refactor: use our own merge instead of lodash

We have a narrow set of rules for merging objects and lodash's more
aggressive merge may have unintended consequences when the values
being merged are not plain objects.

package.json

@@ -40,8 +40,6 @@
  "duplexer3": "^0.1.4",
  "extend": "^3.0.1",
  "get-stream": "^3.0.0",
- "lodash.clonedeep": "^4.5.0",
- "lodash.mergewith": "^4.6.1",
  "mimic-response": "^1.0.0",
  "p-cancelable": "^0.5.0",
  "to-readable-stream": "^1.0.0",

readme.md

@@ -406,12 +406,14 @@ client.get('/demo');
 
 #### got.assignOptions(parentOptions, newOptions)
 
-Extends parent options. Options are deeply merged to a new object as follows:
-
-- If either value is `null`, a primitive, or an `Array`, the result is the newOptions value.
-- If the parentOptions value is an instance of `URL`, the resulting value is the result of `new URL(new, parent)`.
-- If the newOptions value is `undefined` the key is removed.
-- If the newOptions value is an `Object`, its values are merged recursively.
+Extends parent options. Options are deeply merged to a new object. The value of each key is determined as follows:
+
+- If the newOptions value is `undefined` the key is omitted from the result.
+- If the parentOptions value is an instance of `URL` and the newOptions value is a `string` or `URL`, a new URL instance is created with the p `new URL(new, parent)`.
+- If the newOptions value is a plain `Object`
+ - If the parentOptions value is a plain `Object`, both values are merged recursively into a new `Object`.
+ - Otherwise, only the newOptions value is merged recurively into a new `Object`.
+- Otherwise, the newOptions value is assigned to the key.
 
 Avoid using [object spread](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax#Spread_in_object_literals) as it doesn't work recursively:
 

source/assign-options.js

@@ -1,36 +1,30 @@
 const url = require('url');
-const mergeWith = require('lodash.mergewith');
-const cloneDeep = require('lodash.clonedeep');
 const is = require('@sindresorhus/is');
 
 module.exports = (defaults, options = {}) => {
- return mergeWith(
- {opts: cloneDeep(defaults)},
- {opts: options},
- customizer
- ).opts;
+ return merge({}, defaults, options);
 };
 
-function customizer(objValue, srcValue) {
- if (is.array(srcValue) || is.array(objValue)) {
- return cloneDeep(srcValue);
- }
- if (objValue instanceof url.URL) {
- return new url.URL(srcValue, objValue);
- }
- if (![objValue, srcValue].some(is.array) && [objValue, srcValue].every(is.object)) {
- // When both args are non-array objects, delete keys for which the source
- // value is undefined (null is a significant value places, e.g. `encoding`).
- const deleteKeys = [];
- for (const key in srcValue) {
- if (is.undefined(srcValue[key])) {
- deleteKeys.push(key);
+function merge(target = {}, ...sources) {
+ for (const source of sources) {
+ for (const [key, sourceValue] of Object.entries(source)) {
+ const targetValue = target[key];
+ if (is.undefined(sourceValue)) {
+ delete target[key];
+ } else if (is.urlInstance(targetValue) && (
+ is.urlInstance(sourceValue) || is.string(sourceValue)
+ )) {
+ target[key] = new url.URL(sourceValue, targetValue);
+ } else if (is.plainObject(sourceValue)) {
+ if (is.plainObject(targetValue)) {
+ target[key] = merge({}, targetValue, sourceValue);
+ } else {
+ target[key] = merge({}, sourceValue);
+ }
+ } else {
+ target[key] = sourceValue;
  }
  }
- const result = mergeWith(objValue, srcValue, customizer);
- for (const key of deleteKeys) {
- delete result[key];
- }
- return result;
  }
+ return target;
 }

test/create.js

@@ -77,11 +77,11 @@ test('custom headers (extend)', async t => {
  t.is(headers.unicorn, 'rainbow');
 });
 
-test('extend overwrites arrays with copy', t => {
+test('extend overwrites arrays', t => {
  const statusCodes = [408];
  const a = got.extend({retry: {statusCodes}});
  t.deepEqual(a.defaults.options.retry.statusCodes, statusCodes);
- t.not(a.defaults.options.retry.statusCodes, statusCodes);
+ t.is(a.defaults.options.retry.statusCodes, statusCodes);
 });
 
 test('extend removes object values set to undefined', t => {