chore!: drop support of NPM 5 (#6051)

Author: haoqunjiang

docs/migrations/migrate-from-v4.md

@@ -37,6 +37,7 @@ If you want to migrate manually and gradually, you can run `vue upgrade <the-plu
 ### For All Packages
 
 * Drop support of Node.js 8, 11, 13
+* Drop support of NPM 5
 
 ### The `vue` Command (The Global `@vue/cli` Package)
 

packages/@vue/cli-service/package.json

@@ -72,16 +72,14 @@
     "thread-loader": "^3.0.0",
     "url-loader": "^4.1.1",
     "vue-loader": "^15.9.2",
+    "vue-loader-v16": "npm:vue-loader@^16.0.0-beta.7",
     "vue-style-loader": "^4.1.2",
     "webpack": "^4.0.0",
     "webpack-bundle-analyzer": "^3.8.0",
     "webpack-chain": "^6.4.0",
     "webpack-dev-server": "^3.11.0",
     "webpack-merge": "^4.2.2"
   },
-  "optionalDependencies": {
-    "vue-loader-v16": "npm:vue-loader@^16.0.0-beta.7"
-  },
   "peerDependencies": {
     "@vue/compiler-sfc": "^3.0.0-beta.14",
     "vue-template-compiler": "^2.0.0"

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

@@ -126,13 +126,11 @@ class PackageManager {
       const npmVersion = stripAnsi(execa.sync('npm', ['--version']).stdout)
 
       if (semver.lt(npmVersion, MIN_SUPPORTED_NPM_VERSION)) {
-        warn(
+        throw new Error(
           'You are using an outdated version of NPM.\n' +
-          'there may be unexpected errors during installation.\n' +
+          'It does not support some core functionalities of Vue CLI.\n' +
           'Please upgrade your NPM version.'
         )
-
-        this.needsNpmInstallFix = true
       }
 
       if (semver.gte(npmVersion, '7.0.0')) {
@@ -356,28 +354,6 @@ class PackageManager {
       }
     }
 
-    if (this.needsNpmInstallFix) {
-      // if npm 5, split into several `npm add` calls
-      // see https://github.com/vuejs/vue-cli/issues/5800#issuecomment-675199729
-      const pkg = resolvePkg(this.context)
-      if (pkg.dependencies) {
-        const deps = Object.entries(pkg.dependencies).map(([dep, range]) => `${dep}@${range}`)
-        await this.runCommand('install', deps)
-      }
-
-      if (pkg.devDependencies) {
-        const devDeps = Object.entries(pkg.devDependencies).map(([dep, range]) => `${dep}@${range}`)
-        await this.runCommand('install', [...devDeps, '--save-dev'])
-      }
-
-      if (pkg.optionalDependencies) {
-        const devDeps = Object.entries(pkg.devDependencies).map(([dep, range]) => `${dep}@${range}`)
-        await this.runCommand('install', [...devDeps, '--save-optional'])
-      }
-
-      return
-    }
-
     return await this.runCommand('install', this.needsPeerDepsFix ? ['--legacy-peer-deps'] : [])
   }