railsでmysql2 gemのインストールができない

# mysql2 installができない

## 症状

bundle install する時にmysql2 gem installが失敗する。

```sh
planner (master) ✗ bundle install --path vendor/bundle
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Fetching gem metadata from https://rubygems.org/.........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies...
Using rake 12.3.1
Using concurrent-ruby 1.1.3
Using i18n 1.1.1
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.5
Using activesupport 5.2.1
Using builder 3.2.3
Using erubi 1.7.1
Using mini_portile2 2.3.0
Using nokogiri 1.8.5
Using rails-dom-testing 2.0.3
Using crass 1.0.4
Using loofah 2.2.3
Using rails-html-sanitizer 1.0.4
Using actionview 5.2.1
Using rack 2.0.6
Using rack-test 1.1.0
Using actionpack 5.2.1
Using nio4r 2.3.1
Using websocket-extensions 0.1.3
Using websocket-driver 0.7.0
Using actioncable 5.2.1
Using globalid 0.4.1
Using activejob 5.2.1
Using mini_mime 1.0.1
Using mail 2.7.1
Using actionmailer 5.2.1
Using activemodel 5.2.1
Using arel 9.0.0
Using activerecord 5.2.1
Using mimemagic 0.3.2
Using marcel 0.3.3
Using activestorage 5.2.1
Using bindex 0.5.0
Using msgpack 1.2.4
Using bootsnap 1.3.2
Using bundler 1.17.1
Using byebug 10.0.2
Using ffi 1.9.25
Using multi_json 1.13.1
Using jbuilder 2.8.0
Using rb-fsevent 0.10.3
Using rb-inotify 0.9.10
Using ruby_dep 1.5.0
Using listen 3.1.5
Using method_source 0.9.2
Fetching mysql2 0.5.2
Installing mysql2 0.5.2 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /Users/devtopia/Apps/study/planner/vendor/bundle/ruby/2.5.0/gems/mysql2-0.5.2/ext/mysql2
/usr/local/var/rbenv/versions/2.5.3/bin/ruby -r ./siteconf20181121-46807-1gaptqn.rb extconf.rb
checking for rb_absint_size()... yes
checking for rb_absint_singlebit_p()... yes
checking for rb_wait_for_single_fd()... yes
-----
Using mysql_config at /usr/local/bin/mysql_config
-----
checking for mysql.h... yes
checking for errmsg.h... yes
checking for SSL_MODE_DISABLED in mysql.h... yes
checking for SSL_MODE_PREFERRED in mysql.h... yes
checking for SSL_MODE_REQUIRED in mysql.h... yes
checking for SSL_MODE_VERIFY_CA in mysql.h... yes
checking for SSL_MODE_VERIFY_IDENTITY in mysql.h... yes
checking for MYSQL.net.vio in mysql.h... yes
checking for MYSQL.net.pvio in mysql.h... no
checking for MYSQL_ENABLE_CLEARTEXT_PLUGIN in mysql.h... yes
checking for SERVER_QUERY_NO_GOOD_INDEX_USED in mysql.h... yes
checking for SERVER_QUERY_NO_INDEX_USED in mysql.h... yes
checking for SERVER_QUERY_WAS_SLOW in mysql.h... yes
checking for MYSQL_OPTION_MULTI_STATEMENTS_ON in mysql.h... yes
checking for MYSQL_OPTION_MULTI_STATEMENTS_OFF in mysql.h... yes
checking for my_bool in mysql.h... no
-----
Don't know how to set rpath on your system, if MySQL libraries are not in path mysql2 may not load
-----
-----
Setting libpath to /usr/local/Cellar/mysql/8.0.12/lib
-----
creating Makefile

current directory: /Users/devtopia/Apps/study/planner/vendor/bundle/ruby/2.5.0/gems/mysql2-0.5.2/ext/mysql2
make "DESTDIR=" clean

current directory: /Users/devtopia/Apps/study/planner/vendor/bundle/ruby/2.5.0/gems/mysql2-0.5.2/ext/mysql2
make "DESTDIR="
compiling client.c
compiling infile.c
compiling mysql2_ext.c
compiling result.c
compiling statement.c
linking shared-object mysql2/mysql2.bundle
ld: library not found for -lssl
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [mysql2.bundle] Error 1

make failed, exit code 2

Gem files will remain installed in /Users/devtopia/Apps/study/planner/vendor/bundle/ruby/2.5.0/gems/mysql2-0.5.2 for inspection.
Results logged to /Users/devtopia/Apps/study/planner/vendor/bundle/ruby/2.5.0/extensions/x86_64-darwin-18/2.5.0-static/mysql2-0.5.2/gem_make.out

An error occurred while installing mysql2 (0.5.2), and Bundler cannot continue.
Make sure that `gem install mysql2 -v '0.5.2' --source 'https://rubygems.org/'` succeeds before bundling.

In Gemfile:
  mysql2
```

