Generate shim headers for libpng

tools/generate_shim_headers/generate_shim_headers.py

Index: tools/generate_shim_headers/generate_shim_headers.py
diff --git a/tools/generate_shim_headers/generate_shim_headers.py b/tools/generate_shim_headers/generate_shim_headers.py
new file mode 100755
index 0000000000000000000000000000000000000000..23aca3449d3ef1abfbc0217205cbb0679ba6ed50
--- /dev/null
+++ b/tools/generate_shim_headers/generate_shim_headers.py
@@ -0,0 +1,64 @@
+#!/usr/bin/env python
+# Copyright (c) 2012 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.
+
+"""
+Generates shim headers that mirror the directory structure of bundled headers,
+but just forward to the system ones.
+
+This allows seamless compilation against system headers with no changes
+to our source code.
+"""
+
+
+import optparse
+import os.path
+import sys
+
+
+SHIM_TEMPLATE = """
+#if defined(OFFICIAL_BUILD)
+#error shim headers must not be used in official builds!
+#endif
+
+#include <%s>
+"""
+
+
+def GeneratorMain(argv):
+  parser = optparse.OptionParser()
+  parser.add_option('--headers-root')
+  parser.add_option('--output-directory')
+  parser.add_option('--outputs', action='store_true')
+  parser.add_option('--generate', action='store_true')
+
+  options, args = parser.parse_args(argv)
+
+  if not options.headers_root:
+    parser.error('Missing --headers-root parameter.')
+  if not options.output_directory:
+    parser.error('Missing --output-directory parameter.')
+
+  source_tree_root = os.path.abspath(
+    os.path.join(os.path.dirname(__file__), '..', '..'))

[Mark Mentovai, 2012/12/17 23:02:41]

I’m surprised we don’t have a better way to find the source root in Python
already written.

[Paweł Hajdan Jr., 2012/12/17 23:18:26]

I'd prefer to use that one, to avoid various issues with PYTHONPATH. I can take
a deeper look though if you think I should.

[Mark Mentovai, 2012/12/17 23:23:24]

Paweł Hajdan Jr. wrote:
If there’s something that’s prebaked that we can use here, I think we should.
What’s written here now amounts to a hard-code. Doing something for PYTHONPATH
may also, but the difference is that if this script moves in the source tree,
the hard-code that you’ve written will allow this script to run and silently
produce bad output, and the only build errors will come later in the build,
where they’ll be more difficult to track down to this script. A PYTHONPATH
hard-code, if necessary, at least moves the potential for build errors right
into this script, right at the source of the problem if the script ever moves.

[Paweł Hajdan Jr., 2012/12/17 23:35:48]

There are path_utils.py in tools/python/google, but that's equivalent to
dirname(__file__), so would actually make things worse IMHO.

I'd rather leave this as-is. This is not used at all during Google Chrome build,
only custom Chromium builds when -Duse_system_ options are used.

+
+  target_directory = os.path.join(
+    options.output_directory,
+    os.path.relpath(options.headers_root, source_tree_root))
+  for header_filename in args:
+    if options.generate and not os.path.exists(target_directory):

[Mark Mentovai, 2012/12/17 23:02:41]

You can pull this outside the loop.

(Either add len(args) >= 1 if you really don’t want to mkdir if there are no
args, or assert earlier in the program that len(args) >= 1.)

[Paweł Hajdan Jr., 2012/12/17 23:18:26]

Done.

+      os.makedirs(target_directory)
+    if options.outputs:
+      yield os.path.join(target_directory, header_filename)
+    if options.generate:
+      with open(os.path.join(target_directory, header_filename), 'w') as f:
+        f.write(SHIM_TEMPLATE % header_filename)
+
+
+def DoMain(argv):
+  return '\n'.join(GeneratorMain(argv))
+
+
+if __name__ == '__main__':
+  DoMain(sys.argv[1:])