To be fair, I don't know if the Bun team ever did try to upstream it. In their Twitter thread announcing their vibe-coded fork of the Zig compiler, they said they wouldn't bother trying to upstream their changes because of Zig's policy banning LLM-authored contributions. Still probably a calculated political move to cut ties with Zig and muster community support for a Rust rewrite. https://x.com/bunjavascript/status/2048428104893542781