新しい端末で新しい環境を構築していく際にeventmachineというGemでタイトルのエラーが出て約２日悩まされたのでまとめていきます。
ちなみに今までOSアップデートでmacOSを使っていたためこの手の問題は無かったです。
環境
MacBookPro Mojave - macOS 10.14.6
事象
$ bundle install
...
Installing eventmachine 1.2.7 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
current directory: /private/var/folders/p8/37pd2jf119jd4tlmf0nm85kw0000gn/T/bundler20191213-83767-sh7gkueventmachine-1.2.7/gems/eventmachine-1.2.7/ext
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20191213-83767-1nxkkq.rb extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h
extconf failed, exit code 1
Gem files will remain installed in /var/folders/p8/37pd2jf119jd4tlmf0nm85kw0000gn/T/bundler20191213-83767-sh7gkueventmachine-1.2.7/gems/eventmachine-1.2.7 for inspection.
Results logged to /var/folders/p8/37pd2jf119jd4tlmf0nm85kw0000gn/T/bundler20191213-83767-sh7gkueventmachine-1.2.7/extensions/universal-darwin-18/2.3.0/eventmachine-1.2.7/gem_make.out
An error occurred while installing eventmachine (1.2.7), and Bundler cannot continue.
Make sure that `gem install eventmachine -v '1.2.7' --source 'https://rubygems.org/'` succeeds before bundling.
In Gemfile:
appium_lib was resolved to 9.16.1, which depends on
appium_lib_core was resolved to 2.2.0, which depends on
faye-websocket was resolved to 0.10.7, which depends on
eventmachine
$ sudo gem install eventmachine
Building native extensions. This could take a while...
ERROR: Error installing eventmachine:
ERROR: Failed to build gem native extension.
current directory: /Library/Ruby/Gems/2.3.0/gems/eventmachine-1.2.7/ext
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20191213-83820-1pf9cvb.rb extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h
extconf failed, exit code 1
Gem files will remain installed in /Library/Ruby/Gems/2.3.0/gems/eventmachine-1.2.7 for inspection.
Results logged to /Library/Ruby/Gems/2.3.0/extensions/universal-darwin-18/2.3.0/eventmachine-1.2.7/gem_make.out
一度消して単体で入れ直してみる
それでも上手く入りませんでした。
$ sudo rm -fr /Library/Ruby/Gems/2.3.0/gems/eventmachine-1.2.7
$ sudo gem install eventmachine
Building native extensions. This could take a while...
ERROR: Error installing eventmachine:
ERROR: Failed to build gem native extension.
current directory: /Library/Ruby/Gems/2.3.0/gems/eventmachine-1.2.7/ext
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20191213-83844-1xn766m.rb extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h
extconf failed, exit code 1
Gem files will remain installed in /Library/Ruby/Gems/2.3.0/gems/eventmachine-1.2.7 for inspection.
Results logged to /Library/Ruby/Gems/2.3.0/extensions/universal-darwin-18/2.3.0/eventmachine-1.2.7/gem_make.out
解決方法
ググってみるとdocker界隈でも似たような現象があったようです。
Can't run docker-sync after upgrading to Xcode 11 #679を参考にするとAdamBDがMojaveユーザーはこれで直ると言っていたので試したところ上手くいきました。
ちなみにXcodeをインストールしたのちにCommandLineToolsを公式からインストールしていましたが、それで上記の状況だったのでCLIでの対応が必要なようです。
$ sudo rm -rf /Library/Developer/CommandLineTools
$ xcode-select --install
$ sudo xcodebuild -license accept
$ open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg
$ sudo gem install eventmachine
Building native extensions. This could take a while...
Successfully installed eventmachine-1.2.7
Parsing documentation for eventmachine-1.2.7
Installing ri documentation for eventmachine-1.2.7
Done installing documentation for eventmachine after 4 seconds
1 gem installed