From 6ff72045dee098e5a95f42c27b2f2cf167f0d52d Mon Sep 17 00:00:00 2001
From: Taylor Yu <tlyu@mit.edu>
Date: Thu, 7 Oct 2021 17:58:52 -0500
Subject: [PATCH 1/8] bootstrap: don't use `--merges` to find commits

Shallow clones can cause `git rev-list --merges` to miss merge
commits. Omit it, because the most recent bors commit is
almost always a merge commit.
---
 src/bootstrap/bootstrap.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 05d7b0f611f72..49121869282d3 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -460,7 +460,7 @@ def download_toolchain(self, stage0=True, rustc_channel=None):
             # LLVM more often than necessary.
             #
             # This git command finds that commit SHA, looking for bors-authored
-            # merges that modified src/llvm-project or other relevant version
+            # commits that modified src/llvm-project or other relevant version
             # stamp files.
             #
             # This works even in a repository that has not yet initialized
@@ -470,7 +470,7 @@ def download_toolchain(self, stage0=True, rustc_channel=None):
             ]).decode(sys.getdefaultencoding()).strip()
             llvm_sha = subprocess.check_output([
                 "git", "rev-list", "--author=bors@rust-lang.org", "-n1",
-                "--merges", "--first-parent", "HEAD",
+                "--first-parent", "HEAD",
                 "--",
                 "{}/src/llvm-project".format(top_level),
                 "{}/src/bootstrap/download-ci-llvm-stamp".format(top_level),
@@ -685,7 +685,7 @@ def maybe_download_ci_toolchain(self):
         # Only commits merged by bors will have CI artifacts.
         merge_base = [
             "git", "rev-list", "--author=bors@rust-lang.org", "-n1",
-            "--merges", "--first-parent", "HEAD"
+            "--first-parent", "HEAD"
         ]
         commit = subprocess.check_output(merge_base, universal_newlines=True).strip()
 

From 8e467421decb43a1f1adc353c4984df7eecd0af7 Mon Sep 17 00:00:00 2001
From: Taylor Yu <tlyu@mit.edu>
Date: Thu, 7 Oct 2021 18:20:38 -0500
Subject: [PATCH 2/8] bootstrap: add error messages re shallow history

Exit with an error if we can't find a commit hash for downloading
LLVM or rustc snapshots.
---
 src/bootstrap/bootstrap.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 49121869282d3..817850b1ec7eb 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -540,6 +540,12 @@ def _download_component_helper(
         unpack(tarball, tarball_suffix, self.bin_root(stage0), match=pattern, verbose=self.verbose)
 
     def _download_ci_llvm(self, llvm_sha, llvm_assertions):
+        if not llvm_sha:
+            print("error: could not find commit hash for downloading LLVM")
+            print("help: maybe your repository history is too shallow?")
+            print("help: consider disabling `download-ci-llvm`")
+            print("help: or fetch enough history to include one upstream commit")
+            exit(1)
         cache_prefix = "llvm-{}-{}".format(llvm_sha, llvm_assertions)
         cache_dst = os.path.join(self.build_dir, "cache")
         rustc_cache = os.path.join(cache_dst, cache_prefix)
@@ -688,6 +694,12 @@ def maybe_download_ci_toolchain(self):
             "--first-parent", "HEAD"
         ]
         commit = subprocess.check_output(merge_base, universal_newlines=True).strip()
+        if not commit:
+            print("error: could not find commit hash for downloading rustc")
+            print("help: maybe your repository history is too shallow?")
+            print("help: consider disabling `download-rustc`")
+            print("help: or fetch enough history to include one upstream commit")
+            exit(1)
 
         # Warn if there were changes to the compiler or standard library since the ancestor commit.
         status = subprocess.call(["git", "diff-index", "--quiet", commit, "--", compiler, library])

