rebase: don't use rebased node as dirstate p2 (BC)

When rebasing a node, we currently use the rebased node as p2 in the
dirstate until just before we commit it (we then change to the desired
parents). This p2 is visible to the user when the rebase gets
interrupted because of merge conflicts. That can be useful to the user
as a reminder of which commit is currently being rebased, but I
believe it's incorrect for a few reasons:

 * I think the dirstate parents should be the ones that will be set
   when the commit is created.

 * I think having two parents means that you're merging those two
   commits, but when rebasing, you're generally grafting, not merging.

 * When rebasing a merge commit, we should use the two desired parents
   as dirstate parents (and we clearly can't have the rebased node as
   a third dirstate parent).

 * `hg graft` (and `hg update --merge`) sets only one parent and `hg
   rebase` should be consistent with that.

I realize that this is a somewhat large user-visible change, but I
think it's worth it because it will simplify things quite a bit.

Differential Revision: https://phab.mercurial-scm.org/D7827

hgext/rebase.py

@@ -618,6 +618,7 b' class rebaseruntime(object):'
                         repo,
                         rev,
                         p1,
+                        p2,
                         base,
                         self.collapsef,
                         dest,
@@ -642,10 +643,6 b' class rebaseruntime(object):'
                 newnode = self._concludenode(rev, p1, p2, editor)
             else:
                 # Skip commit if we are collapsing
-                if self.inmemory:
-                    self.wctx.setbase(repo[p1])
-                else:
-                    repo.setparents(repo[p1].node())
                 newnode = None
             # Update the state
             if newnode is not None:
@@ -1468,7 +1465,7 b' def commitnode(repo, p1, p2, editor, ext'
         return newnode
 
 
-def rebasenode(repo, rev, p1, base, collapse, dest, wctx):
+def rebasenode(repo, rev, p1, p2, base, collapse, dest, wctx):
     """Rebase a single revision rev on top of p1 using base as merge ancestor"""
     # Merge phase
     # Update to destination and merge it with local
@@ -1502,6 +1499,7 b' def rebasenode(repo, rev, p1, base, coll'
         labels=[b'dest', b'source'],
         wc=wctx,
     )
+    wctx.setparents(p1ctx.node(), repo[p2].node())
     if collapse:
         copies.graftcopies(wctx, ctx, repo[dest])
     else:

relnotes/next

@@ -21,6 +21,11 b''
 
 == Backwards Compatibility Changes ==
 
+ * When `hg rebase` pauses for merge conflict resolution, the working
+   copy will no longer have the rebased node as a second parent. You
+   can use the new `conflictparents()` revset for finding the other
+   parent during a conflict.
+
 
 == Internal API Changes ==
 

tests/test-rebase-abort.t

@@ -236,7 +236,7 b' Rebase and abort without generating new '
   [1]
 
   $ hg tglog
-  @  4:draft 'C1'
+  %  4:draft 'C1'
   |
   o  3:draft 'B bis'
   |

tests/test-rebase-collapse.t

@@ -712,7 +712,7 b' Test aborted editor on final message'
   |
   | @  2: 82b8abf9c185 'D'
   | |
-  @ |  1: f899f3910ce7 'B'
+  % |  1: f899f3910ce7 'B'
   |/
   o  0: 4a2df7238c3b 'A'
   
@@ -736,7 +736,7 b' Test aborted editor on final message'
   unresolved conflicts (see hg resolve, then hg rebase --continue)
   [1]
   $ hg tglog
-  @  3: 63668d570d21 'C'
+  %  3: 63668d570d21 'C'
   |
   | @  2: 82b8abf9c185 'D'
   | |

tests/test-rebase-conflicts.t

@@ -456,15 +456,14 b' Test where the conflict happens when reb'
   warning: conflicts while merging conflict! (edit, then use 'hg resolve --mark')
   unresolved conflicts (see hg resolve, then hg rebase --continue)
   [1]
-The current parents are not 7 and 8 even though that's what we're merging
   $ hg tglog
   @  8:draft 'E'
   |
-  | o  7:draft 'D'
+  | @  7:draft 'D'
   |/
   o  6:draft 'C'
   |
-  | @    5:draft 'F'
+  | %    5:draft 'F'
   | |\
   | | o  4:draft 'E'
   | | |

tests/test-rebase-interruptions.t

@@ -294,7 +294,7 b' Test rebase interrupted by hooks'
   $ hg tglogp
   @  7: 401ccec5e39f secret 'C'
   |
-  | @  6: a0b2430ebfb8 secret 'F'
+  | o  6: a0b2430ebfb8 secret 'F'
   | |
   o |  5: 45396c49d53b public 'B'
   | |
@@ -345,7 +345,7 b' Test rebase interrupted by hooks'
   $ hg tglogp
   @  7: 401ccec5e39f secret 'C'
   |
-  | @  6: a0b2430ebfb8 secret 'F'
+  | o  6: a0b2430ebfb8 secret 'F'
   | |
   o |  5: 45396c49d53b public 'B'
   | |
@@ -395,7 +395,7 b' Test rebase interrupted by hooks'
   $ hg tglogp
   @  7: 401ccec5e39f secret 'C'
   |
-  | @  6: a0b2430ebfb8 secret 'F'
+  | o  6: a0b2430ebfb8 secret 'F'
   | |
   o |  5: 45396c49d53b public 'B'
   | |

tests/test-rebase-obsolete.t

@@ -1795,19 +1795,15 b' rebasestate may contain hidden hashes. "'
   $ hg log -G
   @  2:b18e25de2cf5 D
   |
-  | @  1:2ec65233581b B (pruned using prune)
-  |/
   o  0:426bada5c675 A
   
   $ hg summary
   parent: 2:b18e25de2cf5 tip
    D
-  parent: 1:2ec65233581b  (obsolete)
-   B
   branch: default
-  commit: 2 modified, 1 unknown, 1 unresolved (merge)
+  commit: 1 modified, 1 added, 1 unknown, 1 unresolved
   update: (current)
-  phases: 3 draft
+  phases: 2 draft
   rebase: 0 rebased, 2 remaining (rebase --continue)
 
   $ hg rebase --abort

tests/test-rebase-parameters.t

@@ -481,11 +481,9 b' Test --tool parameter:'
   $ hg summary
   parent: 1:56daeba07f4b 
    c2
-  parent: 2:e4e3f3546619 tip
-   c2b
   branch: default
-  commit: 1 modified, 1 unresolved (merge)
-  update: (current)
+  commit: 1 unresolved (clean)
+  update: 1 new changesets, 2 branch heads (merge)
   phases: 3 draft
   rebase: 0 rebased, 1 remaining (rebase --continue)
 

tests/test-rebase-transaction.t

@@ -114,7 +114,7 b' continued'
   |
   | @  4: Z
   | |
-  @ |  3: C
+  % |  3: C
   | |
   | o  2: Y
   | |
@@ -123,9 +123,9 b' continued'
   o  0: A
   
   $ hg st
-  M C
   M conflict
   A B
+  A C
   ? conflict.orig
   $ echo resolved > conflict
   $ hg resolve -m