import { DeepPartial } from './deep-partial.js';
/**
 * Recursively merge `source` into `target`, producing a new object.
 *
 * - Plain objects are merged key-by-key; nested objects are merged recursively.
 * - `undefined` values in `source` are skipped (existing `target` values are preserved).
 * - Non-plain values (arrays, `Date`, `RegExp`, primitives, functions) in `source`
 *   replace the corresponding `target` value outright.
 *
 * @param target - The base object.
 * @param source - Partial overrides to apply on top of `target`.
 * @returns A new merged object of type `T`.
 */
export declare function deepmerge<T>(target: T, source: DeepPartial<T>): T;