mac: Let mac_sdk default to the oldest available SDK that's at least 10.6

Having to manually set mac_sdk was a FAQ when Xcode 4 was released. Now
we're using the 10.6 SDK by default, but Xcode 4.4 ships only with the
10.7 and 10.8 SDKs, so it'll likely become a FAQ again. Automatically
set mac_sdk to something sensible.

(People who explicitly say "mac_sdk=10.6" will have to stop doing so
when they switch to Xcode 4.4.)

BUG=121162
TEST=Build without mac_sdk in GYP_DEFINES. Something useful happens
with Xcode 3.2.6, Xcode 4, Xcode 4.4.


Review URL: https://chromiumcodereview.appspot.com/10824055

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148817 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

@@ -645,7 +645,7 @@
     # these defaults. If the SDK is installed someplace that Xcode doesn't
     # know about, set mac_sdk_path to the path to the SDK. If set to a
     # non-empty string, mac_sdk_path will be used in preference to mac_sdk.
-    'mac_sdk%': '10.6',
+    # mac_sdk gets its default value elsewhere in this file.
     'mac_sdk_path%': '',
     'mac_deployment_target%': '10.5',
 
@@ -1020,6 +1020,7 @@
           }],
 
           ['branding=="Chrome" and buildtype=="Official"', {
+            'mac_sdk%': '10.6',
             # Enable uploading crash dumps.
             'mac_breakpad_uploads%': 1,
             # Enable dumping symbols at build time for use by Mac Breakpad.
@@ -1027,6 +1028,7 @@
             # Enable Keystone auto-update support.
             'mac_keystone%': 1,
           }, { # else: branding!="Chrome" or buildtype!="Official"
+            'mac_sdk%': '<!(python mac/find_sdk.py 10.6)',
             'mac_breakpad_uploads%': 0,
             'mac_breakpad%': 0,
             'mac_keystone%': 0,

build/mac/find_sdk.py

+#!/usr/bin/env python
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import os
+import re
+import subprocess
+import sys
+
+"""Prints the lowest locally available SDK version greater than or equal to a
+given minimum sdk version to standard output.
+
+Usage:
+  python find_sdk.py 10.6  # Ignores SDKs < 10.6
+"""
+
+def parse_version(version_str):
+  """'10.6' => [10, 6]"""
+  return map(int, re.findall(r'(\d+)', version_str))
+
+
+def main(min_sdk_version):
+  job = subprocess.Popen(['xcode-select', '-print-path'],
+                         stdout=subprocess.PIPE,
+                         stderr=subprocess.STDOUT)
+  out, err = job.communicate()
+  if job.returncode != 0:
+    print >>sys.stderr, out
+    print >>sys.stderr, err
+    raise Exception(('Error %d running xcode-select, you might have to run '
+      '|sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer| '
+      'if you are using Xcode 4.') % job.returncode)
+  # The Developer folder moved in Xcode 4.3.
+  xcode43_sdk_path = os.path.join(
+      out.rstrip(), 'Platforms/MacOSX.platform/Developer/SDKs')
+  if os.path.isdir(xcode43_sdk_path):
+    sdk_dir = xcode43_sdk_path
+  else:
+    sdk_dir = os.path.join(out.rstrip(), 'SDKs')
+  sdks = [re.findall('^MacOSX(10\.\d+)\.sdk$', s) for s in os.listdir(sdk_dir)]
+  sdks = [s[0] for s in sdks if s]  # [['10.5'], ['10.6']] => ['10.5', '10.6']
+  sdks = [s for s in sdks  # ['10.5', '10.6'] => ['10.6']
+          if parse_version(s) >= parse_version(min_sdk_version)]
+  if not sdks:
+    raise Exception('No %s+ SDK found' % min_sdk_version)
+  print sorted(sdks, key=parse_version)[0]
+
+
+if __name__ == '__main__':
+  if sys.platform != 'darwin':
+    raise Exception("This script only runs on Mac")
+  main(min_sdk_version=sys.argv[1])