export_all in rabbit_variable_queue breaks compilation in Erlang 20

[goncalotomas]

Erlang 20 generates a warning when export_all is used inside a module. It is used at least in rabbit_variable_queue.erl:362. The proposed workaround to the warning is to use the nowarn_export_all flag, but removing the warnings_as_errors would also "fix" the compilation issue.
I as not able to submit a pull request with the nowarn_exportall approach because I don't understand where you'd add this particular flag without a rebar.config file.

Here is the official statement of the new warning from the Erlang 20 Release notes:

           OTP-14071    Application(s): compiler, stdlib

           By default, there will now be a warning when export_all
           is used. The warning can be disabled using
           nowarn_export_all.

[michaelklishin]

@goncalotomas thanks. We've been working on OTP 20 compatibility for about a month now and have never observed this. Can you please clarify how are you building the server?

RabbitMQ uses a patched version of erlang.mk, not rebar.

[michaelklishin]

Related to #1243.

[michaelklishin]

So the line was introduced in 492e23b and not present in stable.

I suspect it was added for more convenient debugging from the shell and can be removed.

[michaelklishin]

Managed to reproduce it with a clean umbrella clone.

[goncalotomas]

Having installed Erlang 20, I just cloned the repository and ran make.