# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@octobus.net>
# Date 1512861606 -3600
# Node ID 8dcb9e929a5773e350347fb23e8d27458f437b17
# Parent  d57400a0f4c3e51e85279e52c5376e885d622397
stablerange: fallback to a more naive approach to find subrange

As suspected, using "bheads" was bit good enough in some case and we have to
fall back to the approach used in "basic".

On the evolve repo (about 3K changeset) this approach is about 60% slower than
the previous (wrong) code.

diff -r d57400a0f4c3 -r 8dcb9e929a57 hgext3rd/evolve/stablerange.py
--- a/hgext3rd/evolve/stablerange.py	Sat Dec 09 22:49:07 2017 +0100
+++ b/hgext3rd/evolve/stablerange.py	Sun Dec 10 00:20:06 2017 +0100
@@ -570,7 +570,6 @@
 
     def _slicesrangeatmerge(self, repo, rangeid, globalindex):
         localindex = globalindex - rangeid[1]
-        cl = repo.changelog
 
         result = []
         allrevs = self.revsfromrange(repo, rangeid)
@@ -581,19 +580,24 @@
             # revision we needs
             result.append((bottomrevs[-1], rangeid[1]))
         else:
-            parentrevs = cl.parentrevs
-            parents = self._parents
-            bheads = set(bottomrevs)
-            du = bheads.difference_update
-            for r in bottomrevs:
-                du(parents(r, parentrevs))
-            seen = 0
-            for r in bottomrevs:
-                seen += 1
-                # XXX bheads might not be a good enough criteria
-                if r in bheads:
-                    result.append((r, self.depthrev(repo, r) - seen))
-                    seen = 0
+            head = None
+            headrange = None
+            skip = None
+            for rev in bottomrevs[::-1]:
+                if head is None:
+                    head = rev
+                    headrange = self.revsfromrange(repo, (head, 0))
+                    skip = self.depthrev(repo, rev) - 1
+                elif rev != headrange[skip - 1]:
+                    result.append((head, skip))
+                    head = rev
+                    headrange = self.revsfromrange(repo, (head, 0))
+                    skip = self.depthrev(repo, rev) - 1
+                else:
+                    skip -= 1
+            result.append((head, skip))
+
+            result.reverse()
 
         # top part is trivial
         top = (rangeid[0], globalindex)