0155 - Goccia.build reports a GC-stress build

Date: 2026-10-22 Area: runtime, testing, gc Related: ADR 0024, #1679

Context

The weekly GC-stress job now runs every tests/ file under the GC-stress build, which collects every 8 dispatched instructions. A collection marks the whole live heap, so a case that builds N objects costs time proportional to N times the heap. Seventeen files build thousands to hundreds of thousands of objects (nested Proxies, bound-function and class chains, the deep chains the marker tests, WeakMap chains, FinalizationRegistry registrations, long source lists) and ran past a 15-minute cap under stress, though each passes in seconds in an ordinary build. Their small cases are the ones most likely to catch a missing GC root, so excluding or time-capping whole files loses coverage the job exists to provide.

Decision

Goccia.build.gcStress is true in a GC-stress build and false otherwise. It is an enumerable, read-only boolean beside os, arch and date, fixed at compile time by GOCCIA_GC_STRESS. A test reads it to shrink a large N under stress, or to skip a case whose point is a size past an engine bound, while its other cases still run under stress.

Considered options

• A per-file list in scripts/gc-stress.ts with a short wall-clock cap, reported as stress-slow. Rejected: a capped file reports nothing about its fast cases.
• An environment variable read by the test runner. Rejected: it reaches only the test runner, and the build, not the environment, decides the collection schedule.

Consequences

• One more compile-time property on Goccia.build; ordinary builds report false.
• Tests that rely on it must also guard typeof Goccia, as other Goccia.build users do, so they still run on other engines.