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Merged
Princesseuh merged 4 commits into from
Jan 16, 2026
Merged

fix(css): prevent CSS double-bundling (#14991) #15017

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d12c47a
fix(css): prevent double-bundling when CSS imported from multiple loc…
ixchio Dec 14, 2025
a55d4be
chore: update pnpm-lock.yaml for new test fixture
ixchio Dec 14, 2025
77d3fe8
Merge branch 'main' into fix/css-double-bundle-clean
ixchio Dec 19, 2025
27d731c
Merge branch 'main' into fix/css-double-bundle-clean
Princesseuh Jan 13, 2026
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5 changes: 5 additions & 0 deletions .changeset/fix-css-double-bundle.md
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---
"astro": patch
---

Fixes CSS double-bundling when the same CSS file is imported in both a page's frontmatter and a component's script tag
19 changes: 18 additions & 1 deletion packages/astro/src/core/build/plugins/plugin-css.ts
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Expand Up @@ -185,6 +185,7 @@ function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[] {
},
async generateBundle(_outputOptions, bundle) {
const inlineConfig = settings.config.build.inlineStylesheets;

Object.entries(bundle).forEach(([id, stylesheet]) => {
if (
stylesheet.type !== 'asset' ||
Expand All @@ -211,7 +212,23 @@ function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[] {
internals.pagesByKeys.forEach((pageData) => {
const orderingInfo = pagesToCss[pageData.moduleSpecifier]?.[stylesheet.fileName];
if (orderingInfo !== undefined) {
pageData.styles.push({ ...orderingInfo, sheet });
// Check if this stylesheet was already added to this page.
// We check both inline (by content) and external (by src) styles to prevent
// duplicates that can occur when CSS is imported from both a page's frontmatter
// and a component's script tag, or when the same plugin runs in both SSR and client builds.
const alreadyAdded = pageData.styles.some((s) => {
if (s.sheet.type === 'external' && sheet.type === 'external') {
return s.sheet.src === sheet.src;
}
if (s.sheet.type === 'inline' && sheet.type === 'inline') {
return s.sheet.content === sheet.content;
}
return false;
});

if (!alreadyAdded) {
pageData.styles.push({ ...orderingInfo, sheet });
}
sheetAddedToPage = true;
}
});
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60 changes: 60 additions & 0 deletions packages/astro/test/css-double-bundle.test.js
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import assert from 'node:assert/strict';
import { before, describe, it } from 'node:test';
import * as cheerio from 'cheerio';
import { loadFixture } from './test-utils.js';

describe('CSS Double Bundling Prevention', function () {
/** @type {import('./test-utils').Fixture} */
let fixture;

before(async () => {
fixture = await loadFixture({
root: './fixtures/css-double-bundle/',
});
await fixture.build();
});

it('CSS imported in both page frontmatter and component script should only be bundled once', async () => {
const html = await fixture.readFile('/index.html');
const $ = cheerio.load(html);

// Get all CSS content (both inline and linked)
let allCss = '';

// Check inline styles
$('style').each((_, el) => {
allCss += $(el).html();
});

// Check linked stylesheets
const cssLinks = $('link[rel="stylesheet"][href^="/_astro/"]');
for (let i = 0; i < cssLinks.length; i++) {
const href = cssLinks.eq(i).attr('href');
const cssContent = await fixture.readFile(href.replace(/^\//, '/'));
allCss += cssContent;
}

// Count occurrences of the CSS rule - should appear exactly once
const matches = allCss.match(/button\s*\{[^}]*background:\s*purple/g) || [];

assert.equal(
matches.length,
1,
`Expected CSS rule "button{background:purple}" to appear exactly once, but found ${matches.length} occurrences. CSS should not be double-bundled when imported from both page frontmatter and component script.`,
);
});

it('CSS should still be present in the build output', async () => {
const html = await fixture.readFile('/index.html');
const $ = cheerio.load(html);

// Should have either inline styles or linked stylesheet
const hasInlineStyle = $('style').length > 0;
const hasLinkedStylesheet = $('link[rel="stylesheet"]').length > 0;

assert.ok(
hasInlineStyle || hasLinkedStylesheet,
'Expected CSS to be present in the build output (either inline or as a linked stylesheet)',
);
});
});
3 changes: 3 additions & 0 deletions packages/astro/test/fixtures/css-double-bundle/astro.config.mjs
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import { defineConfig } from 'astro/config';

export default defineConfig({});
8 changes: 8 additions & 0 deletions packages/astro/test/fixtures/css-double-bundle/package.json
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{
"name": "@test/css-double-bundle",
"version": "0.0.0",
"private": true,
"dependencies": {
"astro": "workspace:*"
}
}
5 changes: 5 additions & 0 deletions packages/astro/test/fixtures/css-double-bundle/src/components/Button.astro
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<button>Button</button>

<script>
import "../styles/base.css";
</script>
13 changes: 13 additions & 0 deletions packages/astro/test/fixtures/css-double-bundle/src/pages/index.astro
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---
import "../styles/base.css";
import Button from "../components/Button.astro";
---

<html lang="en">
<head>
<meta charset="utf-8" />
</head>
<body>
<Button />
</body>
</html>
3 changes: 3 additions & 0 deletions packages/astro/test/fixtures/css-double-bundle/src/styles/base.css
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button {
background: purple;
}
6 changes: 6 additions & 0 deletions pnpm-lock.yaml
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