【mastodon】bundle install でエラーが出たのでメモ

はじめに

mastodonを読むと勉強になるということで、
bundle installしたらさっそくエラーが発生したのでメモ

Failed to locate protobuf

current directory:
/mastodon/vendor/bundle/ruby/2.5.0/gems/cld3-3.2.2/ext/cld3
.rbenv/versions/2.5.0/bin/ruby -r ./siteconf20180326-69724-1yq4plx.rb extconf.rb
Failed to locate protobuf

To see why this extension failed to compile, please check the mkmf.log which can be found here:

/mastodon/vendor/bundle/ruby/2.5.0/extensions/x86_64-darwin-16/2.5.0-static/cld3-3.2.2/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in
/mastodon/vendor/bundle/ruby/2.5.0/gems/cld3-3.2.2 for inspection.
Results logged to
/mastodon/vendor/bundle/ruby/2.5.0/extensions/x86_64-darwin-16/2.5.0-static/cld3-3.2.2/gem_make.out

An error occurred while installing cld3 (3.2.2), and Bundler cannot continue.
Make sure that `gem install cld3 -v '3.2.2'` succeeds before bundling.

gem install cld3 -v '3.2.2' をやってみたけどダメで、
protobufというパッケージが必要だということで　
brew install protobuf を実行したら通った。

今度はこれが出てきた。

ERROR: could not find idn library!
current directory:
/mastodon/vendor/bundle/ruby/2.5.0/gems/idn-ruby-0.1.0/ext
/.rbenv/versions/2.5.0/bin/ruby -r ./siteconf20180326-5783-ruj5ss.rb extconf.rb
checking for -lidn... no
ERROR: could not find idn library!

  Please install the GNU IDN library or alternatively specify at least one
  of the following options if the library can only be found in a non-standard
  location:
    --with-idn-dir=/path/to/non/standard/location
        or
    --with-idn-lib=/path/to/non/standard/location/lib
    --with-idn-include=/path/to/non/standard/location/include

*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=.rbenv/versions/2.5.0/bin/$(RUBY_BASE_NAME)
	--with-idn-dir
	--without-idn-dir
	--with-idn-include
	--without-idn-include=${idn-dir}/include
	--with-idn-lib
	--without-idn-lib=${idn-dir}/lib
	--with-idnlib
	--without-idnlib

To see why this extension failed to compile, please check the mkmf.log which can be found here:

/mastodon/vendor/bundle/ruby/2.5.0/extensions/x86_64-darwin-16/2.5.0-static/idn-ruby-0.1.0/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in
/mastodon/vendor/bundle/ruby/2.5.0/gems/idn-ruby-0.1.0 for inspection.
Results logged to
/mastodon/vendor/bundle/ruby/2.5.0/extensions/x86_64-darwin-16/2.5.0-static/idn-ruby-0.1.0/gem_make.out
An error occurred while installing idn-ruby (0.1.0), and Bundler cannot continue.
Make sure that `gem install idn-ruby -v '0.1.0'` succeeds before bundling.

これも brew install libidn したら通ったが
なぜこの２つが必要なのかは、よく分かっていないので
教えていただけら嬉しいです。