Add `ModelSchema::type_for_attribute` to the public API

We want this method to be the single canonical source of information
about type metadata related to a model. This is the method I've been
continuously recommending people use if they need this sort of access,
as I have no plans to remove or change it at any point in the future.

We can do ourselves a favor and get people to use this instead of
relying on some other part of the internals that they shouldn't be by
making this method public.

1 files changed, 12 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index f26c8471bc..722d7b5fce 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -255,7 +255,18 @@ module ActiveRecord
         @attribute_types ||= Hash.new(Type::Value.new)
       end
 
-      def type_for_attribute(attr_name) # :nodoc:
+      # Returns the type of the attribute with the given name, after applying
+      # all modifiers. This method is the only valid source of information for
+      # anything related to the types of a model's attributes. This method will
+      # access the database and load the model's schema if it is required.
+      #
+      # The return value of this method will implement the interface described
+      # by ActiveModel::Type::Value (though the object itself may not subclass
+      # it).
+      #
+      # +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]
       end