[flow] enable exact_empty_objects (#25973)

This enables the "exact_empty_objects" setting for Flow which makes
empty objects exact instead of building up the type as properties are
added in code below. This is in preparation to Flow 191 which makes this
the default and removes the config.

More about the change in the Flow blog
[here](https://medium.com/flow-type/improved-handling-of-the-empty-object-in-flow-ead91887e40c).

Author: kassens

packages/react-client/src/ReactFlightClient.js

@@ -393,7 +393,9 @@ function createElement(
     // We don't really need to add any of these but keeping them for good measure.
     // Unfortunately, _store is enumerable in jest matchers so for equality to
     // work, I need to keep it or make _store non-enumerable in the other file.
-    element._store = {};
+    element._store = ({}: {
+      validated?: boolean,
+    });
     Object.defineProperty(element._store, 'validated', {
       configurable: false,
       enumerable: false,

packages/react-debug-tools/src/ReactDebugHooks.js

@@ -524,7 +524,7 @@ function buildTree(
   readHookLog: Array<HookLogEntry>,
   includeHooksSource: boolean,
 ): HooksTree {
-  const rootChildren = [];
+  const rootChildren: Array<HooksNode> = [];
   let prevStack = null;
   let levelChildren = rootChildren;
   let nativeHookID = 0;
@@ -557,7 +557,7 @@ function buildTree(
       // The remaining part of the new stack are custom hooks. Push them
       // to the tree.
       for (let j = stack.length - commonSteps - 1; j >= 1; j--) {
-        const children = [];
+        const children: Array<HooksNode> = [];
         const stackFrame = stack[j];
         const levelChild: HooksNode = {
           id: null,

packages/react-devtools-shared/src/backend/NativeStyleEditor/setupNativeStyleEditor.js

@@ -170,7 +170,7 @@ function measureStyle(
 }
 
 function shallowClone(object: Object): Object {
-  const cloned = {};
+  const cloned: {[string]: $FlowFixMe} = {};
   for (const n in object) {
     cloned[n] = object[n];
   }

packages/react-devtools-shared/src/backend/console.js

@@ -79,7 +79,7 @@ const injectedRenderers: Map<
 > = new Map();
 
 let targetConsole: Object = console;
-let targetConsoleMethods = {};
+let targetConsoleMethods: {[string]: $FlowFixMe} = {};
 for (const method in console) {
   targetConsoleMethods[method] = console[method];
 }
@@ -97,7 +97,7 @@ export function dangerous_setTargetConsoleForTesting(
 ): void {
   targetConsole = targetConsoleForTesting;
 
-  targetConsoleMethods = {};
+  targetConsoleMethods = ({}: {[string]: $FlowFixMe});
   for (const method in targetConsole) {
     targetConsoleMethods[method] = console[method];
   }
@@ -179,7 +179,7 @@ export function patch({
       return;
     }
 
-    const originalConsoleMethods = {};
+    const originalConsoleMethods: {[string]: $FlowFixMe} = {};
 
     unpatchFn = () => {
       for (const method in originalConsoleMethods) {
@@ -318,7 +318,7 @@ export function patchForStrictMode() {
       return;
     }
 
-    const originalConsoleMethods = {};
+    const originalConsoleMethods: {[string]: $FlowFixMe} = {};
 
     unpatchForStrictModeFn = () => {
       for (const method in originalConsoleMethods) {

packages/react-devtools-shared/src/backend/legacy/renderer.js

@@ -785,7 +785,7 @@ export function attach(
 
       let owner = element._owner;
       if (owner) {
-        owners = [];
+        owners = ([]: Array<SerializedElement>);
         while (owner != null) {
           owners.push({
             displayName: getData(owner).displayName || 'Unknown',
@@ -807,8 +807,8 @@ export function attach(
     }
 
