Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

必要なライブラリが足りない

bundle install
...
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.
...
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

原因

This gem links against MySQL's libmysqlclient library or Connector/C library, and compatible alternatives such as MariaDB. You may need to install a package such as libmariadb-dev, libmysqlclient-dev, mysql-devel, or other appropriate package for your system. See below for system-specific instructions.

https://github.com/brianmario/mysql2?tab=readme-ov-file#linux-and-otherunixes:~:text=This%20gem%20links,system%2Dspecific%20instructions.

You may need to install a package such as libmariadb-dev, libmysqlclient-dev, mysql-devel, or default-libmysqlclient-dev;

感想

libmariadb-dev, libmysqlclient-dev, mysql-devel, or default-libmysqlclient-devが足りないと考える

試しにlibmysqlclient-devをインストールしたらbundle install完了した。