refactor flutter upgrade to be 2 part, with the second part re-entrant (#38325)

packages/flutter_tools/lib/src/commands/upgrade.dart

@@ -20,12 +20,19 @@ import 'channel.dart';
 
 class UpgradeCommand extends FlutterCommand {
   UpgradeCommand() {
-    argParser.addFlag(
+    argParser
-      'force',
+      ..addFlag(
-      abbr: 'f',
+        'force',
-      help: 'force upgrade the flutter branch, potentially discarding local changes.',
+        abbr: 'f',
-      negatable: false,
+        help: 'Force upgrade the flutter branch, potentially discarding local changes.',
-    );
+        negatable: false,
+      )
+      ..addFlag(
+        'continue',
+        hide: true,
+        negatable: false,
+        help: 'For the second half of the upgrade flow requiring the new version of Flutter. Should not be invoked manually, but re-entrantly by the standard upgrade command.',
+      );
   }
 
   @override
@@ -45,7 +52,12 @@ class UpgradeCommand extends FlutterCommand {
   @override
   Future<FlutterCommandResult> runCommand() async {
     final UpgradeCommandRunner upgradeCommandRunner = UpgradeCommandRunner();
-    await upgradeCommandRunner.runCommand(argResults['force'], GitTagVersion.determine(), FlutterVersion.instance);
+    await upgradeCommandRunner.runCommand(
+      argResults['force'],
+      argResults['continue'],
+      GitTagVersion.determine(),
+      FlutterVersion.instance,
+    );
     return null;
   }
 }
@@ -53,7 +65,25 @@ class UpgradeCommand extends FlutterCommand {
 
 @visibleForTesting
 class UpgradeCommandRunner {
-  Future<FlutterCommandResult> runCommand(bool force, GitTagVersion gitTagVersion, FlutterVersion flutterVersion) async {
+  Future<FlutterCommandResult> runCommand(
+    bool force,
+    bool continueFlow,
+    GitTagVersion gitTagVersion,
+    FlutterVersion flutterVersion,
+  ) async {
+    if (!continueFlow) {
+      await runCommandFirstHalf(force, gitTagVersion, flutterVersion);
+    } else {
+      await runCommandSecondHalf(flutterVersion);
+    }
+    return null;
+  }
+
+  Future<void> runCommandFirstHalf(
+    bool force,
+    GitTagVersion gitTagVersion,
+    FlutterVersion flutterVersion,
+  ) async {
     await verifyUpstreamConfigured();
     if (!force && gitTagVersion == const GitTagVersion.unknown()) {
       // If the commit is a recognized branch and not master,
@@ -87,10 +117,31 @@ class UpgradeCommandRunner {
     await resetChanges(gitTagVersion);
     await upgradeChannel(flutterVersion);
     await attemptFastForward();
+    await flutterUpgradeContinue();
+  }
+
+  Future<void> flutterUpgradeContinue() async {
+    final int code = await runCommandAndStreamOutput(
+      <String>[
+        fs.path.join('bin', 'flutter'),
+        'upgrade',
+        '--continue',
+        '--no-version-check',
+      ],
+      workingDirectory: Cache.flutterRoot,
+      allowReentrantFlutter: true,
+    );
+    if (code != 0) {
+      throwToolExit(null, exitCode: code);
+    }
+  }
+
+  // This method should only be called if the upgrade command is invoked
+  // re-entrantly with the `--continue` flag
+  Future<void> runCommandSecondHalf(FlutterVersion flutterVersion) async {
     await precacheArtifacts();
     await updatePackages(flutterVersion);
     await runDoctor();
-    return null;
   }
 
   Future<bool> hasUncomittedChanges() async {

packages/flutter_tools/test/general.shard/commands/upgrade_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:convert';
+
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
@@ -16,6 +18,21 @@ import 'package:process/process.dart';
 import '../../src/common.dart';
 import '../../src/context.dart';
 
