JS loader caues unnecessary/unwanted/unexpected transformations

[spamshaker]

What version of Bun is running?

1.1.40+b5b51004e

What platform is your computer?

Darwin 24.2.0 arm64 arm

What steps can reproduce the bug?

given I have an input sample.mjs:

export const  __filename = new URL(import.meta.url).pathname;
export const __dirname = __filename.split('/').slice(0, -1).join('/');

console.log({ __dirname, __filename });

run
bun build sample.mjs

What is the expected behavior?

the output should not be touched and look like following which esbuild does
esbuild sample.mjs gives correct result:

"use strict";
export const __filename = new URL(import.meta.url).pathname;
export const __dirname = __filename.split("/").slice(0, -1).join("/");
console.log({ __dirname, __filename });

What do you see instead?

// sample.mjs
var __filename2 = new URL(import.meta.url).pathname;
var __dirname2 = __filename2.split("/").slice(0, -1).join("/");
console.log({ __dirname: __dirname2, __filename: __filename2 });
export {
  __filename2 as __filename,
  __dirname2 as __dirname
};

Additional information

const should never be transformed to var in esm as it has different behaviors