- Because pkgs/by-name/fo/foo exists, the attribute `pkgs.foo` must be defined like

    foo = callPackage ./pkgs/by-name/fo/foo/package.nix { /* ... */ };

  However, in this PR, the first `callPackage` argument is not a path. See the definition in all-packages.nix:3:

    foo = self.callPackage ({ someDrv, someFlag }: someDrv) { someFlag = true; };

This PR introduces the problems listed above. Please fix them before merging, otherwise the base branch would break.
