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.

Userland/DynamicLoader/main.cpp

@@ -188,8 +188,7 @@ static void allocate_tls()
         total_tls_size += data.value->tls_size();
     }
     if (total_tls_size) {
-        void* tls_address = allocate_tls(total_tls_size);
-        (void)tls_address;
+        [[maybe_unused]] void* tls_address = allocate_tls(total_tls_size);
         VERBOSE("from userspace, tls_address: %p", tls_address);
     }
     g_total_tls_size = total_tls_size;
@@ -211,7 +210,7 @@ static void initialize_libc()
 
     res = global_symbol_lookup("__libc_init");
     ASSERT(res.found);
-    typedef void libc_init_func(void);
+    typedef void libc_init_func();
     ((libc_init_func*)res.address)();
 }
 
@@ -262,8 +261,7 @@ static FlatPtr loader_main(auxv_t* auxvp)
     map_dependencies(main_program_name);
 
     VERBOSE("loaded all dependencies");
-    for (auto& lib : g_loaders) {
-        (void)lib;
+    for ([[maybe_unused]] auto& lib : g_loaders) {
         VERBOSE("%s - tls size: $u, tls offset: %u", lib.key.characters(), lib.value->tls_size(), lib.value->tls_offset());
     }
 
@@ -301,8 +299,7 @@ void _start(int argc, char** argv, char** envp)
 
     FlatPtr entry = loader_main(auxvp);
     VERBOSE("Loaded libs:\n");
-    for (auto& obj : g_loaded_objects) {
-        (void)obj;
+    for ([[maybe_unused]] auto& obj : g_loaded_objects) {
         VERBOSE("%s: %p\n", obj.key.characters(), obj.value->base_address().as_ptr());
     }
 

Userland/Tests/LibC/accuracy-strtod.cpp

@@ -263,11 +263,11 @@ static long long cast_ll(double d)
         long long as_ll;
     };
     typedef char assert_double_8bytes[sizeof(double) == 8 ? 1 : -1];
-    (void)sizeof(assert_double_8bytes);
+    [[maybe_unused]] auto double_size = sizeof(assert_double_8bytes);
     typedef char assert_ll_8bytes[sizeof(long long) == 8 ? 1 : -1];
-    (void)sizeof(assert_ll_8bytes);
+    [[maybe_unused]] auto longlong_size = sizeof(assert_ll_8bytes);
     typedef char assert_readable_8bytes[sizeof(readable_t) == 8 ? 1 : -1];
-    (void)sizeof(assert_readable_8bytes);
+    [[maybe_unused]] auto readable8_size = sizeof(assert_readable_8bytes);
     readable_t readable;
     readable.as_double = d;
     return readable.as_ll;
@@ -280,9 +280,9 @@ static bool is_strtod_close(strtod_fn_t strtod_fn, const char* test_string, cons
         unsigned char as_bytes[8];
     };
     typedef char assert_double_8bytes[sizeof(double) == 8 ? 1 : -1];
-    (void)sizeof(assert_double_8bytes);
+    [[maybe_unused]] auto double_size = sizeof(assert_double_8bytes);
     typedef char assert_readable_8bytes[sizeof(readable_t) == 8 ? 1 : -1];
-    (void)sizeof(assert_readable_8bytes);
+    [[maybe_unused]] auto readable8_size = sizeof(assert_readable_8bytes);
     readable_t readable;
     char* endptr = (char*)0x123;
 

Userland/allocate.cpp

@@ -31,7 +31,7 @@
 #include <string.h>
 #include <unistd.h>
 
-static void usage(void)
+static void usage()
 {
     printf("usage: allocate [number [unit (B/KiB/MiB)]]\n");
     exit(1);

Userland/crash.cpp

@@ -170,8 +170,7 @@ int main(int argc, char** argv)
         Crash("Division by zero", []() {
             volatile int lala = 10;
             volatile int zero = 0;
-            volatile int test = lala / zero;
-            UNUSED_PARAM(test);
+            [[maybe_unused]] volatile int test = lala / zero;
             return Crash::Failure::DidNotCrash;
         }).run(run_type);
     }
@@ -196,8 +195,7 @@ int main(int argc, char** argv)
             if (!uninitialized_memory)
                 return Crash::Failure::UnexpectedError;
 
-            volatile auto x = uninitialized_memory[0][0];
-            UNUSED_PARAM(x);
+            [[maybe_unused]] volatile auto x = uninitialized_memory[0][0];
             return Crash::Failure::DidNotCrash;
         }).run(run_type);
     }
@@ -209,8 +207,7 @@ int main(int argc, char** argv)
                 return Crash::Failure::UnexpectedError;
 
             free(uninitialized_memory);
-            volatile auto x = uninitialized_memory[4][0];
-            UNUSED_PARAM(x);
+            [[maybe_unused]] volatile auto x = uninitialized_memory[4][0];
             return Crash::Failure::DidNotCrash;
         }).run(run_type);
     }
@@ -305,8 +302,7 @@ int main(int argc, char** argv)
 
             free(ptr);
             dbgprintf("ptr = %p\n", ptr);
-            volatile auto foo = *ptr;
-            UNUSED_PARAM(foo);
+            [[maybe_unused]] volatile auto foo = *ptr;
             return Crash::Failure::DidNotCrash;
         }).run(run_type);
     }

