Adds GN build files for building in GN based projects.

tools/gypi_to_gn.py

Index: tools/gypi_to_gn.py
===================================================================
--- tools/gypi_to_gn.py	(revision 0)
+++ tools/gypi_to_gn.py	(revision 0)
@@ -0,0 +1,167 @@
+# 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.
+
+"""Converts a given gypi file to a python scope and writes the result to stdout.
+
+It is assumed that the file contains a toplevel dictionary, and this script
+will return that dictionary as a GN "scope" (see example below). This script
+does not know anything about GYP and it will not expand variables or execute
+conditions.
+
+It will strip conditions blocks.
+
+A variables block at the top level will be flattened so that the variables
+appear in the root dictionary. This way they can be returned to the GN code.
+
+Say your_file.gypi looked like this:
+  {
+     'sources': [ 'a.cc', 'b.cc' ],
+     'defines': [ 'ENABLE_DOOM_MELON' ],
+  }
+
+You would call it like this:
+  gypi_values = exec_script("//build/gypi_to_gn.py",
+                            [ rebase_path("your_file.gypi") ],
+                            "scope",
+                            [ "your_file.gypi" ])
+
+Notes:
+ - The rebase_path call converts the gypi file from being relative to the
+   current build file to being system absolute for calling the script, which
+   will have a different current directory than this file.
+
+ - The "scope" parameter tells GN to interpret the result as a series of GN
+   variable assignments.
+
+ - The last file argument to exec_script tells GN that the given file is a
+   dependency of the build so Ninja can automatically re-run GN if the file
+   changes.
+
+Read the values into a target like this:
+  component("mycomponent") {
+    sources = gypi_values.sources
+    defines = gypi_values.defines
+  }
+
+Sometimes your .gypi file will include paths relative to a different
+directory than the current .gn file. In this case, you can rebase them to
+be relative to the current directory.
+  sources = rebase_path(gypi_values.sources, ".",
+                        "//path/gypi/input/values/are/relative/to")
+
+This script will tolerate a 'variables' in the toplevel dictionary or not. If
+the toplevel dictionary just contains one item called 'variables', it will be
+collapsed away and the result will be the contents of that dictinoary. Some
+.gypi files are written with or without this, depending on how they expect to
+be embedded into a .gyp file.
+
+This script also has the ability to replace certain substrings in the input.
+Generally this is used to emulate GYP variable expansion. If you passed the
+argument "--replace=<(foo)=bar" then all instances of "<(foo)" in strings in
+the input will be replaced with "bar":
+
+  gypi_values = exec_script("//build/gypi_to_gn.py",
+                            [ rebase_path("your_file.gypi"),
+                              "--replace=<(foo)=bar"],
+                            "scope",
+                            [ "your_file.gypi" ])
+
+"""
+
+import gn_helpers
+from optparse import OptionParser
+import sys
+
+def LoadPythonDictionary(path):
+  file_string = open(path).read()
+  try:
+    file_data = eval(file_string, {'__builtins__': None}, None)
+  except SyntaxError, e:
+    e.filename = path
+    raise
+  except Exception, e:
+    raise Exception("Unexpected error while reading %s: %s" % (path, str(e)))
+
+  assert isinstance(file_data, dict), "%s does not eval to a dictionary" % path
+
+  # Flatten any variables to the top level.
+  if 'variables' in file_data:
+    file_data.update(file_data['variables'])
+    del file_data['variables']
+
+  # Strip any conditions.
+  if 'conditions' in file_data:
+    del file_data['conditions']
+  if 'target_conditions' in file_data:
+    del file_data['target_conditions']
+
+  # Strip targets in the toplevel, since some files define these and we can't
+  # slurp them in.
+  if 'targets' in file_data:
+    del file_data['targets']
+
+  return file_data
+
+
+def ReplaceSubstrings(values, search_for, replace_with):
+  """Recursively replaces substrings in a value.
+
+  Replaces all substrings of the "search_for" with "repace_with" for all
+  strings occurring in "values". This is done by recursively iterating into
+  lists as well as the keys and values of dictionaries."""
+  if isinstance(values, str):
+    return values.replace(search_for, replace_with)
+
+  if isinstance(values, list):
+    return [ReplaceSubstrings(v, search_for, replace_with) for v in values]
+
+  if isinstance(values, dict):
+    # For dictionaries, do the search for both the key and values.
+    result = {}
+    for key, value in values.items():
+      new_key = ReplaceSubstrings(key, search_for, replace_with)
+      new_value = ReplaceSubstrings(value, search_for, replace_with)
+      result[new_key] = new_value
+    return result
+
+  # Assume everything else is unchanged.
+  return values
+
+def main():
+  parser = OptionParser()
+  parser.add_option("-r", "--replace", action="append",
+    help="Replaces substrings. If passed a=b, replaces all substrs a with b.")
+  (options, args) = parser.parse_args()
+
+  if len(args) != 1:
+    raise Exception("Need one argument which is the .gypi file to read.")
+
+  data = LoadPythonDictionary(args[0])
+  if options.replace:
+    # Do replacements for all specified patterns.
+    for replace in options.replace:
+      split = replace.split('=')
+      # Allow "foo=" to replace with nothing.
+      if len(split) == 1:
+        split.append('')
+      assert len(split) == 2, "Replacement must be of the form 'key=value'."
+      data = ReplaceSubstrings(data, split[0], split[1])
+
+  # Sometimes .gypi files use the GYP syntax with percents at the end of the
+  # variable name (to indicate not to overwrite a previously-defined value):
+  #   'foo%': 'bar',
+  # Convert these to regular variables.
+  for key in data:
+    if len(key) > 1 and key[len(key) - 1] == '%':
+      data[key[:-1]] = data[key]
+      del data[key]
+
+  print gn_helpers.ToGNString(data)
+
+if __name__ == '__main__':
+  try:
+    main()
+  except Exception, e:
+    print str(e)
+    sys.exit(1)