(alert deprecated): Core.Sys.is_directory [since 2021-04] Use [Sys_unix]

[mimoo]

I'll write my investigation following this error message as a thread, perhaps it can serve as feedback for the user experience of using this library (or ocaml more generally)

I'm getting this error message

(alert deprecated): Core.Sys.is_directory
[since 2021-04] Use [Sys_unix]

the message seems weird, as it seems to imply to move to a function that will only work on unix systems.

anyway, I am on a unix system, so screw windows I guess. So I tried using Core.Sys_unix.is_directory but it doesn't seem to exist.

usually I would expect the error message to link me to more information, but no so I'm still digging.

[mimoo]

On the Core documentation here https://ocaml.org/p/core/v0.15.0/doc/Core/Sys/index.html I can see that a lot of things are marked as Use_Sys_unix` but no indication seems to appear on what that is. I wish I could search the value Use_Sys_unix` in the documentation of Core but there doesn't seem to be a functionality to search in all the documentation

[mimoo]

Looks like there is a package called Core_unix https://ocaml.org/u/fc567798a08fe03047f17d3fa542a580/core_unix/v0.15.0/doc/Sys_unix/index.html which seems to be related to Core. It's weird, I thought we only had Core and Base now, instead of Core/Base/Core_kernel, but there still seem to be a Core/Base/Core_unix? And tha module offers a Sys_unix https://ocaml.org/u/fc567798a08fe03047f17d3fa542a580/core_unix/v0.15.0/doc/Sys_unix/index.html so I guess that's what I should use

[mimoo]

I look for the line to add to my opam file in the documentation, something like "core_unix" {>= "0.15.0"}, I can't find it. I guess I'll write it myself, but if I was starting with a blank opam file it would have been annoying

[mimoo]

hum... so now I have two opens:

open Core
open Core_unix

I'm really wondering if this will be an issue, or if I should import one before the other, let's see...

[mimoo]

now I'm getting:

9 |       let is_dir = Sys_unix.is_directory file in
                       ^^^^^^^^^^^^^^^^^^^^^
Error: Unbound module Sys_unix

how is this possible? Sys_unix is in the doc https://ocaml.org/p/core_unix/v0.15.0/doc/Sys_unix/index.html

[mimoo]

maybe I don't have the right version of core_unix?

opam installed-libraries
opam: unknown command `installed-libraries'.
Usage: opam COMMAND ...
Try `opam --help' for more information.

urg...

opam list | grep core
core                        v0.15.0     Industrial strength alternative to OCaml's standard library
core_kernel                 v0.15.0     Industrial strength alternative to OCaml's standard library
core_unix                   v0.15.0     Unix-specific portions of Core

ok looks like I have the same version as the doc, what could it be?

[mimoo]

OK, thanks to ocaml-lsp I manage to click on Core_unix and jump to the source. I see open! Core in the code, what is this ! after open? Stackoverflow has the answer fortunately https://stackoverflow.com/questions/22607755/what-does-open-mean

I still can't find any information there on a Sys_unix. I feel like giving up

[mimoo]

ok let's try another path, google "sys_unix" ocaml. Nothing useful in the search result. Looking for "core_unix" ocaml I don't find anything useful as well. Well, I'll give up for today.

[mimoo]

right before giving up, I think I vaguely remember that maybe importing core_unix.sys_unix in my dune file might work to import subpackages in an opam release. HOLE SHIT IT WORKED. Another "interesting" way in which opam and dune seem to interact

[shlomenu]

Just wanted to add that I encountered the same message, and was not able to access any library called sys_unix as installable through OPAM, or namespaced via Core or Core_unix. I encountered the issue upon upgrading to Core 15.1 from 14.2; my codebase had previously compiled while using functions from Core.Sys, and then I began receiving the same warning reported by @mimoo.

I was able to solve it simply by referencing Caml.Sys following open Core, as I noticed that this was how the source of the core_unix package seemed to be accessing a Sys-like module after its own open! Core statement.

I find the current tiers of Jane Street stdlib overlays to be quite confusing. I understand the motivation was to eliminate core_kernel. It looks like progress was made in this direction as Core v15 now includes its own Core.Core_kernel_stable module (I assume as a step towards deprecation of the independent core_kernel package). However, the independent core_kernel package still exists and is being upgraded, and even contains some data structures (such as Pairing_heap) whose implementations do not appear to be available through Core or Base (or Core_unix) and are depended upon by tests in their repositories. It seems that welcome improvements are afoot, but it is also a challenge to deal with opaque changes to such commonly referenced namespaces as Sys.

[rnollet]

Thanks for this thread. I had the same question.
Indeed, the READMEs in core_unix say that these are the old Core.Sys and Core.Unix :

• https://github.com/janestreet/core_unix/tree/master/sys_unix
• https://github.com/janestreet/core_unix/tree/master/core_unix