Message extensions cannot have required fields.

[Anthony Sampton]

After the latest release (2.6.0) all my protos wouldn't compile.
Protoc gives me the following error: "Message extensions cannot have required fields."

Can anyone explain me why can't I use the required field in extention in the code below?

message MyMsgA {
    extensions 100 to max;
    required int32 i = 1;
}
 
message MyMsgB {
    extend MyMsgA {
        required MyMsgB b_data = 100;
    }
    required string s = 1;
}

Thanks in advance.

[Anthony Sampton]

I'm pretty sure it's not only me who faced with this problem, BUMP.

[Oliver Jowett]

Presumably this is because, if your example was allowed, a valid
MyMsgA encoding would no longer be a valid MyMsgB encoding.

Oliver

On 25 October 2014 13:28, Anthony Sampton <anthony...@gmail.com> wrote:
>
> I'm pretty sure it's not only me who faced with this problem, BUMP.
>

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[Oliver Jowett]

On 25 October 2014 14:15, Oliver Jowett <oliver...@gmail.com> wrote:
> Presumably this is because, if your example was allowed, a valid
> MyMsgA encoding would no longer be a valid MyMsgB encoding.

Sorry, I mean, "would no longer be a valid encoding of MyMsgA as
extended by the extension declared within MyMsgB".

Oliver

[Feng Xiao]

This is working as intended. Extensions, by its definition, is something optionally attached to a message and it doesn't make sense for it to be required, and technically there is no way to enforce this requirement because a binary can be compiled without the extension definition in which case there is no way to know whether the extension is required or optional.

And the change in 2.6.0 is actually a bug fix because in previous versions the required label is simply ignored and the extension is treated as optional any way.

On Sat, Oct 25, 2014 at 5:28 AM, Anthony Sampton <anthony...@gmail.com> wrote:

I'm pretty sure it's not only me who faced with this problem, BUMP.

--

[Feng Xiao]

To clarify, required extensions are disallowed, required fields in an extension message is allowed. I.e., the following is ok:

message A {

  extensions 1 to max;

}

message B {

  extend A { optional B extension = 1; }

  required string s = 1;