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import {Dictionary, PlatformShim} from '../typings/common-types.js';import {YError} from '../yerror.js';
let previouslyVisitedConfigs: string[] = [];let shim: PlatformShim;export function applyExtends(  config: Dictionary,  cwd: string,  mergeExtends: boolean,  _shim: PlatformShim): Dictionary {  shim = _shim;  let defaultConfig = {};
  if (Object.prototype.hasOwnProperty.call(config, 'extends')) {    if (typeof config.extends !== 'string') return defaultConfig;    const isPath = /\.json|\..*rc$/.test(config.extends);    let pathToDefault: string | null = null;    if (!isPath) {      try {        pathToDefault = require.resolve(config.extends);      } catch (_err) {        // maybe the module uses key for some other reason,        // err on side of caution.        return config;      }    } else {      pathToDefault = getPathToDefaultConfig(cwd, config.extends);    }
    checkForCircularExtends(pathToDefault);
    previouslyVisitedConfigs.push(pathToDefault);
    defaultConfig = isPath      ? JSON.parse(shim.readFileSync(pathToDefault, 'utf8'))      : require(config.extends);    delete config.extends;    defaultConfig = applyExtends(      defaultConfig,      shim.path.dirname(pathToDefault),      mergeExtends,      shim    );  }
  previouslyVisitedConfigs = [];
  return mergeExtends    ? mergeDeep(defaultConfig, config)    : Object.assign({}, defaultConfig, config);}
function checkForCircularExtends(cfgPath: string) {  if (previouslyVisitedConfigs.indexOf(cfgPath) > -1) {    throw new YError(`Circular extended configurations: '${cfgPath}'.`);  }}
function getPathToDefaultConfig(cwd: string, pathToExtend: string) {  return shim.path.resolve(cwd, pathToExtend);}
function mergeDeep(config1: Dictionary, config2: Dictionary) {  const target: Dictionary = {};  function isObject(obj: Dictionary | any): obj is Dictionary {    return obj && typeof obj === 'object' && !Array.isArray(obj);  }  Object.assign(target, config1);  for (const key of Object.keys(config2)) {    if (isObject(config2[key]) && isObject(target[key])) {      target[key] = mergeDeep(config1[key], config2[key]);    } else {      target[key] = config2[key];    }  }  return target;}