nix/doc/manual/rl-next/enter-debugger-more-reliably-in-let-and-calls.md

synopsis	prs	issues
The `--debugger` will start more reliably in `let` expressions and function calls	9917	6649

Previously, if you attempted to evaluate this file with the debugger:

let
  a = builtins.trace "before inner break" (
    builtins.break "hello"
  );
  b = builtins.trace "before outer break" (
    builtins.break a
  );
in
  b

Nix would correctly enter the debugger at builtins.break a, but if you asked it to :continue, it would skip over the builtins.break "hello" expression entirely.

Now, Nix will correctly enter the debugger at both breakpoints.