chore: check WORKERS_CI env variable to determine if we're building for Cloudflare Workers (#13733)

Inspired by unjs/std-env#156

~This PR detects the `WORKERS_CI` environment variable so that
`adapter-auto` and `adapter-cloudflare` can work with Cloudflare's
[Workers Git
integration](https://developers.cloudflare.com/workers/ci-cd/builds/) to
build the app without requiring a wrangler configuration from the user.~

I've changed the scope of the PR to focus on only the Cloudflare adapter
because we'll may end up deprecating adapter-auto. Also, it doesn't work
well with adapter-auto since it requires a wrangler config file.

---

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---------

Co-authored-by: Chew Tee Ming <chew.tee.ming@nindatech.com>
Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

Author: 3 people

.changeset/plenty-cougars-wave.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': patch
+---
+
+chore: check the `WORKERS_CI` environment variable to determine if we're building for Cloudflare Workers

packages/adapter-cloudflare/utils.js

@@ -9,7 +9,7 @@ export function is_building_for_cloudflare_pages(wrangler_config) {
 		return true;
 	}
 
-	if (wrangler_config.main || wrangler_config.assets) {
+	if (!!process.env.WORKERS_CI || wrangler_config.main || wrangler_config.assets) {
 		return false;
 	}
 

packages/adapter-cloudflare/utils.spec.js

@@ -68,6 +68,15 @@ describe('detects Cloudflare Workers project', () => {
 			)
 		).toBe(false);
 	});
+
+	test('WORKERS_CI environment variable', () => {
+		vi.stubEnv('WORKERS_CI', '1');
+		const result = is_building_for_cloudflare_pages(
+			/** @type {import('wrangler').Unstable_Config} */ ({})
+		);
+		vi.unstubAllEnvs();
+		expect(result).toBe(false);
+	});
 });
 
 describe('validates Wrangler config', () => {