Fix restart flow for preview-dart-2 mode. (#12496)

* Fix restart flow for preview-dart-2 mode.

Restart in preview-dart-2 needs to use kernel file and it has to be complete, rather than incremental kernel file.

* Add curly braces

* Do full compile on restart

* Roll engine to pick up changes to hot reload for preview-dart-2

bin/internal/engine.version

-2a84f18c795d24ba95baed360fcb58b3dc66d661
+248af2d5b6b5a4fd32c87bac68c624a62d8d9432

packages/flutter_tools/lib/src/compile.dart

@@ -174,4 +174,11 @@ class ResidentCompiler {
   void reject() {
     _server.stdin.writeln('reject');
   }
+
+  /// Should be invoked when frontend server compiler should forget what was
+  /// accepted previously so that next call to [recompile] produces complete
+  /// kernel file.
+  void reset() {
+    _server.stdin.writeln('reset');
+  }
 }

packages/flutter_tools/lib/src/devfs.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:convert' show BASE64, UTF8;
 
+import 'package:flutter_tools/src/artifacts.dart';
 import 'package:json_rpc_2/json_rpc_2.dart' as rpc;
 
 import 'asset.dart';
@@ -369,6 +370,7 @@ class DevFS {
     bool bundleDirty: false,
     Set<String> fileFilter,
     ResidentCompiler generator,
+    bool fullRestart: false,
   }) async {
     // Mark all entries as possibly deleted.
     for (DevFSContent content in _entries.values) {
@@ -441,7 +443,11 @@ class DevFS {
         if (content is DevFSFileContent)
           invalidatedFiles.add(content.file.uri.toString());
       printTrace('Compiling dart to kernel with ${invalidatedFiles.length} updated files');
-      final String compiledBinary = await generator.recompile(mainPath, invalidatedFiles);
+      final String compiledBinary = fullRestart
+        ? await compile(
+              sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
+              mainPath: mainPath)
+        : await generator.recompile(mainPath, invalidatedFiles);
       if (compiledBinary != null && compiledBinary.isNotEmpty)
         dirtyEntries.putIfAbsent(
           Uri.parse(target + '.dill'),

packages/flutter_tools/lib/src/resident_runner.dart

@@ -331,7 +331,8 @@ class FlutterDevice {
     String target,
     AssetBundle bundle,
     bool bundleDirty: false,
-    Set<String> fileFilter
+    Set<String> fileFilter,
+    bool fullRestart: false
   }) async {
     final Status devFSStatus = logger.startProgress(
       'Syncing files to device ${device.name}...',
@@ -345,7 +346,8 @@ class FlutterDevice {
         bundle: bundle,
         bundleDirty: bundleDirty,
         fileFilter: fileFilter,
-        generator: generator
+        generator: generator,
+        fullRestart: fullRestart
       );
     } on DevFSException {
       devFSStatus.cancel();

packages/flutter_tools/lib/src/run_hot.dart

@@ -241,7 +241,7 @@ class HotRunner extends ResidentRunner {
     return devFSUris;
   }
 
-  Future<bool> _updateDevFS() async {
+  Future<bool> _updateDevFS({ bool fullRestart: false }) async {
     if (!_refreshDartDependencies()) {
       // Did not update DevFS because of a Dart source error.
       return false;
@@ -261,6 +261,7 @@ class HotRunner extends ResidentRunner {
         bundle: assetBundle,
         bundleDirty: rebuildBundle,
         fileFilter: _dartDependencies,
+        fullRestart: fullRestart
       );
       if (!result)
         return false;
@@ -334,15 +335,19 @@ class HotRunner extends ResidentRunner {
     }
 
     final Stopwatch restartTimer = new Stopwatch()..start();
-    final bool updatedDevFS = await _updateDevFS();
+    if (previewDart2) {
+      for (FlutterDevice device in flutterDevices) {
+        // Reset generator so that full kernel file is produced for VM to
+        // restart from.
+        if (device.generator != null)
+          device.generator.reset();
+      }
+    }
+    final bool updatedDevFS = await _updateDevFS(fullRestart: true);
     if (!updatedDevFS)
       return new OperationResult(1, 'DevFS synchronization failed');
     // Check if the isolate is paused and resume it.
     for (FlutterDevice device in flutterDevices) {
-      // VM must have accepted the kernel binary, there will be no reload
-      // report, so we let incremental compiler know that source code was accepted.
-      if (device.generator != null)
-        device.generator.accept();
       for (FlutterView view in device.views) {
         if (view.uiIsolate != null) {
           // Reload the isolate.
@@ -357,7 +362,7 @@ class HotRunner extends ResidentRunner {
     }
     // We are now running from source.
     _runningFromSnapshot = false;
-    await _launchFromDevFS(mainPath);
+    await _launchFromDevFS(previewDart2 ? mainPath + '.dill' : mainPath);
     restartTimer.stop();
     printTrace('Restart performed in '
         '${getElapsedAsMilliseconds(restartTimer.elapsed)}.');