[PATCH 2 of 2 stable] graft: fix graft across merges of duplicates of grafted changes

[Mads Kiilerich]

# HG changeset patch
# User Mads Kiilerich <madski at unity3d.com>
# Date 1494283376 -7200
#      Tue May 09 00:42:56 2017 +0200
# Branch stable
# Node ID dd256de590dfd363fa5d497d566d456f471b8d52
# Parent  6710017995b4e8b361d6ad5b897ff7d0cc658285
graft: fix graft across merges of duplicates of grafted changes

Graft used findmissingrevs to find the candidates for graft duplicates in the
destination. That function operates with the constraint:

  2. N is not an ancestor of any node in 'common'

For our purpose, we do however need:

  2. There are nodes in 'common' that doesn't have N as ancestor

The right candiates for graft duplicates could be computed with a revset:

  only(destination,transitiveroots(graftset))

where transitiveroots would be a revset function for 'transitive root' and
return changesets in set with no ancestor changeset in set. There doesn't seem
to be any such function readily available, and we thus use the approximation of
just using the smallest revision in the graft set.

This change will graft more correctly, but it will also in some cases make
graft slower by making it search through a bigger and unnecessary large sets of
changes to find duplicates.

diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2295,7 +2295,8 @@ def _dograft(ui, repo, *revs, **opts):
         # check ancestors for earlier grafts
         ui.debug('scanning for duplicate grafts\n')
 
-        for rev in repo.changelog.findmissingrevs(revs, [crev]):
+        expr = revsetlang.formatspec('only(%d,min(%ld))', crev, revs)
+        for rev in scmutil.revrange(repo, [expr]):
             ctx = repo[rev]
             n = ctx.extra().get('source')
             if n in ids:
diff --git a/tests/test-graft.t b/tests/test-graft.t
--- a/tests/test-graft.t
+++ b/tests/test-graft.t
@@ -1341,16 +1341,15 @@ Grafting of plain changes correctly dete
   skipping already grafted revision 5:43e9eb70dab0 (was grafted from 4:6c9a1289e5f1)
   grafting 2:42127f193bcd "b"
 
-Extending the graft range to include a merge will unfortunately make us miss
-that 3 and 5 should be skipped:
+Extending the graft range to include a (skipped) merge of 3 will not prevent us from
+also detecting that both 3 and 5 should be skipped:
 
   $ hg up -qCr 4
   $ hg graft --tool :local -r 2::7
   skipping ungraftable merge revision 6
+  skipping already grafted revision 3:ca093ca2f1d9 (was grafted from 1:13ec5badbf2a)
   skipping already grafted revision 5:43e9eb70dab0 (was grafted from 4:6c9a1289e5f1)
   grafting 2:42127f193bcd "b"
-  grafting 3:ca093ca2f1d9 "x"
-  note: graft of 3:ca093ca2f1d9 created no changes to commit
   grafting 7:d3c3f2b38ecc "xx"
   note: graft of 7:d3c3f2b38ecc created no changes to commit