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site_scons/site_tools/windows_hard_link.py

Index: site_scons/site_tools/windows_hard_link.py
===================================================================
--- site_scons/site_tools/windows_hard_link.py	(revision 0)
+++ site_scons/site_tools/windows_hard_link.py	(revision 0)
@@ -0,0 +1,108 @@
+#!/usr/bin/python2.4
+# Copyright 2008, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Hard link support for Windows.
+
+This module is a SCons tool which should be include in the topmost windows
+environment.  It is usually included by the target_platform_windows tool.
+"""
+
+
+import os
+import stat
+import sys
+import SCons
+
+if sys.platform in ('win32', 'cygwin'):
+  # Only attempt to load pywin32 on Windows systems
+  try:
+    import win32file
+  except ImportError:
+    print ('Warning: Unable to load win32file module; using copy instead of'
+           ' hard linking for env.Install().  Is pywin32 present?')
+
+#------------------------------------------------------------------------------
+# Python 2.4 and 2.5's os module doesn't support os.link on Windows, even
+# though Windows does have hard-link capability on NTFS filesystems.  So by
+# default, SCons will insist on copying files instead of linking them as it
+# does on other (linux,mac) OS's.
+#
+# Use the CreateHardLink() functionality from pywin32 to provide hard link
+# capability on Windows also.
+
+
+def _HardLink(fs, src, dst):
+  """Hard link function for hooking into SCons.Node.FS.
+
+  Args:
+    fs: Filesystem class to use.
+    src: Source filename to link to.
+    dst: Destination link name to create.
+
+  Raises:
+    OSError: The link could not be created.
+  """
+  # A hard link shares file permissions from the source.  On Windows, the write
+  # access of the file itself determines whether the file can be deleted
+  # (unlike Linux/Mac, where it's the write access of the containing
+  # directory).  So if we made a link from a read-only file, the only way to
+  # delete it would be to make the link writable, which would have the
+  # unintended effect of making the source writable too.
+  #
+  # So if the source is read-only, we can't hard link from it.
+  if not stat.S_IMODE(fs.stat(src)[stat.ST_MODE]) & stat.S_IWRITE:
+    raise OSError('Unsafe to hard-link read-only file: %s' % src)
+
+  # If the file is writable, only hard-link from it if it was build by SCons.
+  # Those files shouldn't later become read-only.  We don't hard-link from
+  # writable files which SCons didn't create, because those could become
+  # read-only (for example, following a 'p4 submit'), which as indicated above
+  # would make our link read-only too.
+  if not fs.File(src).has_builder():
+    raise OSError('Unsafe to hard-link file not built by SCons: %s' % src)
+
+  try:
+    win32file.CreateHardLink(dst, src)
+  except win32file.error, msg:
+    # Translate errors into standard OSError which SCons expects.
+    raise OSError(msg)
+
+
+#------------------------------------------------------------------------------
+
+
+def generate(env):
+  # NOTE: SCons requires the use of this name, which fails gpylint.
+  """SCons entry point for this tool."""
+  env = env  # Silence gpylint
+
+  # Patch in our hard link function, if we were able to load pywin32
+  if 'win32file' in globals():
+    SCons.Node.FS._hardlink_func = _HardLink