From 58cc18c56b9d9422b376fdf5c51c20fb0e494e66 Mon Sep 17 00:00:00 2001
From: John Kugelman <john@kugelman.name>
Date: Sun, 10 Oct 2021 01:50:06 -0400
Subject: [PATCH 3/8] Add #[must_use] to alloc constructors

---
 library/alloc/src/boxed.rs                      | 12 ++++++++++++
 library/alloc/src/collections/binary_heap.rs    |  2 ++
 library/alloc/src/collections/btree/map.rs      |  1 +
 library/alloc/src/collections/btree/set.rs      |  1 +
 library/alloc/src/collections/linked_list.rs    |  1 +
 library/alloc/src/collections/vec_deque/mod.rs  |  2 ++
 library/alloc/src/raw_vec.rs                    |  3 +++
 library/alloc/src/rc.rs                         |  6 ++++++
 library/alloc/src/string.rs                     |  2 ++
 library/alloc/src/sync.rs                       |  6 ++++++
 library/alloc/src/vec/mod.rs                    |  2 ++
 src/test/ui/weak-new-uninhabited-issue-48493.rs |  4 ++--
 12 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index 85f908a7f5c7b..bd4f52560421b 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -187,6 +187,7 @@ impl<T> Box<T> {
     #[cfg(not(no_global_oom_handling))]
     #[inline(always)]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new(x: T) -> Self {
         box x
     }
@@ -211,6 +212,7 @@ impl<T> Box<T> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     #[inline]
     pub fn new_uninit() -> Box<mem::MaybeUninit<T>> {
         Self::new_uninit_in(Global)
@@ -237,6 +239,7 @@ impl<T> Box<T> {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed() -> Box<mem::MaybeUninit<T>> {
         Self::new_zeroed_in(Global)
     }
@@ -245,6 +248,7 @@ impl<T> Box<T> {
     /// `x` will be pinned in memory and unable to be moved.
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "pin", since = "1.33.0")]
+    #[must_use]
     #[inline(always)]
     pub fn pin(x: T) -> Pin<Box<T>> {
         (box x).into()
@@ -339,6 +343,7 @@ impl<T, A: Allocator> Box<T, A> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[must_use]
     #[inline]
     pub fn new_in(x: T, alloc: A) -> Self {
         let mut boxed = Self::new_uninit_in(alloc);
@@ -395,6 +400,7 @@ impl<T, A: Allocator> Box<T, A> {
     /// ```
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[cfg(not(no_global_oom_handling))]
+    #[must_use]
     // #[unstable(feature = "new_uninit", issue = "63291")]
     pub fn new_uninit_in(alloc: A) -> Box<mem::MaybeUninit<T>, A> {
         let layout = Layout::new::<mem::MaybeUninit<T>>();
@@ -459,6 +465,7 @@ impl<T, A: Allocator> Box<T, A> {
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[cfg(not(no_global_oom_handling))]
     // #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed_in(alloc: A) -> Box<mem::MaybeUninit<T>, A> {
         let layout = Layout::new::<mem::MaybeUninit<T>>();
         // NOTE: Prefer match over unwrap_or_else since closure sometimes not inlineable.
@@ -503,6 +510,7 @@ impl<T, A: Allocator> Box<T, A> {
     /// `x` will be pinned in memory and unable to be moved.
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[must_use]
     #[inline(always)]
     pub fn pin_in(x: T, alloc: A) -> Pin<Self>
     where
@@ -561,6 +569,7 @@ impl<T> Box<[T]> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_uninit_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
         unsafe { RawVec::with_capacity(len).into_box(len) }
     }
@@ -585,6 +594,7 @@ impl<T> Box<[T]> {
     /// [zeroed]: mem::MaybeUninit::zeroed
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
         unsafe { RawVec::with_capacity_zeroed(len).into_box(len) }
     }
@@ -681,6 +691,7 @@ impl<T, A: Allocator> Box<[T], A> {