Userland/df.cpp

@@ -78,14 +78,11 @@ int main(int argc, char** argv)
         auto fs = fs_object.get("class_name").to_string();
         auto total_block_count = fs_object.get("total_block_count").to_u32();
         auto free_block_count = fs_object.get("free_block_count").to_u32();
-        auto total_inode_count = fs_object.get("total_inode_count").to_u32();
-        auto free_inode_count = fs_object.get("free_inode_count").to_u32();
+        [[maybe_unused]] auto total_inode_count = fs_object.get("total_inode_count").to_u32();
+        [[maybe_unused]] auto free_inode_count = fs_object.get("free_inode_count").to_u32();
         auto block_size = fs_object.get("block_size").to_u32();
         auto mount_point = fs_object.get("mount_point").to_string();
 
-        (void)total_inode_count;
-        (void)free_inode_count;
-
         printf("%-10s", fs.characters());
 
         if (flag_human_readable) {

Userland/dmesg.cpp

@@ -31,7 +31,7 @@
 #include <stdio.h>
 #include <unistd.h>
 
-int main(int argc, char** argv)
+int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
 {
     if (pledge("stdio rpath", nullptr) < 0) {
         perror("pledge");
@@ -45,8 +45,6 @@ int main(int argc, char** argv)
 
     unveil(nullptr, nullptr);
 
-    (void)argc;
-    (void)argv;
     auto f = Core::File::construct("/proc/dmesg");
     if (!f->open(Core::IODevice::ReadOnly)) {
         fprintf(stderr, "open: failed to open /proc/dmesg: %s\n", f->error_string());

Userland/functrace.cpp

@@ -84,7 +84,7 @@ static void print_syscall(PtraceRegisters& regs, size_t depth)
 
 static NonnullOwnPtr<HashMap<void*, X86::Instruction>> instrument_code()
 {
-    (void)demangle("foo"); // Required for linked with __cxa_demangle
+    [[maybe_unused]] auto r = demangle("foo"); // Required for linked with __cxa_demangle
     auto instrumented = make<HashMap<void*, X86::Instruction>>();
     g_debug_session->elf().image().for_each_section_of_type(SHT_PROGBITS, [&](const ELF::Image::Section& section) {
         if (section.name() != ".text")

Userland/lsirq.cpp

@@ -31,11 +31,8 @@
 #include <LibCore/File.h>
 #include <stdio.h>
 
-int main(int argc, char** argv)
+int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
 {
-    UNUSED_PARAM(argc);
-    UNUSED_PARAM(argv);
-
     if (pledge("stdio rpath", nullptr) < 0) {
         perror("pledge");
         return 1;

Userland/lspci.cpp

@@ -32,11 +32,8 @@
 #include <LibPCIDB/Database.h>
 #include <stdio.h>
 
-int main(int argc, char** argv)
+int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
 {
-    UNUSED_PARAM(argc);
-    UNUSED_PARAM(argv);
-
     if (pledge("stdio rpath", nullptr) < 0) {
         perror("pledge");
         return 1;

Userland/more.cpp

@@ -36,15 +36,12 @@ static void wait_for_key()
     printf("\033[7m--[ more ]--\033[0m");
     fflush(stdout);
     char dummy;
-    (void)read(key_fd, &dummy, 1);
+    [[maybe_unused]] auto rc = read(key_fd, &dummy, 1);
     printf("\n");
 }
 
-int main(int argc, char** argv)
+int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
 {
-    (void)argc;
-    (void)argv;
-
     if (pledge("stdio rpath tty", nullptr) < 0) {
         perror("pledge");
         return 1;

Userland/sort.cpp

@@ -32,16 +32,13 @@
 #include <stdlib.h>
 #include <string.h>
 
-int main(int argc, char** argv)
+int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
 {
     if (pledge("stdio", nullptr) > 0) {
         perror("pledge");
         return 1;
     }
 
-    UNUSED_PARAM(argc);
-    UNUSED_PARAM(argv);
-
     Vector<String> lines;
 
     for (;;) {

Userland/test-web.cpp

@@ -364,7 +364,7 @@ JSFileResult TestRunner::run_file_test(const String& test_path)
             new_interpreter.run(new_interpreter.global_object(), *file_program.value());
 
             auto& before_initial_page_load = new_interpreter.vm().get_variable("__BeforeInitialPageLoad__", new_interpreter.global_object()).as_function();
-            (void)new_interpreter.vm().call(before_initial_page_load, JS::js_undefined());
+            [[maybe_unused]] auto rc_before = new_interpreter.vm().call(before_initial_page_load, JS::js_undefined());
             if (new_interpreter.exception())
                 new_interpreter.vm().clear_exception();
 
@@ -374,7 +374,7 @@ JSFileResult TestRunner::run_file_test(const String& test_path)
 
             // Finally run the test by calling "__AfterInitialPageLoad__"
             auto& after_initial_page_load = new_interpreter.vm().get_variable("__AfterInitialPageLoad__", new_interpreter.global_object()).as_function();
-            (void)new_interpreter.vm().call(after_initial_page_load, JS::js_undefined());
+            [[maybe_unused]] auto rc_after = new_interpreter.vm().call(after_initial_page_load, JS::js_undefined());
             if (new_interpreter.exception())
                 new_interpreter.vm().clear_exception();
 

Userland/w.cpp

@@ -85,8 +85,7 @@ int main()
     json.value().as_object().for_each_member([&](auto& tty, auto& value) {
         const JsonObject& entry = value.as_object();
         auto uid = entry.get("uid").to_u32();
-        auto pid = entry.get("pid").to_i32();
-        (void)pid;
+        [[maybe_unused]] auto pid = entry.get("pid").to_i32();
 
         auto login_time = Core::DateTime::from_timestamp(entry.get("login_at").to_number<time_t>());
         auto login_at = login_time.to_string("%b%d %H:%M:%S");