[flutter_tools] Add flutter update-packages --synthetic-package-path (#115665)

* allow persisting synthetic package with option

* allow presisting synthetic packages dir

* fix

* fix bug and add tests

* clean up tests

* nits

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

@@ -99,6 +99,14 @@ class UpdatePackagesCommand extends FlutterCommand {
         abbr: 'j',
         help: 'Causes the "pub get" runs to happen concurrently on this many '
               'CPUs. Defaults to the number of CPUs that this machine has.',
+      )
+      ..addOption(
+        'synthetic-package-path',
+        help: 'Write the synthetic monolithic pub package generated to do '
+              'version solving to a persistent path. By default, a temporary '
+              'directory that is deleted before the command exits. By '
+              'providing this path, a Flutter maintainer can inspect further '
+              'exactly how version solving was achieved.',
       );
   }
 
@@ -106,7 +114,10 @@ class UpdatePackagesCommand extends FlutterCommand {
   final String name = 'update-packages';
 
   @override
-  final String description = 'Update the packages inside the Flutter repo.';
+  final String description = 'Update the packages inside the Flutter repo. '
+                             'This is intended for CI and repo maintainers. '
+                             'Normal Flutter developers should not have to '
+                             'use this command.';
 
   @override
   final List<String> aliases = <String>['upgrade-packages'];
@@ -144,6 +155,22 @@ class UpdatePackagesCommand extends FlutterCommand {
       ..writeAsBytesSync(data, flush: true);
   }
 
+  late final Directory _syntheticPackageDir = (() {
+    final String? optionPath = stringArg('synthetic-package-path');
+    if (optionPath == null) {
+      return globals.fs.systemTempDirectory.createTempSync('flutter_update_packages.');
+    }
+    final Directory syntheticPackageDir = globals.fs.directory(optionPath);
+    if (!syntheticPackageDir.existsSync()) {
+      syntheticPackageDir.createSync(recursive: true);
+    }
+    globals.printStatus(
+      'The synthetic package with all pub dependencies across the repo will '
+      'be written to ${syntheticPackageDir.absolute.path}.',
+    );
+    return syntheticPackageDir;
+  })();
+
   @override
   Future<FlutterCommandResult> runCommand() async {
     final List<Directory> packages = runner!.getRepoPackages();
@@ -218,15 +245,19 @@ class UpdatePackagesCommand extends FlutterCommand {
     // attempt to download any necessary package versions to the pub cache to
     // warm the cache.
     final PubDependencyTree tree = PubDependencyTree(); // object to collect results
-    final Directory tempDir = globals.fs.systemTempDirectory.createTempSync('flutter_update_packages.');
     await _generateFakePackage(
-      tempDir: tempDir,
+      tempDir: _syntheticPackageDir,
       dependencies: doUpgrade ? explicitDependencies.values : allDependencies.values,
       pubspecs: pubspecs,
       tree: tree,
       doUpgrade: doUpgrade,
     );
 
+    // Only delete the synthetic package if it was done in a temp directory
+    if (stringArg('synthetic-package-path') == null) {
+      _syntheticPackageDir.deleteSync(recursive: true);
+    }
+
     if (doUpgrade) {
       final bool done = _upgradePubspecs(
         tree: tree,
@@ -380,57 +411,49 @@ class UpdatePackagesCommand extends FlutterCommand {
     required bool doUpgrade,
   }) async {
     Directory? temporaryFlutterSdk;
-    try {
-      final File fakePackage = _pubspecFor(tempDir);
-      fakePackage.createSync();
-      fakePackage.writeAsStringSync(
-        generateFakePubspec(
-          dependencies,
-          doUpgrade: doUpgrade,
-        ),
+    final Directory syntheticPackageDir = tempDir.childDirectory('synthetic_package');
+    final File fakePackage = _pubspecFor(syntheticPackageDir);
+    fakePackage.createSync(recursive: true);
+    fakePackage.writeAsStringSync(
+      generateFakePubspec(
+        dependencies,
+        doUpgrade: doUpgrade,
+      ),
+    );
+    // Create a synthetic flutter SDK so that transitive flutter SDK
+    // constraints are not affected by this upgrade.
+    if (doUpgrade) {
+      temporaryFlutterSdk = createTemporaryFlutterSdk(
+        globals.logger,
+        globals.fs,
+        globals.fs.directory(Cache.flutterRoot),
+        pubspecs,
+        tempDir,
       );
-      // Create a synthetic flutter SDK so that transitive flutter SDK
-      // constraints are not affected by this upgrade.
-      if (doUpgrade) {
-        temporaryFlutterSdk = createTemporaryFlutterSdk(
-          globals.logger,
-          globals.fs,
-          globals.fs.directory(Cache.flutterRoot),
-          pubspecs,
-        );
-      }
+    }
 
