IDL build: Split global objects computation from global constructors computation

Source/bindings/scripts/compute_global_objects.py

Index: Source/bindings/scripts/compute_global_objects.py
diff --git a/Source/bindings/scripts/compute_global_objects.py b/Source/bindings/scripts/compute_global_objects.py
new file mode 100755
index 0000000000000000000000000000000000000000..b3f868d75054f4354f3b71da0c33eb5f41fb862f
--- /dev/null
+++ b/Source/bindings/scripts/compute_global_objects.py
@@ -0,0 +1,99 @@
+#!/usr/bin/python
+#
+# 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.
+
+"""Compute global objects.
+
+Global objects are defined by interfaces with [Global] or [PrimaryGlobal] on
+their definition: http://heycam.github.io/webidl/#Global
+
+Design document: http://www.chromium.org/developers/design-documents/idl-build
+"""
+
+import optparse
+import os
+import sys
+
+from utilities import get_file_contents, idl_filename_to_interface_name, get_interface_extended_attributes_from_idl, read_file_to_list, write_pickle_file
+
+GLOBAL_EXTENDED_ATTRIBUTES = frozenset([
+    'Global',
+    'PrimaryGlobal',
+])
+
+
+def parse_options():
+    parser = optparse.OptionParser()
+    parser.add_option('--idl-files-list', help='file listing IDL files')
+    parser.add_option('--write-file-only-if-changed', type='int', help='if true, do not write an output file if it would be identical to the existing one, which avoids unnecessary rebuilds in ninja')
+
+    options, args = parser.parse_args()
+
+    if options.idl_files_list is None:
+        parser.error('Must specify a file listing IDL files using --idl-files-list.')
+    if options.write_file_only_if_changed is None:
+        parser.error('Must specify whether output files are only written if changed using --write-file-only-if-changed.')
+    options.write_file_only_if_changed = bool(options.write_file_only_if_changed)
+    if len(args) != 1:
+        parser.error('Must specify a single output pickle filename as argument.')
+
+    return options, args[0]
+
+
+def idl_file_to_global_names(idl_filename):
+    """Returns global names, if any, for an IDL file.
+
+    If the [Global] or [PrimaryGlobal] extended attribute is declared with an
+    identifier list argument, then those identifiers are the interface's global
+    names; otherwise, the interface has a single global name, which is the
+    interface's identifier (http://heycam.github.io/webidl/#Global).
+    """
+    interface_name = idl_filename_to_interface_name(idl_filename)
+    full_path = os.path.realpath(idl_filename)
+    idl_file_contents = get_file_contents(full_path)
+    extended_attributes = get_interface_extended_attributes_from_idl(idl_file_contents)
+
+    global_keys = GLOBAL_EXTENDED_ATTRIBUTES.intersection(
+        extended_attributes.iterkeys())
+    if not global_keys:
+        return
+    if len(global_keys) > 1:
+        raise ValueError('The [Global] and [PrimaryGlobal] extended attributes '

[haraken, 2014/06/02 07:41:30]

Is it worth supporting extended attribute values for [PrimaryGlobal]? I guess
it's just used in Window as [PrimaryGlobal] (with no extended attribute values).

[Nils Barth (inactive), 2014/06/02 07:55:13]

It's defined as such in the spec:
"""The [Global] and [PrimaryGlobal] extended attributes must either take no
arguments or take an identifier list."""
http://heycam.github.io/webidl/#Global

I think this is just for simplicity: it means we can treat them both the same,
even though we don't expect that [PrimaryGlobal] will be used for anything
except Window.
(It's a bit general, admittedly.)

+                         'MUST NOT be declared on the same interface.')
+    global_key = next(iter(global_keys))

[haraken, 2014/06/02 07:41:30]

Nit: Can we write:

global_key = global_keys[0]

?

[Nils Barth (inactive), 2014/06/02 07:55:13]

No, b/c it's a (frozen) set.
We could do list(global_keys)[0], but next(iter(...)) is a bit more Pythonic.

There was a long discussion a few years ago about syntax sugar for this, and it
was rejected:
http://bugs.python.org/issue7212

+
+    global_value = extended_attributes[global_key]
+    if global_value:
+        # FIXME: In spec names are comma-separated, which makes parsing very
+        # difficult (https://www.w3.org/Bugs/Public/show_bug.cgi?id=24959).
+        return global_value.split('&')
+    return [interface_name]
+
+
+def interface_name_global_names(idl_files):
+    """Yields pairs (interface_name, global_names) found in IDL files."""
+    for idl_filename in idl_files:
+        interface_name = idl_filename_to_interface_name(idl_filename)
+        global_names = idl_file_to_global_names(idl_filename)
+        if global_names:
+            yield interface_name, global_names
+
+
+################################################################################
+
+def main():
+    options, global_objects_filename = parse_options()
+
+    # Input IDL files are passed in a file, due to OS command line length
+    # limits. This is generated at GYP time, which is ok b/c files are static.
+    idl_files = read_file_to_list(options.idl_files_list)
+
+    write_pickle_file(global_objects_filename,
+                      dict(interface_name_global_names(idl_files)),
+                      options.write_file_only_if_changed)
+
+
+if __name__ == '__main__':
+    sys.exit(main())