Properly cast input in update_all

The documentation claims that given values go through "normal AR type
casting and serialization", which to me implies
`serialize(cast(value))`, not just serialization. The docs were changed
to use this wording in #22492. The tests I cited in that PR (which is
the same test modified in this commit), is worded in a way that implies
it should be using `cast` as well.

It's possible that I originally meant "normal type casting" to imply
just the call to `serialize`, but given that `update_all(archived:
params['archived'])` seems to be pretty common, I'm inclined to make
this change as long as no tests are broken from it.

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   `update_all` will now pass its values to `Type#cast` before passing them to
+    `Type#serialize`. This means that `update_all(foo: 'true')` will properly
+    persist a boolean.
+
+    *Sean Griffin*
+
 *   Add new error class `StatementTimeout` which will be raised
     when statement timeout exceeded.
 

activerecord/lib/active_record/sanitization.rb

@@ -110,7 +110,8 @@ def expand_hash_conditions_for_aggregates(attrs) # :doc:
         def sanitize_sql_hash_for_assignment(attrs, table) # :doc:
           c = connection
           attrs.map do |attr, value|
-            value = type_for_attribute(attr.to_s).serialize(value)
+            type = type_for_attribute(attr.to_s)
+            value = type.serialize(type.cast(value))
             "#{c.quote_table_name_for_assignment(table, attr)} = #{c.quote(value)}"
           end.join(", ")
         end

activerecord/test/cases/relation_test.rb

@@ -288,13 +288,18 @@ def type
         :string
       end
 
+      def cast(value)
+        raise value unless value == "value from user"
+        "cast value"
+      end
+
       def deserialize(value)
         raise value unless value == "type cast for database"
         "type cast from database"
       end
 
       def serialize(value)
-        raise value unless value == "value from user"
+        raise value unless value == "cast value"
         "type cast for database"
       end
     end