build(mach): locate vs via vswhere on win32

mach

@@ -11,8 +11,9 @@
 
 from __future__ import print_function, unicode_literals
 
-
+import itertools
 import os
+import subprocess
 import sys
 
 
@@ -23,9 +24,104 @@ def main(args):
     mach = mach_bootstrap.bootstrap(topdir)
     sys.exit(mach.run(sys.argv[1:]))
 
+def validate_pair(ob):
+  if not (len(ob) == 2):
+    print("Unexpected result:", ob, file=sys.stderr)
+    return False
+  else:
+    return True
+
+def consume(iter):
+  try:
+    while True: next(iter)
+  except StopIteration:
+    pass
+
+def get_environment_from_batch_command(env_cmd, initial=None):
+  """
+  Take a command (either a single command or list of arguments)
+  and return the environment created after running that command.
+  Note that if the command must be a batch file or .cmd file, or the
+  changes to the environment will not be captured.
+  If initial is supplied, it is used as the initial environment passed
+  to the child process.
+  """
+  if not isinstance(env_cmd, (list, tuple)):
+    env_cmd = [env_cmd]
+  # Construct the command that will alter the environment.
+  env_cmd = subprocess.list2cmdline(env_cmd)
+  # Create a tag so we can tell in the output when the proc is done.
+  tag = 'END OF BATCH COMMAND'
+  # Construct a cmd.exe command to do accomplish this.
+  cmd = 'cmd.exe /s /c "{env_cmd} && echo "{tag}" && set"'.format(**vars())
+  # Launch the process.
+  proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, env=initial)
+  # Parse the output sent to stdout.
+  lines = proc.stdout
+  # Consume whatever output occurs until the tag is reached.
+  consume(itertools.takewhile(lambda l: tag not in l, lines))
+  # Define a way to handle each KEY=VALUE line.
+  handle_line = lambda l: l.rstrip().split('=',1)
+  # Parse key/values into pairs.
+  pairs = map(handle_line, lines)
+  # Make sure the pairs are valid.
+  valid_pairs = filter(validate_pair, pairs)
+  # Construct a dictionary of the pairs.
+  result = dict(valid_pairs)
+  # Let the process finish.
+  proc.communicate()
+  return result
+
+def get_vs_env(vs_version, arch):
+  """
+  Returns the env object for VS building environment.
+  The vs_version can be strings like "[15.0,16.0)", meaning 2017, but not the next version.
+  The arch has to be one of "x86", "amd64", "arm", "x86_amd64", "x86_arm", "amd64_x86",
+  "amd64_arm", e.g. the args passed to vcvarsall.bat.
+  """
+
+  # vswhere can't handle spaces, like "[15.0, 16.0)" should become "[15.0,16.0)"
+  vs_version = vs_version.replace(" ", "")
+
+  # Find visual studio
+  proc = subprocess.Popen(
+    "C:\\Program Files (x86)\\Microsoft Visual Studio\\Installer\\vswhere.exe "
+    "-property installationPath "
+    "-requires Microsoft.VisualStudio.Component.VC.CoreIde "
+    "-format value "
+    "-version {0}".format(vs_version),
+    stdout=subprocess.PIPE)
+
+  location = proc.stdout.readline().rstrip()
+  # Launch the process.
+  vsvarsall = "{0}\\VC\\Auxiliary\\Build\\vcvarsall.bat".format(location)
+
+  return get_environment_from_batch_command([vsvarsall, arch])
+
+def import_vs_env():
+    if sys.platform != 'win32':
+        return
+
+    if ('PROGRAMFILES(X86)' in os.environ) == False:
+        print('32-bit Windows is currently unsupported.')
+        sys.exit(-1)
+
+    arch = 'x64'
+    if os.path.isfile("C:\\Program Files (x86)\\Microsoft Visual Studio\\Installer\\vswhere.exe"):
+        env = get_vs_env('[15.0,16.0)', arch)
+        os.environ.update(env)
+    elif 'VS140COMNTOOLS' in os.environ:
+        vs14vsvarsall = os.path.abspath(os.path.join(os.environ['VS140COMNTOOLS'], '..\\..\\VC\\vcvarsall.bat'))
+        env = get_environment_from_batch_command([vs14vsvarsall, arch])
+        os.environ.update(env)
+    else:
+        print("Visual Studio 2017 is not installed.\nDownload and install Visual Studio 2017 from https://www.visualstudio.com/")
+        sys.exit(-1)
 
 if __name__ == '__main__':
     sys.dont_write_bytecode = True
+    import_vs_env()
+
     if sys.platform == 'win32':
         # This is a complete hack to work around the fact that Windows
         # multiprocessing needs to import the original module (ie: this