Translate classes with mutable fields (#387)

Classes with mutable fields can modify the mutable fields even in const
methods. For this reason, the receiver of const methods in classes that
contain mutable fields should be `&mut` instead of `&`.

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -1123,7 +1123,7 @@ bool Converter::ConvertCXXMethodDecl(clang::CXXMethodDecl *decl) {
 }
 
 std::string Converter::GetSelfMaybeWithMut(const clang::CXXMethodDecl *decl) {
-  return decl->isConst() ? "&self" : "&mut self";
+  return MethodNeedsMutableReceiver(decl) ? "&mut self" : "&self";
 }
 
 std::string Converter::GetCtorName(clang::CXXConstructorDecl *decl) {
@@ -3210,12 +3210,22 @@ void Converter::SetUFCSReceiver(clang::Expr *base, bool is_arrow,
   }
   Buffer buf(*this);
   PushExprKind push(*this, ExprKind::LValue);
-  StrCat(method->isConst() ? "&" : "&mut");
+  auto object_type = is_arrow ? base->getType()->getPointeeType()
+                              : base->getType().getNonReferenceType();
+  bool cast_mut =
+      MethodNeedsMutableReceiver(method) && object_type.isConstQualified();
+  StrCat(MethodNeedsMutableReceiver(method) ? "&mut" : "&");
+  if (cast_mut) {
+    StrCat("*(&raw const");
+  }
   if (is_arrow) {
     ConvertArrow(base);
   } else {
     Convert(base);
   }
+  if (cast_mut) {
+    StrCat(").cast_mut()");
+  }
   ufcs_receiver_ = std::move(buf).str();
 }
 
@@ -4451,7 +4461,7 @@ std::string Converter::GetComparisonCall(const clang::FunctionDecl *op,
   auto record = GetRecordName(decl);
   auto arg = std::format("{} as *const {}", rhs, record);
   if (const auto *method = clang::dyn_cast<clang::CXXMethodDecl>(op)) {
-    auto recv = method->isConst()
+    auto recv = !MethodNeedsMutableReceiver(method)
                     ? std::string(lhs)
                     : std::format("&mut *(&raw const *{}).cast_mut()", lhs);
     return std::format("{}::{}({}, {})", GetUFCSName(method),

cpp2rust/converter/converter_lib.cpp

@@ -402,6 +402,15 @@ bool IsRValueConvertingConstructor(const clang::CXXConstructorDecl *ctor) {
          ctor->getParamDecl(0)->getType()->isRValueReferenceType();
 }
 
+bool MethodNeedsMutableReceiver(const clang::CXXMethodDecl *method) {
+  if (!method->isConst()) {
+    return true;
+  }
+  return std::any_of(method->getParent()->field_begin(),
+                     method->getParent()->field_end(),
+                     [](const clang::FieldDecl *f) { return f->isMutable(); });
+}
+
 bool IsPassThroughConstructor(const clang::CXXConstructorDecl *ctor) {
   return !IsConvertibleCopyOrMoveConstructor(ctor) &&
          (ctor->isCopyOrMoveConstructor() ||

cpp2rust/converter/converter_lib.h

@@ -97,6 +97,8 @@ bool IsRValueConvertingConstructor(const clang::CXXConstructorDecl *ctor);
 
 bool IsPassThroughConstructor(const clang::CXXConstructorDecl *ctor);
 
+bool MethodNeedsMutableReceiver(const clang::CXXMethodDecl *method);
+
 bool IsConvertibleCXXRecordDecl(const clang::CXXRecordDecl *decl);
 
 bool IsConvertibleCXXMethodDecl(const clang::CXXMethodDecl *decl);

tests/unit/class.cpp

@@ -36,6 +36,21 @@ struct Route {
   }
 };
 
+struct Counter {
+  int v;
+  mutable int calls;
+
+  int Get() const {
+    ++calls;
+    return v;
+  }
+
+  bool operator==(const Counter &o) const {
+    ++calls;
+    return v == o.v;
+  }
+};
+
 int RandomRoute(Route &route) {
   if (route.path.first % 2) {
     return route.path.SetFirst(route.path.SetSecond(10));
@@ -49,5 +64,15 @@ int main() {
   Route route2 = {{1, 0}, 10};
   double old_cost = route1.SetCost(route2.SetCost(15));
   assert(RandomRoute(route1) + RandomRoute(route2) + old_cost == 9);
+  Counter c1{3, 0};
+  const Counter c2{3, 0};
+  const Counter *pc = &c1;
+  assert(c1.Get() == 3);
+  assert(c2.Get() == 3);
+  assert(pc->Get() == 3);
+  assert(c1 == c2);
+  assert(c2 == c1);
+  assert(c1.calls == 3);
+  assert(c2.calls == 2);
   return 0;
 }

