lix/src/libexpr/settings/debugger-on-trace.md

name, internalName, type, default

name	internalName	type	default
debugger-on-trace	builtinsTraceDebugger	bool	false

If set to true and the --debugger flag is given, builtins.trace will enter the debugger like builtins.break.

This is useful for debugging warnings in third-party Nix code.