Everywhere: Switch from (void) to [[maybe_unused]] (#4473)

Problem:
- `(void)` simply casts the expression to void. This is understood to
  indicate that it is ignored, but this is really a compiler trick to
  get the compiler to not generate a warning.

Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.

Note:
- Functions taking a `(void)` argument list have also been changed to
  `()` because this is not needed and shows up in the same grep
  command.

Libraries/LibC/assert.h

@@ -41,7 +41,7 @@ __attribute__((noreturn)) void __assertion_failed(const char* msg);
         } while (0)
 #    define ASSERT_NOT_REACHED() assert(false)
 #else
-#    define assert(expr) ((void)0)
+#    define assert(expr) (void(0))
 #    define ASSERT_NOT_REACHED() CRASH()
 #endif
 

Libraries/LibC/sched.cpp

@@ -36,15 +36,13 @@ int sched_yield()
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-int sched_get_priority_min(int policy)
+int sched_get_priority_min([[maybe_unused]] int policy)
 {
-    (void)policy;
     return 0; // Idle
 }
 
-int sched_get_priority_max(int policy)
+int sched_get_priority_max([[maybe_unused]] int policy)
 {
-    (void)policy;
     return 3; // High
 }
 

Libraries/LibC/stdio.cpp

@@ -1179,15 +1179,13 @@ int vfscanf(FILE* stream, const char* fmt, va_list ap)
     return vsscanf(buffer, fmt, ap);
 }
 
-void flockfile(FILE* filehandle)
+void flockfile([[maybe_unused]] FILE* filehandle)
 {
-    (void)filehandle;
     dbgprintf("FIXME: Implement flockfile()\n");
 }
 
-void funlockfile(FILE* filehandle)
+void funlockfile([[maybe_unused]] FILE* filehandle)
 {
-    (void)filehandle;
     dbgprintf("FIXME: Implement funlockfile()\n");
 }
 

Libraries/LibC/stdlib.cpp

@@ -804,11 +804,9 @@ size_t mbstowcs(wchar_t*, const char*, size_t)
     ASSERT_NOT_REACHED();
 }
 
-int mbtowc(wchar_t* wch, const char* data, size_t data_size)
+int mbtowc(wchar_t* wch, const char* data, [[maybe_unused]] size_t data_size)
 {
     // FIXME: This needs a real implementation.
-    UNUSED_PARAM(data_size);
-
     if (wch && data) {
         *wch = *data;
         return 1;
@@ -1023,7 +1021,7 @@ unsigned long long strtoull(const char* str, char** endptr, int base)
 // Serenity's PRNG is not cryptographically secure. Do not rely on this for
 // any real crypto! These functions (for now) are for compatibility.
 // TODO: In the future, rand can be made deterministic and this not.
-uint32_t arc4random(void)
+uint32_t arc4random()
 {
     char buf[4];
     syscall(SC_getrandom, buf, 4, 0);
@@ -1073,15 +1071,13 @@ int posix_openpt(int flags)
     return open("/dev/ptmx", flags);
 }
 
-int grantpt(int fd)
+int grantpt([[maybe_unused]] int fd)
 {
-    (void)fd;
     return 0;
 }
 
-int unlockpt(int fd)
+int unlockpt([[maybe_unused]] int fd)
 {
-    (void)fd;
     return 0;
 }
 }

Libraries/LibC/stdlib.h

@@ -41,13 +41,13 @@ __BEGIN_DECLS
 __attribute__((malloc)) __attribute__((alloc_size(1))) void* malloc(size_t);
 __attribute__((malloc)) __attribute__((alloc_size(1, 2))) void* calloc(size_t nmemb, size_t);
 size_t malloc_size(void*);
-void serenity_dump_malloc_stats(void);
+void serenity_dump_malloc_stats();
 void free(void*);
 __attribute__((alloc_size(2))) void* realloc(void* ptr, size_t);
 char* getenv(const char* name);
 int putenv(char*);
 int unsetenv(const char*);
-int clearenv(void);
+int clearenv();
 int setenv(const char* name, const char* value, int overwrite);
 int atoi(const char*);
 long atol(const char*);
@@ -87,7 +87,7 @@ void srand(unsigned seed);
 long int random();
 void srandom(unsigned seed);
 
-uint32_t arc4random(void);
+uint32_t arc4random();
 void arc4random_buf(void*, size_t);
 uint32_t arc4random_uniform(uint32_t);
 

