[Libguestfs] Minimum OCaml compiler version (2021/2022 edition)

Previously: https://listman.redhat.com/archives/libguestfs/2020-March/msg00063.html https://listman.redhat.com/archives/libguestfs/2017-September/msg00203.html Our current minimum version across projects is 4.03. We still use "noalloc" in a few places which causes this warning: ocamlopt.opt -warn-error +A-3 -c NBDKit.ml -o NBDKit.cmx File "NBDKit.ml", line 155, characters 0-70: 155 | external set_name : string -> unit = "ocaml_nbdkit_set_name" "noalloc" ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Alert deprecated: [@@noalloc] should be used instead of "noalloc" I just noticed now that this change was made in 4.03 -- I will go ahead and fix this everywhere today. Should we move to a newer minimum version? If we moved to 4.07 then we could also get rid of the warnings about Pervasives (replaced by Stdlib), eg: File "std_utils.ml", line 329, characters 26-44: 329 | let sort_uniq ?(cmp = Pervasives.compare) xs = ^^^^^^^^^^^^^^^^^^ Alert deprecated: module Stdlib.Pervasives Use Stdlib instead. However 4.07 was only released in 2018, and this would mean removing RHEL 7 compatibility (officially -- it's sort of unofficially not supported already). More irritatingly, FreeBSD is stuck on 4.05. There are no particularly compelling new features at the moment. Here are the common distros and versions (< 4.07 marked with '*'): Arch (Extra) OCaml 4.12 Debian stable OCaml 4.11 Debian testing OCaml 4.11 Fedora 31 OCaml 4.08 Fedora 35 OCaml 4.12 FreeBSD (ports) OCaml 4.05 * OpenSUSE OCaml 4.13 RHEL 7 OCaml 4.05 * RHEL 8 OCaml 4.07 RHEL 9 OCaml 4.11 Ubuntu 16.04 OCaml 4.02 * Ubuntu 18.04 OCaml 4.05 * Ubuntu 20.04 OCaml 4.08 Ubuntu 21.04 OCaml 4.11 And here are the release dates of the OCaml compiler: OCaml version Release date 4.02 2014-08 4.03 2016-04 4.04 2016-11 4.05 2017-07 4.06 2017-11 4.07 2018-07 4.08 2019-06 4.09 2019-09 4.10 2020-02 4.11 2020-08 4.12 2021-02 4.13 2021-09 Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v