bundle installでmysqlがエラーになる

新しくrailsアプリを作ろうとnewしたら、bundle installの途中でエラーでコケた。

こんなエラーメッセージが出る。

Installing mysql2 0.4.10 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /path/vendor/bundle/ruby/2.4.0/gems/mysql2-0.4.10/ext/mysql2
/Users/expamle/.rbenv/versions/2.4.2/bin/ruby -r ./siteconf20171122-57537-19ybj8o.rb extconf.rb
checking for rb_absint_size()... yes
checking for rb_absint_singlebit_p()... yes
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
checking for rb_big_cmp()... 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
-----
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/5.7.20/lib
-----
creating Makefile

current directory: /path/vendor/bundle/ruby/2.4.0/gems/mysql2-0.4.10/ext/mysql2
make "DESTDIR=" clean

current directory: /path/vendor/bundle/ruby/2.4.0/gems/mysql2-0.4.10/ext/mysql2
make "DESTDIR="
compiling client.c
compiling infile.c
compiling mysql2_ext.c
compiling result.c
result.c:326:40: warning: incompatible pointer types assigning to 'my_bool *' (aka 'char *') from 'bool *' [-Wincompatible-pointer-types]
    wrapper->result_buffers[i].is_null = &wrapper->is_null[i];
                                       ^ ~~~~~~~~~~~~~~~~~~~~
result.c:328:40: warning: incompatible pointer types assigning to 'my_bool *' (aka 'char *') from 'bool *' [-Wincompatible-pointer-types]
    wrapper->result_buffers[i].error   = &wrapper->error[i];
                                       ^ ~~~~~~~~~~~~~~~~~~
2 warnings generated.
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

早速、Google先生に聞く。答えがすぐ見つかる。

Error when trying to install app with mysql2 gem

ビルドのフラグを追加しろってのが一番の回答になってるけど、もう1個の方のxcodeのコマンドラインツール入れろってのをやってみた。

xcode-select --install

解決した。