     // Not implemented
-    const errors = [];
-    const warnings = [];
+    const errors: Array<[string, number]> = [];
+    const warnings: Array<[string, number]> = [];
 
     return {
       id,

packages/react-devtools-shared/src/backend/legacy/utils.js

@@ -22,7 +22,7 @@ export function decorateMany(
   source: Object,
   fns: {[attr: string]: Function, ...},
 ): Object {
-  const olds = {};
+  const olds: {[string]: $FlowFixMe} = {};
   for (const name in fns) {
     olds[name] = decorate(source, name, fns[name]);
   }

packages/react-devtools-shared/src/backend/profilingHooks.js

@@ -52,7 +52,7 @@ let supportsUserTiming =
 let supportsUserTimingV3 = false;
 if (supportsUserTiming) {
   const CHECK_V3_MARK = '__v3';
-  const markOptions = {};
+  const markOptions = ({}: {startTime?: number});
   Object.defineProperty(markOptions, 'startTime', {
     get: function() {
       supportsUserTimingV3 = true;

packages/react-devtools-shared/src/backend/renderer.js

@@ -3252,7 +3252,7 @@ export function attach(
 
     let owners = null;
     if (_debugOwner) {
-      owners = [];
+      owners = ([]: Array<SerializedElement>);
       let owner: null | Fiber = _debugOwner;
       while (owner !== null) {
         owners.push(fiberToSerializedElement(owner));
@@ -3265,7 +3265,7 @@ export function attach(
 
     let hooks = null;
     if (usesHooks) {
-      const originalConsoleMethods = {};
+      const originalConsoleMethods: {[string]: $FlowFixMe} = {};
 
       // Temporarily disable all console logging before re-running the hook.
       for (const method in console) {

packages/react-devtools-shared/src/backend/utils.js

@@ -20,8 +20,8 @@ export function cleanForBridge(
   path?: Array<string | number> = [],
 ): DehydratedData | null {
   if (data !== null) {
-    const cleanedPaths = [];
-    const unserializablePaths = [];
+    const cleanedPaths: Array<Array<string | number>> = [];
+    const unserializablePaths: Array<Array<string | number>> = [];
     const cleanedData = dehydrate(
       data,
       cleanedPaths,

packages/react-devtools-shared/src/devtools/utils.js

@@ -198,7 +198,7 @@ const STACK_SOURCE_LOCATION = /([^\s]+) \((.+):(.+):(.+)\)/;
 export function stackToComponentSources(
   stack: string,
 ): Array<[string, ?Stack]> {
-  const out = [];
+  const out: Array<[string, ?Stack]> = [];
   stack
     .split(STACK_DELIMETER)
     .slice(1)

packages/react-devtools-shared/src/devtools/views/Components/types.js

@@ -125,14 +125,16 @@ export type InspectedElement = {
 
 // TODO: Add profiling type
 
+type Data =
+  | string
+  | Dehydrated
+  | Unserializable
+  | Array<Dehydrated>
+  | Array<Unserializable>
+  | {[string]: Data};
+
 export type DehydratedData = {
   cleaned: Array<Array<string | number>>,
-  data:
-    | string
-    | Dehydrated
-    | Unserializable
-    | Array<Dehydrated>
-    | Array<Unserializable>
-    | {[key: string]: string | Dehydrated | Unserializable, ...},
+  data: Data,
   unserializable: Array<Array<string | number>>,
 };

packages/react-devtools-shared/src/devtools/views/Profiler/CommitTreeBuilder.js

@@ -150,6 +150,7 @@ function updateTree(
 
   // Clone nodes before mutating them so edits don't affect them.
   const getClonedNode = (id: number): CommitTreeNode => {
+    // $FlowFixMe[prop-missing] - recommended fix is to use object spread operator
     const clonedNode = ((Object.assign(
       {},
       nodes.get(id),

packages/react-devtools-shared/src/devtools/views/utils.js

@@ -134,7 +134,7 @@ export function serializeDataForCopy(props: Object): string {
 
 export function serializeHooksForCopy(hooks: HooksTree | null): string {
   // $FlowFixMe "HooksTree is not an object"
-  const cloned = Object.assign([], hooks);
+  const cloned = Object.assign(([]: Array<any>), hooks);
 
   const queue = [...cloned];
 

packages/react-devtools-shared/src/hook.js

@@ -29,7 +29,7 @@ export function installHook(target: any): DevToolsHook | null {
   }
 
   let targetConsole: Object = console;
-  let targetConsoleMethods = {};
+  let targetConsoleMethods: {[string]: $FlowFixMe} = {};
   for (const method in console) {
     targetConsoleMethods[method] = console[method];
   }
@@ -39,7 +39,7 @@ export function installHook(target: any): DevToolsHook | null {
   ): void {
     targetConsole = targetConsoleForTesting;
 
