Fix the bug in differentiate sectioned collection

DifferenceKit.xcodeproj/project.pbxproj

@@ -143,8 +143,8 @@
  6B5B4097211066BF00A931DB /* ElementPathTest.swift */,
  6B5B4098211066BF00A931DB /* ChangesetTest.swift */,
  6B5B4099211066BF00A931DB /* MeasurementTest.swift */,
- 6B5B409A211066BF00A931DB /* Info.plist */,
  6B5B409B211066BF00A931DB /* TestTools.swift */,
+ 6B5B409A211066BF00A931DB /* Info.plist */,
  );
  path = Tests;
  sourceTree = "<group>";

Sources/Algorithm.swift

@@ -129,6 +129,7 @@ public extension StagedChangeset where Collection: RangeReplaceableCollection, C
  let contiguousTargetSections = ContiguousArray(targetSections.map { ContiguousArray($0.elements) })
 
  var firstStageSections = ContiguousArray<Section>()
+ var secondStageSections = ContiguousArray<Section>()
  var thirdStageSections = ContiguousArray<Section>()
 
  var sourceElementTraces = contiguousSourceSections.map { section in
@@ -142,7 +143,9 @@ public extension StagedChangeset where Collection: RangeReplaceableCollection, C
  var flattenSourceIdentifiers = ContiguousArray<ElementIdentifier>()
  var flattenSourceElementPaths = ContiguousArray<ElementPath>()
 
+ secondStageSections.reserveCapacity(contiguousTargetSections.count)
  thirdStageSections.reserveCapacity(contiguousTargetSections.count)
+
  flattenSourceIdentifiers.reserveCapacity(flattenSourceCount)
  flattenSourceElementPaths.reserveCapacity(flattenSourceCount)
 
@@ -254,7 +257,6 @@ public extension StagedChangeset where Collection: RangeReplaceableCollection, C
  elementDeleted.append(sourceElementPath)
  sourceElementTraces[sourceElementPath].isTracked = true
  offsetByDelete += 1
- continue
  }
 
  let section = Section(model: sourceSections[sourceSectionIndex].model, elements: firstStageElements)
@@ -265,15 +267,21 @@ public extension StagedChangeset where Collection: RangeReplaceableCollection, C
  for targetSectionIndex in contiguousTargetSections.indices {
  // Should not calculate the element updates/moves/insertions in the inserted section.
  guard let sourceSectionIndex = sectionResult.metadata.targetReferences[targetSectionIndex] else {
+ secondStageSections.append(targetSections[targetSectionIndex])
  thirdStageSections.append(targetSections[targetSectionIndex])
  continue
  }
 
  var untrackedSourceIndex: Int? = 0
  let targetElements = contiguousTargetSections[targetSectionIndex]
 
- let section = Section(model: sourceSections[sourceSectionIndex].model, elements: targetElements)
- thirdStageSections.append(section)
+ let sectionDeleteOffset = sectionResult.metadata.sourceTraces[sourceSectionIndex].deleteOffset
+
+ let secondStageSection = firstStageSections[sourceSectionIndex - sectionDeleteOffset]
+ secondStageSections.append(secondStageSection)
+
+ let thirdStageSection = Section(model: secondStageSection.model, elements: targetElements)
+ thirdStageSections.append(thirdStageSection)
 
  for targetElementIndex in targetElements.indices {
  untrackedSourceIndex = untrackedSourceIndex.flatMap { index in
@@ -324,32 +332,6 @@ public extension StagedChangeset where Collection: RangeReplaceableCollection, C
  // The 2nd stage changeset includes only the section insertions and moves and the collection
  // that its changes applied to 1st stage collection.
  if !sectionResult.inserted.isEmpty || !sectionResult.moved.isEmpty {
- var secondStageSections = ContiguousArray<Section>()
- secondStageSections.reserveCapacity(contiguousTargetSections.count)
-
- for targetSectionIndex in contiguousTargetSections.indices {
- guard let sourceSectionIndex = sectionResult.metadata.targetReferences[targetSectionIndex] else {
- secondStageSections.append(targetSections[targetSectionIndex])
- continue
- }
-
- let sourceElements = contiguousSourceSections[sourceSectionIndex]
- var sectionChangedElements = ContiguousArray<Element>()
- sectionChangedElements.reserveCapacity(sourceElements.count)
-
- for sourceElementIndex in sourceElements.indices {
- guard let targetElementPath = sourceElementTraces[sourceSectionIndex][sourceElementIndex].reference else {
- continue
- }
-
- let targetElement = contiguousTargetSections[targetElementPath]
- sectionChangedElements.append(targetElement)
- }
-
- let section = Section(model: sourceSections[sourceSectionIndex].model, elements: sectionChangedElements)
- secondStageSections.append(section)
- }
-
  changesets.append(
  Changeset(
  data: Collection(secondStageSections),

Tests/AlgorithmTest.swift

@@ -647,4 +647,23 @@ extension AlgorithmTestCase {
 
  XCTAssertReproducible(source: source, target: target)
  }
+
+ func testComplicated11() {
+ let source = [
+ Section(model: 1, elements: ["A", "B", "C", "D"]),
+ Section(model: 2, elements: ["E", "F", "G", "H", "I"]),
+ Section(model: 3, elements: ["J", "K", "L", "M"]),
+ Section(model: 4, elements: ["N", "O", "P", "Q"])
+ ]
+
+ let target = [
+ Section(model: 1, elements: ["A", "B", "C", "D"]),
+ Section(model: 2, elements: ["G"]),
+ Section(model: 3, elements: ["E", "F", "H", "I"]),
+ Section(model: 3, elements: ["J", "K", "L", "M"]),
+ Section(model: 4, elements: ["N", "O", "P", "Q"])
+ ]
+
+ XCTAssertReproducible(source: source, target: target)
+ }
 }

Tests/TestTools.swift

@@ -2,6 +2,7 @@ import XCTest
 import DifferenceKit
 
 extension Int: Differentiable {}
+extension String: Differentiable {}
 
 enum D: Differentiable {
  case a, b, c, d, e