Merge pull request #33853 from yahonda/use_utf8mb4_only_if_available

 Validate if `utf8mb4` character set and longer index key prefix is supported

2 files changed, 19 insertions, 3 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 0bb5dfe313..942a6ca282 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Bump minimum MySQL version to 5.5.8.
+
+    *Yasuo Honda*
+
 *   Use MySQL utf8mb4 character set by default.
 
     `utf8mb4` character set with 4-Byte encoding supports supplementary characters including emoji.
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 2d287d56e8..5d4fc8324f 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -53,8 +53,8 @@ module ActiveRecord
 
         @statements = StatementPool.new(self.class.type_cast_config_to_integer(config[:statement_limit]))
 
-        if version < "5.1.10"
-          raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.1.10."
+        if version < "5.5.8"
+          raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.5.8."
         end
       end
 
@@ -114,6 +114,14 @@ module ActiveRecord
         true
       end
 
+      def supports_longer_index_key_prefix?
+        if mariadb?
+          version >= "10.2.2"
+        else
+          version >= "5.7.9"
+        end
+      end
+
       def get_advisory_lock(lock_name, timeout = 0) # :nodoc:
         query_value("SELECT GET_LOCK(#{quote(lock_name.to_s)}, #{timeout})") == 1
       end
@@ -250,8 +258,12 @@ module ActiveRecord
       def create_database(name, options = {})
         if options[:collation]
           execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT COLLATE #{quote_table_name(options[:collation])}"
+        elsif options[:charset]
+          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET #{quote_table_name(options[:charset])}"
+        elsif supports_longer_index_key_prefix?
+          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET `utf8mb4`"
         else
-          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET #{quote_table_name(options[:charset] || 'utf8mb4')}"
+          raise "Configure a supported :charset and ensure innodb_large_prefix is enabled to support indexes on varchar(255) string columns."
         end
       end