From a53bbb0a984bb4a6df51907aedaf14a5b2542353 Mon Sep 17 00:00:00 2001
From: Kate <kit.ty.kate@disroot.org>
Date: Thu, 2 Sep 2021 12:07:02 +0100
Subject: [PATCH] Fallback on dnf if yum does not exist on RHEL-based systems
 (backports https://github.com/ocaml/opam/pull/4825)

Co-authored-by: R. Boujbel <rjbou@ocamlpro.com>
---
 master_changes.md            | 16 ++++++++++++++++
 src/state/opamSysInteract.ml | 14 +++++++++++---
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/master_changes.md b/master_changes.md
index 78cfb2eac73..36f5bd6a849 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -53,6 +53,22 @@ New option/command/subcommand are prefixed with ◈.
 
 ## External dependencies
   *
+  * Set `DEBIAN_FRONTEND=noninteractive` for unsafe-yes confirmation level [#4735 @dra27 - partially fix #4731] [2.1.0~rc2 #4739]
+  * Fix depext alpine tagged repositories handling [#4763 @rjbou] [2.1.0~rc2 #4758]
+  * Homebrew: Add support for casks and full-names [#4801 @kit-ty-kate]
+  * Disable the detection of available packages on RHEL-based distributions.
+    This fixes an issue on RHEL-based distributions where yum list used to detect available
+    and installed packages would wait for user input without showing any output and/or fail
+    in some cases [#4791 @kit-ty-kate - fixes #4790]
+  * Archlinux: handle virtual package detection [#4831 @rjbou - partial fix #4759]
+  * Fallback on dnf if yum does not exist on RHEL-based systems [#4825 @kit-ty-kate]
+
+## Format upgrade
+  * Fix format upgrade when there is missing local switches in the config file [#4763 @rjbou - fix #4713] [2.1.0~rc2 #4715]
+  * Fix not recorded local switch handling, with format upgrade [#4763 @rjbou] [2.1.0~rc2 #4715]
+  * Set opam root version to 2.1 [#4763 @rjbou] [2.1.0~rc2 #4715]
+  * Fix 2.1~alpha2 to 2.1 format upgrade with reinit [#4763 @rjbou - fix #4748] [2.1.0~rc2 #4750]
+  * Fix bypass-check handling on reinit [#4750 @rjbou] [#4763 @rjbou] [2.1.0~rc2 #4750 #4756]
 
 ## Sandbox
   *
diff --git a/src/state/opamSysInteract.ml b/src/state/opamSysInteract.ml
index bdd7594c8eb..69349f502da 100644
--- a/src/state/opamSysInteract.ml
+++ b/src/state/opamSysInteract.ml
@@ -130,6 +130,14 @@ let family =
   ) in
   fun () -> Lazy.force family
 
+let yum_cmd = lazy begin
+  if OpamSystem.resolve_command "yum" <> None then
+    "yum"
+  else if OpamSystem.resolve_command "dnf" <> None then
+    "dnf"
+  else
+    raise (OpamSystem.Command_not_found "yum or dnf")
+end
 
 let packages_status packages =
   let (+++) pkg set = OpamSysPkg.Set.add (OpamSysPkg.of_string pkg) set in
@@ -635,11 +643,11 @@ let install_packages_commands_t sys_packages =
     let epel_release = "epel-release" in
     let install_epel rest =
       if List.mem epel_release packages then
-        ["yum", "install"::yes ["-y"] [epel_release]] @ rest
+        [Lazy.force yum_cmd, "install"::yes ["-y"] [epel_release]] @ rest
       else rest
     in
     install_epel
-      ["yum", "install"::yes ["-y"]
+      [Lazy.force yum_cmd, "install"::yes ["-y"]
                 (OpamStd.String.Set.of_list packages
                  |> OpamStd.String.Set.remove epel_release
                  |> OpamStd.String.Set.elements);
@@ -704,7 +712,7 @@ let update () =
     match family () with
     | Alpine -> Some ("apk", ["update"])
     | Arch -> Some ("pacman", ["-Sy"])
-    | Centos -> Some ("yum", ["makecache"])
+    | Centos -> Some (Lazy.force yum_cmd, ["makecache"])
     | Debian -> Some ("apt-get", ["update"])
     | Gentoo -> Some ("emerge", ["--sync"])
     | Homebrew -> Some ("brew", ["update"])