Turn on performance based cops

Use attr_reader/attr_writer instead of methods

method is 12% slower

Use flat_map over map.flatten(1)

flatten is 66% slower

Use hash[]= instead of hash.merge! with single arguments

merge! is 166% slower

See https://github.com/rails/rails/pull/32337 for more conversation

3 files changed, 3 insertions, 5 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
index 901717ae3d..204691006c 100644
--- a/activerecord/lib/active_record/connection_adapters/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
@@ -57,9 +57,7 @@ module ActiveRecord
 
         private
 
-          def uri
-            @uri
-          end
+          attr_reader :uri
 
           def uri_parser
             @uri_parser ||= URI::Parser.new
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
index 2087938d7c..1cf210d85b 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -36,7 +36,7 @@ module ActiveRecord
               end
 
               indexes.last[-2] << row[:Column_name]
-              indexes.last[-1][:lengths].merge!(row[:Column_name] => row[:Sub_part].to_i) if row[:Sub_part]
+              indexes.last[-1][:lengths][row[:Column_name]] = row[:Sub_part].to_i if row[:Sub_part]
               indexes.last[-1][:orders].merge!(row[:Column_name] => :desc) if row[:Collation] == "D"
             end
           end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index 4c57bd48ab..544d720428 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -117,7 +117,7 @@ module ActiveRecord
         end
 
         def configure_connection
-          @connection.query_options.merge!(as: :array)
+          @connection.query_options[:as] = :array
           super
         end