[analysis_server] Add a missing "break" to ChangeBuilder that could result in duplicate imports

Changes that add combinators to an import would also insert a duplicate import if they were not the last import, due to a missing "break" as they looped over the existing imports.

Change-Id: I3bf106a200be9ad102487f749df9fe4a9e89fb79
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/383260
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_dart.dart

diff --git a/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_dart.dart b/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_dart.dart
index 53c5c33..fed3d05 100644
--- a/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_dart.dart
+++ b/pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_dart.dart
@@ -1984,6 +1984,7 @@
 
           if (isReplacement) {
             insert(replace: existingImport);
+            break;
           } else if (isDart) {
             if (!isExistingDart || isNewBeforeExisting) {
               insert(

pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart

diff --git a/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart b/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
index c2c666a..d82a3b5 100644
--- a/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
+++ b/pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart
@@ -1831,6 +1831,37 @@
             "import 'package:test/test_a.dart' show A, Other;A"));
   }
 
+  /// The same test as [test_writeType_shownImport] but where the updated
+  /// import is not the last import. This verifies the code that updates imports
+  /// correctly breaks after updating the import so it does not also import a
+  /// duplicate.
+  Future<void> test_writeType_shownImport_nonLast() async {
+    var aPath = convertPath('/home/test/lib/test_a.dart');
+    var aContent = 'class A {} class Other {}';
+    addSource(aPath, aContent);
+    var bPath = convertPath('/home/test/lib/test_b.dart');
+    var bContent = '''
+import 'package:test/test_a.dart' show Other;
+import 'package:test/test_b.dart';
+''';
+    addSource(bPath, bContent);
+
+    var builder = await newBuilder();
+    var typeA = await _getType(aPath, 'A');
+    await builder.addDartFileEdit(bPath, (builder) {
+      builder.addInsertion(bContent.length, (builder) {
+        builder.writeType(typeA);
+      });
+    });
+    var edits = getEdits(builder);
+    expect(edits, hasLength(2));
+    var edited = SourceEdit.applySequence(bContent, edits);
+    expect(edited, equalsIgnoringWhitespace('''
+import 'package:test/test_a.dart' show A, Other;
+import 'package:test/test_b.dart';
+A'''));
+  }
+
   Future<void> test_writeType_shownImportUnsorted() async {
     var aPath = convertPath('/home/test/lib/test_a.dart');
     var aContent = 'class A {} class B {} class C {} class D {}';