Fix for Erlang installation with asdf on macOS 11 Big Sur

Issue

There is an open issue with installing Erlang on macOS 11 Big Sur - https://github.com/erlang/otp/pull/2865

I use asdf (https://asdf-vm.com/#/) to manage versions of my local Elixir and Erlang applications. Recently I noticed that when I want to install (using asdf install ) Erlang version specified in .tool-versions file I see that error:

You are natively building Erlang/OTP for a later version of MacOSX
  than current version (11.1). You either need to
  cross-build Erlang/OTP, or set the environment variable
  MACOSX_DEPLOYMENT_TARGET to 11.1 (or a lower version).

Solution

I manage to overcome this. My strategy was to install desired Erlang version with another tool to build and manage Erlang instances - kerl (https://github.com/kerl/kerl) - and inject that installation to asdf.

Steps to solve the issue:

1. Install Kerl (I assume you use Homebrew).
   $ brew install kerl

2. Set configuration options for Kerl.
   $ export KERL_CONFIGURE_OPTIONS="--disable-debug --without-javac"

3. Try to build your version of Erlang (it will fail!). In that example I'm installing version 21.3.8. If you want another version, just replace 21.3.8 to a version you want in all following commands.
   $ kerl build 21.3.8 21.3.8

4. Open OTP configuration file (I assume you use VSCode - that's why you can see code. Replace with your editor.)
   $ code ~/.kerl/builds/21.3.8/otp_src_21.3.8/configure.in

5. Find that line
   #if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ > $int_macosx_version
   and replace it with that line:
   #if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ > $int_macosx_version && false

6. Try to build it again. Now it should work. Will take some time so be patient!
   $ kerl build 21.3.8 21.3.8

7. Make a directory for a new version of Erlang in your asdf directory.
   $ mkdir ~/.asdf/installs/erlang/21.3.8

8. Install (copy) Erlang installed via kerl to asdf.
   $ kerl install 21.3.8 ~/.asdf/installs/erlang/21.3.8

9. Close your console and open again (or open new window) and go to you project. Run asdf install to ensure you have your Elixir and Erlang versions installed.
   $ asdf install

10. Compile your Elixir app.
    $ mix compile

And that's it!

If you have any comments or questions, find my on Twitter: https://twitter.com/k_kempinski