fix(hir,runtime): Annex B B.3.3 hoisting precedence + legacy method aliases (#5346)

[proggeramlug]

Summary

Three self-contained, non-eval clusters from the test262 annexB tail (#5346). Builds on the already-merged #5356 (B.3.3 skip cases). All changes fully flip tests green with zero regressions.

annexB parity: 776/1026 (75.6%) → 793/1026 (77.3%), +17 pass.

1. B.3.3 hoisting precedence — global-code/*existing-fn-no-init (8)

When a sloppy block-nested function f(){} and a same-named top-level function f(){} coexist at program scope, F is already in declaredFunctionNames, so B.3.3 must not create a fresh undefined legacy var — the function declaration owns the entry binding.

A non-reassigned top-level function f is otherwise called straight through lookup_func and never bound to the var slot, so the legacy var shadowed it as undefined and f() threw TypeError: value is not a function at entry:

assert.sameValue(f(), 'outer declaration'); // Perry threw here
if (true) function f() { return 'inner declaration'; }
function f() { return 'outer declaration'; }

Fix: seed the legacy-var slot with FuncRef(func_id) (and mark it function-valued) when a same-named top-level function exists. The block-level declaration still overwrites it, so existing-fn-update stays green. lower/lower_module_fn.rs.

2. String.prototype.trimLeft / trimRight (8)

These Annex B legacy names must be the same function objects as trimStart/trimEnd — trimLeft === trimStart, .name === "trimStart", real own data properties — not independent thunks (they already worked as method calls, but String.prototype.trimLeft was undefined). Alias the installed property value.

3. Date.prototype.toGMTString (1)

Same legacy-alias requirement: toGMTString === toUTCString. It was installed as a second independent thunk, failing the reference-equality check.

A new install_proto_method_alias helper installs an alias as the same function object with the standard { writable: true, enumerable: false, configurable: true } method descriptor.

Validation

• Each fix matches node v26 exactly (trim aliases + .name, toGMTString === toUTCString, f() = outer at entry / inner after the block).
• Full annexB differential: +17 pass, 0 regressions (diffed failure sets before/after).
• Smoke-tested ordinary function hoisting, reassignment + block-shadow, and the B.3.3-positive (block-only) case — all match Node.

Remaining annexB tail (separate follow-ups, deliberately out of scope)

• regex (~25): legacy/lookbehind/control escapes — the categorical Rust regex crate gap noted in CLAUDE.md.
• String.prototype.substr edge cases (~6): length/start coercion + error ordering.
• escape/unescape not-a-constructor (2): the per-closure non-constructable flag already makes isConstructor correct via the dynamic path, but the literal new escape() codegen special-case bypasses js_new_function_construct — needs a codegen change.
• B.3.4 var-in-catch (catch-redeclared-*, 4): catch-param vs hoisted-var assignment resolution.
• dynamic eval (~184): AOT limitation, per the issue.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved Annex B compatibility for legacy JavaScript method aliases by preserving function identity for prototype methods (e.g., Date.prototype.toGMTString now aliases toUTCString).
  • Ensured String.prototype.trimLeft and String.prototype.trimRight reference the same functions as trimStart and trimEnd, respectively.
  • Fixed sloppy-mode hoisting behavior for block-nested function declarations to maintain correct entry-time semantics.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 36f144e4-a0ca-4aa2-8de0-5db2f2817f13

📥 Commits

Reviewing files that changed from the base of the PR and between 2354f8e and cdca560.

📒 Files selected for processing (5)

• clusterAg
• crates/perry-hir/src/lower/lower_module_fn.rs
• crates/perry-runtime/src/object/date_proto_thunks.rs
• crates/perry-runtime/src/object/global_this.rs
• crates/perry-runtime/src/object/string_proto_thunks.rs

🚧 Files skipped from review as they are similar to previous changes (4)

• crates/perry-runtime/src/object/string_proto_thunks.rs
• crates/perry-runtime/src/object/date_proto_thunks.rs
• crates/perry-hir/src/lower/lower_module_fn.rs
• crates/perry-runtime/src/object/global_this.rs

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📝 Walkthrough

Walkthrough

The PR implements two Annex B compliance fixes: in the HIR lowerer, hoisted var slots for block-nested sloppy-mode function declarations are now conditionally seeded with a FuncRef (instead of always Undefined) when a same-named implemented top-level function exists. In the runtime, a new install_proto_method_alias helper ensures legacy aliases (trimLeft, trimRight, toGMTString) are reference-identical to their canonical counterparts.

Changes

Annex B compliance: hoisted var seeding and prototype method aliasing

Layer / File(s)	Summary
Annex B.3.3 hoisted var slot initialization crates/perry-hir/src/lower/lower_module_fn.rs	The prepass in lower_module_full now seeds the hoisted var slot with Expr::FuncRef(func_id) and marks it function-valued when a same-named implemented top-level function is found in functions_with_bodies; otherwise it retains Expr::Undefined.
install_proto_method_alias helper + String/Date Annex B aliases crates/perry-runtime/src/object/global_this.rs, crates/perry-runtime/src/object/string_proto_thunks.rs, crates/perry-runtime/src/object/date_proto_thunks.rs	Adds install_proto_method_alias that assigns an existing function value to an alias property name with standard built-in descriptor attributes. Wires trimLeft→trimStart, trimRight→trimEnd, and toGMTString→toUTCString through this helper instead of installing independent thunks.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• test262 annexB/language tail — 303 fails after #5319 (B.3.3 residual + missed-negatives + dynamic eval) #5346: The hoisted var initialization fix (undefined→FuncRef) directly addresses the identified Annex B.3.3 "initialized binding is not..." compliance gap where hoisted slots must be seeded with the function reference when a same-named top-level function exists.

Possibly related PRs

• PerryTS/perry#5319: Introduces the Annex B.3.3 sloppy-mode block-function hoisting prepass in lower_module_full that this PR builds upon, using that prepass logic to seed the hoisted var slots conditionally.
• PerryTS/perry#5356: Also modifies Annex B.3.3 handling of the legacy hoisted var for block-nested sloppy functions, specifically adjusting when the var is skipped, which is the complementary decision point to this PR's slot-initialization change.

Poem

🐇 Hop, hop! The slots are seeded right,
No more undefined in the night.
FuncRef blooms where functions roam,
And aliases share a single home—
trimLeft, toGMTString, side by side,
With canonical kin they proudly hide. ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main changes: fixing Annex B B.3.3 hoisting precedence and implementing legacy method aliases, with a specific issue reference.
Description check	✅ Passed	The description comprehensively covers all three fixes with clear explanations, validation details, code examples, and explicitly defers remaining work, despite missing some optional template sections.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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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