feat: add ESM support when bundling with NFT

[eduardoboucas]

- Summary

Adds support for ESM functions when bundling with NFT. We look for ESM files in the NFT cache and, for each one that is found, we use esbuild to transpile them down to CJS. We then replace the original files with the transpiled ones in the archive.

- Test plan

Included the NFT variation in 3 tests.

- A picture of a cute animal (not mandatory but encouraged)

[netlify-team-account-1]

approving since tests are green, and it looks fine. One thing I don't understand, maybe you can give some insight:

Once ESM files are transpiled, what happens to them? I understand that each ESM file gets a CJS equivalent at some tmp destination. I'd assume that these tmp files are used to replace the ESM ones at some point, but I can't find where that happens 🤔

[eduardoboucas]

Once ESM files are transpiled, what happens to them? I understand that each ESM file gets a CJS equivalent at some tmp destination. I'd assume that these tmp files are used to replace the ESM ones at some point, but I can't find where that happens 🤔

You're absolutely correct. I think the part you're missing happens in a Map called aliases (which, as most things, could have a better name), which maps paths that should be in the archive to the paths they should take inside the zip.

Example:

{
  "/tmp/function-1-transpiled.js" => "/netlify/functions/function-1.js"
}

With this aliases object, when we find /tmp/function-1-transpiled.js in the list of files to include, we rename it to /netlify/functions/function-1.js, which is the expected path of the original, untranspiled file.

Each bundler is responsible for creating this aliases file, which is then used at the archive creation time.

Does that help?

[netlify-team-account-1]

yes, that helped! thank you :)

[github-actions]

⏱ Benchmark results

largeDepsEsbuild: 8.4s

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• T (current commit): 8.4s

largeDepsNft: 53.8s

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• T (current commit): 53.8s

largeDepsZisi: 1m 7.5s

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• T (current commit): 1m 7.5s