Upgrades from opam 2.1.0~beta4 to 2.1.0~rc2 remove the opam config file

[kit-ty-kate]

FROM ocaml/opam
RUN opam --version # 2.0.8
RUN opam switch
RUN opam list
RUN bash -c 'echo | sh <(curl -sL https://raw.githubusercontent.com/ocaml/opam/2.1.0-rc/shell/install.sh) --dev'
RUN opam --version # 2.1.0~beta4
RUN opam switch
RUN opam list
RUN bash -c 'echo | sh <(curl -sL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh) --dev'
RUN opam --version # 2.1.0~rc2
RUN opam switch # ????
RUN opam list # ????

Everything goes well until the 4 last commands:

Step 9/12 : RUN bash -c 'echo | sh <(curl -sL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh) --dev'
 ---> Running in 25d672d35b24
## Downloading opam 2.1.0~rc2 for linux on x86_64...
## Downloaded.
## Where should it be installed ? [/usr/bin] Write access to /usr/bin required, using 'sudo'.
Command: mv /usr/bin/opam /usr/bin/opam.2.1.0~beta4
## /usr/bin/opam backed up as opam.2.1.0~beta4
## Backing up /home/opam/.opam to .opam.2.1.0~beta4 (this may take a while)
## /home/opam/.opam backed up as .opam.2.1.0~beta4
Write access to /usr/bin required, using 'sudo'.
Command: install -m 755 /tmp/opam-2.1.0-rc2-x86_64-linux /usr/bin/opam
## opam 2.1.0~rc2 installed to /usr/bin
## Converting the opam root format & updating
Configuring from /home/opam/.opamrc and then from built-in defaults.
Checking for available remotes: [ERROR] In /home/opam/.opam/config:
        unsupported or missing file format version; should be 2.0 or older [skipped]

rsync and local, git.
  - you won't be able to use mercurial repositories unless you install the hg command on your system.
  - you won't be able to use darcs repositories unless you install the darcs command on your system.

This version of opam requires an update to the layout of /home/opam/.opam from version 2.0 to version 2.1, which can't be reverted.
You may want to back it up before going further.

Continue? [Y/n] y
Format upgrade done.

<><> Updating repositories ><><><><><><><><><><><><><><><><><><><><><><><><><><>
[default] no changes from file:///home/opam/opam-repository
## Run this script again with '--restore 2.1.0~beta4' to revert.
Removing intermediate container 25d672d35b24
 ---> b02b09b4e36c
Step 10/12 : RUN opam --version # 2.1.0~rc2
 ---> Running in dba4eb5dc8b9
2.1.0~rc2
Removing intermediate container dba4eb5dc8b9
 ---> 102e94473826
Step 11/12 : RUN opam switch # ????
 ---> Running in a0c5d1ad38e7
#  switch  compiler  description
Removing intermediate container a0c5d1ad38e7
 ---> 40cf093b1ec3
Step 12/12 : RUN opam list # ????
 ---> Running in a04b5dd02d7f
# No matches found

Looking inside the ~/.opam directory reveals a mostly unchanged opam root, however ~/.opam/config does not have any switches:

