Cached timestamps for toolchain update script

tools/win/toolchain/get_toolchain_if_necessary.py

Index: tools/win/toolchain/get_toolchain_if_necessary.py
diff --git a/tools/win/toolchain/get_toolchain_if_necessary.py b/tools/win/toolchain/get_toolchain_if_necessary.py
index e93e6f029fa4352b3f9d39ec5242c25d18df6f97..da21f95983d985eb92f8cef0af0e8d00bc528797 100644
--- a/tools/win/toolchain/get_toolchain_if_necessary.py
+++ b/tools/win/toolchain/get_toolchain_if_necessary.py
@@ -2,7 +2,9 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import ctypes.wintypes
 import hashlib
+import json
 import os
 import subprocess
 import sys
@@ -11,23 +13,83 @@ import sys
 BASEDIR = os.path.dirname(os.path.abspath(__file__))
 
 
+GetFileAttributes = ctypes.windll.kernel32.GetFileAttributesW
+GetFileAttributes.argtypes = (ctypes.wintypes.LPWSTR,)
+GetFileAttributes.restype = ctypes.wintypes.DWORD
+FILE_ATTRIBUTE_HIDDEN = 0x2
+FILE_ATTRIBUTE_SYSTEM = 0x4
+
+
+def IsHidden(file_path):
+  """Returns whether the given |file_path| has the 'system' or 'hidden'
+  attribute set."""
+  p = GetFileAttributes(file_path)
+  assert p != 0xffffffff
+  return bool(p & (FILE_ATTRIBUTE_HIDDEN | FILE_ATTRIBUTE_SYSTEM))
+
+
+def GetFileList(root):
+  """Gets a normalized list of files under |root|."""
+  assert not os.path.isabs(root)
+  assert os.path.normpath(root) == root
+  file_list = []
+  for base, _, files in os.walk(root):
+    paths = [os.path.join(base, f) for f in files]
+    file_list.extend(x.lower() for x in paths if not IsHidden(x))
+  return sorted(file_list)
+
+
+def MakeTimestampsFileName(root):
+  return os.path.join(root, '..', '.timestamps')
+
+
 def CalculateHash(root):
   """Calculates the sha1 of the paths to all files in the given |root| and the
   contents of those files, and returns as a hex string."""
-  assert not os.path.isabs(root)
-  assert os.path.normpath(root) == root
+  file_list = GetFileList(root)
+
+  # Check whether we previously saved timestamps in $root/../.timestamps. If
+  # we didn't, or they don't match, then do the full calculation, otherwise
+  # return the saved value.
+  timestamps_file = MakeTimestampsFileName(root)
+  timestamps_data = {'files': [], 'sha1': ''}
+  if os.path.exists(timestamps_file):
+    with open(timestamps_file, 'rb') as f:
+      try:
+        timestamps_data = json.load(f)
+      except ValueError:
+        # json couldn't be loaded, empty data will force a re-hash.
+        pass
+
+  matches = len(file_list) == len(timestamps_data['files'])
+  if matches:
+    for disk, cached in zip(file_list, timestamps_data['files']):
+      if disk != cached[0] or os.stat(disk).st_mtime != cached[1]:
+        matches = False
+        break
+  if matches:
+    return timestamps_data['sha1']
+
   digest = hashlib.sha1()
-  count = 0
-  for root, dirs, files in os.walk(root):
-    dirs.sort()
-    for name in sorted(f.lower() for f in files):
-      path = os.path.join(root, name)
-      digest.update(path.lower())
-      with open(path, 'rb') as f:
-        digest.update(f.read())
+  for path in file_list:
+    digest.update(path)
+    with open(path, 'rb') as f:
+      digest.update(f.read())
   return digest.hexdigest()
 
 
+def SaveTimestampsAndHash(root, sha1):
+  """Save timestamps and the final hash to be able to early-out more quickly
+  next time."""
+  file_list = GetFileList(root)
+  timestamps_data = {
+    'files': [[f, os.stat(f).st_mtime] for f in file_list],
+    'sha1': sha1,
+  }
+  with open(MakeTimestampsFileName(root), 'wb') as f:
+    json.dump(timestamps_data, f)
+
+
 def main():
   if sys.platform not in ('win32', 'cygwin'):
     return 0
@@ -48,9 +110,9 @@ def main():
       desired_hash = f.read().strip()
 
   # If the current hash doesn't match what we want in the file, nuke and pave.
-  # Note that this script is only run when a .sha1 file is updated (per DEPS)
-  # so this relatively expensive step of hashing everything only happens when
-  # the toolchain is updated.
+  # Typically this script is only run when the .sha1 one file is updated, but
+  # directly calling "gclient runhooks" will also run it, so we cache
+  # based on timestamps to make that case fast.
   current_hash = CalculateHash(target_dir)
   if current_hash != desired_hash:
     print 'Windows toolchain out of date or doesn\'t exist, updating...'
@@ -60,14 +122,15 @@ def main():
         sys.executable,
         'src\\tools\\win\\toolchain\\toolchain2013.py',
         '--targetdir', target_dir])
+    current_hash = CalculateHash(target_dir)
+    if current_hash != desired_hash:
+      print >> sys.stderr, (
+          'Got wrong hash after pulling a new toolchain. '
+          'Wanted \'%s\', got \'%s\'.' % (
+              desired_hash, current_hash))
+      return 1
+    SaveTimestampsAndHash(target_dir, current_hash)
 
-  current_hash = CalculateHash(target_dir)
-  if current_hash != desired_hash:
-    print >> sys.stderr, (
-        'Got wrong hash after pulling a new toolchain. '
-        'Wanted \'%s\', got \'%s\'.' % (
-            desired_hash, current_hash))
-    return 1
   return 0