Make InputValue JSONEncodable & add some TODOs

Sources/Apollo/GraphQLMap.swift

@@ -2,7 +2,7 @@
 import ApolloAPI
 #endif
 
-#warning("TODO: Delete")
+#warning("TODO: Delete?")
 public typealias GraphQLMap = [String: JSONEncodable?]
 
 fileprivate extension Dictionary where Key == String, Value == JSONEncodable? {

Sources/ApolloAPI/CodegenV1/GraphQLOperation.swift

@@ -13,6 +13,7 @@ public protocol GraphQLOperation: AnyObject {
 
   var queryDocument: String { get }
 
+  #warning("TODO: We need to support setting a null value AND a nil value. Considering just going back to using GraphQLMap, or else this should be [String: GraphQLOptional<InputValue>].")
   var variables: [String: InputValue]? { get }
 
   associatedtype Data: RootSelectionSet

Sources/ApolloAPI/InputValue.swift

@@ -1,5 +1,6 @@
 import Foundation
 
+#warning("TODO: It might be more performant to just use the raw values like before commit: e7a9b2c27f9d01764943f1aa7ff9d759d8762bff - We should run performance tests and try reverting and see what performance is like.")
 /// Represents an input value to an argument on a `GraphQLField`'s `FieldArguments`.
 ///
 /// - See: [GraphQLSpec - Input Values](http://spec.graphql.org/June2018/#sec-Input-Values)
@@ -27,6 +28,20 @@ public indirect enum InputValue {
   case none
 }
 
+// MARK: - JSONEncodable
+
+extension InputValue: JSONEncodable {
+  public var jsonValue: JSONValue {
+    switch self {
+    case let .scalar(value): return value
+    case let .variable(variableName): return "$\(variableName)"
+    case let .list(values): return values.map { $0.jsonValue }
+    case let .object(valueObject): return valueObject.mapValues { $0.jsonValue }
+    case .none: return NSNull()
+    }
+  }
+}
+
 // MARK: - InputValueConvertible
 
 extension InputValue: InputValueConvertible {

Sources/ApolloAPI/ScalarTypes.swift

@@ -3,6 +3,7 @@ public protocol AnyScalarType {}
 public protocol ScalarType:
   AnyScalarType,
   JSONDecodable,
+  JSONEncodable,
   Cacheable,
   InputValueConvertible {}