[vcs-log-graph] compute correct start layout indexes for the branch heads

Since branch heads are now being used as the start nodes for building graph layout, a head commit might be visited earlier from another head, giving it a layout index different from the currentLayoutIndex value.

This commit avoids the problem altogether by computing layout indexes array for heads after all layout indexes have been calculated.

follow-up: 1cd228ff6107d0ca03d5f3172f9940e0d55d9e4f

GitOrigin-RevId: c01942bad60c09979711769905ac35a43b9c98f0

platform/vcs-log/graph/src/com/intellij/vcs/log/graph/impl/facade/SimpleGraphInfo.java

@@ -92,12 +92,7 @@ public final class SimpleGraphInfo<CommitId> implements PermanentGraphInfo<Commi
     }
 
     ContainerUtil.sort(headNodeIndexes, Comparator.comparingInt(o -> layoutIndexes[o]));
-    int[] starts = new int[headNodeIndexes.size()];
-    for (int i = 0; i < starts.length; i++) {
-      starts[i] = layoutIndexes[headNodeIndexes.getInt(i)];
-    }
-
-    GraphLayoutImpl newLayout = new GraphLayoutImpl(layoutIndexes, headNodeIndexes, starts);
+    GraphLayoutImpl newLayout = new GraphLayoutImpl(layoutIndexes, headNodeIndexes);
 
     return new SimpleGraphInfo<>(newLinearGraph, newLayout, commitIdMapping, timestampGetter,
                                  LinearGraphUtils.convertIdsToNodeIndexes(linearGraph, branchNodeIds));

platform/vcs-log/graph/src/com/intellij/vcs/log/graph/impl/permanent/GraphLayoutBuilder.kt

@@ -25,13 +25,11 @@ object GraphLayoutBuilder {
     val sortedHeads = IntArrayList(allHeads).sortCatching(comparator)
 
     val layoutIndex = IntArray(graph.nodesCount())
-    val startLayoutIndexForHead = IntArray(sortedHeads.size)
     var currentLayoutIndex = 1
     for (i in sortedHeads.indices) {
-      startLayoutIndexForHead[i] = currentLayoutIndex
       currentLayoutIndex = dfs(graph, sortedHeads.getInt(i), currentLayoutIndex, layoutIndex)
     }
-    return GraphLayoutImpl(layoutIndex, sortedHeads, startLayoutIndexForHead)
+    return GraphLayoutImpl(layoutIndex, sortedHeads)
   }
 
   /**

platform/vcs-log/graph/src/com/intellij/vcs/log/graph/impl/permanent/GraphLayoutImpl.kt

@@ -7,9 +7,8 @@ import it.unimi.dsi.fastutil.ints.IntList
 import java.util.*
 import kotlin.math.max
 
-class GraphLayoutImpl(layoutIndex: IntArray,
-                      private val headNodeIndex: IntList,
-                      private val startLayoutIndexForHead: IntArray) : GraphLayout {
+class GraphLayoutImpl(layoutIndex: IntArray, private val headNodeIndex: IntList) : GraphLayout {
+  private val startLayoutIndexForHead = getLayoutIndexesForHeads(layoutIndex, headNodeIndex)
   private val layoutIndex = CompressedIntList.newInstance(layoutIndex)
 
   override fun getLayoutIndex(nodeIndex: Int) = layoutIndex[nodeIndex]
@@ -25,3 +24,11 @@ class GraphLayoutImpl(layoutIndex: IntArray,
     return if (i < 0) max(0, (-i - 2)) else i
   }
 }
+
+private fun getLayoutIndexesForHeads(layoutIndexes: IntArray, headNodeIndexes: IntList): IntArray {
+  val result = IntArray(headNodeIndexes.size)
+  for (i in result.indices) {
+    result[i] = layoutIndexes[headNodeIndexes.getInt(i)]
+  }
+  return result
+}