Merge pull request #5026 from juanrgon/issue-5020--2.2.x-fix

Backport fix to Issue #5020 to 2.2.x

lib/graphql/dataloader/source.rb

@@ -187,7 +187,11 @@ def result_for(key)
         end
         result = @results[key]
 
-        raise result if result.class <= StandardError
+        if result.is_a?(StandardError)
+          # Dup it because the rescuer may modify it.
+          # (This happens for GraphQL::ExecutionErrors, at least)
+          raise result.dup
+        end
 
         result
       end

spec/graphql/execution_error_spec.rb

@@ -399,4 +399,99 @@
     ]
     assert_equal(expected_errors, result["errors"])
   end
+
+  describe "when using DataLoaders" do
+    let(:schema) do
+      item_error_loader = Class.new(GraphQL::Dataloader::Source) do
+        def fetch(keys)
+          keys.map { |key| GraphQL::ExecutionError.new("Error for #{key}") }
+        end
+      end
+
+      query_type = Class.new(GraphQL::Schema::Object) do
+        graphql_name "Query"
+        field :item, String do
+          argument :key, String
+        end
+        define_method(:item) do |key:|
+          dataloader.with(item_error_loader).load(key)
+        end
+      end
+
+      Class.new(GraphQL::Schema) do
+        query query_type
+        use GraphQL::Dataloader
+      end
+    end
+
+    let(:result) { schema.execute(query_string) }
+
+    describe "when querying for unique items" do
+      let(:query_string) {
+        <<-GRAPHQL
+          query {
+            query0: item(key: "a")
+            query1: item(key: "b")
+          }
+        GRAPHQL
+      }
+
+      it "returns unique execution errors locations and paths" do
+        expected_result = {
+          "data" => {
+            "query0" => nil,
+            "query1" => nil
+          },
+          "errors" => [
+            {
+              "message" => "Error for a",
+              "locations" => [{"line" => 2, "column" => 13}],
+              "path" => ["query0"]
+            },
+            {
+              "message" => "Error for b",
+              "locations" => [{"line" => 3, "column" => 13}],
+              "path" => ["query1"]
+            }
+          ]
+        }
+
+        assert_equal(expected_result, result.to_h)
+      end
+    end
+
+    describe "when querying for duplicate items" do
+      let(:query_string) {
+        <<-GRAPHQL
+          query {
+            query0: item(key: "a")
+            query1: item(key: "a")
+          }
+        GRAPHQL
+      }
+
+      it "returns execution errors for duplicate items" do
+        expected_result = {
+          "data" => {
+            "query0" => nil,
+            "query1" => nil
+          },
+          "errors" => [
+            {
+              "message" => "Error for a",
+              "locations" => [{"line" => 2, "column" => 13}],
+              "path" => ["query0"]
+            },
+            {
+              "message" => "Error for a",
+              "locations" => [{"line" => 3, "column" => 13}],
+              "path" => ["query1"]
+            }
+          ]
+        }
+
+        assert_equal(expected_result, result.to_h)
+      end
+    end
+  end
 end