✨ add no-callback-literal rule (#179)

Author: feross

docs/rules/no-callback-literal.md

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+# node/no-callback-literal
+
+> Ensures the Node.js error-first callback pattern is followed
+
+When invoking a callback function which uses the Node.js error-first callback pattern, all of your errors should either use the `Error` class or a subclass of it. It is also acceptable to use `undefined` or `null` if there is no error.
+
+## 📖 Rule Details
+
+When a function is named `cb` or `callback`, then it must be invoked with a first argument that is `undefined`, `null`, an `Error` class, or a subclass or `Error`.
+
+Examples of :-1: **incorrect** code for this rule:
+
+```js
+/*eslint node/no-callback-literal: "error" */
+
+cb('this is an error string');
+cb({ a: 1 });
+callback(0);
+```
+
+Examples of :+1: **correct** code for this rule:
+
+```js
+/*eslint node/no-callback-literal: "error" */
+
+cb(undefined);
+cb(null, 5);
+callback(new Error('some error'));
+callback(someVariable);
+```
+
+### Options
+
+```json
+{
+    "rules": {
+        "node/no-callback-literal": "error"
+    }
+}
+```
+
+## 🔎 Implementation
+
+- [Rule source](../../lib/rules/no-callback-literal.js)
+- [Test source](../../tests/lib/rules/no-callback-literal.js)

lib/rules/no-callback-literal.js

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+/**
+ * @author Jamund Ferguson
+ * See LICENSE file in root directory for full license.
+ */
+"use strict"
+
+module.exports = {
+    meta: {
+        docs: {
+            description:
+                "ensure Node.js-style error-first callback pattern is followed",
+            category: "Possible Errors",
+            recommended: false,
+            url:
+                "https://github.com/mysticatea/eslint-plugin-node/blob/v9.1.0/docs/rules/no-callback-literal.md",
+        },
+        type: "problem",
+        fixable: null,
+        schema: [],
+    },
+
+    create(context) {
+        const callbackNames = ["callback", "cb"]
+
+        function isCallback(name) {
+            return callbackNames.indexOf(name) > -1
+        }
+
+        return {
+            CallExpression(node) {
+                const errorArg = node.arguments[0]
+                const calleeName = node.callee.name
+
+                if (
+                    errorArg &&
+                    !couldBeError(errorArg) &&
+                    isCallback(calleeName)
+                ) {
+                    context.report({
+                        node,
+                        message:
+                            "Unexpected literal in error position of callback.",
+                    })
+                }
+            },
+        }
+    },
+}
+
+/**
+ * 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": {
+            const 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
+    }
+}

tests/lib/rules/no-callback-literal.js

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+/**
+ * @author Jamund Ferguson
+ * See LICENSE file in root directory for full license.
+ */
+"use strict"
+
+const RuleTester = require("eslint").RuleTester
+const rule = require("../../../lib/rules/no-callback-literal")
+
+const 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(new Error("error"))',
+        "callback(friendly, data)",
+        "callback(undefined, data)",
+        "callback(null, data)",
+        "callback(x, data)",
+        'callback(new Error("error"), data)',
+        "callback(x = obj, data)",
+        "callback((1, a), data)",
+        "callback(a || b, data)",
+        "callback(a ? b : c, data)",
+        "callback(a ? 1 : c, data)",
+        "callback(a ? b : 1, data)",
+
+        // cb()
+        "cb()",
+        "cb(undefined)",
+        "cb(null)",
+        'cb(undefined, "super")',
+        'cb(null, "super")',
+    ],
+
+    invalid: [
+        // callback
+        {
+            code: 'callback(false, "snork")',
+            errors: [
+                {
+                    message:
+                        "Unexpected literal in error position of callback.",
+                },
+            ],
+        },
+        {
+            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(false)",
+            errors: [
+                {
+                    message:
+                        "Unexpected literal in error position of callback.",
+                },
+            ],
+        },
+        {
+            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.",
+                },
+            ],
+        },
+        {
+            code: "callback((a, 1), data)",
+            errors: [
+                {
+                    message:
+                        "Unexpected literal in error position of callback.",
+                },
+            ],
+        },
+    ],
+})