-      // Next we run "pub get" on it in order to force the download of any
-      // needed packages to the pub cache, upgrading if requested.
-      await pub.get(
+    // Next we run "pub get" on it in order to force the download of any
+    // needed packages to the pub cache, upgrading if requested.
+    await pub.get(
+      context: PubContext.updatePackages,
+      project: FlutterProject.fromDirectory(syntheticPackageDir),
+      upgrade: doUpgrade,
+      offline: boolArgDeprecated('offline'),
+      flutterRootOverride: temporaryFlutterSdk?.path,
+    );
+
+    if (doUpgrade) {
+      // If upgrading, we run "pub deps --style=compact" on the result. We
+      // pipe all the output to tree.fill(), which parses it so that it can
+      // create a graph of all the dependencies so that we can figure out the
+      // transitive dependencies later. It also remembers which version was
+      // selected for each package.
+      await pub.batch(
+        <String>['deps', '--style=compact'],
         context: PubContext.updatePackages,
-        project: FlutterProject.fromDirectory(tempDir),
-        upgrade: doUpgrade,
-        offline: boolArgDeprecated('offline'),
-        flutterRootOverride: temporaryFlutterSdk?.path,
+        directory: syntheticPackageDir.path,
+        filter: tree.fill,
       );
-
-      if (doUpgrade) {
-        // If upgrading, we run "pub deps --style=compact" on the result. We
-        // pipe all the output to tree.fill(), which parses it so that it can
-        // create a graph of all the dependencies so that we can figure out the
-        // transitive dependencies later. It also remembers which version was
-        // selected for each package.
-        await pub.batch(
-          <String>['deps', '--style=compact'],
-          context: PubContext.updatePackages,
-          directory: tempDir.path,
-          filter: tree.fill,
-        );
-      }
-    } finally {
-      // Cleanup the temporary SDK
-      try {
-        temporaryFlutterSdk?.deleteSync(recursive: true);
-      } on FileSystemException {
-        // Failed to delete temporary SDK.
-      }
-      tempDir.deleteSync(recursive: true);
     }
   }
 
@@ -1577,6 +1600,7 @@ Directory createTemporaryFlutterSdk(
   FileSystem fileSystem,
   Directory realFlutter,
   List<PubspecYaml> pubspecs,
+  Directory tempDir,
 ) {
   final Set<String> currentPackages = <String>{};
   for (final FileSystemEntity entity in realFlutter.childDirectory('packages').listSync()) {
@@ -1591,8 +1615,7 @@ Directory createTemporaryFlutterSdk(
     pubspecsByName[pubspec.name] = pubspec;
   }
 
-  final Directory directory = fileSystem.systemTempDirectory
-    .createTempSync('flutter_upgrade_sdk.')
+  final Directory directory = tempDir.childDirectory('flutter_upgrade_sdk')
     ..createSync();
   // Fill in version info.
   realFlutter.childFile('version')

packages/flutter_tools/test/commands.shard/hermetic/update_packages_test.dart

@@ -87,6 +87,7 @@ void main() {
     late Directory flutterSdk;
     late Directory flutter;
     late FakePub pub;
+    late FakeProcessManager processManager;
 
     setUpAll(() {
       Cache.disableLocking();
@@ -105,13 +106,14 @@ void main() {
       flutter.childFile('pubspec.yaml').writeAsStringSync(kFlutterPubspecYaml);
       Cache.flutterRoot = flutterSdk.absolute.path;
       pub = FakePub(fileSystem);
+      processManager = FakeProcessManager.empty();
     });
 
