Add support for eslint when initializing cloud functions (firebase#242)

* added .eslintrc file, lint option in package.json, and lint rules in eslint.json

lib/init/features/functions/javascript.js

@@ -1,17 +1,36 @@
 'use strict';
 
+var _ = require('lodash');
 var fs = require('fs');
 var path = require('path');
 
 var npmDependencies = require('./npm-dependencies');
+var prompt = require('../../../prompt');
 
 var TEMPLATE_ROOT = path.resolve(__dirname, '../../../../templates/init/functions/javascript/');
 var INDEX_TEMPLATE = fs.readFileSync(path.join(TEMPLATE_ROOT, 'index.js'), 'utf8');
-var PACKAGE_TEMPLATE = fs.readFileSync(path.join(TEMPLATE_ROOT, 'package.json'), 'utf8');
+var PACKAGE_LINTING_TEMPLATE = fs.readFileSync(path.join(TEMPLATE_ROOT, 'package.lint.json'), 'utf8');
+var PACKAGE_NO_LINTING_TEMPLATE = fs.readFileSync(path.join(TEMPLATE_ROOT, 'package.nolint.json'), 'utf8');
+var ESLINT_TEMPLATE = fs.readFileSync(path.join(TEMPLATE_ROOT, 'eslint.json'), 'utf8');
 
 module.exports = function(setup, config) {
-  return config.askWriteProjectFile('functions/package.json', PACKAGE_TEMPLATE).then(function() {
-    return config.askWriteProjectFile('functions/index.js', INDEX_TEMPLATE);
+  return prompt(setup.functions, [
+    {
+      name: 'lint',
+      type: 'confirm',
+      message: 'Do you want to use ESLint to catch probable bugs and enforce style?',
+      default: true
+    }
+  ]).then(function() {
+    if (setup.functions.lint) {
+      _.set(setup, 'config.functions.predeploy', 'npm --prefix functions run lint');
+      return config.askWriteProjectFile('functions/package.json', PACKAGE_LINTING_TEMPLATE).then(function() {
+        config.askWriteProjectFile('functions/.eslintrc.json', ESLINT_TEMPLATE);
+      });
+    }
+    return config.askWriteProjectFile('functions/package.json', PACKAGE_NO_LINTING_TEMPLATE);
+  }).then(function() {
+    return config.askWriteProjectFile('functions/src/index.js', INDEX_TEMPLATE);
   }).then(function() {
     return npmDependencies.askInstallDependencies(setup, config);
   });

templates/init/functions/javascript/eslint.json

@@ -0,0 +1,79 @@
+{
+  "parserOptions": {
+    // Required for certain syntax usages
+    "ecmaVersion": 6
+  },
+  "plugins": [
+    "promise"
+  ],
+  "rules": {
+    // Warn against comparing against -0
+    "no-compare-neg-zero": 1,
+
+    // Warn against assignment operators in conditional expressions
+    "no-cond-assign": 1,
+
+    // Warn against comma operators
+    "no-sequences": 1,
+
+    // Warn against constant expressions in conditions
+    "no-constant-condition": 1,
+
+    // Warn against control characters in regular expressions
+    "no-control-regex": 1,
+
+    // Warn against duplicate arguments in function definitions
+    "no-dupe-args": 1,
+
+    // Warn against duplicate keys in object literals
+    "no-dupe-keys": 1,
+
+    // Warn against duplicate case labels
+    "no-duplicate-case": 1,
+
+    // Warn against empty block statements
+    "no-empty": 1,
+
+    // Warn against empty character classes in regular expressions
+    "no-empty-character-class": 1,
+
+    // Warn against reassigning exceptions in catch clauses
+    "no-ex-assign": 1,
+
+    // Warn against unnecessary boolean casts
+    "no-extra-boolean-cast": 1,
+
+    // Warn against unnecessary semicolons
+    "no-extra-semi": 1,
+
+    // Warn against reassigning function declarations
+    "no-func-assign": 1,
+
+    // Warn against variable or function declarations in nested blocks
+    "no-inner-declarations": 1,
+
+    // Warn against invalid regular expression strings in RegExp constructors
+    "no-invalid-regexp": 1,
+
+    // Warn against irregular whitespace outside of strings and comments
+    "no-irregular-whitespace": 1,
+
+    // Warn against calling global object properties as functions
+    "no-obj-calls": 1,
+
+    // Warn against confusing multiline expressions
+    "no-unexpected-multiline": 1,
+
+    // Warn against unreachable code after return, throw, continue, and break statements
+    "no-unreachable": 1,
+
+    // Warn against reassigning function parameters
+    "no-param-reassign": 1,
+
+    // Return inside each then() to create readable and reusable Promise chains.
+    "promise/always-return": 2,
+
+    // Prefer async/await to the callback pattern
+    "promise/prefer-await-to-callbacks": 1
+  }
+}

templates/init/functions/javascript/package.lint.json

@@ -0,0 +1,21 @@
+{
+  "name": "functions",
+  "description": "Cloud Functions for Firebase",
+  "scripts": {
+    "lint": "./node_modules/.bin/eslint .",
+    "serve": "firebase serve --only functions",
+    "shell": "firebase experimental:functions:shell",
+    "start": "npm run shell",
+    "deploy": "firebase deploy --only functions",
+    "logs": "firebase functions:log"
+  },
+  "dependencies": {
+    "firebase-admin": "~5.4.2",
+    "firebase-functions": "^0.7.1"
+  },
+  "devDependencies": {
+    "eslint": "^4.12.0",
+    "eslint-plugin-promise": "^3.6.0"
+  },
+  "private": true
+}