Thanks for working on this.

If this makes topkg work out of the box, can you please simplify the topkg.run command accordingly as part of this PR; thanks.

As a minor remark, I find the wording “make [it] work” a bit misleading: it still does not work but is automatically rewritten into something that does; right?

OK, I did this. Tried running nox-review but my nix daemon ran out of memory :(

@GrahamcOfBorg build ocamlPackages.decompress

Failure on x86_64-linux (full log)

Attempted: ocamlPackages.decompress

unpacking source archive /nix/store/lrdsqf4imhdzm99x0j28azzfiwr65m2k-source
source root is source
patching sources
configuring
no configure script, doing nothing
building
Cannot find file topfind.
Unknown directive `require'.
builder for '/nix/store/r88r3z2g1qi2152bmwyv5qg4crmj6j92-ocaml4.06.1-decompress-0.6.drv' failed with exit code 2
error: build of '/nix/store/r88r3z2g1qi2152bmwyv5qg4crmj6j92-ocaml4.06.1-decompress-0.6.drv' failed

Failure on aarch64-linux (full log)

Attempted: ocamlPackages.decompress

source root is source
patching sources
updateAutotoolsGnuConfigScriptsPhase
configuring
no configure script, doing nothing
building
Cannot find file topfind.
Unknown directive `require'.
builder for '/nix/store/k2wx9wamx947ryq5sy2d680w1ly4rxmc-ocaml4.06.1-decompress-0.6.drv' failed with exit code 2
error: build of '/nix/store/k2wx9wamx947ryq5sy2d680w1ly4rxmc-ocaml4.06.1-decompress-0.6.drv' failed

Failure on x86_64-darwin (full log)

Attempted: ocamlPackages.decompress

unpacking source archive /nix/store/lrdsqf4imhdzm99x0j28azzfiwr65m2k-source
source root is source
patching sources
configuring
no configure script, doing nothing
building
Cannot find file topfind.
Unknown directive `require'.
builder for '/nix/store/9jlrvqjg1052mk4alb44xa9rxfzh8rmp-ocaml4.06.1-decompress-0.6.drv' failed with exit code 2
error: build of '/nix/store/9jlrvqjg1052mk4alb44xa9rxfzh8rmp-ocaml4.06.1-decompress-0.6.drv' failed

Ugh, thanks for finding that ... looks like the substituter needs to be a bit more generous with the syntax it allows...

You can also try nix-review instead of nox-review, which takes less memory for evaluation.

Hm. So I fixed decompress, but digestif fails because it has a #directory "pkg" directive before #use "topfind". This intentionally doesn't get patched because there could be a topfind in the new directory that would take precedence. So I'll have to fix packages like this individually I guess...

I’m starting to wonder whether this is a good thing to do (to rewrite source code so as to turn relative paths into absolute ones). It does not really help.

Thinking aloud: maybe a way to address this issue would be to acknowledge that findlib belongs to OCaml and ship topfind & co. as part of the standard library…

Honestly i'm not too against that idea. Another alternative would be to have a wrapper of ocaml in findlib, but that runs into PATH ordering issues; another yet is to have a wrapper in ocaml itself that lets setup hooks add options, like the C compilers use. Unfortunately the way ocaml handles include path options makes that one needlessly difficult in some ways...

I really only want these scripts to work out of the box, I am not wedded to this method.

Make sense to have a wrapper, than people do not have to patch there source code as well.

This pull request has been mentioned on Nix community. There might be relevant details there:

https://discourse.nixos.org/t/ocaml-utop-on-nixos-not-detecting-libraries/1587/5

Are there any updates on this pull request, please?

Thank you for your contributions.
This has been automatically marked as stale because it has had no activity for 180 days.
If this is still important to you, we ask that you leave a comment below. Your comment can be as simple as "still important to me". This lets people see that at least one person still cares about this. Someone will have to do this at most twice a year if there is no other activity.
Here are suggestions that might help resolve this more quickly:

1. Search for maintainers and people that previously touched the
   related code and @ mention them in a comment.
2. Ask on the NixOS Discourse. 3. Ask on the #nixos channel on
   irc.freenode.net.

Closing due to inactivity. Feel free to reopen the discussion.