Expected

As per proto3's language guide:

Message fields can be one of the following:

• singular: a well-formed message can have zero or one of this field (but not more than one). And this is the default field rule for proto3 syntax.

Hence, I would expect the TypeScript code to allow singular fields to be undefined

syntax = "proto3";

message Message {
  bytes payload = 1;
}

should generate

export interface Message {
  payload?: Uint8Array
}

Actual

syntax = "proto3";

message Message {
  bytes payload = 1;
}

generates

export interface Message {
  payload: Uint8Array
}

Note

When using the optional keyword, I can get the desired effect:

 message Message {
  optional bytes payload = 1;
}

export interface Message {
  payload?: Uint8Array
}

However, optional is not part of the proto3 syntax.