[log] IDEA-121875 Enable manual commits sorting in VCS that support it

If the VCS can return unordered commits faster (like Git does),
request more unordered commits & sort them by hands.

platform/vcs-log/api/src/com/intellij/vcs/log/VcsLogProvider.java

@@ -95,4 +95,10 @@ public interface VcsLogProvider {
   @NotNull
   Collection<String> getContainingBranches(@NotNull VirtualFile root, @NotNull Hash commitHash) throws VcsException;
 
+  /**
+   * Return true if the VCS supports some mode in which commits can be received faster, but unordered. <br/>
+   * In this case the VCS Log will order commits manually
+   */
+  boolean supportsFastUnorderedCommits();
+
 }

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

@@ -440,7 +440,12 @@ public class VcsLogDataHolder implements Disposable, VcsLogDataProvider {
       RecentCommitsInfo info = entry.getValue();
 
       // in this case new commits won't be attached to the log, but will substitute existing ones.
-      List<TimedVcsCommit> firstBlockCommits = new VcsLogSorter<TimedVcsCommit>().sortByDateTopoOrder(info.firstBlockCommits);
+      List<TimedVcsCommit> firstBlockCommits = info.firstBlockCommits;
+      if (getLogProvider(root).supportsFastUnorderedCommits()) {
+        // => we requested unordered => have to order them ourselves
+        firstBlockCommits = new VcsLogSorter<TimedVcsCommit>().sortByDateTopoOrder(firstBlockCommits);
+        firstBlockCommits = new ArrayList<TimedVcsCommit>(firstBlockCommits.subList(0, Math.min(firstBlockCommits.size(), commitCount)));
+      }
       logsToBuild.put(root, firstBlockCommits);
       refsByRoot.put(root, info.newRefs);
     }
@@ -479,7 +484,11 @@ public class VcsLogDataHolder implements Disposable, VcsLogDataProvider {
       VcsLogProvider logProvider = entry.getValue();
 
       StopWatch sw = StopWatch.start("readFirstBlock for " + root.getName());
-      List<? extends VcsFullCommitDetails> firstBlockDetails = logProvider.readFirstBlock(root, ordered, commitsCount);
+
+      boolean orderedForRepo = ordered && !logProvider.supportsFastUnorderedCommits(); // will order manually
+      int commitCountForRepo = orderedForRepo ? commitsCount : commitsCount * 2; // but need to request more commits
+
+      List<? extends VcsFullCommitDetails> firstBlockDetails = logProvider.readFirstBlock(root, orderedForRepo, commitCountForRepo);
       sw.report();
       sw = StopWatch.start("readAllRefs for" + root.getName());
       Collection<VcsRef> newRefs = logProvider.readAllRefs(root);

plugins/git4idea/src/git4idea/log/GitLogProvider.java

@@ -259,6 +259,11 @@ public class GitLogProvider implements VcsLogProvider {
     return GitBranchUtil.getBranches(myProject, root, true, true, commitHash.asString());
   }
 
+  @Override
+  public boolean supportsFastUnorderedCommits() {
+    return true;
+  }
+
   private static String prepareParameter(String paramName, String value) {
     return "--" + paramName + "=" + value; // no value quoting needed, because the parameter itself will be quoted by GeneralCommandLine
   }

plugins/hg4idea/src/org/zmlx/hg4idea/log/HgLogProvider.java

@@ -246,6 +246,11 @@ public class HgLogProvider implements VcsLogProvider {
     return HgHistoryUtil.getDescendingHeadsOfBranches(myProject, root, commitHash);
   }
 
+  @Override
+  public boolean supportsFastUnorderedCommits() {
+    return false;
+  }
+
   private static String prepareParameter(String paramName, String value) {
     return "--" + paramName + "=" + value; // no value escaping needed, because the parameter itself will be quoted by GeneralCommandLine
   }