fix: __dirname and __filename collisions

[amorriscode]

What does this PR do?

This PR resolves issues with __dirname and __filename collisions (#17188) by creating unique variables when __dirname or __filename are used in a bundle.

How did you verify your code works?

• I included a test for the new code, or existing tests cover it
• I ran my tests locally and they pass (bun-debug test test-file-name.test)
• Used the debug build to test the fix

Reproduction

When multiple files utilize __dirname/__filename Bun hoists the values to the top of the module code. However, since it is a var it can be overwritten effectively making it so only __dirname/__filename values collide.

Before

// test2/test.ts
var __dirname = "/Users/anthony/dev/test/test2", __filename = "/Users/anthony/dev/test/test2/test.ts";
function test() {
  console.log(__filename);
  console.log(__dirname);
}

// index.ts
var __dirname = "/Users/anthony/dev/test", __filename = "/Users/anthony/dev/test/index.ts";
console.log(__filename);
console.log(__dirname);
test();

In this single JS output, __dirname ends up evaluating to /Users/anthony/dev/test in both places it is called because that is the last value the var is assigned to.

After

The collision no longer occurs because usages of __dirname and __filename get unique values.

// test2/test.ts
var __dirname_af38e5cdfa6876c9 = "/Users/anthony/dev/test/test2", __filename_9b03b912cc9c01cd = "/Users/anthony/dev/test/test2/test.ts";
function test() {
  console.log(__filename_9b03b912cc9c01cd);
  console.log(__dirname_af38e5cdfa6876c9);
}

// index.ts
var __dirname_58f1efdc5b67fffe = "/Users/anthony/dev/test", __filename_c508108910e49d6d = "/Users/anthony/dev/test/index.ts";
console.log(__filename_c508108910e49d6d);
console.log(__dirname_58f1efdc5b67fffe);
test();

[Jarred-Sumner]

Thank you for this - the changes look like they work as expected, but I think we need to add an option to control the behavior of __dirname and __filename and similar.

This collision is intentional and important for making things like .node addons bundle successfully. The behavior of __dirname and __filename when bundled is ambiguous.