Split toolchain update and install lookup to make generation faster

build/vs_toolchain.py

Index: build/vs_toolchain.py
diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index 247703b8654094dd91eb4767eff3593eaa5561e7..4b925f0799f2ade1abbb97834b44ebdddc591a85 100644
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -8,7 +8,6 @@ import pipes
 import shutil
 import subprocess
 import sys
-import tempfile
 
 
 script_dir = os.path.dirname(os.path.realpath(__file__))
@@ -16,46 +15,23 @@ chrome_src = os.path.abspath(os.path.join(script_dir, os.pardir))
 SRC_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(1, os.path.join(chrome_src, 'tools'))
 sys.path.insert(0, os.path.join(chrome_src, 'tools', 'gyp', 'pylib'))
+json_data_file = os.path.join(script_dir, 'win_toolchain.json')
 
 
 import gyp
 
 
-def GetDesiredVsToolchainHashes():
-  """Load a list of SHA1s corresponding to the toolchains that we want installed
-  to build with."""
-  sha1path = os.path.join(script_dir, 'toolchain_vs2013.hash')
-  with open(sha1path, 'rb') as f:
-    return f.read().strip().splitlines()
-
-
-def DownloadVsToolchain():
-  """Download the Visual Studio toolchain on Windows.
-
-  If on Windows, request that depot_tools install/update the automatic
-  toolchain, and then use it (unless opted-out) and return a tuple containing
-  the x64 and x86 paths. Otherwise return None.
+def SetEnvironmentAndGetRuntimeDllDirs():
+  """Sets up os.environ to use the depot_tools VS toolchain with gyp, and
+  returns the location of the VS runtime DLLs so they can be copied into
+  the output directory after gyp generation.
   """
   vs2013_runtime_dll_dirs = None
   depot_tools_win_toolchain = \
       bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', '1')))
   if sys.platform in ('win32', 'cygwin') and depot_tools_win_toolchain:
-    import find_depot_tools
-    depot_tools_path = find_depot_tools.add_depot_tools_to_path()
-    temp_handle, data_file = tempfile.mkstemp(suffix='.json')
-    os.close(temp_handle)
-    get_toolchain_args = [
-        sys.executable,
-        os.path.join(depot_tools_path,
-                    'win_toolchain',
-                    'get_toolchain_if_necessary.py'),
-        '--output-json', data_file,
-      ] + GetDesiredVsToolchainHashes()
-    subprocess.check_call(get_toolchain_args)
-
-    with open(data_file, 'r') as tempf:
+    with open(json_data_file, 'r') as tempf:
       toolchain_data = json.load(tempf)
-    os.unlink(data_file)
 
     toolchain = toolchain_data['path']
     version = toolchain_data['version']
@@ -132,18 +108,58 @@ def CopyVsRuntimeDlls(output_dir, runtime_dirs):
   copy_runtime(out_release_nacl64, x64, 'msvc%s120.dll')
 
 
+def _GetDesiredVsToolchainHashes():
+  """Load a list of SHA1s corresponding to the toolchains that we want installed
+  to build with."""
+  sha1path = os.path.join(script_dir, 'toolchain_vs2013.hash')
+  with open(sha1path, 'rb') as f:
+    return f.read().strip().splitlines()
+
+
+def Update():
+  """Requests an update of the toolchain to the specific hashes we have at
+  this revision. The update outputs a .json of the various configuration
+  information required to pass to gyp which we use in |GetToolchainDir()|.
+  """
+  depot_tools_win_toolchain = \
+      bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', '1')))
+  if sys.platform in ('win32', 'cygwin') and depot_tools_win_toolchain:
+    import find_depot_tools
+    depot_tools_path = find_depot_tools.add_depot_tools_to_path()
+    json_data_file = os.path.join(script_dir, 'win_toolchain.json')
+    get_toolchain_args = [
+        sys.executable,
+        os.path.join(depot_tools_path,
+                    'win_toolchain',
+                    'get_toolchain_if_necessary.py'),
+        '--output-json', json_data_file,
+      ] + _GetDesiredVsToolchainHashes()
+    subprocess.check_call(get_toolchain_args)
+
+  return 0
+
+
+def GetToolchainDir():
+  """Gets location information about the current toolchain (must have been
+  previously updated by 'update')."""
+  SetEnvironmentAndGetRuntimeDllDirs()
+  print '["%s", "%s"]' % (
+      os.environ['GYP_MSVS_OVERRIDE_PATH'], os.environ['WINDOWSSDKDIR'])
+
+
 def main():
-  if len(sys.argv) < 2:
-    print >>sys.stderr, 'Expected either "get_toolchain_dir" or "copy_dlls"'
+  if not sys.platform.startswith(('win32', 'cygwin')):
+    return 0
+  commands = {
+      'update': Update,
+      'get_toolchain_dir': GetToolchainDir,
+      # TODO(scottmg): Add copy_dlls for GN builds (gyp_chromium calls
+      # CopyVsRuntimeDlls via import, currently).
+  }
+  if len(sys.argv) < 2 or sys.argv[1] not in commands:
+    print >>sys.stderr, 'Expected one of: %s' % ', '.join(commands)
     return 1
-  if sys.argv[1] == 'get_toolchain_dir':
-    DownloadVsToolchain()
-    print '["%s", "%s"]' % (
-        os.environ['GYP_MSVS_OVERRIDE_PATH'], os.environ['WINDOWSSDKDIR'])
-  else:
-    print >>sys.stderr, 'TODO: not implemented "%s"' % sys.argv[1]
-    return 1
-  return 0
+  return commands[sys.argv[1]]()
 
 
 if __name__ == '__main__':