Move hoisted script analysis optimization as experimental (#8011)

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

6 files changed, 88 insertions, 38 deletions

diff --git a/.changeset/wild-jobs-tan.md b/.changeset/wild-jobs-tan.md
new file mode 100644
index 000000000..8372c01b1
--- /dev/null
+++ b/.changeset/wild-jobs-tan.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Move hoisted script analysis optimization behind the `experimental.optimizeHoistedScript` option
diff --git a/packages/astro/src/@types/astro.ts b/packages/astro/src/@types/astro.ts
index 1e594332d..c2a7c3823 100644
--- a/packages/astro/src/@types/astro.ts
+++ b/packages/astro/src/@types/astro.ts
@@ -1272,6 +1272,28 @@ export interface AstroUserConfig {
 		 * ```
 		 */
 		viewTransitions?: boolean;
+
+		/**
+		 * @docs
+		 * @name experimental.optimizeHoistedScript
+		 * @type {boolean}
+		 * @default `false`
+		 * @version 2.10.4
+		 * @description
+		 * Prevents unused components' scripts from being included in a page unexpectedly.
+		 * The optimization is best-effort and may inversely miss including the used scripts. Make sure to double-check your built pages
+		 * before publishing.
+		 * Enable hoisted script analysis optimization by adding the experimental flag:
+		 *
+		 * ```js
+		 * {
+		 * 	experimental: {
+		 *		optimizeHoistedScript: true,
+		 * 	},
+		 * }
+		 * ```
+		 */
+		optimizeHoistedScript?: boolean;
 	};
 
 	// Legacy options to be removed
diff --git a/packages/astro/src/core/build/plugins/index.ts b/packages/astro/src/core/build/plugins/index.ts
index 3a44824d6..decfefd04 100644
--- a/packages/astro/src/core/build/plugins/index.ts
+++ b/packages/astro/src/core/build/plugins/index.ts
@@ -16,7 +16,7 @@ import { pluginSSR, pluginSSRSplit } from './plugin-ssr.js';
 export function registerAllPlugins({ internals, options, register }: AstroBuildPluginContainer) {
 	register(pluginComponentEntry(internals));
 	register(pluginAliasResolve(internals));
-	register(pluginAnalyzer(internals));
+	register(pluginAnalyzer(options, internals));
 	register(pluginInternals(internals));
 	register(pluginRenderers(options));
 	register(pluginMiddleware(options, internals));
diff --git a/packages/astro/src/core/build/plugins/plugin-analyzer.ts b/packages/astro/src/core/build/plugins/plugin-analyzer.ts
index c05328005..f1229cb38 100644
--- a/packages/astro/src/core/build/plugins/plugin-analyzer.ts
+++ b/packages/astro/src/core/build/plugins/plugin-analyzer.ts
@@ -5,10 +5,10 @@ import type { BuildInternals } from '../internal.js';
 import type { AstroBuildPlugin } from '../plugin.js';
 
 import type { ExportDefaultDeclaration, ExportNamedDeclaration, ImportDeclaration } from 'estree';
-import { walk } from 'estree-walker';
 import { PROPAGATED_ASSET_FLAG } from '../../../content/consts.js';
 import { prependForwardSlash } from '../../../core/path.js';
 import { getTopLevelPages, moduleIsTopLevelPage, walkParentInfos } from '../graph.js';
+import type { StaticBuildOptions } from '../types.js';
 import { getPageDataByViteID, trackClientOnlyPageDatas } from '../internal.js';
 
 function isPropagatedAsset(id: string) {
@@ -30,29 +30,28 @@ async function doesParentImportChild(
 ): Promise<'no' | 'dynamic' | string[]> {
 	if (!childInfo || !parentInfo.ast || !childExportNames) return 'no';
 
