fix: prevent redundant restarts on rapid changes and recover from app crashes in watch mode (#6036)

Two issues in the livesync watch loop:

1. Multiple rapid file changes caused each webpack recompilation to trigger a
   separate sync+restart, even when earlier restarts were already stale. Added
   exhaustMapWithTrailing semantics: while a sync is in progress, incoming
   compilation events are coalesced per-platform into a single pending event
   that runs after the current sync completes.

2. If the app crashed at certain times (e.g. during JS startup), the error
   handler removed the device from the descriptor list and stopped watchers,
   permanently killing the watch loop. Fixed by no longer calling stop() on
   transient sync errors — the device stays in the list and retries on the
   next file change. Also added .catch() to the promise action chain so a
   rejected action no longer breaks all subsequent chained actions.

Author: edusperoni

lib/controllers/run-controller.ts

@@ -26,6 +26,15 @@ import { injector } from "../common/yok";
 
 export class RunController extends EventEmitter implements IRunController {
 	private prepareReadyEventHandler: any = null;
+	private _syncInProgress = false;
+	private _pendingSyncs: Map<
+		string,
+		{
+			data: IFilesChangeEventData;
+			projectData: IProjectData;
+			liveSyncInfo: ILiveSyncInfo;
+		}
+	> = new Map();
 
 	constructor(
 		protected $analyticsService: IAnalyticsService,
@@ -97,16 +106,11 @@ export class RunController extends EventEmitter implements IRunController {
 						projectData,
 						prepareData,
 					);
-					if (changesInfo.hasChanges) {
-						await this.syncChangedDataOnDevices(
-							data,
-							projectData,
-							liveSyncInfo,
-						);
+					if (!changesInfo.hasChanges) {
+						return;
 					}
-				} else {
-					await this.syncChangedDataOnDevices(data, projectData, liveSyncInfo);
 				}
+				this.scheduleSyncOnDevices(data, projectData, liveSyncInfo);
 			};
 
 			this.prepareReadyEventHandler = handler.bind(this);
@@ -840,11 +844,11 @@ export class RunController extends EventEmitter implements IRunController {
 					watchInfo.connectTimeout = null;
 					await watchAction();
 				}
-			} catch (err) {
+			} catch (err: any) {
 				this.$logger.warn(
 					`Unable to apply changes for device: ${
 						device.deviceInfo.identifier
-					}. Error is: ${err && err.message}.`,
+					}. Error is: ${err && err.message}. Will retry on next change.`,
 				);
 
 				this.emitCore(RunOnDeviceEvents.runOnDeviceError, {
@@ -856,12 +860,6 @@ export class RunController extends EventEmitter implements IRunController {
 						],
 					error: err,
 				});
-
-				await this.stop({
-					projectDir: projectData.projectDir,
-					deviceIdentifiers: [device.deviceInfo.identifier],
-					stopOptions: { shouldAwaitAllActions: false },
-				});
 			}
 		};
 
@@ -885,20 +883,85 @@ export class RunController extends EventEmitter implements IRunController {
 		);
 	}
 
+	private scheduleSyncOnDevices(
+		data: IFilesChangeEventData,
+		projectData: IProjectData,
+		liveSyncInfo: ILiveSyncInfo,
+	): void {
+		if (this._syncInProgress) {
+			const platform = data.platform;
+			const existing = this._pendingSyncs.get(platform);
+			if (existing) {
+				existing.data = this.mergeFilesChangeEvents(existing.data, data);
+			} else {
+				this._pendingSyncs.set(platform, { data, projectData, liveSyncInfo });
+			}
+			return;
+		}
+
+		this.executeSyncOnDevices(data, projectData, liveSyncInfo);
+	}
+
+	private async executeSyncOnDevices(
+		data: IFilesChangeEventData,
+		projectData: IProjectData,
+		liveSyncInfo: ILiveSyncInfo,
+	): Promise<void> {
+		this._syncInProgress = true;
+		try {
+			await this.syncChangedDataOnDevices(data, projectData, liveSyncInfo);
+		} catch (err: any) {
+			this.$logger.trace(`Error during sync on devices: ${err.message || err}`);
+		} finally {
+			const nextEntry = this._pendingSyncs.entries().next();
+			if (!nextEntry.done) {
+				const [platform, pending] = nextEntry.value;
+				this._pendingSyncs.delete(platform);
+				this.executeSyncOnDevices(
+					pending.data,
+					pending.projectData,
+					pending.liveSyncInfo,
+				);
+			} else {
+				this._syncInProgress = false;
+			}
+		}
+	}
+
+	private mergeFilesChangeEvents(
+		a: IFilesChangeEventData,
+		b: IFilesChangeEventData,
+	): IFilesChangeEventData {
+		return {
+			files: [...new Set([...a.files, ...b.files])],
+			staleFiles: [
+				...new Set([...(a.staleFiles || []), ...(b.staleFiles || [])]),
+			],
+			hasOnlyHotUpdateFiles: a.hasOnlyHotUpdateFiles && b.hasOnlyHotUpdateFiles,
+			hasNativeChanges: a.hasNativeChanges || b.hasNativeChanges,
+			hmrData: b.hmrData,
+			platform: b.platform,
+		};
+	}
+
 	private async addActionToChain<T>(
 		projectDir: string,
 		action: () => Promise<T>,
 	): Promise<T> {
 		const liveSyncInfo =
 			this.$liveSyncProcessDataService.getPersistedData(projectDir);
 		if (liveSyncInfo) {
-			liveSyncInfo.actionsChain = liveSyncInfo.actionsChain.then(async () => {
-				if (!liveSyncInfo.isStopped) {
-					liveSyncInfo.currentSyncAction = action();
-					const res = await liveSyncInfo.currentSyncAction;
-					return res;
-				}
-			});
+			liveSyncInfo.actionsChain = liveSyncInfo.actionsChain
+				.then(async () => {
+					if (!liveSyncInfo.isStopped) {
+						liveSyncInfo.currentSyncAction = action();
+						const res = await liveSyncInfo.currentSyncAction;
+						return res;
+					}
+				})
+				.catch((err: any) => {
+					this.$logger.warn(`Error in action chain: ${err.message || err}`);
+				});
 
 			const result = await liveSyncInfo.actionsChain;
 			return result;