-    targetConsoleMethods = {};
+    targetConsoleMethods = ({}: {[string]: $FlowFixMe});
     for (const method in targetConsole) {
       targetConsoleMethods[method] = console[method];
     }
@@ -250,7 +250,7 @@ export function installHook(target: any): DevToolsHook | null {
       return;
     }
 
-    const originalConsoleMethods = {};
+    const originalConsoleMethods: {[string]: $FlowFixMe} = {};
 
     unpatchFn = () => {
       for (const method in originalConsoleMethods) {
@@ -516,9 +516,9 @@ export function installHook(target: any): DevToolsHook | null {
   }
 
   // TODO: More meaningful names for "rendererInterfaces" and "renderers".
-  const fiberRoots = {};
+  const fiberRoots: {[RendererID]: Set<mixed>} = {};
   const rendererInterfaces = new Map();
-  const listeners = {};
+  const listeners: {[string]: Array<Handler>} = {};
   const renderers = new Map();
 
   const hook: DevToolsHook = {

packages/react-devtools-shared/src/hooks/astUtils.js

@@ -362,7 +362,7 @@ function getPotentialHookDeclarationsFromAST(sourceAST: File): NodePath[] {
 export function getHookNamesMappingFromAST(
   sourceAST: File,
 ): $ReadOnlyArray<{name: string, start: Position}> {
-  const hookStack = [];
+  const hookStack: Array<{name: string, start: $FlowFixMe}> = [];
   const hookNames = [];
   const pushFrame = (name: string, node: Node) => {
     const nameInfo = {name, start: {...node.loc.start}};

packages/react-devtools-shared/src/hooks/generateHookMap.js

@@ -63,7 +63,7 @@ export function generateHookMap(sourceAST: File): HookMap {
   const hookNamesMapping = getHookNamesMappingFromAST(sourceAST);
   const namesMap: Map<string, number> = new Map();
   const names = [];
-  const mappings = [];
+  const mappings: Array<HookMapLine> = [];
 
   let currentLine = null;
   hookNamesMapping.forEach(({name, start}) => {

packages/react-devtools-shared/src/hydration.js

@@ -16,7 +16,7 @@ import {
   setInObject,
 } from './utils';
 
-import type {DehydratedData} from 'react-devtools-shared/src/devtools/views/Components/types';
+import type {DehydratedData} from './devtools/views/Components/types';
 
 export const meta = {
   inspectable: (Symbol('inspectable'): symbol),
@@ -124,13 +124,7 @@ export function dehydrate(
   path: Array<string | number>,
   isPathAllowed: (path: Array<string | number>) => boolean,
   level?: number = 0,
-):
-  | string
-  | Dehydrated
-  | Unserializable
-  | Array<Dehydrated>
-  | Array<Unserializable>
-  | {[key: string]: string | Dehydrated | Unserializable, ...} {
+): $PropertyType<DehydratedData, 'data'> {
   const type = getDataType(data);
 
   let isPathAllowedCheck;
@@ -304,7 +298,9 @@ export function dehydrate(
       if (level >= LEVEL_THRESHOLD && !isPathAllowedCheck) {
         return createDehydrated(type, true, data, cleaned, path);
       } else {
-        const object = {};
+        const object: {
+          [string]: $PropertyType<DehydratedData, 'data'>,
+        } = {};
         getAllEnumerableKeys(data).forEach(key => {
           const name = key.toString();
           object[name] = dehydrate(

packages/react-devtools-shell/src/app/InspectableElements/CircularReferences.js

@@ -14,8 +14,15 @@ const arrayTwo = [];
 arrayTwo.push(arrayOne);
 arrayOne.push(arrayTwo);
 
-const objectOne = {};
-const objectTwo = {objectOne};
+type ObjectOne = {
+  objectTwo?: ObjectTwo,
+};
+type ObjectTwo = {
+  objectOne: ObjectOne,
+};
+
+const objectOne: ObjectOne = {};
+const objectTwo: ObjectTwo = {objectOne};
 objectOne.objectTwo = objectTwo;
 
 export default function CircularReferences(): React.Node {

packages/react-devtools-shell/src/app/index.js

@@ -33,7 +33,7 @@ ignoreErrors([
 ignoreWarnings(['Warning: componentWillReceiveProps has been renamed']);
 ignoreLogs([]);
 
