Support ctx.exports in the Vite plugin

[jamesopstad]

Fixes #000.

ctx.exports is now supported in the runtime (see https://developers.cloudflare.com/workers/runtime-apis/context/#exports). In vite dev, the user's Worker entry module is not the top-level module that workerd sees. Instead the top-level module exports proxy classes that interface with Vite to fetch the user's code. Because of this, ctx.exports would not automatically work as the exports to include in this module can not be determined from the user's config. We now run the code in the user's Worker entry module when starting the dev server to determine the exports that should be included.

Summary

Initial server start

• Miniflare is started and the Worker entry modules are populated with exports derived from the user's Worker config files (across all Workers).
• A request is made to the Workers to get the export names and types for the exports defined in the user's Worker entry modules.
• The exports types are compared to those that were used when starting Miniflare. If they differ then Miniflare is restarted.

Note that restarting the Vite dev server itself is not possible during the initial start as the server has not yet been fully initialised. Restarting Miniflare is therefore the better option during this phase and is more optimal.

Updates to Worker entry modules

• When a Worker entry module is updated, a message is sent to the dev server with the latest export types.
• If the export types have changed then the Vite dev server is restarted.

Note that restarting Miniflare without also restarting the dev server is problematic at this stage. This is because the dev server restart includes teardown and reinitialisation of environments that would otherwise have to be replicated somehow. Restarting the dev server is the best option in this phase and makes the behaviour of updating export types equivalent to updating the Worker config file.

---

• Tests
  • Tests included
  • Tests not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: already documented
• Wrangler V3 Backport
  • Wrangler PR:
  • Not necessary because: not a Wrangler change

[changeset-bot]

🦋 Changeset detected

Latest commit: 37146eb

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

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commit: 37146eb

[github-actions]

Failed to automatically backport this PR's changes to Wrangler v3. Please manually create a PR targeting the v3-maintenance branch with your changes. Thank you for helping us keep Wrangler v3 supported!

Depending on your changes, running git rebase --onto v3-maintenance main james/ctx-exports might be a good starting point.

Notes:

• your PR branch should be named v3-backport-11238
• add the skip-v3-pr label to the current PR to stop this workflow from failing

[ascorbic]

Could you update the description to give some background for the change – why it's needed, how it's used etc?

[jamesopstad]

Could you update the description to give some background for the change – why it's needed, how it's used etc?

Updated.

[edmundhung]

I am still going through the second half of the commits. Just a few nits so far

[edmundhung]

Looks good. Just a few minor nits.