[wrangler] Support source phase imports

.changeset/four-planes-attend.md

@@ -0,0 +1,7 @@
+---
+"wrangler": patch
+---
+
+Fix source phase imports in bundled and non-bundled Workers
+
+Wrangler now preserves `import source` syntax when it runs esbuild, including module format detection and bundled deploy output. This fixes both `--no-bundle` and bundled deployments for Workers that import WebAssembly using source phase imports.

packages/wrangler/src/__tests__/deploy/build.test.ts

@@ -1153,6 +1153,18 @@ describe("deploy", () => {
 			await runWrangler("deploy index.js --dry-run --outdir dist");
 			expect(fs.readFileSync("dist/index.js", "utf-8")).toMatch(scriptContent);
 		});
+
+		it("should preserve source phase imports without error", async ({
+			expect,
+		}) => {
+			writeWranglerConfig();
+			const scriptContent = `import source mod from './mod.wasm';
+export default { fetch() { return new Response(mod); } };`;
+			fs.writeFileSync("index.js", scriptContent);
+			fs.writeFileSync("mod.wasm", "");
+			await runWrangler("deploy index.js --no-bundle --dry-run --outdir dist");
+			expect(fs.readFileSync("dist/index.js", "utf-8")).toMatch(scriptContent);
+		});
 	});
 	describe("--no-bundle --minify", () => {
 		it("should warn that no-bundle and minify can't be used together", async ({

packages/wrangler/src/__tests__/deploy/formats.test.ts

@@ -931,6 +931,52 @@ export default{
 				}
 			`);
 		});
+
+		it("should copy source phase wasm imports to --outdir if specified", async ({
+			expect,
+		}) => {
+			writeWranglerConfig();
+			fs.writeFileSync(
+				"./index.js",
+				`
+import txt from './textfile.txt';
+import source hello from './hello.wasm';
+export default {
+  async fetch() {
+    return new Response(txt + hello);
+  }
+}
+`
+			);
+			fs.writeFileSync("./textfile.txt", "Hello, World!");
+			fs.writeFileSync("./hello.wasm", "Hello wasm World!");
+			mockSubDomainRequest();
+			mockUploadWorkerRequest({
+				expectedModules: {
+					"./0a0a9f2a6772942557ab5355d76af442f8f65e01-textfile.txt":
+						"Hello, World!",
+					"./d025a03cd31e98e96fb5bd5bce87f9bca4e8ce2c-hello.wasm":
+						"Hello wasm World!",
+				},
+			});
+			await runWrangler("deploy index.js --outdir some-dir");
+
+			expect(fs.existsSync("some-dir/index.js")).toBe(true);
+			expect(fs.existsSync("some-dir/index.js.map")).toBe(true);
+			expect(fs.readFileSync("some-dir/index.js", "utf8")).toContain(
+				'import source hello from "./d025a03cd31e98e96fb5bd5bce87f9bca4e8ce2c-hello.wasm";'
+			);
+			expect(
+				fs.existsSync(
+					"some-dir/0a0a9f2a6772942557ab5355d76af442f8f65e01-textfile.txt"
+				)
+			).toBe(true);
+			expect(
+				fs.existsSync(
+					"some-dir/d025a03cd31e98e96fb5bd5bce87f9bca4e8ce2c-hello.wasm"
+				)
+			).toBe(true);
+		});
 	});
 	describe("--outfile", () => {
 		it("should generate worker bundle at --outfile if specified", async ({
@@ -1056,6 +1102,56 @@ export default{
 			`);
 		});
 
+		it("should include source phase wasm imports in the worker bundle", async ({
+			expect,
+		}) => {
+			writeWranglerConfig();
+			fs.writeFileSync(
+				"./index.js",
+				`
+import txt from './textfile.txt';
+import source hello from './hello.wasm';
+export default {
+  async fetch() {
+    return new Response(txt + hello);
+  }
+}
+`
+			);
+			fs.writeFileSync("./textfile.txt", "Hello, World!");
+			fs.writeFileSync("./hello.wasm", "Hello wasm World!");
+			mockSubDomainRequest();
+			mockUploadWorkerRequest({
+				expectedModules: {
+					"./0a0a9f2a6772942557ab5355d76af442f8f65e01-textfile.txt":
+						"Hello, World!",
+					"./d025a03cd31e98e96fb5bd5bce87f9bca4e8ce2c-hello.wasm":
+						"Hello wasm World!",
+				},
+			});
+			await runWrangler("deploy index.js --outfile some-dir/worker.bundle");
+
+			expect(fs.existsSync("some-dir/worker.bundle")).toBe(true);
+			expect(
+				fs
+					.readFileSync("some-dir/worker.bundle", "utf8")
+					.replace(
+						/------formdata-undici-0.[0-9]*/g,
+						"------formdata-undici-0.test"
+					)
+					.replace(/wrangler_(.+?)_default/g, "wrangler_default")
+			).toContain(
+				dedent`
+					// index.js
+					import txt from "./0a0a9f2a6772942557ab5355d76af442f8f65e01-textfile.txt";
+					import source hello from "./d025a03cd31e98e96fb5bd5bce87f9bca4e8ce2c-hello.wasm";
+				`
+			);
+			expect(fs.readFileSync("some-dir/worker.bundle", "utf8")).toContain(
+				'Content-Disposition: form-data; name="./d025a03cd31e98e96fb5bd5bce87f9bca4e8ce2c-hello.wasm"; filename="./d025a03cd31e98e96fb5bd5bce87f9bca4e8ce2c-hello.wasm"'
+			);
+		});
+
 		it("should include bindings in the worker bundle", async ({ expect }) => {
 			writeWranglerConfig({
 				kv_namespaces: [{ binding: "KV", id: "kv-namespace-id" }],

packages/wrangler/src/__tests__/guess-worker-format.test.ts

@@ -113,4 +113,21 @@ describe("guess worker format", () => {
 		);
 		expect(guess.exports).toStrictEqual(["Hello", "default"]);
 	});
+
+	it("should detect a modules worker that uses source phase imports", async ({
+		expect,
+	}) => {
+		await writeFile("./mod.wasm", "");
+		await writeFile(
+			"./index.js",
+			`import source mod from './mod.wasm';
+export default { fetch() { return new Response(mod); } };`
+		);
+		const guess = await guessWorkerFormat(
+			path.join(process.cwd(), "./index.js"),
+			process.cwd(),
+			undefined
+		);
+		expect(guess.format).toBe("modules");
+	});
 });

packages/wrangler/src/deployment-bundle/bundle.ts

@@ -46,6 +46,7 @@ export const COMMON_ESBUILD_OPTIONS = {
 	// v8 supports es2024 features as of 11.9
 	// workerd uses [v8 version 14.2 as of 2025-10-17](https://developers.cloudflare.com/workers/platform/changelog/#2025-10-17)
 	target: "es2024",
+	supported: { "import-source": true },
 	loader: { ".js": "jsx", ".mjs": "jsx", ".cjs": "jsx" },
 } as const;
 
@@ -384,6 +385,7 @@ export async function bundleWorker(
 			: undefined,
 		format: entry.format === "modules" ? "esm" : "iife",
 		target: COMMON_ESBUILD_OPTIONS.target,
+		supported: COMMON_ESBUILD_OPTIONS.supported,
 		sourcemap: sourcemap ?? true,
 		// Include a reference to the output folder in the sourcemap.
 		// This is omitted by default, but we need it to properly resolve source paths in error output.