feat: experimental native bun support

[pi0]

🔗 Linked issue

resolves #154

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

When running in Bun runtime we can leverage Bun's native typescript and CJS handling.

Running current fixtures against Bun, it seems platform support is extremely good and we can directly depend on Bun's require implementation 💯

There might be more runtime differences but I think generally for the sake of performance, worth to make Jiti bypass all transforms.

Known issues:

• import.meta.env is not supported
• Inside typescript files, cannot import with .mts as .mjs

On known issues, jiti falls back to it's default behavior to increase compatibility

/cc @birkskyum @paperdave @Jarred-Sumner

TODO:

• Cache invalidation support (important for config reload like nuxt.config.ts)
• Disable when custom transform options/plugins are provided (untyped babel plugin)
• Allow opting-out (using JITI_EXPERIMENTAL_BUN: false or experimentalBun: false)

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[Jarred-Sumner]

Inside typescript files, cannot import with .mjs extension

This sounds like a bug. Does it really not work in general with .mjs or is there something more specific going wrong?

[Jarred-Sumner]

To make import.meta.env work, I think you could override the getter on the import.meta object and define an env property to return either Bun.env or process.env.

Something like

const proto = Object.getPrototypeOf(import.meta)
proto.env = process.env 

[pi0]

This sounds like a bug. Does it really not work in general with .mjs or is there something more specific going wrong?

Reproduction: https://github.com/unjs/jiti/blob/main/test/fixtures/typescript/index.ts

.mjs from .ts work in general. It is related to .mts support

[pi0]

To make import.meta.env work, I think you could override the getter on the import.meta object and define an env property to return either Bun.env or process.env.

Thanks! I wasn't sure if extending import.meta is something safe for Bun but i can add polyfill like this if seems good to you! Just to make sure it is not planned in short term for native import.meta.env support?

[AndreyYolkin]

What do you think about moving Bun detection into https://github.com/unjs/std-env?