Use import order to sort CSS in prod (#4724)

* Use import order to sort CSS in prod

* Adding a changeset

* Pass through the parent id

* Update remaining test

9 files changed, 92 insertions, 20 deletions

diff --git a/.changeset/many-tables-brush.md b/.changeset/many-tables-brush.md
new file mode 100644
index 000000000..45337df3e
--- /dev/null
+++ b/.changeset/many-tables-brush.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Use import order to sort CSS in the build
diff --git a/packages/astro/src/core/build/graph.ts b/packages/astro/src/core/build/graph.ts
index 8db52a1c9..e55361d75 100644
--- a/packages/astro/src/core/build/graph.ts
+++ b/packages/astro/src/core/build/graph.ts
@@ -7,19 +7,21 @@ export function* walkParentInfos(
 	id: string,
 	ctx: { getModuleInfo: GetModuleInfo },
 	depth = 0,
-	seen = new Set<string>()
-): Generator<[ModuleInfo, number], void, unknown> {
+	seen = new Set<string>(),
+	childId = '',
+): Generator<[ModuleInfo, number, number], void, unknown> {
 	seen.add(id);
 	const info = ctx.getModuleInfo(id);
 	if (info) {
-		yield [info, depth];
+		let order = childId ? info.importedIds.indexOf(childId) : 0;
+		yield [info, depth, order];
 	}
 	const importers = (info?.importers || []).concat(info?.dynamicImporters || []);
 	for (const imp of importers) {
 		if (seen.has(imp)) {
 			continue;
 		}
-		yield* walkParentInfos(imp, ctx, ++depth, seen);
+		yield* walkParentInfos(imp, ctx, ++depth, seen, id);
 	}
 }
 
@@ -34,7 +36,7 @@ export function moduleIsTopLevelPage(info: ModuleInfo): boolean {
 export function* getTopLevelPages(
 	id: string,
 	ctx: { getModuleInfo: GetModuleInfo }
-): Generator<[ModuleInfo, number], void, unknown> {
+): Generator<[ModuleInfo, number, number], void, unknown> {
 	for (const res of walkParentInfos(id, ctx)) {
 		if (moduleIsTopLevelPage(res[0])) {
 			yield res;
diff --git a/packages/astro/src/core/build/internal.ts b/packages/astro/src/core/build/internal.ts
index 7d8485fe5..ae1c48361 100644
--- a/packages/astro/src/core/build/internal.ts
+++ b/packages/astro/src/core/build/internal.ts
@@ -191,14 +191,26 @@ export function sortedCSS(pageData: PageBuildData) {
 	return Array.from(pageData.css)
 		.sort((a, b) => {
 			let depthA = a[1].depth,
-				depthB = b[1].depth;
+				depthB = b[1].depth,
+				orderA = a[1].order,
+				orderB = b[1].order;
 
-			if (depthA === -1) {
+			if(orderA === -1 && orderB >= 0) {
+				return 1;
+			} else if(orderB === -1 && orderA >= 0) {
 				return -1;
-			} else if (depthB === -1) {
+			} else if(orderA > orderB) {
 				return 1;
+			} else if(orderA < orderB) {
+				return -1;
 			} else {
-				return depthA > depthB ? -1 : 1;
+				if (depthA === -1) {
+					return -1;
+				} else if (depthB === -1) {
+					return 1;
+				} else {
+					return depthA > depthB ? -1 : 1;
+				}
 			}
 		})
 		.map(([id]) => id);
diff --git a/packages/astro/src/core/build/types.ts b/packages/astro/src/core/build/types.ts
index 90da4b0ef..42a4b0716 100644
--- a/packages/astro/src/core/build/types.ts
+++ b/packages/astro/src/core/build/types.ts
@@ -18,7 +18,7 @@ export interface PageBuildData {
 	component: ComponentPath;
 	route: RouteData;
 	moduleSpecifier: string;
-	css: Map<string, { depth: number }>;
+	css: Map<string, { depth: number; order: number; }>;
 	hoistedScript: { type: 'inline' | 'external'; value: string } | undefined;
 }
 export type AllPagesData = Record<ComponentPath, PageBuildData>;
diff --git a/packages/astro/src/core/build/vite-plugin-css.ts b/packages/astro/src/core/build/vite-plugin-css.ts
index 28e88cf65..202bd5319 100644
--- a/packages/astro/src/core/build/vite-plugin-css.ts
+++ b/packages/astro/src/core/build/vite-plugin-css.ts
@@ -110,7 +110,7 @@ export function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[]
 					importedCss: Set<string>;
 				};
 
