Return database connection into pool after configuration

When application code being loaded `has_closure_tree` method will get
database connection implicitly and will not return it into the pool.

In some circumstances this connection will not be available
for request processing at runtime anymore.

lib/closure_tree/has_closure_tree.rb

@@ -29,6 +29,8 @@ def has_closure_tree(options = {})
 
       include ClosureTree::DeterministicOrdering if _ct.order_option?
       include ClosureTree::NumericDeterministicOrdering if _ct.order_is_numeric?
+
+      connection_pool.checkin(connection_pool.active_connection?) if connection_pool.active_connection?
     rescue StandardError => e
       raise e unless ClosureTree.configuration.database_less
     end

lib/closure_tree/has_closure_tree_root.rb

@@ -81,6 +81,8 @@ def has_closure_tree_root(assoc_name, options = {})
 
         @closure_tree_roots[assoc_name][assoc_map] = root
       end
+
+      connection_pool.checkin(connection_pool.active_connection?) if connection_pool.active_connection?
     end
   end
 end

spec/pool_spec.rb

@@ -0,0 +1,27 @@
+require 'spec_helper'
+
+describe 'Configuration' do
+  it 'returns connection to the pool after has_closure_tree setup' do
+    class TypeDuplicate < ActiveRecord::Base
+      self.table_name = "namespace_type#{table_name_suffix}"
+      has_closure_tree
+    end
+    expect(ActiveRecord::Base.connection_pool.active_connection?).to be_nil
+  end
+
+  it 'returns connection to the pool after has_closure_tree setup with order' do
+    class MetalDuplicate < ActiveRecord::Base
+      self.table_name = "#{table_name_prefix}metal#{table_name_suffix}"
+      has_closure_tree order: 'sort_order', name_column: 'value'
+    end
+    expect(ActiveRecord::Base.connection_pool.active_connection?).to be_nil
+  end
+
+  it 'returns connection to the pool after has_closure_tree_root setup' do
+    class GroupDuplicate < ActiveRecord::Base
+      self.table_name = "#{table_name_prefix}group#{table_name_suffix}"
+      has_closure_tree_root :root_user
+    end
+    expect(ActiveRecord::Base.connection_pool.active_connection?).to be_nil
+  end
+end