## 原因

mysql2 gemはcompileしてinstallされますが、bundle installした時にエラーが発生しました。
メッセージを全部貼っておいたせいで長く見えますが、肝心のところはここです。

```sh
... snip ...
ld: library not found for -lssl
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [mysql2.bundle] Error 1
... snip ...
```

ライブラリを見つけない。
原因はコレみたいですが、opensslは設置されています。

```sh
 planner (master) ✗ brew list | grep ssl
39:openssl
```

## 対応

mysql2 gemのgithubのissuesで解決方法を見つけました。

https://github.com/brianmario/mysql2/issues/1005

```sh
$ bundle config --local build.mysql2 "--with-ldflags=-L/usr/local/opt/openssl/lib --with-cppflags=-I/usr/local/opt/openssl/include"
```

これでmysql2 gemが無事にinstallされました。

```sh
 planner (master) ✗ bundle config --local build.mysql2 "--with-ldflags=-L/usr/local/opt/openssl/lib --with-cppflags=-I/usr/local/opt/openssl/include"
You are replacing the current local value of build.mysql2, which is currently nil
 planner (master) ✗ bundle install --path vendor/bundle
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Fetching gem metadata from https://rubygems.org/.........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies...
Using rake 12.3.1
Using concurrent-ruby 1.1.3
Using i18n 1.1.1
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.5
Using activesupport 5.2.1
Using builder 3.2.3
Using erubi 1.7.1
Using mini_portile2 2.3.0
Using nokogiri 1.8.5
Using rails-dom-testing 2.0.3
Using crass 1.0.4
Using loofah 2.2.3
Using rails-html-sanitizer 1.0.4
Using actionview 5.2.1
Using rack 2.0.6
Using rack-test 1.1.0
Using actionpack 5.2.1
Using nio4r 2.3.1
Using websocket-extensions 0.1.3
Using websocket-driver 0.7.0
Using actioncable 5.2.1
Using globalid 0.4.1
Using activejob 5.2.1
Using mini_mime 1.0.1
Using mail 2.7.1
Using actionmailer 5.2.1
Using activemodel 5.2.1
Using arel 9.0.0
Using activerecord 5.2.1
Using mimemagic 0.3.2
Using marcel 0.3.3
Using activestorage 5.2.1
Using bindex 0.5.0
Using msgpack 1.2.4
Using bootsnap 1.3.2
Using bundler 1.17.1
Using byebug 10.0.2
Using ffi 1.9.25
Using multi_json 1.13.1
Using jbuilder 2.8.0
Using rb-fsevent 0.10.3
Using rb-inotify 0.9.10
Using ruby_dep 1.5.0
Using listen 3.1.5
Using method_source 0.9.2
Fetching mysql2 0.5.2
Installing mysql2 0.5.2 with native extensions
Fetching puma 3.12.0
Installing puma 3.12.0 with native extensions
Fetching rack-proxy 0.6.5
Installing rack-proxy 0.6.5
Fetching thor 0.20.3
Installing thor 0.20.3
Fetching railties 5.2.1
Installing railties 5.2.1
Fetching sprockets 3.7.2
Installing sprockets 3.7.2
Fetching sprockets-rails 3.2.1
Installing sprockets-rails 3.2.1
Fetching rails 5.2.1
Installing rails 5.2.1
Fetching spring 2.0.2
Installing spring 2.0.2
Fetching spring-watcher-listen 2.0.1
Installing spring-watcher-listen 2.0.1
Fetching web-console 3.7.0
Installing web-console 3.7.0
Fetching webpacker 3.5.5
Installing webpacker 3.5.5
Bundle complete! 12 Gemfile dependencies, 59 gems now installed.
Bundled gems are installed into `./vendor/bundle`
```

githubが登場しなかったらこの業界で飯を食うのは難しかったと思います。