test(gc): make gc_write_barrier_stress tests optional (off the blocking cargo-test gate)

[proggeramlug]

Why

The cargo-test job intermittently failed on two tests — tenured_mutation_stress and structured_clone_gc_churn_stress in crates/perry/tests/gc_write_barrier_stress.rs — across unrelated PRs. They are a fundamentally different shape from everything else in the gate:

• they compile + run a binary under the slowest GC mode (PERRY_GC_FORCE_EVACUATE + PERRY_GC_VERIFY_EVACUATION),
• they're ~200s each (they dominate the whole job's runtime), and
• they hunt a rare corruption window (CI: gc_write_barrier_stress red on main (missing old→young remembered-set edges → segfault) #5029) — so they're nondeterministic by design.

A stress/fuzz test looking for a rare race is the wrong thing to put on a per-PR blocking gate: one flake blocks every unrelated PR. Proof it's PR-independent: #5115 — a one-line, test-only change — failed tenured_mutation_stress on its own CI.

(#5115 already raised the timeout 120s→300s, which fixed the timeout flake; this addresses the remaining corruption-crash flake.)

What

• #[ignore] both stress tests, so the per-PR cargo test -p perry skips them. The gate stays meaningful — every fast, deterministic unit/integration test still blocks — and runs ~6–7 min faster.
• Add an opt-in, non-blocking gc-stress CI job (continue-on-error: true, gated by the run-extended-tests label / workflow_dispatch / tag push — same convention as the existing parity / compile-smoke jobs) that runs them with --ignored. The signal is preserved without blocking PRs.

Run locally: cargo test -p perry --test gc_write_barrier_stress -- --ignored

Verified: default cargo test -p perry --test gc_write_barrier_stress now reports 0 passed; 0 failed; 2 ignored.

Note

The underlying corruption (#5029) is real — PERRY_GC_VERIFY_EVACUATION only aborts on a genuine un-rewritten live slot (a latent use-after-free), so it shouldn't be buried. Recommend reopening #5029 to track the GC fix; this change only stops a nondeterministic stress test from gating every PR.

Once this merges, the open feature PRs go green after a rebase (their cargo-test will skip these flaky tests). No version bump / changelog per maintainer instruction.

Summary by CodeRabbit

• Tests

  • Generational write-barrier stress tests now run opt-in by default with enhanced documentation of potential edge cases.

• Chores

  • Added optional CI job for extended stress testing, triggered via tag pushes, manual workflow dispatch, or PR labels.

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

Two GC write-barrier stress tests (tenured_mutation_stress and structured_clone_gc_churn_stress) are marked #[ignore] with a reference to issue #5029, removing them from the default CI gate. A new optional gc-stress CI job is added to run these ignored tests on tag pushes, manual dispatch, or a PR label opt-in.

Changes

GC Stress Test Opt-In and CI Job

Layer / File(s)	Summary
Mark stress tests as opt-in with #[ignore] crates/perry/tests/gc_write_barrier_stress.rs	Both tenured_mutation_stress and structured_clone_gc_churn_stress receive #[ignore = "#5029: ..."] attributes and expanded documentation describing the nondeterministic corruption window, excluding them from the default test run.
Add gc-stress CI job .github/workflows/test.yml	A new non-blocking gc-stress job (continue-on-error: true) runs cargo test -p perry --test gc_write_barrier_stress -- --ignored with a 30-minute timeout. It is triggered by tag pushes, workflow_dispatch with run_extended_tests=true, or a run-extended-tests PR label, and provisions clang with the existing linker workaround.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• PerryTS/perry#5115: Modifies the same gc_write_barrier_stress.rs stress tests to address CI flakiness, with a focus on test timeouts rather than opt-in gating.

Poem

🐇 Hop, hop, the stressful tests once blocked the gate,
Now #[ignore]'d, they politely wait.
A special job will summon them with care,
On tags and labels, when reviewers dare.
No flaky failures block the merge of fate! 🌿

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: making gc_write_barrier_stress tests optional by removing them from the blocking cargo-test gate.
Description check	✅ Passed	The description is comprehensive and addresses all key template sections including Why, What, Related issue context, and verification steps, clearly explaining the rationale and implementation.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/gc-stress-optional

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