dune was showing this error when using lwt_ppx:
File "/nix/store/sz4cg32ph84lapgs50xv73s3a0baqq2s-ocaml4.08.1-lwt_ppx-4.2.1/lib/ocaml/4.08.1/site-lib/lwt_ppx/dune-package", line 11, characters 56-75:
11 | (requires compiler-libs.common ocaml-migrate-parsetree ppx_tools_versioned)
^^^^^^^^^^^^^^^^^^^
Error: Library "ppx_tools_versioned" not found.
-> required by library "lwt_ppx" in
/nix/store/sz4cg32ph84lapgs50xv73s3a0baqq2s-ocaml4.08.1-lwt_ppx-4.2.1/lib/ocaml/4.08.1/site-lib/lwt_ppx
-> required by executable wizytests in dune:6
Hint: try: dune external-lib-deps --missing @@default
d5053d12eb