[PATCH 4 of 7] destutil: explicitly remove descendants from destmerge candidates

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1454951526 -3600
#      Mon Feb 08 18:12:06 2016 +0100
# Node ID 4cccc4e95970f32885a3e896c668f3e00b11bd45
# Parent  b989484b0b89e62846830c0ce20bb567b2d866df
# EXP-Topic destination
# Available At http://hg.netv6.net/marmoute-wip/mercurial/
#              hg pull http://hg.netv6.net/marmoute-wip/mercurial/ -r 4cccc4e95970
destutil: explicitly remove descendants from destmerge candidates

While 'hg merge' will refuse to pick a default destination if the working copy
is not on a head, this will be a common and valid case for rebase. In this
case, we will need to exclude from the candidate destination all descendants
from the rebased set.

We make a step forward in that direction by removing descendants of the working
copy from the candidate destinations instead of manually filtering the working
copy parent at the end of the process.

A later changeset will make it possible to specify the source set.

diff --git a/mercurial/destutil.py b/mercurial/destutil.py
--- a/mercurial/destutil.py
+++ b/mercurial/destutil.py
@@ -210,45 +210,46 @@ def _destmergebranch(repo, action='merge
     """find merge destination based on branch heads"""
     node = None
     parent = repo.dirstate.p1()
     branch = repo.dirstate.branch()
     bheads = repo.branchheads(branch)
-    nbhs = [bh for bh in bheads if not repo[bh].bookmarks()]
 
     if parent not in bheads:
         # Case A: working copy if not on a head.
         #
         # This is probably a user mistake We bailout pointing at 'hg update'
         if len(repo.heads()) <= 1:
             msg, hint = msgdestmerge['nootherheadsbehind'][action]
         else:
             msg, hint = msgdestmerge['notatheads'][action]
         raise error.Abort(msg, hint=hint)
-    elif len(nbhs) > 2:
-        # Case B: There is more than 2 anonymous heads
+    # remove current head from the set
+    bheads = [bh for bh in bheads if bh != parent]
+    # filters out bookmarked heads
+    nbhs = [bh for bh in bheads if not repo[bh].bookmarks()]
+    if len(nbhs) > 1:
+        # Case B: There is more than 1 other anonymous heads
         #
         # This means that there will be more than 1 candidate. This is
         # ambiguous. We abort asking the user to pick as explicit destination
         # instead.
         msg, hint = msgdestmerge['toomanyheads'][action]
-        msg %= (branch, len(bheads))
+        msg %= (branch, len(bheads) + 1)
         raise error.Abort(msg, hint=hint)
-    elif len(nbhs) <= 1:
-        # Case B: There is no other anonymous head that the one we are one
+    elif not nbhs:
+        # Case B: There is no other anonymous heads
         #
         # This means that there is no natural candidate to merge with.
         # We abort, with various messages for various cases.
-        if len(bheads) > 1:
+        if bheads:
             msg, hint = msgdestmerge['bookmarkedheads'][action]
         elif len(repo.heads()) > 1:
             msg, hint = msgdestmerge['nootherbranchheads'][action]
             msg %= branch
         else:
             msg, hint = msgdestmerge['nootherheads'][action]
         raise error.Abort(msg, hint=hint)
-    elif parent == nbhs[0]:
-        node = nbhs[-1]
     else:
         node = nbhs[0]
     assert node is not None
     return node