Set up Flow - Yay! (#6682)

This just configures flow to be checked and fixes our existing
Flow typed files.

Possible enhancements:

Export .js.flow declarations from the build. Unclear whether this
will be a supported workflow in the future or not, so let's wait
on that.

We should fail builds and CI on Flow errors.

Ideally we should lint for Flow style guides (like no space before
colon).

.flowconfig

@@ -0,0 +1,34 @@
+[ignore]
+
+.*/build/.*
+.*/node_modules/y18n/.*
+.*/__mocks__/.*
+.*/__tests__/.*
+
+# Ignore Docs
+.*/docs/.*
+
+[include]
+
+[libs]
+./node_modules/fbjs/flow/lib
+./flow
+
+[options]
+module.system=haste
+
+esproposal.class_static_fields=enable
+esproposal.class_instance_fields=enable
+
+munge_underscores=false
+
+suppress_type=$FlowIssue
+suppress_type=$FlowFixMe
+suppress_type=$FixMe
+
+suppress_comment=\\(.\\|\n\\)*\\$FlowFixMe\\($\\|[^(]\\|(\\(>=0\\.\\(2[0-4]\\|1[0-9]\\|[0-9]\\).[0-9]\\)? *\\(site=[a-z,_]*\\)?)\\)
+suppress_comment=\\(.\\|\n\\)*\\$FlowIssue\\((\\(>=0\\.\\(2[0-4]\\|1[0-9]\\|[0-9]\\).[0-9]\\)? *\\(site=[a-z,_]*\\)?)\\)? #[0-9]+
+suppress_comment=\\(.\\|\n\\)*\\$FlowFixedInNextDeploy
+
+[version]
+0.24.0

flow/environment.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
+/* eslint-disable */
+
+declare var __REACT_DEVTOOLS_GLOBAL_HOOK__: any; /*?{
+  inject: ?((stuff: Object) => void)
+};*/
+
+// temporary patches for React.Component and React.Element
+declare var ReactComponent: typeof React$Component;
+declare var ReactElement: typeof React$Element;

flow/react-native-host-hooks.js

@@ -0,0 +1,44 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
+/* eslint-disable */
+
+declare module 'deepDiffer' {
+  declare function exports(one: any, two: any): bool;
+}
+declare module 'deepFreezeAndThrowOnMutationInDev' {
+  declare function exports<T>(obj : T) : T;
+}
+declare module 'flattenStyle' { }
+declare module 'InitializeJavaScriptAppEngine' { }
+declare module 'RCTEventEmitter' {
+  declare function register() : void;
+}
+declare module 'TextInputState' {
+  declare function blurTextInput(object : any) : void;
+  declare function focusTextInput(object : any) : void;
+}
+declare module 'UIManager' {
+  declare var customBubblingEventTypes : Object;
+  declare var customDirectEventTypes : Object;
+  declare function createView() : void;
+  declare function manageChildren() : void;
+  declare function measure() : void;
+  declare function measureInWindow() : void;
+  declare function measureLayout() : void;
+  declare function removeRootView() : void;
+  declare function removeSubviewsFromContainerWithID() : void;
+  declare function replaceExistingNonRootView() : void;
+  declare function setChildren() : void;
+  declare function setChildren() : void;
+  declare function updateView() : void;
+}
+declare module 'View' { }

src/renderers/native/ReactNativeAttributePayload.js

@@ -394,6 +394,7 @@ function diffProperties(
       // default: fallthrough case when nested properties are defined
       removedKeys = null;
       removedKeyCount = 0;
+      // $FlowFixMe - We think that attributeConfig is not CustomAttributeConfiguration at this point so we assume it must be AttributeConfiguration.
       updatePayload = diffNestedProperty(
         updatePayload,
         prevProp,

src/renderers/native/ReactNativeBridgeEventPlugin.js

@@ -43,10 +43,10 @@ var ReactNativeBridgeEventPlugin = {
    * @see {EventPluginHub.extractEvents}
    */
   extractEvents: function(
-    topLevelType,
-    targetInst,
-    nativeEvent,
-    nativeEventTarget
+    topLevelType: string,
+    targetInst: Object,
+    nativeEvent: Event,
+    nativeEventTarget: Object
   ): ?Object {
     var bubbleDispatchConfig = customBubblingEventTypes[topLevelType];
     var directDispatchConfig = customDirectEventTypes[topLevelType];

src/renderers/native/ReactNativeContainerInfo.js

@@ -11,7 +11,7 @@
  */
 'use strict';
 
-function ReactNativeContainerInfo(tag) {
+function ReactNativeContainerInfo(tag: number) {
   var info = {
     _tag: tag,
   };

src/renderers/native/ReactNativeMount.js

@@ -233,7 +233,7 @@ var ReactNativeMount = {
    */
   unmountComponentFromNode: function(
     instance: ReactComponent,
-    containerID: string
+    containerID: number
   ) {
     // Call back into native to remove all of the subviews from this container
     ReactReconciler.unmountComponent(instance);