[PATCH 6 of 7 checkunknown] batchget: add support for backing up files

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1451733661 28800
#      Sat Jan 02 03:21:01 2016 -0800
# Node ID d2b847835e055f08e538ecf3ad336b7a1cb57e30
# Parent  c1ad84b3d9c0cc4c80e8df426dc9d8bf4c4fc488
# Available At http://42.netv6.net/sid0-wip/hg/
#              hg pull http://42.netv6.net/sid0-wip/hg/ -r d2b847835e05
batchget: add support for backing up files

We're going to use this in an upcoming feature.

diff --git a/mercurial/merge.py b/mercurial/merge.py
--- a/mercurial/merge.py
+++ b/mercurial/merge.py
@@ -971,11 +971,26 @@ def batchget(repo, mctx, actions):
     verbose = repo.ui.verbose
     fctx = mctx.filectx
     wwrite = repo.wwrite
+    ui = repo.ui
     i = 0
     for f, args, msg in actions:
         repo.ui.debug(" %s: %s -> g\n" % (f, msg))
         if verbose:
             repo.ui.note(_("getting %s\n") % f)
+
+        if args[1]: # backup
+            absf = repo.wjoin(f)
+            orig = scmutil.origpath(ui, repo, absf)
+            try:
+                # TODO Mercurial has always aborted if an untracked directory
+                # is replaced by a tracked file, or generally with
+                # file/directory merges. This needs to be sorted out.
+                if repo.wvfs.isfileorlink(f):
+                    util.rename(absf, orig)
+            except OSError as e:
+                if e.errno != errno.ENOENT:
+                    raise
+
         wwrite(f, fctx(f).data(), args[0])
         if i == 100:
             yield i, f