Freeze and dedup quote_column_name and quote_table_name caches

Avoid corrupting the cache by mutating the return value, and also
sligthly reduce memory usage when the quoting format often return
an unmodified string.

Author: byroot

activerecord/lib/active_record/connection_adapters/mysql/quoting.rb

@@ -30,11 +30,11 @@ def cast_bound_value(value)
         end
 
         def quote_column_name(name)
-          QUOTED_COLUMN_NAMES[name] ||= "`#{super.gsub('`', '``')}`"
+          QUOTED_COLUMN_NAMES[name] ||= "`#{super.gsub('`', '``')}`".freeze
         end
 
         def quote_table_name(name)
-          QUOTED_TABLE_NAMES[name] ||= super.gsub(".", "`.`").freeze
+          QUOTED_TABLE_NAMES[name] ||= -super.gsub(".", "`.`").freeze
         end
 
         def unquoted_true

activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb

@@ -86,12 +86,7 @@ def quote_string(s) # :nodoc:
         # - "schema.name".table_name
         # - "schema.name"."table.name"
         def quote_table_name(name) # :nodoc:
-          QUOTED_TABLE_NAMES[name] ||= Utils.extract_schema_qualified_name(name.to_s).quoted.freeze
-        end
-
-        # Quotes schema names for use in SQL queries.
-        def quote_schema_name(name)
-          PG::Connection.quote_ident(name)
+          QUOTED_TABLE_NAMES[name] ||= -Utils.extract_schema_qualified_name(name.to_s).quoted.freeze
         end
 
         def quote_table_name_for_assignment(table, attr)
@@ -103,6 +98,9 @@ def quote_column_name(name) # :nodoc:
           QUOTED_COLUMN_NAMES[name] ||= PG::Connection.quote_ident(super).freeze
         end
 
+        # Quotes schema names for use in SQL queries.
+        alias_method :quote_schema_name, :quote_column_name
+
         # Quote date/time values for use in SQL input.
         def quoted_date(value) # :nodoc:
           if value.year <= 0

activerecord/lib/active_record/connection_adapters/sqlite3/quoting.rb

@@ -16,11 +16,11 @@ def quote_table_name_for_assignment(table, attr)
         end
 
         def quote_table_name(name)
-          QUOTED_TABLE_NAMES[name] ||= super.gsub(".", "\".\"").freeze
+          QUOTED_TABLE_NAMES[name] ||= -super.gsub(".", "\".\"").freeze
         end
 
         def quote_column_name(name)
-          QUOTED_COLUMN_NAMES[name] ||= %Q("#{super.gsub('"', '""')}")
+          QUOTED_COLUMN_NAMES[name] ||= %Q("#{super.gsub('"', '""')}").freeze
         end
 
         def quoted_time(value)