[refactor] Make collection wrappers take their marshal object. (#8)

This commit makes collections accept their marshal object, instead of
referencing a singleton. This will make it easier to make marshals
have a defined scope.

proto/marshal/collections/__init__.py

@@ -0,0 +1,24 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from .map import MapComposite
+from .repeated import Repeated
+from .repeated import RepeatedComposite
+
+
+__all__ = (
+    'MapComposite',
+    'Repeated',
+    'RepeatedComposite',
+)

proto/marshal/collections/map.py

@@ -0,0 +1,81 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import collections
+
+from proto.utils import cached_property
+
+
+class MapComposite(collections.MutableMapping):
+    """A view around a mutable sequence in protocol buffers.
+
+    This implements the full Python MutableMapping interface, but all methods
+    modify the underlying field container directly.
+    """
+    @cached_property
+    def _pb_type(self):
+        """Return the protocol buffer type for this sequence."""
+        # Huzzah, another hack. Still less bad than RepeatedComposite.
+        return type(self.pb.GetEntryClass()().value)
+
+    def __init__(self, sequence, *, marshal):
+        """Initialize a wrapper around a protobuf map.
+
+        Args:
+            sequence: A protocol buffers map.
+            marshal (~.MarshalRegistry): An instantiated marshal, used to
+                convert values going to and from this map.
+        """
+        self._pb = sequence
+        self._marshal = marshal
+
+    def __contains__(self, key):
+        # Protocol buffers is so permissive that querying for the existence
+        # of a key will in of itself create it.
+        #
+        # By taking a tuple of the keys and querying that, we avoid sending
+        # the lookup to protocol buffers and therefore avoid creating the key.
+        return key in tuple(self.keys())
+
+    def __getitem__(self, key):
+        # We handle raising KeyError ourselves, because otherwise protocol
+        # buffers will create the key if it does not exist.
+        if key not in self:
+            raise KeyError(key)
+        return self._marshal.to_python(self._pb_type, self.pb[key])
+
+    def __setitem__(self, key, value):
+        pb_value = self._marshal.to_proto(self._pb_type, value, strict=True)
+
+        # Directly setting a key is not allowed; however, protocol buffers
+        # is so permissive that querying for the existence of a key will in
+        # of itself create it.
+        #
+        # Therefore, we create a key that way (clearing any fields that may
+        # be set) and then merge in our values.
+        self.pb[key].Clear()
+        self.pb[key].MergeFrom(pb_value)
+
+    def __delitem__(self, key):
+        self.pb.pop(key)
+
+    def __len__(self):
+        return len(self.pb)
+
+    def __iter__(self):
+        return iter(self.pb)
+
+    @property
+    def pb(self):
+        return self._pb

proto/marshal/collections/repeated.py

@@ -0,0 +1,127 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import collections
+import copy
+
+from proto.utils import cached_property
+
+
+class Repeated(collections.MutableSequence):
+    """A view around a mutable sequence in protocol buffers.
+
+    This implements the full Python MutableSequence interface, but all methods
+    modify the underlying field container directly.
+    """
+    def __init__(self, sequence, *, marshal):
+        """Initialize a wrapper around a protobuf repeated field.
+
+        Args:
+            sequence: A protocol buffers repeated field.
+            marshal (~.MarshalRegistry): An instantiated marshal, used to
+                convert values going to and from this map.
+        """
+        self._pb = sequence
+        self._marshal = marshal
+
+    def __copy__(self):
+        """Copy this object and return the copy."""
+        return type(self)(self.pb[:], marshal=self._marshal)
+
+    def __delitem__(self, key):
+        """Delete the given item."""
+        del self.pb[key]
+
+    def __eq__(self, other):
+        if hasattr(other, 'pb'):
+            return tuple(self.pb) == tuple(other.pb)
+        return tuple(self.pb) == tuple(other)
+
+    def __getitem__(self, key):
+        """Return the given item."""
+        return self.pb[key]
+
+    def __len__(self):
+        """Return the length of the sequence."""
+        return len(self.pb)
+
+    def __ne__(self, other):
+        return not self == other
+
+    def __repr__(self):
+        return repr(self.pb)
+
+    def __setitem__(self, key, value):
+        self.pb[key] = value
+
+    def insert(self, index: int, value):
+        """Insert ``value`` in the sequence before ``index``."""
+        self.pb.insert(index, value)
+
+    def sort(self, *, key: str = None, reverse: bool = False):
+        """Stable sort *IN PLACE*."""
+        self.pb.sort(key=key, reverse=reverse)
+
+    @property
+    def pb(self):
+        return self._pb
+
+
+class RepeatedComposite(Repeated):
+    """A view around a mutable sequence of messages in protocol buffers.
+
+    This implements the full Python MutableSequence interface, but all methods
+    modify the underlying field container directly.
+    """
+    @cached_property
+    def _pb_type(self):
+        """Return the protocol buffer type for this sequence."""
+        # There is no public-interface mechanism to determine the type
+        # of what should go in the list (and the C implementation seems to
+        # have no exposed mechanism at all).
+        #
+        # If the list has members, use the existing list members to
+        # determine the type.
+        if len(self.pb) > 0:
+            return type(self.pb[0])
+
+        # We have no members in the list.
+        # In order to get the type, we create a throw-away copy and add a
+        # blank member to it.
+        canary = copy.deepcopy(self.pb).add()
+        return type(canary)
+
+    def __getitem__(self, key):
+        return self._marshal.to_python(self._pb_type, self.pb[key])
+
+    def __setitem__(self, key, value):
+        pb_value = self._marshal.to_proto(self._pb_type, value, strict=True)
+
+        # Protocol buffers does not define a useful __setitem__, so we
+        # have to pop everything after this point off the list and reload it.
+        after = [pb_value]
+        while self.pb[key:]:
+            after.append(self.pb.pop(key))
+        self.pb.extend(after)
+
+    def insert(self, index: int, value):
+        """Insert ``value`` in the sequence before ``index``."""
+        pb_value = self._marshal.to_proto(self._pb_type, value, strict=True)
+
+        # Protocol buffers does not define a useful insert, so we have
+        # to pop everything after this point off the list and reload it.
+        after = [pb_value]
+        while self.pb[index:]:
+            after.append(self.pb.pop(index))
+        self.pb.extend(after)