Preserves result order

Fixes GraphQLSwift#60

Author: NeedleInAJayStack

Package.resolved

@@ -1,6 +1,15 @@
 {
   "object": {
     "pins": [
+      {
+        "package": "swift-collections",
+        "repositoryURL": "https://github.com/apple/swift-collections",
+        "state": {
+          "branch": null,
+          "revision": "d45e63421d3dff834949ac69d3c37691e994bd69",
+          "version": "0.0.3"
+        }
+      },
       {
         "package": "swift-nio",
         "repositoryURL": "https://github.com/apple/swift-nio.git",

Package.swift

@@ -8,12 +8,14 @@ let package = Package(
     ],
     dependencies: [
         .package(url: "https://github.com/apple/swift-nio.git", .upToNextMajor(from: "2.10.1")),
+        .package(url: "https://github.com/apple/swift-collections", .upToNextMajor(from: "0.0.3")),
     ],
     targets: [
         .target(
             name: "GraphQL", 
             dependencies: [
                 .product(name: "NIO", package: "swift-nio"),
+                .product(name: "OrderedCollections", package: "swift-collections"),
             ]
         ),
         .testTarget(name: "GraphQLTests", dependencies: ["GraphQL"]),

Sources/GraphQL/Execution/Execute.swift

@@ -1,5 +1,6 @@
 import Dispatch
 import NIO
+import OrderedCollections
 
 /**
  * Terminology
@@ -97,8 +98,8 @@ public protocol FieldExecutionStrategy {
         parentType: GraphQLObjectType,
         sourceValue: Any,
         path: IndexPath,
-        fields: [String: [Field]]
-    ) throws -> Future<[String: Any]>
+        fields: OrderedDictionary<String, [Field]>
+    ) throws -> Future<OrderedDictionary<String, Any>>
 }
 
 public protocol MutationFieldExecutionStrategy: FieldExecutionStrategy {}
@@ -117,9 +118,9 @@ public struct SerialFieldExecutionStrategy: QueryFieldExecutionStrategy, Mutatio
         parentType: GraphQLObjectType,
         sourceValue: Any,
         path: IndexPath,
-        fields: [String: [Field]]
-    ) throws -> Future<[String: Any]> {
-        var results = [String: Future<Any>]()
+        fields: OrderedDictionary<String, [Field]>
+    ) throws -> Future<OrderedDictionary<String, Any>> {
+        var results = OrderedDictionary<String, Future<Any>>()
 
         try fields.forEach { field in
             let fieldASTs = field.value
@@ -169,15 +170,16 @@ public struct ConcurrentDispatchFieldExecutionStrategy: QueryFieldExecutionStrat
         parentType: GraphQLObjectType,
         sourceValue: Any,
         path: IndexPath,
-        fields: [String: [Field]]
-    ) throws -> Future<[String: Any]> {
+        fields: OrderedDictionary<String, [Field]>
+    ) throws -> Future<OrderedDictionary<String, Any>> {
         let resultsQueue = DispatchQueue(
             label: "\(dispatchQueue.label) results",
             qos: dispatchQueue.qos
         )
 
         let group = DispatchGroup()
-        var results: [String: Future<Any>] = [:]
+        // preserve field order by assigning to null and filtering later
+        var results: OrderedDictionary<String, Future<Any>?> = fields.mapValues { _ -> Future<Any>? in return nil }
         var err: Error? = nil
 
         fields.forEach { field in
@@ -213,7 +215,7 @@ public struct ConcurrentDispatchFieldExecutionStrategy: QueryFieldExecutionStrat
             throw error
         }
 
-        return results.flatten(on: exeContext.eventLoopGroup)
+        return results.compactMapValues({ $0 }).flatten(on: exeContext.eventLoopGroup)
     }
 
 }
@@ -323,7 +325,6 @@ func execute(
 //                errors: executeErrors,
 //                result: result
 //            )
-
             return result
         }
     } catch let error as GraphQLError {
@@ -417,9 +418,9 @@ func executeOperation(
     exeContext: ExecutionContext,
     operation: OperationDefinition,
     rootValue: Any
-) throws -> Future<[String: Any]> {
+) throws -> Future<OrderedDictionary<String, Any>> {
     let type = try getOperationRootType(schema: exeContext.schema, operation: operation)
-    var inputFields: [String : [Field]] = [:]
+    var inputFields: OrderedDictionary<String, [Field]> = [:]
     var visitedFragmentNames: [String : Bool] = [:]
 
     let fields = try collectFields(
@@ -494,9 +495,9 @@ func collectFields(
     exeContext: ExecutionContext,
     runtimeType: GraphQLObjectType,
     selectionSet: SelectionSet,
-    fields: inout [String: [Field]],
+    fields: inout OrderedDictionary<String, [Field]>,
     visitedFragmentNames: inout [String: Bool]
-) throws -> [String: [Field]] {
+) throws -> OrderedDictionary<String, [Field]> {
     var visitedFragmentNames = visitedFragmentNames
 
     for selection in selectionSet.selections {
@@ -1109,7 +1110,7 @@ func completeObjectValue(
     }
 
     // Collect sub-fields to execute to complete this value.
-    var subFieldASTs: [String: [Field]] = [:]
+    var subFieldASTs: OrderedDictionary<String, [Field]> = [:]
     var visitedFragmentNames: [String: Bool] = [:]
 
     for fieldAST in fieldASTs {

Sources/GraphQL/Map/Map.swift

@@ -1,3 +1,5 @@
+import OrderedCollections
+
 // MARK: MapError
 
 public enum MapError : Error {
@@ -14,7 +16,7 @@ public enum Map {
     case number(Number)
     case string(String)
     case array([Map])
-    case dictionary([String: Map])
+    case dictionary(OrderedDictionary<String, Map>)
 
     public static func int(_ value: Int) -> Map {
         return .number(Number(value))
@@ -58,7 +60,7 @@ extension Map {
         self = .array(array)
     }
 
