Fix returning gapped arrays

Author: no1seman

graphql/execute.lua

@@ -208,7 +208,7 @@ local function completeValue(fieldType, result, subSelections, context, opts)
 
     local innerType = fieldType.ofType
     local values = {}
-    for i, value in ipairs(result) do
+    for i, value in pairs(result) do
       values[i] = completeValue(innerType, value, subSelections, context)
     end
 

graphql/util.lua

@@ -213,37 +213,23 @@ local function check(obj, obj_name, type_1, type_2, type_3)
     end
 end
 
---- Check whether table is an array.
----
---- Based on [that][1] implementation.
---- [1]: https://github.com/mpx/lua-cjson/blob/db122676/lua/cjson/util.lua
----
---- @tparam table table to check
---- @return[1] `true` if passed table is an array (includes the empty table
---- case)
---- @return[2] `false` otherwise
-local function is_array(table)
-    if type(table) ~= 'table' then
-        return false
-    end
-
-    local max = 0
-    local count = 0
-    for k, _ in pairs(table) do
-        if type(k) == 'number' then
-            if k > max then
-                max = k
-            end
-            count = count + 1
-        else
-            return false
-        end
-    end
-    if max > count * 2 then
+local function is_array(t)
+  if type(t) ~= 'table' then
+     return false
+  end
+  local n = #t
+  if n > 0 then
+     for k in next, t, n do
+        if type(k) ~= 'number' or k < 0 then return false end
+     end
+     return true
+  end
+  for k in pairs(t) do
+     if type(k) ~= 'number' or k < 0 then
         return false
     end
-
-    return max >= 0
+  end
+  return true
 end
 
 -- Copied from tarantool/tap

test/integration/graphql_test.lua

@@ -2147,3 +2147,36 @@ function g.test_non_finite_float()
             query_schema, nil, nil, {variables = variables})
     end
 end
+
+function g.test_gapped_arrays_output()
+    local query = [[
+        query ($x: [String]) { test(arg: $x) }
+    ]]
+
+    local function callback(_, args)
+        setmetatable(args.arg, {__serialize='array'})
+        return args.arg
+    end
+
+    local query_schema = {
+        ['test'] = {
+            kind = types.list(types.string),
+            arguments = {
+                arg = types.list(types.string),
+            },
+            resolve = callback,
+        }
+    }
+
+    local test_values = {
+        {[3] = 'a', [1] = 'b', [6] = 'c'},
+        {[3] = 'a', [1] = 'b', [7] = 'c'},
+    }
+
+    for _, v in ipairs(test_values) do
+        local variables = {x = v}
+        local res = check_request(query, query_schema, nil, nil, {variables = variables})
+        t.assert_type(res, 'table')
+        t.assert_equals(json.encode(res.test), json.encode(v))
+    end
+end