merge: migrate to context manager for changing dirstate parents

mercurial/merge.py

@@ -1696,7 +1696,7 def update(repo, node, branchmerge, forc
         stats = applyupdates(repo, actions, wc, p2, overwrite, labels=labels)
 
         if not partial:
-            repo.dirstate.beginparentchange()
+            with repo.dirstate.parentchange():
             repo.setparents(fp1, fp2)
             recordupdates(repo, actions, branchmerge)
             # update completed, clear state
@@ -1704,7 +1704,6 def update(repo, node, branchmerge, forc
 
             if not branchmerge:
                 repo.dirstate.setbranch(p2.branch())
-            repo.dirstate.endparentchange()
 
     if not partial:
         repo.hook('update', parent1=xp1, parent2=xp2, error=stats[3])
@@ -1742,10 +1741,9 def graft(repo, ctx, pctx, labels, keepp
         parents.remove(pctx)
         pother = parents[0].node()
 
-    repo.dirstate.beginparentchange()
+    with repo.dirstate.parentchange():
     repo.setparents(repo['.'].node(), pother)
     repo.dirstate.write(repo.currenttransaction())
     # fix up dirstate for copies and renames
     copies.duplicatecopies(repo, ctx.rev(), pctx.rev())
-    repo.dirstate.endparentchange()
     return stats