Rollup merge of #89786 - jkugelman:must-use-len-and-is_empty, r=josht…

…riplett

Add #[must_use] to len and is_empty

Parent issue: #89692

r? `@joshtriplett`

library/alloc/src/collections/binary_heap.rs

@@ -1052,6 +1052,7 @@ impl<T> BinaryHeap<T> {
  ///
  /// assert_eq!(heap.len(), 2);
  /// ```
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn len(&self) -> usize {
  self.data.len()
@@ -1075,6 +1076,7 @@ impl<T> BinaryHeap<T> {
  ///
  /// assert!(!heap.is_empty());
  /// ```
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn is_empty(&self) -> bool {
  self.len() == 0

library/alloc/src/collections/btree/map.rs

@@ -2212,6 +2212,7 @@ impl<K, V> BTreeMap<K, V> {
  /// a.insert(1, "a");
  /// assert_eq!(a.len(), 1);
  /// ```
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
  pub const fn len(&self) -> usize {
@@ -2232,6 +2233,7 @@ impl<K, V> BTreeMap<K, V> {
  /// a.insert(1, "a");
  /// assert!(!a.is_empty());
  /// ```
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
  pub const fn is_empty(&self) -> bool {

library/alloc/src/collections/btree/set.rs

@@ -1046,6 +1046,7 @@ impl<T> BTreeSet<T> {
  /// v.insert(1);
  /// assert_eq!(v.len(), 1);
  /// ```
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
  pub const fn len(&self) -> usize {
@@ -1064,6 +1065,7 @@ impl<T> BTreeSet<T> {
  /// v.insert(1);
  /// assert!(!v.is_empty());
  /// ```
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
  pub const fn is_empty(&self) -> bool {

library/alloc/src/collections/btree/set/tests.rs

@@ -610,8 +610,8 @@ fn test_send() {
 #[test]
 fn test_ord_absence() {
  fn set<K>(mut set: BTreeSet<K>) {
- set.is_empty();
- set.len();
+ let _ = set.is_empty();
+ let _ = set.len();
  set.clear();
  let _ = set.iter();
  let _ = set.into_iter();

library/alloc/src/collections/linked_list.rs

@@ -583,6 +583,7 @@ impl<T> LinkedList<T> {
  /// assert!(!dl.is_empty());
  /// ```
  #[inline]
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn is_empty(&self) -> bool {
  self.head.is_none()
@@ -609,6 +610,7 @@ impl<T> LinkedList<T> {
  /// assert_eq!(dl.len(), 3);
  /// ```
  #[inline]
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn len(&self) -> usize {
  self.len

library/alloc/src/string.rs

@@ -1547,6 +1547,7 @@ impl String {
  /// assert_eq!(fancy_f.chars().count(), 3);
  /// ```
  #[inline]
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn len(&self) -> usize {
  self.vec.len()
@@ -1566,6 +1567,7 @@ impl String {
  /// assert!(!v.is_empty());
  /// ```
  #[inline]
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn is_empty(&self) -> bool {
  self.len() == 0

library/core/src/ptr/non_null.rs

@@ -449,6 +449,7 @@ impl<T> NonNull<[T]> {
  /// ```
  #[unstable(feature = "slice_ptr_len", issue = "71146")]
  #[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
+ #[must_use]
  #[inline]
  pub const fn len(self) -> usize {
  self.as_ptr().len()

library/core/src/str/mod.rs

@@ -140,6 +140,7 @@ impl str {
  /// ```
  #[stable(feature = "rust1", since = "1.0.0")]
  #[rustc_const_stable(feature = "const_str_len", since = "1.39.0")]
+ #[must_use]
  #[inline]
  pub const fn len(&self) -> usize {
  self.as_bytes().len()
@@ -158,9 +159,10 @@ impl str {
  /// let s = "not empty";
  /// assert!(!s.is_empty());
  /// ```
- #[inline]
  #[stable(feature = "rust1", since = "1.0.0")]
  #[rustc_const_stable(feature = "const_str_is_empty", since = "1.39.0")]
+ #[must_use]
+ #[inline]
  pub const fn is_empty(&self) -> bool {
  self.len() == 0
  }

