fix(wrangler): show friendly error when D1 export output is a directory (#12065)

Co-authored-by: Edmund Hung <me@edmund.dev>

Author: langningchen

.changeset/cute-pets-fry.md

@@ -0,0 +1,5 @@
+---
+"wrangler": patch
+---
+
+Improve error message when `d1 export --output` points to a directory

packages/wrangler/src/__tests__/d1/export.test.ts

@@ -24,6 +24,16 @@ describe("export", () => {
 		);
 	});
 
+	it("should throw if output is a directory", async () => {
+		fs.mkdirSync("test-dir");
+
+		await expect(
+			runWrangler("d1 export db --output test-dir")
+		).rejects.toThrowError(
+			`Please specify a file path for --output, not a directory.`
+		);
+	});
+
 	it("should throw if local and remote are both set", async () => {
 		await expect(
 			runWrangler("d1 export db --local --remote --output test-local.sql")

packages/wrangler/src/d1/export.ts

@@ -1,3 +1,4 @@
+import { statSync } from "node:fs";
 import fs from "node:fs/promises";
 import path from "node:path";
 import { spinner, spinnerWhile } from "@cloudflare/cli/interactive";
@@ -82,6 +83,13 @@ export const d1ExportCommand = createCommand({
 			throw new UserError(`You cannot specify both --no-schema and --no-data`);
 		}
 
+		const stats = statSync(output, { throwIfNoEntry: false });
+		if (stats?.isDirectory()) {
+			throw new UserError(
+				`Please specify a file path for --output, not a directory.`
+			);
+		}
+
 		// Allow multiple --table x --table y flags or none
 		const tables: string[] = table
 			? Array.isArray(table)