Backport: fix scanPrototypesFor cache when class init is in flight#38
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The memoization in 7d67a95 caches the merged prototype-chain values per (constructor, key) pair. When `customElements.define` upgrades a pre-existing element mid-class-body, the constructor runs before the subclass's `static <key> = ...` fields have initialized, so the first scan caches a result missing the subclass's own value. All subsequent instances then inherit the wrong merged metadata (e.g. empty assignableAttributes). Track the constructor's own-property status alongside each cached entry and recompute when it flips. Plugin-style in-place mutations to the cached arrays still propagate. Add a regression test in test/supportTest.js. Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
scanPrototypesForentry alongside the constructor'shasOwnProperty(key)status, and invalidates when it flips. Without this, an instance constructed mid-class-init (e.g.customElements.defineupgrading a pre-existing element before the subclass'sstatic <key> = ...field has run) locks in a result missing the subclass's own value, and every subsequent instance inherits the wrong merged metadata.test/supportTest.js.CHANGELOG.mdhunk to match the prior 1.x backports (Memoize scanPrototypesFor to avoid per-instance prototype walks #30, fix KompElement.include dedupe colliding on default-export plugins #35).Test plan
npm test— full suite passes (36 passing), including the four newscanPrototypesForcases.🤖 Generated with Claude Code