Fix returning data and error for multiple resolvers

32c97f0 introduced returning data and errors acc. spec #7.1.2 but
previous implementation didn't take into account that execution may
include multiple resolvers and each of them may return both data and
errors. This PR fixes the logic to collect all errors from all resolvers
into a single array that can be returned to requester.

Based on PR #19 by @no1seman

Author: no1seman

graphql/execute.lua

@@ -313,7 +313,6 @@ end
 
 evaluateSelections = function(objectType, object, selections, context)
   local result = {}
-  local errors
   local err
   local fields = collectFields(objectType, selections, {}, {}, context)
   for _, field in ipairs(fields) do
@@ -322,14 +321,14 @@ evaluateSelections = function(objectType, object, selections, context)
     result[field.name], err = getFieldEntry(objectType, object, {field.selection},
                                        context)
     if err ~= nil then
-        errors = errors or {}
-        table.insert(errors, err)
+        context.errors = context.errors or {}
+        table.insert(context.errors, err)
     end
     if result[field.name] == nil then
         result[field.name] = box.NULL
     end
   end
-  return result, errors
+  return result, context.errors
 end
 
 local function execute(schema, tree, rootValue, variables, operationName)

test/integration/graphql_test.lua

@@ -1158,4 +1158,49 @@ function g.test_both_data_and_error_result()
         {message = 'Simple error A'},
         {message = 'Simple error B'},
     })
+
+    query = [[{
+        prefix {
+            test_A: test(arg: "A")
+            test_B: test(arg: "B")
+        }
+    }]]
+
+    local function callback_external()
+        return {}, {message = 'Simple error from external resolver'}
+    end
+
+    local function callback_internal(_, args)
+        return args[1].value, {message = 'Simple error from internal resolver ' .. args[1].value}
+    end
+
+    query_schema = {
+        ['prefix'] = {
+            kind = types.object({
+                name = 'prefix',
+                fields = {
+                    ['test'] = {
+                        kind = types.string.nonNull,
+                        arguments = {
+                            arg = types.string.nonNull,
+                            arg2 = types.string,
+                            arg3 = types.int,
+                            arg4 = types.long,
+                        },
+                        resolve = callback_internal,
+                    }
+                },
+            }),
+            arguments = {},
+            resolve = callback_external,
+        }
+    }
+
+    data, errors = check_request(query, query_schema)
+    t.assert_equals(data, {prefix = {test_A = 'A', test_B = 'B'}})
+    t.assert_equals(errors,  {
+        {message = "Simple error from internal resolver A"},
+        {message = "Simple error from internal resolver B"},
+        {message = "Simple error from external resolver"},
+    }, "Errors from each resolver were returned")
 end