[PATCH 3 of 5] phases: move root phase assignment to it's own function

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1412707357 25200
#      Tue Oct 07 11:42:37 2014 -0700
# Node ID 9291d6a89c9b9bf93cbb920c98795fa13fbd6fa0
# Parent  34e934d15e8c9a8c5809dc1909cbdfcba1017603
phases: move root phase assignment to it's own function

This moves the initial root phase assignment to it's own function. Future
patches which make phase calculations lazy will use this function to pre-fill
certain phases which can be deduced from the roots.

diff --git a/mercurial/phases.py b/mercurial/phases.py
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -167,6 +167,8 @@ class phasecache(object):
         if self._phaserevs is None:
             repo = repo.unfiltered()
             revs = [public] * len(repo.changelog)
+            self._phaserevs = revs
+            self._populatephaseroots(repo)
             for phase in trackedphases:
                 roots = map(repo.changelog.rev, self.phaseroots[phase])
                 if roots:
@@ -174,11 +176,27 @@ class phasecache(object):
                         revs[rev] = phase
                     for rev in repo.changelog.descendants(roots):
                         revs[rev] = phase
-            self._phaserevs = revs
         return self._phaserevs
+
     def invalidate(self):
         self._phaserevs = None
 
+    def _populatephaseroots(self, repo):
+        """Fills the _phaserevs cache with phases for the roots.
+        """
+        cl = repo.changelog
+        phaserevs = self._phaserevs
+        for phase in trackedphases:
+            roots = map(cl.rev, self.phaseroots[phase])
+            for root in roots:
+                phaserevs[root] = phase
+                # We know that the parent of a root has a phase less than
+                # the root, so if phase == 1, the parent must be phase 0.
+                if phase == 1:
+                    for parent in cl.parentrevs(root):
+                        if parent != -1:
+                            phaserevs[parent] = 0
+
     def phase(self, repo, rev):
         # We need a repo argument here to be able to build _phaserevs
         # if necessary. The repository instance is not stored in