error:
       … while evaluating the attribute 'set'
         at /pwd/lang/eval-fail-dup-dynamic-attrs.nix:2:3:
            1| {
            2|   set = { "${"" + "b"}" = 1; };
             |   ^
            3|   set = { "${"b" + ""}" = 2; };

       error: dynamic attribute 'b' already defined at /pwd/lang/eval-fail-dup-dynamic-attrs.nix:2:11
       at /pwd/lang/eval-fail-dup-dynamic-attrs.nix:3:11:
            2|   set = { "${"" + "b"}" = 1; };
            3|   set = { "${"b" + ""}" = 2; };
             |           ^
            4| }
