Add a sys feature to re-export ledger_secure_sdk_sys as the sys module

Author: bigspider

ledger_device_sdk/Cargo.toml

@@ -30,6 +30,13 @@ nano_nbgl = [ "ledger_secure_sdk_sys/nano_nbgl" ]
 debug_csdk = [ "ledger_secure_sdk_sys/debug_csdk" ]
 io_new = []  # switch to new 'io' module
 
+# When enabled, this feature re-exports the `ledger_secure_sdk_sys` crate containing the
+# Ledger C SDK bindings through the `sys` module. Use it to access low-level (unsafe) FFI
+# functions, types, and constants directly from the underlying C SDK.
+# It is preferred to not enable this feature if possible, using instead the safe
+# abstractions in `ledger_device_sdk`, but it is provided for advanced use cases.
+sys = []
+
 default = [ "heap" ]
 
 [lints.rust.unexpected_cfgs]

ledger_device_sdk/src/lib.rs

@@ -59,13 +59,19 @@ pub fn exiting_panic(_info: &PanicInfo) -> ! {
     ledger_secure_sdk_sys::exit_app(0);
 }
 
-// re-export exit_app
+// Re-export exit_app
 pub use ledger_secure_sdk_sys::buttons;
 pub use ledger_secure_sdk_sys::exit_app;
 
-// re-export include_gif macro
+// Re-export include_gif macro
 pub use include_gif::include_gif;
 
+// Re-export the underlying Ledger C SDK bindings when the `sys` feature is enabled.
+// This provides direct (unsafe) FFI access. Prefer the safe abstractions in this crate
+// when possible.
+#[cfg(feature = "sys")]
+pub use ledger_secure_sdk_sys as sys;
+
 use ledger_secure_sdk_sys::{pic_rs, pic_rs_mut};
 
 /// Helper macro that sets an external panic handler