Add #[must_use] to core and std constructors

library/core/src/alloc/layout.rs

@@ -119,6 +119,7 @@ impl Layout {
     /// Constructs a `Layout` suitable for holding a value of type `T`.
     #[stable(feature = "alloc_layout", since = "1.28.0")]
     #[rustc_const_stable(feature = "alloc_layout_const_new", since = "1.42.0")]
+    #[must_use]
     #[inline]
     pub const fn new<T>() -> Self {
         let (size, align) = size_align::<T>();

library/core/src/hash/sip.rs

@@ -157,6 +157,7 @@ impl SipHasher {
         since = "1.13.0",
         reason = "use `std::collections::hash_map::DefaultHasher` instead"
     )]
+    #[must_use]
     pub fn new() -> SipHasher {
         SipHasher::new_with_keys(0, 0)
     }
@@ -168,6 +169,7 @@ impl SipHasher {
         since = "1.13.0",
         reason = "use `std::collections::hash_map::DefaultHasher` instead"
     )]
+    #[must_use]
     pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher {
         SipHasher(SipHasher24 { hasher: Hasher::new_with_keys(key0, key1) })
     }

library/core/src/lazy.rs

@@ -83,6 +83,7 @@ impl<T> From<T> for OnceCell<T> {
 impl<T> OnceCell<T> {
     /// Creates a new empty cell.
     #[unstable(feature = "once_cell", issue = "74465")]
+    #[must_use]
     pub const fn new() -> OnceCell<T> {
         OnceCell { inner: UnsafeCell::new(None) }
     }

library/core/src/mem/maybe_uninit.rs

@@ -312,6 +312,7 @@ impl<T> MaybeUninit<T> {
     /// ```
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
     #[rustc_const_stable(feature = "const_maybe_uninit", since = "1.36.0")]
+    #[must_use]
     #[inline(always)]
     #[rustc_diagnostic_item = "maybe_uninit_uninit"]
     pub const fn uninit() -> MaybeUninit<T> {
@@ -349,6 +350,7 @@ impl<T> MaybeUninit<T> {
     /// ```
     #[unstable(feature = "maybe_uninit_uninit_array", issue = "none")]
     #[rustc_const_unstable(feature = "maybe_uninit_uninit_array", issue = "none")]
+    #[must_use]
     #[inline(always)]
     pub const fn uninit_array<const LEN: usize>() -> [Self; LEN] {
         // SAFETY: An uninitialized `[MaybeUninit<_>; LEN]` is valid.
@@ -391,6 +393,7 @@ impl<T> MaybeUninit<T> {
     /// // This is undefined behavior. ⚠️
     /// ```
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
+    #[must_use]
     #[inline]
     #[rustc_diagnostic_item = "maybe_uninit_zeroed"]
     pub fn zeroed() -> MaybeUninit<T> {

library/core/src/num/nonzero.rs

@@ -50,6 +50,7 @@ macro_rules! nonzero_integers {
                 /// The value must not be zero.
                 #[$stability]
                 #[$const_new_unchecked_stability]
+                #[must_use]
                 #[inline]
                 pub const unsafe fn new_unchecked(n: $Int) -> Self {
                     // SAFETY: this is guaranteed to be safe by the caller.
@@ -59,6 +60,7 @@ macro_rules! nonzero_integers {
                 /// Creates a non-zero if the given value is not zero.
                 #[$stability]
                 #[rustc_const_stable(feature = "const_nonzero_int_methods", since = "1.47.0")]
+                #[must_use]
                 #[inline]
                 pub const fn new(n: $Int) -> Option<Self> {
                     if n != 0 {

library/core/src/sync/atomic.rs

@@ -290,6 +290,7 @@ impl AtomicBool {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_atomic_new", since = "1.24.0")]
+    #[must_use]
     pub const fn new(v: bool) -> AtomicBool {
         AtomicBool { v: UnsafeCell::new(v as u8) }
     }
@@ -1392,6 +1393,7 @@ macro_rules! atomic_int {
             #[inline]
             #[$stable]
             #[$const_stable]
+            #[must_use]
             pub const fn new(v: $int_type) -> Self {
                 Self {v: UnsafeCell::new(v)}
             }

