Install system packages required by OCaml 5.1+ in the ocaml stage

OCaml 5.1+ can optionally use libzstd for compressing marshalled data.
Install this package in the ocaml image. It's not needed in the opam
stage.

Future work might remove uneeded packages from the opam image, like
libx11 that the graphics library depends on, for OCaml 4.09+.

CHANGES.md

@@ -1,6 +1,9 @@
 unreleased
 ----------
 
+- Install system packages required by OCaml in the ocaml stage,
+  starting with OCaml 5.1 and libzstd.
+  (@MisterDA #149, review by @kit-ty-kate)
 - Add OracleLinux 9. (@MisterDA #155)
 - Optimize and fix Linux package install.
   (@MisterDA #147, #151, #153, #154, review by @kit-ty-kate)

src-opam/linux.ml

@@ -45,6 +45,11 @@ module RPM = struct
        libX11-devel which m4 diffutils findutils%s"
       (match extra with None -> "" | Some x -> " " ^ x)
 
+  let ocaml_depexts v =
+    if Ocaml_version.compare v Ocaml_version.Releases.v5_1_0 >= 0 then
+      Some "zstd"
+    else None
+
   let add_user ?uid ?gid ?(sudo = false) username =
     let uid = match uid with Some u -> sprintf "-u %d " u | None -> "" in
     let gid = match gid with Some g -> sprintf "-g %d " g | None -> "" in
@@ -90,6 +95,11 @@ module Apt = struct
           libx11-dev%s"
          (match extra with None -> "" | Some x -> " " ^ x)
 
+  let ocaml_depexts v =
+    if Ocaml_version.compare v Ocaml_version.Releases.v5_1_0 >= 0 then
+      Some "libzstd-dev"
+    else None
+
   let add_user ?uid ?gid ?(sudo = false) username =
     let uid = match uid with Some u -> sprintf "--uid %d " u | None -> "" in
     let gid = match gid with Some g -> sprintf "--gid %d " g | None -> "" in
@@ -125,6 +135,11 @@ module Apk = struct
        libx11-dev nano coreutils xz ncurses-dev%s"
       (match extra with None -> "" | Some x -> " " ^ x)
 
+  let ocaml_depexts v =
+    if Ocaml_version.compare v Ocaml_version.Releases.v5_1_0 >= 0 then
+      Some "zstd"
+    else None
+
   let add_user ?uid ?gid ?(sudo = false) username =
     let home = "/home/" ^ username in
     (match gid with
@@ -180,6 +195,11 @@ module Zypper = struct
           rsync gzip%s"
          (match extra with None -> "" | Some x -> " " ^ x)
 
+  let ocaml_depexts v =
+    if Ocaml_version.compare v Ocaml_version.Releases.v5_1_0 >= 0 then
+      Some "zstd"
+    else None
+
   let add_user ?uid ?gid ?(sudo = false) username =
     let home = "/home/" ^ username in
     run "useradd %s%s -d %s -m --user-group %s"
@@ -216,6 +236,11 @@ module Pacman = struct
        coreutils xz ncurses diffutils unzip%s"
       (match extra with None -> "" | Some x -> " " ^ x)
 
+  let ocaml_depexts v =
+    if Ocaml_version.compare v Ocaml_version.Releases.v5_1_0 >= 0 then
+      Some "zstd"
+    else None
+
   let add_user ?uid ?gid ?(sudo = false) username =
     let home = "/home/" ^ username in
     run "useradd %s%s -d %s -m --user-group %s"

src-opam/linux.mli

@@ -48,6 +48,10 @@ module RPM : sig
   (** [dev_packages ?extra ()] will install the base development tools and [sudo],
       [passwd] and [git].  Extra packages may also be optionally supplied via [extra]. *)
 
+  val ocaml_depexts : Ocaml_version.t -> string option
+  (** [ocaml_depexts v] returns packages that are required by the
+      OCaml distribution at version [v]. *)
+
   val install_system_ocaml : t
   (** Install the system OCaml packages via Yum *)
 end
@@ -69,6 +73,10 @@ module Apt : sig
   (** [dev_packages ?extra ()] will install the base development tools and [sudo],
       [passwd] and [git] and X11.  Extra packages may also be optionally supplied via [extra]. *)
 
