opam init error (2.1.0~beta2) when checking sandboxing (OPAM_SWITCH_PREFIX: unbound variable)

[gasche]

I'm running opam init from a fresh Ubunutu virtual machine with just the bare dependencies installed. I get the following message, which suggests a problem in the way opam checks whether sandboxing works.

[ERROR] Sandboxing is not working on your platform ubuntu:
        "~/.opam/opam-init/hooks/sandbox.sh build sh -c echo SUCCESS >/tmp/t &&
        cat /tmp/t" exited with code 1
        "/home/gscherer/.opam/opam-init/hooks/sandbox.sh: ligne 96:
        OPAM_SWITCH_PREFIX : variable sans liaison"

My understanding is that opam init tries to check whether sandbox.sh works, but then the script fails because OPAM_SWITCH_PREFIX is undefined, which I expect is standard if opam init has not run ever yet on the machine. Interpreting this as a failure of sandboxing (and then suggesting that users disable it) looks like a UI bug to me; opam init should instead check sandboxing in a more robust way.

---

The opam config report output is as follows:

# opam config report
# opam-version         2.1.0~beta2 
# self-upgrade         no
# system               arch=x86_64 os=linux os-distribution=ubuntu os-version=18.04
[ERROR] Opam has not been initialised, please run `opam init'
# read-state           OpamStd.OpamSys.Exit(50)

[gasche]

I do not get this error with opam 2.0.7 on the same system.

[rjbou]

Indeed, it a beta2 new feature (cf. #4284). This problem is fixed in #4370, and be available in next beta.
Thanks for the report!

[gasche]

Ah, sorry for missing the two other issue reports (I did look for OPAM_SWITCH_PREFIX... and then did not use it in my own issue title), #4397 and #4368, and thanks for the quick triaging.