Use drop instead of the toilet closure `|_| ()`

src/liballoc/tests/arc.rs

@@ -142,7 +142,7 @@ fn shared_from_iter_trustedlen_normal() {
 
     // Try a ZST to make sure it is handled well.
     {
-        let iter = (0..SHARED_ITER_MAX).map(|_| ());
+        let iter = (0..SHARED_ITER_MAX).map(drop);
         let vec = iter.clone().collect::<Vec<_>>();
         let rc = iter.collect::<Rc<[_]>>();
         assert_eq!(&*vec, &*rc);

src/liballoc/tests/rc.rs

@@ -138,7 +138,7 @@ fn shared_from_iter_trustedlen_normal() {
 
     // Try a ZST to make sure it is handled well.
     {
-        let iter = (0..SHARED_ITER_MAX).map(|_| ());
+        let iter = (0..SHARED_ITER_MAX).map(drop);
         let vec = iter.clone().collect::<Vec<_>>();
         let rc = iter.collect::<Rc<[_]>>();
         assert_eq!(&*vec, &*rc);

src/librustc_parse/parser/diagnostics.rs

@@ -866,7 +866,7 @@ impl<'a> Parser<'a> {
         let appl = Applicability::MachineApplicable;
         if self.token.span == DUMMY_SP || self.prev_span == DUMMY_SP {
             // Likely inside a macro, can't provide meaninful suggestions.
-            return self.expect(&token::Semi).map(|_| ());
+            return self.expect(&token::Semi).map(drop);
         } else if !sm.is_multiline(self.prev_span.until(self.token.span)) {
             // The current token is in the same line as the prior token, not recoverable.
         } else if self.look_ahead(1, |t| {
@@ -905,7 +905,7 @@ impl<'a> Parser<'a> {
                 .emit();
             return Ok(());
         }
-        self.expect(&token::Semi).map(|_| ()) // Error unconditionally
+        self.expect(&token::Semi).map(drop) // Error unconditionally
     }
 
     pub(super) fn parse_semi_or_incorrect_foreign_fn_body(

src/libstd/io/buffered.rs

@@ -232,7 +232,7 @@ impl<R: Seek> BufReader<R> {
                 }
             }
         }
-        self.seek(SeekFrom::Current(offset)).map(|_| ())
+        self.seek(SeekFrom::Current(offset)).map(drop)
     }
 }
 

src/libstd/sys/unix/android.rs

@@ -93,12 +93,12 @@ pub fn ftruncate64(fd: c_int, size: u64) -> io::Result<()> {
 
     unsafe {
         match ftruncate64.get() {
-            Some(f) => cvt_r(|| f(fd, size as i64)).map(|_| ()),
+            Some(f) => cvt_r(|| f(fd, size as i64)).map(drop),
             None => {
                 if size > i32::max_value() as u64 {
                     Err(io::Error::new(io::ErrorKind::InvalidInput, "cannot truncate >2GB"))
                 } else {
-                    cvt_r(|| ftruncate(fd, size as i32)).map(|_| ())
+                    cvt_r(|| ftruncate(fd, size as i32)).map(drop)
                 }
             }
         }
@@ -107,7 +107,7 @@ pub fn ftruncate64(fd: c_int, size: u64) -> io::Result<()> {
 
 #[cfg(target_pointer_width = "64")]
 pub fn ftruncate64(fd: c_int, size: u64) -> io::Result<()> {
-    unsafe { cvt_r(|| ftruncate(fd, size as i64)).map(|_| ()) }
+    unsafe { cvt_r(|| ftruncate(fd, size as i64)).map(drop) }
 }
 
 #[cfg(target_pointer_width = "32")]

src/libstd/sys/unix/fs.rs

@@ -814,7 +814,7 @@ impl File {
             use crate::convert::TryInto;
             let size: off64_t =
                 size.try_into().map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
-            cvt_r(|| unsafe { ftruncate64(self.0.raw(), size) }).map(|_| ())
+            cvt_r(|| unsafe { ftruncate64(self.0.raw(), size) }).map(drop)
         }
     }
 

src/libstd/sys/unix/net.rs

@@ -324,7 +324,7 @@ impl Socket {
 
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         let mut nonblocking = nonblocking as libc::c_int;
-        cvt(unsafe { libc::ioctl(*self.as_inner(), libc::FIONBIO, &mut nonblocking) }).map(|_| ())
+        cvt(unsafe { libc::ioctl(*self.as_inner(), libc::FIONBIO, &mut nonblocking) }).map(drop)
     }
 
     pub fn take_error(&self) -> io::Result<Option<io::Error>> {

src/libstd/sys/unix/os.rs

@@ -529,7 +529,7 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
 
     unsafe {
         let _guard = env_lock();
-        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(|_| ())
+        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
     }
 }
 
