update: set custom conflict label for base commit

Differential Revision: https://phab.mercurial-scm.org/D12022

mercurial/merge.py

@@ -2280,7 +2280,7 def update(ctx, updatecheck=None, wc=Non
         ctx.rev(),
         branchmerge=False,
         force=False,
-        labels=[b'working copy', b'destination'],
+        labels=[b'working copy', b'destination', b'working copy parent'],
         updatecheck=updatecheck,
         wc=wc,
     )

tests/test-conflict.t

@@ -308,7 +308,7 internal:mergediff
   2
   3
   <<<<<<<
-  ------- base
+  ------- working copy parent
   +++++++ working copy
    4
   +4.5
@@ -346,7 +346,7 copy in full and the diff from base to d
   3.5
   4.5
   5.5
-  ------- base
+  ------- working copy parent
   +++++++ destination
    3
   -4

tests/test-update-branches.t

@@ -292,14 +292,14 Cases are run as shown in that table, ro
   # To mark files as resolved:  hg resolve --mark FILE
   
   $ cat a
-  <<<<<<< working copy: 6efa171f091b - test: 3
+  <<<<<<< working copy:        6efa171f091b - test: 3
   three
   dirty
-  ||||||| base:         6efa171f091b - test: 3
+  ||||||| working copy parent: 6efa171f091b - test: 3
   three
   =======
   four
-  >>>>>>> destination:  d047485b3896 b1 - test: 4
+  >>>>>>> destination:         d047485b3896 b1 - test: 4
   $ rm a.orig
 
   $ echo 'update.check = noconflict' >> .hg/hgrc