[PATCH 2 of 2 stable] rebase: handle rebasing of merges of destination ancestors

[Mads Kiilerich]

# HG changeset patch
# User Mads Kiilerich <madski at unity3d.com>
# Date 1415409531 -3600
#      Sat Nov 08 02:18:51 2014 +0100
# Branch stable
# Node ID 4f80b7a3cdf219d1c8e5b3a7f2d539cd035cf8c4
# Parent  8f689654b7d3d6b7c2b370cd5e38198b625e4fc6
rebase: handle rebasing of merges of destination ancestors

A situation with several merges from another branch can be 'straightened out'
by rebasing (or grafting) on top of the other branch. One problem is merges
that merges an ancestor of the rebase destination. Graft will skip such merges
as 'ungraftable merge revision'. Rebase would try to rebase them ... and could
fail.

Now, the problem is solved by skipping such ancestor merges when rebasing.

diff --git a/hgext/rebase.py b/hgext/rebase.py
--- a/hgext/rebase.py
+++ b/hgext/rebase.py
@@ -547,7 +547,21 @@ def rebasenode(repo, rev, p1, state, col
         base = repo[rev].p1().node()
     else:
         # In case of merge, we need to pick the right parent as merge base.
-        #
+
+        margedancestors = list(repo.revs('parents(%d)&::%d',
+                                         repo[rev].rev(), repo[p1].rev()))
+        if margedancestors:
+            repo.ui.warn(_('%s is merging %s which is an ancestor of '
+                           'the rebase target and is ignored\n') %
+                         (rev, margedancestors[0]))
+            # TODO: If all ancestors all the way back to 'branching point' has
+            # been rebased (no cherry picking), we could use
+            #   base = repo[margedancestors[0]].node()
+            # to use the merge snapshot as a checkpoint to verify that rebase
+            # conflicts has been resolved as the merge conflicts was resolved.
+            # If resolved the same way, the rebase of the merge willbe a noop.
+            return None
+
         # Imagine we have:
         # - M: currently rebase revision in this step
         # - A: one parent of M
diff --git a/tests/test-rebase-collapse.t b/tests/test-rebase-collapse.t
--- a/tests/test-rebase-collapse.t
+++ b/tests/test-rebase-collapse.t
@@ -113,6 +113,7 @@ Rebasing E onto H:
 
   $ hg phase --force --secret 6
   $ hg rebase --source 4 --collapse
+  6 is merging 5 which is an ancestor of the rebase target and is ignored
   saved backup bundle to $TESTTMP/a2/.hg/strip-backup/*-backup.hg (glob)
 
   $ hg tglog
@@ -153,6 +154,7 @@ Rebasing G onto H with custom message:
   > true
   > EOF
   $ HGEDITOR="sh $TESTTMP/checkeditform.sh" hg rebase --source 4 --collapse -m 'custom message' -e
+  6 is merging 5 which is an ancestor of the rebase target and is ignored
   HGEDITFORM=rebase.collapse
   saved backup bundle to $TESTTMP/a3/.hg/strip-backup/*-backup.hg (glob)
 
diff --git a/tests/test-rebase-detach.t b/tests/test-rebase-detach.t
--- a/tests/test-rebase-detach.t
+++ b/tests/test-rebase-detach.t
@@ -325,6 +325,7 @@ Verify that target is not selected as ex
   $ hg ci -m "J"
 
   $ hg rebase -s 8 -d 7 --collapse --config ui.merge=internal:other
+  9 is merging 7 which is an ancestor of the rebase target and is ignored
   saved backup bundle to $TESTTMP/a6/.hg/strip-backup/*-backup.hg (glob)
 
   $ hg tglog
diff --git a/tests/test-rebase-newancestor.t b/tests/test-rebase-newancestor.t
--- a/tests/test-rebase-newancestor.t
+++ b/tests/test-rebase-newancestor.t
@@ -76,15 +76,11 @@ that often happens when trying to rebase
   $ touch devstuff
   $ hg ci -Aqm 'real dev stuff'
   $ hg rebase -r 'branch(dev)' -d default
-  remote changed f which local deleted
-  use (c)hanged version or leave (d)eleted? c
-  local changed f which remote deleted
-  use (c)hanged version or (d)elete? c
+  4 is merging 1 which is an ancestor of the rebase target and is ignored
+  5 is merging 2 which is an ancestor of the rebase target and is ignored
   saved backup bundle to $TESTTMP/repo2/.hg/strip-backup/*-backup.hg (glob)
   $ hg tglog
-  @  4: 'real dev stuff'
-  |
-  o  3: 'merge f stuff'
+  @  3: 'real dev stuff'
   |
   o  2: 'remove f'
   |
diff --git a/tests/test-rebase-scenario-global.t b/tests/test-rebase-scenario-global.t
--- a/tests/test-rebase-scenario-global.t
+++ b/tests/test-rebase-scenario-global.t
@@ -117,6 +117,7 @@ E onto H - skip of G:
   $ cd a3
 
   $ hg rebase -s 4 -d 7
+  6 is merging 5 which is an ancestor of the rebase target and is ignored
   saved backup bundle to $TESTTMP/a3/.hg/strip-backup/*-backup.hg (glob)
 
   $ hg tglog
@@ -143,6 +144,7 @@ F onto E - rebase of a branching point (
   $ cd a4
 
   $ hg rebase -s 5 -d 4
+  6 is merging 4 which is an ancestor of the rebase target and is ignored
   saved backup bundle to $TESTTMP/a4/.hg/strip-backup/*-backup.hg (glob)
 
   $ hg tglog