Provide location information for interface errors

2 files changed, 21 insertions, 3 deletions

diff --git a/src/Language/GraphQL/Execute/Execution.hs b/src/Language/GraphQL/Execute/Execution.hs
index b671c13..742a6a9 100644
--- a/src/Language/GraphQL/Execute/Execution.hs
+++ b/src/Language/GraphQL/Execute/Execution.hs
@@ -132,12 +132,13 @@ completeValue (Out.ObjectBaseType objectType) fields result =
 completeValue (Out.InterfaceBaseType interfaceType) fields result
     | Type.Object objectMap <- result = do
         let abstractType = Internal.AbstractInterfaceType interfaceType
+        let Transform.Field _ _ _ _ location = NonEmpty.head fields
         concreteType <- resolveAbstractType abstractType objectMap
         case concreteType of
             Just objectType -> executeSelectionSet result objectType
                 $ mergeSelectionSets fields
             Nothing -> addError null
-                $ Error "Interface value completion failed." [] []
+                $ Error "Interface value completion failed." [location] []
 completeValue (Out.UnionBaseType unionType) fields result
     | Type.Object objectMap <- result = do
         let abstractType = Internal.AbstractUnionType unionType
@@ -148,7 +149,8 @@ completeValue (Out.UnionBaseType unionType) fields result
                 $ mergeSelectionSets fields
             Nothing -> addError null
                 $ Error "Union value completion failed." [location] []
-completeValue _ _ _ = addError null $ Error "Value completion failed." [] []
+completeValue _ (Transform.Field _ _ _ _ location :| _) _ =
+    addError null $ Error "Value completion failed." [location] []
 
 mergeSelectionSets :: MonadCatch m
     => NonEmpty (Transform.Field m)
diff --git a/tests/Language/GraphQL/ExecuteSpec.hs b/tests/Language/GraphQL/ExecuteSpec.hs
index f5bfd33..815e315 100644
--- a/tests/Language/GraphQL/ExecuteSpec.hs
+++ b/tests/Language/GraphQL/ExecuteSpec.hs
@@ -218,7 +218,7 @@ spec =
                         $ parse document "" "{ philosopher { school } }"
                 in actual `shouldBe` expected
 
-            it "gives location information for invalid interfaces" $
+            it "gives location information for non-null unions" $
                 let data'' = Aeson.object
                         [ "philosopher" .= Aeson.object
                             [ "interest" .= Aeson.Null
@@ -234,6 +234,22 @@ spec =
                         $ parse document "" "{ philosopher { interest } }"
                 in actual `shouldBe` expected
 
+            it "gives location information for invalid interfaces" $
+                let data'' = Aeson.object
+                        [ "philosopher" .= Aeson.object
+                            [ "majorWork" .= Aeson.Null
+                            ]
+                        ]
+                    executionErrors = pure $ Error
+                        { message = "Interface value completion failed."
+                        , locations = [Location 1 17]
+                        , path = []
+                        }
+                    expected = Response data'' executionErrors
+                    Right (Right actual) = either (pure . parseError) execute'
+                        $ parse document "" "{ philosopher { majorWork { title } } }"
+                in actual `shouldBe` expected
+
         context "Subscription" $
             it "subscribes" $
                 let data'' = Aeson.object