[iOS] Fix compilation of official build with Xcode 8.

build/config/mac/mac_sdk.gni

 # Copyright 2014 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("//build/config/chrome_build.gni")
 
 # See https://bugs.chromium.org/p/webrtc/issues/detail?id=5453.
 # We can drop the rtc_require_mac_10_7_deployment flag when Chromium
 # also requires a 10.7 deployment target.
 import("//build_overrides/build.gni")
 
 declare_args() {
   # Minimum supported version of the Mac SDK.
   mac_sdk_min = mac_sdk_min_build_override
 
   # Minimum supported version of OSX.
   mac_deployment_target = mac_deployment_target_build_override
 
   # Path to a specific version of the Mac SDK, not including a backslash at
   # the end. If empty, the path to the lowest version greater than or equal to
   # mac_sdk_min is used.
   mac_sdk_path = ""
 
   # The SDK name as accepted by xcodebuild.
   mac_sdk_name = "macosx"
 }
 
+_verify_sdk = is_chrome_branded && is_official_build &&
+              current_toolchain != host_toolchain

[Dirk Pranke, 2016/08/08 23:15:06]

I know we discussed this a bit back and forth over email, but I think you maybe
drew the wrong conclusion, and I think it's fine to require the same sdk version
for both target and host toolchains.

It is reasonable to still guard this on something since we don't need to call
things twice, though.

[sdefresne, 2016/08/08 23:21:27]

The issue is that Chrome on iOS wants to soon require Xcode 8 for the
compilation. One of the bots we have sets both is_chrome_branded and
is_official_build to true (it is used to build the version that is tested).

The problem is that those flags are propagated from the main toolchain to the
host toolchain. When building the tools for the host toolchain, we do not really
care about building and official / branded version, we're fine with just
building release.

Since Xcode 8 does not contains 10.10 SDK, the "gn gen" steps fails with the
following error:

  ERROR at //build/config/mac/mac_sdk.gni:43:34: Array subscript out of range.
  mac_sdk_version = find_sdk_lines[1]
                                   ^
  You gave me 1 but I was expecting something from 0 to 1, inclusive.

(issue https://codereview.chromium.org/2218773004/ is here to make the error
cleaner).

Maybe the correct check should be target_os != "ios" instead. WDYT?

[Dirk Pranke, 2016/08/08 23:36:28]

Change to current_toolchain == default_toolchain, maybe (as we discussed).

+
 find_sdk_args = [ "--print_sdk_path" ]
-if (is_chrome_branded && is_official_build) {
+if (_verify_sdk) {
   find_sdk_args += [
     "--verify",
     mac_sdk_min,
     "--sdk_path=" + mac_sdk_path,
   ]
 } else {
   find_sdk_args += [ mac_sdk_min ]
 }
 
 # The tool will print the SDK path on the first line, and the version on the
@@ skipping 29 matching lines @@
       "          either upgrade Xcode to the latest version or install the Mac OS X")
   print(
       "          $mac_sdk_min_build_override SDK. For more information, see https://crbug.com/620127.")
   print()
   print(" Current SDK Version:   $mac_sdk_version")
   print(" Current Xcode Version: $xcode_version ($xcode_build)")
   print(
       "********************************************************************************")
   assert(false, "SDK is incompatible with Xcode")
 }