Support microsecond datetime precision on MariaDB 5.3+.

We support microsecond datetime precision for MySQL 5.6.4+. MariaDB has
supported it since 5.3.0, but even 10.x versions return a compatible
version string like `5.5.5-10.1.8-MariaDB-log` which we parse as 5.5.5,
before MySQL supported microsecond precision.

Specialize our version check to account for MariaDB to fix.

Author: jeremy

activerecord/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   MariaDB 5.3+ supports microsecond datetime precision.
+
+    *Jeremy Daer*
+
 *   Delegate `empty?`, `none?` and `one?`. Now they can be invoked as model class methods.
 
     Example:

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -121,7 +121,11 @@ def supports_views?
       end
 
       def supports_datetime_with_precision?
-        version >= '5.6.4'
+        if mariadb?
+          version >= '5.3.0'
+        else
+          version >= '5.6.4'
+        end
       end
 
       def supports_advisory_locks?

activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb

@@ -0,0 +1,45 @@
+require "cases/helper"
+
+class Mysql2DatetimePrecisionQuotingTest < ActiveRecord::Mysql2TestCase
+  setup do
+    @connection = ActiveRecord::Base.connection
+  end
+
+  test 'microsecond precision for MySQL gte 5.6.4' do
+    stub_version '5.6.4'
+    assert_microsecond_precision
+  end
+
+  test 'no microsecond precision for MySQL lt 5.6.4' do
+    stub_version '5.6.3'
+    assert_no_microsecond_precision
+  end
+
+  test 'microsecond precision for MariaDB gte 5.3.0' do
+    stub_version '5.5.5-10.1.8-MariaDB-log'
+    assert_microsecond_precision
+  end
+
+  test 'no microsecond precision for MariaDB lt 5.3.0' do
+    stub_version '5.2.9-MariaDB'
+    assert_no_microsecond_precision
+  end
+
+  private
+    def assert_microsecond_precision
+      assert_match_quoted_microsecond_datetime(/\.000001\z/)
+    end
+
+    def assert_no_microsecond_precision
+      assert_match_quoted_microsecond_datetime(/\d\z/)
+    end
+
+    def assert_match_quoted_microsecond_datetime(match)
+      assert_match match, @connection.quoted_date(Time.now.change(usec: 1))
+    end
+
+    def stub_version(full_version_string)
+      @connection.stubs(:full_version).returns(full_version_string)
+      @connection.remove_instance_variable(:@version) if @connection.instance_variable_defined?(:@version)
+    end
+end

activerecord/test/cases/adapters/mysql2/quoting_test.rb

@@ -1,7 +1,7 @@
 require 'cases/helper'
 require 'support/schema_dumping_helper'
 
-if ActiveRecord::Base.connection.supports_datetime_with_precision?
+if subsecond_precision_supported?
 class DateTimePrecisionTest < ActiveRecord::TestCase
   include SchemaDumpingHelper
   self.use_transactional_tests = false

activerecord/test/cases/date_time_precision_test.rb

@@ -1,7 +1,7 @@
 require 'cases/helper'
 require 'support/schema_dumping_helper'
 
-if ActiveRecord::Base.connection.supports_datetime_with_precision?
+if subsecond_precision_supported?
 class TimePrecisionTest < ActiveRecord::TestCase
   include SchemaDumpingHelper
   self.use_transactional_tests = false