Railsの、bundle install でmysql2で失敗する（１分で解決する方法）

現象

今まで同じパソコン（環境）で、新しくRailsのプロジェクトを作成したら、bundle install の時に以下のようなエラーが出た。最近毎回ここでつまずくので、忘れないようにメモしておきます。

gem_make.out

current directory: /Users/hoge/projects/test/vendor/bundle/ruby/2.4.0/gems/mysql2-0.5.2/ext/mysql2
/Users/hoge/.rbenv/versions/2.4.0/bin/ruby -r ./siteconf20190725-32260-xmt1vk.rb extconf.rb
checking for rb_absint_size()... yes
checking for rb_absint_singlebit_p()... yes
checking for rb_wait_for_single_fd()... yes
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Using mysql_config at /usr/local/bin/mysql_config
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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... yes
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Don't know how to set rpath on your system, if MySQL libraries are not in path mysql2 may not load
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Setting libpath to /usr/local/Cellar/mysql/5.7.18/lib
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creating Makefile

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

  /Users/hoge/projects/test/vendor/bundle/ruby/2.4.0/extensions/x86_64-darwin-16/2.4.0-static/mysql2-0.5.2/mkmf.log

current directory: /Users/hoge/projects/test/vendor/bundle/ruby/2.4.0/gems/mysql2-0.5.2/ext/mysql2
make "DESTDIR=" clean

current directory: /Users/hoge/projects/test/vendor/bundle/ruby/2.4.0/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

環境

• macOS Mojave 10.14.5
• ruby 2.4.0
• Rails 5.0.1

対処方法

コンパイルする際に必要なライブラリやインクルードファイルの指定を、バンドルの設定をローカルの環境に合わせて追加する。

BUNDLE_BUILD__MYSQL2: "--with-ldflags=-L/usr/local/opt/openssl/lib --with-cppflags=-I/usr/local/opt/openssl/include"