Docserver: Add support for viewing docs with a codereview patch applied

chrome/common/extensions/docs/server2/chained_compiled_file_system.py

+# Copyright 2013 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.
+
+from compiled_file_system import CompiledFileSystem
+from file_system import FileNotFoundError
+
+class ChainedCompiledFileSystem(CompiledFileSystem):

[not at google - send to devlin, 2013/05/11 20:39:53]

comment

[not at google - send to devlin, 2013/05/11 20:39:53]

pls always use composition not inheritance - particularly in python, in which
object graphs are confusing enough already.

the only exception to this is interfaces/mixins like
FileSystem/ObjectStore/Patcher/etc are. You will notice there is no case of
implementation inheritance in the docserver, except where enforced by libraries.

What I imagine this class might look like:

class ChainedCompiledFileSystem(object):
  # Comment like...
  '''A CompiledFileSystem implementation which gets its data from a chain of
delegate
  CompiledFileSystems. ... the reason why you need it...
  '''
  def Factory(object):
    def __init__(self, compiled_fs_factory_chain):
      self._compiled_fs_factory_chain = compiled_fs_factory_chain

    def Create(self, populate_function, cls, category=None):
      compiled_fs_chain = [factory(populate_function, cls, category)
                           for factory in self._compiled_fs_factory_chain]
      return ChainedCompiledFileSystem(compiled_fs_chain)

  def __init__(self, compiled_fs_chain):
    self._compiled_fs_chain = compiled_fs_chain

  def GetFromFile(self, path, binary=False):
    for compiled_fs in self._compiled_fs_chain:
      try:
        return compiled_fs.GetFromFile(path, binary)
      except FileNotFoundError:
        continue
    # For stack trace.
    self._compiled_fs_chain[-1].GetFromFile(path, binary)
    raise AssertionError()

  def GetFromFileListing(self, path):
    ...

which does away with file_system - but from what I can tell, if the chain passed
into this file has the patched file system first, it will get that version
first?

[方觉(Fang Jue), 2013/05/12 03:01:47]

Done.

[方觉(Fang Jue), 2013/05/12 03:01:47]

Done.

+  class Factory(CompiledFileSystem.Factory):
+    def __init__(self,
+                 file_system,
+                 object_store_creator,
+                 base_compiled_fs_factory=None):
+      self._file_system = file_system
+      self._object_store_creator = object_store_creator
+      self._base_compiled_fs_factory = base_compiled_fs_factory
+
+    def Create(self, populate_function, cls, category=None):
+      fs = self._Create(populate_function, cls, category,
+          ChainedCompiledFileSystem)
+      fs._base_compiled_fs = self._base_compiled_fs_factory.Create(
+          populate_function, cls, category)
+      return fs
+

[not at google - send to devlin, 2013/05/11 20:39:53]

seems to me like this class could just as easily compose the file system that it
inherits from?

+  def GetFromFile(self, path, binary=False):
+    # It's possible that a new file is added in this compiled file system
+    # and it doesn't exist in base_compiled_fs.
+    try:
+      version = self._file_system.Stat(path).version
+      cache_entry = self._base_compiled_fs._GetCacheEntryFromFile(path,
+                                                                  binary)
+      if version == cache_entry.version:
+        return cache_entry.cache_data
+    except FileNotFoundError:
+      pass
+    return CompiledFileSystem.GetFromFile(self, path, binary)
+
+  def GetFromFileListing(self, path):
+    if not path.endswith('/'):
+      path += '/'
+    try:
+      version = self._file_system.Stat(path).version
+      cache_entry = self._base_compiled_fs._GetCacheEntryFromFileListing(
+          path)
+      if version == cache_entry.version:
+        return cache_entry.cache_data
+    except FileNotFoundError:
+      pass
+    return CompiledFileSystem.GetFromFileListing(self, path)