1 files changed, 83 insertions, 0 deletions
diff --git a/packages/integrations/cloudflare/src/utils/non-server-chunk-detector.ts b/packages/integrations/cloudflare/src/utils/non-server-chunk-detector.ts
new file mode 100644
index 000000000..c7e766802
--- /dev/null
+++ b/packages/integrations/cloudflare/src/utils/non-server-chunk-detector.ts
@@ -0,0 +1,83 @@
+import type { OutputBundle } from 'rollup';
+import type { Plugin } from 'vite';
+
+/**
+ * A Vite bundle analyzer that identifies chunks that are not used for server rendering.
+ *
+ * The chunks injected by Astro for prerendering are flagged as non-server chunks.
+ * Any chunks that is only used by a non-server chunk are also flagged as non-server chunks.
+ * This continues transitively until all non-server chunks are found.
+ */
+export class NonServerChunkDetector {
+	private nonServerChunks?: string[];
+
+	public getPlugin(): Plugin {
+		return {
+			name: 'non-server-chunk-detector',
+			generateBundle: (_, bundle) => {
+				this.processBundle(bundle);
+			},
+		};
+	}
+
+	private processBundle(bundle: OutputBundle) {
+		const chunkNamesToFiles = new Map<string, string>();
+
+		const entryChunks: string[] = [];
+		const chunkToDependencies = new Map<string, string[]>();
+
+		for (const chunk of Object.values(bundle)) {
+			if (chunk.type !== 'chunk') continue;
+
+			// Construct a mapping from a chunk name to its file name
+			chunkNamesToFiles.set(chunk.name, chunk.fileName);
+			// Construct a mapping from a chunk file to all the modules it imports
+			chunkToDependencies.set(chunk.fileName, [...chunk.imports, ...chunk.dynamicImports]);
+
+			if (chunk.isEntry) {
+				// Entry chunks should always be kept around since they are to be imported by the runtime
+				entryChunks.push(chunk.fileName);
+			}
+		}
+
+		const chunkDecisions = new Map<string, boolean>();
+
+		for (const entry of entryChunks) {
+			// Entry chunks are used on the server
+			chunkDecisions.set(entry, true);
+		}
+
+		for (const chunk of ['prerender', 'prerender@_@astro']) {
+			// Prerender chunks are not used on the server
+			const fileName = chunkNamesToFiles.get(chunk);
+			if (fileName) {
+				chunkDecisions.set(fileName, false);
+			}
+		}
+
+		// Start a stack of chunks that are used on the server
+		const chunksToWalk = [...entryChunks];
+
+		// Iterate over the chunks, traversing the transitive dependencies of the chunks used on the server
+		for (let chunk = chunksToWalk.pop(); chunk; chunk = chunksToWalk.pop()) {
+			for (const dep of chunkToDependencies.get(chunk) ?? []) {
+				// Skip dependencies already flagged, dependencies may be repeated and/or circular
+				if (chunkDecisions.has(dep)) continue;
+
+				// A dependency of a module used on the server is also used on the server
+				chunkDecisions.set(dep, true);
+				// Add the dependency to the stack so its own dependencies are also flagged
+				chunksToWalk.push(dep);
+			}
+		}
+
+		// Any chunk not flagged as used on the server is a non-server chunk
+		this.nonServerChunks = Array.from(chunkToDependencies.keys()).filter(
+			(chunk) => !chunkDecisions.get(chunk)
+		);
+	}
+
+	public getNonServerChunks(): string[] {
+		return this.nonServerChunks ?? [];
+	}
+}