Add no-object-as-default-parameter rule

docs/rules/no-object-as-default-parameter.md

@@ -0,0 +1,29 @@
+# Disallow the use of objects as default parameters
+
+Default parameters should not be passed to a function through an object literal. The `foo = {a: false}` parameter works fine if only used with one option. As soon as additional options are added, you risk replacing the whole `foo = {a: false, b: true}` object when passing only one option: `{a: true}`. For this reason, object destructuring should be used instead.
+
+
+## Fail
+
+```js
+const abc = (foo = {a: false}) => {};
+```
+
+```js
+const abc = (foo = {a: false, b: 123}) => {};
+```
+
+
+## Pass
+
+```js
+const abc = (foo = {}) => {};
+```
+
+```js
+const abc = (foo = false) => {};
+```
+
+```js
+const foo = ({a = false, b = 123}) => {};
+```

index.js

@@ -39,6 +39,7 @@ module.exports = {
 				'unicorn/no-nested-ternary': 'error',
 				'unicorn/no-new-buffer': 'error',
 				'unicorn/no-null': 'error',
+				'unicorn/no-object-as-default-parameter': 'error',
 				'unicorn/no-process-exit': 'error',
 				'unicorn/no-reduce': 'error',
 				'unicorn/no-unreadable-array-destructuring': 'error',

readme.md

@@ -55,6 +55,7 @@ Configure it in `package.json`.
 			"unicorn/no-nested-ternary": "error",
 			"unicorn/no-new-buffer": "error",
 			"unicorn/no-null": "error",
+			"unicorn/no-object-as-default-parameter": "error",
 			"unicorn/no-process-exit": "error",
 			"unicorn/no-reduce": "error",
 			"unicorn/no-unreadable-array-destructuring": "error",
@@ -116,6 +117,7 @@ Configure it in `package.json`.
 - [no-nested-ternary](docs/rules/no-nested-ternary.md) - Disallow nested ternary expressions. *(partly fixable)*
 - [no-new-buffer](docs/rules/no-new-buffer.md) - Enforce the use of `Buffer.from()` and `Buffer.alloc()` instead of the deprecated `new Buffer()`. *(fixable)*
 - [no-null](docs/rules/no-null.md) - Disallow the use of the `null` literal.
+- [no-object-as-default-parameter](docs/rules/no-object-as-default-parameter.md) - Disallow the use of objects as default parameters.
 - [no-process-exit](docs/rules/no-process-exit.md) - Disallow `process.exit()`.
 - [no-reduce](docs/rules/no-reduce.md) - Disallow `Array#reduce()` and `Array#reduceRight()`.
 - [no-unreadable-array-destructuring](docs/rules/no-unreadable-array-destructuring.md) - Disallow unreadable array destructuring.

rules/no-object-as-default-parameter.js

@@ -0,0 +1,38 @@
+'use strict';
+const getDocumentationUrl = require('./utils/get-documentation-url');
+
+const MESSAGE_ID = 'noObjectAsDefaultParameter';
+
+const objectParameterSelector = [
+	':matches(FunctionDeclaration, ArrowFunctionExpression)',
+	'>',
+	'AssignmentPattern',
+	'[left.type="Identifier"]',
+	'[right.type="ObjectExpression"]',
+	'[right.properties.length>0]'
+].join('');
+
+const create = context => {
+	return {
+		[objectParameterSelector]: node => {
+			context.report({
+				node,
+				messageId: MESSAGE_ID,
+				data: {parameter: node.left.name}
+			});
+		}
+	};
+};
+
+module.exports = {
+	create,
+	meta: {
+		type: 'problem',
+		docs: {
+			url: getDocumentationUrl(__filename)
+		},
+		messages: {
+			[MESSAGE_ID]: 'Do not use an object literal as default for parameter `{{parameter}}`.'
+		}
+	}
+};

test/no-object-as-default-parameter.js

@@ -0,0 +1,72 @@
+import test from 'ava';
+import avaRuleTester from 'eslint-ava-rule-tester';
+import rule from '../rules/no-object-as-default-parameter';
+
+const ruleTester = avaRuleTester(test, {
+	env: {
+		es6: true
+	}
+});
+
+const error = {
+	messageId: 'noObjectAsDefaultParameter',
+	data: {parameter: 'foo'}
+};
+
+ruleTester.run('no-object-as-default-parameter', rule, {
+	valid: [
+		'const abc = {};',
+		'const abc = {foo: 123};',
+		'function abc(foo) {}',
+		'function abc(foo = null) {}',
+		'function abc(foo = undefined) {}',
+		'function abc(foo = 123) {}',
+		'function abc(foo = true) {}',
+		'function abc(foo = \'bar\') {}',
+		'function abc(foo = 123, bar = \'foo\') {}',
+		'function abc(foo = {}) {}',
+		'function abc({foo = 123} = {}) {}',
+		'const abc = foo => {};',
+		'const abc = (foo = null) => {};',
+		'const abc = (foo = undefined) => {};',
+		'const abc = (foo = 123) => {};',
+		'const abc = (foo = true) => {};',
+		'const abc = (foo = \'bar\') => {};',
+		'const abc = (foo = 123, bar = \'foo\') => {};',
+		'const abc = (foo = {}) => {};',
+		'const abc = ({a = true, b = \'foo\'}) => {};',
+		'const {abc = {foo: 1}} = bar;',
+		'const {abc = {null: \'baz\'}} = bar;',
+		'const {abc = {foo: undefined}} = undefined;'
+	],
+	invalid: [
+		{
+			code: 'function abc(foo = {a: 123}) {}',
+			errors: [error]
+		},
+		{
+			code: 'function abc(foo = {a: false}) {}',
+			errors: [error]
+		},
+		{
+			code: 'function abc(foo = {a: \'bar\'}) {}',
+			errors: [error]
+		},
+		{
+			code: 'function abc(foo = {a: \'bar\', b: {c: true}}) {}',
+			errors: [error]
+		},
+		{
+			code: 'const abc = (foo = {a: false}) => {};',
+			errors: [error]
+		},
+		{
+			code: 'const abc = (foo = {a: 123, b: false}) => {};',
+			errors: [error]
+		},
+		{
+			code: 'const abc = (foo = {a: false, b: 1, c: "test", d: null}) => {};',
+			errors: [error]
+		}
+	]
+});