fix(plugin-vue): compiler is null on rollup (#6566)

Author: sxzz

packages/plugin-vue/src/index.ts

@@ -97,7 +97,7 @@ export default function vuePlugin(rawOptions: Options = {}): Plugin {
     reactivityTransform,
     root: process.cwd(),
     sourceMap: true,
-    compiler: null as any // to be set in configResolved
+    compiler: null as any // to be set in buildStart
   }
 
   // Temporal handling for 2.7 breaking change
@@ -135,15 +135,18 @@ export default function vuePlugin(rawOptions: Options = {}): Plugin {
         ...options,
         root: config.root,
         sourceMap: config.command === 'build' ? !!config.build.sourcemap : true,
-        isProduction: config.isProduction,
-        compiler: options.compiler || resolveCompiler(config.root)
+        isProduction: config.isProduction
       }
     },
 
     configureServer(server) {
       options.devServer = server
     },
 
+    buildStart() {
+      options.compiler = options.compiler || resolveCompiler(options.root)
+    },
+
     async resolveId(id) {
       // component export helper
       if (id === EXPORT_HELPER_ID) {