I ran into the first instance of path interpolation syntax slipping into nixpkgs today: NixOS/nixpkgs#188466. Our lib/minver.nix prescribes that we support everything from 2.3 upwards.

Without CI to catch it, it is quite understandable that contributors accidentally introduce such changes (who remembers the changelog precisely?). Running the eval checks on the oldest supported Nix version should be enough, as any accepted Nix expressions under 2.3 should be forwards compatible.