Add a way to map navigation target offsets to the edited content

Change-Id: Ia5e10cbc1a3510e6764fa67e5e6d47c9f19dbc48
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/119165
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/edit/nnbd_migration/info_builder.dart

@@ -6,6 +6,7 @@ import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/edit/fix/dartfix_listener.dart';
 import 'package:analysis_server/src/edit/nnbd_migration/instrumentation_information.dart';
 import 'package:analysis_server/src/edit/nnbd_migration/migration_info.dart';
+import 'package:analysis_server/src/edit/nnbd_migration/offset_mapper.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -123,17 +124,7 @@ class InfoBuilder {
       List<RegionInfo> regions = unitInfo.regions;
       List<SourceEdit> edits = fileEdit.edits;
       edits.sort((first, second) => first.offset.compareTo(second.offset));
-      // Compute the deltas for the regions that will be computed as we apply the
-      // edits. We need the deltas because the offsets to the regions are relative
-      // to the edited source, but the edits are being applied in reverse order so
-      // the offset in the pre-edited source will not match the offset in the
-      // post-edited source. The deltas compensate for that difference.
-      List<int> deltas = [];
-      int previousDelta = 0;
-      for (SourceEdit edit in edits) {
-        deltas.add(previousDelta);
-        previousDelta += (edit.replacement.length - edit.length);
-      }
+      OffsetMapper mapper = OffsetMapper.forEdits(edits);
       // Apply edits in reverse order and build the regions.
       int index = edits.length - 1;
       for (SourceEdit edit in edits.reversed) {
@@ -141,19 +132,20 @@ class InfoBuilder {
         int length = edit.length;
         String replacement = edit.replacement;
         int end = offset + length;
-        int delta = deltas[index--];
         // Insert the replacement text without deleting the replaced text.
         content = content.replaceRange(end, end, replacement);
         FixInfo fixInfo = _findFixInfo(sourceInfo, offset);
         String explanation = '${fixInfo.fix.description.appliedMessage}.';
         List<RegionDetail> details = _computeDetails(fixInfo);
         if (length > 0) {
-          regions.add(RegionInfo(offset + delta, length, explanation, details));
+          regions.add(
+              RegionInfo(mapper.map(offset), length, explanation, details));
         }
-        regions.add(
-            RegionInfo(end + delta, replacement.length, explanation, details));
+        regions.add(RegionInfo(
+            mapper.map(end), replacement.length, explanation, details));
       }
       regions.sort((first, second) => first.offset.compareTo(second.offset));
+      unitInfo.offsetMapper = mapper;
     }
     unitInfo.content = content;
     return unitInfo;
@@ -173,7 +165,7 @@ class InfoBuilder {
     return null;
   }
 
-  /// Return the navigation target
+  /// Return the navigation target corresponding to the given [origin].
   NavigationTarget _targetFor(EdgeOriginInfo origin) {
     AstNode node = origin.node;
     String filePath = origin.source.fullName;

pkg/analysis_server/lib/src/edit/nnbd_migration/migration_info.dart

@@ -2,6 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:analysis_server/src/edit/nnbd_migration/offset_mapper.dart';
 import 'package:analyzer/src/generated/utilities_general.dart';
 
 /// The migration information associated with a single library.
@@ -81,12 +82,17 @@ class UnitInfo {
   String content;
 
   /// The information about the regions that have an explanation associated with
-  /// them.
+  /// them. The offsets in these regions are offsets into the post-edit content.
   final List<RegionInfo> regions = [];
 
-  /// The navigation targets that are located in this file.
+  /// The navigation targets that are located in this file. The offsets in these
+  /// targets are offsets into the pre-edit content.
   final Set<NavigationTarget> targets = {};
 
