[vcs-log] avoid walking graph with cycles indefinitely

Commit graphs can have cycles in them due to grafts usage. During walking such graphs entering the same commits twice needs to be avoided. In order to do so, after a commit was pushed to the stack, it is removed from newCommitsMap that acts as a pool of not processed commits.

IDEA-195247

platform/vcs-log/impl/src/com/intellij/vcs/log/data/VcsLogJoiner.java

@@ -23,6 +23,9 @@ import org.jetbrains.annotations.NotNull;
 
 import java.util.*;
 
+import static com.intellij.util.ObjectUtils.notNull;
+import static com.intellij.util.containers.ContainerUtil.getFirstItem;
+
 /**
  * Attaches the block of latest commits, which was read from the VCS, to the existing log structure.
  *
@@ -202,14 +205,14 @@ public class VcsLogJoiner<CommitId, Commit extends GraphCommit<CommitId>> {
 
     private void insertAllUseStack() {
       while (!newCommitsMap.isEmpty()) {
-        commitsStack.push(newCommitsMap.values().iterator().next());
+        visitCommit(notNull(getFirstItem(newCommitsMap.values())));
         while (!commitsStack.isEmpty()) {
           Commit currentCommit = commitsStack.peek();
           boolean allParentsWereAdded = true;
           for (CommitId parentHash : currentCommit.getParents()) {
             Commit parentCommit = newCommitsMap.get(parentHash);
             if (parentCommit != null) {
-              commitsStack.push(parentCommit);
+              visitCommit(parentCommit);
               allParentsWereAdded = false;
               break;
             }
@@ -232,12 +235,16 @@ public class VcsLogJoiner<CommitId, Commit extends GraphCommit<CommitId>> {
           }
 
           list.add(insertIndex, currentCommit);
-          newCommitsMap.remove(currentCommit.getId());
           commitsStack.pop();
         }
       }
     }
 
+    private void visitCommit(@NotNull Commit commit) {
+      commitsStack.push(commit);
+      newCommitsMap.remove(commit.getId());
+    }
+
     @NotNull
     public List<Commit> getResultList() {
       insertAllUseStack();