Tracing Bun.resolve

[vjpr]

Is there a way to debug how Bun is resolving something?

I am working in a pnpm monorepo.

TypeError: supportsColor.supportsColor is not a function. (In 'supportsColor.supportsColor(stream)', 'supportsColor.supportsColor' is an instance of Object)

  at /root/node_modules/.pnpm/supports-hyperlinks@2.3.0/node_modules/supports-hyperlinks/index.js
  ...

It seems that supports-color is resolving to a newer version where the supportsColor export was removed.

I logged the resolved path like so:

const supportsColor = require('supports-color');
console.log(require('supports-color/package.json').version)

const file = Bun.resolveSync('supports-color', import.meta.dir)
console.log(file)

And I get this:

7.2.0
/bun-vfs/node_modules/supports-color/index.js

7.2.0 is the correct package version. But when I try to modify the exports from the path on disk, they are not being changed.

Here is the output:

const supportsColor = require('supports-color');
console.log(supportsColor)
console.log(supportsColor.supportsColor)

{
  __esModule: true,
  default: [Getter],
  stderr: [Getter],
  stdout: [Getter],
  supportsColor: [Getter],
  [Symbol(CommonJSTransformed)]: true
}
{
  stdout: {
    level: 2,
    hasBasic: true,
    has256: true,
    has16m: false
  },
  stderr: {
    level: 2,
    hasBasic: true,
    has256: true,
    has16m: false
  }
}

---

1. Is there a way to show the resolution trace?
2. Can this be written to disk to be inspected in finder/bash?
3. How does the resolution algorithm work?

[vjpr]

This gives me the results I desire:

console.log(require('supports-color/index.js').supportsColor)
console.log(Bun.resolveSync('supports-color/index.js', import.meta.dir))

/xxx/node_modules/.pnpm/supports-color@7.2.0/node_modules/supports-color/index.js

But this doesn't:

console.log(Bun.resolveSync('supports-color', import.meta.dir))
console.log(require('supports-color').supportsColor)

/bun-vfs/node_modules/supports-color/index.js

Seems like an issue to do with naked imports.

---

I think the bug is related to something going on here:

https://bun.sh/docs/runtime/modules#importing-commonjs-from-commonjs

module, exports, and require are very much like the module, exports, and require in Node.js. These are assigned via a with scope in C++. An internal Map stores the exports object to handle cyclical require calls before the module is fully loaded.

Once the CommonJS module is successfully evaluated, a Synthetic Module Record is created with the default ES Module export set to module.exports and keys of the module.exports object are re-exported as named exports (if the module.exports object is an object).

[vjpr]

Looks like its being detected as a "node-fallback", but its actually not a node built-in.

There is also @vercel/fetch in that list so maybe it is a hack to get it to work.

bun/src/node_fallbacks.zig

Line 31 in 557aac6

const supports_color_code: string = @embedFile("./node-fallbacks/out/supports-color.js");

[vjpr]

See: #2040 (comment)