Allow metadata file to inherit values from another configuration file

chainedconfigparser.py

Index: chainedconfigparser.py
===================================================================
new file mode 100644
--- /dev/null
+++ b/chainedconfigparser.py
@@ -0,0 +1,112 @@
+# coding: utf-8
+
+# This file is part of the Adblock Plus build tools,
+# Copyright (C) 2006-2012 Eyeo GmbH
+#
+# Adblock Plus is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# Adblock Plus is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+
+# Note: These are the base functions common to all packagers, the actual
+# packagers are implemented in packagerGecko and packagerChrome.
+
+import os, codecs, ConfigParser
+
+class ChainedConfigParser:

[Sebastian Noack, 2013/11/05 12:19:38]

I find this approach slightly overkill. I would prefer something as simple as
following instead:


def read_with_inheritance(path):
  files = []
  basedir = os.path.dirname(path)

  try:
    while True:
      file = codecs.open(path, 'rb', encoding='utf-8')
      files.insert(0, file)

      parser = ConfigParser.SafeConfigParser()
      parser.readfp(path)

      try:
        path = parser.get('default', 'inherit')
      except (ConfigParser.NoSectionError, ConfigParser.NoOptionError):
        file.close()
        files.remove(file)
        break

      path = os.path.join(basedir, *path.split('/'))

    for file in files:
      file.seek(0)
      parser.readfp(file)
  finally:
    for file in files:
      file.close()

  return parser

[Wladimir Palant, 2013/11/05 12:45:38]

That was a consideration of course. However, we need to be able to resolve
relative paths in configs - basedir isn't fixed, it's rather dependent on the
config file. Consider the following file foo/metadata:

  [default]
  inherit = bar/metadata
  [mapping]
  icon.png = icon64.png

And foo/bar/metadata (typically inside a subrepository):

  [mapping]
  contentScript.js = default/contentScript.js

Whoever writes foo/bar/metadata file shouldn't need to think about files that
will inherit from it - it's obvious that the relative path
default/contentScript.js here should be resolved relative to the foo/bar/
directory. On the other hand, the relative path icon64.png in foo/metadata file
should be resolved relative to the foo/ directory.

I see now that the change that actually allowed retrieving the source directory
for each setting was part of a different review. I've added this change here but
packager.py is no longer part of the patchset because of that.

[Sebastian Noack, 2013/11/05 13:13:25]

Fair enough, LGTM.

+  """
+    This class provides essentially the same interfaces as SafeConfigParser but
+    allows chaining configuration files so that one config file provides the
+    default values for the other. To specify the config file to inherit from
+    a config file needs to contain the following option:
+
+    [default]
+    inherit = foo/bar.config
+
+    The value of the inherit option has to be a relative path with forward
+    slashes as delimiters. Up to 5 configuration files can be chained this way,
+    longer chains are disallowed to deal with circular references.
+
+    A main API difference to SafeConfigParser is the way a class instance is
+    constructed: a file path has to be passed, this file is assumed to be
+    encoded as UTF-8. Also, ChainedConfigParser data is read-only and the
+    options are case-sensitive.
+  """
+
+  def __init__(self, path):
+    self.chain = []
+    self.read_path(path)
+
+  def read_path(self, path):
+    if len(self.chain) >= 5:
+      raise Exception('Too much inheritance in config files')
+
+    config = ConfigParser.SafeConfigParser()
+    config.optionxform = str
+    handle = codecs.open(path, 'rb', encoding='utf-8')
+    config.readfp(handle)
+    handle.close()
+    self.chain.append(config)
+
+    if config.has_section('default') and config.has_option('default', 'inherit'):
+      parts = config.get('default', 'inherit').split('/')
+      defaults_path = os.path.join(os.path.dirname(path), *parts)
+      self.read_path(defaults_path)
+
+  def defaults(self):
+    result = {}
+    for config in reverse(self.chain):
+      for key, value in config.defaults().iteritems():
+        result[key] = value
+    return result
+
+  def sections(self):
+    result = set()
+    for config in self.chain:
+      for section in config.sections():
+        result.add(section)
+    return list(result)
+
+  def has_section(self, section):
+    for config in self.chain:
+      if config.has_section(section):
+        return True
+    return False
+
+  def options(self, section):
+    result = set()
+    for config in self.chain:
+      if config.has_section(section):
+        for option in config.options(section):
+          result.add(option)
+    return list(result)
+
+  def has_option(self, section, option):
+    for config in self.chain:
+      if config.has_section(section) and config.has_option(section, option):
+        return True
+    return False
+
+  def get(self, section, option):
+    for config in self.chain:
+      if config.has_section(section) and config.has_option(section, option):
+        return config.get(section, option)
+    raise ConfigParser.NoOptionError(option, section)
+
+  def items(self, section):
+    seen = set()
+    result = []
+    for config in self.chain:
+      if config.has_section(section):
+        for name, value in config.items(section):
+          if name not in seen:
+            seen.add(name)
+            result.append((name, value))
+    return result