Support default expression for MySQL

MySQL 8.0.13 and higher supports default value to be a function or
expression.

https://dev.mysql.com/doc/refman/8.0/en/create-table.html

3 files changed, 19 insertions, 0 deletions

diff --git a/activerecord/test/cases/defaults_test.rb b/activerecord/test/cases/defaults_test.rb
index 0f957d41cf..5d02e59ef6 100644
--- a/activerecord/test/cases/defaults_test.rb
+++ b/activerecord/test/cases/defaults_test.rb
@@ -106,6 +106,13 @@ if current_adapter?(:Mysql2Adapter)
   class MysqlDefaultExpressionTest < ActiveRecord::TestCase
     include SchemaDumpingHelper
 
+    if supports_default_expression?
+      test "schema dump includes default expression" do
+        output = dump_table_schema("defaults")
+        assert_match %r/t\.binary\s+"uuid",\s+limit: 36,\s+default: -> { "\(uuid\(\)\)" }/i, output
+      end
+    end
+
     if subsecond_precision_supported?
       test "schema dump datetime includes default expression" do
         output = dump_table_schema("datetime_defaults")
diff --git a/activerecord/test/cases/helper.rb b/activerecord/test/cases/helper.rb
index 68be685e4b..730cd663a2 100644
--- a/activerecord/test/cases/helper.rb
+++ b/activerecord/test/cases/helper.rb
@@ -48,6 +48,15 @@ def mysql_enforcing_gtid_consistency?
   current_adapter?(:Mysql2Adapter) && "ON" == ActiveRecord::Base.connection.show_variable("enforce_gtid_consistency")
 end
 
+def supports_default_expression?
+  if current_adapter?(:PostgreSQLAdapter)
+    true
+  elsif current_adapter?(:Mysql2Adapter)
+    conn = ActiveRecord::Base.connection
+    !conn.mariadb? && conn.version >= "8.0.13"
+  end
+end
+
 def supports_savepoints?
   ActiveRecord::Base.connection.supports_savepoints?
 end
diff --git a/activerecord/test/schema/mysql2_specific_schema.rb b/activerecord/test/schema/mysql2_specific_schema.rb
index 499280cb0c..ccca9a2d9b 100644
--- a/activerecord/test/schema/mysql2_specific_schema.rb
+++ b/activerecord/test/schema/mysql2_specific_schema.rb
@@ -19,6 +19,9 @@ ActiveRecord::Schema.define do
     t.datetime :fixed_time, default: "2004-01-01 00:00:00"
     t.column :char1, "char(1)", default: "Y"
     t.string :char2, limit: 50, default: "a varchar field"
+    if supports_default_expression?
+      t.binary :uuid, limit: 36, default: -> { "(uuid())" }
+    end
   end
 
   create_table :binary_fields, force: true do |t|