Use installed workerd version as default compat date instead of now

`wrangler dev` would previously use the current date as the default
compatibility date if one wasn't set in `wrangler.toml`. Before the
previous commit, this would show a warning if it was greater than the
installed `workerd` version. Whilst using the current date as the
default would no longer log a warning with this change, if there was
an update it would. This change sets the default to the `workerd`
version instead.

.changeset/five-suits-rest.md

@@ -0,0 +1,17 @@
+---
+"wrangler": minor
+---
+
+fix: suppress compatibility date fallback warnings if no `wrangler` update is available
+
+If a compatibility date greater than the installed version of `workerd` was
+configured, a warning would be logged. This warning was only actionable if a new
+version of `wrangler` was available. The intent here was to warn if a user set
+a new compatibility date, but forgot to update `wrangler` meaning changes
+enabled by the new date wouldn't take effect. This change hides the warning if
+no update is available.
+
+It also changes the default compatibility date for `wrangler dev` sessions
+without a configured compatibility date to the installed version of `workerd`.
+This previously defaulted to the current date, which may have been unsupported
+by the installed runtime.

packages/wrangler/src/__tests__/dev.test.tsx

@@ -1,4 +1,5 @@
 import * as fs from "node:fs";
+import module from "node:module";
 import getPort from "get-port";
 import { rest } from "msw";
 import patchConsole from "patch-console";
@@ -68,7 +69,14 @@ describe("wrangler dev", () => {
 			});
 			fs.writeFileSync("index.js", `export default {};`);
 			await runWrangler("dev");
-			const currentDate = new Date().toISOString().substring(0, 10);
+
+			const miniflareEntry = require.resolve("miniflare");
+			const miniflareRequire = module.createRequire(miniflareEntry);
+			const miniflareWorkerd = miniflareRequire("workerd") as {
+				compatibilityDate: string;
+			};
+			const currentDate = miniflareWorkerd.compatibilityDate;
+
 			expect(std.out).toMatchInlineSnapshot(`""`);
 			expect(std.warn.replaceAll(currentDate, "<current-date>"))
 				.toMatchInlineSnapshot(`

packages/wrangler/src/index.ts

@@ -1,3 +1,4 @@
+import module from "node:module";
 import os from "node:os";
 import TOML from "@iarna/toml";
 import chalk from "chalk";
@@ -813,8 +814,15 @@ export async function main(argv: string[]): Promise<void> {
 export function getDevCompatibilityDate(
 	config: Config,
 	compatibilityDate = config.compatibility_date
-) {
-	const currentDate = new Date().toISOString().substring(0, 10);
+): string {
+	// Get the maximum compatibility date supported by the installed Miniflare
+	const miniflareEntry = require.resolve("miniflare");
+	const miniflareRequire = module.createRequire(miniflareEntry);
+	const miniflareWorkerd = miniflareRequire("workerd") as {
+		compatibilityDate: string;
+	};
+	const currentDate = miniflareWorkerd.compatibilityDate;
+
 	if (config.configPath !== undefined && compatibilityDate === undefined) {
 		logger.warn(
 			`No compatibility_date was specified. Using today's date: ${currentDate}.\n` +