Beam files aren't built with rebar3 3.14.4 + Elixir 1.12.0-rc.1 + build_embedded: true

[fhunleth]

Environment

• Elixir & Erlang/OTP versions (elixir --version):

$ elixir --version
Erlang/OTP 23 [erts-11.2] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1]

Elixir 1.12.0-rc.1 (ce321f8) (compiled with Erlang/OTP 23)

And

$ /Users/fhunleth/.asdf/installs/elixir/1.12.0-rc.1-otp-23/.mix/rebar3 --version
rebar 3.14.4 on Erlang/OTP 23 Erts 11.2

Since old rebar3 versions could affect this and that was originally an issue in my setup, I deleted all rebar3 binaries every where else and reproduced on two machines.

• Operating system:

OSX and Ubuntu

Current behavior

Here's a demo: https://github.com/fhunleth/elixir_rebar3_test

When I build that test project, no .beam files get built in cowlib. This causes problems later on.

So far I've been able to narrow this down to whether build_embedded is enabled or not.

[fhunleth]

Updates:

1. rebar3 builds cowlib successfully. The problem doesn't have to do with rebar3 or how rebar3 is invoked.
2. The problem is that the _build/dev/lib/cowlib/ebin is erased and then the contents of deps/cowlib/ebin are copied over. This is what makes it look like cowlib hadn't been built, but it was built.

If you change symlink_ebin to false at https://github.com/elixir-lang/elixir/blob/v1.12/lib/mix/lib/mix/tasks/deps.compile.ex#L329, it "fixes" the problem. I don't think it's the right fix, but that's where I've gotten so far.

[josevalim]

No longer symlinking ebins is the right thing but it won’t work for old rebar versions, so it is hard to get a fix for now that works for everybody. I will revert the breaking change on v1.12 but keep it in master and add the symlink ebin fix. Thanks for digging deeper!

[fhunleth]

Thanks! This is the only issue I've found on Nerves with Elixir 1.12. Everything else appears to work great.

[fhunleth]

FYI - I confirmed that a328bb8 fixes the issue with the Nerves project where I first encountered it. Thanks! 🎉