fix(runtime): WeakMap/WeakSet method VALUE reads resolve the prototype thunk

[proggeramlug]

Problem

A value read of a WeakMap/WeakSet method (w.add, wm.set,
typeof w.has) returned undefined. Method calls (w.add(k)) dispatch
through js_native_call_method's weak arms, but the by-name property-read path
(js_object_get_field_by_name) had no equivalent, so a bare read yielded
undefined and any subsequent call or .bind threw:

const s = new WeakSet();
const f = s.add.bind(s, obj);   // TypeError: Bind must be called on a function

react-server-dom's client-chunk preload dedup does exactly
u.add.bind(u, chunk) on a module-level WeakSet, so every Next.js App Router
dynamic route 500'd during flight resolution (#5989).

Fix

In js_object_get_field_by_name, detect a WeakMap/WeakSet receiver (via the
existing GC-header-safe weak_class_id_from_receiver, already guarded against
the small-handle band) and, for a known method name with no own-key shadow,
return the brand-checking prototype thunk from
collection_proto_method_value — the same thunk Map/Set value reads already
resolve. Own keys keep precedence (a fresh instance only carries the internal
__perry_wk_entries sentinel, which is not a method name).

Validation

New gap test test_gap_weak_method_value_read.ts, byte-for-byte against
node --experimental-strip-types: typeof reads, .bind(...) + call,
stored-method .call(...), WeakMap.set/get round-trip, the bound value being
a real function (.bind/.call present), a method-call regression guard, and
own-key precedence over a shadowed method name.

Summary by CodeRabbit

• Bug Fixes
  • Fixed method lookups on WeakMap and WeakSet instances so methods such as get, set, has, delete, and add return callable functions as expected.
  • Preserved support for detached and bound method calls.
  • Ensured custom instance properties continue to override prototype methods.

[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: 1b5c2f72-17fa-47ea-8918-4a903388f0b1

📥 Commits

Reviewing files that changed from the base of the PR and between 7b54ac6 and 089ebf4.

📒 Files selected for processing (2)

• crates/perry-runtime/src/object/field_get_set/get_field_by_name.rs
• test-files/test_gap_weak_method_value_read.ts

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📝 Walkthrough

Walkthrough

WeakMap and WeakSet field lookup now returns callable prototype methods for recognized method names when no own property shadows them. A regression test covers bound calls, method-value calls, direct calls, function characteristics, and own-property precedence.

Changes

Weak collection method values

Layer / File(s)	Summary
WeakMap and WeakSet method resolution crates/perry-runtime/src/object/field_get_set/get_field_by_name.rs	Adds a weak collection slow path that maps recognized method names to prototype thunk values while preserving own-property lookup precedence.
Method value regression coverage test-files/test_gap_weak_method_value_read.ts	Tests WeakMap and WeakSet method reads through bind and call, direct invocation, callable function properties, and own-property shadowing.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• PerryTS/perry#5550: Addresses related WeakMap/WeakSet method handling during HIR pre-scanning and lowering.
• PerryTS/perry#5851: Modifies related runtime field resolution and weak method prototype dispatch.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description is detailed, but it doesn't follow the repository template and omits required sections like Summary, Changes, Related issue, and Test plan.	Rewrite it to match the template headings and add a Related issue, a concrete Test plan with commands run, and the checklist items.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the main runtime change: WeakMap/WeakSet method value reads now resolve to prototype thunks.
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.

✨ 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 fix/weak-method-value-read

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