Failed to build gem native extension - unknown type name 'my_bool'

[PandaWhisperer]

Problem

My Rails app was having issues connecting to my database this morning (unfortunately I don't have the error message anymore), so I decided to reinstall the msyql2 gem. This failed with the following error message:

Installing mysql2 0.4.3 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /Users/christoph/.rvm/gems/ruby-2.2.9@cloudcma/gems/mysql2-0.4.3/ext/mysql2
/Users/christoph/.rvm/rubies/ruby-2.2.9/bin/ruby -r ./siteconf20180618-59236-1dwk0nr.rb extconf.rb
checking for ruby/thread.h... yes
checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
checking for rb_thread_blocking_region()... no
checking for rb_wait_for_single_fd()... yes
checking for rb_hash_dup()... yes
checking for rb_intern3()... yes
-----
Using mysql_config at /usr/local/bin/mysql_config
-----
checking for mysql.h... yes
checking for errmsg.h... yes
checking for mysqld_error.h... yes
-----
Setting rpath to /usr/local/Cellar/mysql/8.0.11/lib
-----
creating Makefile

current directory: /Users/christoph/.rvm/gems/ruby-2.2.9@cloudcma/gems/mysql2-0.4.3/ext/mysql2
make "DESTDIR=" clean

current directory: /Users/christoph/.rvm/gems/ruby-2.2.9@cloudcma/gems/mysql2-0.4.3/ext/mysql2
make "DESTDIR="
compiling infile.c
In file included from infile.c:1:
In file included from ./mysql2_ext.h:41:
./result.h:24:3: error: unknown type name 'my_bool'
  my_bool *is_null;
  ^
./result.h:25:3: error: unknown type name 'my_bool'
  my_bool *error;
  ^
2 errors generated.
make: *** [infile.o] Error 1

make failed, exit code 2

Gem files will remain installed in /Users/christoph/.rvm/gems/ruby-2.2.9@cloudcma/gems/mysql2-0.4.3 for inspection.
Results logged to /Users/christoph/.rvm/gems/ruby-2.2.9@cloudcma/extensions/x86_64-darwin-17/2.2.0/mysql2-0.4.3/gem_make.out

An error occurred while installing mysql2 (0.4.3), and Bundler cannot continue.
Make sure that `gem install mysql2 -v '0.4.3'` succeeds before bundling.

System Specs

This is on a MacBook Pro, OS X 10.13.3 (High Sierra), mysql 8.0.11 installed via homebrew.

Interestingly, I've had the same version of the gem installed on this very same computer before, so it must have been able to compile at some point. Not sure what happened in the meantime that would break it.

Steps taken so far

• Uninstalled and re-installed mysql2 gem
• Uninstalled and re-installed mysql

I also tried upgrading the gem to a newer version (0.5.1 installs without a hitch), but the app I'm using it with is a Rails 4 app, and according to #950 that means I have to stick to the 0.4.x release.

[PandaWhisperer]

Update: looks like version 0.4.10 installs cleanly.