Add target_cpu builtin variable to gclient

This CL adds target_cpu and target_cpu_only variables.  The logic is:

* If target_cpu is defined in .gclient, use it.  Otherwise, initialize it as an
  empty list.
* If not target_cpu_only, add the host arch to the list too.

detect_host_arch.py is copied directly from the Chromium repo.

BUG=807986
R=dpranke

Change-Id: I27621cbc81ad6a844648525863b92ffdd3b1d03a
Reviewed-on: https://chromium-review.googlesource.com/902441
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>

detect_host_arch.py

+#!/usr/bin/env python
+# 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.
+
+"""Outputs host CPU architecture in format recognized by gyp."""
+
+import platform
+import re
+import sys
+
+
+def HostArch():
+  """Returns the host architecture with a predictable string."""
+  host_arch = platform.machine()
+
+  # Convert machine type to format recognized by gyp.
+  if re.match(r'i.86', host_arch) or host_arch == 'i86pc':
+    host_arch = 'x86'
+  elif host_arch in ['x86_64', 'amd64']:
+    host_arch = 'x64'
+  elif host_arch.startswith('arm'):
+    host_arch = 'arm'
+  elif host_arch.startswith('aarch64'):
+    host_arch = 'arm64'
+  elif host_arch.startswith('mips'):
+    host_arch = 'mips'
+  elif host_arch.startswith('ppc'):
+    host_arch = 'ppc'
+  elif host_arch.startswith('s390'):
+    host_arch = 's390'
+
+
+  # platform.machine is based on running kernel. It's possible to use 64-bit
+  # kernel with 32-bit userland, e.g. to give linker slightly more memory.
+  # Distinguish between different userland bitness by querying
+  # the python binary.
+  if host_arch == 'x64' and platform.architecture()[0] == '32bit':
+    host_arch = 'x86'
+  if host_arch == 'arm64' and platform.architecture()[0] == '32bit':
+    host_arch = 'arm'
+
+  return host_arch
+
+def DoMain(_):
+  """Hook to be called from gyp without starting a separate python
+  interpreter."""
+  return HostArch()
+
+if __name__ == '__main__':
+  print DoMain([])

gclient.py

@@ -75,6 +75,10 @@
 #   Example:
 #     target_os = [ "ios" ]
 #     target_os_only = True
+#
+# Specifying a target CPU
+#   To specify a target CPU, the variables target_cpu and target_cpu_only
+#   are available and are analagous to target_os and target_os_only.
 
 from __future__ import print_function
 
@@ -94,6 +98,7 @@ import sys
 import time
 import urlparse
 
+import detect_host_arch
 import fix_encoding
 import gclient_eval
 import gclient_scm
@@ -348,6 +353,10 @@ class DependencySettings(object):
     else:
       return self.parent.target_os
 
+  @property
+  def target_cpu(self):
+    return self.parent.target_cpu
+
   def get_custom_deps(self, name, url):
     """Returns a custom deps if applicable."""
     if self.parent:
@@ -1301,6 +1310,15 @@ class Dependency(gclient_utils.WorkItem, DependencySettings):
         'checkout_mac': 'mac' in self.target_os,
         'checkout_win': 'win' in self.target_os,
         'host_os': _detect_host_os(),
+
+        'checkout_arm': 'arm' in self.target_cpu,
+        'checkout_arm64': 'arm64' in self.target_cpu,
+        'checkout_x86': 'x86' in self.target_cpu,
+        'checkout_mips': 'mips' in self.target_cpu,
+        'checkout_ppc': 'ppc' in self.target_cpu,
+        'checkout_s390': 's390' in self.target_cpu,
+        'checkout_x64': 'x64' in self.target_cpu,
+        'host_cpu': detect_host_arch.HostArch(),
     }
     # Variables defined in DEPS file override built-in ones.
     result.update(self._vars)
@@ -1384,6 +1402,7 @@ solutions = [
     if 'all' in enforced_os:
       enforced_os = self.DEPS_OS_CHOICES.itervalues()
     self._enforced_os = tuple(set(enforced_os))
+    self._enforced_cpu = detect_host_arch.HostArch(),
     self._root_dir = root_dir
     self.config_content = None
 
@@ -1438,6 +1457,13 @@ it or fix the checkout.
     else:
       self._enforced_os = tuple(set(self._enforced_os).union(target_os))
 
+    # Append any target CPU that is not already being enforced to the tuple.
+    target_cpu = config_dict.get('target_cpu', [])
+    if config_dict.get('target_cpu_only', False):
+      self._enforced_cpu = tuple(set(target_cpu))
+    else:
+      self._enforced_cpu = tuple(set(self._enforced_cpu).union(target_cpu))
+
     cache_dir = config_dict.get('cache_dir', self._options.cache_dir)
     if cache_dir:
       cache_dir = os.path.join(self.root_dir, cache_dir)
@@ -1450,6 +1476,10 @@ it or fix the checkout.
       raise gclient_utils.Error('Can\'t use target_os_only if target_os is '
                                 'not specified')
 
+    if not target_cpu and config_dict.get('target_cpu_only', False):
+      raise gclient_utils.Error('Can\'t use target_cpu_only if target_cpu is '
+                                'not specified')
+
     deps_to_add = []
     for s in config_dict.get('solutions', []):
       try:
@@ -1811,6 +1841,10 @@ it or fix the checkout.
   def target_os(self):
     return self._enforced_os
 
+  @property
+  def target_cpu(self):
+    return self._enforced_cpu
+
 
 class GitDependency(Dependency):
   """A Dependency object that represents a single git checkout."""