The current Rust codegen (specifically here) generates an args struct with Option<T> fields even when those fields are marked as (required) in the .fbs definition.

Example:

table Message {
  name: string (required);
}

pub struct MessageArgs {
  pub name: Option<flatbuffers::WIPOffset<&'a str>>,
}

// ... 

let msg = Message::create(&mut builder, &MessageArgs { ..Default::default() }); // panic, oh no

It would be nice for compile-time safety if creating these flatbuffer messages it was a compile-time failure if things were not specified (and I would be prepared to live with a flag that disables the builder style completely in that case).