@@ -538,7 +538,7 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
 
     unsafe {
         let _guard = env_lock();
-        cvt(libc::unsetenv(nbuf.as_ptr())).map(|_| ())
+        cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
     }
 }
 

src/libstd/sys/unix/pipe.rs

@@ -99,11 +99,11 @@ pub fn read2(p1: AnonPipe, v1: &mut Vec<u8>, p2: AnonPipe, v2: &mut Vec<u8>) ->
 
         if fds[0].revents != 0 && read(&p1, v1)? {
             p2.set_nonblocking(false)?;
-            return p2.read_to_end(v2).map(|_| ());
+            return p2.read_to_end(v2).map(drop);
         }
         if fds[1].revents != 0 && read(&p2, v2)? {
             p1.set_nonblocking(false)?;
-            return p1.read_to_end(v1).map(|_| ());
+            return p1.read_to_end(v1).map(drop);
         }
     }
 

src/libstd/sys/unix/process/process_unix.rs

@@ -425,7 +425,7 @@ impl Process {
                 "invalid argument: can't kill an exited process",
             ))
         } else {
-            cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(|_| ())
+            cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
         }
     }
 

src/libstd/sys/vxworks/fs.rs

@@ -340,7 +340,7 @@ impl File {
     }
 
     pub fn truncate(&self, size: u64) -> io::Result<()> {
-        return cvt_r(|| unsafe { ftruncate(self.0.raw(), size as off_t) }).map(|_| ());
+        return cvt_r(|| unsafe { ftruncate(self.0.raw(), size as off_t) }).map(drop);
     }
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {

src/libstd/sys/vxworks/net.rs

@@ -261,7 +261,7 @@ impl Socket {
 
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         let mut nonblocking = nonblocking as libc::c_int;
-        cvt(unsafe { libc::ioctl(*self.as_inner(), libc::FIONBIO, &mut nonblocking) }).map(|_| ())
+        cvt(unsafe { libc::ioctl(*self.as_inner(), libc::FIONBIO, &mut nonblocking) }).map(drop)
     }
 
     pub fn take_error(&self) -> io::Result<Option<io::Error>> {

src/libstd/sys/vxworks/os.rs

@@ -279,7 +279,7 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
 
     unsafe {
         let _guard = env_lock();
-        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(|_| ())
+        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
     }
 }
 
@@ -288,7 +288,7 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
 
     unsafe {
         let _guard = env_lock();
-        cvt(libc::unsetenv(nbuf.as_ptr())).map(|_| ())
+        cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
     }
 }
 

src/libstd/sys/vxworks/pipe.rs

@@ -66,11 +66,11 @@ pub fn read2(p1: AnonPipe, v1: &mut Vec<u8>, p2: AnonPipe, v2: &mut Vec<u8>) ->
 
         if fds[0].revents != 0 && read(&p1, v1)? {
             p2.set_nonblocking_pipe(false)?;
-            return p2.read_to_end(v2).map(|_| ());
+            return p2.read_to_end(v2).map(drop);
         }
         if fds[1].revents != 0 && read(&p2, v2)? {
             p1.set_nonblocking_pipe(false)?;
-            return p1.read_to_end(v1).map(|_| ());
+            return p1.read_to_end(v1).map(drop);
         }
     }
 

src/libstd/sys/vxworks/process/process_vxworks.rs

@@ -138,7 +138,7 @@ impl Process {
                 "invalid argument: can't kill an exited process",
             ))
         } else {
-            cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(|_| ())
+            cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
         }
     }
 

src/libstd/sys/wasi/os.rs

@@ -151,7 +151,7 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
 
     unsafe {
         let _guard = env_lock();
-        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(|_| ())
+        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
     }
 }
 