Libraries/LibC/syslog.cpp

@@ -94,7 +94,7 @@ void closelog_r(struct syslog_data* data)
     data->maskpri = LOG_UPTO(LOG_DEBUG);
 }
 
-void closelog(void)
+void closelog()
 {
     closelog_r(&global_log_data);
 }

Libraries/LibC/syslog.h

@@ -61,8 +61,8 @@ struct syslog_data {
 #define LOG_DAEMON   ( 3 << 3)
 #define LOG_AUTH     ( 4 << 3)
 #define LOG_SYSLOG   ( 5 << 3)
-#define LOG_LPR      ( 6 << 3) 
-#define LOG_NEWS     ( 7 << 3) 
+#define LOG_LPR      ( 6 << 3)
+#define LOG_NEWS     ( 7 << 3)
 #define LOG_UUCP     ( 8 << 3)
 #define LOG_CRON     ( 9 << 3)
 #define LOG_AUTHPRIV (10 << 3)
@@ -169,7 +169,7 @@ void vsyslog(int, const char* message, va_list);
 void vsyslog_r(int, struct syslog_data* data, const char* message, va_list);
 void openlog(const char*, int, int);
 void openlog_r(const char*, int, int, struct syslog_data*);
-void closelog(void);
+void closelog();
 void closelog_r(struct syslog_data*);
 int setlogmask(int);
 int setlogmask_r(int, struct syslog_data*);

Libraries/LibC/termcap.cpp

@@ -39,10 +39,8 @@ char PC;
 char* UP;
 char* BC;
 
-int tgetent(char* bp, const char* name)
+int tgetent([[maybe_unused]] char* bp, [[maybe_unused]] const char* name)
 {
-    (void)bp;
-    (void)name;
 #ifdef TERMCAP_DEBUG
     fprintf(stderr, "tgetent: bp=%p, name='%s'\n", bp, name);
 #endif
@@ -120,9 +118,8 @@ char* tgetstr(const char* id, char** area)
 
 #pragma GCC diagnostic pop
 
-int tgetflag(const char* id)
+int tgetflag([[maybe_unused]] const char* id)
 {
-    (void)id;
 #ifdef TERMCAP_DEBUG
     fprintf(stderr, "tgetflag: '%s'\n", id);
 #endif
@@ -143,17 +140,13 @@ int tgetnum(const char* id)
     ASSERT_NOT_REACHED();
 }
 
-char* tgoto(const char* cap, int col, int row)
+char* tgoto([[maybe_unused]] const char* cap, [[maybe_unused]] int col, [[maybe_unused]] int row)
 {
-    (void)cap;
-    (void)col;
-    (void)row;
     ASSERT_NOT_REACHED();
 }
 
-int tputs(const char* str, int affcnt, int (*putc)(int))
+int tputs(const char* str, [[maybe_unused]] int affcnt, int (*putc)(int))
 {
-    (void)affcnt;
     size_t len = strlen(str);
     for (size_t i = 0; i < len; ++i)
         putc(str[i]);

Libraries/LibC/termios.cpp

@@ -51,10 +51,8 @@ int tcsetattr(int fd, int optional_actions, const struct termios* t)
     return -1;
 }
 
-int tcflow(int fd, int action)
+int tcflow([[maybe_unused]] int fd, [[maybe_unused]] int action)
 {
-    (void)fd;
-    (void)action;
     ASSERT_NOT_REACHED();
 }
 

Libraries/LibC/ulimit.cpp

@@ -31,18 +31,14 @@
 
 extern "C" {
 
-long ulimit(int cmd, long newlimit)
+long ulimit([[maybe_unused]] int cmd, [[maybe_unused]] long newlimit)
 {
-    (void)cmd;
-    (void)newlimit;
     ASSERT_NOT_REACHED();
     return -1;
 }
 
-int getrusage(int who, struct rusage* usage)
+int getrusage([[maybe_unused]] int who, [[maybe_unused]] struct rusage* usage)
 {
-    (void)who;
-    (void)usage;
     dbg() << "LibC: getrusage is not implemented";
     return -1;
 }

Libraries/LibC/unistd.cpp

@@ -515,11 +515,8 @@ int mknod(const char* pathname, mode_t mode, dev_t dev)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-long fpathconf(int fd, int name)
+long fpathconf([[maybe_unused]] int fd, [[maybe_unused]] int name)
 {
-    (void)fd;
-    (void)name;
-
     switch (name) {
     case _PC_PATH_MAX:
         return PATH_MAX;
@@ -530,10 +527,8 @@ long fpathconf(int fd, int name)
     ASSERT_NOT_REACHED();
 }
 
