Prevent normalization of polymorphic association

Polymorphic associations have no klass names, so those should be not
normalized. Fixes #588.

Add tests using an action_storage like schema and add changelog entry.

CHANGELOG.md

@@ -1,3 +1,5 @@
+* [#592](https://github.com/CanCanCommunity/cancancan/pull/592): Prevent normalization of through polymorphic associations.([@eloyesp][])
+
 ## 3.0.1
 
 * [#583](https://github.com/CanCanCommunity/cancancan/pull/583): Fix regression when using a method reference block. ([@coorasse][])
@@ -643,3 +645,4 @@ Please read the [guide on migrating from CanCanCan 2.x to 3.0](https://github.co
 [@andrew-aladev]: https://github.com/andrew-aladev
 [@phaedryx]: https://github.com/phaedryx
 [@kaspernj]: https://github.com/kaspernj
+[@eloyesp]: https://github.com/eloyesp

lib/cancan/model_adapters/conditions_normalizer.rb

@@ -31,14 +31,18 @@ def calculate_result_hash(model_class, key, value)
             raise WrongAssociationName, "Association '#{key}' not defined in model '#{model_class.name}'"
           end
 
-          if reflection.options[:through].present?
+          if normalizable_association? reflection
             key = reflection.options[:through]
             value = { reflection.source_reflection_name => value }
             reflection = model_class.reflect_on_association(key)
           end
 
           { key => normalize_conditions(reflection.klass.name.constantize, value) }
         end
+
+        def normalizable_association?(reflection)
+          reflection.options[:through].present? && !reflection.options[:source_type].present?
+        end
       end
     end
   end

spec/cancan/model_adapters/conditions_normalizer_spec.rb

@@ -24,13 +24,22 @@
         t.integer :user_id
         t.integer :article_id
       end
+
+      create_table(:attachments) do |t|
+        t.references :record, polymorphic: true
+        t.integer :blob_id
+      end
+
+      create_table(:blob) do |t|
+      end
     end
 
     class Article < ActiveRecord::Base
       has_many :spread_comments
       has_many :comments, through: :spread_comments
       has_many :mentions
       has_many :mentioned_users, through: :mentions, source: :user
+      has_many :attachments, as: :record
     end
 
     class Comment < ActiveRecord::Base
@@ -53,6 +62,16 @@ class User < ActiveRecord::Base
       has_many :mentions
       has_many :mentioned_articles, through: :mentions, source: :article
     end
+
+    class Attachment < ActiveRecord::Base
+      belongs_to :record, polymorphic: true
+      belongs_to :blob
+    end
+
+    class Blob < ActiveRecord::Base
+      has_many :attachments
+      has_many :articles, through: :attachments, source: :record, source_type: 'Article'
+    end
   end
 
   it 'simplifies has_many through associations' do
@@ -61,6 +80,12 @@ class User < ActiveRecord::Base
     expect(rule.conditions).to eq(spread_comments: { article: { mentions: { user: { name: 'pippo' } } } })
   end
 
+  it 'does not simplifies has_many through polymorphic associations' do
+    rule = CanCan::Rule.new(true, :read, Blob, articles: { id: 11 })
+    CanCan::ModelAdapters::ConditionsNormalizer.normalize(Blob, [rule])
+    expect(rule.conditions).to eq(articles: { id: 11 })
+  end
+
   it 'normalizes the has_one through associations' do
     class Supplier < ActiveRecord::Base
       has_one :accountant