Merge pull request #15 from xjamundx/no-callback-literal

New Rule: no-callback-literal (fixes #12)

Author: feross

README.md

@@ -13,6 +13,7 @@ ESlint Rules for the Standard Linter
     'standard/object-curly-even-spacing': [2, "either"]
     'standard/array-bracket-even-spacing': [2, "either"],
     'standard/computed-property-even-spacing': [2, "even"]
+    'standard/no-callback-literal': [2, ["cb", "callback", "next"]]
   }
 }
 ```
@@ -24,4 +25,5 @@ There are several rules that were created specifically for the `standard` linter
 - `object-curly-even-spacing` - Like `object-curly-spacing` from ESLint except it has an `either` option which lets you have 1 or 0 spaces padding.
 - `array-bracket-even-spacing` - Like `array-bracket-even-spacing` from ESLint except it has an `either` option which lets you have 1 or 0 spacing padding.
 - `computed-property-even-spacing` - Like `computed-property-spacing` around ESLint except is has an `even` option which lets you have 1 or 0 spacing padding.
+- `no-callback-literal` - Ensures that we strictly follow the callback pattern with `undefined`, `false`, `null` or an error object in the first position of a callback.
 

index.js

@@ -4,11 +4,13 @@ module.exports = {
   rules: {
     'array-bracket-even-spacing': require('./rules/array-bracket-even-spacing.js'),
     'computed-property-even-spacing': require('./rules/computed-property-even-spacing.js'),
-    'object-curly-even-spacing': require('./rules/object-curly-even-spacing.js')
+    'object-curly-even-spacing': require('./rules/object-curly-even-spacing.js'),
+    'no-callback-literal': require('./rules/no-callback-literal.js')
   },
   rulesConfig: {
     'object-curly-even-spacing': 0,
     'array-bracket-even-spacing': 0,
-    'computed-property-even-spacing': 0
+    'computed-property-even-spacing': 0,
+    'no-callback-literal': 0
   }
 }

rules/no-callback-literal.js

@@ -0,0 +1,77 @@
+/**
+ * Ensures that the callback pattern is followed properly
+ * with an Error object (or undefined or null) in the first position.
+ */
+
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Helpers
+// ------------------------------------------------------------------------------
+
+/**
+ * Determine if a node has a possiblity to be an Error object
+ * @param  {ASTNode}  node  ASTNode to check
+ * @returns {boolean}       True if there is a chance it contains an Error obj
+ */
+function couldBeError (node) {
+  switch (node.type) {
+    case 'Identifier':
+    case 'CallExpression':
+    case 'NewExpression':
+    case 'MemberExpression':
+    case 'TaggedTemplateExpression':
+    case 'YieldExpression':
+      return true // possibly an error object.
+
+    case 'AssignmentExpression':
+      return couldBeError(node.right)
+
+    case 'SequenceExpression':
+      var exprs = node.expressions
+      return exprs.length !== 0 && couldBeError(exprs[exprs.length - 1])
+
+    case 'LogicalExpression':
+      return couldBeError(node.left) || couldBeError(node.right)
+
+    case 'ConditionalExpression':
+      return couldBeError(node.consequent) || couldBeError(node.alternate)
+
+    default:
+      return node.value === null || node.value === false
+  }
+}
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  meta: {
+    docs: {}
+  },
+
+  create: function (context) {
+    var callbackNames = context.options[0] || ['callback', 'next', 'cb']
+
+    function isCallback (name) {
+      return callbackNames.indexOf(name) > -1
+    }
+
+    return {
+
+      CallExpression: function (node) {
+        var errorArg = node.arguments[0]
+        if (errorArg && isCallback(node.callee.name)) {
+          if (!couldBeError(errorArg)) {
+            context.report(node, 'Unexpected literal in error position of callback.')
+          } else if (node.arguments.length > 1 && errorArg.type === 'Identifier') {
+            if (errorArg.name === 'undefined') {
+              context.report(node, 'Expected null instead found undefined.')
+            }
+          }
+        }
+      }
+    }
+  }
+}

tests/no-callback-literal.js

@@ -0,0 +1,85 @@
+/**
+ * @fileoverview Tests for the no-callback-literal rule
+ * @author Jamund Ferguson
+ * @copyright 2016 Jamund Ferguson. All rights reserved.
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+var RuleTester = require('eslint').RuleTester
+var rule = require('../rules/no-callback-literal')
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+var ruleTester = new RuleTester()
+ruleTester.run('no-callback-literal', rule, {
+  valid: [
+
+    // random stuff
+    'horse()',
+    'sort(null)',
+    'require("zyx")',
+    'require("zyx", data)',
+
+    // callback()
+    'callback()',
+    'callback(undefined)',
+    'callback(null)',
+    'callback(x)',
+    'callback(false)',
+    'callback(new Error("error"))',
+    'callback(friendly, data)',
+    'callback(null, data)',
+    'callback(x, data)',
+    'callback(new Error("error"), data)',
+
+    // cb()
+    'cb()',
+    'cb(false)',
+    'cb(undefined)',
+    'cb(null)',
+    'cb(null, "super")',
+
+    // next()
+    'next()',
+    'next(undefined)',
+    'next(null)',
+    'next(null, "super")',
+    'next(false, "super")',
+
+    // custom callback
+    {
+      code: 'callback(44); next("55"); power(new Error("super thing")); power(null);',
+      options: [['power']]
+    }
+  ],
+
+  invalid: [
+    // callback
+    { code: 'callback(undefined, "snork")', errors: [{ message: 'Expected null instead found undefined.' }] },
+    { code: 'callback("help")', errors: [{ message: 'Unexpected literal in error position of callback.' }] },
+    { code: 'callback("help", data)', errors: [{ message: 'Unexpected literal in error position of callback.' }] },
+
+    // cb
+    { code: 'cb(undefined, "snork")', errors: [{ message: 'Expected null instead found undefined.' }] },
+    { code: 'cb("help")', errors: [{ message: 'Unexpected literal in error position of callback.' }] },
+    { code: 'cb("help", data)', errors: [{ message: 'Unexpected literal in error position of callback.' }] },
+
+    // next
+    { code: 'next(undefined, "snork")', errors: [{ message: 'Expected null instead found undefined.' }] },
+    { code: 'next("help")', errors: [{ message: 'Unexpected literal in error position of callback.' }] },
+    { code: 'next("help", data)', errors: [{ message: 'Unexpected literal in error position of callback.' }] },
+
+    // custom callback name
+    {
+      code: 'nexty(44)',
+      options: [['nexty']],
+      errors: [{ message: 'Unexpected literal in error position of callback.' }]
+    }
+  ]
+})