Fix runtime error when aggregating results with error-containing left-value

src/com/walmartlabs/lacinia/executor.clj

@@ -181,9 +181,16 @@
   is an ResultTuple."
   [left-value right-value]
   (if (su/is-result-tuple? right-value)
-    (let [{:keys [alias value]} right-value]
-      (if (contains? left-value alias)
+    (let [{:keys [alias value]} right-value
+      left-alias-value (alias left-value)]
+      (cond
+        (= left-alias-value :com.walmartlabs.lacinia.schema/null)
+        left-value
+
+        (map? left-alias-value)
         (update left-value alias deep-merge value)
+
+        :else
         (assoc left-value alias value)))
     (deep-merge left-value right-value)))
 

test/com/walmartlabs/lacinia/executor_test.clj

@@ -0,0 +1,95 @@
+;; Copyright (c) 2017-present Walmart, Inc.
+;;
+;; Licensed under the Apache License, Version 2.0 (the "License")
+;; you may not use this file except in compliance with the License.
+;; You may obtain a copy of the License at
+;;
+;;     http://www.apache.org/licenses/LICENSE-2.0
+;;
+;; Unless required by applicable law or agreed to in writing, software
+;; distributed under the License is distributed on an "AS IS" BASIS,
+;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;; See the License for the specific language governing permissions and
+;; limitations under the License.
+
+(ns com.walmartlabs.lacinia.executor-test
+  "Tests for errors and exceptions inside field resolvers, and for the exception converter."
+  (:require
+    [clojure.test :refer [deftest is]]
+    [com.walmartlabs.lacinia.resolve :refer [resolve-as]]
+    [com.walmartlabs.test-utils :refer [execute]]
+    [com.walmartlabs.lacinia.schema :as schema]))
+
+(deftest deep-merge-on-error
+  (let [test-schema {:interfaces
+                     {:Node
+                      {:fields {:id {:type '(non-null String)}}}}
+
+                     :objects
+                     {:Post
+                      {:implements [:Node]
+                       :fields     {:id     {:type '(non-null String)}
+                                    :author {:type    '(non-null :Author)
+                                             :resolve (fn [_ _ _]
+                                                        {:id "2000"})}
+                                    :title  {:type    'String
+                                             :resolve (fn [_ _ _]
+                                                        "Hello, World!")}}}
+
+                      :Author
+                      {:implements [:Node]
+                       :fields     {:id     {:type '(non-null String)}
+                                    :name   {:type    '(non-null String)
+                                             :resolve (fn [_ _ _]
+                                                        "John Doe")}
+                                    :absurd {:type    '(non-null String)
+                                             :resolve (fn [_ _ _]
+                                                        (resolve-as nil {:message "This field can't be resolved."}))}}}}
+
+                     :queries
+                     {:node {:type    '(non-null :Node)
+                             :args    {:id {:type '(non-null String)}}
+                             :resolve (fn [ctx args v]
+                                        (let [{:keys [episode]} args]
+                                          (schema/tag-with-type {:id "1000"} :Post)))}}}
+        compiled-schema (schema/compile test-schema)]
+
+    (is (= {:data   nil,
+            :errors [{:message "This field can't be resolved.", :locations [{:line 4, :column 5}], :path [:node :author :absurd]}]}
+           (execute compiled-schema "
+fragment PostFragment on Post {
+  author {
+    absurd
+  }
+}
+query MyQuery {
+  node(id: \"1000\") {
+    ... on Post {
+      ...PostFragment
+      author {
+        name
+      }
+    }
+    id
+  }
+}")))
+
+    (is (= {:data   nil,
+            :errors [{:message "This field can't be resolved.", :locations [{:line 4, :column 5}], :path [:node :author :absurd]}]}
+           (execute compiled-schema "
+fragment PostFragment on Post {
+  author {
+    absurd
+  }
+}
+query MyQuery {
+  node(id: \"1000\") {
+    ... on Post {
+      author {
+        name
+      }
+      ...PostFragment
+    }
+    id
+  }
+}")))))