Deparse DO statements (#109)

* Unit test for DO statement

* Implement deparse of DO statement

lib/pg_query/deparse.rb

@@ -162,6 +162,8 @@ def deparse_item(item, context = nil) # rubocop:disable Metrics/CyclomaticComple
         deparse_variable_set_stmt(node)
       when VACUUM_STMT
         deparse_vacuum_stmt(node)
+      when DO_STMT
+        deparse_do_stmt(node)
       when STRING
         if context == A_CONST
           format("'%s'", node['str'].gsub("'", "''"))
@@ -571,6 +573,15 @@ def deparse_vacuum_options(node)
       output
     end
 
+    def deparse_do_stmt(node)
+      output = []
+      output << 'DO'
+      statement, *rest = node['args']
+      output << "$$#{statement['DefElem']['arg']['String']['str']}$$"
+      output += rest.map { |item| deparse_item(item) }
+      output.join(' ')
+    end
+
     def deparse_cte(node)
       output = []
       output << node['ctename']

lib/pg_query/node_types.rb

@@ -34,6 +34,7 @@ class PgQuery
   DECLARE_CURSOR_STMT = 'DeclareCursorStmt'.freeze
   DEF_ELEM = 'DefElem'.freeze
   DELETE_STMT = 'DeleteStmt'.freeze
+  DO_STMT = 'DoStmt'.freeze
   DROP_STMT = 'DropStmt'.freeze
   EXECUTE_STMT = 'ExecuteStmt'.freeze
   EXPLAIN_STMT = 'ExplainStmt'.freeze

spec/lib/pg_query/deparse_spec.rb

@@ -1117,6 +1117,20 @@
         it { is_expected.to eq oneline_query }
       end
     end
+
+    context 'DO' do
+      context 'basic statement' do
+        let(:query) { 'DO $$BEGIN PERFORM * FROM information_schema.tables; END$$' }
+
+        it { is_expected.to eq oneline_query }
+      end
+
+      context 'with language' do
+        let(:query) { 'DO $$ BEGIN PERFORM * FROM information_schema.tables; END $$ language "plpgsql"' }
+
+        it { is_expected.to eq oneline_query }
+      end
+    end
   end
 
   describe '#deparse' do