Fix UpdateQueue flow types

This makes the types for UpdateQueue a bit more sound though it's still
not quite right. Not sure how to properly State so that it works with
partial state updates, replaceState, and updater functions.

This at least gives us more safety for non-Fiber update queues, like
FiberRoot's completionCallbacks queue.

Author: acdlite

src/renderers/dom/fiber/ReactDOMFiberEntry.js

@@ -694,7 +694,7 @@ function renderSubtreeIntoContainer(
 type PublicRoot = {
   render(children: ReactNodeList, callback: ?() => mixed): void,
   prerender(children: ReactNodeList): Work,
-  unmount(callback: ?() => mixed): Work,
+  unmount(callback: ?() => mixed): void,
 
   _reactRootContainer: *,
   _getComponent: () => DOMContainer,

src/renderers/noop/ReactNoopEntry.js

@@ -410,7 +410,7 @@ var ReactNoop = {
       logHostInstances(container.children, depth + 1);
     }
 
-    function logUpdateQueue(updateQueue: UpdateQueue, depth) {
+    function logUpdateQueue(updateQueue: UpdateQueue<mixed>, depth) {
       log('  '.repeat(depth + 1) + 'QUEUED UPDATES');
       const firstUpdate = updateQueue.first;
       if (!firstUpdate) {

src/renderers/shared/fiber/ReactFiber.js

@@ -115,7 +115,7 @@ export type Fiber = {|
   memoizedProps: any, // The props used to create the output.
 
   // A queue of state updates and callbacks.
-  updateQueue: UpdateQueue | null,
+  updateQueue: UpdateQueue<any> | null,
 
   // The state used to create the output
   memoizedState: any,

src/renderers/shared/fiber/ReactFiberReconciler.js

@@ -320,7 +320,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
       const blockUpdate = {
         priorityLevel: null,
         expirationTime,
-        partialState: nextState,
+        partialState: null,
         callback: null,
         isReplace: false,
         isForced: false,

src/renderers/shared/fiber/ReactFiberScheduler.js

@@ -985,7 +985,7 @@ module.exports = function<T, P, I, TI, PI, C, CX, PL>(
       nextRenderExpirationTime,
     );
 
-    loop: while (
+    while (
       shouldContinueWorking(minPriorityLevel, nextPriorityLevel, deadline)
     ) {
       if (nextRenderExpirationTime <= mostRecentCurrentTime) {

src/renderers/shared/fiber/ReactFiberUpdateQueue.js

@@ -30,8 +30,7 @@ type PartialState<State, Props> =
   | $Subtype<State>
   | ((prevState: State, props: Props) => $Subtype<State>);
 
-// Callbacks are not validated until invocation
-type Callback = mixed;
+type Callback = () => mixed;
 
 export type Update<State> = {
   priorityLevel: PriorityLevel | null,
@@ -69,7 +68,7 @@ let _queue1;
 let _queue2;
 
 function createUpdateQueue<State>(): UpdateQueue<State> {
-  const queue: UpdateQueue = {
+  const queue: UpdateQueue<State> = {
     first: null,
     last: null,
     hasForceUpdate: false,
@@ -82,7 +81,7 @@ function createUpdateQueue<State>(): UpdateQueue<State> {
 }
 exports.createUpdateQueue = createUpdateQueue;
 
-function cloneUpdate(update: Update<State>): Update<State> {
+function cloneUpdate<State>(update: Update<State>): Update<State> {
   return {
     priorityLevel: update.priorityLevel,
     expirationTime: update.expirationTime,
@@ -97,7 +96,7 @@ function cloneUpdate(update: Update<State>): Update<State> {
 
 const COALESCENCE_THRESHOLD: ExpirationTime = 10;
 
-function insertUpdateIntoPosition(
+function insertUpdateIntoPosition<State>(
   queue: UpdateQueue<State>,
   update: Update<State>,
   insertAfter: Update<State> | null,
@@ -138,7 +137,7 @@ function insertUpdateIntoPosition(
 
 // Returns the update after which the incoming update should be inserted into
 // the queue, or null if it should be inserted at beginning.
-function findInsertionPosition(
+function findInsertionPosition<State>(
   queue: UpdateQueue<State>,
   update: Update<State>,
 ): Update<State> | null {
@@ -214,7 +213,7 @@ function ensureUpdateQueues(fiber: Fiber) {
 // we shouldn't make a copy.
 //
 // If the update is cloned, it returns the cloned update.
-function insertUpdateIntoFiber(
+function insertUpdateIntoFiber<State>(
   fiber: Fiber,
   update: Update<State>,
   currentTime: ExpirationTime,
@@ -304,8 +303,8 @@ function insertUpdateIntoFiber(
 }
 exports.insertUpdateIntoFiber = insertUpdateIntoFiber;
 
-function insertUpdateIntoQueue(
-  queue: UpdateQueue,
+function insertUpdateIntoQueue<State>(
+  queue: UpdateQueue<State>,
   update: Update<State>,
   currentTime: ExpirationTime,
 ) {
@@ -337,13 +336,14 @@ function getStateFromUpdate(update, instance, prevState, props) {
   const partialState = update.partialState;
   if (typeof partialState === 'function') {
     const updateFn = partialState;
+    // $FlowFixMe - Idk how to type State correctly.
     return updateFn.call(instance, prevState, props);
   } else {
     return partialState;
   }
 }
 
-function processUpdateQueue(
+function processUpdateQueue<State>(
   queue: UpdateQueue<State>,
   instance: mixed,
   prevState: State,
@@ -382,6 +382,7 @@ function processUpdateQueue(
       partialState = getStateFromUpdate(update, instance, state, props);
       if (partialState) {
         if (dontMutatePrevState) {
+          // $FlowFixMe - Idk how to type State properly.
           state = Object.assign({}, state, partialState);
         } else {
           state = Object.assign(state, partialState);
@@ -416,7 +417,7 @@ function processUpdateQueue(
 }
 exports.processUpdateQueue = processUpdateQueue;
 
-function beginUpdateQueue(
+function beginUpdateQueue<State>(
   current: Fiber | null,
   workInProgress: Fiber,
   queue: UpdateQueue<State>,