Backport MySQL 8.0.1 my_bool fix from PR 919

ext/mysql2/extconf.rb

@@ -104,6 +104,12 @@ def asplode lib
   asplode h unless have_header h
 end
 
+mysql_h = [prefix, 'mysql.h'].compact.join('/')
+
+# my_bool is replaced by C99 bool in MySQL 8.0, but we want
+# to retain compatibility with the typedef in earlier MySQLs.
+have_type('my_bool', mysql_h)
+
 # These gcc style flags are also supported by clang and xcode compilers,
 # so we'll use a does-it-work test instead of an is-it-gcc test.
 gcc_flags = ' -Wall -funroll-loops'

ext/mysql2/mysql2_ext.h

@@ -1,6 +1,14 @@
 #ifndef MYSQL2_EXT
 #define MYSQL2_EXT
 
+/* MySQL 8.0 replaces my_bool with C99 bool. Earlier versions of MySQL had
+ * a typedef to char. Gem users reported failures on big endian systems when
+ * using C99 bool types with older MySQLs due to mismatched behavior. */
+#ifndef HAVE_TYPE_MY_BOOL
+#include <stdbool.h>
+typedef bool my_bool;
+#endif
+
 /* tell rbx not to use it's caching compat layer
    by doing this we're making a promise to RBX that
    we'll never modify the pointers we get back from RSTRING_PTR */