Always prefer class types to query types when casting group

When `group` is used in combination with any calculation method, the
resulting hash uses the grouping expression as the key. Currently we're
incorrectly always favoring the type reported by the query, instead of
the type known by the class. This causes differing behavior depending on
whether the adaptor actually gives proper types with the query or not.
After this change, the behavior will be the same on all adaptors -- we
see if we know the type from the class, fall back to the type from the
query, and finally fall back to the identity type.

Fixes rails#25595

Author: sgrif

activerecord/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Using `group` with an attribute that has a custom type will properly cast
+    the hash keys after calling a calculation method like `count`. Fixes #25595.
+
+    *Sean Griffin*
+
 *   Ensure concurrent invocations of the connection reaper cannot allocate the
     same connection to two threads.
 

activerecord/lib/active_record/model_schema.rb

@@ -278,8 +278,12 @@ def attribute_types # :nodoc:
       #
       # +attr_name+ The name of the attribute to retrieve the type for. Must be
       # a string
-      def type_for_attribute(attr_name)
-        attribute_types[attr_name]
+      def type_for_attribute(attr_name, &block)
+        if block
+          attribute_types.fetch(attr_name, &block)
+        else
+          attribute_types[attr_name]
+        end
       end
 
       # Returns a hash where the keys are column names and the values are

activerecord/lib/active_record/relation/calculations.rb

@@ -308,8 +308,10 @@ def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:
 
       Hash[calculated_data.map do |row|
         key = group_columns.map { |aliaz, col_name|
-          column = calculated_data.column_types.fetch(aliaz) do
-            type_for(col_name)
+          column = type_for(col_name) do
+            calculated_data.column_types.fetch(aliaz) do
+              Type::Value.new
+            end
           end
           type_cast_calculated_value(row[aliaz], column)
         }
@@ -342,9 +344,9 @@ def column_alias_for(keys)
       @klass.connection.table_alias_for(table_name)
     end
 
-    def type_for(field)
+    def type_for(field, &block)
       field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split('.').last
-      @klass.type_for_attribute(field_name)
+      @klass.type_for_attribute(field_name, &block)
     end
 
     def type_cast_calculated_value(value, type, operation = nil)

activerecord/test/cases/calculations_test.rb

@@ -1,4 +1,5 @@
 require "cases/helper"
+require "models/book"
 require 'models/club'
 require 'models/company'
 require "models/contract"
@@ -789,4 +790,9 @@ def permit!
     assert_equal 50, result[1].credit_limit
     assert_equal 50, result[2].credit_limit
   end
+
+  def test_group_by_attribute_with_custom_type
+    Book.create!(status: :published)
+    assert_equal({ "published" => 1 }, Book.group(:status).count)
+  end
 end