[PATCH V4] update: warn if cwd was deleted

[Stanislau Hlebik]

# HG changeset patch
# User Stanislau Hlebik <stash at fb.com>
# Date 1473865427 25200
#      Wed Sep 14 08:03:47 2016 -0700
# Node ID 84ef6a5bc6556f59ed8935a5f716be53a6e17951
# Parent  f148bfa40489269be2e48046734f81065129847a
update: warn if cwd was deleted

During update directories are deleted as soon as they have no entries.
But if current working directory is deleted then it cause problems
in complex commands like 'hg split'. This commit adds a warning
that will help users figure the problem faster.

diff --git a/mercurial/merge.py b/mercurial/merge.py
--- a/mercurial/merge.py
+++ b/mercurial/merge.py
@@ -1036,6 +1036,10 @@
     unlink = util.unlinkpath
     wjoin = repo.wjoin
     audit = repo.wvfs.audit
+    try:
+        cwd = os.getcwd()
+    except OSError:
+        cwd = None
     i = 0
     for f, args, msg in actions:
         repo.ui.debug(" %s: %s -> r\n" % (f, msg))
@@ -1053,6 +1057,16 @@
         i += 1
     if i > 0:
         yield i, f
+    if cwd:
+        # cwd was present before we started to remove files
+        # let's check if it is present after we removed them
+        try:
+            os.getcwd()
+        except OSError:
+            # Print a warning if cwd was deleted
+            repo.ui.warn(_("current directory was removed "
+                           "(consider changing to repo root: %s)\n") %
+                         repo.root)
 
 def batchget(repo, mctx, actions):
     """apply gets to the working directory
diff --git a/tests/test-rebase-scenario-global.t b/tests/test-rebase-scenario-global.t
--- a/tests/test-rebase-scenario-global.t
+++ b/tests/test-rebase-scenario-global.t
@@ -758,6 +758,7 @@
   $ hg commit -m 'second source with subdir'
   $ hg rebase -b . -d 1 --traceback
   rebasing 2:779a07b1b7a0 "first source commit"
+  current directory was removed (consider changing to repo root: $TESTTMP/cwd-vanish)
   rebasing 3:a7d6f3a00bf3 "second source with subdir" (tip)
   saved backup bundle to $TESTTMP/cwd-vanish/.hg/strip-backup/779a07b1b7a0-853e0073-backup.hg (glob)
 
diff --git a/tests/test-update-names.t b/tests/test-update-names.t
--- a/tests/test-update-names.t
+++ b/tests/test-update-names.t
@@ -72,3 +72,14 @@
   $ cd ..
 
 #endif
+
+Test that warning is printed if cwd is deleted during update
+  $ hg init r4 && cd r4
+  $ mkdir dir
+  $ cd dir
+  $ echo a > a
+  $ echo b > b
+  $ hg add a b
+  $ hg ci -m "file and dir"
+  $ hg up -q null
+  current directory was removed (consider changing to repo root: $TESTTMP/r1/r4)