Cross-repo recipe package system.

third_party/recipe_engine/field_composer.py

-# Copyright 2013-2015 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.
-
-
-class FieldComposerError(BaseException):
-  """Base error class for this module."""
-  pass
-
-
-class RegistryConflict(FieldComposerError):
-  pass
-
-
-class DegenerateRegistryError(FieldComposerError):
-  pass
-
-
-class CompositionUndefined(FieldComposerError):
-  pass
-
-
-class FieldComposer(object):
-
-  def __init__(self, fields, registered_functors):
-    """Initialize the internal registry mapping names to functors."""
-    try:
-      self._registry = {
-        name: {'combine': value['combine']}
-        for name, value in registered_functors.iteritems()}
-    except KeyError:
-      raise DegenerateRegistryError(
-          'Registry entries must contain key "combine."')
-    self._fields = fields
-
-  def __contains__(self, key):
-    return key in self._fields
-
-  def __getitem__(self, key):
-    return self._fields[key]
-
-  def get(self, index, default=None):
-    """Wrapper for self._fields.get."""
-    return self._fields.get(index, default)
-
-  def iteritems(self):
-    """Wrapper for self._fields.iteritems."""
-    return self._fields.iteritems()
-
-  def compose(self, second_compositor):
-    """Return the monoidal composition of two FieldComposers."""
-    # If second_compositor is a FieldComposer, registries shouldn't conflict.
-    if isinstance(second_compositor, dict):
-      second_compositor = FieldComposer(second_compositor, {})
-    new_registry = self._registry.copy()
-    second_registry = second_compositor._registry
-    for key, value in second_registry.iteritems():
-      if key in self._registry and value != self._registry[key]:
-        raise RegistryConflict('Conflicting values for key %s.' % key)
-      new_registry[key] = value
-
-    # populate new field dictionary with composed values
-    all_keys = set().union(self._fields, second_compositor._fields)
-    new_fields = {}
-    for name in all_keys:
-      if name not in new_registry:
-        raise CompositionUndefined(
-            "No combine function registered for %s." % name)
-      if name in second_compositor:
-        new_value = self.get_with_context(name, second_compositor[name])
-      else:
-        # Name is in exactly one compositor, so get that value.
-        new_value = self[name]
-      new_fields[name] = new_value
-
-    # create and return the new compositor
-    return FieldComposer(new_fields, new_registry)
-
-  def get_with_context(self, key, value):
-    """Combine the current value for key (if any) with value."""
-    if key not in self._registry:
-      raise CompositionUndefined(
-          "No combine function registered for %s." % key)
-    if key in self:
-      return self._registry[key]['combine'](self.get(key), value)
-    return value