Add support for substring replacement in gypi_to_gn

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
index 1446d811630c1fd2023291aed5c1dd6194ca6c39..d753d10dd29203b29e573a127256704bc74438db 100644
--- a/build/gypi_to_gn.py
+++ b/build/gypi_to_gn.py
@@ -46,6 +46,24 @@ 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
@@ -66,17 +84,61 @@ def LoadPythonDictionary(path):
   assert 'conditions' not in file_data, \
       "The file %s has conditions in it, these aren't supported." % path
 
+  # If the contents of the root is a dictionary with exactly one kee
+  # "variables", promote the contents of that to the top level. Some .gypi
+  # files contain this and some don't depending on how they expect to be
+  # embedded in a .gyp file. We don't actually care either way so collapse it
+  # away.
+  if len(file_data) == 1 and 'variables' in file_data:
+    return file_data['variables']
+
   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])
+
   print gn_helpers.ToGNString(data)
 
 if __name__ == '__main__':