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;
 }