Decline for-loop environment reuse when a pattern default embeds a closure#2739
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ForLoopMayCapture scanned init declarator initializers, test, update and
body for capturing closures, but never the declarator binding patterns
themselves — a destructuring default like
for (let i = 0, { f = () => i } = {}; i < 3; i++) { fns.push(f); }
embeds a closure the scan missed, so the per-iteration environment was
reused/pooled in place and the escaped closure observed the final value
of i (3) instead of the captured iteration's (0, matching V8), or a
reset binding after the loop re-entered.
Same eligibility-scan family as the for-header TDZ fix (sebastienros#2709); the
gate only declines an optimization, generic per-iteration semantics
take over.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0115tQFNyyQqc1HQGPLUgZND
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Pre-release review find in the same eligibility-scan family as #2709.
ForLoopMayCapturescanned the init declarators' initializers (plus test/update/body) for capturing closures, but never the declarator binding patterns themselves. A destructuring default embeds an expression the scan missed:With the closure invisible to the scan, the loop reused/pooled its per-iteration environment in place, so the escaped closure observed the final
i— and with environment pooling, re-entering the loop could reset the binding the closure captured. The fix runs the existing escape visitor over non-identifier declarator ids; the gate only declines an optimization, so generic per-iteration semantics take over.Repro verified against V8 before/after. Full suite plus Test262 green.
🤖 Generated with Claude Code
https://claude.ai/code/session_0115tQFNyyQqc1HQGPLUgZND