borrow the more flexible extconf from the mysqlplus project

ext/extconf.rb

@@ -1,21 +1,80 @@
 # encoding: UTF-8
 require 'mkmf'
 
-dir_config('mysql')
+# borrowed from mysqlplus
+# http://github.com/oldmoe/mysqlplus/blob/master/ext/extconf.rb
+dirs = ENV['PATH'].split(':') + %w[
+  /opt
+  /opt/local
+  /opt/local/mysql
+  /opt/local/lib/mysql5
+  /usr
+  /usr/local
+  /usr/local/mysql
+  /usr/local/mysql-*
+  /usr/local/lib/mysql5
+].map{|dir| "#{dir}/bin" }
 
-if !have_header('mysql.h') && !have_header('mysql/mysql.h')
+GLOB = "{#{dirs.join(',')}}/{mysql_config,mysql_config5}"
-  raise 'MySQL headers not found, maybe try manually specifying --with-mysql-dir=/path/to/mysql/installation'
+
+if /mswin32/ =~ RUBY_PLATFORM
+  inc, lib = dir_config('mysql')
+  exit 1 unless have_library("libmysql")
+elsif mc = (with_config('mysql-config') || Dir[GLOB].first) then
+  mc = Dir[GLOB].first if mc == true
+  cflags = `#{mc} --cflags`.chomp
+  exit 1 if $? != 0
+  libs = `#{mc} --libs`.chomp
+  exit 1 if $? != 0
+  $CPPFLAGS += ' ' + cflags
+  $libs = libs + " " + $libs
+else
+  inc, lib = dir_config('mysql', '/usr/local')
+  libs = ['m', 'z', 'socket', 'nsl', 'mygcc']
+  while not find_library('mysqlclient', 'mysql_query', lib, "#{lib}/mysql") do
+    exit 1 if libs.empty?
+    have_library(libs.shift)
   end
+end
+
+if have_header('mysql.h') then
+  src = "#include <errmsg.h>\n#include <mysqld_error.h>\n"
+elsif have_header('mysql/mysql.h') then
+  src = "#include <mysql/errmsg.h>\n#include <mysql/mysqld_error.h>\n"
+else
+  exit 1
+end
+
+# make mysql constant
+File.open("conftest.c", "w") do |f|
+  f.puts src
+end
+if defined? cpp_command then
+  cpp = Config.expand(cpp_command(''))
+else
+  cpp = Config.expand sprintf(CPP, $CPPFLAGS, $CFLAGS, '')
+end
+if /mswin32/ =~ RUBY_PLATFORM && !/-E/.match(cpp)
+  cpp << " -E"
+end
+unless system "#{cpp} > confout" then
+  exit 1
+end
+File.unlink "conftest.c"
+
+error_syms = []
+IO.foreach('confout') do |l|
+  next unless l =~ /errmsg\.h|mysqld_error\.h/
+  fn = l.split(/\"/)[1]
+  IO.foreach(fn) do |m|
+    if m =~ /^#define\s+([CE]R_[0-9A-Z_]+)/ then
+      error_syms << $1
+    end
+  end
+end
+File.unlink 'confout'
 
 $CFLAGS << ' -Wall -Wextra -funroll-loops'
 # $CFLAGS << ' -O0 -ggdb3'
 
-if have_library('mysqlclient')
-  if RUBY_VERSION =~ /1.9/
-    $CFLAGS << ' -DRUBY_19_COMPATIBILITY'
-  end
-
 create_makefile('mysql2_ext')
-else
-  raise 'libmysql not found, maybe try manually specifying --with-mysql-lib=/path/to/mysql/libs'
-end

ext/mysql2_ext.h

@@ -1,10 +1,17 @@
 #include <time.h>
 #include <ruby.h>
 
+#ifdef HAVE_MYSQL_H
+#include <mysql.h>
+#include <mysql_com.h>
+#include <errmsg.h>
+#include <mysqld_error.h>
+#else
 #include <mysql/mysql.h>
 #include <mysql/mysql_com.h>
 #include <mysql/errmsg.h>
 #include <mysql/mysqld_error.h>
+#endif
 
 #ifdef HAVE_RUBY_ENCODING_H
 #include <ruby/encoding.h>