Notify serverless-offline when watched files trigger rebuild

[aldenquimby]

This is my first time contributing. Please let me know what you'd like to see in terms of tests, documentation, etc - thanks!

Background

• With a default serverless-offline + serverless-esbuild setup, watching for changes does not work
• See Esbuild watch with sls offline not working #108

Problem

• The --reloadHandler solution proposed in the above issue drastically hurts local dev performance on a large project

Proposal

• Leverage POC for externally triggering cleanup of lambda functions dherault/serverless-offline#1093 to tell serverless-offline when it needs to clear the cache

Alternatives

• If serverless-esbuild should expose lifecycle events to be hookable #158 was built, this may not be necessary
• For example with serverless-webpack, which already supports lifecycle hooks, I use a custom plugin to solve this exact same problem:

class OfflineInvalidate {
  constructor(serverless) {
    this.hooks = {
      'after:webpack:compile:watch:compile': () =>
        serverless.pluginManager.spawn('offline:functionsUpdated'),
    };
  }
}
module.exports = OfflineInvalidate;

• I'd still prefer this proposed PR, so that watching "just works" with a default setup

[floydspace]

I agree with your statement, currently, we don't have lifecycle events, so this workaround would be fair to have till the time we implement hooks, (if we ever do that)

[github-actions]

🎉 This PR is included in version 1.47.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[pslm93]

Hi could you please provide a simple example for making hot reload work when utilizing serverless-offline + serverless-build? I am unable to get this to work. What should the watch pattern be? I see in examples that the pattern is an array but my IDE complains that the pattern must be a string. What should be done for serverless offline?
I have the following in my serverless.yml file:

plugins:
  - serverless-domain-manager
  - serverless-esbuild
  - serverless-newrelic-lambda-layers
  - serverless-prune-plugin
  - serverless-offline
  
  custom:
     esbuild:
       external:
         - deasync
         - newrelic
       watch:
         pattern: "src/**/*.(js|ts)"
       bundle: true
       minify: true
       sourcemap: true

But when I have my application running by sls offline, when I update anything in my code, the changes don't trigger a rebuild. Thank you so much for your help.

[aldenquimby]

@pslm93 any chance you can link to an example repo? I have a similar configuration, and it's working for me after this PR.

To debug, I think the first step is to determine if the problem is with esbuild, or with serverless-offline. Add keepOutputDirectory: true under esbuild in your serverless.yml so you can see the .esbuild directory. Change a source file, and you should see the JS output update accordingly automatically. If it doesn't update, the problem is with esbuild and your watch config. If it does update, the problem is with serverless-offline.