-long pathconf(const char* path, int name)
+long pathconf([[maybe_unused]] const char* path, int name)
 {
-    (void)path;
-
     switch (name) {
     case _PC_PATH_MAX:
         return PATH_MAX;
@@ -614,9 +609,8 @@ void sysbeep()
     syscall(SC_beep);
 }
 
-int fsync(int fd)
+int fsync([[maybe_unused]] int fd)
 {
-    UNUSED_PARAM(fd);
     dbgprintf("FIXME: Implement fsync()\n");
     return 0;
 }

Libraries/LibChess/Chess.cpp

@@ -770,8 +770,7 @@ Board::Result Board::game_result() const
         return Result::InsufficientMaterial;
 
     bool are_legal_moves = false;
-    generate_moves([&](Move m) {
-        (void)m;
+    generate_moves([&]([[maybe_unused]] Move m) {
         are_legal_moves = true;
         return IterationDecision::Break;
     });

Libraries/LibChess/UCICommand.cpp

@@ -316,9 +316,8 @@ String BestMoveCommand::to_string() const
     return builder.build();
 }
 
-InfoCommand InfoCommand::from_string(const StringView& command)
+InfoCommand InfoCommand::from_string([[maybe_unused]] const StringView& command)
 {
-    (void)command;
     // FIXME: Implement this.
     ASSERT_NOT_REACHED();
 }

Libraries/LibELF/DynamicLoader.cpp

@@ -391,7 +391,7 @@ void DynamicLoader::do_relocations(size_t total_tls_size)
             // Eagerly BIND_NOW the PLT entries, doing all the symbol looking goodness
             // The patch method returns the address for the LAZY fixup path, but we don't need it here
             VERBOSE("patching plt reloaction: 0x%x\n", relocation.offset_in_section());
-            (void)m_dynamic_object->patch_plt_entry(relocation.offset_in_section());
+            [[maybe_unused]] auto rc = m_dynamic_object->patch_plt_entry(relocation.offset_in_section());
         } else {
             // LAZY-ily bind the PLT slots by just adding the base address to the offsets stored there
             // This avoids doing symbol lookup, which might be expensive
@@ -408,7 +408,7 @@ void DynamicLoader::do_relocations(size_t total_tls_size)
 }
 
 // Defined in <arch>/plt_trampoline.S
-extern "C" void _plt_trampoline(void) __attribute__((visibility("hidden")));
+extern "C" void _plt_trampoline() __attribute__((visibility("hidden")));
 
 void DynamicLoader::setup_plt_trampoline()
 {

Libraries/LibGUI/JSSyntaxHighlighter.cpp

@@ -63,9 +63,8 @@ bool JSSyntaxHighlighter::is_identifier(void* token) const
     return js_token == JS::TokenType::Identifier;
 }
 
-bool JSSyntaxHighlighter::is_navigatable(void* token) const
+bool JSSyntaxHighlighter::is_navigatable([[maybe_unused]] void* token) const
 {
-    (void)token;
     return false;
 }
 

Libraries/LibGfx/Bitmap.cpp

@@ -364,13 +364,11 @@ Bitmap::~Bitmap()
     delete[] m_palette;
 }
 
-void Bitmap::set_mmap_name(const StringView& name)
+void Bitmap::set_mmap_name([[maybe_unused]] const StringView& name)
 {
     ASSERT(m_needs_munmap);
 #ifdef __serenity__
     ::set_mmap_name(m_data, size_in_bytes(), name.to_string().characters());
-#else
-    (void)name;
 #endif
 }
 
@@ -431,7 +429,7 @@ ShareableBitmap Bitmap::to_shareable_bitmap(pid_t peer_pid) const
     return ShareableBitmap(*bitmap);
 }
 
-Optional<BackingStore> Bitmap::allocate_backing_store(BitmapFormat format, const IntSize& size, Purgeable purgeable)
+Optional<BackingStore> Bitmap::allocate_backing_store(BitmapFormat format, const IntSize& size, [[maybe_unused]] Purgeable purgeable)
 {
     if (size_would_overflow(format, size))
         return {};
@@ -444,7 +442,6 @@ Optional<BackingStore> Bitmap::allocate_backing_store(BitmapFormat format, const
     int map_flags = purgeable == Purgeable::Yes ? (MAP_PURGEABLE | MAP_PRIVATE) : (MAP_ANONYMOUS | MAP_PRIVATE);
     data = mmap_with_name(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0, String::format("GraphicsBitmap [%dx%d]", size.width(), size.height()).characters());
 #else
-    UNUSED_PARAM(purgeable);
     int map_flags = (MAP_ANONYMOUS | MAP_PRIVATE);
     data = mmap(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0);
 #endif

