Use lodash.mergewith instead of deep-assign (#251)

Fixes #241.

lib/options-manager.js

@@ -2,7 +2,7 @@
 const os = require('os');
 const path = require('path');
 const arrify = require('arrify');
-const deepAssign = require('deep-assign');
+const mergeWith = require('lodash.mergewith');
 const multimatch = require('multimatch');
 const pathExists = require('path-exists');
 const pkgConf = require('pkg-conf');
@@ -43,6 +43,13 @@ const DEFAULT_CONFIG = {
 	}
 };
 
+// Keep the same behaviour in mergeWith as deepAssign
+const mergeFn = (prev, val) => {
+	if (Array.isArray(prev) && Array.isArray(val)) {
+		return val;
+	}
+};
+
 const normalizeOpts = opts => {
 	opts = Object.assign({}, opts);
 
@@ -85,7 +92,7 @@ const mergeWithPkgConf = opts => {
 	return Object.assign({}, conf, opts);
 };
 
-// Define the shape of deep properties for deepAssign
+// Define the shape of deep properties for mergeWith
 const emptyOptions = () => ({
 	rules: {},
 	settings: {},
@@ -96,10 +103,11 @@ const emptyOptions = () => ({
 });
 
 const buildConfig = opts => {
-	const config = deepAssign(
+	const config = mergeWith(
 		emptyOptions(),
 		DEFAULT_CONFIG,
-		opts
+		opts,
+		mergeFn
 	);
 
 	if (opts.space) {
@@ -199,8 +207,8 @@ const findApplicableOverrides = (path, overrides) => {
 
 const mergeApplicableOverrides = (baseOptions, applicableOverrides) => {
 	applicableOverrides = applicableOverrides.map(normalizeOpts);
-	const overrides = [emptyOptions(), baseOptions].concat(applicableOverrides);
-	return deepAssign.apply(null, overrides);
+	const overrides = [emptyOptions(), baseOptions].concat(applicableOverrides, mergeFn);
+	return mergeWith.apply(null, overrides);
 };
 
 // Creates grouped sets of merged options together with the paths they apply to.

package.json

@@ -72,7 +72,6 @@
 	"dependencies": {
 		"arrify": "^1.0.0",
 		"debug": "^2.2.0",
-		"deep-assign": "^1.0.0",
 		"eslint": "^3.18.0",
 		"eslint-config-xo": "^0.18.0",
 		"eslint-formatter-pretty": "^1.0.0",
@@ -86,6 +85,7 @@
 		"has-flag": "^2.0.0",
 		"ignore": "^3.2.6",
 		"lodash.isequal": "^4.4.0",
+		"lodash.mergewith": "^4.6.0",
 		"meow": "^3.4.2",
 		"multimatch": "^2.1.0",
 		"open-editor": "^1.0.1",