Method mergeMappings

yaml/_loader_state.ts:430–460

(
    destination: Record<string, unknown>,
    source: Record<string, unknown>,
    overridableKeys: Set<string>,
  )

    if (detected) return { tag, anchor, kind: "sequence", result };
  }
  mergeMappings(
    destination: Record<string, unknown>,
    source: Record<string, unknown>,
    overridableKeys: Set<string>,
  ) {
    if (!isObject(source)) {
      throw this.#createError(
        "Cannot merge mappings: the provided source object is unacceptable",
      );
    }

    for (const [key, value] of Object.entries(source)) {
      if (Object.hasOwn(destination, key)) continue;
      // `Object.defineProperty` is significantly slower than direct
      // assignment in V8. Direct assignment produces an identical descriptor
      // (writable/enumerable/configurable) for ordinary keys; the only
      // sensitive case is `__proto__`, where direct assignment would mutate
      // the prototype chain instead of creating an own property.
      if (key === "__proto__") {
        Object.defineProperty(destination, key, {
          value,
          writable: true,
          enumerable: true,
          configurable: true,
        });
      } else {
        destination[key] = value;
      }
      overridableKeys.add(key);
    }
  }
  storeMappingPair(
    result: Record<string, unknown>,
    overridableKeys: Set<string>,