error:
       … in the right operand of the update (//) operator

         at /pwd/lang/eval-fail-recursion.nix:1:12:

            1| let a = {} // a; in a.foo
             |            ^
            2|

       error: infinite recursion encountered

       at /pwd/lang/eval-fail-recursion.nix:1:15:

            1| let a = {} // a; in a.foo
             |               ^
            2|
