【Rails】MySQL2がbundle installした時エラーになったので対処法を調べてみた

スクールの課題で`Git`からアプリをクローンし、
自身のPCで環境構築する際に`bundle install`したら、エラーを出したので、対処法を調べて見ました。
以下、エラー時の状況と対処手順です。


# エラー内容

`gem`のインストールをする為、`bundle install`を行ったところエラー発生

```コンソール
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /Users/motoike/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/mysql2-0.4.10/ext/mysql2
/Users/motoike/.rbenv/versions/2.5.1/bin/ruby -r ./siteconf20200126-32549-89onao.rb extconf.rb
checking for rb_absint_size()... yes
checking for rb_absint_singlebit_p()... yes
checking for ruby/thread.h... yes
r 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/opt/mysql@5.6/bin/mysql_config
-----
checking for mysql.h... yes
checking for errmsg.h... yes
checking for SSL_MODE_DISABLED in mysql.h... no
checking for MYSQL_OPT_SSL_ENFORCE in mysql.h... no
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/opt/mysql@5.6/lib
-----
creating Makefile

current directory: /Users/motoike/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/mysql2-0.4.10/ext/mysql2
make "DESTDIR=" clean

current directory: /Users/motoike/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/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

Gem files will remain installed in /Users/motoike/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/mysql2-0.4.10 for inspection.
Results logged to /Users/motoike/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/extensions/x86_64-darwin-19/2.5.0/mysql2-0.4.10/gem_make.out

An error occurred while installing mysql2 (0.4.10), and Bundler cannot continue.
Make sure that `gem install mysql2 -v '0.4.10' --source 'https://rubygems.org/'` succeeds before bundling.

In Gemfile:
  mysql2
```

# 解決する為の手順

ターミナルで`brew info openssl`を実行します。

```
openssl@1.1 is keg-only, which means it was not symlinked into /usr/local,
because openssl/libressl is provided by macOS so don't link an incompatible version.

If you need to have openssl@1.1 first in your PATH run:
  echo 'export PATH="/usr/local/opt/openssl@1.1/bin:$PATH"' >> ~/.zshrc

For compilers to find openssl@1.1 you may need to set:
  export LDFLAGS="-L/usr/local/opt/openssl@1.1/lib"
  export CPPFLAGS="-I/usr/local/opt/openssl@1.1/include"

For pkg-config to find openssl@1.1 you may need to set:
  export PKG_CONFIG_PATH="/usr/local/opt/openssl@1.1/lib/pkgconfig"
```
`export LDFLAGS`、`export CPPFLAGS`に着目します。

```
＄ bundle config --local build.mysql2"--with-cppflags=-I/usr/local/opt/openssl@1.1/include"
Settings for `build.mysql2--with-cppflags=-I/usr/local/opt/openssl@1.1/include` in order of priority. The top value will be used
```
と実行してから、

```
＄ bundle config --local build.mysql2 "--with-ldflags=-L/usr/local/opt/openssl@1.1/lib"
You are replacing the current local value of build.mysql2, which is currently nil
```
と実行後、再度`bundle install`する事で、インストールが出来ました。