Consistently apply adapter behavior when serializing arrays

In f1a0fa9 we moved backend specific timestamp behavior out of the type
and into the adapter. This was in line with our general attempt to
reduce the number of adapter specific type subclasses. However, on PG,
the array type performs all serialization, including database encoding
in its serialize method.

This means that we have converted the value into a string before
reaching the database, so no adapter specific logic can be applied (and
this also means that timestamp arrays were using the default `.to_s`
method on the given object, which likely meant timestamps were being
ignored in certain cases as well)

Ultimately I want to do a more in depth refactoring which separates
database serializer objects from the active model type objects, to give
us a less awkward API for introducing the attributes API onto Active
Model.

However, in the short term, we follow the solution we've applied
elsewhere for this. Move behavior off of the type and into the adapter,
and use a data object to allow the type to communicate information up
the stack.

Fixes #27514.

5 files changed, 62 insertions, 17 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 5069c6666f..e614458375 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Respect precision option for arrays of timestamps.
+
+    Fixes #27514.
+
+    *Sean Griffin*
+
 *   Optimize slow model instantiation when using STI and `store_full_sti_class = false` option.
 
     *Konstantin Lazarev*
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
index 8ccdd69b1d..e1a75f8e5e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
@@ -5,6 +5,8 @@ module ActiveRecord
         class Array < Type::Value # :nodoc:
           include Type::Helpers::Mutable
 
+          Data = Struct.new(:encoder, :values) # :nodoc:
+
           attr_reader :subtype, :delimiter
           delegate :type, :user_input_in_time_zone, :limit, :precision, :scale, to: :subtype
 
@@ -17,8 +19,11 @@ module ActiveRecord
           end
 
           def deserialize(value)
-            if value.is_a?(::String)
+            case value
+            when ::String
               type_cast_array(@pg_decoder.decode(value), :deserialize)
+            when Data
+              deserialize(value.values)
             else
               super
             end
@@ -33,11 +38,8 @@ module ActiveRecord
 
           def serialize(value)
             if value.is_a?(::Array)
-              result = @pg_encoder.encode(type_cast_array(value, :serialize))
-              if encoding = determine_encoding_of_strings(value)
-                result.force_encoding(encoding)
-              end
-              result
+              casted_values = type_cast_array(value, :serialize)
+              Data.new(@pg_encoder, casted_values)
             else
               super
             end
@@ -58,6 +60,10 @@ module ActiveRecord
             value.map(&block)
           end
 
+          def changed_in_place?(raw_old_value, new_value)
+            deserialize(raw_old_value) != new_value
+          end
+
           private
 
             def type_cast_array(value, method)
@@ -67,13 +73,6 @@ module ActiveRecord
                 @subtype.public_send(method, value)
               end
             end
-
-            def determine_encoding_of_strings(value)
-              case value
-              when ::Array then determine_encoding_of_strings(value.first)
-              when ::String then value.encoding
-              end
-            end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
index b5031d890f..3783925954 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
@@ -92,6 +92,8 @@ module ActiveRecord
               else
                 super
               end
+            when OID::Array::Data
+              _quote(encode_array(value))
             else
               super
             end
@@ -106,10 +108,37 @@ module ActiveRecord
               { value: value.to_s, format: 1 }
             when OID::Xml::Data, OID::Bit::Data
               value.to_s
+            when OID::Array::Data
+              encode_array(value)
             else
               super
             end
           end
+
+          def encode_array(array_data)
+            encoder = array_data.encoder
+            values = type_cast_array(array_data.values)
+
+            result = encoder.encode(values)
+            if encoding = determine_encoding_of_strings_in_array(values)
+              result.force_encoding(encoding)
+            end
+            result
+          end
+
+          def determine_encoding_of_strings_in_array(value)
+            case value
+            when ::Array then determine_encoding_of_strings_in_array(value.first)
+            when ::String then value.encoding
+            end
+          end
+
+          def type_cast_array(values)
+            case values
+            when ::Array then values.map { |item| type_cast_array(item) }
+            else _type_cast(values)
+            end
+          end
       end
     end
   end
diff --git a/activerecord/test/cases/adapters/postgresql/array_test.rb b/activerecord/test/cases/adapters/postgresql/array_test.rb
index 982a91782f..c78c6178ff 100644
--- a/activerecord/test/cases/adapters/postgresql/array_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/array_test.rb
@@ -21,6 +21,7 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
         t.datetime :datetimes, array: true
         t.hstore :hstores, array: true
         t.decimal :decimals, array: true, default: [], precision: 10, scale: 2
+        t.timestamp :timestamps, array: true, default: [], precision: 6
       end
     end
     PgArray.reset_column_information
@@ -213,7 +214,7 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     x = PgArray.create!(tags: tags)
     x.reload
 
-    assert_equal x.tags_before_type_cast, PgArray.type_for_attribute("tags").serialize(tags)
+    refute x.changed?
   end
 
   def test_quoting_non_standard_delimiters
@@ -221,9 +222,10 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     oid = ActiveRecord::ConnectionAdapters::PostgreSQL::OID
     comma_delim = oid::Array.new(ActiveRecord::Type::String.new, ",")
     semicolon_delim = oid::Array.new(ActiveRecord::Type::String.new, ";")
+    conn = PgArray.connection
 
-    assert_equal %({"hello,",world;}), comma_delim.serialize(strings)
-    assert_equal %({hello,;"world;"}), semicolon_delim.serialize(strings)
+    assert_equal %({"hello,",world;}), conn.type_cast(comma_delim.serialize(strings))
+    assert_equal %({hello,;"world;"}), conn.type_cast(semicolon_delim.serialize(strings))
   end
 
   def test_mutate_array
@@ -319,6 +321,15 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     assert_equal [arrays_of_utf8_strings], @type.deserialize(@type.serialize([arrays_of_utf8_strings]))
   end
 
+  def test_precision_is_respected_on_timestamp_columns
+    time = Time.now.change(usec: 123)
+    record = PgArray.create!(timestamps: [time])
+
+    assert_equal 123, record.timestamps.first.usec
+    record.reload
+    assert_equal 123, record.timestamps.first.usec
+  end
+
   private
     def assert_cycle(field, array)
       # test creation
diff --git a/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb b/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb
index bd45a9daa0..784d77a8d1 100644
--- a/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb
@@ -19,7 +19,7 @@ class PostgresqlTypeLookupTest < ActiveRecord::PostgreSQLTestCase
     big_array = [123456789123456789]
 
     assert_raises(ActiveModel::RangeError) { int_array.serialize(big_array) }
-    assert_equal "{123456789123456789}", bigint_array.serialize(big_array)
+    assert_equal "{123456789123456789}", @connection.type_cast(bigint_array.serialize(big_array))
   end
 
   test "range types correctly respect registration of subtypes" do