fix(wrangler): Fix pages dev watch mode [_worker.js]

[CarmenPopoviciu]

What this PR solves / how to test

The watch mode in pages dev for Advanced Mode projects is currently partially broken, as it only watches for changes in the _worker.js file, but not for changes in any of its imported dependencies. This means that given the following _worker.js file

import { graham } from "./graham-the-dog";
export default {
    fetch(request, env) {
	return new Response(graham)
    }
}

pages dev will reload for any changes in the _worker.js file itself, but not for any changes in graham-the-dog.js, which is its dependency.

Similarly, pages dev will not reload for any changes in non-JS module imports, such as wasm/html/binary module imports.

This commit addresses all the aforementioned issues.

Fixes #4824

Solutions we considered

Our original solution was implemented using esbuild's watch mode (see dd6cd19), which basically meant just enabling the watch flag in buildRawWorker(). Turned out though (via failed test in CI), that this solution introduced a regression for a frameworks corner case...the deletion of _worker.js itself (please see #4877 and #3886).

When used in the context of frameworks, the assets directory served by pages dev gets rebuilt (removed + added back with updated assets) by a separate process, external to wrangler (I'm no expert here on the exact details, but I assume this more or less to be the case). This affects key Pages files, such as _worker.js and _routes.json, which get deleted/added back as part of that assets directory, which in turn, triggers a _worker.js rebuild. If the _worker.js re-build is triggered before the external process gets a chance to add the file back, pages dev will show a bunch of errors in the terminal, which, while accurate, seem to be confusing/annoying for our users. This was fixed by #4877 by completely turning off Worker rebuilds for chokidar "unlink` events.

Unfortunately, the behaviour for this particular use case is very hard to port to esbuild watch mode, since esbuild gives us very limited information wrt to what changed ....so here we are 😢

This lead us to the second implementation (see 5c8fcf0), which, similar to Functions, delegates the entirety of the watch mechanism to chokidar.

How we tested the changes

This PR comes with e2e tests, but in addition to them, we've manually tested these changes in the following scenarios:

• change/remove/add _worker.js
• change in external dependency (eg import { ADD } from "..//**//add")
• change in external module (eg import html from "..//**//my-html.html")
• adding/removing external dependencies
• errors in _worker.js
• errors in dependencies

Author has addressed the following

• Tests
  • TODO (before merge)
  • Included
  • Not necessary because:
• E2E Tests CI Job required? (Use "e2e" label or ask maintainer to run separately)
  • I don't know
  • Required / Maybe required
  • Not required because:
• Changeset (Changeset guidelines)
  • TODO (before merge)
  • Included
  • Not necessary because:
• Public documentation
  • TODO (before merge)
  • Cloudflare docs PR(s):
  • Not necessary because: watch mode is not documented

[changeset-bot]

🦋 Changeset detected

Latest commit: de6fbc2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
wrangler	Patch
@cloudflare/vitest-pool-workers	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

A wrangler prerelease is available for testing. You can install this latest build in your project with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9796131036/npm-package-wrangler-6150

You can reference the automatically updated head of this PR with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/prs/6150/npm-package-wrangler-6150

Or you can use npx with this latest build directly:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9796131036/npm-package-wrangler-6150 dev path/to/script.js

Additional artifacts:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9796131036/npm-package-create-cloudflare-6150 --no-auto-update

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9796131036/npm-package-cloudflare-kv-asset-handler-6150

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9796131036/npm-package-miniflare-6150

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9796131036/npm-package-cloudflare-pages-shared-6150

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/9796131036/npm-package-cloudflare-vitest-pool-workers-6150

Note that these links will no longer work once the GitHub Actions artifact expires.

---

[email protected] includes the following runtime dependencies:

Package	Constraint	Resolved
miniflare	workspace:*	3.20240701.0
workerd	1.20240701.0	1.20240701.0
workerd --version	1.20240701.0	2024-07-01

Please ensure constraints are pinned, and miniflare/workerd minor versions match.

[andyjessop]

Looks great! Just some minor comments, but nothing blocking.

[penalosa]

Approved pending #6150 (comment), which I'm likely misunderstanding