feat(lint): new rule, no-immediate-return

.eslintrc.js

@@ -1,13 +1,20 @@
 module.exports = {
   extends: ['kyt'],
 
+  plugins: ['kyt'],
+
   rules: {
     'no-underscore-dangle': [
       'error',
       {
         allow: ['__setExecReturnValue', '__setExecuteOnFiles', '__webpack_modules__', '__esModule'],
       },
     ],
+    'kyt/css-in-js-namespace': 'error',
+    'kyt/default-props': 'error',
+    'kyt/no-direct-moment-import': 'error',
+    'kyt/no-immediate-return': 'error',
+    'kyt/validate-double-underscore-dirs': 'error',
   },
 
   overrides: [

package.json

@@ -50,6 +50,7 @@
     "eslint-plugin-jest-formatting": "2.0.1",
     "eslint-plugin-json": "2.1.2",
     "eslint-plugin-jsx-a11y": "6.4.1",
+    "eslint-plugin-kyt": "file:packages/eslint-plugin-kyt",
     "eslint-plugin-prettier": "3.3.1",
     "eslint-plugin-react": "7.23.1",
     "eslint-plugin-react-hooks": "4.2.0",

packages/eslint-plugin-kyt/lib/index.js

@@ -1,11 +1,13 @@
-const defaultProps = require('./rules/default-props').rule;
 const cssInJsNamespace = require('./rules/css-in-js-namespace').rule;
+const defaultProps = require('./rules/default-props').rule;
 const noDirectMomentImport = require('./rules/no-direct-moment-import').rule;
+const noImmediateReturn = require('./rules/no-immediate-return').rule;
 const validateDoubleUnderscoreDirs = require('./rules/validate-double-underscore-dirs').rule;
 
 exports.rules = {
-  'default-props': defaultProps,
   'css-in-js-namespace': cssInJsNamespace,
+  'default-props': defaultProps,
   'no-direct-moment-import': noDirectMomentImport,
+  'no-immediate-return': noImmediateReturn,
   'validate-double-underscore-dirs': validateDoubleUnderscoreDirs,
 };

packages/eslint-plugin-kyt/lib/rules/no-immediate-return.js

@@ -0,0 +1,42 @@
+const message = 'Do not declare a variable and then immediately return it. Just return it.';
+
+exports.message = message;
+
+exports.rule = {
+  create: context => {
+    let inExpression;
+
+    const checkForImmediateReturn = node => {
+      if (inExpression || !node.body.body) {
+        return;
+      }
+
+      const len = node.body.body.length;
+      for (let i = 0; i < len; i += 1) {
+        const n = node.body.body[i];
+        const next = node.body.body[i + 1];
+        if (next && n.type === 'VariableDeclaration' && n.declarations.length === 1) {
+          const name = n.declarations[0].id.name;
+          if (next.type === 'ReturnStatement' && name === next.argument.name) {
+            context.report({
+              node: next,
+              message,
+            });
+          }
+        }
+      }
+    };
+
+    return {
+      ExpressionStatement() {
+        inExpression = true;
+      },
+      'ExpressionStatement:exit': () => {
+        inExpression = false;
+      },
+      FunctionDeclaration: checkForImmediateReturn,
+      ArrowFunctionExpression: checkForImmediateReturn,
+      FunctionExpression: checkForImmediateReturn,
+    };
+  },
+};

packages/eslint-plugin-kyt/tests/no-immediate-return.js

@@ -0,0 +1,53 @@
+const { RuleTester } = require('eslint');
+const { rule, message } = require('../lib/rules/no-immediate-return');
+
+RuleTester.setDefaultConfig({
+  parserOptions: {
+    ecmaVersion: 6,
+  },
+});
+
+const ruleTester = new RuleTester();
+
+ruleTester.run('no-immediate-return', rule, {
+  valid: [
+    {
+      code: `function Foo() { const foo = ''; const bar = ''; return foo; }`,
+    },
+    {
+      code: `const Foo = () => { const foo = ''; const bar = ''; return foo; }`,
+    },
+    {
+      code: `class Foo { render() { const foo = ''; const bar = ''; return foo; } }`,
+    },
+  ],
+  invalid: [
+    {
+      code: `function Foo() { const foo = ''; return foo; }`,
+      errors: [
+        {
+          message,
+          type: 'ReturnStatement',
+        },
+      ],
+    },
+    {
+      code: `const Foo = () => { const foo = ''; return foo; }`,
+      errors: [
+        {
+          message,
+          type: 'ReturnStatement',
+        },
+      ],
+    },
+    {
+      code: `class Foo { render() { const foo = ''; return foo; } }`,
+      errors: [
+        {
+          message,
+          type: 'ReturnStatement',
+        },
+      ],
+    },
+  ],
+});

packages/kyt-core/src/config/StartServerPlugin.js

@@ -42,12 +42,14 @@ class StartServerPlugin {
   _getExecArgv() {
     const { options } = this;
     const execArgv = (options.nodeArgs || []).concat(process.execArgv);
+    // eslint-disable-next-line kyt/no-immediate-return
     return execArgv;
   }
 
   _getArgs() {
     const { options } = this;
     const argv = options.args || [];
+    // eslint-disable-next-line kyt/no-immediate-return
     return argv;
   }