Add presubmit test for trailing whitespace. (#19412)

Checks only changed source files (C++, Dart, Java, ObjC) for trailing whitespace.

.cirrus.yml

@@ -17,6 +17,7 @@ task:
     # run pub get in all the repo packages
     ./bin/flutter update-packages
 
+    git fetch origin master
   matrix:
     - name: docs
       env:
@@ -25,11 +26,15 @@ task:
     - name: analyze
       env:
         SHARD: analyze
-      test_script: dart ./dev/bots/test.dart
+      test_script: |
+        export TEST_COMMIT_RANGE="$(git merge-base --fork-point FETCH_HEAD HEAD)..HEAD"
+        dart ./dev/bots/test.dart
     - name: tests-linux
       env:
         SHARD: tests
-      test_script: dart ./dev/bots/test.dart
+      test_script: |
+        export TEST_COMMIT_RANGE="$(git merge-base --fork-point FETCH_HEAD HEAD)..HEAD"
+        dart ./dev/bots/test.dart
       container:
         cpu: 4
         memory: 8G
@@ -48,8 +53,10 @@ task:
   setup_script:
     - bin\flutter.bat config --no-analytics
     - bin\flutter.bat update-packages
-  test_all_script:
-    - bin\cache\dart-sdk\bin\dart.exe -c dev\bots\test.dart
+    - git fetch origin master
+  test_all_script: |
+    export TEST_COMMIT_RANGE="$(git merge-base --fork-point FETCH_HEAD HEAD)..HEAD"
+    bin\cache\dart-sdk\bin\dart.exe -c dev\bots\test.dart
 
 task:
   name: tests-macos
@@ -61,6 +68,7 @@ task:
   setup_script:
     - bin/flutter config --no-analytics
     - bin/flutter update-packages
-  test_all_script:
-    - ulimit -S -n 2048 # https://github.com/flutter/flutter/issues/2976
-    - bin/cache/dart-sdk/bin/dart -c dev/bots/test.dart
+  test_all_script: |
+    ulimit -S -n 2048 # https://github.com/flutter/flutter/issues/2976
+    export TEST_COMMIT_RANGE="$(git merge-base --fork-point FETCH_HEAD HEAD)..HEAD"
+    bin/cache/dart-sdk/bin/dart -c dev/bots/test.dart

dev/bots/test.dart

@@ -95,6 +95,41 @@ Future<Null> _verifyInternationalizations() async {
   print('Contents of $localizationsFile matches output of gen_localizations.dart script.');
 }
 
+Future<Null> _checkForTrailingSpaces() async {
+  if (!Platform.isWindows) {
+    final String commitRange = Platform.environment.containsKey('TEST_COMMIT_RANGE')
+        ? Platform.environment['TEST_COMMIT_RANGE']
+        : 'master..HEAD';
+    print('Checking for trailing whitespace in source files.');
+    final List<String> fileTypes = <String>[
+      '*.dart', '*.cxx', '*.cpp', '*.cc', '*.c', '*.C', '*.h', '*.java', '*.mm', '*.m',
+    ];
+    final EvalResult changedFilesResult = await _evalCommand(
+      'git', <String>['diff', '-U0', '--no-color', '--name-only', commitRange, '--'] + fileTypes,
+      workingDirectory: flutterRoot,
+    );
+    if (changedFilesResult.stdout == null) {
+      print('No Results for whitespace check.');
+      return;
+    }
+    final List<String> changedFiles = changedFilesResult.stdout.trim().split('\n')
+        .where((String item) => item.trim().isNotEmpty).toList();
+    if (changedFiles.isNotEmpty) {
+      await _runCommand('grep',
+        <String>[
+          '--line-number',
+          '--extended-regexp',
+          r'[[:space:]]+$',
+        ] + changedFiles,
+        workingDirectory: flutterRoot,
+        printOutput: false,
+        expectFailure: true, // Just means a non-zero exit code is expected.
+        expectedExitCode: 1, // Indicates that zero lines were found.
+      );
+    }
+  }
+}
+
 Future<Null> _analyzeRepo() async {
   await _verifyGeneratedPluginRegistrants(flutterRoot);
   await _verifyNoBadImportsInFlutter(flutterRoot);
@@ -123,6 +158,8 @@ Future<Null> _analyzeRepo() async {
     options: <String>['--flutter-repo', '--watch', '--benchmark'],
   );
 
+  await _checkForTrailingSpaces();
+
   // Try an analysis against a big version of the gallery.
   await _runCommand(dart,
     <String>['--preview-dart-2', path.join(flutterRoot, 'dev', 'tools', 'mega_gallery.dart')],
@@ -331,6 +368,7 @@ Future<Null> _runCommand(String executable, List<String> arguments, {
   String workingDirectory,
   Map<String, String> environment,
   bool expectFailure = false,
+  int expectedExitCode,
   bool printOutput = true,
   bool skip = false,
   Duration timeout = _kLongTimeout,
@@ -363,7 +401,7 @@ Future<Null> _runCommand(String executable, List<String> arguments, {
     stderr.writeln('Process timed out after $timeout');
     return expectFailure ? 0 : 1;
   });
-  if ((exitCode == 0) == expectFailure) {
+  if ((exitCode == 0) == expectFailure || (expectedExitCode != null && exitCode != expectedExitCode)) {
     if (!printOutput) {
       stdout.writeln(utf8.decode((await savedStdout).expand((List<int> ints) => ints).toList()));
       stderr.writeln(utf8.decode((await savedStderr).expand((List<int> ints) => ints).toList()));

dev/bots/travis_script.sh

@@ -59,5 +59,5 @@ elif [ "$SHARD" = "docs" ]; then
     ./dev/bots/docs.sh
   fi
 else
-  dart ./dev/bots/test.dart
+  TEST_COMMIT_RANGE="${TRAVIS_COMMIT_RANGE}" dart ./dev/bots/test.dart
 fi