Make client.device fulfill type constraints

Summary:
This is an interesting invariant that TS caught here. We
expect `getDevice()` to always return a device but it
cannot because it's set lazily. John Knox suggested we instead
set up a promise in the constructor and resolve it instead of
overriding the stateful promise later.

Reviewed By: jknoxville

Differential Revision: D17313468

fbshipit-source-id: 8fd75f2720546abf67beead23db56216f1a5e0df

src/Client.tsx

@@ -115,7 +115,9 @@ export default class Client extends EventEmitter {
   responder: Partial<Responder<string, any>>;
   store: Store;
   activePlugins: Set<string>;
-  device: Promise<BaseDevice> | undefined;
+  device: Promise<BaseDevice>;
+  _deviceResolve: (device: BaseDevice) => void = _ => {};
+  _deviceSet: boolean = false;
   logger: Logger;
   lastSeenDeviceList: Array<BaseDevice>;
   broadcastCallbacks: Map<string, Map<string, Set<Function>>>;
@@ -154,6 +156,10 @@ export default class Client extends EventEmitter {
     this.activePlugins = new Set();
     this.lastSeenDeviceList = [];
 
+    this.device = new Promise((resolve, _reject) => {
+      this._deviceResolve = resolve;
+    });
+
     const client = this;
     // node.js doesn't support requestIdleCallback
     const rIC =
@@ -211,11 +217,11 @@ export default class Client extends EventEmitter {
      However, clients can connect before a device is registered, so wait a
      while for the device to be registered if it isn't already. */
   setMatchingDevice(): void {
-    if (this.device) {
+    if (this._deviceSet) {
       return;
     }
-    this.device = reportPlatformFailures(
-      new Promise((resolve, reject) => {
+    reportPlatformFailures(
+      new Promise<BaseDevice>((resolve, reject) => {
         const device = this.store
           .getState()
           .connections.devices.find(
@@ -248,7 +254,10 @@ export default class Client extends EventEmitter {
         }, 5000);
       }),
       'client-setMatchingDevice',
-    );
+    ).then(device => {
+      this._deviceSet = true;
+      this._deviceResolve(device);
+    });
   }
 
   supportsPlugin(Plugin: typeof FlipperPlugin): boolean {

src/plugin.tsx

@@ -120,7 +120,7 @@ export abstract class FlipperBasePlugin<
   reducers: {
     [actionName: string]: (state: State, actionData: any) => Partial<State>;
   } = {};
-  app: App;
+  app: App | null = null;
   onKeyboardAction: ((action: string) => void) | undefined;
 
   toJSON() {