Remove :timestamp column type

The `:timestamp` type for columns is unused. All database adapters treat
them as the same database type. All code in `ActiveRecord` which changes
its behavior based on the column's type acts the same in both cases.
However, when the type is passed to code that checks for the `:datetime`
type, but not `:timestamp` (such as XML serialization), the result is
unexpected behavior.

Existing schema definitions will continue to work, and the `timestamp`
type is transparently aliased to `datetime`.

12 files changed, 16 insertions, 26 deletions

diff --git a/activerecord/lib/active_record/attribute_assignment.rb b/activerecord/lib/active_record/attribute_assignment.rb
index 87ecbe54f1..816fb51942 100644
--- a/activerecord/lib/active_record/attribute_assignment.rb
+++ b/activerecord/lib/active_record/attribute_assignment.rb
@@ -149,7 +149,7 @@ module ActiveRecord
       end
 
       def read_time
-        # If column is a :time (and not :date or :timestamp) there is no need to validate if
+        # If column is a :time (and not :date or :datetime) there is no need to validate if
         # there are year/month/day fields
         if column.type == :time
           # if the column is a time set the values to their defaults as January 1, 1970, but only if they're nil
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index d01e9aea59..979dfb207e 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -35,7 +35,7 @@ module ActiveRecord
 
       extend ActiveSupport::Concern
 
-      ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :timestamp, :time, :date]
+      ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :time, :date]
 
       included do
         class_attribute :attribute_types_cached_by_default, instance_writer: false
@@ -52,7 +52,7 @@ module ActiveRecord
         end
 
         # Returns the attributes which are cached. By default time related columns
-        # with datatype <tt>:datetime, :timestamp, :time, :date</tt> are cached.
+        # with datatype <tt>:datetime, :time, :date</tt> are cached.
         def cached_attributes
           @cached_attributes ||= columns.select { |c| cacheable_column?(c) }.map { |col| col.name }.to_set
         end
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
index f168282ea3..dfebb2cf56 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -28,7 +28,7 @@ module ActiveRecord
 
       module ClassMethods
         protected
-        # Defined for all +datetime+ and +timestamp+ attributes when +time_zone_aware_attributes+ are enabled.
+        # Defined for all +datetime+ attributes when +time_zone_aware_attributes+ are enabled.
         # This enhanced write method will automatically convert the time passed to it to the zone stored in Time.zone.
         def define_method_attribute=(attr_name)
           if create_time_zone_conversion_attribute?(attr_name, columns_hash[attr_name])
@@ -51,7 +51,7 @@ module ActiveRecord
         def create_time_zone_conversion_attribute?(name, column)
           time_zone_aware_attributes &&
             !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym) &&
-            (:datetime == column.type || :timestamp == column.type)
+            (:datetime == column.type)
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index f54fcc4040..117c0f0969 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -262,6 +262,7 @@ module ActiveRecord
       alias :belongs_to :references
 
       def new_column_definition(name, type, options) # :nodoc:
+        type = aliased_types[type] || type
         column = create_column_definition name, type
         limit = options.fetch(:limit) do
           native[type][:limit] if native[type].is_a?(Hash)
@@ -292,6 +293,12 @@ module ActiveRecord
       def native
         @native
       end
+
+      def aliased_types
+        HashWithIndifferentAccess.new(
+          timestamp: :datetime,
+        )
+      end
     end
 
