nanopb not applying options

Question

I have the following proto definition

syntax = "proto3";

message SimpleMessage {
  repeated int32 lucky_numbers = 1;
}

and options file

SimpleMessage.lucky_numbers max_size:10 fixed_length:true

I run protoc with the following

protoc --plugin=protoc-gen-nanopb=nanopb/generator/protoc-gen-nanopb ./simple.proto "--nanopb_out=-v -f simple.options:."

and it correctly picks up options (don't know why it prints the same stuff twice)

Options for SimpleMessage.lucky_numbers: max_size: 10
proto3: true
fixed_length: true

Now when I check the generated simple.pb.h, I see that

/* Struct definitions */
typedef struct _SimpleMessage {
    pb_callback_t lucky_numbers;
} SimpleMessage;

I was expecting int32_t lucky_numbers[10]; as the documentation indicated. Any idea where I went wrong?