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in operator: inherited properties on Object.create receivers report false #6145

Description

@proggeramlug

Summary

key in obj returns false for every inherited property when obj was created
by Object.create(proto) — both the custom prototype's own keys and
Object.prototype members.

Repro

const o = Object.create({ mid: 1 });
o.own = 2;
console.log("own" in o);       // true  ✓
console.log("mid" in o);       // node: true   perry: false  ✗
console.log("toString" in o);  // node: true   perry: false  ✗
console.log("mid" in Object.create(Object.create({ mid: 1 }))); // node: true  perry: false ✗

Root cause

Object.create(proto) models [[Prototype]] via a synthetic class_id →
prototype object
(CLASS_PROTOTYPE_OBJECTS), the mechanism the field-GET path
walks (resolve_proto_chain_field). The in operator's walk
(ordinary_has_property in has_property.rs) only follows recorded static
prototypes (object_static_prototype), which Object.create never populates,
so it stops at the receiver's own keys. The Object.prototype fallback
(ordinary_object_prototype_property_value) additionally bails when
class_id != 0, and the Object.create result carries the synthetic class_id —
so even "toString" in o was reported absent.

class / Object.setPrototypeOf / __proto__ receivers were already correct.

Activity

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