Make const variables that need destruction mut in unsafe (#515)

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -480,7 +480,7 @@ bool Converter::NeedsMut(const clang::VarDecl *decl, clang::QualType type,
   auto *method_or_null =
       curr_function_ ? clang::dyn_cast<clang::CXXMethodDecl>(curr_function_)
                      : nullptr;
-  return ((hoisted_decls_.contains(decl) ||
+  return ((hoisted_decls_.contains(decl) || NeedsScopedDestructor(decl) ||
            (!type.isConstQualified() && !type->isReferenceType())) &&
           ((method_or_null == nullptr) || !method_or_null->isVirtual()) &&
           !IsGlobalVar(decl) && name != "_");
@@ -627,8 +627,21 @@ bool Converter::VisitVarDecl(clang::VarDecl *decl) {
   return false;
 }
 
-void Converter::EmitScopedDestructor(const clang::VarDecl *decl) {
+bool Converter::NeedsScopedDestructor(const clang::VarDecl *decl) const {
   if (in_function_formals_ || !decl->isLocalVarDecl() || IsGlobalVar(decl)) {
+    return false;
+  }
+  auto type = decl->getType();
+  if (auto lambda = AsLambdaClass(type);
+      lambda && LambdaNeedsDestruction(lambda)) {
+    return true;
+  }
+  return !type->isReferenceType() && !type->isArrayType() &&
+         TypeNeedsDestruction(type);
+}
+
+void Converter::EmitScopedDestructor(const clang::VarDecl *decl) {
+  if (!NeedsScopedDestructor(decl)) {
     return;
   }
   auto type = decl->getType();
@@ -640,10 +653,6 @@ void Converter::EmitScopedDestructor(const clang::VarDecl *decl) {
                        GetNamedDeclAsString(decl)));
     return;
   }
-  if (type->isReferenceType() || type->isArrayType() ||
-      !TypeNeedsDestruction(type)) {
-    return;
-  }
   auto name = GetNamedDeclAsString(decl);
   StrCat(token::kSemiColon,
          std::format("let _dtor_{0} = ScopedDestructorUnsafe::new(&raw mut "

cpp2rust/converter/converter.h

@@ -150,6 +150,8 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
   virtual std::string DestroyMembers(const clang::CXXRecordDecl *decl);
 
+  bool NeedsScopedDestructor(const clang::VarDecl *decl) const;
+
   virtual void EmitScopedDestructor(const clang::VarDecl *decl);
 
   void EmitDeallocation(clang::CXXDeleteExpr *expr,

tests/unit/destructor.cpp

@@ -106,5 +106,12 @@ int main() {
   assert(order[1] == 2);
   assert(order[2] == 1);
 
+  int before = global;
+  {
+    const S cs;
+    (void)cs;
+  }
+  assert(global == before + 1);
+
   return 0;
 }

tests/unit/out/refcount/destructor.rs

@@ -183,6 +183,13 @@ fn main_0() -> i32 {
             order_1.with(|rc| rc.borrow()[__idx])
         }) == 1)
     );
+    let mut before: i32 = global_0.with(|rc| *rc.borrow());
+    {
+        let cs: Value<S> = Rc::new(RefCell::new(<S>::default()));
+        let _dtor_cs = ScopedDestructor::new(&cs, |__p| __p.destructor());
+        &(*cs.borrow_mut());
+    }
+    assert!((global_0.with(|rc| *rc.borrow()) == (before + 1)));
     return 0;
 }
 pub trait ArrayMemberImpl {

tests/unit/out/unsafe/destructor.rs

@@ -198,6 +198,13 @@ unsafe fn main_0() -> i32 {
     assert!((((*std::cell::LazyCell::force_mut(&mut *&raw mut order_1))[(0) as usize]) == (3)));
     assert!((((*std::cell::LazyCell::force_mut(&mut *&raw mut order_1))[(1) as usize]) == (2)));
     assert!((((*std::cell::LazyCell::force_mut(&mut *&raw mut order_1))[(2) as usize]) == (1)));
+    let mut before: i32 = (*std::cell::LazyCell::force_mut(&mut *&raw mut global_0));
+    {
+        let mut cs: S = <S>::default();
+        let _dtor_cs = ScopedDestructorUnsafe::new(&raw mut cs, S::destructor);
+        &(cs);
+    }
+    assert!(((*std::cell::LazyCell::force_mut(&mut *&raw mut global_0)) == ((before) + (1))));
     return 0;
 }
 pub unsafe fn __cpp2rust_init_globals() {