nix/doc/manual/rl-next/relative-path-flakes.md

synopsis	prs
Support for relative path inputs	10089

Flakes can now refer to other flakes in the same repository using relative paths, e.g.

inputs.foo.url = "path:./foo";

uses the flake in the foo subdirectory of the referring flake. For more information, see the documentation on the path flake input type.

This feature required a change to the lock file format. Previous Nix versions will not be able to use lock files that have locks for relative path inputs in them.