+	// If we're dynamically importing the child, return `dynamic` directly to opt-out of optimization
 	if (childExportNames === 'dynamic' || parentInfo.dynamicallyImportedIds?.includes(childInfo.id)) {
 		return 'dynamic';
 	}
 
 	const imports: Array<ImportDeclaration> = [];
 	const exports: Array<ExportNamedDeclaration | ExportDefaultDeclaration> = [];
-	walk(parentInfo.ast, {
-		enter(node) {
-			if (node.type === 'ImportDeclaration') {
-				imports.push(node as ImportDeclaration);
-			} else if (
-				node.type === 'ExportDefaultDeclaration' ||
-				node.type === 'ExportNamedDeclaration'
-			) {
-				exports.push(node as ExportNamedDeclaration | ExportDefaultDeclaration);
-			}
-		},
-	});
-	// All of the aliases the current component is imported as
+	for (const node of (parentInfo.ast as any).body) {
+		if (node.type === 'ImportDeclaration') {
+			imports.push(node);
+		} else if (node.type === 'ExportDefaultDeclaration' || node.type === 'ExportNamedDeclaration') {
+			exports.push(node);
+		}
+	}
+
+	// All local import names that could be importing the child component
 	const importNames: string[] = [];
 	// All of the aliases the child component is exported as
 	const exportNames: string[] = [];
 
+	// Iterate each import, find it they import the child component, if so, check if they
+	// import the child component name specifically. We can verify this with `childExportNames`.
 	for (const node of imports) {
 		const resolved = await this.resolve(node.source.value as string, parentInfo.id);
 		if (!resolved || resolved.id !== childInfo.id) continue;
@@ -67,14 +66,17 @@ async function doesParentImportChild(
 			}
 		}
 	}
+
+	// Iterate each export, find it they re-export the child component, and push the exported name to `exportNames`
 	for (const node of exports) {
 		if (node.type === 'ExportDefaultDeclaration') {
 			if (node.declaration.type === 'Identifier' && importNames.includes(node.declaration.name)) {
 				exportNames.push('default');
-				// return
 			}
 		} else {
-			// handle `export { x } from 'something';`, where the export and import are in the same node
+			// Handle:
+			// export { Component } from './Component.astro'
+			// export { Component as AliasedComponent } from './Component.astro'
 			if (node.source) {
 				const resolved = await this.resolve(node.source.value as string, parentInfo.id);
 				if (!resolved || resolved.id !== childInfo.id) continue;
@@ -85,6 +87,9 @@ async function doesParentImportChild(
 					}
 				}
 			}
+			// Handle:
+			// export const AliasedComponent = Component
+			// export const AliasedComponent = Component, let foo = 'bar'
 			if (node.declaration) {
 				if (node.declaration.type !== 'VariableDeclaration') continue;
 				for (const declarator of node.declaration.declarations) {
@@ -95,6 +100,9 @@ async function doesParentImportChild(
 					}
 				}
 			}
+			// Handle:
+			// export { Component }
+			// export { Component as AliasedComponent }
 			for (const specifier of node.specifiers) {
 				if (importNames.includes(specifier.local.name)) {
 					exportNames.push(specifier.exported.name);
@@ -115,7 +123,10 @@ async function doesParentImportChild(
 	return exportNames;
 }
 
-export function vitePluginAnalyzer(internals: BuildInternals): VitePlugin {
+export function vitePluginAnalyzer(
+	options: StaticBuildOptions,
+	internals: BuildInternals
+): VitePlugin {
 	function hoistedScriptScanner() {
 		const uniqueHoistedIds = new Map<string, string>();
 		const pageScripts = new Map<
@@ -139,6 +150,7 @@ export function vitePluginAnalyzer(internals: BuildInternals): VitePlugin {
 				}
 
