Nix wrote half of my debugger

Nix has developed a debugger for its deterministic VM, Rewind. The debugger is integrated with the source panel, stack frames, bookmarks, and thread lanes. It leverages Nix's ability to access the exact inputs of a program, debug symbols, sources, and libraries, as well as the derivation that packages are built from. Rewind's VM runs on a single CPU, which helps in isolating race conditions.

It runs the build multiple times with different schedules, narrowing down the failure to a specific step. The debugger allows users to see the source of the program at the playhead, stack frames, and even execute gdb commands on a fork of the run. If the source is not enough, users can use rewind gdb to inspect the program's state.

Rewind also provides a Compare tab that shows the differences between two runs, helping to identify the exact step where a race condition occurs.