Track number of package dependencies in Flutter (#20722)

dev/devicelab/bin/tasks/technical_debt__cost.dart

@@ -43,24 +43,51 @@ Future<double> findCostsForFile(File file) async {
   return total;
 }
 
-const String _kBenchmarkKey = 'technical_debt_in_dollars';
+Future<double> findCostsForRepo() async {
+  final Process git = await startProcess(
+    'git',
+    <String>['ls-files', '--full-name', flutterDirectory.path],
+    workingDirectory: flutterDirectory.path,
+  );
+  double total = 0.0;
+  await for (String entry in git.stdout.transform(utf8.decoder).transform(const LineSplitter()))
+    total += await findCostsForFile(new File(path.join(flutterDirectory.path, entry)));
+  final int gitExitCode = await git.exitCode;
+  if (gitExitCode != 0)
+    throw new Exception('git exit with unexpected error code $gitExitCode');
+  return total;
+}
+
+Future<int> countDependencies() async {
+  final Process subprocess = await startProcess(
+    'flutter',
+    <String>['update-packages', '--transitive-closure'],
+    workingDirectory: flutterDirectory.path,
+  );
+  final List<String> lines = await subprocess.stdout.transform(utf8.decoder).transform(const LineSplitter()).toList();
+  final int subprocessExitCode = await subprocess.exitCode;
+  if (subprocessExitCode != 0)
+    throw new Exception('flutter exit with unexpected error code $subprocessExitCode');
+  final int count = lines.where((String line) => line.contains('->')).length;
+  if (count < 2) // we'll always have flutter and flutter_test, at least...
+    throw new Exception('"flutter update-packages --transitive-closure" returned bogus output:\n${lines.join("\n")}');
+  return count;
+}
+
+const String _kCostBenchmarkKey = 'technical_debt_in_dollars';
+const String _kNumberOfDependenciesKey = 'dependencies_count';
 
 Future<Null> main() async {
   await task(() async {
-    final Process git = await startProcess(
-      'git',
-      <String>['ls-files', '--full-name', flutterDirectory.path],
-      workingDirectory: flutterDirectory.path,
-    );
-    double total = 0.0;
-    await for (String entry in git.stdout.transform(utf8.decoder).transform(const LineSplitter()))
-      total += await findCostsForFile(new File(path.join(flutterDirectory.path, entry)));
-    final int gitExitCode = await git.exitCode;
-    if (gitExitCode != 0)
-      throw new Exception('git exit with unexpected error code $gitExitCode');
     return new TaskResult.success(
-      <String, dynamic>{_kBenchmarkKey: total},
-      benchmarkScoreKeys: <String>[_kBenchmarkKey],
+      <String, dynamic>{
+        _kCostBenchmarkKey: await findCostsForRepo(),
+        _kNumberOfDependenciesKey: await countDependencies(),
+      },
+      benchmarkScoreKeys: <String>[
+        _kCostBenchmarkKey,
+        _kNumberOfDependenciesKey,
+      ],
     );
   });
 }