     testUsingContext('updates packages', () async {
       final UpdatePackagesCommand command = UpdatePackagesCommand();
       await createTestCommandRunner(command).run(<String>['update-packages']);
       expect(pub.pubGetDirectories, equals(<String>[
-        '/.tmp_rand0/flutter_update_packages.rand0',
+        '/.tmp_rand0/flutter_update_packages.rand0/synthetic_package',
         '/flutter/examples',
         '/flutter/packages/flutter',
       ]));
@@ -119,9 +121,9 @@ void main() {
     }, overrides: <Type, Generator>{
       Pub: () => pub,
       FileSystem: () => fileSystem,
-      ProcessManager: () => FakeProcessManager.any(),
+      ProcessManager: () => processManager,
       Cache: () => Cache.test(
-        processManager: FakeProcessManager.any(),
+        processManager: processManager,
       ),
     });
 
@@ -132,19 +134,19 @@ void main() {
         '--force-upgrade',
       ]);
       expect(pub.pubGetDirectories, equals(<String>[
-        '/.tmp_rand0/flutter_update_packages.rand0',
+        '/.tmp_rand0/flutter_update_packages.rand0/synthetic_package',
         '/flutter/examples',
         '/flutter/packages/flutter',
       ]));
       expect(pub.pubBatchDirectories, equals(<String>[
-        '/.tmp_rand0/flutter_update_packages.rand0',
+        '/.tmp_rand0/flutter_update_packages.rand0/synthetic_package',
       ]));
     }, overrides: <Type, Generator>{
       Pub: () => pub,
       FileSystem: () => fileSystem,
-      ProcessManager: () => FakeProcessManager.any(),
+      ProcessManager: () => processManager,
       Cache: () => Cache.test(
-        processManager: FakeProcessManager.any(),
+        processManager: processManager,
       ),
     });
 
@@ -156,19 +158,44 @@ void main() {
         '--jobs=1',
       ]);
       expect(pub.pubGetDirectories, equals(<String>[
-        '/.tmp_rand0/flutter_update_packages.rand0',
+        '/.tmp_rand0/flutter_update_packages.rand0/synthetic_package',
         '/flutter/examples',
         '/flutter/packages/flutter',
       ]));
       expect(pub.pubBatchDirectories, equals(<String>[
-        '/.tmp_rand0/flutter_update_packages.rand0',
+        '/.tmp_rand0/flutter_update_packages.rand0/synthetic_package',
       ]));
     }, overrides: <Type, Generator>{
       Pub: () => pub,
       FileSystem: () => fileSystem,
-      ProcessManager: () => FakeProcessManager.any(),
+      ProcessManager: () => processManager,
       Cache: () => Cache.test(
-        processManager: FakeProcessManager.any(),
+        processManager: processManager,
+      ),
+    });
+
+    testUsingContext('force updates packages --synthetic-package-path', () async {
+      final UpdatePackagesCommand command = UpdatePackagesCommand();
+      const String dir = '/path/to/synthetic/package';
+      await createTestCommandRunner(command).run(<String>[
+        'update-packages',
+        '--force-upgrade',
+        '--synthetic-package-path=$dir',
+      ]);
+      expect(pub.pubGetDirectories, equals(<String>[
+        '$dir/synthetic_package',
+        '/flutter/examples',
+        '/flutter/packages/flutter',
+      ]));
+      expect(pub.pubBatchDirectories, equals(<String>[
+        '$dir/synthetic_package',
+      ]));
+    }, overrides: <Type, Generator>{
+      Pub: () => pub,
+      FileSystem: () => fileSystem,
+      ProcessManager: () => processManager,
+      Cache: () => Cache.test(
+        processManager: processManager,
       ),
     });
   });

packages/flutter_tools/test/general.shard/update_packages_test.dart

@@ -121,6 +121,7 @@ void main() {
       fileSystem,
       flutterSdk,
       <PubspecYaml>[flutterPubspec],
+      fileSystem.systemTempDirectory,
     );
 
     expect(result, exists);