Initial patch for the web modules layered platform proposal.

Source/bindings/scripts/code_generator_web_modules.py

Index: Source/bindings/scripts/code_generator_web_modules.py
diff --git a/Source/bindings/scripts/code_generator_web_modules.py b/Source/bindings/scripts/code_generator_web_modules.py
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+++ b/Source/bindings/scripts/code_generator_web_modules.py
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+# Copyright 2015 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.
+
+"""Generate Blink WebModules bindings (.h and .cpp files).
+
+These are used to expose C++ bindings to the rest of Blink for building
+features on top of web APIs instead of baking them into the core code.
+The way these APIs work is to wrap a pointer to the underlying type and
+then pass the wrapped thing by value. Compilers will optimize the
+wrapper out entirely, so there is no performance overhead, but lets
+us enforce that a strictly controlled API surface is exposed to the calling
+code.
+
+We don't want to expose the bad parts of the platform, so we only expose
+APIs that have the WebModulesExposed annotation.
+
+Input: An object of class IdlDefinitions, containing an IDL interface X
+Output: WebModuleX.h and WebModuleX.cpp
+
+Design doc: http://www.chromium.org/developers/design-documents/idl-compiler
+"""
+
+import os
+import posixpath
+import sys
+
+# TODO(ojan): Share this path handling code with code_generator_v8.py..
+
+# Path handling for libraries and templates
+# Paths have to be normalized because Jinja uses the exact template path to
+# determine the hash used in the cache filename, and we need a pre-caching step
+# to be concurrency-safe. Use absolute path because __file__ is absolute if
+# module is imported, and relative if executed directly.
+# If paths differ between pre-caching and individual file compilation, the cache
+# is regenerated, which causes a race condition and breaks concurrent build,
+# since some compile processes will try to read the partially written cache.
+module_path, module_filename = os.path.split(os.path.realpath(__file__))
+third_party_dir = os.path.normpath(os.path.join(
+    module_path, os.pardir, os.pardir, os.pardir, os.pardir))
+templates_dir = os.path.normpath(os.path.join(
+    module_path, os.pardir, 'templates'))
+# Make sure extension is .py, not .pyc or .pyo, so doesn't depend on caching
+module_pyname = os.path.splitext(module_filename)[0] + '.py'
+
+# jinja2 is in chromium's third_party directory.
+# Insert at 1 so at front to override system libraries, and
+# after path[0] == invoking script dir
+sys.path.insert(1, third_party_dir)
+import jinja2
+
+from v8_utilities import cpp_name
+from utilities import idl_filename_to_component
+
+
+def initialize_jinja_env(cache_dir):
+    return jinja2.Environment(
+        loader=jinja2.FileSystemLoader(templates_dir),
+        # Bytecode cache is not concurrency-safe unless pre-cached:
+        # if pre-cached this is read-only, but writing creates a race condition.
+        bytecode_cache=jinja2.FileSystemBytecodeCache(cache_dir),
+        keep_trailing_newline=True,  # newline-terminate generated files
+        lstrip_blocks=True,  # so can indent control flow tags
+        trim_blocks=True)
+
+
+def web_modules_class_name(interface_name):
+    return "WebModule" + interface_name
+
+
+def includes_for_type(component, idl_type):
+    base_idl_type = idl_type.preprocessed_type.base_type
+
+    # TODO(ojan): Make this work for things that have more dependencies (e.g. NodeLists).
+    # e.g. see v8_types.includes_for_type.
+    return set(['bindings/%s/webmodules/WebModule%s.h' % (component, base_idl_type)])
+
+
+class Attribute(object):
+    def __init__(self, name, idl_type):
+        self.name = name
+        self.idl_type = idl_type
+
+
+class CodeGeneratorWebModules(object):
+    def __init__(self, info_provider, cache_dir, output_dir):
+        self.info_provider = info_provider
+        self.jinja_env = initialize_jinja_env(cache_dir)
+        self.output_dir = output_dir
+
+    def generate_code(self, definitions, definition_name):
+        """Returns .h/.cpp code as ((path, content)...)."""
+        # TODO(ojan): Make this work for dictionaries as well.
+        assert(definition_name in definitions.interfaces)
+        return self.generate_interface_code(
+            definitions, definition_name,
+            definitions.interfaces[definition_name])
+
+    def generate_interface_code(self, definitions, interface_name, interface):
+        interface_info = self.info_provider.interfaces_info[interface_name]
+        full_path = interface_info.get('full_path')
+        component = idl_filename_to_component(full_path)
+
+        attributes = []
+        type_includes = set()
+        for attribute in interface.attributes:
+            if 'WebModulesExposed' in attribute.extended_attributes:
+                type_includes = type_includes.union(
+                    includes_for_type(component, attribute.idl_type))
+
+                # TODO(ojan): handle void return types
+                return_type = 'WebModule%s' % attribute.idl_type.preprocessed_type.base_type
+                attribute = Attribute(cpp_name(attribute), return_type)
+                attributes.append(attribute)
+
+        template_context = {
+            'class_name': web_modules_class_name(interface_name),
+            'header_includes': sorted([
+                interface_info['include_path'],
+            ] + list(type_includes)),
+            'attributes': attributes,
+            'interface_name': interface_name
+        }
+
+        header_path = posixpath.join(self.output_dir, 'WebModule%s.h' % interface_name)
+        cpp_path = posixpath.join(self.output_dir, 'WebModule%s.cpp' % interface_name)
+
+        header_template = self.jinja_env.get_template('web_modules_interface.h')
+        cpp_template = self.jinja_env.get_template('web_modules_interface.cpp')
+
+        return (
+            (header_path, header_template.render(template_context)),
+            (cpp_path, cpp_template.render(template_context)),
+        )