Auto merge of #90437 - matthiaskrgr:rollup-vd8uqm6, r=matthiaskrgr

Rollup of 4 pull requests

Successful merges:

 - #89068 (Restructure std::rt (part 2))
 - #89786 (Add #[must_use] to len and is_empty)
 - #90430 (Add #[must_use] to remaining std functions (A-N))
 - #90431 (Add #[must_use] to remaining std functions (O-Z))

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

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/backtrace.rs

@@ -110,6 +110,7 @@ use crate::vec::Vec;
 /// previous point in time. In some instances the `Backtrace` type may
 /// internally be empty due to configuration. For more information see
 /// `Backtrace::capture`.
+#[must_use]
 pub struct Backtrace {
     inner: Inner,
 }
@@ -355,6 +356,7 @@ impl Backtrace {
     /// Returns the status of this backtrace, indicating whether this backtrace
     /// request was unsupported, disabled, or a stack trace was actually
     /// captured.
+    #[must_use]
     pub fn status(&self) -> BacktraceStatus {
         match self.inner {
             Inner::Unsupported => BacktraceStatus::Unsupported,
@@ -366,6 +368,7 @@ impl Backtrace {
 
 impl<'a> Backtrace {
     /// Returns an iterator over the backtrace frames.
+    #[must_use]
     #[unstable(feature = "backtrace_frames", issue = "79676")]
     pub fn frames(&'a self) -> &'a [BacktraceFrame] {
         if let Inner::Captured(c) = &self.inner { &c.force().frames } else { &[] }

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

@@ -1707,13 +1707,15 @@ impl<'a, K, V, S> RawEntryMut<'a, K, V, S> {
 impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
     /// Gets a reference to the key in the entry.
     #[inline]
+    #[must_use]
     #[unstable(feature = "hash_raw_entry", issue = "56167")]
     pub fn key(&self) -> &K {
         self.base.key()
     }
 
     /// Gets a mutable reference to the key in the entry.
     #[inline]
+    #[must_use]
     #[unstable(feature = "hash_raw_entry", issue = "56167")]
     pub fn key_mut(&mut self) -> &mut K {
         self.base.key_mut()
@@ -1730,6 +1732,7 @@ impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
 
     /// Gets a reference to the value in the entry.
     #[inline]
+    #[must_use]
     #[unstable(feature = "hash_raw_entry", issue = "56167")]
     pub fn get(&self) -> &V {
         self.base.get()
@@ -1746,13 +1749,15 @@ impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
 
     /// Gets a mutable reference to the value in the entry.
     #[inline]
+    #[must_use]
     #[unstable(feature = "hash_raw_entry", issue = "56167")]
     pub fn get_mut(&mut self) -> &mut V {
         self.base.get_mut()
     }
 
     /// Gets a reference to the key and value in the entry.
     #[inline]
+    #[must_use]
     #[unstable(feature = "hash_raw_entry", issue = "56167")]
     pub fn get_key_value(&mut self) -> (&K, &V) {
         self.base.get_key_value()