Add support for reading .gypi files.

build/gypi_to_gn.py

Index: build/gypi_to_gn.py
diff --git a/build/gypi_to_gn.py b/build/gypi_to_gn.py
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+++ b/build/gypi_to_gn.py
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+# 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 gn_helpers
+from optparse import OptionParser
+
+# 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 check for the presence of a "conditions" value in the
+# dictionary and will abort if it is present). It also does not support nested
+# dictionaries.
+#
+# 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")
+
+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:
+    ExceptionAppend(e, 'while reading ' + path)
+    raise
+
+  if not isinstance(file_data, dict):
+    raise Error("%s does not evaluate to a dictionary" % path)
+
+  if 'conditions' in file_data:
+    raise Error("The file %s has conditions in it. These aren't supported." %
+               path)
+  return file_data
+
+
+def main():
+  parser = OptionParser()
+  (options, args) = parser.parse_args()
+
+  if len(args) != 1:
+    raise Error("Need one argument which is the .gypi file to read.")
+
+  data = LoadPythonDictionary(args[0])
+  gn_helpers.PrintValue(data)
+
+main()