opam@92a8720d34dd:~$ diff -ru .opam.2.1.0~beta4/ .opam
diff -ru .opam.2.1.0~beta4/config .opam/config
--- .opam.2.1.0~beta4/config	2021-07-09 14:37:34.000000000 +0100
+++ .opam/config	2021-07-09 14:48:14.688880274 +0100
@@ -1,17 +1,43 @@
-opam-version: "2.1"
-repositories: "default"
-installed-switches: "4.12"
-switch: "4.12"
-jobs: 31
+opam-version: "2.0"
+opam-root-version: "2.1"
 download-jobs: 3
 eval-variables: [
-  sys-ocaml-version
-  ["ocamlc" "-vnum"]
-  "OCaml version present on your system independently of opam, if any"
+  [
+    sys-ocaml-version
+    ["ocamlc" "-vnum"]
+    "OCaml version present on your system independently of opam, if any"
+  ]
+  [
+    sys-ocaml-arch
+    [
+      "sh"
+      "-c"
+      "ocamlc -config 2>/dev/null | tr -d '\\r' | grep '^architecture: ' | sed -e 's/.*: //' -e 's/i386/i686/' -e 's/amd64/x86_64/'"
+    ]
+    "Target architecture of the OCaml compiler present on your system"
+  ]
+  [
+    sys-ocaml-cc
+    [
+      "sh"
+      "-c"
+      "ocamlc -config 2>/dev/null | tr -d '\\r' | grep '^ccomp_type: ' | sed -e 's/.*: //'"
+    ]
+    "Host C Compiler type of the OCaml compiler present on your system"
+  ]
+  [
+    sys-ocaml-libc
+    [
+      "sh"
+      "-c"
+      "ocamlc -config 2>/dev/null | tr -d '\\r' | grep '^os_type: ' | sed -e 's/.*: //' -e 's/Win32/msvc/' -e '/^msvc$/!s/.*/libc/'"
+    ]
+    "Host C Runtime Library type of the OCaml compiler present on your system"
+  ]
 ]
-default-compiler: [
-  "ocaml-system" {>= "4.02.3"}
-  "ocaml-base-compiler"
+default-compiler: ["ocaml-system" "ocaml-base-compiler"]
+default-invariant: [
+  "ocaml" {>= "4.05.0"}
 ]
 depext: true
 depext-run-installs: true
diff -ru .opam.2.1.0~beta4/opam-init/env_hook.sh .opam/opam-init/env_hook.sh
--- .opam.2.1.0~beta4/opam-init/env_hook.sh	2021-07-09 14:37:34.000000000 +0100
+++ .opam/opam-init/env_hook.sh	2021-07-09 14:48:14.688880274 +0100
@@ -1,7 +1,7 @@
 OPAMNOENVNOTICE=true; export OPAMNOENVNOTICE;
 _opam_env_hook() {
  local previous_exit_status=$?;
- eval $(opam env --shell=bash --readonly 2> /dev/null);
+ eval $(opam env --shell=bash --readonly 2> /dev/null <&- );
  return $previous_exit_status;
 };
 if ! [[ "$PROMPT_COMMAND" =~ _opam_env_hook ]]; then
diff -ru .opam.2.1.0~beta4/opam-init/env_hook.zsh .opam/opam-init/env_hook.zsh
--- .opam.2.1.0~beta4/opam-init/env_hook.zsh	2021-07-09 14:37:34.000000000 +0100
+++ .opam/opam-init/env_hook.zsh	2021-07-09 14:48:14.688880274 +0100
@@ -1,6 +1,6 @@
 OPAMNOENVNOTICE=true; export OPAMNOENVNOTICE;
 _opam_env_hook() {
-    eval $(opam env --shell=zsh --readonly 2> /dev/null);
+    eval $(opam env --shell=zsh --readonly 2> /dev/null <&-);
 }
 typeset -ag precmd_functions;
 if [[ -z ${precmd_functions[(r)_opam_env_hook]} ]]; then
diff -ru .opam.2.1.0~beta4/opam-init/hooks/sandbox.sh .opam/opam-init/hooks/sandbox.sh
--- .opam.2.1.0~beta4/opam-init/hooks/sandbox.sh	2021-07-09 14:37:34.000000000 +0100
+++ .opam/opam-init/hooks/sandbox.sh	2021-07-09 14:48:14.684880247 +0100
@@ -11,10 +11,12 @@
     exit 10
 fi
 
-ARGS=(--unshare-net --new-session)
+# --new-session requires bubblewrap 0.1.7
+# --die-with-parent requires bubblewrap 0.1.8
+ARGS=(--unshare-net --new-session --die-with-parent)
 ARGS=("${ARGS[@]}" --proc /proc --dev /dev)
-ARGS=("${ARGS[@]}" --bind "${TMPDIR:-/tmp}" /tmp)
-ARGS=("${ARGS[@]}" --setenv TMPDIR /tmp --setenv TMP /tmp --setenv TEMPDIR /tmp --setenv TEMP /tmp)
+ARGS=("${ARGS[@]}" --setenv TMPDIR /opam-tmp --setenv TMP /opam-tmp --setenv TEMPDIR /opam-tmp --setenv TEMP /opam-tmp)
+ARGS=("${ARGS[@]}" --tmpfs /opam-tmp)
 ARGS=("${ARGS[@]}" --tmpfs /run)
 
 add_mount() {
@@ -55,7 +57,7 @@
 # use OPAM_USER_PATH_RO variable to add them
 # the OPAM_USER_PATH_RO format is the same as PATH
 # ie: export OPAM_USER_PATH_RO=/nix/store:/rw/usrlocal
-add_sys_mounts /usr /bin /lib /lib32 /lib64 /etc /opt /home /var
+add_sys_mounts /usr /bin /lib /lib32 /lib64 /etc /opt /home /var /tmp
 
