--- a/mercurial/hg.py	Mon Feb 13 16:03:05 2017 -0800
+++ b/mercurial/hg.py	Mon Feb 13 00:05:55 2017 -0800
@@ -743,12 +743,13 @@
      * none: don't check (merge working directory changes into destination)
      * linear: check that update is linear before merging working directory
                changes into destination
+     * noconflict: check that the update does not result in file merges
 
     This returns whether conflict is detected at updating or not.
     """
     if updatecheck is None:
         updatecheck = ui.config('experimental', 'updatecheck')
-        if updatecheck not in ('abort', 'none', 'linear'):
+        if updatecheck not in ('abort', 'none', 'linear', 'noconflict'):
             # If not configured, or invalid value configured
             updatecheck = 'linear'
     with repo.wlock():

--- a/mercurial/merge.py	Mon Feb 13 16:03:05 2017 -0800
+++ b/mercurial/merge.py	Mon Feb 13 00:05:55 2017 -0800
@@ -1465,21 +1465,27 @@
     The table below shows all the behaviors of the update command
     given the -c and -C or no options, whether the working directory
     is dirty, whether a revision is specified, and the relationship of
-    the parent rev to the target rev (linear or not). Match from top first.
+    the parent rev to the target rev (linear or not). Match from top first. The
+    -n option doesn't exist on the command line, but represents the
+    experimental.updatecheck=noconflict option.
 
     This logic is tested by test-update-branches.t.
 
-    -c  -C  -m  dirty  rev  linear  |  result
-     y   y   *    *     *     *     |    (1)
-     y   *   y    *     *     *     |    (1)
-     *   y   y    *     *     *     |    (1)
-     *   *   *    *     n     n     |     x
-     *   *   *    n     *     *     |    ok
-     n   n   n    y     *     y     |   merge
-     n   n   n    y     y     n     |    (2)
-     n   n   y    y     *     *     |   merge
-     n   y   n    y     *     *     |  discard
-     y   n   n    y     *     *     |    (3)
+    -c  -C  -n  -m  dirty  rev  linear  |  result
+     y   y   *   *    *     *     *     |    (1)
+     y   *   y   *    *     *     *     |    (1)
+     y   *   *   y    *     *     *     |    (1)
+     *   y   y   *    *     *     *     |    (1)
+     *   y   *   y    *     *     *     |    (1)
+     *   *   y   y    *     *     *     |    (1)
+     *   *   *   *    *     n     n     |     x
+     *   *   *   *    n     *     *     |    ok
+     n   n   n   n    y     *     y     |   merge
+     n   n   n   n    y     y     n     |    (2)
+     n   n   n   y    y     *     *     |   merge
+     n   n   y   n    y     *     *     |  merge if no conflict
+     n   y   n   n    y     *     *     |  discard
+     y   n   n   n    y     *     *     |    (3)
 
     x = can't happen
     * = don't-care
@@ -1499,7 +1505,7 @@
         # updatecheck='abort' to better suppport some of these callers.
         if updatecheck is None:
             updatecheck = 'linear'
-        assert updatecheck in ('none', 'linear')
+        assert updatecheck in ('none', 'linear', 'noconflict')
     # If we're doing a partial update, we need to skip updating
     # the dirstate, so make a note of any partial-ness to the
     # update here.
@@ -1593,6 +1599,13 @@
             repo, wc, p2, pas, branchmerge, force, mergeancestor,
             followcopies, matcher=matcher, mergeforce=mergeforce)
 
+        if updatecheck == 'noconflict':
+            for f, (m, args, msg) in actionbyfile.iteritems():
+                if m not in ('g', 'k', 'r'):
+                    msg = _("uncommitted changes")
+                    hint = _("commit or update --merge to allow merge")
+                    raise error.Abort(msg, hint=hint)
+
         # Prompt and create actions. Most of this is in the resolve phase
         # already, but we can't handle .hgsubstate in filemerge or
         # subrepo.submerge yet so we have to keep prompting for it.

--- a/tests/test-update-branches.t	Mon Feb 13 16:03:05 2017 -0800
+++ b/tests/test-update-branches.t	Mon Feb 13 00:05:55 2017 -0800
@@ -255,6 +255,65 @@
   >>>>>>> destination:  d047485b3896 b1 - test: 4
   $ rm a.orig
 
+  $ echo 'updatecheck = noconflict' >> .hg/hgrc
+
+  $ revtest 'none dirty cross'  dirty 3 4
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  parent=4
+  M foo
+
+  $ revtest 'none dirty linear' dirty 1 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  parent=2
+  M foo
+
+  $ revtest 'none dirty linear' dirty 1 2 -c
+  abort: uncommitted changes
+  parent=1
+  M foo
+
+  $ revtest 'none dirty linear' dirty 1 2 -C
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  parent=2
+
+Locally added file is allowed
+  $ hg up -qC 3
+  $ echo a > bar
+  $ hg add bar
+  $ hg up -q 4
+  $ hg st
+  A bar
+  $ hg forget bar
+  $ rm bar
+
+Locally removed file is allowed
+  $ hg up -qC 3
+  $ hg rm a
+  $ hg up -q 4
+  abort: uncommitted changes
+  (commit or update --merge to allow merge)
+  [255]
+
+File conflict is not allowed
+  $ hg up -qC 3
+  $ echo dirty >> a
+  $ hg up -q 4
+  abort: uncommitted changes
+  (commit or update --merge to allow merge)
+  [255]
+  $ hg up -m 4
+  merging a
+  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges
+  [1]
+  $ rm a.orig
+
+Change/delete conflict is not allowed
+  $ hg up -qC 3
+  $ hg rm foo
+  $ hg up -q 4
+
 Uses default value of "linear" when value is misspelled
   $ echo 'updatecheck = linyar' >> .hg/hgrc