FieldMask path to oneof block does not validate

[mattnathan]

What version of protobuf and what language are you using?
Version:

github.com/golang/protobuf v1.5.2
libprotoc 3.15.8
protoc-gen-go v1.26.0

What did you do?

Given a proto like

message Msg {
  oneof strings {
    string s1 = 1;
    string s2 = 2;
  }
}

After compiling into Go I ran

var Msg *myproto.Msg
mask, err := fieldmaskpb.New(Msg, "strings")
if err != nil {
  panic(err)
}
fmt.Println("Success")

What did you expect to see?

Success

I'd expect to be able to define a field mask for all options in a oneof block.

What did you see instead?

panic: proto: invalid path "strings" for message "myproto.Msg"

Anything else we should know about your project / environment?

I totally get that I could pass fieldmaskpb.New(Msg, "s1", "s2") but this result surprised me and quick Googling didn't show any related results so I thought I'd raise it here.

[neild]

Field masks treat fields in oneofs as regular fields. For your example message, the possible paths are "s1" or "s2". See the documentation section "Field Masks and Oneof Fields":
https://pkg.go.dev/google.golang.org/protobuf/types/known/fieldmaskpb#FieldMask

Note that field masks are not Go specific; the Go implementation does not have any control over their specification.

[mattnathan]

I have no idea why I missed those docs. I guess this can be closed then, was still a little surprised but I guess that's what the specification says.