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
     // #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_uninit_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> {
         unsafe { RawVec::with_capacity_in(len, alloc).into_box(len) }
     }
@@ -708,6 +719,7 @@ impl<T, A: Allocator> Box<[T], A> {
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
     // #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> {
         unsafe { RawVec::with_capacity_zeroed_in(len, alloc).into_box(len) }
     }
diff --git a/library/alloc/src/collections/binary_heap.rs b/library/alloc/src/collections/binary_heap.rs
index 4ed3702f7d224..01453e2710def 100644
--- a/library/alloc/src/collections/binary_heap.rs
+++ b/library/alloc/src/collections/binary_heap.rs
@@ -364,6 +364,7 @@ impl<T: Ord> BinaryHeap<T> {
     /// heap.push(4);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new() -> BinaryHeap<T> {
         BinaryHeap { data: vec![] }
     }
@@ -383,6 +384,7 @@ impl<T: Ord> BinaryHeap<T> {
     /// heap.push(4);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn with_capacity(capacity: usize) -> BinaryHeap<T> {
         BinaryHeap { data: Vec::with_capacity(capacity) }
     }
diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index d6032372168f1..7de80291cbbea 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -502,6 +502,7 @@ impl<K, V> BTreeMap<K, V> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[must_use]
     pub const fn new() -> BTreeMap<K, V> {
         BTreeMap { root: None, length: 0 }
     }
diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 16150ceeb62c1..2699f3fba397d 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -248,6 +248,7 @@ impl<T> BTreeSet<T> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[must_use]
     pub const fn new() -> BTreeSet<T> {
         BTreeSet { map: BTreeMap::new() }
     }
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
index a769c558b4fa9..6dcba318c3598 100644
--- a/library/alloc/src/collections/linked_list.rs
+++ b/library/alloc/src/collections/linked_list.rs
@@ -417,6 +417,7 @@ impl<T> LinkedList<T> {
     #[inline]
     #[rustc_const_stable(feature = "const_linked_list_new", since = "1.32.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub const fn new() -> Self {
         LinkedList { head: None, tail: None, len: 0, marker: PhantomData }
     }
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index e996784bbad28..09ae1f7eebd09 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -475,6 +475,7 @@ impl<T> VecDeque<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn new() -> VecDeque<T> {
         VecDeque::new_in(Global)
     }
@@ -490,6 +491,7 @@ impl<T> VecDeque<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn with_capacity(capacity: usize) -> VecDeque<T> {
         Self::with_capacity_in(capacity, Global)
     }
diff --git a/library/alloc/src/raw_vec.rs b/library/alloc/src/raw_vec.rs
index be21018512d8b..75dbd4678bb47 100644
--- a/library/alloc/src/raw_vec.rs
+++ b/library/alloc/src/raw_vec.rs
@@ -69,6 +69,7 @@ impl<T> RawVec<T, Global> {
     /// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a
     /// `RawVec` with capacity `usize::MAX`. Useful for implementing
     /// delayed allocation.
+    #[must_use]
     pub const fn new() -> Self {
         Self::new_in(Global)
     }
@@ -87,6 +88,7 @@ impl<T> RawVec<T, Global> {
     ///
     /// Aborts on OOM.
     #[cfg(not(no_global_oom_handling))]
+    #[must_use]
     #[inline]
     pub fn with_capacity(capacity: usize) -> Self {
         Self::with_capacity_in(capacity, Global)
@@ -94,6 +96,7 @@ impl<T> RawVec<T, Global> {
 