+  /// The object used to map the pre-edit offsets in the navigation targets to
+  /// the post-edit offsets in the [content].
+  OffsetMapper offsetMapper = OffsetMapper.identity;
+
   /// Initialize a newly created unit.
   UnitInfo(this.path);
 }

pkg/analysis_server/lib/src/edit/nnbd_migration/offset_mapper.dart

@@ -0,0 +1,73 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analyzer_plugin/protocol/protocol_common.dart';
+
+/// An object that can map the offsets before a sequence of edits to the offsets
+/// after applying the edits.
+abstract class OffsetMapper {
+  /// A mapper used for files that were not modified.
+  static OffsetMapper identity = _IdentityMapper();
+
+  /// Return a mapper representing the file modified by the given [edits].
+  factory OffsetMapper.forEdits(List<SourceEdit> edits) => _EditMapper(edits);
+
+  /// Return the post-edit offset that corresponds to the given pre-edit
+  /// [offset].
+  int map(int offset);
+}
+
+/// A mapper used for files that were modified by a set of edits.
+class _EditMapper implements OffsetMapper {
+  /// A list whose elements are the highest pre-edit offset for which the
+  /// corresponding element of [_deltas] should be applied.
+  List<int> _offsets = [];
+
+  /// A list whose elements are the deltas to be applied for all pre-edit
+  /// offsets that are less than or equal to the corresponding element of
+  /// [_offsets].
+  List<int> _deltas = [];
+
+  /// Initialize a newly created mapper based on the given set of [edits].
+  _EditMapper(List<SourceEdit> edits) {
+    _initializeDeltas(edits);
+  }
+
+  @override
+  int map(int offset) => offset + _deltaFor(offset);
+
+  /// Return the delta to be added to the pre-edit [offset] to produce the
+  /// post-edit offset.
+  int _deltaFor(int offset) {
+    for (int i = 0; i < _offsets.length; i++) {
+      int currentOffset = _offsets[i];
+      if (currentOffset >= offset || currentOffset < 0) {
+        return _deltas[i];
+      }
+    }
+    // We should never get here because [_initializeDeltas] always adds an
+    // offset/delta pair at the end of the list whose offset is less than zero.
+    return 0;
+  }
+
+  /// Initialize the list of old offsets and deltas used by [_deltaFor].
+  void _initializeDeltas(List<SourceEdit> edits) {
+    int previousDelta = 0;
+    for (SourceEdit edit in edits) {
+      int offset = edit.offset;
+      int length = edit.length;
+      _offsets.add(offset);
+      _deltas.add(previousDelta);
+      previousDelta += (edit.replacement.length - length);
+    }
+    _offsets.add(-1);
+    _deltas.add(previousDelta);
+  }
+}
+
+/// A mapper used for files that were not modified.
+class _IdentityMapper implements OffsetMapper {
+  @override
+  int map(int offset) => offset;
+}

pkg/analysis_server/test/src/edit/nnbd_migration/offset_mapper_test.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analysis_server/src/edit/nnbd_migration/offset_mapper.dart';
+import 'package:analysis_server/src/protocol_server.dart';
+import 'package:test/test.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../../../analysis_abstract.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(OffsetMapperTest);
+  });
+}
+
+@reflectiveTest
+class OffsetMapperTest extends AbstractAnalysisTest {
+  test_identity() {
+    OffsetMapper mapper = OffsetMapper.identity;
+    expect(mapper.map(0), 0);
+    expect(mapper.map(20), 20);
+    expect(mapper.map(0xFFFFFF), 0xFFFFFF);
+  }
+
+  test_multipleEdits() {
+    OffsetMapper mapper = OffsetMapper.forEdits([
+      SourceEdit(13, 0, '?'),
+      SourceEdit(21, 0, '!'),
+      SourceEdit(32, 0, '?'),
+    ]);
+    expect(mapper.map(0), 0);
+    expect(mapper.map(13), 13);
+    expect(mapper.map(14), 15);
+    expect(mapper.map(21), 22);
+    expect(mapper.map(22), 24);
+    expect(mapper.map(32), 34);
+    expect(mapper.map(33), 36);
+    expect(mapper.map(55), 58);
+  }
+
+  test_singleEdit() {
+    OffsetMapper mapper = OffsetMapper.forEdits([
+      SourceEdit(13, 0, '?'),
+    ]);
+    expect(mapper.map(0), 0);
+    expect(mapper.map(13), 13);
+    expect(mapper.map(14), 15);
+  }
+}

pkg/analysis_server/test/src/edit/nnbd_migration/test_all.dart

@@ -5,9 +5,11 @@
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'info_builder_test.dart' as info_builder;
+import 'offset_mapper_test.dart' as offset_mapper;
 
 main() {
   defineReflectiveSuite(() {
     info_builder.main();
+    offset_mapper.main();
   }, name: 'nnbd_migration');
 }