Libraries/LibGfx/PBMLoader.cpp

@@ -118,10 +118,8 @@ static int read_number(Streamer& streamer)
     return sb.to_string().to_uint().value_or(0);
 }
 
-static bool read_comment(PBMLoadingContext& context, Streamer& streamer)
+static bool read_comment([[maybe_unused]] PBMLoadingContext& context, Streamer& streamer)
 {
-    (void)context;
-
     bool exist = false;
     u8 byte;
 

Libraries/LibGfx/PGMLoader.cpp

@@ -135,10 +135,8 @@ static bool read_number(Streamer& streamer, u16* value)
     return true;
 }
 
-static bool read_comment(PGMLoadingContext& context, Streamer& streamer)
+static bool read_comment([[maybe_unused]] PGMLoadingContext& context, Streamer& streamer)
 {
-    (void)context;
-
     bool exist = false;
     u8 byte;
 

Libraries/LibGfx/PPMLoader.cpp

@@ -138,10 +138,8 @@ static bool read_number(Streamer& streamer, u16* value)
     return true;
 }
 
-static bool read_comment(PPMLoadingContext& context, Streamer& streamer)
+static bool read_comment([[maybe_unused]] PPMLoadingContext& context, Streamer& streamer)
 {
-    (void)context;
-
     bool exist = false;
     u8 byte;
 

Libraries/LibHTTP/Job.cpp

@@ -271,11 +271,10 @@ void Job::on_socket_connected()
 
                     // we've read everything, now let's get the next chunk
                     size = -1;
-                    auto line = read_line(PAGE_SIZE);
+                    [[maybe_unused]] auto line = read_line(PAGE_SIZE);
 #ifdef JOB_DEBUG
                     dbg() << "Line following (should be empty): _" << line << "_";
 #endif
-                    (void)line;
                 }
                 m_current_chunk_remaining_size = size;
             }

Libraries/LibIPC/Decoder.cpp

@@ -166,7 +166,7 @@ bool Decoder::decode(Dictionary& dictionary)
     return true;
 }
 
-bool Decoder::decode(File& file)
+bool Decoder::decode([[maybe_unused]] File& file)
 {
 #ifdef __serenity__
     int fd = recvfd(m_sockfd);
@@ -177,8 +177,7 @@ bool Decoder::decode(File& file)
     file = File(fd);
     return true;
 #else
-    (void)file;
-    (void)m_sockfd;
+    [[maybe_unused]] auto fd = m_sockfd;
     warnln("fd passing is not supported on this platform, sorry :(");
     return false;
 #endif

Libraries/LibJS/Forward.h

@@ -42,7 +42,7 @@
     JS::Value name([[maybe_unused]] JS::VM& vm, [[maybe_unused]] JS::GlobalObject& global_object)
 
 #define JS_DEFINE_NATIVE_SETTER(name) \
-    void name([[maybe_unused]] JS::VM& vm, [[maybe_unused]] JS::GlobalObject& global_object, JS::Value value)
+    void name([[maybe_unused]] JS::VM& vm, [[maybe_unused]] JS::GlobalObject& global_object, [[maybe_unused]] JS::Value value)
 
 // NOTE: Proxy is not included here as it doesn't have a prototype - m_proxy_constructor is initialized separately.
 #define JS_ENUMERATE_NATIVE_OBJECTS_EXCLUDING_TEMPLATES                                           \

Libraries/LibJS/Runtime/Accessor.h

@@ -63,7 +63,7 @@ public:
         if (!m_setter)
             return;
         // FIXME: It might be nice if we had a way to communicate to our caller if an exception happened after this.
-        (void)vm().call(*m_setter, this_value, setter_value);
+        [[maybe_unused]] auto rc = vm().call(*m_setter, this_value, setter_value);
     }
 
     void visit_edges(Cell::Visitor& visitor) override

Libraries/LibJS/Runtime/IteratorOperations.cpp

@@ -87,9 +87,8 @@ Object* iterator_next(Object& iterator, Value value)
     return &result.as_object();
 }
 
