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Deletes empty output client-side JavaScript bundles.
This updates the Rollup config to avoid generating empty bundles. This used to be a warning, but now the bundles are not emitted at all. The build process will properly skip injecting a pointless `<script>` tag, so everything works as expected.
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5 files changed

Lines changed: 107 additions & 4 deletions

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‎examples/empty_script/BUILD.bazel‎

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load("//:index.bzl", "prerender_pages", "web_resources_devserver")
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load("//tools/jasmine:defs.bzl", "jasmine_web_test_suite")
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load("//tools/typescript:defs.bzl", "ts_project")
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prerender_pages(
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name = "site",
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entry_point = "./site.js",
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prerender = ":prerender",
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scripts = ":scripts",
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)
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ts_project(
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name = "prerender",
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srcs = ["site.tsx"],
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deps = [
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"//:node_modules/@rules_prerender/preact",
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"//:node_modules/preact",
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],
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)
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ts_project(
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name = "scripts",
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srcs = ["empty_script.mts"],
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)
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web_resources_devserver(
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name = "devserver",
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resources = ":site",
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)
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ts_project(
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name = "test_lib",
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srcs = ["test.mts"],
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testonly = True,
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deps = [
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"//common/testing:devserver",
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"//common/testing:webdriver",
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"//:node_modules/@types/jasmine",
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],
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)
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jasmine_web_test_suite(
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name = "test",
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browsers = ["//tools/browsers:chromium-local"],
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data = [":devserver"],
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deps = [":test_lib"],
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)

‎examples/empty_script/empty_script.mts‎

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// Empty script, should not be injected into the page.

‎examples/empty_script/site.tsx‎

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import { PrerenderResource, renderToHtml, includeScript } from '@rules_prerender/preact';
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export default function*(): Generator<PrerenderResource, void, void> {
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yield PrerenderResource.fromHtml('/index.html', renderToHtml(
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<html>
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<head>
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<meta charSet="utf8" />
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<title>Empty script</title>
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</head>
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<body>
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<h2>Empty script</h2>
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{includeScript('./empty_script.mjs', import.meta)}
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</body>
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</html>
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));
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}

‎examples/empty_script/test.mts‎

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import { useDevserver } from '../../common/testing/devserver.mjs';
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import { useWebDriver } from '../../common/testing/webdriver.mjs';
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describe('empty_scripts', () => {
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const devserver = useDevserver('examples/empty_script/devserver.sh');
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const wd = useWebDriver(devserver);
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describe('index page', () => {
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it('renders without a script', async () => {
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const browser = wd.get();
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await browser.url('/');
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expect(await browser.$('h2').getText()).toBe('Empty script');
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// Expect only the live reload script.
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const scripts = await browser.$$('script');
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expect(scripts.length).toBe(1);
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});
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});
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});

‎packages/rules_prerender/rollup.config.mts‎

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import { nodeResolve } from '@rollup/plugin-node-resolve';
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import { RollupOptions } from 'rollup';
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import { Plugin, RollupOptions } from 'rollup';
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/**
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* Deletes any empty output bundles before they are written to disk. This
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* prevents the build process from injecting an empty script onto the page.
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*/
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const deleteEmptyBundles: Plugin = {
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name: 'delete-empty-bundles',
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// Called right before writing output bundles to disk.
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generateBundle(_options, bundle): void {
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for (const [ key, value ] of Object.entries(bundle)) {
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if (value.type === 'chunk' && value.isEntry && value.code.trim() === '') {
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delete bundle[key];
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}
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}
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},
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};
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export default {
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plugins: [
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// Needed to support absolute imports.
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nodeResolve({ browser: true }),
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deleteEmptyBundles,
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],
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// Fail the build on any warning.
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onwarn(warning) {
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if (warning.code === 'EMPTY_BUNDLE') {
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// Give a better suggestion when no JavaScript is generated.
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console.warn('Generated an empty JavaScript bundle, do you have'
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+ ' any JavaScript?\n\n' + warning.message);
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// Ignore empty output errors because the `deleteEmptyBundles`
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// plugin will delete them after the fact. This is not considered a
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// problem and does not need to warn or error.
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return;
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}
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