@@ -160,7 +160,7 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
 
     unsafe {
         let _guard = env_lock();
-        cvt(libc::unsetenv(nbuf.as_ptr())).map(|_| ())
+        cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
     }
 }
 

src/libstd/sys/windows/fs.rs

@@ -923,6 +923,6 @@ fn symlink_junction_inner(target: &Path, junction: &Path) -> io::Result<()> {
             &mut ret,
             ptr::null_mut(),
         ))
-        .map(|_| ())
+        .map(drop)
     }
 }

src/libstd/sys/windows/handle.rs

@@ -156,7 +156,7 @@ impl RawHandle {
     }
 
     pub fn cancel_io(&self) -> io::Result<()> {
-        unsafe { cvt(c::CancelIo(self.raw())).map(|_| ()) }
+        unsafe { cvt(c::CancelIo(self.raw())).map(drop) }
     }
 
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {

src/libstd/sys/windows/net.rs

@@ -355,7 +355,7 @@ impl Socket {
     #[cfg(not(target_vendor = "uwp"))]
     fn set_no_inherit(&self) -> io::Result<()> {
         sys::cvt(unsafe { c::SetHandleInformation(self.0 as c::HANDLE, c::HANDLE_FLAG_INHERIT, 0) })
-            .map(|_| ())
+            .map(drop)
     }
 
     #[cfg(target_vendor = "uwp")]

src/libstd/sys/windows/os.rs

@@ -247,7 +247,7 @@ pub fn chdir(p: &path::Path) -> io::Result<()> {
     let mut p = p.encode_wide().collect::<Vec<_>>();
     p.push(0);
 
-    cvt(unsafe { c::SetCurrentDirectoryW(p.as_ptr()) }).map(|_| ())
+    cvt(unsafe { c::SetCurrentDirectoryW(p.as_ptr()) }).map(drop)
 }
 
 pub fn getenv(k: &OsStr) -> io::Result<Option<OsString>> {
@@ -272,12 +272,12 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
     let k = to_u16s(k)?;
     let v = to_u16s(v)?;
 
-    cvt(unsafe { c::SetEnvironmentVariableW(k.as_ptr(), v.as_ptr()) }).map(|_| ())
+    cvt(unsafe { c::SetEnvironmentVariableW(k.as_ptr(), v.as_ptr()) }).map(drop)
 }
 
 pub fn unsetenv(n: &OsStr) -> io::Result<()> {
     let v = to_u16s(n)?;
-    cvt(unsafe { c::SetEnvironmentVariableW(v.as_ptr(), ptr::null()) }).map(|_| ())
+    cvt(unsafe { c::SetEnvironmentVariableW(v.as_ptr(), ptr::null()) }).map(drop)
 }
 
 pub fn temp_dir() -> PathBuf {

src/libstd/sys_common/mod.rs

@@ -36,7 +36,7 @@ macro_rules! rtunwrap {
         match $e {
             $ok(v) => v,
             ref err => {
-                let err = err.as_ref().map(|_| ()); // map Ok/Some which might not be Debug
+                let err = err.as_ref().map(drop); // map Ok/Some which might not be Debug
                 rtabort!(concat!("unwrap failed: ", stringify!($e), " = {:?}"), err)
             }
         }

src/libstd/sys_common/net.rs

@@ -659,7 +659,7 @@ impl UdpSocket {
 
     pub fn connect(&self, addr: io::Result<&SocketAddr>) -> io::Result<()> {
         let (addrp, len) = addr?.into_inner();
-        cvt_r(|| unsafe { c::connect(*self.inner.as_inner(), addrp, len) }).map(|_| ())
+        cvt_r(|| unsafe { c::connect(*self.inner.as_inner(), addrp, len) }).map(drop)
     }
 }
 

src/test/ui/async-await/issues/issue-64433.rs

@@ -23,7 +23,7 @@ impl B {
 async fn can_error(some_string: &str) -> Result<(), String> {
     let a = A { inner: vec![some_string, "foo"] };
     let mut b = B {};
-    Ok(b.something_with_a(a).await.map(|_| ())?)
+    Ok(b.something_with_a(a).await.map(drop)?)
 }
 
 fn main() {

src/test/ui/nll/issue-50343.rs

@@ -3,6 +3,6 @@
 #![deny(unused_mut)]
 
 fn main() {
-    vec![42].iter().map(|_| ()).count();
+    vec![42].iter().map(drop).count();
     vec![(42, 22)].iter().map(|(_x, _y)| ()).count();
 }

src/test/ui/paths-containing-nul.rs

@@ -17,7 +17,7 @@ fn assert_invalid_input<T>(on: &str, result: io::Result<T>) {
                               "{} returned a strange {:?} on a path with NUL", on, e.kind()),
         }
     }
-    inner(on, result.map(|_| ()))
+    inner(on, result.map(drop))
 }
 
 fn main() {