MySQL Gem Install Error on Ruby 2.4

Question

I have a problem with an install of mysql gem. This is my error :

gem install mysql -v '2.9.1'
Building native extensions.  This could take a while...
ERROR:  Error installing mysql:
    ERROR: Failed to build gem native extension.

    current directory: /usr/local/rvm/gems/ruby-2.4.0/gems/mysql-2.9.1/ext/mysql_api
/usr/local/rvm/rubies/ruby-2.4.0/bin/ruby -r ./siteconf20170107-4120-x2dv85.rb extconf.rb
checking for mysql_ssl_set()... yes
checking for rb_str_set_len()... yes
checking for rb_thread_start_timer()... no
checking for mysql.h... yes
creating Makefile

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

  /usr/local/rvm/gems/ruby-2.4.0/extensions/x86_64-linux/2.4.0/mysql-2.9.1/mkmf.log

current directory: /usr/local/rvm/gems/ruby-2.4.0/gems/mysql-2.9.1/ext/mysql_api
make "DESTDIR=" clean

current directory: /usr/local/rvm/gems/ruby-2.4.0/gems/mysql-2.9.1/ext/mysql_api
make "DESTDIR="
compiling mysql.c
mysql.c: In function ‘stmt_bind_result’:
mysql.c:1320:74: error: ‘rb_cFixnum’ undeclared (first use in this function)
  else if (argv[i] == rb_cNumeric || argv[i] == rb_cInteger || argv[i] == rb_cFixnum)
                                                                          ^
mysql.c:1320:74: note: each undeclared identifier is reported only once for each function it appears in
mysql.c: At top level:
cc1: warning: unrecognized command line option "-Wno-self-assign"
cc1: warning: unrecognized command line option "-Wno-constant-logical-operand"
cc1: warning: unrecognized command line option "-Wno-parentheses-equality"
cc1: warning: unrecognized command line option "-Wno-tautological-compare"
Makefile:241: recipe for target 'mysql.o' failed
make: *** [mysql.o] Error 1

make failed, exit code 2

Gem files will remain installed in /usr/local/rvm/gems/ruby-2.4.0/gems/mysql-2.9.1 for inspection.
Results logged to /usr/local/rvm/gems/ruby-2.4.0/extensions/x86_64-linux/2.4.0/mysql-2.9.1/gem_make.out

When i try this command sudo gem install mysql -v '2.9.1', it's works, and I read this line to justify it...

sudo gem install mysql -v '2.9.1'
Building native extensions.  This could take a while...
Successfully installed mysql-2.9.1
Parsing documentation for mysql-2.9.1
Done installing documentation for mysql after 0 seconds
1 gem installed

I don't understand what happened and how to solved this. If someone could help me...

Answer 1

The mysql gem is one of many gems which doesn't like the unification of the integer types in Ruby 2.4.

Unfortunately, since the mysql gem isn't really maintained anymore, I wouldn't hold my breath for an updated version. As a workaround, you can switch to a Ruby version before 2.4, e.g. Ruby 2.3.3.

Alternatively, you could switch to the mysql2 gem which is actively maintained, has a similar API to the mysql gem and in its latest version is compatible with Ruby 2.4.