Move DatabaseAlreadyExists detection to DB adapter

Previously it was the responsibility of the database tasks to translate
the invalid statement from creating a duplicate database into an
ActiveRecord::Tasks::DatabaseAlreadyExists error.

It's actually easier for us to do this detection inside of the adapter,
where we already do a case statement on the return code to translate the
error.

This commit introduces ActiveRecord::DatabaseAlreadyExists, a subclass
of StatementInvalid, and updates both AbstractMysqlAdapter and
PostgresqlAdapter to return this more specific exception in that case.

Because this is a subclass of the old exception, StatementInvalid, it
should be backwards compatible with any code expecting that from
create_database.

This works for both create_database and exectute("CREATE DATABASE")

2 files changed, 3 insertions, 5 deletions

diff --git a/activerecord/test/cases/tasks/mysql_rake_test.rb b/activerecord/test/cases/tasks/mysql_rake_test.rb
index ac3c5bc26e..4b039395e8 100644
--- a/activerecord/test/cases/tasks/mysql_rake_test.rb
+++ b/activerecord/test/cases/tasks/mysql_rake_test.rb
@@ -93,11 +93,9 @@ if current_adapter?(:Mysql2Adapter)
         with_stubbed_connection_establish_connection do
           ActiveRecord::Base.connection.stub(
             :create_database,
-            proc { raise ActiveRecord::StatementInvalid }
+            proc { raise ActiveRecord::DatabaseAlreadyExists }
           ) do
-            ActiveRecord::Base.connection.stub(:error_number, 1007) do
-              ActiveRecord::Tasks::DatabaseTasks.create @configuration
-            end
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
             assert_equal "Database 'my-app-db' already exists\n", $stderr.string
           end
diff --git a/activerecord/test/cases/tasks/postgresql_rake_test.rb b/activerecord/test/cases/tasks/postgresql_rake_test.rb
index f9df650687..d74ba0580d 100644
--- a/activerecord/test/cases/tasks/postgresql_rake_test.rb
+++ b/activerecord/test/cases/tasks/postgresql_rake_test.rb
@@ -129,7 +129,7 @@ if current_adapter?(:PostgreSQLAdapter)
         with_stubbed_connection_establish_connection do
           ActiveRecord::Base.connection.stub(
             :create_database,
-            proc { raise ActiveRecord::Tasks::DatabaseAlreadyExists }
+            proc { raise ActiveRecord::DatabaseAlreadyExists }
           ) do
             ActiveRecord::Tasks::DatabaseTasks.create @configuration