FnProto

    pub const FnProto = struct {
        params_start: ExtraIndex,
        params_end: ExtraIndex,
        /// Populated if align(A) is present.
        align_expr: OptionalIndex,
        /// Populated if addrspace(A) is present.
        addrspace_expr: OptionalIndex,
        /// Populated if linksection(A) is present.
        section_expr: OptionalIndex,
        /// Populated if callconv(A) is present.
        callconv_expr: OptionalIndex,
    }