My initial reaction was that this is pure insanity but in fairness this is a fairly 1:1 port of existing code, so the developer's mental model of it should still match fairly well.

For instance look at this Zig function: https://github.com/oven-sh/bun/blob/ed1a70f81708d7d137de8de0...

Versus this Rust version: https://github.com/oven-sh/bun/blob/ed1a70f81708d7d137de8de0...

I did pick that at random but it does look like the best case. I skimmed through a lot of the Rust code and there's a surprisingly small amount of `unsafe`.

Still pretty insane to merge this in such a short time with so little testing, but I can easily think of bigger software engineering mistakes. Hell it's not like Bun even needs to be commercially successful any more.

It’s still 400k more lines

Dunno where you got that number from but it's half that. Tokei says:

  ===============================================================================
   Language            Files        Lines         Code     Comments       Blanks
  ===============================================================================
   Zig                  1298       711112       577946        57772        75394
   Rust                 1443       931232       737485       114373        79374
So it's 28% more lines of code (not comments/blanks).

Rust is mostly ~20% bigger. Except comments. Where they basically doubled... what's with that?