dirstateguard: use mktemp-like functionality to generate the backup filenames

Previously these were generated with names like:
`dirstate.backup.commit.<memory address of dirstateguard>`

This could cause problems if two hg commands ran at the same time that used the
same memory address, (which is apparently not uncommon if chg is involved), as
memory addresses are not unique across processes.

This issue was reported in the post-review comments on
http://phab.mercurial-scm.org/D9952.

Differential Revision: https://phab.mercurial-scm.org/D10504

mercurial/dirstateguard.py

@@ -1,84 +1,97 b''
 # dirstateguard.py - class to allow restoring dirstate after failure
 #
 # Copyright 2005-2007 Olivia Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
+import os
 from .i18n import _
 
 from . import (
     error,
     narrowspec,
+    requirements,
     util,
 )
 
 
 class dirstateguard(util.transactional):
     """Restore dirstate at unexpected failure.
 
     At the construction, this class does:
 
     - write current ``repo.dirstate`` out, and
     - save ``.hg/dirstate`` into the backup file
 
     This restores ``.hg/dirstate`` from backup file, if ``release()``
     is invoked before ``close()``.
 
     This just removes the backup file at ``close()`` before ``release()``.
     """
 
     def __init__(self, repo, name):
         self._repo = repo
         self._active = False
         self._closed = False
-        self._backupname = b'dirstate.backup.%s.%d' % (name, id(self))
-        self._narrowspecbackupname = b'narrowspec.backup.%s.%d' % (
-            name,
-            id(self),
-        )
+
+        def getname(prefix):
+            fd, fname = repo.vfs.mkstemp(prefix=prefix)
+            os.close(fd)
+            return fname
+
+        self._backupname = getname(b'dirstate.backup.%s.' % name)
         repo.dirstate.savebackup(repo.currenttransaction(), self._backupname)
-        narrowspec.savewcbackup(repo, self._narrowspecbackupname)
+        # Don't make this the empty string, things may join it with stuff and
+        # blindly try to unlink it, which could be bad.
+        self._narrowspecbackupname = None
+        if requirements.NARROW_REQUIREMENT in repo.requirements:
+            self._narrowspecbackupname = getname(
+                b'narrowspec.backup.%s.' % name
+            )
+            narrowspec.savewcbackup(repo, self._narrowspecbackupname)
         self._active = True
 
     def __del__(self):
         if self._active:  # still active
             # this may occur, even if this class is used correctly:
             # for example, releasing other resources like transaction
             # may raise exception before ``dirstateguard.release`` in
             # ``release(tr, ....)``.
             self._abort()
 
     def close(self):
         if not self._active:  # already inactivated
             msg = (
                 _(b"can't close already inactivated backup: %s")
                 % self._backupname
             )
             raise error.Abort(msg)
 
         self._repo.dirstate.clearbackup(
             self._repo.currenttransaction(), self._backupname
         )
-        narrowspec.clearwcbackup(self._repo, self._narrowspecbackupname)
+        if self._narrowspecbackupname:
+            narrowspec.clearwcbackup(self._repo, self._narrowspecbackupname)
         self._active = False
         self._closed = True
 
     def _abort(self):
-        narrowspec.restorewcbackup(self._repo, self._narrowspecbackupname)
+        if self._narrowspecbackupname:
+            narrowspec.restorewcbackup(self._repo, self._narrowspecbackupname)
         self._repo.dirstate.restorebackup(
             self._repo.currenttransaction(), self._backupname
         )
         self._active = False
 
     def release(self):
         if not self._closed:
             if not self._active:  # already inactivated
                 msg = (
                     _(b"can't release already inactivated backup: %s")
                     % self._backupname
                 )
                 raise error.Abort(msg)
             self._abort()