Fix SDL generation for interfaces

lib/absinthe/schema/notation/sdl_render.ex

@@ -118,7 +118,7 @@ defmodule Absinthe.Schema.Notation.SDL.Render do
       "type",
       concat([
         string(object_type.name),
-        implements(object_type.interface_blueprints)
+        implements(object_type.interfaces, type_definitions)
       ]),
       render_list(object_type.fields, type_definitions)
     )
@@ -364,12 +364,17 @@ defmodule Absinthe.Schema.Notation.SDL.Render do
     |> concat()
   end
 
-  defp implements([]) do
+  defp implements([], _) do
     empty()
   end
 
-  defp implements(interface_types) do
-    interface_names = Enum.map(interface_types, & &1.name)
+  defp implements(interface_identifiers, type_definitions) do
+    interface_names =
+      Enum.map(interface_identifiers, fn interface_identifier ->
+        Enum.find_value(type_definitions, fn type ->
+          if interface_identifier == type.identifier, do: type.name
+        end)
+      end)
 
     concat([
       " implements ",

test/mix/tasks/absinthe.schema.sdl_test.exs

@@ -13,9 +13,30 @@ defmodule Mix.Tasks.Absinthe.Schema.SdlTest do
 
     type Query {
       helloWorld(name: String!): String
+      interfaceField: Being
+    }
+
+    interface Being {
+      name: String
+    }
+
+    type Human implements Being {
+      name: String
+    }
+
+    type Robot implements Being {
+      name: String
     }
     """
     |> import_sdl
+
+    def hydrate(%Absinthe.Blueprint.Schema.InterfaceTypeDefinition{}, _) do
+      {:resolve_type, &__MODULE__.resolve_type/1}
+    end
+
+    def hydrate(_node, _ancestors), do: []
+
+    def resolve_type(_), do: false
   end
 
   @test_schema "Mix.Tasks.Absinthe.Schema.SdlTest.TestSchema"
@@ -63,10 +84,27 @@ defmodule Mix.Tasks.Absinthe.Schema.SdlTest do
       field :hello_world, :mod do
         arg :name, non_null(:string)
       end
+
+      field :interface_field, :being
     end
 
     object :mod do
     end
+
+    interface :being do
+      field :name, :string
+      resolve_type(fn obj, _ -> obj.type end)
+    end
+
+    object :human do
+      interface :being
+      field :name, :string
+    end
+
+    object :robot do
+      interface :being
+      field :name, :string
+    end
   end
 
   @test_mod_schema "Mix.Tasks.Absinthe.Schema.SdlTest.TestSchemaWithMods"
@@ -111,6 +149,7 @@ defmodule Mix.Tasks.Absinthe.Schema.SdlTest do
 
       assert schema =~ "type Mod {"
       assert schema =~ "modField: String"
+      assert schema =~ "type Robot implements Being"
     end
   end
 end