Only accept the hermetic toolchain license if newer.

Accepting an older license will break newer toolchains.  Check if a bot's
last agreed to toolchain is newer.  If it's older, accept the hermetic toolchain.

BUG=

Review-Url: https://codereview.chromium.org/1956073003
Cr-Original-Commit-Position: refs/heads/master@{#392356}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 10dc9038e9e0e42efa7a53c4f6857a6749ceea0b

mac_toolchain.py

@@ -19,6 +19,7 @@ versions can be modified to allow for user input on developer machines.
 """
 
 import os
+import plistlib
 import shutil
 import subprocess
 import sys
@@ -97,16 +98,57 @@ def CanAccessToolchainBucket():
   proc.communicate()
   return proc.returncode == 0
 
+def LoadPlist(path):
+  """Loads Plist at |path| and returns it as a dictionary."""
+  fd, name = tempfile.mkstemp()
+  try:
+    subprocess.check_call(['plutil', '-convert', 'xml1', '-o', name, path])
+    with os.fdopen(fd, 'r') as f:
+      return plistlib.readPlist(f)
+  finally:
+    os.unlink(name)
+
 
 def AcceptLicense(directory):
-  """Use xcodebuild to accept new toolchain license.  This only
-  works if xcodebuild and xcode-select are in sudoers."""
-  xcodebuild_dir = os.path.join(TOOLCHAIN_BUILD_DIR, 'Contents/Developer')
+  """Use xcodebuild to accept new toolchain license if necessary.  Don't accept
+  the license if a newer license has already been accepted. This only works if
+  xcodebuild and xcode-select are passwordless in sudoers."""
+
+  # Check old license
+  try:
+    target_license_plist_path = \
+        os.path.join(TOOLCHAIN_BUILD_DIR,
+                     *['Contents','Resources','LicenseInfo.plist'])
+    target_license_plist = LoadPlist(target_license_plist_path)
+    build_type = target_license_plist['licenseType']
+    build_version = target_license_plist['licenseID']
+
+    accepted_license_plist = LoadPlist(
+        '/Library/Preferences/com.apple.dt.Xcode.plist')
+    agreed_to_key = 'IDELast%sLicenseAgreedTo' % build_type
+    last_license_agreed_to = accepted_license_plist[agreed_to_key]
+
+    # Historically all Xcode build numbers have been in the format of AANNNN, so
+    # a simple string compare works.  If Xcode's build numbers change this may
+    # need a more complex compare.
+    if build_version <= last_license_agreed_to:
+      # Don't accept the license of older toolchain builds, this will break the
+      # license of newer builds.
+      return
+  except (subprocess.CalledProcessError, KeyError) as e:
+    # If there's never been a license of type |build_type| accepted,
+    # |target_license_plist_path| or |agreed_to_key| may not exist.
+    pass
+
+  print "Accepting license."
   old_path = subprocess.Popen(['/usr/bin/xcode-select', '-p'],
                                stdout=subprocess.PIPE).communicate()[0].strip()
-  subprocess.check_call(['sudo', '/usr/bin/xcode-select', '-s', xcodebuild_dir])
-  subprocess.check_call(['sudo', '/usr/bin/xcodebuild', '-license', 'accept'])
-  subprocess.check_call(['sudo', '/usr/bin/xcode-select', '-s', old_path])
+  try:
+    build_dir = os.path.join(TOOLCHAIN_BUILD_DIR, 'Contents/Developer')
+    subprocess.check_call(['sudo', '/usr/bin/xcode-select', '-s', build_dir])
+    subprocess.check_call(['sudo', '/usr/bin/xcodebuild', '-license', 'accept'])
+  finally:
+    subprocess.check_call(['sudo', '/usr/bin/xcode-select', '-s', old_path])
 
 
 def UseLocalMacSDK():