fix(dev-server-rollup): await buildStart in serverStart

Author: bashmish

.changeset/red-tigers-brush.md

@@ -0,0 +1,5 @@
+---
+'@web/dev-server-rollup': patch
+---
+
+fix: await buildStart in serverStart

packages/dev-server-core/src/test-helpers.ts

@@ -55,7 +55,8 @@ export async function createTestServer(
   return { server, port, host: `http://localhost:${port}` };
 }
 
-export const timeout = (ms = 0) => new Promise(resolve => setTimeout(resolve, ms));
+export const timeout = <T>(ms = 0, value?: T): Promise<T> =>
+  new Promise(resolve => setTimeout(value ? () => resolve(value) : resolve, ms));
 
 export async function fetchText(url: string, init?: RequestInit) {
   const response = await fetch(url, init);

packages/dev-server-rollup/src/rollupAdapter.ts

@@ -106,7 +106,7 @@ export function rollupAdapter(
         transformedOptions = rollupInputOptions;
       }
       if (typeof rollupPlugin.buildStart === 'function') {
-        rollupPlugin.buildStart?.call(
+        await rollupPlugin.buildStart?.call(
           rollupPluginContexts.pluginContext,
           rollupPluginContexts.normalizedInputOptions,
         );

packages/dev-server-rollup/test/node/unit.test.ts

@@ -2,10 +2,47 @@ import { Plugin as RollupPlugin, AcornNode } from 'rollup';
 import { expect } from 'chai';
 import path from 'path';
 
-import { createTestServer, fetchText, expectIncludes } from './test-helpers';
+import { createTestServer, fetchText, expectIncludes, timeout } from './test-helpers';
 import { fromRollup } from '../../src/index';
 
 describe('@web/dev-server-rollup', () => {
+  describe('buildStart', () => {
+    it('awaits buildStart when starting a server', async () => {
+      let resolveBuildStartCalled: undefined | ((value: void) => void);
+      const buildStartCalledPromise = new Promise(resolve => (resolveBuildStartCalled = resolve));
+
+      let resolveBuildStart: undefined | ((value: void) => void);
+      const plugin: RollupPlugin = {
+        name: 'my-plugin',
+        buildStart() {
+          if (resolveBuildStartCalled) {
+            resolveBuildStartCalled();
+          }
+          return new Promise(resolve => (resolveBuildStart = resolve));
+        },
+      };
+
+      const serverPromise = createTestServer({
+        plugins: [fromRollup(() => plugin)()],
+      });
+
+      await buildStartCalledPromise;
+
+      try {
+        const res = await Promise.race([serverPromise, timeout(0, 'timeout')]);
+        expect(res).to.equal('timeout');
+        if (resolveBuildStart) {
+          resolveBuildStart();
+        }
+        const res2 = await Promise.race([serverPromise, timeout(0, 'timeout')]);
+        expect(res2).not.to.equal('timeout');
+      } finally {
+        const { server } = await serverPromise;
+        server.stop();
+      }
+    });
+  });
+
   describe('resolveId', () => {
     it('can resolve imports, returning a string', async () => {
       const plugin: RollupPlugin = {