Ppx_tools not working in uTop 2.0.1

[mseri]

As mentioned in https://discuss.ocaml.org/t/ppx-tools-not-working-in-utop/367 The new utop has a problem with ppx_tools:

$ utop -require ppx_tools
File "_none_", line 1:
Error: Reference to undefined global `Longident'

I think it's an issue with utop. The following set of packages works without problems

ocamlfind       1.7.3  A library manager for OCaml
ppx_tools  5.0+4.03.0  Tools for authors of ppx rewriters and other syntactic tools
utop           1.19.3 (pinned)  Universal toplevel for OCaml

while this other presents the issue we both saw:

ocamlfind       1.7.3  A library manager for OCaml
ppx_tools  5.0+4.03.0  Tools for authors of ppx rewriters and other syntactic tools
utop            2.0.1 (pinned)  Universal toplevel for OCaml

[ghost]

It's because utop 2.0.1 declares its dependency on compiler-libs while the older version did not.

Technically this is a very obscure problem; the compiler libraries contain a lot of generic root modules (Misc, Path, ...) that are very likely to clash with root modules from user libraries and the OCaml toplevel uses the compiler libraries. As a result the OCaml toplevel is expunged, i.e. the modules from the compiler libraries are made hidden from what the user can use inside the toplevel. utop does the same.

ppx_tools uses the compiler libraries as well, but because utop thinks they are already available as the utop library depends on them, it doesn't try to load them again. There is probably a complicated way around this.

Alternatively, you can try utop-full which is not expunged. The only limitation is that you cannot load root modules such as Misc or Path in it.

[reynir]

I'm seeing this issue in https://github.com/reynir/ocp-index-top/issues/9 as well. It's a toplevel directive for looking up documentation for identifiers. Do you have any advice on making it work in utop? I have an issue about inadverdently exposing compiler-libs, so I understand the motivation for the change in utop 2.0.1 https://github.com/reynir/ocp-index-top/issues/1. Thanks!

[ghost]

Well, appart from using utop-full I'm not sure. We could restore the previous behavior that allowed to load the compiler libs in utop, but this was causing other bugs. The real solution would be to just not expunge utop, but then the name clashes might be a problem. Hopefully this will be sorted when we get namespaces in OCaml and can namespace the compiler libraries.

[let-def]

Same problem here, reason toplevel built on top of utop stopped working.

The dependency chain is: reason -> ocaml-migrate-parsetree -> compiler-libs.common -> Misc. Resulting in Error: Reference to undefined global `Misc'.

[ghost]

How is the reason toplevel built? If you link a custom toplevel, you should only get this error if you expunge the toplevel

[let-def]

It's utop with a custom init that replaces parsing and printing.

[ghost]

Maybe it should be a custom toplevel instead?

[let-def]

Maybe. In the meantime we are happy with utop-full. Thanks.

[XVilka]

@diml is there any issue/PR to track the namespacing of the compiler libs?

[ghost]

There is this ticket that's related: https://caml.inria.fr/mantis/view.php?id=6704

Namespacing the compiler libs like the stdlib would be nice, though it's likely to be a little bit painful to adapt the makefiles.