diff --git a/mercurial/phases.py b/mercurial/phases.py
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -352,7 +352,7 @@
                 _trackphasechange(phasetracking, rev, None, revphase)
         repo.invalidatevolatilesets()
 
-    def advanceboundary(self, repo, tr, targetphase, nodes):
+    def advanceboundary(self, repo, tr, targetphase, nodes, dryrun=None):
         """Set all 'nodes' to phase 'targetphase'
 
         Nodes with a phase lower than 'targetphase' are not affected.
@@ -366,6 +366,17 @@
 
         repo = repo.unfiltered()
 
+        rejected = list() # set of rejected nodes
+        changes = [set(), set(), set()]
+        # `changes` stores revs (whose phases will be changed) in three
+        # different sets where each set is for different phase and ordered
+        # from --public to --secret.
+
+        # Find nodes that are not in a compatible phase and will be rejected
+        getphase = repo._phasecache.phase
+        rejected = [repo[n].rev() for n in nodes
+                    if getphase(repo, repo[n].rev()) < targetphase]
+
         delroots = [] # set of root deleted by this path
         for phase in xrange(targetphase + 1, len(allphases)):
             # filter nodes that are not in a compatible phase already
@@ -377,6 +388,12 @@
             olds = self.phaseroots[phase]
 
             affected = repo.revs('%ln::%ln', olds, nodes)
+            if dryrun:
+                faffected = filter(lambda x: getphase(repo,
+                                                      repo[x].rev()) == phase,
+                                   affected)
+                changes[phase].update(faffected)
+                continue
             for r in affected:
                 _trackphasechange(phasetracking, r, self.phase(repo, r),
                                   targetphase)
@@ -387,6 +404,8 @@
                 self._updateroots(phase, roots, tr)
                 # some roots may need to be declared for lower phases
                 delroots.extend(olds - roots)
+        if dryrun:
+            return rejected, changes
         # declare deleted root in the target phase
         if targetphase != 0:
             self._retractboundary(repo, tr, targetphase, delroots)
@@ -478,16 +497,30 @@
         # (see branchmap one)
         self.invalidate()
 
-def advanceboundary(repo, tr, targetphase, nodes):
+def advanceboundary(repo, tr, targetphase, nodes, dryrun=None):
     """Add nodes to a phase changing other nodes phases if necessary.
 
     This function move boundary *forward* this means that all nodes
     are set in the target phase or kept in a *lower* phase.
 
-    Simplify boundary to contains phase roots only."""
+    Simplify boundary to contains phase roots only.
+
+    If dryrun is true then it will not perform any action and only calculate
+    `rejected` and `changes`, where:
+    rejected - list of rejected nodes
+    changes - list of three sets (each for different phase and ordered
+              from --public to --secret) where each set contains those
+              revisions whose phases are changed or can be changed (depends
+              of dryrun value) from their current phase to targetphase.
+    
+    Returns `rejected` and `changes`.
+    """
     phcache = repo._phasecache.copy()
-    phcache.advanceboundary(repo, tr, targetphase, nodes)
-    repo._phasecache.replace(phcache)
+    rejected, changes = phcache.advanceboundary(repo, tr, targetphase, nodes,
+                                                dryrun=dryrun)
+    if not dryrun:
+        repo._phasecache.replace(phcache)
+    return rejected, changes
 
 def retractboundary(repo, tr, targetphase, nodes):
     """Set nodes back to a phase changing other nodes phases if