-    public init(_ dictionary: [String: Map]) {
+    public init(_ dictionary: OrderedDictionary<String, Map>) {
         self = .dictionary(dictionary)
     }
 
@@ -86,7 +88,7 @@ extension Map {
         self = array.map({ Map($0) }) ?? .null
     }
 
-    public init(_ dictionary: [String: Map]?) {
+    public init(_ dictionary: OrderedDictionary<String, Map>?) {
         self = dictionary.map({ Map($0) }) ?? .null
     }
 }
@@ -107,8 +109,8 @@ public func map(from value: Any?) throws -> Map {
     }
 
     if
-        let value = value as? [String: Any],
-        let dictionary: [String: Map] = try? value.reduce(into: [:], { result, pair in
+        let value = value as? OrderedDictionary<String, Any>,
+        let dictionary: OrderedDictionary<String, Map> = try? value.reduce(into: [:], { result, pair in
             result[pair.key] = try map(from: pair.value)
         })
     {
@@ -152,7 +154,7 @@ extension Map {
             self = .string(string)
         case let array as [Map]:
             self = .array(array)
-        case let dictionary as [String: Map]:
+        case let dictionary as OrderedDictionary<String, Map>:
             self = .dictionary(dictionary)
         default:
             throw MapError.incompatibleType
@@ -243,7 +245,7 @@ extension Map {
         return try? arrayValue()
     }
 
-    public var dictionary: [String: Map]? {
+    public var dictionary: OrderedDictionary<String, Map>? {
         return try? dictionaryValue()
     }
 }
@@ -372,7 +374,7 @@ extension Map {
         }
     }
 
-    public func dictionaryValue(converting: Bool = false) throws -> [String: Map] {
+    public func dictionaryValue(converting: Bool = false) throws -> OrderedDictionary<String, Map> {
         guard converting else {
             return try get()
         }
@@ -487,7 +489,7 @@ extension Map {
                     if let existingDictionary = dictionary[key]?.dictionary,
                         let newDictionary = newValue.dictionary,
                         merging {
-                        var combinedDictionary: [String: Map] = [:]
+                        var combinedDictionary: OrderedDictionary<String, Map> = [:]
 
                         for (key, value) in existingDictionary {
                             combinedDictionary[key] = value
@@ -617,8 +619,20 @@ extension Map : Codable {
         else if let array = try? container.decode([Map].self) {
             self = .array(array)
         }
-            
-        else if let dictionary = try? container.decode([String: Map].self) {
+        
+        else if let _ = try? container.decode([String: Map].self) {
+            // Override OrderedDictionary default (unkeyed alternating key-value)
+            // Instead decode as a keyed container (like normal Dictionary) but use the order of the input
+            let container = try decoder.container(keyedBy: _DictionaryCodingKey.self)
+            var orderedDictionary: OrderedDictionary<String, Map> = [:]
+            for key in container.allKeys {
+                let value = try container.decode(Map.self, forKey: key)
+                orderedDictionary[key.stringValue] = value
+            }
+            self = .dictionary(orderedDictionary)
+        }
+        
+        else if let dictionary = try? container.decode(OrderedDictionary<String, Map>.self) {
             self = .dictionary(dictionary)
         }
 
@@ -642,9 +656,32 @@ extension Map : Codable {
         case let .array(array):
             try container.encode(array)
         case let .dictionary(dictionary):
-            try container.encode(dictionary)
+            // Override OrderedDictionary default (unkeyed alternating key-value)
+            // Instead decode as a keyed container (like normal Dictionary) in the order of our OrderedDictionary
+            var container = encoder.container(keyedBy: _DictionaryCodingKey.self)
+            for (key, value) in dictionary {
+              let codingKey = _DictionaryCodingKey(stringValue: key)!
+              try container.encode(value, forKey: codingKey)
+            }
         }
     }
+    
+    /// A wrapper for dictionary keys which are Strings or Ints.
+    /// This is copied from Swift core: https://github.com/apple/swift/blob/256a9c5ad96378daa03fa2d5197b4201bf16db27/stdlib/public/core/Codable.swift#L5508
+    internal struct _DictionaryCodingKey: CodingKey {
+      internal let stringValue: String
+      internal let intValue: Int?
+
+      internal init?(stringValue: String) {
+        self.stringValue = stringValue
+        self.intValue = Int(stringValue)
+      }
+
+      internal init?(intValue: Int) {
+        self.stringValue = "\(intValue)"
+        self.intValue = intValue
+      }
+    }
 }
 // MARK: Equatable
 
@@ -738,7 +775,7 @@ extension Map : ExpressibleByArrayLiteral {
 
 extension Map : ExpressibleByDictionaryLiteral {
     public init(dictionaryLiteral elements: (String, Map)...) {
-        var dictionary = [String: Map](minimumCapacity: elements.count)
+        var dictionary = OrderedDictionary<String, Map>(minimumCapacity: elements.count)
 
         for (key, value) in elements {
             dictionary[key] = value
@@ -847,7 +884,7 @@ extension Map {
             }
         }
 
-        func serialize(dictionary: [String: Map]) -> String {
+        func serialize(dictionary: OrderedDictionary<String, Map>) -> String {
             var string = "{"
             var index = 0