Flow fixes

src/mutate.js

@@ -38,7 +38,6 @@ type RelayMutationConfig = (
     |}
 );
 
-
 export type MutationConfig = {
     query: Relay.QL,
     variables: {[variableName: string]: any},
@@ -47,16 +46,36 @@ export type MutationConfig = {
     configs?: RelayMutationConfig[]
 };
 
-export type MutationPromise = {
+declare class MutationPromise<+R> {
+    constructor(callback: (
+        resolve: (result: MutationPromise<R> | R) => void,
+        reject: (error: any) => void
+    ) => mixed): void,
+
+    then<U>(
+        onFulfill?: (value: R) => MutationPromise<U> | U,
+        onReject?: (error: any) => MutationPromise<U> | U
+    ): MutationPromise<U>,
+
+    catch<U>(
+        onReject?: (error: any) => MutationPromise<U> | U
+    ): MutationPromise<R | U>,
+
+    onUploadProgress<T>(
+        cb: ProgressCallback
+    ): MutationPromise<T>,
+
     abort: () => void,
-    onUploadProgress: (cb: ProgressCallback) => MutationPromise,
-    then: (any) => MutationPromise,
-    catch: (any) => void
-};
-export type Mutate = (config: MutationConfig) => MutationPromise;
 
+    static resolve<T>(object: MutationPromise<T> | T): MutationPromise<T>,
+    static reject<T>(error?: any): MutationPromise<T>,
+    static all<Elem, T:Iterable<Elem>>(promises: T): MutationPromise<$TupleMap<T, typeof $await>>,
+    static race<T, Elem: MutationPromise<T> | T>(promises: Array<Elem>): MutationPromise<T>
+}
+
+export type Mutate = (config: MutationConfig) => MutationPromise<*>;
 
-export default function mutate(env: Relay.Environment, config: MutationConfig): MutationPromise {
+export default function mutate(env: Relay.Environment, config: MutationConfig): MutationPromise<*> {
     const {query, variables, files = null, optimisticResponse, configs = []} = config;
 
     var mutation;