Can't build javascript backend with nix

Summary

Tried to build the javascript backend using the instructions in in the wiki. Fails with

       > /nix/store/3qnm3nwjajgqa771dmi2dnwxrw0kzq5m-stdenv-linux/setup: line 116: --datadir=$doc/share/doc/ghc: No such file or directory
       > /nix/store/3qnm3nwjajgqa771dmi2dnwxrw0kzq5m-stdenv-linux/setup: line 131: pop_var_context: head of shell_variables not a function context

Steps to reproduce

Job log is here: https://gitlab.horizon-haskell.net/ghc/horizon-ghc/-/jobs/1429953

nix build .#ghc