--- a/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialVcsSupport.java	Thu Feb 28 19:13:52 2013 +0400
+++ b/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/MercurialVcsSupport.java	Thu Feb 28 20:38:04 2013 +0400
@@ -477,8 +477,8 @@
                                                @NotNull RepositoryStateData toState,
                                                @NotNull CheckoutRules rules) throws VcsException {
     List<ModificationData> changes = new ArrayList<ModificationData>();
-    OperationContext ctx = new OperationContext(this, myRepoFactory);
-    Set<String> prevStateRevisions = new HashSet<String>(fromState.getBranchRevisions().values());
+    HgVcsRoot hgRoot = myHgVcsRootFactory.createHgRoot(root);
+    OperationContext ctx = new OperationContext(this, myRepoFactory, myHgPathProvider, fromState, toState);
     for (Map.Entry<String, String> entry : toState.getBranchRevisions().entrySet()) {
       String branch = entry.getKey();
       String toRevision = entry.getValue();
@@ -488,7 +488,7 @@
       if (toRevision.equals(fromRevision))
         continue;
 
-      List<String> fromRevisions = getFromRevisionsForBranch(ctx, root, prevStateRevisions, fromRevision, toRevision);
+      List<String> fromRevisions = ctx.getFromRevisionsForBranch(hgRoot, fromRevision, toRevision);
       List<ModificationData> branchChanges = collectChanges(ctx, root, fromRevisions, toRevision, rules);
       for (ModificationData change : branchChanges) {
         if (!ctx.isReportedModification(change)) {
@@ -502,52 +502,6 @@
   }
 
 
-  /**
-   * Collecting changes is per branch. We usually take branch revision in fromState,
-   * revision in toState and collect changes between them. This can lead to redundant
-   * changes being reported. Consider the following graph:
-   *
-   * default
-   * | topic
-   * |  |
-   * V  V
-   *101
-   * |\
-   * | 100
-   * | |
-   *99 |
-   *.....
-   * | |
-   * |/
-   * 1
-   *
-   * When changes are collected between states {default:99, topic:100} and {default: 101, topic:100},
-   * plugin reports changes from 1 to 101, even though it probably has reported changes reachable
-   * from 100 earlier.
-   *
-   * This method detects such a case and returns [99, 100] as fromRevisions for 101.
-   */
-  @NotNull
-  private List<String> getFromRevisionsForBranch(@NotNull OperationContext ctx,
-                                                 @NotNull VcsRoot root,
-                                                 @NotNull Set<String> prevStateRevisions,
-                                                 @NotNull String fromRevision,
-                                                 @NotNull String toRevision) throws VcsException {
-    List<String> fromRevisions = new ArrayList<String>();
-    fromRevisions.add(fromRevision);
-
-    HgVcsRoot hgRoot = myHgVcsRootFactory.createHgRoot(root);
-    ctx.syncRepository(hgRoot);
-    ServerHgRepo repo = createRepo(ctx, hgRoot);
-    List<String> parentRevisions = repo.parents().ofRevision(toRevision).call();
-    for (String parent : parentRevisions) {
-      if (!fromRevision.equals(parent) && prevStateRevisions.contains(parent))
-        fromRevisions.add(parent);
-    }
-
-    return fromRevisions;
-  }
-
   @NotNull
   public List<ModificationData> collectChanges(@NotNull VcsRoot fromRoot, @NotNull String fromRootRevision,
                                                @NotNull VcsRoot toRoot, @Nullable String toRootRevision,
@@ -594,7 +548,9 @@
   }
 
   public List<ModificationData> collectChanges(@NotNull VcsRoot root, @NotNull String fromVersion, @Nullable String currentVersion, @NotNull CheckoutRules checkoutRules) throws VcsException {
-    OperationContext ctx = new OperationContext(this, myRepoFactory);
+    if (currentVersion == null)
+      return emptyList();
+    OperationContext ctx = new OperationContext(this, myRepoFactory, myHgPathProvider, fromVersion, currentVersion);
     List<ModificationData> changes = collectChanges(ctx, root, asList(fromVersion), currentVersion, checkoutRules);
     changes.addAll(getSubrepoChanges(ctx, root, changes));
     return changes;