 # C compilers using `ccache` will write to a shared cache directory
 # that remain writeable. ccache seems widespread in some Fedora systems.
@@ -76,15 +78,20 @@
 }
 
 add_dune_cache_mount() {
-  u_cache=${XDG_CACHE_HOME:-$HOME/.cache}
-  u_dune_cache=$u_cache/dune
-  cache=$(readlink -m "$u_cache")
-  dune_cache=$cache/dune
-  dune_cache=$(readlink -m "$u_dune_cache")
+  local u_cache=${XDG_CACHE_HOME:-$HOME/.cache}
+  local u_dune_cache=$u_cache/dune
+  local cache=$(readlink -m "$u_cache")
+  local dune_cache=$cache/dune
+  local dune_cache=$(readlink -m "$u_dune_cache")
   mkdir -p "${dune_cache}"
   add_mount rw "$u_dune_cache" "$dune_cache"
 }
 
+# mount unusual path in ro
+if  [ -n "${OPAM_USER_PATH_RO-}" ]; then
+   add_mounts ro $(echo "${OPAM_USER_PATH_RO}" | sed 's|:| |g')
+fi
+
 # When using opam variable that must be defined at action time, add them also
 # at init check in OpamAuxCommands.check_and_revert_sandboxing (like
 # OPAM_SWITCH_PREFIX).
@@ -92,32 +99,20 @@
 COMMAND="$1"; shift
 case "$COMMAND" in
     build)
-        # mount unusual path in ro
-        if  [ -n "${OPAM_USER_PATH_RO-}" ]; then
-           add_mounts ro $(echo "${OPAM_USER_PATH_RO}" | sed 's|:| |g')
-        fi
         add_mounts ro "$OPAM_SWITCH_PREFIX"
         add_mounts rw "$PWD"
         add_ccache_mount
         add_dune_cache_mount
         ;;
     install)
-        # mount unusual path in ro
-        if  [ -n "${OPAM_USER_PATH_RO-}" ]; then
-           add_mounts ro  $(echo "${OPAM_USER_PATH_RO}" | sed 's|:| |g')
-        fi
         add_mounts rw "$OPAM_SWITCH_PREFIX"
         add_mounts ro "$OPAM_SWITCH_PREFIX/.opam-switch"
         add_mounts rw "$PWD"
         ;;
     remove)
-        # mount unusual path in ro
-        if  [ -n "${OPAM_USER_PATH_RO-}" ]; then
-           add_mounts ro $(echo "${OPAM_USER_PATH_RO}" | sed 's|:| |g')
-        fi
         add_mounts rw "$OPAM_SWITCH_PREFIX"
         add_mounts ro "$OPAM_SWITCH_PREFIX/.opam-switch"
-        if [ "X${PWD#$OPAM_SWITCH_PREFIX}/.opam-switch/" != "X${PWD}" ]; then
+        if [ "X${PWD#$OPAM_SWITCH_PREFIX/.opam-switch/}" != "X${PWD}" ]; then
           add_mounts rw "$PWD"
         fi
         ;;
@@ -127,4 +122,5 @@
 esac
 
 # Note: we assume $1 can be trusted, see https://github.com/projectatomic/bubblewrap/issues/259
+# As of now we are compatible up to 0.1.8, '--' can be added here when we require >= 0.3.0
 exec bwrap "${ARGS[@]}" "$@"
diff -ru .opam.2.1.0~beta4/opam-init/hooks/sandbox.sh.hash .opam/opam-init/hooks/sandbox.sh.hash
--- .opam.2.1.0~beta4/opam-init/hooks/sandbox.sh.hash	2021-07-09 14:37:34.000000000 +0100
+++ .opam/opam-init/hooks/sandbox.sh.hash	2021-07-09 14:48:14.684880247 +0100
@@ -1 +1 @@
-md5=c51ece9376c419167196f4438f0babcd
\ No newline at end of file
+md5=0ff6dc2bfbe090e3944ce2674aa21357
\ No newline at end of file
Only in .opam.2.1.0~beta4/plugins/bin: opam-depext
Binary files .opam.2.1.0~beta4/repo/default.tar.gz and .opam/repo/default.tar.gz differ
diff -ru .opam.2.1.0~beta4/repo/repos-config .opam/repo/repos-config
--- .opam.2.1.0~beta4/repo/repos-config	2021-07-09 14:39:03.000000000 +0100
+++ .opam/repo/repos-config	2021-07-09 14:49:27.877377522 +0100
@@ -1 +1,2 @@
+opam-version: "2.0"
 repositories: "default" {"file:///home/opam/opam-repository"}
Only in .opam/repo: state-21F1960C.cache
Only in .opam.2.1.0~beta4/repo: state.cache

Hit by @NathanReb