refactor: avoid version check affecting startup time

Author: yyx990803

.gitignore

@@ -6,3 +6,4 @@ packages/test
 dist
 temp
 .vuerc
+.version

packages/@vue/cli/.npmignore

@@ -1,2 +1,3 @@
 __tests__/
-__mocks__/
+__mocks__/
+.version

packages/@vue/cli/lib/create.js

@@ -58,6 +58,7 @@ async function create (projectName, options) {
         if (!action) {
           return
         } else if (action === 'overwrite') {
+          console.log(`\nRemoving ${chalk.cyan(targetDir)}...`)
           await fs.remove(targetDir)
         }
       }

packages/@vue/cli/lib/util/getVersions.js

@@ -1,24 +1,56 @@
+const fs = require('fs-extra')
+const path = require('path')
+const fsCachePath = path.resolve(__dirname, '.version')
+
 module.exports = async function getVersions () {
-  const current = require(`../../package.json`).version
   let latest
-  if (process.env.VUE_CLI_LATEST_VERSION) {
-    // cached value
-    latest = process.env.VUE_CLI_LATEST_VERSION
-  } else if (process.env.VUE_CLI_TEST || process.env.VUE_CLI_DEBUG) {
-    // test/debug, use local version
-    latest = process.env.VUE_CLI_LATEST_VERSION = current
-  } else {
-    const getPackageVersion = require('./getPackageVersion')
-    const res = await getPackageVersion('vue-cli-version-marker', 'latest')
-    if (res.statusCode === 200) {
-      latest = process.env.VUE_CLI_LATEST_VERSION = res.body.version
-    } else {
-      // fallback to local version
-      latest = process.env.VUE_CLI_LATEST_VERSION = current
+  const current = require(`../../package.json`).version
+  if (process.env.VUE_CLI_TEST || process.env.VUE_CLI_DEBUG) {
+    return {
+      latest: current,
+      current
+    }
+  }
+
+  if (fs.existsSync(fsCachePath)) {
+    // if we haven't check for a new version in a week, force a full check
+    // before proceeding.
+    const lastChecked = (await fs.stat(fsCachePath)).mtimeMs
+    const daysPassed = (Date.now() - lastChecked) / (60 * 60 * 1000 * 24)
+    if (daysPassed > 7) {
+      await getAndCacheLatestVersion(current)
     }
+    latest = await fs.readFile(fsCachePath, 'utf-8')
+  } else {
+    // if the cache file doesn't exist, this is likely a fresh install
+    // so no need to check
+    latest = current
   }
+
+  // Do a check in the background. The cached file will be used for the next
+  // startup within a week.
+  getAndCacheLatestVersion(current)
+
   return {
     current,
     latest
   }
 }
+
+// fetch the latest version and save it on disk
+// so that it is available immediately next time
+let sentCheckRequest = false
+async function getAndCacheLatestVersion (current) {
+  if (sentCheckRequest) {
+    return
+  }
+  sentCheckRequest = true
+  const getPackageVersion = require('./getPackageVersion')
+  const res = await getPackageVersion('vue-cli-version-marker', 'latest')
+  if (res.statusCode === 200) {
+    const { version } = res.body
+    if (version !== current) {
+      await fs.writeFile(fsCachePath, version)
+    }
+  }
+}