merge with stable

mercurial/filemerge.py

@@ -138,9 +138,6 b' def filemerge(repo, mynode, orig, fcd, f'
     if not fco.cmp(fcd): # files identical?
         return None
 
-    if fca == fco: # backwards, use working dir parent as ancestor
-        fca = fcd.parents()[0]
-
     ui = repo.ui
     fd = fcd.path()
     binary = isbin(fcd) or isbin(fco) or isbin(fca)

mercurial/merge.py

@@ -270,7 +270,12 b' def applyupdates(repo, action, wctx, mct'
             repo.ui.debug("preserving %s for resolve of %s\n" % (f, fd))
             fcl = wctx[f]
             fco = mctx[f2]
-            fca = fcl.ancestor(fco, actx) or repo.filectx(f, fileid=nullrev)
+            if mctx == actx: # backwards, use working dir parent as ancestor
+                fca = fcl.parents()[0]
+            else:
+                fca = fcl.ancestor(fco, actx)
+            if not fca:
+                fca = repo.filectx(f, fileid=nullrev)
             ms.add(fcl, fco, fca, fd, flags)
             if f != fd and move:
                 moves.append(f)

tests/test-bisect.out

@@ -237,7 +237,7 b' user: test'
 date:        Thu Jan 01 00:00:01 1970 +0000
 summary:     msg 1
 
-abort: Inconsistent state, 31:58c80a7c8a40 is good and bad
+abort: starting revisions are not directly related
 error
 Testing changeset 15:e7fa0811edb0 (32 changesets remaining, ~5 tests)
 5cd978ea5149