fix: optimize the judgment on whether HTTPS has been set in options (#…

…7202)

packages/@vue/cli-service/lib/commands/serve.js

@@ -101,7 +101,11 @@ module.exports = (api, options) => {
     }
 
     // resolve server options
-    const useHttps = args.https || projectDevServerOptions.https || defaults.https
+    const modesUseHttps = ['https', 'http2']
+    const serversUseHttps = ['https', 'spdy']
+    const optionsUseHttps = modesUseHttps.some(modeName => !!projectDevServerOptions[modeName]) ||
+      (typeof projectDevServerOptions.server === 'string' && serversUseHttps.includes(projectDevServerOptions.server))
+    const useHttps = args.https || optionsUseHttps || defaults.https
     const protocol = useHttps ? 'https' : 'http'
     const host = args.host || process.env.HOST || projectDevServerOptions.host || defaults.host
     portfinder.basePort = args.port || process.env.PORT || projectDevServerOptions.port || defaults.port