runtime: builtin own-property descriptor attributes wrong + getOwnPropertyDescriptor returns undefined

[proggeramlug]

Summary

Built-in own properties are installed with wrong descriptor attributes, and
Object.getOwnPropertyDescriptor returns undefined for many builtin own
properties. A fresh parity sweep (2026-06-02, on top of the #3655 fixes) shows
~170 failures in this single subsystem — now the largest behavioral cluster.

This is the direct follow-on to #3655 / closed #3143: those made name/length
exist as own properties, but (a) their descriptor flags are wrong and (b) other
builtin own properties aren't visible to the reflection APIs at all.

Two sub-bugs (same subsystem)

(a) Wrong descriptor attributes — ~140 failures. Builtin name/length/
method/constant own properties report the wrong {writable, enumerable, configurable}. Spec: function name/length are {writable:false, enumerable:false, configurable:true}. Perry reports them non-configurable
(and some as writable).

• built-ins/ArrayBuffer/{name,length}.js — "length descriptor should be configurable" / "should not be writable"
• built-ins/AsyncFunction/{instance-has-name,instance-length}.js
• built-ins/AsyncGeneratorFunction/{name,length}.js
• spans TypedArray, NativeErrors, Map, Set, WeakMap, WeakSet, BigInt, Symbol,
  Boolean, ArrayBuffer (18 categories total)

(b) getOwnPropertyDescriptor returns undefined — ~30 failures. For builtin
methods/constants the descriptor lookup returns undefined, so test262's
verifyProperty dereferences it ("Cannot read properties of undefined (reading
'enumerable'/'value')") or Object(undefined) throws ("Cannot convert undefined
or null to object").

• built-ins/Math/prop-desc.js — Cannot read properties of undefined (reading 'enumerable')
• built-ins/Math/{length,name}.js — … (reading 'value')
• built-ins/ArrayIteratorPrototype/{length,name}.js, AsyncFunction/AsyncFunction-{length,name,prototype}.js — Cannot convert undefined or null to object

Repro

console.log(Object.getOwnPropertyDescriptor(Array.from, 'name'));
// expect { value:'from', writable:false, enumerable:false, configurable:true }
console.log(Object.getOwnPropertyDescriptor(Math, 'abs'));   // Perry: undefined
console.log(Object.getOwnPropertyDescriptor(Math.abs, 'length')); // Perry: undefined

Why high-leverage

One descriptor-installation/reflection fix clears ~170 failures across ~25
categories, and unblocks verifyProperty-based assertions that currently abort
on this check across the whole test262 built-ins tree.

Suggested scope

(1) Install builtin own name/length/method/constant properties with the
spec-correct descriptor attributes; (2) make Object.getOwnPropertyDescriptor /
getOwnPropertyNames see builtin own properties (Math, iterator prototypes,
function objects).

---

Filed from the parity-gap radar (scripts/parity_gap_report.py), 2026-06-02
re-sweep. Follow-on to #3655 / #3143.

[andrewtdiz]

I am taking this as part of a focused runtime descriptor/prototype-method cut with #4141. Intended PR scope: make builtin own method/constant descriptors visible through Object.getOwnPropertyDescriptor/Object.getOwnPropertyNames for representative builtin namespaces/functions, install Generator/AsyncGenerator prototype method descriptors, and cover the current reflection regressions with focused parity tests. Non-goals: the active TypedArray constructor PR #4143 and unrelated primitive reflective brand checks in #4115.

[andrewtdiz]

Opened draft PR #4149 for a focused descriptor slice:

• installs descriptor-visible Math own methods/constants with Node-compatible attrs
• keeps escaped Math. reads routed through the real namespace object
• adds parity coverage for Math method/constant descriptors and function name/length descriptors

Validation includes the Node 25 descriptor parity filter, generator-intrinsics smoke, cargo build, fmt, diff, and file-size checks.

[andrewtdiz]

Updated draft PR #4149 with the rebased descriptor implementation at commit 2ed014f. The refreshed cut adds escaped Math method routing, the focused Math/global descriptor fixture, the generator prototype descriptor fixture, and current local validation: release build, both descriptor parity filters, cargo runtime object tests, fmt, diff checks, and file-size check.