- 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, it isn't defined that way. See the definition in all-packages.nix:4

    foo = self.bar;

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