mysql2 Ruby Gem failed to install ubuntu 20.04 - ruby-on-rails

Question

Does anyone know what causes this and how I can fix it? I am trying to install a ruby gem for my project which is an old project running on rails 3, but I'm running on ubuntu 20.04. All I am doing is essentially running bundle install and then I get everything else working except this ruby gem. Please advise!
current directory: /home/decil/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/mysql2-0.3.21/ext/mysql2
make "DESTDIR=" clean
current directory: /home/decil/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/mysql2-0.3.21/ext/mysql2
make "DESTDIR="
compiling client.c
client.c: In function ‘nogvl_read_query_result’:
client.c:439:3: error: unknown type name ‘my_bool’; did you mean ‘bool’?
439 | my_bool res = mysql_read_query_result(client);
| ^~~~~~~
| bool
client.c: In function ‘rb_query’:
client.c:687:14: warning: passing argument 1 of ‘rb_rescue2’ from incompatible pointer type [-Wincompatible-pointer-types]
687 | rb_rescue2(do_send_query, (VALUE)&args, disconnect_and_raise, self, rb_eException, (VALUE)0);
| ^~~~~~~~~~~~~
| |
| VALUE (*)(void *) {aka long unsigned int (*)(void *)}
In file included from /home/decil/.rbenv/versions/2.7.1/include/ruby-2.7.0/ruby.h:33,
from ./mysql2_ext.h:8,
from client.c:1:
/home/decil/.rbenv/versions/2.7.1/include/ruby-2.7.0/ruby/ruby.h:1988:18: note: expected ‘VALUE (*)(VALUE)’ {aka ‘long unsigned int (*)(long unsigned int)’} but argument is of type ‘VALUE (*)(void *)’ {aka ‘long unsigned int (*)(void *)’}
1988 | VALUE rb_rescue2(VALUE(*)(VALUE),VALUE,VALUE(*)(VALUE,VALUE),VALUE,...);
| ^~~~~~~~~~~~~~~
client.c:695:16: warning: passing argument 1 of ‘rb_rescue2’ from incompatible pointer type [-Wincompatible-pointer-types]
695 | rb_rescue2(do_query, (VALUE)&async_args, disconnect_and_raise, self, rb_eException, (VALUE)0);
| ^~~~~~~~
| |
| VALUE (*)(void *) {aka long unsigned int (*)(void *)}
In file included from /home/decil/.rbenv/versions/2.7.1/include/ruby-2.7.0/ruby.h:33,
from ./mysql2_ext.h:8,
from client.c:1:
/home/decil/.rbenv/versions/2.7.1/include/ruby-2.7.0/ruby/ruby.h:1988:18: note: expected ‘VALUE (*)(VALUE)’ {aka ‘long unsigned int (*)(long unsigned int)’} but argument is of type ‘VALUE (*)(void *)’ {aka ‘long unsigned int (*)(void *)’}
1988 | VALUE rb_rescue2(VALUE(*)(VALUE),VALUE,VALUE(*)(VALUE,VALUE),VALUE,...);
| ^~~~~~~~~~~~~~~
client.c: In function ‘_mysql_client_options’:
client.c:762:3: error: unknown type name ‘my_bool’; did you mean ‘bool’?
762 | my_bool boolval;
| ^~~~~~~
| bool
client.c:797:10: error: ‘MYSQL_SECURE_AUTH’ undeclared (first use in this function); did you mean ‘MYSQL_DEFAULT_AUTH’?
797 | case MYSQL_SECURE_AUTH:
| ^~~~~~~~~~~~~~~~~
| MYSQL_DEFAULT_AUTH
client.c:797:10: note: each undeclared identifier is reported only once for each function it appears in
client.c: In function ‘set_secure_auth’:
client.c:1185:38: error: ‘MYSQL_SECURE_AUTH’ undeclared (first use in this function); did you mean ‘MYSQL_DEFAULT_AUTH’?
1185 | return _mysql_client_options(self, MYSQL_SECURE_AUTH, value);
| ^~~~~~~~~~~~~~~~~
| MYSQL_DEFAULT_AUTH
client.c:1186:1: warning: control reaches end of non-void function [-Wreturn-type]
1186 | }
| ^
client.c: At top level:
cc1: warning: unrecognized command line option ‘-Wno-self-assign’
cc1: warning: unrecognized command line option ‘-Wno-parentheses-equality’
cc1: warning: unrecognized command line option ‘-Wno-constant-logical-operand’
make: *** [Makefile:245: client.o] Error 1

Answer 1

I had a similar issue with version 0.4.5, It worked fine for me with version 0.4.10
Try with the below on your Gemfile:
gem 'mysql2', '0.4.10'

Answer 2

The latest version of the mysql2 gem compatible with Rails 3 is v0.3.21 (source).
mysql2 gem v0.3.21 depends on the my_bool datatype in MySQL itself.
MySQL 5.7 has the my_bool datatype but it was removed in MySQL 8.0 (source).
Ubuntu 20.04 does not have MySQL 5.7, only 8.0+ (source).
Therefore you need to install MySQL 5.7 from MySQL's own apt repositories and stop your server from installing any MySQL stuff from Ubuntu's apt repositories.
I just did all this and successfully got a Rails 3.2 app running on Ubuntu 20.04 LTS.
(Also, Rails 3.2.x is only compatible with Ruby <= 2.3.x.)

Answer 3

my env:ruby2.3,rails3,ubuntu20 server
first of all uninstall mysql5.8, and install mysql5.7
you can see this
enter link description here
but the most important is that make sure the libmysqlclient-dev's version before you install gem mysql2'0.3.11' .
the default libmysqlclient-dev's version is 8.0
i download the
libmysqlclient20_5.7.35-1ubuntu18.04_amd64.deb
libmysqlclient-dev_5.7.35-1ubuntu18.04_amd64.deb
and install them sudo dpkg -i them
that ok