+  val ocaml_depexts : Ocaml_version.t -> string option
+  (** [ocaml_depexts v] returns packages that are required by the
+      OCaml distribution at version [v]. *)
+
   val install_system_ocaml : t
   (** Install the system OCaml packages via [apt-get] *)
 end
@@ -85,6 +93,10 @@ module Apk : sig
   (** [dev_packages ?extra ()] will install the base development tools and [sudo],
       [passwd] and [git].  Extra packages may also be optionally supplied via [extra]. *)
 
+  val ocaml_depexts : Ocaml_version.t -> string option
+  (** [ocaml_depexts v] returns packages that are required by the
+      OCaml distribution at version [v]. *)
+
   val add_user : ?uid:int -> ?gid:int -> ?sudo:bool -> string -> t
   (** [add_user username] will install a new user with name [username] and a locked
       password.  If [sudo] is true then root access with no password will also be
@@ -117,6 +129,10 @@ module Zypper : sig
   (** [dev_packages ?extra ()] will install the base development tools and [sudo],
       [passwd] and [git].  Extra packages may also be optionally supplied via [extra]. *)
 
+  val ocaml_depexts : Ocaml_version.t -> string option
+  (** [ocaml_depexts v] returns packages that are required by the
+      OCaml distribution at version [v]. *)
+
   val install_system_ocaml : t
   (** Install the system OCaml packages via [zypper] *)
 end
@@ -138,6 +154,10 @@ module Pacman : sig
   (** [dev_packages ?extra ()] will install the base development tools and [sudo],
       [passwd] and [git].  Extra packages may also be optionally supplied via [extra]. *)
 
+  val ocaml_depexts : Ocaml_version.t -> string option
+  (** [ocaml_depexts v] returns packages that are required by the
+      OCaml distribution at version [v]. *)
+
   val install_system_ocaml : t
   (** Install the system OCaml packages via [pacman] *)
 end

src-opam/opam.ml

@@ -507,6 +507,24 @@ let gen_opam2_distro ?win10_revision ?winget ?(clone_opam_repo = true) ?arch
   in
   (D.tag_of_distro d, fn @@ clone @@ pers)
 
+let ocaml_depexts distro v =
+  let open Linux in
+  match D.package_manager distro with
+  | `Apk ->
+      Option.fold ~none:empty ~some:(Apk.install "%s") (Apk.ocaml_depexts v)
+  | `Apt ->
+      Option.fold ~none:empty ~some:(Apt.install "%s") (Apt.ocaml_depexts v)
+  | `Yum ->
+      Option.fold ~none:empty ~some:(RPM.install "%s") (RPM.ocaml_depexts v)
+  | `Zypper ->
+      Option.fold ~none:empty ~some:(Zypper.install "%s")
+        (Zypper.ocaml_depexts v)
+  | `Pacman ->
+      Option.fold ~none:empty ~some:(Pacman.install "%s")
+        (Pacman.ocaml_depexts v)
+  | `Windows -> empty
+  | `Cygwin -> empty
+
 let create_switch ~arch distro t =
   let create_switch switch pkg =
     run "opam switch create %s %s" (OV.to_string switch) pkg

src-opam/opam.mli

@@ -68,6 +68,11 @@ val gen_opam2_distro :
    will be build in an prepended build stage. If specified, then
    winget will be pulled from the [winget] external image. *)
 
+val ocaml_depexts : Distro.t -> Ocaml_version.t -> Dockerfile.t
+(** [ocaml_depexts distro version] returns packages that are
+    required under [distro] by the OCaml distribution at version
+    [version].  *)
+
 val all_ocaml_compilers :
   string -> Ocaml_version.arch -> Distro.t -> string * Dockerfile.t
 (** [all_ocaml_compilers hub_id arch distro] will generate an opam2