library/core/src/task/wake.rs

@@ -39,6 +39,7 @@ impl RawWaker {
     #[rustc_promotable]
     #[stable(feature = "futures_api", since = "1.36.0")]
     #[rustc_const_stable(feature = "futures_api", since = "1.36.0")]
+    #[must_use]
     pub const fn new(data: *const (), vtable: &'static RawWakerVTable) -> RawWaker {
         RawWaker { data, vtable }
     }

library/core/src/time.rs

@@ -181,6 +181,7 @@ impl Duration {
     #[stable(feature = "duration", since = "1.3.0")]
     #[inline]
     #[rustc_const_unstable(feature = "duration_consts_2", issue = "72440")]
+    #[must_use]
     pub const fn new(secs: u64, nanos: u32) -> Duration {
         let secs = match secs.checked_add((nanos / NANOS_PER_SEC) as u64) {
             Some(secs) => secs,

library/std/src/collections/hash/map.rs

@@ -223,6 +223,7 @@ impl<K, V> HashMap<K, V, RandomState> {
     /// let mut map: HashMap<&str, i32> = HashMap::new();
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new() -> HashMap<K, V, RandomState> {
         Default::default()
@@ -240,6 +241,7 @@ impl<K, V> HashMap<K, V, RandomState> {
     /// let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
         HashMap::with_capacity_and_hasher(capacity, Default::default())
@@ -2891,6 +2893,7 @@ impl RandomState {
     #[inline]
     #[allow(deprecated)]
     // rand
+    #[must_use]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
     pub fn new() -> RandomState {
         // Historically this function did not cache keys from the OS and instead
@@ -2943,6 +2946,7 @@ impl DefaultHasher {
     /// instances created through `new` or `default`.
     #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
     #[allow(deprecated)]
+    #[must_use]
     pub fn new() -> DefaultHasher {
         DefaultHasher(SipHasher13::new_with_keys(0, 0))
     }

library/std/src/collections/hash/set.rs

@@ -126,6 +126,7 @@ impl<T> HashSet<T, RandomState> {
     /// let set: HashSet<i32> = HashSet::new();
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new() -> HashSet<T, RandomState> {
         Default::default()
@@ -144,6 +145,7 @@ impl<T> HashSet<T, RandomState> {
     /// assert!(set.capacity() >= 10);
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize) -> HashSet<T, RandomState> {
         HashSet { base: base::HashSet::with_capacity_and_hasher(capacity, Default::default()) }

library/std/src/ffi/os_str.rs

@@ -119,6 +119,7 @@ impl OsString {
     /// let os_string = OsString::new();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub fn new() -> OsString {
         OsString { inner: Buf::from_string(String::new()) }
@@ -199,6 +200,7 @@ impl OsString {
     /// assert_eq!(capacity, os_string.capacity());
     /// ```
     #[stable(feature = "osstring_simple_functions", since = "1.9.0")]
+    #[must_use]
     #[inline]
     pub fn with_capacity(capacity: usize) -> OsString {
         OsString { inner: Buf::with_capacity(capacity) }

library/std/src/fs.rs

@@ -744,6 +744,7 @@ impl OpenOptions {
     /// let file = options.read(true).open("foo.txt");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new() -> Self {
         OpenOptions(fs_imp::OpenOptions::new())
     }
@@ -2184,6 +2185,7 @@ impl DirBuilder {
     /// let builder = DirBuilder::new();
     /// ```
     #[stable(feature = "dir_builder", since = "1.6.0")]
+    #[must_use]
     pub fn new() -> DirBuilder {
         DirBuilder { inner: fs_imp::DirBuilder::new(), recursive: false }
     }

library/std/src/io/mod.rs

@@ -1206,6 +1206,7 @@ impl<'a> IoSlice<'a> {
     ///
     /// Panics on Windows if the slice is larger than 4GB.
     #[stable(feature = "iovec", since = "1.36.0")]
+    #[must_use]
     #[inline]
     pub fn new(buf: &'a [u8]) -> IoSlice<'a> {
         IoSlice(sys::io::IoSlice::new(buf))

