[proggeramlug]

Lands #8711.

gc_mutable_scanner_rewrites_listener_roots could only observe a rewrite when the collector actually moved the root — and a unit-test heap is normally too quiet for the evacuation policy to pick the copying path. So the test could pass having exercised nothing.

This is a strengthening, not a relaxation — worth saying plainly, because "make the test deterministic" is a phrase that usually means the opposite. It:

• forces evacuation under the existing GC_TEST_LOCK, restoring any runner-supplied PERRY_GC_FORCE_EVACUATE on Drop;
• adds an ordinary shadow-stack root as a control, whose rewrite proves the cycle copied live objects independently of scan_net_roots — so a listener left at its old address is now an actual scanner failure rather than an ambiguous result;
• asserts the subject actually ran:

assert!(copying_minor_cycles() > before,
    "minor GC did not run the copying collector, so the scanner was not exercised");
assert!(moved_objects_total() > before,
    "copying minor did not relocate an object, so the scanner was not exercised");

That is exactly the #7024/#7025 lesson — a gate must assert its subject was live, not merely that nothing threw.

I checked the one thing that could bite: std::env::set_var is process-global, but all four tests in perry-ext-net take GC_TEST_LOCK, and each crate's tests run in their own process, so the mutation is properly serialized.

Validation

• All 30 lint-job checkers pass
• perry-ext-net (RUST_TEST_THREADS=1): 28 passed, 0 failed
• Ran the target test 5× consecutively: 5/5 pass — it is in fact deterministic now, not merely passing once

Carries skip-changelog. No version bump.

Summary by CodeRabbit

• Tests
  • Improved garbage-collection tests to verify object relocation and root updates during copying collection.
  • Added safeguards to preserve the test environment and ensure reliable cleanup after each test.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: d1e96f7a-1ac1-44d4-b2b6-baba6d4e87e8

📥 Commits

Reviewing files that changed from the base of the PR and between 2ecdd1a and 77bf735.

📒 Files selected for processing (1)

• crates/perry-ext-net/src/tests.rs

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📝 Walkthrough

Walkthrough

Changes

GC test evacuation coverage

Layer / File(s)	Summary
Forced evacuation test guard crates/perry-ext-net/src/tests.rs	GcTestGuard forces evacuation, preserves the prior PERRY_GC_FORCE_EVACUATE value, uses shadow-stack slot 1, and restores the environment during cleanup.
Scanner relocation assertions crates/perry-ext-net/src/tests.rs	The mutable scanner test adds a control root and verifies copying collection, object movement, and rewriting of both control and listener roots.

Estimated code review effort: 2 (Simple) | ~10 minutes

✨ 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 merge/b19

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