Translate empty unions in unsafe

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -957,6 +957,9 @@ void Converter::EmitRustUnion(clang::RecordDecl *decl) {
   StrCat(keyword::kPub, keyword::kUnion, GetRecordName(decl));
   {
     PushBrace brace(*this);
+    if (decl->field_empty()) {
+      StrCat("__empty: u8,");
+    }
     for (auto *field : decl->fields()) {
       VisitFieldDecl(field);
     }

tests/unit/out/refcount/union_basic.rs

@@ -44,12 +44,45 @@ impl ByteRepr for basic {
         }
     }
 }
+pub struct empty {
+    __bytes: Value<Box<[u8]>>,
+}
+impl empty {}
+impl Clone for empty {
+    fn clone(&self) -> Self {
+        empty {
+            __bytes: Rc::new(RefCell::new(self.__bytes.borrow().clone())),
+        }
+    }
+}
+impl Default for empty {
+    fn default() -> Self {
+        empty {
+            __bytes: Rc::new(RefCell::new(Box::from([0u8; 1]))),
+        }
+    }
+}
+impl ByteRepr for empty {
+    fn byte_size() -> usize {
+        1
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        buf.copy_from_slice(&self.__bytes.borrow());
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        empty {
+            __bytes: Rc::new(RefCell::new(Box::from(buf))),
+        }
+    }
+}
 pub fn main() {
     __cpp2rust_init_globals();
     std::process::exit(main_0());
 }
 fn main_0() -> i32 {
     let u: Value<basic> = Rc::new(RefCell::new(<basic>::default()));
+    let e: Value<empty> = Rc::new(RefCell::new(<empty>::default()));
+    &(*e.borrow_mut());
     (*u.borrow_mut()).i().write(42);
     assert!((((*u.borrow()).i().read()) == 42));
     (*u.borrow_mut()).f().write(3.140000105E+0);

tests/unit/out/unsafe/union_basic.rs

@@ -17,6 +17,16 @@ impl Default for basic {
         unsafe { std::mem::zeroed() }
     }
 }
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub union empty {
+    __empty: u8,
+}
+impl Default for empty {
+    fn default() -> Self {
+        unsafe { std::mem::zeroed() }
+    }
+}
 pub fn main() {
     unsafe {
         __cpp2rust_init_globals();
@@ -25,6 +35,8 @@ pub fn main() {
 }
 unsafe fn main_0() -> i32 {
     let mut u: basic = <basic>::default();
+    let mut e: empty = <empty>::default();
+    &(e);
     u.i = 42;
     assert!(((u.i) == (42)));
     u.f = 3.140000105E+0;

tests/unit/union_basic.cpp

@@ -5,8 +5,12 @@ union basic {
   float f;
 };
 
+union empty {};
+
 int main(void) {
   union basic u;
+  union empty e;
+  (void)e;
 
   u.i = 42;
   assert(u.i == 42);