Add support for hot reload in Dart projects

Fixes Dart-Code#2708.

package.json

@@ -551,6 +551,11 @@
 					"light": "media/commands/hot-reload-tb.png"
 				}
 			},
+			{
+				"command": "dart.hotReload",
+				"title": "Hot Reload",
+				"category": "Dart"
+			},
 			{
 				"command": "flutter.openTimeline",
 				"title": "Open Observatory Timeline",
@@ -1004,6 +1009,10 @@
 					"command": "flutter.openTimeline",
 					"when": "dart-code:anyFlutterProjectLoaded && inDebugMode"
 				},
+				{
+					"command": "dart.hotReload",
+					"when": "inDebugMode"
+				},
 				{
 					"command": "dart.openDevTools",
 					"when": "dart-code:anyProjectLoaded"

src/debug/dart_debug_impl.ts

@@ -1697,9 +1697,13 @@ export class DartDebugSession extends DebugSession {
 					this.logDapResponse(response);
 					this.sendResponse(response);
 					break;
+				case "hotReload":
+					await this.reloadSources();
+					this.logDapResponse(response);
+					this.sendResponse(response);
+					break;
 				// Flutter requests that may be sent during test runs or other places
 				// that we don't currently support.
-				case "hotReload":
 				case "hotRestart":
 					// TODO: Get rid of this!
 					this.log(`Ignoring Flutter customRequest ${request} for non-Flutter-run app`, LogSeverity.Warn);
@@ -2193,6 +2197,16 @@ export class DartDebugSession extends DebugSession {
 			setTimeout(() => this.pollForMemoryUsage(), this.pollforMemoryMs).unref();
 	}
 
+	private async reloadSources(): Promise<void> {
+		if (!this.vmService)
+			return;
+
+		const result = await this.vmService.getVM();
+		const vm = result.result as VM;
+
+		await Promise.all(vm.isolates.map((isolateRef) => this.vmService!.callMethod("reloadSources", { isolateId: isolateRef.id })));
+	}
+
 	protected logStdout(message: string) {
 		this.logToUserBuffered(message, "stdout");
 	}

src/extension/commands/debug.ts

@@ -138,8 +138,9 @@ export class DebugCommands implements IAmDisposable {
 		}));
 
 		// Misc custom debug commands.
-		this.disposables.push(vs.commands.registerCommand("_flutter.hotReload.touchBar", (args: any) => vs.commands.executeCommand("flutter.hotReload", args)));
-		this.disposables.push(vs.commands.registerCommand("flutter.hotReload", async (args?: any) => {
+		this.disposables.push(vs.commands.registerCommand("_flutter.hotReload.touchBar", (args: any) => vs.commands.executeCommand("dart.hotReload", args)));
+		this.disposables.push(vs.commands.registerCommand("_flutter.hotReload", (args: any) => vs.commands.executeCommand("dart.hotReload", args)));
+		this.disposables.push(vs.commands.registerCommand("dart.hotReload", async (args?: any) => {
 			if (!debugSessions.length)
 				return;
 			if (!!workspaceContext.config?.flutterSyncScript) {

