[opam.2.1.0~alpha] Errors while fetching sources return with exit code 31 instead of 40

[kit-ty-kate]

With opam 2.0, failures when fetching an archive that is inaccessible returns the exit code 40. For instance, with opam-repository in its current state (ocaml/opam-repository@a7eaf84):

$ opam install rfsm.1.4.2
[...]
[ERROR] The sources of the following couldn't be obtained, aborting:
          - rfsm.1.4.2: curl error code 404

$ echo $?
40

In opam 2.1.0~alpha however, even though the man page still specifies that:

EXIT STATUS
[...]
       40  Sync error. Could not fetch some remotes from the network. This can
           be a partial error.

the same command returns the exit code 31 instead:

$ opam install rfsm.1.4.2
[...]
#=== ERROR while fetching sources for rfsm.1.4.2 ==============================#
https://github.com/jserot/rfsm/archive/v1.4.2.tar.gz (curl: code 404 while downloading https://github.com/jserot/rfsm/archive/v1.4.2.tar.gz)

[...]
$ echo $?
31

[rjbou]

It's a consequence of #3777, as the download is now in the graph action, its failure is then an package action failure, which is 31.

Thanks for the report!