Serverless not working with Netlify esbuild

[5t3ph]

Describe the bug
Deploying an 11ty site on Netlify with the esbuild function bundling does not successfully retain the serverless functionality, so serverless pages are inaccessible.

To Reproduce

1. Clone this repo with the reduced test case of a very basic serverless setup including the esbuild parts for Netlify: https://github.com/5t3ph/11ty-serverless-esbuild-test
2. Deploy to Netlify
3. Observe that the serverless page does not load, but displays an error similar to the following

{"errorType":"Error","errorMessage":"Cannot find module '/var/task/netlify/functions/possum/eleventy-serverless-map.json'\nRequire stack:\n- /var/task/node_modules/@11ty/eleventy/src/Serverless.js\n- /var/task/node_modules/@11ty/eleventy/src/Eleventy.js\n- /var/task/netlify/functions/possum/index.js\n- /var/task/possum.js\n- /var/runtime/UserFunction.js\n- /var/runtime/index.js","trace":["Error: Cannot find module '/var/task/netlify/functions/possum/eleventy-serverless-map.json'","Require stack:","- /var/task/node_modules/@11ty/eleventy/src/Serverless.js","- /var/task/node_modules/@11ty/eleventy/src/Eleventy.js","- /var/task/netlify/functions/possum/index.js","- /var/task/possum.js","- /var/runtime/UserFunction.js","- /var/runtime/index.js","    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:902:15)","    at Function.Module._load (internal/modules/cjs/loader.js:746:27)","    at Module.require (internal/modules/cjs/loader.js:974:19)","    at require (internal/modules/cjs/helpers.js:93:18)","    at Serverless.getContentMap (/var/task/node_modules/@11ty/eleventy/src/Serverless.js:102:22)","    at Serverless.isServerlessUrl (/var/task/node_modules/@11ty/eleventy/src/Serverless.js:117:27)","    at Runtime.handler (/var/task/netlify/functions/possum/index.js:45:14)"]}

live page link

Expected behavior
The serverless page loads successfully.

Environment:

• New Netlify build (focal)
• Eleventy Version: ^1.0.0

Additional context
Discovered esbuild was needed to deploy a site that was going to use the prismic plugin. Then the serverless component that allows live previewing from Prismic CMS wouldn't function on deploy. The same issue was repro'd in the demo repo with a basic serverless setup.

[zachleat]

Agree that there is something to fix here but in the mean time here’s some netlify.toml addition that I’ve used to “make it work” now with esbuild:

[functions]
node_bundler = "esbuild"

[functions.possum]
included_files = [
  "./netlify/functions/possum/**/*",
  "./netlify/functions/possum/.cache/**/*"
]

[zachleat]

I did test this on your test case repo here: 5t3ph/11ty-serverless-esbuild-test@main...zachleat:main

https://main--peppy-lebkuchen-2767ab.netlify.app/

[zachleat]

Stale per project slipstream changes in #3074.

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