proto3 'optional' keyword support

[zs-dima]

Currently optional Timestamp and optional Duration generate non-nullable types.
However proto3 'optional' keyword means nullable types.

Could be nice to fix this issue to be able to have nullable and non-nullable proto3 types processed correctly.

protocolbuffers/protobuf#2168
protocolbuffers/protobuf#8822

Thanks in advance

[tomasweigenast]

Any update?

[osa1]

However proto3 'optional' keyword means nullable types.

@zs-dima Do you have the source for that? I'm aware of two design documents related to optional in proto3:

• https://github.com/protocolbuffers/protobuf/blob/main/docs/field_presence.md
• https://github.com/protocolbuffers/protobuf/blob/main/docs/implementing_proto3_presence.md

As far as I can see none of these say that optional means the value needs to be nullable. You should be able to check for an optional field's presence, and in protobuf.dart we provide this with hasX methods (where X is the field name).

[osa1]

Support for optional syntax in proto3 files was implemented in #444 (merged as 1319847).

[wb14123]

@osa1 hasX is helpful for reading the fields. However it doesn't provide much type safe. I think make the type nullable would be much more handy.

I'm also wondering the writing of optional fields. If I want a structure with an optional field to be null, do I just init the structure without assign that field? And if I want to update a field from not null value to null value, how can I do it?

[zs-dima]

@osa1 thanks a lot for looking into
nullable - means that optional could has or could not has value
therefore hasX properties are added - to check if nullable field has value or not.

[ryuujo1573]

However proto3 'optional' keyword means nullable types.

@zs-dima Do you have the source for that? I'm aware of two design documents related to optional in proto3:

• https://github.com/protocolbuffers/protobuf/blob/main/docs/field_presence.md
• https://github.com/protocolbuffers/protobuf/blob/main/docs/implementing_proto3_presence.md

As far as I can see none of these say that optional means the value needs to be nullable. You should be able to check for an optional field's presence, and in protobuf.dart we provide this with hasX methods (where X is the field name).

Many thanks but sorry to be here to mention:
We should not use the hasFoo property in languages of null-safety, and instead, we use much simpler syntax which is like:

Foo? get foo => $_getIZ(2);
// ...
foo?.doSomething(); // this conditionally calls the function only if `foo` is not null.

which is in place of

if (hasFoo) {
    foo.doSomething();
}

Also, we can benefit from Foo? syntax when initializing models for response, e.g.

var msg = CameraImageMessage()
  ..width = rawImage.width
  ..height = rawImage.height;
msg.planes
  ..clear()
  ..addAll(rawImage.planes.map((e) => CameraImageMessage_Plane()
    ..height = e.height // this errors when setter of field in ⬆️Cam...Plane receives no nullable value.
    ..width = e.width
    ..data = e.bytes
    ..bytesPerPixel = e.bytesPerPixel
    ..bytesPerRow = e.bytesPerRow));

With property foo (setter/getter) being type Foo?, we can easily initialize generated models with corresponding nullable sources.

To my understandings, the default in proto3 is singular which is equivalent to nullable. (zero for null, and one for normal T)

Thank you.

[osa1]

To answer my own question and elaborate, the field presence spec clearly specifies that the default value for message fields should be null:

When serializing, fields with no presence are not serialized if they contain their default value.
...
For messages, the default is the language-specific null value.

So yes, we should use nullable return types for getters in fields with message types, and return null when the field is not present. #309 is another report of this issue.

[daviddomkar]

I would also like to have the optional types nullable. So far this is the most anoying thing with this package I came across. It is so easy to make a mistake to not check if the value exist with the hasX() method. Native dart null safety would be a much better approach.

[talksik]

how have people worked around it? it's super annoying because I have nested objects in a protobuf response and so I have to do a nest hasX check as far as I know