-const unmountFunctions = [];
+const unmountFunctions: Array<() => void | boolean> = [];
 
 function createContainer() {
   const container = document.createElement('div');

packages/react-devtools-timeline/src/TimelineSearchContext.js

@@ -40,7 +40,7 @@ type Action =
 
 type Dispatch = (action: Action) => void;
 
-const EMPTY_ARRAY = [];
+const EMPTY_ARRAY: Array<ReactComponentMeasure> = [];
 
 function reducer(state: State, action: Action): State {
   let {searchIndex, searchRegExp, searchResults, searchText} = state;

packages/react-dom-bindings/src/client/ReactDOMComponent.js

@@ -672,7 +672,7 @@ export function diffProperties(
       for (styleName in lastStyle) {
         if (lastStyle.hasOwnProperty(styleName)) {
           if (!styleUpdates) {
-            styleUpdates = {};
+            styleUpdates = ({}: {[string]: $FlowFixMe});
           }
           styleUpdates[styleName] = '';
         }
@@ -725,7 +725,7 @@ export function diffProperties(
             (!nextProp || !nextProp.hasOwnProperty(styleName))
           ) {
             if (!styleUpdates) {
-              styleUpdates = {};
+              styleUpdates = ({}: {[string]: string});
             }
             styleUpdates[styleName] = '';
           }
@@ -737,7 +737,7 @@ export function diffProperties(
             lastProp[styleName] !== nextProp[styleName]
           ) {
             if (!styleUpdates) {
-              styleUpdates = {};
+              styleUpdates = ({}: {[string]: $FlowFixMe});
             }
             styleUpdates[styleName] = nextProp[styleName];
           }

packages/react-dom-bindings/src/client/ReactDOMFloatClient.js

@@ -792,6 +792,7 @@ export function getResource(
 function preloadPropsFromRawProps(
   rawBorrowedProps: PreloadQualifyingProps,
 ): PreloadProps {
+  // $FlowFixMe[prop-missing] - recommended fix is to use object spread operator
   return Object.assign({}, rawBorrowedProps);
 }
 
@@ -805,6 +806,7 @@ function titlePropsFromRawProps(
 }
 
 function stylePropsFromRawProps(rawProps: StyleQualifyingProps): StyleProps {
+  // $FlowFixMe[prop-missing] - recommended fix is to use object spread operator
   const props: StyleProps = Object.assign({}, rawProps);
   props['data-precedence'] = rawProps.precedence;
   props.precedence = null;
@@ -813,6 +815,7 @@ function stylePropsFromRawProps(rawProps: StyleQualifyingProps): StyleProps {
 }
 
 function scriptPropsFromRawProps(rawProps: ScriptQualifyingProps): ScriptProps {
+  // $FlowFixMe[prop-missing] - recommended fix is to use object spread operator
   const props: ScriptProps = Object.assign({}, rawProps);
   return props;
 }
@@ -1318,7 +1321,9 @@ function acquireScriptResource(resource: ScriptResource): Instance {
 }
 
 function attachLoadListeners(instance: Instance, resource: StyleResource) {
-  const listeners = {};
+  const listeners: {
+    [string]: () => mixed,
+  } = {};
   listeners.load = onResourceLoad.bind(
     null,
     instance,

packages/react-dom-bindings/src/client/ReactDOMSelect.js

@@ -77,7 +77,7 @@ function updateOptions(
 
   if (multiple) {
     const selectedValues = (propValue: Array<string>);
-    const selectedValue = {};
+    const selectedValue: {[string]: boolean} = {};
     for (let i = 0; i < selectedValues.length; i++) {
       // Prefix to avoid chaos with special keys.
       selectedValue['$' + selectedValues[i]] = true;

packages/react-dom-bindings/src/client/validateDOMNesting.js

@@ -434,7 +434,7 @@ if (__DEV__) {
     return null;
   };
 
-  const didWarn = {};
+  const didWarn: {[string]: boolean} = {};
 
   validateDOMNesting = function(
     childTag: ?string,