There is currently no way of marking a whole message as deprecated.

My current workaround of doing this is to deprecate all fields.

message MyMessage {
    uint32 id = 1 [deprecated=true];
    string name = 2 [deprecated=true];
}

... but it does not exactly mean the same thing, right ?

It would be great to be able to either mark the message with an option (does that even exist ?)

message MyMessage [deprecated=true] {
    uint32 id = 1;
    string name = 2;
}

or an annotation ?

@deprecated
message MyMessage {
    uint32 id = 1;
    string name = 2;
}

The other nice thing about deprecating the message itself would be that one would not need to find all its usages as field and mark all of them as deprecated fields.