> Assuming the port is actually 1:1 without any behavioral changes, these bugs already exist in the Zig code

The "1:1" assumption is a massive unjustified assumption. Rust and Zig have different memory models, so it's possible to do a "1:1" translation of Zig code to Rust and end up with undefined behavior in Rust.

For example, Zig code might make assumptions about lifetimes based on implicit knowledge of which allocator was used for some memory. That could cause problems in Rust if you erase the lifetime https://github.com/oven-sh/bun/blob/main/src/bun_core/string...

can't help myself: how common to see code like https://github.com/oven-sh/bun/blob/main/src/bun_core/string... instead of simple ilog2()? I guess, ut somewhat explains how they got 700k+ lines of code