feat(eslint): enable caching

Author: yyx990803

packages/@vue/cli-plugin-eslint/index.js

@@ -1,6 +1,8 @@
 module.exports = (api, { lintOnSave }) => {
   if (lintOnSave) {
     const extensions = require('./eslintOptions').extensions(api)
+    const cacheIdentifier = genCacheIdentifier(api.resolve('.'))
+
     api.chainWebpack(webpackConfig => {
       webpackConfig.module
         .rule('eslint')
@@ -14,6 +16,8 @@ module.exports = (api, { lintOnSave }) => {
             .loader('eslint-loader')
             .options({
               extensions,
+              cache: true,
+              cacheIdentifier,
               emitWarning: lintOnSave !== 'error',
               formatter: require('eslint/lib/formatters/codeframe')
             })
@@ -34,3 +38,33 @@ module.exports = (api, { lintOnSave }) => {
     require('./lint')(args, api)
   })
 }
+
+// eslint-loader doesn't bust cache when eslint config changes
+// so we have to manually generate a cache identifier that takes the config
+// into account.
+function genCacheIdentifier (context) {
+  const fs = require('fs')
+  const path = require('path')
+  const files = [
+    '.eslintrc.js',
+    '.eslintrc.yaml',
+    '.eslintrc.yml',
+    '.eslintrc.json',
+    '.eslintrc',
+    'package.json'
+  ]
+
+  const configTimeStamp = (() => {
+    for (const file of files) {
+      if (fs.existsSync(path.join(context, file))) {
+        return fs.statSync(file).mtimeMs
+      }
+    }
+  })()
+
+  return JSON.stringify({
+    'eslint-loader': require('eslint-loader/package.json').version,
+    'eslint': require('eslint/package.json').version,
+    'config': configTimeStamp
+  })
+}