codegen: derived-ctor this-TDZ on standalone constructor-symbol path (toward #5345)

[proggeramlug]

What

A derived class constructor that never calls super() leaves this uninitialized, so the implicit return this (spec GetThisBinding) must throw a ReferenceError. Perry's inline new path (lower_new) already enforces this, but the default construction path routes new C(...) through the shared <class>_constructor symbol (force_ctor_call), which lacked the check. As a result:

class A extends Array { constructor() {} }
new A();   // should throw ReferenceError — Perry constructed silently

This mirrors the inline path's guard in compile_method's standalone constructor-symbol emission, reusing the exact same predicate combination already battle-tested on the inline path:

• ctor_body_calls_super — a direct super() suppresses the throw
• ctor_body_closure_calls_super + ctor_body_uses_this — a closure-captured super() suppresses, unless the body also dereferences this directly
• ctor_body_has_value_return — a value-bearing return takes the return-override path instead

The four predicates were pub(super) in lower_call::new_helpers; they're promoted to pub(crate) and re-exported so codegen/method.rs can share them (no logic duplication).

Results

Full test262 language/{statements,expressions}/class sweep (8426 cases, differential vs node --experimental-strip-types):

	pass	runtime-fail	parity
before	5046	252	94.0%
after	5070	228	94.4%

+24 cases fixed, 0 regressions. Confirmed by diffing the failing-test sets before/after (not just counts), and by perry-codegen unit tests (16 passed).

Fixes:

• subclass/builtin-objects/*/super-must-be-called (Array, ArrayBuffer, Boolean, DataView, Date, Error, Function, Map, NativeError/{Eval,Range,Reference,Syntax,Type,URI}Error, Number, Promise, RegExp, Set, String, WeakMap, WeakSet)
• subclass/builtin-objects/Object/constructor-return-undefined-throws
• subclass/class-definition-null-proto-this

A spot-check of valid super-calling shapes (conditional super, super in try, super after statements, no-own-ctor forwarding, multi-level subclass, return-override) constructs correctly and matches Node — no false-positive throws.

This is a contained slice of the larger #5345 class tail; it does not close the tracker.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Enhanced ECMAScript compliance for derived constructors. The compiler now enforces the "this-before-super" rule by detecting derived constructors that never call super() and emitting appropriate reference errors to prevent undefined behavior during runtime.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3345673f-0345-47ad-9a9f-8b438c6f7fb0

📥 Commits

Reviewing files that changed from the base of the PR and between f141748 and 88f3603.

📒 Files selected for processing (3)

• crates/perry-codegen/src/codegen/method.rs
• crates/perry-codegen/src/lower_call/mod.rs
• crates/perry-codegen/src/lower_call/new_helpers.rs

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📝 Walkthrough

Walkthrough

Four constructor-body predicate helpers (ctor_body_calls_super, ctor_body_closure_calls_super, ctor_body_uses_this, ctor_body_has_value_return) are widened from pub(super) to pub(crate) in new_helpers.rs and re-exported from lower_call/mod.rs. These predicates are then used in compile_method to detect derived constructors that never call super() and emit a js_throw_reference_error_this_before_super call, terminating the block as unreachable.

Changes

Derived Constructor TDZ Enforcement

Layer / File(s)	Summary
Widen ctor-body predicate visibility and re-export crates/perry-codegen/src/lower_call/new_helpers.rs, crates/perry-codegen/src/lower_call/mod.rs	ctor_body_calls_super, ctor_body_closure_calls_super, ctor_body_uses_this, and ctor_body_has_value_return are widened from pub(super) to pub(crate) in new_helpers.rs. A new pub(crate) use new_helpers::{...} block re-exports all four from lower_call/mod.rs.
Emit this-before-super throw in compile_method crates/perry-codegen/src/codegen/method.rs	In the standalone constructor-symbol path of compile_method, a new ctor_no_super_throw predicate checks for derived constructors whose bodies never call super() (accounting for closure-super(), this-use, and value-return exceptions). When true, emits js_throw_reference_error_this_before_super and marks the block unreachable; otherwise falls through to the existing async/sync lowering.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• PerryTS/perry#5304: Both PRs operate on the same standalone constructor-symbol path in compile_method; #5304 controls when that symbol is emitted or inlined, while this PR adds the TDZ correctness check on that same path.

Poem

🐇 Hoppity-hop through the class hierarchy tree,
Where super() must come before this can be free!
No sneaking past TDZ with a derived ctor call—
A reference error awaits if you skip it at all.
The predicate checks, the block goes unreachable with glee,
ECMAScript compliance, enforced, just for thee! 🎉

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: enforcing derived-constructor TDZ (temporal dead zone / this-before-super) behavior on the standalone constructor-symbol code path, directly matching the file changes in method.rs.
Description check	✅ Passed	The description comprehensively covers the problem statement, solution approach, test results, and related issue reference. It includes what/why/how and concrete validation data, fully matching the template's Summary/Changes/Related issue/Test plan structure.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ 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 worktree-fix-5345-class-test262

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