+Process createMockProcess({ int exitCode = 0, String stdout = '', String stderr = '' }) {
+  final Stream<List<int>> stdoutStream = Stream<List<int>>.fromIterable(<List<int>>[
+    utf8.encode(stdout),
+  ]);
+  final Stream<List<int>> stderrStream = Stream<List<int>>.fromIterable(<List<int>>[
+    utf8.encode(stderr),
+  ]);
+  final Process process = MockProcess();
+
+  when(process.stdout).thenAnswer((_) => stdoutStream);
+  when(process.stderr).thenAnswer((_) => stderrStream);
+  when(process.exitCode).thenAnswer((_) => Future<int>.value(exitCode));
+  return process;
+}
+
 void main() {
   group('UpgradeCommandRunner', () {
     FakeUpgradeCommandRunner fakeCommandRunner;
@@ -29,11 +46,24 @@ void main() {
       fakeCommandRunner = FakeUpgradeCommandRunner();
       realCommandRunner = UpgradeCommandRunner();
       processManager = MockProcessManager();
+      when(processManager.start(
+        <String>[
+          fs.path.join('bin', 'flutter'),
+          'upgrade',
+          '--continue',
+          '--no-version-check',
+        ],
+        environment: anyNamed('environment'),
+        workingDirectory: anyNamed('workingDirectory'),
+      )).thenAnswer((Invocation invocation) async {
+        return Future<Process>.value(createMockProcess());
+      });
       fakeCommandRunner.willHaveUncomittedChanges = false;
     });
 
     test('throws on unknown tag, official branch,  noforce', () async {
       final Future<FlutterCommandResult> result = fakeCommandRunner.runCommand(
+        false,
         false,
         const GitTagVersion.unknown(),
         flutterVersion,
@@ -41,18 +71,22 @@ void main() {
       expect(result, throwsA(isInstanceOf<ToolExit>()));
     });
 
-    test('does not throw on unknown tag, official branch, force', () async {
+    testUsingContext('does not throw on unknown tag, official branch, force', () async {
       final Future<FlutterCommandResult> result = fakeCommandRunner.runCommand(
         true,
+        false,
         const GitTagVersion.unknown(),
         flutterVersion,
       );
       expect(await result, null);
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => processManager,
     });
 
     test('throws tool exit with uncommitted changes', () async {
       fakeCommandRunner.willHaveUncomittedChanges = true;
       final Future<FlutterCommandResult> result = fakeCommandRunner.runCommand(
+        false,
         false,
         gitTagVersion,
         flutterVersion,
@@ -60,30 +94,37 @@ void main() {
       expect(result, throwsA(isA<ToolExit>()));
     });
 
-    test('does not throw tool exit with uncommitted changes and force', () async {
+    testUsingContext('does not throw tool exit with uncommitted changes and force', () async {
       fakeCommandRunner.willHaveUncomittedChanges = true;
+
       final Future<FlutterCommandResult> result = fakeCommandRunner.runCommand(
         true,
-        gitTagVersion,
-        flutterVersion,
-      );
-      expect(await result, null);
-    });
-
-    test('Doesn\'t throw on known tag, dev branch, no force', () async {
-      final Future<FlutterCommandResult> result = fakeCommandRunner.runCommand(
         false,
         gitTagVersion,
         flutterVersion,
       );
       expect(await result, null);
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => processManager,
+    });
+
+    testUsingContext('Doesn\'t throw on known tag, dev branch, no force', () async {
+      final Future<FlutterCommandResult> result = fakeCommandRunner.runCommand(
+        false,
+        false,
+        gitTagVersion,
+        flutterVersion,
+      );
+      expect(await result, null);
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => processManager,
     });
 
     testUsingContext('verifyUpstreamConfigured', () async {
       when(processManager.run(
         <String>['git', 'rev-parse', '@{u}'],
         environment:anyNamed('environment'),
-        workingDirectory: anyNamed('workingDirectory'))
+        workingDirectory: anyNamed('workingDirectory')),
       ).thenAnswer((Invocation invocation) async {
         return FakeProcessResult()
           ..exitCode = 0;
@@ -176,6 +217,7 @@ class FakeUpgradeCommandRunner extends UpgradeCommandRunner {
 }
 
 class MockFlutterVersion extends Mock implements FlutterVersion {}
+class MockProcess extends Mock implements Process {}
 class MockProcessManager extends Mock implements ProcessManager {}
 class FakeProcessResult implements ProcessResult {
   @override