resolve: use "other" changeset from merge state (issue4163)

We can use the "other" data from the recorded merge state instead of inferring
what the other could be from working copy parent. This will allow resolve to
fulfil its duty even when the second parent have been dropped.

Most direct benefit is fixing a regression in backout.

mercurial/commands.py

@@ -4961,7 +4961,6 b' def resolve(ui, repo, *pats, **opts):'
                 ms.mark(f, "u")
             else:
                 wctx = repo[None]
-                mctx = wctx.parents()[-1]
 
                 # backup pre-resolve (merge uses .orig for its own purposes)
                 a = repo.wjoin(f)
@@ -4970,7 +4969,7 b' def resolve(ui, repo, *pats, **opts):'
                 try:
                     # resolve file
                     ui.setconfig('ui', 'forcemerge', opts.get('tool', ''))
-                    if ms.resolve(f, wctx, mctx):
+                    if ms.resolve(f, wctx):
                         ret = 1
                 finally:
                     ui.setconfig('ui', 'forcemerge', '')

mercurial/merge.py

@@ -186,11 +186,12 b' class mergestate(object):'
     def mark(self, dfile, state):
         self._state[dfile][0] = state
         self._dirty = True
-    def resolve(self, dfile, wctx, octx):
+    def resolve(self, dfile, wctx):
         if self[dfile] == 'r':
             return 0
         stateentry = self._state[dfile]
         state, hash, lfile, afile, anode, ofile, onode, flags = stateentry
+        octx = self._repo[self._other]
         fcd = wctx[dfile]
         fco = octx[ofile]
         fca = self._repo.filectx(afile, fileid=anode)
@@ -641,7 +642,7 b' def applyupdates(repo, actions, wctx, mc'
                                  overwrite)
                 continue
             audit(fd)
-            r = ms.resolve(fd, wctx, mctx)
+            r = ms.resolve(fd, wctx)
             if r is not None and r > 0:
                 unresolved += 1
             else:

tests/test-backout.t

@@ -408,3 +408,93 b' on branch1, so no file1 and file2:'
   update: (current)
 
   $ cd ..
+
+
+Test usage of `hg resolve` in case of conflict
+(issue4163)
+
+  $ hg init issue4163
+  $ cd issue4163
+  $ touch foo
+  $ hg add foo
+  $ cat > foo << EOF
+  > one
+  > two
+  > three
+  > four
+  > five
+  > six
+  > seven
+  > height
+  > nine
+  > ten
+  > EOF
+  $ hg ci -m 'initial'
+  $ cat > foo << EOF
+  > one
+  > two
+  > THREE
+  > four
+  > five
+  > six
+  > seven
+  > height
+  > nine
+  > ten
+  > EOF
+  $ hg ci -m 'capital three'
+  $ cat > foo << EOF
+  > one
+  > two
+  > THREE
+  > four
+  > five
+  > six
+  > seven
+  > height
+  > nine
+  > TEN
+  > EOF
+  $ hg ci -m 'capital ten'
+  $ hg backout -r 'desc("capital three")' --tool internal:fail
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges
+  [1]
+  $ hg status
+  $ hg resolve -l  # still unresolved
+  U foo
+  $ hg summary
+  parent: 2:b71750c4b0fd tip
+   capital ten
+  branch: default
+  commit: 1 unresolved (clean)
+  update: (current)
+  $ hg resolve --all --debug
+  picked tool 'internal:merge' for foo (binary False symlink False)
+  merging foo
+  my foo@b71750c4b0fd+ other foo@a30dd8addae3 ancestor foo@913609522437
+   premerge successful
+  $ hg status
+  M foo
+  ? foo.orig
+  $ hg resolve -l
+  R foo
+  $ hg summary
+  parent: 2:b71750c4b0fd tip
+   capital ten
+  branch: default
+  commit: 1 modified, 1 unknown
+  update: (current)
+  $ cat foo
+  one
+  two
+  three
+  four
+  five
+  six
+  seven
+  height
+  nine
+  TEN
+
+