Track number of package dependencies in Flutter (#20831)

* Track number of package dependencies in Flutter

Relands #20774.

* Use evalFlutter instead of startProcess.

That way we don't need `flutter` on the PATH.

dev/devicelab/bin/tasks/technical_debt__cost.dart

@@ -47,10 +47,7 @@ Future<double> findCostsForFile(File file) async {
   return total;
 }
 
-const String _kBenchmarkKey = 'technical_debt_in_dollars';
-
-Future<Null> main() async {
-  await task(() async {
+Future<double> findCostsForRepo() async {
   final Process git = await startProcess(
     'git',
     <String>['ls-files', '--full-name', flutterDirectory.path],
@@ -62,9 +59,34 @@ Future<Null> main() async {
   final int gitExitCode = await git.exitCode;
   if (gitExitCode != 0)
     throw new Exception('git exit with unexpected error code $gitExitCode');
+  return total;
+}
+
+Future<int> countDependencies() async {
+  final List<String> lines = (await evalFlutter(
+    'update-packages',
+    options: <String>['--transitive-closure'],
+  )).split('\n');
+  final int count = lines.where((String line) => line.contains('->')).length;
+  if (count < 2) // we'll always have flutter and flutter_test, at least...
+    throw new Exception('"flutter update-packages --transitive-closure" returned bogus output:\n${lines.join("\n")}');
+  return count;
+}
+
+const String _kCostBenchmarkKey = 'technical_debt_in_dollars';
+const String _kNumberOfDependenciesKey = 'dependencies_count';
+
+Future<Null> main() async {
+  await task(() async {
     return new TaskResult.success(
-      <String, dynamic>{_kBenchmarkKey: total},
-      benchmarkScoreKeys: <String>[_kBenchmarkKey],
+      <String, dynamic>{
+        _kCostBenchmarkKey: await findCostsForRepo(),
+        _kNumberOfDependenciesKey: await countDependencies(),
+      },
+      benchmarkScoreKeys: <String>[
+        _kCostBenchmarkKey,
+        _kNumberOfDependenciesKey,
+      ],
     );
   });
 }

dev/devicelab/lib/framework/utils.dart

@@ -265,7 +265,7 @@ Future<int> exec(
   String executable,
   List<String> arguments, {
   Map<String, String> environment,
-  bool canFail = false,
+  bool canFail = false, // as in, whether failures are ok. False means that they are fatal.
 }) async {
   final Process process = await startProcess(executable, arguments, environment: environment);
 
@@ -300,7 +300,7 @@ Future<String> eval(
   String executable,
   List<String> arguments, {
   Map<String, String> environment,
-  bool canFail = false,
+  bool canFail = false, // as in, whether failures are ok. False means that they are fatal.
 }) async {
   final Process process = await startProcess(executable, arguments, environment: environment);
 
@@ -332,7 +332,7 @@ Future<String> eval(
 
 Future<int> flutter(String command, {
   List<String> options = const <String>[],
-  bool canFail = false,
+  bool canFail = false, // as in, whether failures are ok. False means that they are fatal.
   Map<String, String> environment,
 }) {
   final List<String> args = <String>[command]..addAll(options);
@@ -343,7 +343,7 @@ Future<int> flutter(String command, {
 /// Runs a `flutter` command and returns the standard output as a string.
 Future<String> evalFlutter(String command, {
   List<String> options = const <String>[],
-  bool canFail = false,
+  bool canFail = false, // as in, whether failures are ok. False means that they are fatal.
   Map<String, String> environment,
 }) {
   final List<String> args = <String>[command]..addAll(options);