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.

mercurial/merge.py

@@ -1038,6 +1038,12 b' def batchremove(repo, actions):'
     unlink = util.unlinkpath
     wjoin = repo.wjoin
     audit = repo.wvfs.audit
+    try:
+        cwd = os.getcwd()
+    except OSError as err:
+        if err.errno != errno.ENOENT:
+            raise
+        cwd = None
     i = 0
     for f, args, msg in actions:
         repo.ui.debug(" %s: %s -> r\n" % (f, msg))
@@ -1055,6 +1061,18 b' def batchremove(repo, actions):'
         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 as err:
+            if err.errno != errno.ENOENT:
+                raise
+            # Print a warning if cwd was deleted
+            repo.ui.warn(_("current directory was removed\n"
+                           "(consider changing to repo root: %s)\n") %
+                         repo.root)
 
 def batchget(repo, mctx, actions):
     """apply gets to the working directory

tests/test-rebase-scenario-global.t

@@ -758,6 +758,8 b' Test that rebase is not confused by $CWD'
   $ 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)
 

tests/test-update-names.t

@@ -72,3 +72,15 b' Test update when two commits have symlin'
   $ 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)