[wrangler] Clean up compatibility fallback warnings

.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";
@@ -68,11 +69,18 @@ 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(`
-			        "[33m▲ [43;33m[[43;30mWARNING[43;33m][0m [1mNo compatibility_date was specified. Using today's date: <current-date>.[0m
+			        "[33m▲ [43;33m[[43;30mWARNING[43;33m][0m [1mNo compatibility_date was specified. Using the installed Workers runtime's latest supported date: <current-date>.[0m
 
 			          Add one to your wrangler.toml file:
 			          \`\`\`

packages/wrangler/src/dev/miniflare.ts

@@ -13,6 +13,7 @@
 import { withSourceURLs } from "../deployment-bundle/source-url";
 import { getHttpsOptions } from "../https-options";
 import { logger } from "../logger";
+import { updateCheck } from "../update-check";
 import type { Config } from "../config";
 import type {
 	CfD1Database,
@@ -122,10 +123,19 @@
 
 	warn(message: string) {
 		// Only log warning about requesting a compatibility date after the workerd
-		// binary's version once
+		// binary's version once, and only if there's an update available.
 		if (message.startsWith("The latest compatibility date supported by")) {
 			if (this.#warnedCompatibilityDateFallback) return;
 			this.#warnedCompatibilityDateFallback = true;
+			return void updateCheck().then((maybeNewVersion) => {
+				if (maybeNewVersion === undefined) return;
+				message += [
+					"",
+					"Features enabled by your requested compatibility date may not be available.",
+					`Upgrade to \`wrangler@${maybeNewVersion}\` to remove this warning.`,
+				].join("\n");
+				super.warn(message);
+			});
 		}
 		super.warn(message);
 	}

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";
@@ -806,11 +807,18 @@ 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` +
+			`No compatibility_date was specified. Using the installed Workers runtime's latest supported date: ${currentDate}.\n` +
 				"Add one to your wrangler.toml file:\n" +
 				"```\n" +
 				`compatibility_date = "${currentDate}"\n` +

packages/wrangler/src/update-check.ts

@@ -2,7 +2,7 @@
 import pkg from "../package.json";
 import type { Result } from "update-check";
 
-export async function updateCheck(): Promise<string | undefined> {
+async function doUpdateCheck(): Promise<string | undefined> {
 	let update: Result | null = null;
 	try {
 		// default cache for update check is 1 day
@@ -14,3 +14,11 @@
 	}
 	return update?.latest;
 }
+
+// Memoise update check promise, so we can call this multiple times as required
+// without having to prop drill the result. It's unlikely to change through the
+// process lifetime.
+let updateCheckPromise: Promise<string | undefined>;
+export function updateCheck(): Promise<string | undefined> {
+	return (updateCheckPromise ??= doUpdateCheck());
+}