-void iterator_close(Object& iterator)
+void iterator_close([[maybe_unused]] Object& iterator)
 {
-    (void)iterator;
     TODO();
 }
 

Libraries/LibJS/Runtime/VM.h

@@ -225,10 +225,7 @@ public:
     template<typename... Args>
     [[nodiscard]] ALWAYS_INLINE Value call(Function& function, Value this_value, Args... args)
     {
-        // Are there any values in this argpack?
-        // args = [] -> if constexpr (false)
-        // args = [x, y, z] -> if constexpr ((void)x, true || ...)
-        if constexpr ((((void)args, true) || ...)) {
+        if constexpr (sizeof...(Args) > 0) {
             MarkedValueList arglist { heap() };
             (..., arglist.append(move(args)));
             return call(function, this_value, move(arglist));

Libraries/LibLine/Editor.cpp

@@ -1480,7 +1480,7 @@ Vector<size_t, 2> Editor::vt_dsr()
 
     do {
         more_junk_to_read = false;
-        (void)select(1, &readfds, nullptr, nullptr, &timeout);
+        [[maybe_unused]] auto rc = select(1, &readfds, nullptr, nullptr, &timeout);
         if (FD_ISSET(0, &readfds)) {
             auto nread = read(0, buf, 16);
             if (nread < 0) {

Libraries/LibPthread/pthread.cpp

@@ -460,19 +460,13 @@ int pthread_attr_setstacksize(pthread_attr_t* attributes, size_t stack_size)
     return 0;
 }
 
-int pthread_getschedparam(pthread_t thread, int* policy, struct sched_param* param)
+int pthread_getschedparam([[maybe_unused]] pthread_t thread, [[maybe_unused]] int* policy, [[maybe_unused]] struct sched_param* param)
 {
-    (void)thread;
-    (void)policy;
-    (void)param;
     return 0;
 }
 
-int pthread_setschedparam(pthread_t thread, int policy, const struct sched_param* param)
+int pthread_setschedparam([[maybe_unused]] pthread_t thread, [[maybe_unused]] int policy, [[maybe_unused]] const struct sched_param* param)
 {
-    (void)thread;
-    (void)policy;
-    (void)param;
     return 0;
 }
 

Libraries/LibPthread/pthread.h

@@ -67,7 +67,7 @@ int pthread_attr_setstack(pthread_attr_t* attr, void*, size_t);
 int pthread_attr_getstacksize(const pthread_attr_t*, size_t*);
 int pthread_attr_setstacksize(pthread_attr_t*, size_t);
 
-int pthread_once(pthread_once_t*, void (*)(void));
+int pthread_once(pthread_once_t*, void (*)());
 #define PTHREAD_ONCE_INIT 0
 void* pthread_getspecific(pthread_key_t key);
 int pthread_setspecific(pthread_key_t key, const void* value);
@@ -100,14 +100,14 @@ int pthread_cancel(pthread_t);
 int pthread_cond_destroy(pthread_cond_t*);
 int pthread_cond_timedwait(pthread_cond_t*, pthread_mutex_t*, const struct timespec*);
 
-void pthread_testcancel(void);
+void pthread_testcancel();
 
 int pthread_spin_destroy(pthread_spinlock_t*);
 int pthread_spin_init(pthread_spinlock_t*, int);
 int pthread_spin_lock(pthread_spinlock_t*);
 int pthread_spin_trylock(pthread_spinlock_t*);
 int pthread_spin_unlock(pthread_spinlock_t*);
-pthread_t pthread_self(void);
+pthread_t pthread_self();
 int pthread_detach(pthread_t);
 int pthread_equal(pthread_t, pthread_t);
 int pthread_mutexattr_init(pthread_mutexattr_t*);

Libraries/LibPthread/pthread_once.cpp

@@ -37,7 +37,7 @@ enum State : i32 {
     PERFORMING_WITH_WAITERS,
 };
 
-int pthread_once(pthread_once_t* self, void (*callback)(void))
+int pthread_once(pthread_once_t* self, void (*callback)())
 {
     auto& state = reinterpret_cast<Atomic<State>&>(*self);
 

Libraries/LibWeb/Bindings/WindowObject.cpp

@@ -337,7 +337,6 @@ JS_DEFINE_NATIVE_GETTER(WindowObject::document_getter)
 JS_DEFINE_NATIVE_SETTER(WindowObject::document_setter)
 {
     // FIXME: Figure out what we should do here. Just ignore attempts to set window.document for now.
-    UNUSED_PARAM(value);
 }
 
