update: allow setting default update check to "noconflict"

The new value allows update (linear or not) as long as they don't
result in file merges.

I'm hoping that this value can some day become the default.

mercurial/hg.py

@@ -743,12 +743,13 b' def updatetotally(ui, repo, checkout, br'
      * 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():

mercurial/merge.py

@@ -1465,21 +1465,27 b' def update(repo, node, branchmerge, forc'
     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 b' def update(repo, node, branchmerge, forc'
         # 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 b' def update(repo, node, branchmerge, forc'
             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.

tests/test-update-branches.t

@@ -255,6 +255,65 b' Cases are run as shown in that table, ro'
   >>>>>>> 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