copies: filter out copies grafted from another branch

Consider this simple history:

```
@  3 modify y
|
o  2 copy x to y, modify x
|
| o  1 copy x to y, modify x
|/
o  0 add x

```

If we now rebase commit 3 onto 1, Mercurial will look for copies
between commit 2 and commit 1. It does that by going backwards from 2
to 0 and then forwards from 0 to 1. It will find that x was copied to
y, since that was what happened on the path between them (namely in
commit 1). That leads Mercurial to do a 3-way merge between y@3 and
y@1 with x@2 as base. We want to use y@2 as base instead. That's also
what happened until commit 1d6d1a15. This patch fixes the regression
by adding another filtering step when chaining copies via a
diffbase. The new filtering step removes copies that were the same
between the two branches (same source and destination, but not
necessarily the same contents).

Differential Revision: https://phab.mercurial-scm.org/D10120

mercurial/copies.py

@@ -763,6 +763,11 b' def pathcopies(x, y, match=None):'
             base = x
         x_copies = _forwardcopies(a, x)
         y_copies = _forwardcopies(a, y, base, match=match)
+        same_keys = set(x_copies) & set(y_copies)
+        for k in same_keys:
+            if x_copies.get(k) == y_copies.get(k):
+                del x_copies[k]
+                del y_copies[k]
         x_backward_renames = _reverse_renames(x_copies, x, match)
         copies = _chain(
             x_backward_renames,

tests/test-copies.t

@@ -398,11 +398,8 b' should not report the copy.'
   x -> y
   $ hg debugp1copies -r 2
   x -> y
-BROKEN: These two should not report any copies
   $ hg debugpathcopies 1 2
-  x -> y
   $ hg debugpathcopies 2 1
-  x -> y
 
 Copy x to y on one side of merge, create y and rename to z on the other side.
   $ newrepo

tests/test-graft.t

@@ -223,10 +223,6 b' Graft out of order, skipping a merge and'
   committing changelog
   updating the branch cache
   grafting 5:97f8bfe72746 "5"
-    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
-     on local side:
-      src: 'c' -> dst: 'b' 
-    checking for directory renames
   resolving manifests
    branchmerge: True, force: True, partial: False
    ancestor: 4c60f11aa304, local: 6b9e5368ca4e+, remote: 97f8bfe72746
@@ -240,10 +236,6 b' Graft out of order, skipping a merge and'
   $ HGEDITOR=cat hg graft 4 3 --log --debug
   scanning for duplicate grafts
   grafting 4:9c233e8e184d "4"
-    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
-     on local side:
-      src: 'c' -> dst: 'b' 
-    checking for directory renames
   resolving manifests
    branchmerge: True, force: True, partial: False
    ancestor: 4c60f11aa304, local: 1905859650ec+, remote: 9c233e8e184d