add ActiveRecord::AbstractAdapter#extensions and ActiveRecord::Connec…

…tionAdapters::PostgreSQLAdapter#extensions to allow dumping of enabled extensions to schema.rb, add ActiveRecord::SchemaDumper#extensions to dump extensions to schema.rb

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -177,6 +177,12 @@ def supports_extensions?
         false
       end
 
+      # A list of extensions, to be filled in by databases that
+      # support them (at the moment, postgresql)
+      def extensions
+        []
+      end
+
       # QUOTING ==================================================
 
       # Returns a bind substitution value given a +column+ and list of current

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -605,6 +605,15 @@ def extension_enabled?(name)
         end
       end
 
+      def extensions
+        if supports_extensions?
+          res = exec_query "SELECT extname from pg_extension", "SCHEMA"
+          res.rows.map { |r| res.column_types['extname'].type_cast r.first }
+        else
+          []
+        end
+      end
+
       # Returns the configured supported identifier length supported by PostgreSQL
       def table_alias_length
         @table_alias_length ||= query('SHOW max_identifier_length', 'SCHEMA')[0][0].to_i

activerecord/lib/active_record/schema_dumper.rb

@@ -24,6 +24,7 @@ def self.dump(connection=ActiveRecord::Base.connection, stream=STDOUT)
 
     def dump(stream)
       header(stream)
+      extensions(stream)
       tables(stream)
       trailer(stream)
       stream
@@ -66,6 +67,17 @@ def trailer(stream)
         stream.puts "end"
       end
 
+      def extensions(stream)
+        return unless @connection.supports_extensions?
+        extensions = @connection.extensions
+        stream.puts <<EXTENSIONS
+# These are extensions that must be enabled in order to support this database
+EXTENSIONS
+        extensions.each do |extension|
+          stream.puts " enable_extension #{extension.inspect}"
+        end
+      end
+
       def tables(stream)
         @connection.tables.sort.each do |tbl|
           next if ['schema_migrations', ignore_tables].flatten.any? do |ignored|