はじめに

mysql２をインストールした時に発生した表題のエラーについての対応記録です。

環境

macOS Catalina バージョン10.15.7
gem 3.0.3
mysql Ver 14.14 Distrib 5.7.32, for osx10.15 (x86_64) using EditLine wrapper
rbenv 1.1.2
ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin19]
OpenSSL 1.1.1h 22 Sep 2020

事象

mysql2 gemをインストールした際に下記のエラーが発生した。
ld: library not found for -lsslが原因らしい。

$ gem install mysql2
Building native extensions. This could take a while...
ERROR:  Error installing mysql2:
	ERROR: Failed to build gem native extension.

    current directory: /Users/username/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/mysql2-0.5.3/ext/mysql2
/Users/username/.rbenv/versions/2.6.5/bin/ruby -I /Users/username/.rbenv/versions/2.6.5/lib/ruby/2.6.0 -r ./siteconf20201028-44975-92zd5o.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/opt/mysql@5.7/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... 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@5.7/lib
-----
creating Makefile

current directory: /Users/username/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/mysql2-0.5.3/ext/mysql2
make "DESTDIR=" clean

current directory: /Users/username/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/mysql2-0.5.3/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/username/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/mysql2-0.5.3 for inspection.
Results logged to /Users/username/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/extensions/x86_64-darwin-19/2.6.0/mysql2-0.5.3/gem_make.out

原因

ld: library not found for -lssl は、ライブラリの検索範囲（Setting libpath to /usr/local/opt/mysql@5.7/libで指定されている場所）を検索したがlibsll.dylib（OpenSSLの動的ライブラリ）を見つけられなかったという内容である。
実際に確認したが見当たらなかった。

$ ls -a /usr/local/opt/mysql@5.7/lib
.			libmysqlclient.20.dylib	libmysqlclient.dylib	libmysqlservices.a	plugin
..			libmysqlclient.a	libmysqld.a		pkgconfig

$ brew openssl infoでopensslの情報を確認すると、

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"

と記載してあり、/usr/local/opt/openssl@1.1/libの中にlibssl.dylibが保管されていることが確認できた。

$ ls -a /usr/local/opt/openssl@1.1/lib/  
.			engines-1.1		libcrypto.a		libssl.1.1.dylib	libssl.dylib
..			libcrypto.1.1.dylib	libcrypto.dylib		libssl.a		pkgconfig

解決

以下のオプションを追加することでインストールに成功した。

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

 $ gem install mysql2 -- --with-cflags=\"-I/usr/local/opt/openssl/include\" --with-ldflags=\"-L/usr/local/opt/openssl/lib\"
Building native extensions with: '--with-cflags="-I/usr/local/opt/openssl/include" --with-ldflags="-L/usr/local/opt/openssl/lib"'
This could take a while...
Successfully installed mysql2-0.5.3
Parsing documentation for mysql2-0.5.3
Installing ri documentation for mysql2-0.5.3
Done installing documentation for mysql2 after 0 seconds
1 gem installed

参考