library/std/src/lazy.rs

@@ -171,6 +171,7 @@ impl<T: Eq> Eq for SyncOnceCell<T> {}
 impl<T> SyncOnceCell<T> {
     /// Creates a new empty cell.
     #[unstable(feature = "once_cell", issue = "74465")]
+    #[must_use]
     pub const fn new() -> SyncOnceCell<T> {
         SyncOnceCell {
             once: Once::new(),

library/std/src/net/addr.rs

@@ -131,6 +131,7 @@ impl SocketAddr {
     /// assert_eq!(socket.port(), 8080);
     /// ```
     #[stable(feature = "ip_addr", since = "1.7.0")]
+    #[must_use]
     pub fn new(ip: IpAddr, port: u16) -> SocketAddr {
         match ip {
             IpAddr::V4(a) => SocketAddr::V4(SocketAddrV4::new(a, port)),
@@ -272,6 +273,7 @@ impl SocketAddrV4 {
     /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new(ip: Ipv4Addr, port: u16) -> SocketAddrV4 {
         SocketAddrV4 {
             inner: c::sockaddr_in {
@@ -368,6 +370,7 @@ impl SocketAddrV6 {
     /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new(ip: Ipv6Addr, port: u16, flowinfo: u32, scope_id: u32) -> SocketAddrV6 {
         SocketAddrV6 {
             inner: c::sockaddr_in6 {

library/std/src/net/ip.rs

@@ -442,6 +442,7 @@ impl Ipv4Addr {
     /// ```
     #[rustc_const_stable(feature = "const_ipv4", since = "1.32.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub const fn new(a: u8, b: u8, c: u8, d: u8) -> Ipv4Addr {
         // `s_addr` is stored as BE on all machine and the array is in BE order.
@@ -1192,6 +1193,7 @@ impl Ipv6Addr {
     /// ```
     #[rustc_const_stable(feature = "const_ipv6", since = "1.32.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub const fn new(a: u16, b: u16, c: u16, d: u16, e: u16, f: u16, g: u16, h: u16) -> Ipv6Addr {
         let addr16 = [

library/std/src/os/unix/net/ancillary.rs

@@ -189,6 +189,7 @@ impl SocketCred {
     ///
     /// PID, UID and GID is set to 0.
     #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
+    #[must_use]
     pub fn new() -> SocketCred {
         SocketCred(libc::ucred { pid: 0, uid: 0, gid: 0 })
     }

library/std/src/path.rs

@@ -1145,6 +1145,7 @@ impl PathBuf {
     /// let path = PathBuf::new();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub fn new() -> PathBuf {
         PathBuf { inner: OsString::new() }
@@ -1169,6 +1170,7 @@ impl PathBuf {
     ///
     /// [`with_capacity`]: OsString::with_capacity
     #[stable(feature = "path_buf_capacity", since = "1.44.0")]
+    #[must_use]
     #[inline]
     pub fn with_capacity(capacity: usize) -> PathBuf {
         PathBuf { inner: OsString::with_capacity(capacity) }

library/std/src/sync/barrier.rs

@@ -80,6 +80,7 @@ impl Barrier {
     /// let barrier = Barrier::new(10);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new(n: usize) -> Barrier {
         Barrier {
             lock: Mutex::new(BarrierState { count: 0, generation_id: 0 }),

library/std/src/sync/condvar.rs

@@ -121,6 +121,7 @@ impl Condvar {
     /// let condvar = Condvar::new();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new() -> Condvar {
         Condvar { inner: sys::Condvar::new() }
     }

library/std/src/sync/once.rs

@@ -186,6 +186,7 @@ impl Once {
     #[inline]
     #[stable(feature = "once_new", since = "1.2.0")]
     #[rustc_const_stable(feature = "const_once_new", since = "1.32.0")]
+    #[must_use]
     pub const fn new() -> Once {
         Once { state_and_queue: AtomicUsize::new(INCOMPLETE), _marker: marker::PhantomData }
     }