Function override_methods 

fn override_methods(
    shape: Shape,
    mods: &Modifiers,
    introduces_nulls_fn: Option<TokenStream>,
) -> Vec<TokenStream>

One fn name(&self) -> Ret { expr } per modifier present in mods, in the arity table’s order rather than the attribute’s order, so the generated code is stable against how a call site happens to spell its modifiers.

introduces_nulls_fn fills the table’s introduces_nulls slot, because generate synthesizes that method from the output type and the modifier together. The walk never builds it from mods.