fix(hir): preserve class captures across loop iterations (#9528)

[proggeramlug]

Fixes lexical classic-for class captures that shared the final loop value across every evaluated class instance.

What changed

• Freshen the one-element shared-mutable capture cell at the ECMAScript per-iteration environment boundary, before the update expression runs.
• Leave var-headed loops on their existing shared-binding path.
• Add a structural HIR regression test and a Node-differential gap fixture covering immediate and delayed methods, field initializers, for-of, and the var control.

Verification

• Demonstrated the fixture on unfixed main: delayed classic-loop methods returned method-3 three times while Node returned method-0, method-1, method-2.
• cargo test -p perry-hir --lib: 376 passed, 0 failed, 1 ignored.
• Focused parity harness: 1 passed, 0 failed; output byte-identical to Node.
• Test registration checker passed.

Closes #9528

Summary by CodeRabbit

• Bug Fixes

  • Fixed class closures in for (let …) loops so each iteration retains its own captured value.
  • Preserved shared binding behavior for for (var …) loops.
  • Corrected per-iteration captures across classic for and for-of loops, including delayed methods and field initializers.

• Tests

  • Added regression coverage for lexical and var loop capture behavior.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Team

Run ID: 8c04899b-a138-43c7-b305-fd2cd8f93c75

📥 Commits

Reviewing files that changed from the base of the PR and between 3b9c9de and b93fc8a.

📒 Files selected for processing (4)

• changelog.d/9548-loop-class-captures.md
• crates/perry-hir/src/lower/shared_mutable_capture.rs
• crates/perry-hir/src/lower/tests.rs
• test-files/test_gap_9528_loop_class_capture.ts

Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review.

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📝 Walkthrough

Walkthrough

The loop lowering pass now creates fresh capture cells for lexical classic-for iterations before updates. Tests cover class captures in classic for, for-of, and var loops, including delayed methods and field initializers.

Changes

Loop class capture freshening

Layer / File(s)	Summary
Capture-cell lowering crates/perry-hir/src/lower/shared_mutable_capture.rs	Stmt::For records shared lexical bindings and prepends a LocalSet that copies the current value into a fresh capture cell before the update.
Capture regression coverage crates/perry-hir/src/lower/tests.rs, test-files/test_gap_9528_loop_class_capture.ts, changelog.d/9548-loop-class-captures.md	Tests verify fresh lexical cells, retained class values, for-of captures, and shared var behavior. The changelog documents the fix.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to b93fc

The change corrects lexical class captures across classic-for loop iterations while preserving var-loop behavior, preventing methods and initializers from observing the wrong loop value. No actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: thehypnoo

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 3 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main HIR fix for preserving class captures across loop iterations.
Description check	✅ Passed	The description explains the problem, lists the implementation and test changes, identifies issue #9528, and records verification results. It omits the formal checklist and optional screenshots sectio…
Linked Issues check	✅ Passed	The changes address issue #9528 by freshening lexical classic-for capture cells, preserving var sharing, and adding coverage for classic for, for-of, immediate and delayed methods, field initializers,…
Out of Scope Changes check	✅ Passed	The changelog entry, lowering change, structural HIR test, and regression fixture are directly related to the linked issue and stated pull request objectives. No unrelated changes are evident.

Full details: Description check

Explanation

The description explains the problem, lists the implementation and test changes, identifies issue #9528, and records verification results. It omits the formal checklist and optional screenshots section, but the required content is substantially present.

Full details: Linked Issues check

Explanation

The changes address issue #9528 by freshening lexical classic-for capture cells, preserving var sharing, and adding coverage for classic for, for-of, immediate and delayed methods, field initializers, retained instances, and the var control case.

Full details: Docstring Coverage

Explanation

Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 3 files. (1 skipped: 1 unsupported.)

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[proggeramlug]

Landed via merge train # (rebase-merge, your authorship preserved).

[proggeramlug]

Correction: the landing PR is #9549 — merged (rebase-merge, authorship preserved).