feat(core/rust): exposing vararg functions to uPy

[no changelog]

core/embed/rust/build.rs

@@ -81,6 +81,8 @@ fn generate_micropython_bindings() {
         .allowlist_var("mp_type_fun_builtin_1")
         .allowlist_var("mp_type_fun_builtin_2")
         .allowlist_var("mp_type_fun_builtin_3")
+        .allowlist_type("mp_obj_fun_builtin_var_t")
+        .allowlist_var("mp_type_fun_builtin_var")
         // gc
         .allowlist_function("gc_alloc")
         // iter

core/embed/rust/src/micropython/func.rs

@@ -16,3 +16,21 @@ impl Func {
 
 // SAFETY: We are in a single-threaded environment.
 unsafe impl Sync for Func {}
+
+pub type FuncVar = ffi::mp_obj_fun_builtin_var_t;
+
+impl FuncVar {
+    /// Convert variable argument "static const" function to a MicroPython
+    /// object.
+    pub const fn as_obj(&'static self) -> Obj {
+        // SAFETY:
+        //  - We are an object struct with a base and a type.
+        //  - 'static lifetime holds us in place.
+        //  - MicroPython is smart enough not to mutate `mp_obj_fun_builtin_var_t`
+        //    objects.
+        unsafe { Obj::from_ptr(self as *const _ as *mut _) }
+    }
+}
+
+// SAFETY: We are in a single-threaded environment.
+unsafe impl Sync for FuncVar {}

core/embed/rust/src/micropython/macros.rs

@@ -46,6 +46,40 @@ macro_rules! obj_fn_3 {
     }};
 }
 
+macro_rules! obj_fn_var {
+    ($min:expr, $max:expr, $f:expr) => {{
+        #[allow(unused_unsafe)]
+        unsafe {
+            use $crate::micropython::ffi;
+
+            ffi::mp_obj_fun_builtin_var_t {
+                base: ffi::mp_obj_base_t {
+                    type_: &ffi::mp_type_fun_builtin_var,
+                },
+                sig: ($min << 17u32) | ($max << 1u32) | 0, // min, max, takes_kw
+                fun: ffi::_mp_obj_fun_builtin_var_t__bindgen_ty_1 { var: Some($f) },
+            }
+        }
+    }};
+}
+
+macro_rules! obj_fn_kw {
+    ($min:expr, $f:expr) => {{
+        #[allow(unused_unsafe)]
+        unsafe {
+            use $crate::micropython::ffi;
+
+            ffi::mp_obj_fun_builtin_var_t {
+                base: ffi::mp_obj_base_t {
+                    type_: &ffi::mp_type_fun_builtin_var,
+                },
+                sig: ($min << 17u32) | (0xffff << 1u32) | 1, // min, max, takes_kw
+                fun: ffi::_mp_obj_fun_builtin_var_t__bindgen_ty_1 { kw: Some($f) },
+            }
+        }
+    }};
+}
+
 /// Construct fixed static const `Map` from `key` => `val` pairs.
 macro_rules! obj_map {
     ($($key:expr => $val:expr),*) => ({