library/std/src/ffi/os_str.rs

@@ -669,6 +669,7 @@ impl OsStr {
  /// assert!(!os_str.is_empty());
  /// ```
  #[stable(feature = "osstring_simple_functions", since = "1.9.0")]
+ #[must_use]
  #[inline]
  pub fn is_empty(&self) -> bool {
  self.inner.inner.is_empty()
@@ -700,6 +701,7 @@ impl OsStr {
  /// assert_eq!(os_str.len(), 3);
  /// ```
  #[stable(feature = "osstring_simple_functions", since = "1.9.0")]
+ #[must_use]
  #[inline]
  pub fn len(&self) -> usize {
  self.inner.inner.len()

library/std/src/fs.rs

@@ -1080,6 +1080,7 @@ impl Metadata {
  /// Ok(())
  /// }
  /// ```
+ #[must_use]
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn len(&self) -> u64 {
  self.0.size()

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

@@ -431,12 +431,14 @@ impl<'a> SocketAncillary<'a> {
  }
 
  /// Returns `true` if the ancillary data is empty.
+ #[must_use]
  #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
  pub fn is_empty(&self) -> bool {
  self.length == 0
  }
 
  /// Returns the number of used bytes.
+ #[must_use]
  #[unstable(feature = "unix_socket_ancillary_data", issue = "76915")]
  pub fn len(&self) -> usize {
  self.length

src/tools/clippy/tests/ui/iter_count.fixed

@@ -33,6 +33,7 @@ impl HasIter {
  }
 }
 
+#[allow(unused_must_use)]
 fn main() {
  let mut vec = vec![0, 1, 2, 3];
  let mut boxed_slice: Box<[u8]> = Box::new([0, 1, 2, 3]);
@@ -50,7 +51,7 @@ fn main() {
  linked_list.push_back(1);
  binary_heap.push(1);
 
- let _ = &vec[..].len();
+ &vec[..].len();
  vec.len();
  boxed_slice.len();
  vec_deque.len();
@@ -62,13 +63,13 @@ fn main() {
  binary_heap.len();
 
  vec.len();
- let _ = &vec[..].len();
+ &vec[..].len();
  vec_deque.len();
  hash_map.len();
  b_tree_map.len();
  linked_list.len();
 
- let _ = &vec[..].len();
+ &vec[..].len();
  vec.len();
  vec_deque.len();
  hash_set.len();

src/tools/clippy/tests/ui/iter_count.rs

@@ -33,6 +33,7 @@ impl HasIter {
  }
 }
 
+#[allow(unused_must_use)]
 fn main() {
  let mut vec = vec![0, 1, 2, 3];
  let mut boxed_slice: Box<[u8]> = Box::new([0, 1, 2, 3]);
@@ -50,7 +51,7 @@ fn main() {
  linked_list.push_back(1);
  binary_heap.push(1);
 
- let _ = &vec[..].iter().count();
+ &vec[..].iter().count();
  vec.iter().count();
  boxed_slice.iter().count();
  vec_deque.iter().count();
@@ -62,13 +63,13 @@ fn main() {
  binary_heap.iter().count();
 
  vec.iter_mut().count();
- let _ = &vec[..].iter_mut().count();
+ &vec[..].iter_mut().count();
  vec_deque.iter_mut().count();
  hash_map.iter_mut().count();
  b_tree_map.iter_mut().count();
  linked_list.iter_mut().count();
 
- let _ = &vec[..].into_iter().count();
+ &vec[..].into_iter().count();
  vec.into_iter().count();
  vec_deque.into_iter().count();
  hash_set.into_iter().count();