 				if (hoistedScripts.size) {
+					// These variables are only used for hoisted script analysis optimization
 					const depthsToChildren = new Map<number, ModuleInfo>();
 					const depthsToExportNames = new Map<number, string[] | 'dynamic'>();
 					// The component export from the original component file will always be default.
@@ -147,25 +159,28 @@ export function vitePluginAnalyzer(internals: BuildInternals): VitePlugin {
 					for (const [parentInfo, depth] of walkParentInfos(from, this, function until(importer) {
 						return isPropagatedAsset(importer);
 					})) {
-						depthsToChildren.set(depth, parentInfo);
-						// If at any point
-						if (depth > 0) {
-							// Check if the component is actually imported:
-							const childInfo = depthsToChildren.get(depth - 1);
-							const childExportNames = depthsToExportNames.get(depth - 1);
-
-							const doesImport = await doesParentImportChild.call(
-								this,
-								parentInfo,
-								childInfo,
-								childExportNames
-							);
-
-							if (doesImport === 'no') {
-								// Break the search if the parent doesn't import the child.
-								continue;
+						// If hoisted script analysis optimization is enabled, try to analyse and bail early if possible
+						if (options.settings.config.experimental.optimizeHoistedScript) {
+							depthsToChildren.set(depth, parentInfo);
+							// If at any point
+							if (depth > 0) {
+								// Check if the component is actually imported:
+								const childInfo = depthsToChildren.get(depth - 1);
+								const childExportNames = depthsToExportNames.get(depth - 1);
+
+								const doesImport = await doesParentImportChild.call(
+									this,
+									parentInfo,
+									childInfo,
+									childExportNames
+								);
+
+								if (doesImport === 'no') {
+									// Break the search if the parent doesn't import the child.
+									continue;
+								}
+								depthsToExportNames.set(depth, doesImport);
 							}
-							depthsToExportNames.set(depth, doesImport);
 						}
 
 						if (isPropagatedAsset(parentInfo.id)) {
@@ -310,13 +325,16 @@ export function vitePluginAnalyzer(internals: BuildInternals): VitePlugin {
 	};
 }
 
-export function pluginAnalyzer(internals: BuildInternals): AstroBuildPlugin {
+export function pluginAnalyzer(
+	options: StaticBuildOptions,
+	internals: BuildInternals
+): AstroBuildPlugin {
 	return {
 		build: 'ssr',
 		hooks: {
 			'build:before': () => {
 				return {
-					vitePlugin: vitePluginAnalyzer(internals),
+					vitePlugin: vitePluginAnalyzer(options, internals),
 				};
 			},
 		},
diff --git a/packages/astro/src/core/config/schema.ts b/packages/astro/src/core/config/schema.ts
index 34c1e5549..e7e504738 100644
--- a/packages/astro/src/core/config/schema.ts
+++ b/packages/astro/src/core/config/schema.ts
@@ -46,6 +46,7 @@ const ASTRO_CONFIG_DEFAULTS = {
 	experimental: {
 		assets: false,
 		viewTransitions: false,
+		optimizeHoistedScript: false
 	},
 } satisfies AstroUserConfig & { server: { open: boolean } };
 
@@ -237,6 +238,7 @@ export const AstroConfigSchema = z.object({
 				.boolean()
 				.optional()
 				.default(ASTRO_CONFIG_DEFAULTS.experimental.viewTransitions),
+				optimizeHoistedScript: z.boolean().optional().default(ASTRO_CONFIG_DEFAULTS.experimental.optimizeHoistedScript),
 		})
 		.passthrough()
 		.refine(
diff --git a/packages/astro/test/hoisted-imports.test.js b/packages/astro/test/hoisted-imports.test.js
index 973d7103e..c5ce98e05 100644
--- a/packages/astro/test/hoisted-imports.test.js
+++ b/packages/astro/test/hoisted-imports.test.js
@@ -8,6 +8,9 @@ describe('Hoisted Imports', () => {
 	before(async () => {
 		fixture = await loadFixture({
 			root: './fixtures/hoisted-imports/',
+			experimental: {
+				optimizeHoistedScript: true,
+			},
 		});
 	});