 JS_DEFINE_NATIVE_GETTER(WindowObject::performance_getter)

Libraries/LibWeb/DOM/EventDispatcher.cpp

@@ -48,10 +48,9 @@ namespace Web::DOM {
 
 // FIXME: This shouldn't be here, as retargeting is not only used by the event dispatcher.
 //        When moving this function, it needs to be generalized. https://dom.spec.whatwg.org/#retarget
-static EventTarget* retarget(EventTarget* left, EventTarget* right)
+static EventTarget* retarget(EventTarget* left, [[maybe_unused]] EventTarget* right)
 {
     // FIXME
-    UNUSED_PARAM(right);
     for (;;) {
         if (!is<Node>(left))
             return left;
@@ -110,7 +109,7 @@ bool EventDispatcher::inner_invoke(Event& event, Vector<EventTarget::EventListen
         auto* this_value = Bindings::wrap(global, *event.current_target());
         auto* wrapped_event = Bindings::wrap(global, event);
         auto& vm = global.vm();
-        (void)vm.call(listener.listener->function(), this_value, wrapped_event);
+        [[maybe_unused]] auto rc = vm.call(listener.listener->function(), this_value, wrapped_event);
         if (vm.exception()) {
             vm.clear_exception();
             // FIXME: Set legacyOutputDidListenersThrowFlag if given. (Only used by IndexedDB currently)

Libraries/LibWeb/DOM/Window.cpp

@@ -98,7 +98,7 @@ void Window::timer_did_fire(Badge<Timer>, Timer& timer)
         m_timers.remove(timer.id());
     }
 
-    (void)vm.call(timer.callback(), wrapper());
+    [[maybe_unused]] auto rc = vm.call(timer.callback(), wrapper());
     if (vm.exception())
         vm.clear_exception();
 }
@@ -132,7 +132,7 @@ i32 Window::request_animation_frame(JS::Function& callback)
         auto& function = const_cast<JS::Function&>(static_cast<const JS::Function&>(*handle.cell()));
         auto& vm = function.vm();
         fake_timestamp += 10;
-        (void)vm.call(function, {}, JS::Value(fake_timestamp));
+        [[maybe_unused]] auto rc = vm.call(function, {}, JS::Value(fake_timestamp));
         if (vm.exception())
             vm.clear_exception();
         GUI::DisplayLink::unregister_callback(link_id);

Libraries/LibWeb/Page/EventHandler.cpp

@@ -301,9 +301,8 @@ bool EventHandler::handle_mousemove(const Gfx::IntPoint& position, unsigned butt
     return true;
 }
 
-void EventHandler::dump_selection(const char* event_name) const
+void EventHandler::dump_selection([[maybe_unused]] const char* event_name) const
 {
-    UNUSED_PARAM(event_name);
 #ifdef SELECTION_DEBUG
     dbg() << event_name << " selection start: "
           << layout_root()->selection().start().layout_node << ":" << layout_root()->selection().start().index_in_node << ", end: "

Libraries/LibWeb/TreeNode.h

@@ -359,7 +359,7 @@ inline void TreeNode<T>::append_child(NonnullRefPtr<T> node, bool notify)
         m_first_child = m_last_child;
     if (notify)
         node->inserted_into(static_cast<T&>(*this));
-    (void)node.leak_ref();
+    [[maybe_unused]] auto& rc = node.leak_ref();
 
     if (notify)
         static_cast<T*>(this)->children_changed();
@@ -394,7 +394,7 @@ inline void TreeNode<T>::insert_before(NonnullRefPtr<T> node, RefPtr<T> child, b
     node->m_parent = static_cast<T*>(this);
     if (notify)
         node->inserted_into(static_cast<T&>(*this));
-    (void)node.leak_ref();
+    [[maybe_unused]] auto& rc = node.leak_ref();
 
     if (notify)
         static_cast<T*>(this)->children_changed();
@@ -416,7 +416,7 @@ inline void TreeNode<T>::prepend_child(NonnullRefPtr<T> node)
     if (!m_last_child)
         m_last_child = m_first_child;
     node->inserted_into(static_cast<T&>(*this));
-    (void)node.leak_ref();
+    [[maybe_unused]] auto& rc = node.leak_ref();
 
     static_cast<T*>(this)->children_changed();
 }