bug: built-in prototype methods (Object/Number.prototype isPrototypeOf, hasOwnProperty, …) undefined as property values and via primitive receivers #2059

Summary

A function's built-in name own-property reads back undefined, and Object.getOwnPropertyDescriptor(fn, "name") returns undefined. Per spec, name is a { writable:false, enumerable:false, configurable:true } own data property.

Repro

function foo(a, b) {}
console.log(foo.name);    // expect: "foo"   — Perry: undefined
console.log(foo.length);  // expect: 2       — Perry: 2 (ok)
console.log(Object.getOwnPropertyDescriptor(foo, "name"));
// expect: {value:"foo", writable:false, enumerable:false, configurable:true}
// Perry:  undefined

Why it matters

built-ins/Function was ~20% in the #799 Test262 baseline, dominated (22× in the sample) by Cannot read properties of undefined (reading 'name'). It also breaks Test262's assert.throws, which reports thrown.constructor.name (assert.js:130-131) — degrading error reporting across all negative tests. And it breaks ordinary fn.name usage (router tables, DI containers, logging).

Likely cause

name (and likely other built-in own data properties) is not installed on function objects. Note length works, so the function-object property machinery exists — name specifically is not being populated from the declaration/binding identifier.

Related: #1802 (custom property on a function object reads back undefined) — adjacent, but this is the spec built-in name.

Surfaced by the #799 Test262 radar. Part of #793.