tests/unit/out/refcount/class.rs

@@ -66,6 +66,55 @@ impl ByteRepr for Route {
         }
     }
 }
+#[derive(Default)]
+pub struct Counter {
+    pub v: Value<i32>,
+    pub calls: Value<i32>,
+}
+impl std::cmp::PartialEq for Counter {
+    fn eq(&self, other: &Self) -> bool {
+        {
+            CounterImpl::operator_eq(
+                &Rc::new(RefCell::new(Counter {
+                    v: self.v.clone(),
+                    calls: self.calls.clone(),
+                }))
+                .as_pointer(),
+                Rc::new(RefCell::new(Counter {
+                    v: other.v.clone(),
+                    calls: other.calls.clone(),
+                }))
+                .as_pointer(),
+            )
+        }
+    }
+}
+impl std::cmp::Eq for Counter {}
+impl Clone for Counter {
+    fn clone(&self) -> Self {
+        let __this: Value<Counter> = Rc::new(RefCell::new(Self {
+            v: Rc::new(RefCell::new((*self.v.borrow()))),
+            calls: Rc::new(RefCell::new((*self.calls.borrow()))),
+        }));
+        let this: Ptr<Counter> = __this.as_pointer();
+        Rc::try_unwrap(__this).ok().unwrap().into_inner()
+    }
+}
+impl ByteRepr for Counter {
+    fn byte_size() -> usize {
+        8
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        (*self.v.borrow()).to_bytes(&mut buf[0..4]);
+        (*self.calls.borrow()).to_bytes(&mut buf[4..8]);
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        Self {
+            v: Rc::new(RefCell::new(<i32>::from_bytes(&buf[0..4]))),
+            calls: Rc::new(RefCell::new(<i32>::from_bytes(&buf[4..8]))),
+        }
+    }
+}
 pub fn RandomRoute_0(route: Ptr<Route>) -> i32 {
     if (((*(*(*route.upgrade().deref()).path.borrow()).first.borrow()) % 2) != 0) {
         return ({
@@ -115,8 +164,41 @@ fn main_0() -> i32 {
             + (*old_cost.borrow()))
             == 9_f64)
     );
+    let c1: Value<Counter> = Rc::new(RefCell::new(Counter {
+        v: Rc::new(RefCell::new(3)),
+        calls: Rc::new(RefCell::new(0)),
+    }));
+    let c2: Value<Counter> = Rc::new(RefCell::new(Counter {
+        v: Rc::new(RefCell::new(3)),
+        calls: Rc::new(RefCell::new(0)),
+    }));
+    let pc: Value<Ptr<Counter>> = Rc::new(RefCell::new((c1.as_pointer())));
+    assert!((({ CounterImpl::Get(&c1.as_pointer(),) }) == 3));
+    assert!((({ CounterImpl::Get(&c2.as_pointer(),) }) == 3));
+    assert!((({ CounterImpl::Get(&(*pc.borrow()),) }) == 3));
+    assert!(({ CounterImpl::operator_eq(&c1.as_pointer(), c2.as_pointer(),) }));
+    assert!(({ CounterImpl::operator_eq(&c2.as_pointer(), c1.as_pointer(),) }));
+    assert!(((*(*c1.borrow()).calls.borrow()) == 3));
+    assert!(((*(*c2.borrow()).calls.borrow()) == 2));
     return 0;
 }
+pub trait CounterImpl {
+    fn Get(&self) -> i32;
+    fn operator_eq(&self, o: Ptr<Counter>) -> bool;
+}
+impl CounterImpl for Ptr<Counter> {
+    fn Get(&self) -> i32 {
+        (*(*(*self).upgrade().deref()).calls.borrow_mut()).prefix_inc();
+        return (*(*(*self).upgrade().deref()).v.borrow());
+    }
+    fn operator_eq(&self, o: Ptr<Counter>) -> bool {
+        (*(*(*self).upgrade().deref()).calls.borrow_mut()).prefix_inc();
+        return {
+            let _lhs = (*(*(*self).upgrade().deref()).v.borrow());
+            _lhs == (*(*o.upgrade().deref()).v.borrow())
+        };
+    }
+}
 pub trait PairImpl {
     fn NOP(&self);
     fn GetFirst(&self) -> i32;

tests/unit/out/unsafe/class.rs

@@ -54,6 +54,30 @@ impl Route {
         return old_cost;
     }
 }
+#[repr(C)]
+#[derive(Copy, Clone, Default)]
+pub struct Counter {
+    pub v: i32,
+    pub calls: i32,
+}
+impl Counter {
+    pub unsafe fn Get(&mut self) -> i32 {
+        self.calls.prefix_inc();
+        return self.v;
+    }
+    pub unsafe fn operator_eq(&mut self, o: *const Counter) -> bool {
+        self.calls.prefix_inc();
+        return ((self.v) == ((*o).v));
+    }
+}
+impl std::cmp::PartialEq for Counter {
+    fn eq(&self, other: &Self) -> bool {
+        unsafe {
+            Counter::operator_eq(&mut *(&raw const *self).cast_mut(), other as *const Counter)
+        }
+    }
+}
+impl std::cmp::Eq for Counter {}
 pub unsafe fn RandomRoute_0(route: *mut Route) -> i32 {
     if ((((*route).path.first) % (2)) != 0) {
         return (unsafe {
@@ -101,6 +125,16 @@ unsafe fn main_0() -> i32 {
             + (old_cost))
             == (9_f64))
     );
+    let mut c1: Counter = Counter { v: 3, calls: 0 };
+    let c2: Counter = Counter { v: 3, calls: 0 };
+    let mut pc: *const Counter = (&mut c1 as *mut Counter).cast_const();
+    assert!(((unsafe { Counter::Get(&mut *(&raw const c1).cast_mut(),) }) == (3)));
+    assert!(((unsafe { Counter::Get(&mut *(&raw const c2).cast_mut(),) }) == (3)));
+    assert!(((unsafe { Counter::Get(&mut *(&raw const (*pc)).cast_mut(),) }) == (3)));
+    assert!((unsafe { Counter::operator_eq(&mut *(&raw const c1).cast_mut(), &c2,) }));
+    assert!((unsafe { Counter::operator_eq(&mut *(&raw const c2).cast_mut(), &c1,) }));
+    assert!(((c1.calls) == (3)));
+    assert!(((c2.calls) == (2)));
     return 0;
 }
 pub unsafe fn __cpp2rust_init_globals() {}