feat: new rule prefer-catch (#525)

Adds new rule `prefer-catch` to prefer `catch` over `then(a, b)` or `then(null, b)`.

Co-authored-by: Sebastian Good <[email protected]>

Author: brettz9

README.md

@@ -115,6 +115,7 @@ or start with the recommended rule set:
 | [param-names](docs/rules/param-names.md)                             | Enforce consistent param names and ordering when creating new promises.                    | ✅  |     |     |     |
 | [prefer-await-to-callbacks](docs/rules/prefer-await-to-callbacks.md) | Prefer `async`/`await` to the callback pattern.                                            |     |     |     |     |
 | [prefer-await-to-then](docs/rules/prefer-await-to-then.md)           | Prefer `await` to `then()`/`catch()`/`finally()` for reading Promise values.               |     |     |     |     |
+| [prefer-catch](docs/rules/prefer-catch.md)                           | Prefer `catch` to `then(a, b)`/`then(null, b)` for handling errors.                        |     |     |     | 🔧  |
 | [spec-only](docs/rules/spec-only.md)                                 | Disallow use of non-standard Promise static methods.                                       |     |     |     |     |
 | [valid-params](docs/rules/valid-params.md)                           | Enforces the proper number of arguments are passed to Promise functions.                   |     | ✅  |     |     |
 

__tests__/prefer-catch.js

@@ -0,0 +1,65 @@
+'use strict'
+
+const rule = require('../rules/prefer-catch')
+const { RuleTester } = require('./rule-tester')
+const ruleTester = new RuleTester({
+  parserOptions: {
+    ecmaVersion: 8,
+  },
+})
+
+const message = 'Prefer `catch` to `then(a, b)`/`then(null, b)`.'
+
+ruleTester.run('prefer-catch', rule, {
+  valid: [
+    'prom.then()',
+    'prom.then(fn)',
+    'prom.then(fn1).then(fn2)',
+    'prom.then(() => {})',
+    'prom.then(function () {})',
+    'prom.catch()',
+    'prom.catch(handleErr).then(handle)',
+    'prom.catch(handleErr)',
+  ],
+
+  invalid: [
+    {
+      code: 'hey.then(fn1, fn2)',
+      errors: [{ message }],
+      output: 'hey.catch(fn2).then(fn1)',
+    },
+    {
+      code: 'hey.then(fn1, (fn2))',
+      errors: [{ message }],
+      output: 'hey.catch(fn2).then(fn1)',
+    },
+    {
+      code: 'hey.then(null, fn2)',
+      errors: [{ message }],
+      output: 'hey.catch(fn2)',
+    },
+    {
+      code: 'hey.then(undefined, fn2)',
+      errors: [{ message }],
+      output: 'hey.catch(fn2)',
+    },
+    {
+      code: 'function foo() { hey.then(x => {}, () => {}) }',
+      errors: [{ message }],
+      output: 'function foo() { hey.catch(() => {}).then(x => {}) }',
+    },
+    {
+      code: `
+        function foo() {
+          hey.then(function a() { }, function b() {}).then(fn1, fn2)
+        }
+      `,
+      errors: [{ message }, { message }],
+      output: `
+        function foo() {
+          hey.catch(function b() {}).then(function a() { }).catch(fn2).then(fn1)
+        }
+      `,
+    },
+  ],
+})

docs/rules/prefer-catch.md

@@ -0,0 +1,29 @@
+# Prefer `catch` to `then(a, b)`/`then(null, b)` for handling errors (`promise/prefer-catch`)
+
+🔧 This rule is automatically fixable by the
+[`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+A `then` call with two arguments can make it more difficult to recognize that a
+catch error handler is present and can be less clear as to the order in which
+errors will be handled.
+
+## Rule Details
+
+The second argument of a `then` call may be thought to handle any errors in the
+first argument, but it will only handle errors earlier in the Promise chain.
+
+Examples of **incorrect** code for this rule:
+
+```js
+prom.then(fn1).then(fn2)
+prom.catch(handleErr).then(handle)
+```
+
+Examples of **incorrect** code for this rule:
+
+```js
+hey.then(fn1, fn2)
+hey.then(null, fn2)
+```

index.js

@@ -23,6 +23,7 @@ const pluginPromise = {
     'catch-or-return': require('./rules/catch-or-return'),
     'prefer-await-to-callbacks': require('./rules/prefer-await-to-callbacks'),
     'prefer-await-to-then': require('./rules/prefer-await-to-then'),
+    'prefer-catch': require('./rules/prefer-catch'),
     'no-native': require('./rules/no-native'),
     'no-callback-in-promise': require('./rules/no-callback-in-promise'),
     'no-promise-in-callback': require('./rules/no-promise-in-callback'),