     class AlterTable # :nodoc:
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 8a7a869eec..0c55dbb037 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -382,7 +382,7 @@ module ActiveRecord
         m.alias_type    %r(clob)i,       'text'
         m.register_type %r(date)i,       Type::Date.new
         m.register_type %r(time)i,       Type::Time.new
-        m.register_type %r(timestamp)i,  Type::Timestamp.new
+        m.alias_type    %r(timestamp)i,  'datetime'
         m.register_type %r(datetime)i,   Type::DateTime.new
         m.alias_type    %r(numeric)i,    'decimal'
         m.alias_type    %r(number)i,     'decimal'
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 5eb2e86d48..852b7105d3 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -163,7 +163,6 @@ module ActiveRecord
         :float       => { :name => "float" },
         :decimal     => { :name => "decimal" },
         :datetime    => { :name => "datetime" },
-        :timestamp   => { :name => "datetime" },
         :time        => { :name => "time" },
         :date        => { :name => "date" },
         :binary      => { :name => "blob" },
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index 0087c20b88..25a9cdafcf 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -63,7 +63,7 @@ module ActiveRecord
         when :integer                     then Fixnum
         when :float                       then Float
         when :decimal                     then BigDecimal
-        when :datetime, :timestamp, :time then Time
+        when :datetime, :time             then Time
         when :date                        then Date
         when :text, :string, :binary      then String
         when :boolean                     then Object
@@ -110,7 +110,7 @@ module ActiveRecord
         when :integer              then klass.value_to_integer(value)
         when :float                then value.to_f
         when :decimal              then klass.value_to_decimal(value)
-        when :datetime, :timestamp then klass.string_to_time(value)
+        when :datetime             then klass.string_to_time(value)
         when :time                 then klass.string_to_dummy_time(value)
         when :date                 then klass.value_to_date(value)
         when :binary               then klass.binary_to_string(value)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 59e157744f..39fa75518b 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -216,7 +216,6 @@ module ActiveRecord
         float:       { name: "float" },
         decimal:     { name: "decimal" },
         datetime:    { name: "timestamp" },
-        timestamp:   { name: "timestamp" },
         time:        { name: "time" },
         date:        { name: "date" },
         daterange:   { name: "daterange" },
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 0330fa762c..03ff0d4ead 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -69,7 +69,6 @@ module ActiveRecord
         float:        { name: "float" },
         decimal:      { name: "decimal" },
         datetime:     { name: "datetime" },
-        timestamp:    { name: "datetime" },
         time:         { name: "time" },
         date:         { name: "date" },
         binary:       { name: "blob" },
diff --git a/activerecord/lib/active_record/connection_adapters/type.rb b/activerecord/lib/active_record/connection_adapters/type.rb
index 34b1e9e39e..0268e0d569 100644
--- a/activerecord/lib/active_record/connection_adapters/type.rb
+++ b/activerecord/lib/active_record/connection_adapters/type.rb
@@ -9,7 +9,6 @@ require 'active_record/connection_adapters/type/integer'
 require 'active_record/connection_adapters/type/string'
 require 'active_record/connection_adapters/type/text'
 require 'active_record/connection_adapters/type/time'
-require 'active_record/connection_adapters/type/timestamp'
 require 'active_record/connection_adapters/type/type_map'
 
 module ActiveRecord
diff --git a/activerecord/lib/active_record/connection_adapters/type/date_time.rb b/activerecord/lib/active_record/connection_adapters/type/date_time.rb
index 1d7d3cfbbf..1485fd3d80 100644
--- a/activerecord/lib/active_record/connection_adapters/type/date_time.rb
+++ b/activerecord/lib/active_record/connection_adapters/type/date_time.rb
@@ -1,9 +1,7 @@
-require 'active_record/connection_adapters/type/timestamp'
-
 module ActiveRecord
   module ConnectionAdapters
     module Type
-      class DateTime < Timestamp # :nodoc:
+      class DateTime < Value # :nodoc:
         def type
           :datetime
         end
diff --git a/activerecord/lib/active_record/connection_adapters/type/timestamp.rb b/activerecord/lib/active_record/connection_adapters/type/timestamp.rb
deleted file mode 100644
index 92bf0a1954..0000000000
--- a/activerecord/lib/active_record/connection_adapters/type/timestamp.rb
+++ /dev/null
@@ -1,11 +0,0 @@
-module ActiveRecord
-  module ConnectionAdapters
-    module Type
-      class Timestamp < Value # :nodoc:
-        def type
-          :timestamp
-        end
-      end
-    end
-  end
-end