Add support for reading .gypi files.

build/gn_helpers.py

+# 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 sys
+
+# Helper functions useful when writing scripts that are run from GN's
+# exec_script function.
+
+class Error(Exception):
+  pass
+
+
+def ExceptionAppend(e, msg):
+  """Append a message to the given exception's message."""
+  if not e.args:
+    e.args = (msg,)
+  elif len(e.args) == 1:
+    e.args = (str(e.args[0]) + ' ' + msg,)
+  else:
+    e.args = (str(e.args[0]) + ' ' + msg,) + e.args[1:]
+
+
+def PrintString(value):
+  """Writes a python string as a GN string."""
+  if not isinstance(value, str):
+    raise Error("Argument to PrintList is not a Python list.")
+  if value.find('\n') >= 0:
+    raise Error("Trying to print a string with a newline in it.")
+  sys.stdout.write('"' + value.replace('"', '\\"') + '"')
+
+
+def PrintList(value):
+  """Writes a python list as a GN list."""
+  if not isinstance(value, list):
+    raise Error("Argument to PrintList is not a Python list.")
+  sys.stdout.write('[ ')
+  for i in value:
+    PrintValue(i, False)
+    sys.stdout.write(', ')
+  sys.stdout.write(']')
+
+
+def PrintDict(value):
+  """Writes a python dictionary as a GN scope."""
+  for key in value:
+    if not isinstance(key, str):
+      raise Error("Dictionary key is not a string.")
+    sys.stdout.write(key + " = ")
+    PrintValue(value[key], False)  # No recursive dictionaries.
+    sys.stdout.write('\n')
+
+
+def PrintValue(value, allow_dicts = True):
+  """Prints the given value to stdout.
+
+  allow_dicts indicates if this function will allow converting dictionaries
+  to GN scopes. This is only possible at the top level, you can't nest a
+  GN scope in a list, so this should be set to False for recursive calls."""
+  if isinstance(value, str):
+    PrintString(value)
+  elif isinstance(value, list):
+    PrintList(value)
+  elif isinstance(value, dict):
+    if not allow_dicts:
+      raise Error("Attempting to recursively print a dictionary.")
+    PrintDict(value)
+  elif isinstance(value, int):
+    sys.stdout.write(str(value))
+  else:
+    raise Error("Unsupported type when printing to GN.")
+
+