fix: make wrangler types always generate a d.ts file for module w…

…orders (#5087)

---------

Co-authored-by: Pete Bacon Darwin <pete@bacondarwin.com>

.changeset/weak-tools-judge.md

@@ -0,0 +1,23 @@
+---
+"wrangler": patch
+---
+
+fix: make `wrangler types` always generate a `d.ts` file for module workers
+
+Currently if a config file doesn't define any binding nor module, running
+`wrangler types` against such file would not produce a `d.ts` file.
+
+Producing a `d.ts` file can however still be beneficial as it would define a correct
+env interface (even if empty) that can be expanded/referenced by user code (this can
+be particularly convenient for scaffolding tools that may want to always generate an
+env interface).
+
+Example:
+Before `wrangler types --env-interface MyEnv` run with an empty `wrangler.toml` file
+would not generate any file, after these change it would instead generate a file with
+the following content:
+
+```
+interface MyEnv {
+}
+```

packages/wrangler/src/__tests__/type-generation.test.ts

@@ -234,21 +234,49 @@ describe("generateTypes()", () => {
 		expect(fs.existsSync("./worker-configuration.d.ts")).toBe(true);
 	});
 
-	it("should not create DTS file if there is nothing in the config to generate types from", async () => {
-		fs.writeFileSync("./index.ts", "export default { async fetch () {} };");
-		fs.writeFileSync(
-			"./wrangler.toml",
-			TOML.stringify({
-				compatibility_date: "2022-01-12",
-				name: "test-name",
-				main: "./index.ts",
-			}),
-			"utf-8"
-		);
+	describe("when nothing was found", () => {
+		it("should not create DTS file for service syntax workers", async () => {
+			fs.writeFileSync(
+				"./index.ts",
+				'addEventListener("fetch", event => { event.respondWith(() => new Response("")); })'
+			);
+			fs.writeFileSync(
+				"./wrangler.toml",
+				TOML.stringify({
+					compatibility_date: "2022-01-12",
+					name: "test-name",
+					main: "./index.ts",
+				}),
+				"utf-8"
+			);
 
-		await runWrangler("types");
-		expect(fs.existsSync("./worker-configuration.d.ts")).toBe(false);
-		expect(std.out).toMatchInlineSnapshot(`""`);
+			await runWrangler("types");
+			expect(fs.existsSync("./worker-configuration.d.ts")).toBe(false);
+			expect(std.out).toMatchInlineSnapshot(`""`);
+		});
+
+		it("should create a DTS file with an empty env interface for module syntax workers", async () => {
+			fs.writeFileSync("./index.ts", "export default { async fetch () {} };");
+			fs.writeFileSync(
+				"./wrangler.toml",
+				TOML.stringify({
+					compatibility_date: "2022-01-12",
+					name: "test-name",
+					main: "./index.ts",
+				}),
+				"utf-8"
+			);
+
+			await runWrangler("types");
+			expect(fs.readFileSync("./worker-configuration.d.ts", "utf-8")).toMatch(
+				/interface Env \{\s*\}/
+			);
+			expect(std.out).toMatchInlineSnapshot(`
+			"interface Env {
+			}
+			"
+		`);
+		});
 	});
 
 	it("should create a DTS file at the location that the command is executed from", async () => {

packages/wrangler/src/type-generation.ts

@@ -305,9 +305,9 @@ function writeDTSFile({
 
 	let combinedTypeStrings = "";
 	if (formatType === "modules") {
-		combinedTypeStrings += `interface ${envInterface} {\n${envTypeStructure
-			.map((value) => `\t${value}`)
-			.join("\n")}\n}\n${modulesTypeStructure.join("\n")}`;
+		combinedTypeStrings += `interface ${envInterface} {${envTypeStructure
+			.map((value) => `\n\t${value}`)
+			.join("")}\n}\n${modulesTypeStructure.join("\n")}`;
 	} else {
 		combinedTypeStrings += `export {};\ndeclare global {\n${envTypeStructure
 			.map((value) => `\tconst ${value}`)
@@ -316,7 +316,10 @@ function writeDTSFile({
 
 	const wranglerCommandUsed = ["wrangler", ...process.argv.slice(2)].join(" ");
 
-	if (envTypeStructure.length || modulesTypeStructure.length) {
+	const typesHaveBeenFound =
+		envTypeStructure.length || modulesTypeStructure.length;
+
+	if (formatType === "modules" || typesHaveBeenFound) {
 		fs.writeFileSync(
 			path,
 			[