feat: Add entity interface support

Gemfile

@@ -4,6 +4,5 @@ source 'https://rubygems.org'
 
 gemspec
 
-# Fixes an issue in ruby 3.2, remove when a new version is published
-gem 'appraisal', git: 'https://github.com/thoughtbot/appraisal', ref: 'ea2baff57bc7f9e5f9e7a648916c9ae536325116'
+gem 'appraisal', '~> 2.5.0'
 gem 'graphql', '~> 2.0.0'

Gemfile.lock

@@ -1,13 +1,3 @@
-GIT
-  remote: https://github.com/thoughtbot/appraisal
-  revision: ea2baff57bc7f9e5f9e7a648916c9ae536325116
-  ref: ea2baff57bc7f9e5f9e7a648916c9ae536325116
-  specs:
-    appraisal (2.4.1)
-      bundler
-      rake
-      thor (>= 0.14.0)
-
 PATH
   remote: .
   specs:
@@ -36,6 +26,10 @@ GEM
       i18n (>= 1.6, < 2)
       minitest (>= 5.1)
       tzinfo (~> 2.0)
+    appraisal (2.5.0)
+      bundler
+      rake
+      thor (>= 0.14.0)
     ast (2.4.2)
     builder (3.2.4)
     byebug (11.1.3)
@@ -47,9 +41,7 @@ GEM
     debase-ruby_core_source (3.2.0)
     diff-lcs (1.5.0)
     erubi (1.12.0)
-    google-protobuf (3.22.2-arm64-darwin)
-    google-protobuf (3.22.2-x86_64-darwin)
-    google-protobuf (3.22.2-x86_64-linux)
+    google-protobuf (3.22.2)
     graphql (2.0.19)
     i18n (1.12.0)
       concurrent-ruby (~> 1.0)
@@ -58,7 +50,11 @@ GEM
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
     method_source (1.0.0)
+    mini_portile2 (2.8.4)
     minitest (5.18.0)
+    nokogiri (1.14.2)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
     nokogiri (1.14.2-arm64-darwin)
       racc (~> 1.4)
     nokogiri (1.14.2-x86_64-darwin)
@@ -110,7 +106,7 @@ GEM
     ruby-debug-ide (0.7.3)
       rake (>= 0.8.1)
     ruby-progressbar (1.13.0)
-    thor (1.2.1)
+    thor (1.2.2)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
     unicode-display_width (1.6.1)
@@ -119,6 +115,7 @@ GEM
 PLATFORMS
   arm64-darwin-21
   arm64-darwin-22
+  ruby
   x86_64-darwin-20
   x86_64-darwin-21
   x86_64-darwin-22
@@ -127,7 +124,7 @@ PLATFORMS
 DEPENDENCIES
   actionpack
   apollo-federation!
-  appraisal!
+  appraisal (~> 2.5.0)
   debase (= 0.2.5.beta2)
   graphql (~> 2.0.0)
   pry-byebug

lib/apollo-federation/entities_field.rb

@@ -40,16 +40,15 @@ def _entities(representations:)
 
         # TODO: Use warden or schema?
         type = context.warden.get_type(typename)
-        if type.nil? || type.kind != GraphQL::TypeKinds::OBJECT
+        if type.nil? || ![GraphQL::TypeKinds::OBJECT, GraphQL::TypeKinds::INTERFACE].include?(type.kind)
           # TODO: Raise a specific error class?
           raise "The _entities resolver tried to load an entity for type \"#{typename}\"," \
                 ' but no object type of that name was found in the schema'
         end
 
-        # TODO: What if the type is an interface?
         type_class = class_of_type(type)
 
-        if type_class.underscore_reference_keys
+        if type_class.respond_to?(:underscore_reference_keys) && type_class.underscore_reference_keys
           references.map! do |reference|
             reference.transform_keys do |key|
               GraphQL::Schema::Member::BuildType.underscore(key.to_s).to_sym
@@ -72,7 +71,11 @@ def _entities(representations:)
               # calls return the same object, it might not have the right type
               # Right now, apollo-federation just adds a __typename property to the result,
               # but I don't really like the idea of modifying the resolved object
-              context[resolved_value] = type
+              if type.kind == GraphQL::TypeKinds::INTERFACE
+                context[resolved_value] = context.schema.resolve_type(type, resolved_value, context)
+              else
+                context[resolved_value] = type
+              end
               resolved_value
             end
           end

spec/apollo-federation/entities_field_spec.rb

@@ -223,7 +223,7 @@ def self.resolve_type(_abstract_type, _obj, _ctx)
               let(:typename) { 'TypeNotInSchema' }
 
               it 'raises' do
-                expect(-> { execute_query }).to raise_error(
+                expect { execute_query }.to raise_error(
                   /The _entities resolver tried to load an entity for type "TypeNotInSchema"/,
                 )
               end