Add a test and impl for map field mock value (#335)

Protobuf map fields are special: under the hood they are implemnted as a
sequence of generated type with two fields: 'key', whose type is the
map key type, and 'value', whose type is the map value type.

The user almost never wants to know about this implementation detail,
and the python proto surface allows python dictionaries as rvalues
when assigning to a mapped field.

This change uses dict literals in generated unit tests where flattened
parameters may refer to mapped fields.

Author: software-dov

gapic/schema/wrappers.py

@@ -110,9 +110,16 @@ def mock_value(self) -> str:
             sub = next(iter(self.type.fields.values()))
             answer = f'{self.type.ident}({sub.name}={sub.mock_value})'
 
-        # If this is a repeated field, then the mock answer should
-        # be a list.
-        if self.repeated:
+        if self.map:
+            # Maps are a special case beacuse they're represented internally as
+            # a list of a generated type with two fields: 'key' and 'value'.
+            answer = '{{{}: {}}}'.format(
+                self.type.fields["key"].mock_value,
+                self.type.fields["value"].mock_value,
+            )
+        elif self.repeated:
+            # If this is a repeated field, then the mock answer should
+            # be a list.
             answer = f'[{answer}]'
 
         # Done; return the mock value.
@@ -568,7 +575,6 @@ def field_headers(self) -> Sequence[str]:
     @utils.cached_property
     def flattened_fields(self) -> Mapping[str, Field]:
         """Return the signature defined for this method."""
-        signatures = self.options.Extensions[client_pb2.method_signature]
         cross_pkg_request = self.input.ident.package != self.ident.package
 
         def filter_fields(sig):
@@ -585,6 +591,7 @@ def filter_fields(sig):
 
                 yield name, field
 
+        signatures = self.options.Extensions[client_pb2.method_signature]
         answer: Dict[str, Field] = collections.OrderedDict(
             name_and_field
             for sig in signatures

gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2

@@ -204,9 +204,11 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
         {% endif %} {# different request package #}
 
         {#- Vanilla python protobuf wrapper types cannot _set_ repeated fields #}
-        {%- for key, field in method.flattened_fields.items() if not(field.repeated and method.input.ident.package != method.ident.package) %}
+        {% if method.flattened_fields -%}
         # If we have keyword arguments corresponding to fields on the
         # request, apply these.
+        {% endif -%}
+        {%- for key, field in method.flattened_fields.items() if not(field.repeated and method.input.ident.package != method.ident.package) %}
         if {{ field.name }} is not None:
             request.{{ key }} = {{ field.name }}
         {%- endfor %}

tests/unit/schema/wrappers/test_field.py

@@ -173,6 +173,25 @@ def test_mock_value_repeated():
     assert field.mock_value == "['foo_bar_value']"
 
 
+def test_mock_value_map():
+    entry_msg = make_message(
+        name='SquidEntry',
+        fields=(
+            make_field(name='key', type='TYPE_STRING'),
+            make_field(name='value', type='TYPE_STRING'),
+        ),
+        options=descriptor_pb2.MessageOptions(map_entry=True),
+    )
+    field = make_field(
+        name='squids',
+        type_name='mollusc.SquidEntry',
+        message=entry_msg,
+        label=3,
+        type='TYPE_MESSAGE',
+    )
+    assert field.mock_value == "{'key_value': 'value_value'}"
+
+
 def test_mock_value_enum():
     values = [
         descriptor_pb2.EnumValueDescriptorProto(name='UNSPECIFIED', number=0),
@@ -227,4 +246,26 @@ def make_field(*, message=None, enum=None, **kwargs) -> wrappers.Field:
     if isinstance(kwargs['type'], str):
         kwargs['type'] = T.Value(kwargs['type'])
     field_pb = descriptor_pb2.FieldDescriptorProto(**kwargs)
-    return wrappers.Field(field_pb=field_pb, message=message, enum=enum)
+    field = wrappers.Field(field_pb=field_pb, message=message, enum=enum)
+    return field
+
+
+def make_message(
+    name, package='foo.bar.v1', module='baz', fields=(), meta=None, options=None
+) -> wrappers.MessageType:
+    message_pb = descriptor_pb2.DescriptorProto(
+        name=name,
+        field=[i.field_pb for i in fields],
+        options=options,
+    )
+    return wrappers.MessageType(
+        message_pb=message_pb,
+        fields=collections.OrderedDict((i.name, i) for i in fields),
+        nested_messages={},
+        nested_enums={},
+        meta=meta or metadata.Metadata(address=metadata.Address(
+            name=name,
+            package=tuple(package.split('.')),
+            module=module,
+        )),
+    )