED back.

Fixes hashicorp/terraform-provider-google#19853 — see hashicorp/terraform-provider-google#19853

Why

In the Cloud Build v1 API client (google.golang.org/api/cloudbuild/v1):

type PullRequestFilter struct {
    // ...
    CommentControl string `json:"commentControl,omitempty"`
}

The omitempty JSON tag matches a behavior we can confirm against state output in the issue: a user sets comment_control = "COMMENTS_DISABLED", applies, and on the next plan the provider reads back comment_control = "" from state. Result: comment_control = "" -> "COMMENTS_DISABLED" shows up on every plan, forever.

There are four such fields in mmv1/products/cloudbuild/Trigger.yaml (one per pull_request block — repository_event_config, github, bitbucket_server_trigger_config, and source_to_build); the bug applies to all of them. The mmv1 codebase already has a perfect helper for this exact shape — tpgresource.EmptyOrDefaultStringSuppress(default) — used in roughly a dozen other places (e.g. cloudscheduler/Job.yaml, hypercomputecluster/Cluster.yaml).

GCP API reference: https://cloud.google.com/build/docs/api/reference/rest/v1/projects.triggers#PullRequestFilter

What changed

mmv1 YAML edit to a single file:

mmv1/products/cloudbuild/Trigger.yaml | 4 ++++

Adds diff_suppress_func: 'tpgresource.EmptyOrDefaultStringSuppress("COMMENTS_DISABLED")' on each of the four commentControl fields.

Edge cases tested

#	Scenario	Expected	Verified by
1	comment_control unset in HCL	API returns ""; state stays ""; no diff	Behavior unchanged from main (suppress treats "" == "").
2	comment_control = "COMMENTS_DISABLED" (the OP's case)	First apply: provider sends COMMENTS_DISABLED, API drops it via omitempty, returns "". Read sets state to "". Suppress treats "" vs "COMMENTS_DISABLED" as equal → no diff on next plan.	Static — EmptyOrDefaultStringSuppress is a well-tested helper (utils_test.go:899 TestEmptyOrDefaultStringSuppress).
3	comment_control = "COMMENTS_ENABLED" (non-default)	Provider sends COMMENTS_ENABLED, API persists it, read returns COMMENTS_ENABLED, state matches config → no diff. The suppress helper does not affect the non-default case ("COMMENTS_DISABLED" != "COMMENTS_ENABLED").	Same — covered by helper unit tests.
4	Switching from COMMENTS_DISABLED to COMMENTS_ENABLED	Real change — should show diff and update	Suppress only matches ("", "COMMENTS_DISABLED"); transitions between non-empty values are not suppressed.

Test protocol

Test	Result	Notes
YAML lint / mmv1 generation	n/a in this PR	Will be exercised by mmv1 CI. The change is one extra line per affected field, all using an existing third-party helper.
Live BEFORE/AFTER smoke	not run	A live smoke would require an installed Cloud Build → GitHub connection in the test project (the OP's repro uses google_cloudbuildv2_repository against a real GitHub repo). That's expensive to set up and tear down per scenario, and the diff is structurally proven by the API client's omitempty tag plus a well-established suppression helper.

The author (a human) verified:

1. The API client (api@v0.278.0/cloudbuild/v1/cloudbuild-gen.go:3647) uses json:"commentControl,omitempty".
2. The EmptyOrDefaultStringSuppress helper exists at mmv1/third_party/terraform/tpgresource/common_diff_suppress.go:14 and is unit-tested.
3. The same pattern is used elsewhere in the same DSL.

Resources

• Original issue: google_cloudbuild_trigger.repository_event_config is not saved correctly in state hashicorp/terraform-provider-google#19853
• API reference: https://cloud.google.com/build/docs/api/reference/rest/v1/projects.triggers#PullRequestFilter
• Helper used: tpgresource.EmptyOrDefaultStringSuppress

Disclosure

This PR was implemented with assistance from Claude Code as part of a focused contribution batch. The diff was reviewed manually against the GCP REST API documentation and the vendored Go client, which together confirm the omitempty behavior that produces the permadiff.