--- a/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/OperationContext.java	Thu Feb 28 19:13:52 2013 +0400
+++ b/mercurial-server/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/OperationContext.java	Thu Feb 28 20:38:04 2013 +0400
@@ -4,6 +4,7 @@
 import jetbrains.buildServer.buildTriggers.vcs.mercurial.command.AuthSettings;
 import jetbrains.buildServer.buildTriggers.vcs.mercurial.command.HgVcsRoot;
 import jetbrains.buildServer.vcs.ModificationData;
+import jetbrains.buildServer.vcs.RepositoryStateData;
 import jetbrains.buildServer.vcs.VcsException;
 import jetbrains.buildServer.vcs.VcsRoot;
 import org.jetbrains.annotations.NotNull;
@@ -16,6 +17,9 @@
 
   private final MercurialVcsSupport myVcs;
   private final RepoFactory myRepoFactory;
+  private final HgPathProvider myHgPathProvider;
+  private final RepositoryStateData myFromState;
+  private final RepositoryStateData myToState;
   private Set<File> mySyncedDirs = new HashSet<File>();
   private Map<String, HgVersion> myHgVersions = new HashMap<String, HgVersion>();
   private Map<String, Set<SubrepoChangesInterval>> myProcessedSubrepoChanges = new HashMap<String, Set<SubrepoChangesInterval>>();//subrepo url -> processed changes intervals
@@ -23,11 +27,24 @@
   private Map<File, ServerHgRepo> myRepos = new HashMap<File, ServerHgRepo>();
 
   public OperationContext(@NotNull MercurialVcsSupport vcs,
-                          @NotNull RepoFactory repoFactory) {
+                          @NotNull RepoFactory repoFactory,
+                          @NotNull HgPathProvider hgPathProvider,
+                          @NotNull RepositoryStateData fromState,
+                          @NotNull RepositoryStateData toState) {
     myVcs = vcs;
     myRepoFactory = repoFactory;
+    myHgPathProvider = hgPathProvider;
+    myFromState = fromState;
+    myToState = toState;
   }
 
+  public OperationContext(@NotNull MercurialVcsSupport vcs,
+                          @NotNull RepoFactory repoFactory,
+                          @NotNull HgPathProvider hgPathProvider,
+                          @NotNull String fromVersion,
+                          @NotNull String toVersion) {
+    this(vcs, repoFactory, hgPathProvider, RepositoryStateData.createSingleVersionState(fromVersion), RepositoryStateData.createSingleVersionState(toVersion));
+  }
 
   public void syncRepository(@NotNull final HgVcsRoot root) throws VcsException {
     File dir = myVcs.getWorkingDir(root);
@@ -98,6 +115,51 @@
     return revisions;
   }
 
+
+  /**
+   * Collecting changes is per branch. We usually take branch revision in fromState,
+   * revision in toState and collect changes between them. This can lead to redundant
+   * changes being reported. Consider the following graph:
+   *
+   * default
+   * | topic
+   * |  |
+   * V  V
+   *101
+   * |\
+   * | 100
+   * | |
+   *99 |
+   *.....
+   * | |
+   * |/
+   * 1
+   *
+   * When changes are collected between states {default:99, topic:100} and {default: 101, topic:100},
+   * plugin reports changes from 1 to 101, even though it probably has reported changes reachable
+   * from 100 earlier.
+   *
+   * This method detects such a case and returns [99, 100] as fromRevisions for 101.
+   */
+  @NotNull
+  public List<String> getFromRevisionsForBranch(@NotNull HgVcsRoot root,
+                                                @NotNull String fromRevision,
+                                                @NotNull String toRevision) throws VcsException {
+    List<String> fromRevisions = new ArrayList<String>();
+    fromRevisions.add(fromRevision);
+
+    syncRepository(root);
+
+    ServerHgRepo repo = createRepo(myVcs.getWorkingDir(root), myHgPathProvider.getHgPath(root), root.getAuthSettings());
+    List<String> parentRevisions = repo.parents().ofRevision(toRevision).call();
+    for (String parent : parentRevisions) {
+      if (!fromRevision.equals(parent) && myFromState.getBranchRevisions().values().contains(parent))
+        fromRevisions.add(parent);
+    }
+
+    return fromRevisions;
+  }
+
   private final static class SubrepoChangesInterval extends Pair<List<String>, String> {
     private SubrepoChangesInterval(@NotNull List<String> prevRevisions, @NotNull String currentRevision) {
       super(prevRevisions, currentRevision);