Updating dune to 3.0 could fail #5190
Description
It is hard to reproduce, but I successively did it in two different switches:
#=== ERROR while compiling xdg.3.0 ============================================#
# context 2.1.0 | linux/x86_64 | ocaml-base-compiler.4.12.0 | pinned(git+ssh://git@github.com/ocaml/dune.git#c46b89e1f#c46b89e1)
# path ~/.opam/4.12.0/.opam-switch/build/xdg.3.0
# command ~/.opam/opam-init/hooks/sandbox.sh build dune build -p xdg -j 4 --promote-install-files=false @install
# exit-code 1
# env-file ~/.opam/log/xdg-2046324-72a86d.env
# output-file ~/.opam/log/xdg-2046324-72a86d.out
### output ###
# [...]
# Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
# line 204, characters 8-13
# -> required by ("<unnamed>", ())
# -> required by ("<unnamed>", ())
# -> required by ("load-dir", In_build_dir "default/bench")
# -> required by ("toplevel", ())
#
# I must not crash. Uncertainty is the mind-killer. Exceptions are the
# little-death that brings total obliteration. I will fully express my cases.
# Execution will pass over me and through me. And when it has gone past, I
# will unwind the stack along its path. Where the cases are handled there will
# be nothing. Only I will remain.
I think one switch was starting with a master pinned at a previous version of 3.0 and the other before 3.0 but not sure. However once in this state I'm not able to install xdg. However an opam switch reinstall worked in the second switch.