src/test/dart_debug/debug/dart_cli.test.ts

@@ -11,7 +11,7 @@ import { fsPath, getRandomInt } from "../../../shared/utils/fs";
 import { resolvedPromise } from "../../../shared/utils/promises";
 import { DartDebugClient } from "../../dart_debug_client";
 import { createDebugClient, ensureFrameCategories, ensureMapEntry, ensureNoVariable, ensureVariable, ensureVariableWithIndex, getVariablesTree, isExternalPackage, isLocalPackage, isSdkFrame, isUserCode, spawnDartProcessPaused, startDebugger, waitAllThrowIfTerminates } from "../../debug_helpers";
-import { activate, breakpointFor, closeAllOpenFiles, defer, delay, ensureArrayContainsArray, extApi, getAttachConfiguration, getDefinition, getLaunchConfiguration, getPackages, getResolvedDebugConfiguration, helloWorldBrokenFile, helloWorldDeferredEntryFile, helloWorldDeferredScriptFile, helloWorldExampleSubFolder, helloWorldExampleSubFolderMainFile, helloWorldFolder, helloWorldGettersFile, helloWorldGoodbyeFile, helloWorldHttpFile, helloWorldInspectionFile as helloWorldInspectFile, helloWorldLocalPackageFile, helloWorldLongRunningFile, helloWorldMainFile, helloWorldPartEntryFile, helloWorldPartFile, helloWorldStack60File, helloWorldThrowInExternalPackageFile, helloWorldThrowInLocalPackageFile, helloWorldThrowInSdkFile, myPackageFolder, openFile, positionOf, sb, setConfigForTest, uriFor, waitForResult, watchPromise, writeBrokenDartCodeIntoFileForTest } from "../../helpers";
+import { activate, breakpointFor, closeAllOpenFiles, currentEditor, defer, delay, ensureArrayContainsArray, extApi, getAttachConfiguration, getDefinition, getLaunchConfiguration, getPackages, getResolvedDebugConfiguration, helloWorldBrokenFile, helloWorldDeferredEntryFile, helloWorldDeferredScriptFile, helloWorldExampleSubFolder, helloWorldExampleSubFolderMainFile, helloWorldFolder, helloWorldGettersFile, helloWorldGoodbyeFile, helloWorldHttpFile, helloWorldInspectionFile as helloWorldInspectFile, helloWorldLocalPackageFile, helloWorldLongRunningFile, helloWorldMainFile, helloWorldPartEntryFile, helloWorldPartFile, helloWorldReloadFile, helloWorldStack60File, helloWorldThrowInExternalPackageFile, helloWorldThrowInLocalPackageFile, helloWorldThrowInSdkFile, myPackageFolder, openFile, positionOf, sb, setConfigForTest, setTestContent, uriFor, waitForResult, watchPromise, writeBrokenDartCodeIntoFileForTest } from "../../helpers";
 
 
 describe("dart cli debugger", () => {
@@ -207,6 +207,26 @@ describe("dart cli debugger", () => {
 		assert.equal(config!.cwd, fsPath(helloWorldExampleSubFolder));
 	});
 
+	it("can hot reload", async () => {
+		await openFile(helloWorldReloadFile);
+		const config = await startDebugger(dc, helloWorldReloadFile);
+		await waitAllThrowIfTerminates(dc,
+			dc.configurationSequence(),
+			dc.assertOutputContains("stdout", "ORIGINAL CONTENT"),
+			dc.launch(config),
+		);
+
+		// Replace the content and trigger hot reload.
+		const editor = currentEditor();
+		await setTestContent(editor.document.getText().replace("ORIGINAL CONTENT", "NEW CONTENT"));
+		await editor.document.save();
+
+		await vs.commands.executeCommand("dart.hotReload");
+		await dc.assertOutputContains("stdout", "NEW CONTENT");
+
+		await dc.terminateRequest();
+	});
+
 	it("can launch DevTools externally", async () => {
 
 		// TODO(dantup): Tests for embedded DevTools.

src/test/helpers.ts

@@ -38,6 +38,7 @@ const testFolder = path.join(ext.extensionPath, "src/test");
 // Dart
 export const helloWorldFolder = vs.Uri.file(path.join(testFolder, "test_projects/hello_world"));
 export const helloWorldMainFile = vs.Uri.file(path.join(fsPath(helloWorldFolder), "bin/main.dart"));
+export const helloWorldReloadFile = vs.Uri.file(path.join(fsPath(helloWorldFolder), "bin/reload.dart"));
 export const helloWorldInspectionFile = vs.Uri.file(path.join(fsPath(helloWorldFolder), "bin/inspect.dart"));
 export const helloWorldLongRunningFile = vs.Uri.file(path.join(fsPath(helloWorldFolder), "bin/long_running.dart"));
 export const helloWorldMainLibFile = vs.Uri.file(path.join(fsPath(helloWorldFolder), "lib/basic.dart"));

src/test/test_projects/hello_world/bin/reload.dart

@@ -0,0 +1,9 @@
+import 'dart:async';
+
+main() async {
+  Timer.periodic(Duration(milliseconds: 100), (_) => printSomething());
+}
+
+void printSomething() {
+  print('ORIGINAL CONTENT');
+}