[tests] Using git diff over diff for stability in hot reload tests.

Change-Id: Icdbdf4c569fd8ab5de96560722ac62616185a751
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/406224
Reviewed-by: Nicholas Shahan <[email protected]>
Commit-Queue: Mark Zhou <[email protected]>

Author: Markzipan

pkg/dev_compiler/test/hot_reload_suite.dart

@@ -584,9 +584,7 @@ abstract class HotReloadSuiteRunner {
                 label: test.name);
             File.fromUri(previousTempUri).deleteSync();
             File.fromUri(currentTempUri).deleteSync();
-            var (filteredDiffOutput, filteredCurrentDiff) =
-                _filterLineDeltas(diffOutput, currentDiff);
-            if (filteredDiffOutput != filteredCurrentDiff) {
+            if (diffOutput != currentDiff) {
               reportDiffOutcome(
                   test.name,
                   currentEdit.fileUri,
@@ -906,47 +904,23 @@ abstract class HotReloadSuiteRunner {
       {String label = '', bool commented = true, bool trimHeaders = true}) {
     final file1Path = file1.toFilePath();
     final file2Path = file2.toFilePath();
-    final diffArgs = [
-      '-u',
-      '--width=120',
-      '--expand-tabs',
-      file1Path,
-      file2Path
-    ];
-    _debugPrint("Running diff with 'diff ${diffArgs.join(' ')}'.",
+    final diffArgs = ['diff', '-u', file1Path, file2Path];
+    _debugPrint("Running diff with 'git diff ${diffArgs.join(' ')}'.",
         label: label);
-    final diffProcess = Process.runSync('diff', diffArgs);
+    final diffProcess = Process.runSync('git', diffArgs);
     final errOutput = diffProcess.stderr as String;
     if (errOutput.isNotEmpty) {
-      throw Exception('diff failed with:\n$errOutput');
+      throw Exception('git diff failed with:\n$errOutput');
     }
     var output = diffProcess.stdout as String;
     if (trimHeaders) {
-      // Skip the first two lines.
+      // Skip the diff header. 'git diff' has 5 lines in its header.
       // TODO(markzipan): Add support for Windows-style line endings.
-      output = output.split('\n').skip(2).join('\n');
+      output = output.split('\n').skip(5).join('\n');
     }
     return commented ? '$testDiffSeparator\n/*\n$output*/' : output;
   }
 
-  /// Removes diff lines that show added or removed newlines.
-  ///
-  /// 'diff' can be unstable across platforms around newline offsets.
-  (String, String) _filterLineDeltas(String diff1, String diff2) {
-    bool isBlankLineOrDelta(String s) {
-      var trimmed = s.trim();
-      return trimmed.isEmpty ||
-          (trimmed.startsWith('+') || trimmed.startsWith('-')) &&
-              trimmed.length == 1;
-    }
-
-    var diff1Lines = LineSplitter().convert(diff1)
-      ..removeWhere(isBlankLineOrDelta);
-    var diff2Lines = LineSplitter().convert(diff2)
-      ..removeWhere(isBlankLineOrDelta);
-    return (diff1Lines.join('\n'), diff2Lines.join('\n'));
-  }
-
   /// Returns the code and diff portions of [file] with all leading and trailing
   /// whitespace trimmed.
   (String, String) _splitTestByDiff(Uri file) {

tests/hot_reload/add_library_imports/main.1.dart

@@ -21,7 +21,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -2,12 +2,15 @@
  import 'package:reload_test/reload_test_utils.dart';
  
  import 'dart:math';

tests/hot_reload/add_new_static_field/main.1.dart

@@ -28,7 +28,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -8,10 +8,12 @@
  // Adapted from:
  // https://github.com/dart-lang/sdk/blob/a70adce28e53ff8bb3445fe96f3f1be951d8a417/runtime/vm/isolate_reload_test.cc#L5423
  

tests/hot_reload/bad_class/main.1.reject.dart

@@ -24,7 +24,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -9,7 +9,7 @@
  // https://github.com/dart-lang/sdk/blob/36c0788137d55c6c77f4b9a8be12e557bc764b1c/runtime/vm/isolate_reload_test.cc#L364
  
  class Foo {

tests/hot_reload/call_deleted_top_level_function/main.1.dart

@@ -31,7 +31,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -8,15 +8,14 @@
  // Adapted from:
  // https://github.com/dart-lang/sdk/blob/bf2fba78e006ce4feac43e514c0b8f3ea9e9fbb8/runtime/vm/isolate_reload_test.cc#L2597
  

tests/hot_reload/call_deleted_top_level_function_arity_change/main.1.dart

@@ -35,7 +35,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -8,15 +8,18 @@
  // Adapted from:
  // https://github.com/dart-lang/sdk/blob/bf2fba78e006ce4feac43e514c0b8f3ea9e9fbb8/runtime/vm/isolate_reload_test.cc#L2627
  

tests/hot_reload/class_added/main.1.dart

@@ -25,7 +25,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -9,7 +9,11 @@
  // https://github.com/dart-lang/sdk/blob/f34a2ed99fc1b34cedbd974a5801f8d922121126/runtime/vm/isolate_reload_test.cc#L561
  
  helper() {

tests/hot_reload/class_field_added/main.1.dart

@@ -30,7 +30,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -10,6 +10,7 @@
  
  class Foo {
    var x;

tests/hot_reload/class_field_added/main.2.dart

@@ -31,7 +31,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -11,6 +11,7 @@
  class Foo {
    var x;
    var y;

tests/hot_reload/class_field_removed/main.1.dart

@@ -30,7 +30,6 @@ Future<void> main() async {
 
 /** DIFF **/
 /*
-@@ -11,7 +11,6 @@
  class Foo {
    var x;
    var y;