-				const appendCSSToPage = (pageData: PageBuildData, meta: ViteMetadata, depth: number) => {
+				const appendCSSToPage = (pageData: PageBuildData, meta: ViteMetadata, depth: number, order: number) => {
 					for (const importedCssImport of meta.importedCss) {
 						// CSS is prioritized based on depth. Shared CSS has a higher depth due to being imported by multiple pages.
 						// Depth info is used when sorting the links on the page.
@@ -120,8 +120,15 @@ export function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[]
 							if (depth < cssInfo.depth) {
 								cssInfo.depth = depth;
 							}
+
+							// Update the order, preferring the lowest order we have.
+							if(cssInfo.order === -1) {
+                cssInfo.order = order;
+              } else if(order < cssInfo.order && order > -1) {
+                cssInfo.order = order;
+              }
 						} else {
-							pageData?.css.set(importedCssImport, { depth });
+							pageData?.css.set(importedCssImport, { depth, order });
 						}
 					}
 				};
@@ -161,7 +168,7 @@ export function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[]
 									for (const id of Object.keys(c.modules)) {
 										for (const pageData of getParentClientOnlys(id, this)) {
 											for (const importedCssImport of meta.importedCss) {
-												pageData.css.set(importedCssImport, { depth: -1 });
+												pageData.css.set(importedCssImport, { depth: -1, order: -1 });
 											}
 										}
 									}
@@ -169,12 +176,12 @@ export function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[]
 
 								// For this CSS chunk, walk parents until you find a page. Add the CSS to that page.
 								for (const id of Object.keys(c.modules)) {
-									for (const [pageInfo, depth] of walkParentInfos(id, this)) {
+									for (const [pageInfo, depth, order] of walkParentInfos(id, this)) {
 										if (moduleIsTopLevelPage(pageInfo)) {
 											const pageViteID = pageInfo.id;
 											const pageData = getPageDataByViteID(internals, pageViteID);
 											if (pageData) {
-												appendCSSToPage(pageData, meta, depth);
+												appendCSSToPage(pageData, meta, depth, order);
 											}
 										} else if (
 											options.target === 'client' &&
@@ -184,7 +191,7 @@ export function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[]
 												internals,
 												pageInfo.id
 											)) {
-												appendCSSToPage(pageData, meta, -1);
+												appendCSSToPage(pageData, meta, -1, order);
 											}
 										}
 									}
@@ -211,7 +218,7 @@ export function rollupPluginAstroBuildCSS(options: PluginOptions): VitePlugin[]
 					);
 					if (cssChunk) {
 						for (const pageData of eachPageData(internals)) {
-							pageData.css.set(cssChunk.fileName, { depth: -1 });
+							pageData.css.set(cssChunk.fileName, { depth: -1, order: -1 });
 						}
 					}
 				}
diff --git a/packages/astro/test/css-order.test.js b/packages/astro/test/css-order.test.js
index 02db6b449..944452e93 100644
--- a/packages/astro/test/css-order.test.js
+++ b/packages/astro/test/css-order.test.js
@@ -86,10 +86,25 @@ describe('CSS production ordering', () => {
 				getLinks(html).map((href) => getLinkContent(fixture, href))
 			);
 
-			expect(content).to.have.a.lengthOf(2, 'there are 2 stylesheets');
-			const [, last] = content;
+			expect(content).to.have.a.lengthOf(3, 'there are 3 stylesheets');
+			const [,found] = content;
 
-			expect(last.css).to.match(/#00f/);
+			expect(found.css).to.match(/#00f/);
+		});
+
+		it('CSS injected by injectScript comes first because of import order', async () => {
+			let oneHtml = await fixture.readFile('/one/index.html');
+			let twoHtml = await fixture.readFile('/two/index.html');
+			let threeHtml = await fixture.readFile('/three/index.html');
+
+			for(const html of [oneHtml, twoHtml, threeHtml]) {
+				const content = await Promise.all(
+					getLinks(html).map((href) => getLinkContent(fixture, href))
+				);
+	
+				const [first] = content;
+				expect(first.css).to.include('green', 'Came from the injected script');
+			}
 		});
 	});
 });
diff --git a/packages/astro/test/fixtures/css-order/astro.config.mjs b/packages/astro/test/fixtures/css-order/astro.config.mjs
new file mode 100644
index 000000000..b53e3c0ee
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order/astro.config.mjs
@@ -0,0 +1,14 @@
+import { defineConfig } from 'astro/config';
+
+export default defineConfig({
+	integrations: [
+		{
+			name: 'test-integration',
+			hooks: {
+				'astro:config:setup'({ injectScript }) {
+					injectScript('page-ssr', `import '/src/styles/base.css';`);
+				}
+			}
+		}
+	]
+});
diff --git a/packages/astro/test/fixtures/css-order/src/pages/three.astro b/packages/astro/test/fixtures/css-order/src/pages/three.astro
new file mode 100644
index 000000000..30289168a
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order/src/pages/three.astro
@@ -0,0 +1,14 @@
+<html>
+	<head>
+		<title>Testing</title>
+		<style>
+			body {
+				margin: 2px;
+				color: blueviolet;
+			}
+		</style>
+	</head>
+	<body>
+		<h1>Testing</h1>
+	</body>
+</html>
diff --git a/packages/astro/test/fixtures/css-order/src/styles/base.css b/packages/astro/test/fixtures/css-order/src/styles/base.css
new file mode 100644
index 000000000..828bff206
--- /dev/null
+++ b/packages/astro/test/fixtures/css-order/src/styles/base.css
@@ -0,0 +1,3 @@
+body {
+	background: green;
+}