Mark Bun built-ins as external

[colinhacks]

Users of various Vite-based frameworks have been hitting module resolution errors when trying Bun's built-in modules like bun:sqlite. These frameworks generally rely on esbuild's default behavior of marking Node.js built-ins as external & side-effect-free. This PR does the same for Bun's built-ins: bun:* modules and bun itself.

Happy to update this to explicitly list each Bun builtin: bun:test, bun:ffi, bun:sqlite, etc. But we'll likely update this list several times in the future and I was worried about maintainence burden for esbuild. So currently this PR just checks for the bun: prefix. Unlike Node.js, Bun requires usage of the bun: prefix for its built-in modules.

Some of the issues this fixes

• https://github.com/oven-sh/bun/issues/4761
• https://github.com/oven-sh/bun/issues/4704
• https://github.com/withastro/astro/issues/8476
• https://github.com/vitejs/vite/issues/14351
• https://github.com/oven-sh/bun/issues/4704

[evanw]

I'm not sure this specific direction (adding bun-specific stuff to esbuild's node target) makes sense because that target is for node, not bun.

[Jarred-Sumner]

I'm not sure this specific direction (adding bun-specific stuff to esbuild's node target) makes sense because that target is for node, not bun.

Bun is intended as a drop-in replacement for Node, so if anything in the node target does not work in Bun, it would be a bug in Bun (and not esbuild). A bun target would be more maintenance work for esbuild and would mean existing projects would need to change their esbuild configuration to fully support Bun.

[ersinakinci]

Any update on this? Or does anyone have workarounds?

[evanw]

I'm not sure if this will work for you, but FYI esbuild already has an API to mark things as external: https://esbuild.github.io/api/#external. Specifically --external:bun:* --external:bun will mark bun as external as well as anything starting with bun:.