     /// Like `with_capacity`, but guarantees the buffer is zeroed.
     #[cfg(not(no_global_oom_handling))]
+    #[must_use]
     #[inline]
     pub fn with_capacity_zeroed(capacity: usize) -> Self {
         Self::with_capacity_zeroed_in(capacity, Global)
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 81e97805a7214..bde0dc754fb32 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -452,6 +452,7 @@ impl<T> Rc<T> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_uninit() -> Rc<mem::MaybeUninit<T>> {
         unsafe {
             Rc::from_ptr(Rc::allocate_for_layout(
@@ -484,6 +485,7 @@ impl<T> Rc<T> {
     /// [zeroed]: mem::MaybeUninit::zeroed
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed() -> Rc<mem::MaybeUninit<T>> {
         unsafe {
             Rc::from_ptr(Rc::allocate_for_layout(
@@ -587,6 +589,7 @@ impl<T> Rc<T> {
     /// `value` will be pinned in memory and unable to be moved.
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "pin", since = "1.33.0")]
+    #[must_use]
     pub fn pin(value: T) -> Pin<Rc<T>> {
         unsafe { Pin::new_unchecked(Rc::new(value)) }
     }
@@ -658,6 +661,7 @@ impl<T> Rc<[T]> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_uninit_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
         unsafe { Rc::from_ptr(Rc::allocate_for_slice(len)) }
     }
@@ -684,6 +688,7 @@ impl<T> Rc<[T]> {
     /// [zeroed]: mem::MaybeUninit::zeroed
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
         unsafe {
             Rc::from_ptr(Rc::allocate_for_layout(
@@ -2044,6 +2049,7 @@ impl<T> Weak<T> {
     /// assert!(empty.upgrade().is_none());
     /// ```
     #[stable(feature = "downgraded_weak", since = "1.10.0")]
+    #[must_use]
     pub fn new() -> Weak<T> {
         Weak { ptr: NonNull::new(usize::MAX as *mut RcBox<T>).expect("MAX is not 0") }
     }
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index d88b8e398985a..d1bc80cc0265e 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -378,6 +378,7 @@ impl String {
     #[inline]
     #[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub const fn new() -> String {
         String { vec: Vec::new() }
     }
@@ -422,6 +423,7 @@ impl String {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn with_capacity(capacity: usize) -> String {
         String { vec: Vec::with_capacity(capacity) }
     }
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 6e8da849e64cd..482c3eac5f970 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -448,6 +448,7 @@ impl<T> Arc<T> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_uninit() -> Arc<mem::MaybeUninit<T>> {
         unsafe {
             Arc::from_ptr(Arc::allocate_for_layout(
@@ -480,6 +481,7 @@ impl<T> Arc<T> {
     /// [zeroed]: mem::MaybeUninit::zeroed
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed() -> Arc<mem::MaybeUninit<T>> {
         unsafe {
             Arc::from_ptr(Arc::allocate_for_layout(
@@ -494,6 +496,7 @@ impl<T> Arc<T> {
     /// `data` will be pinned in memory and unable to be moved.
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "pin", since = "1.33.0")]
+    #[must_use]
     pub fn pin(data: T) -> Pin<Arc<T>> {
         unsafe { Pin::new_unchecked(Arc::new(data)) }
     }
@@ -662,6 +665,7 @@ impl<T> Arc<[T]> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_uninit_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> {
         unsafe { Arc::from_ptr(Arc::allocate_for_slice(len)) }
     }
@@ -688,6 +692,7 @@ impl<T> Arc<[T]> {
     /// [zeroed]: mem::MaybeUninit::zeroed
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[must_use]
     pub fn new_zeroed_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> {
         unsafe {
             Arc::from_ptr(Arc::allocate_for_layout(
@@ -1678,6 +1683,7 @@ impl<T> Weak<T> {
     /// assert!(empty.upgrade().is_none());
     /// ```
     #[stable(feature = "downgraded_weak", since = "1.10.0")]
+    #[must_use]
     pub fn new() -> Weak<T> {
         Weak { ptr: NonNull::new(usize::MAX as *mut ArcInner<T>).expect("MAX is not 0") }
     }
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 4f18a054a0d98..a12acb1a1c07f 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -420,6 +420,7 @@ impl<T> Vec<T> {
     #[inline]
     #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub const fn new() -> Self {
         Vec { buf: RawVec::NEW, len: 0 }
     }
@@ -464,6 +465,7 @@ impl<T> Vec<T> {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     pub fn with_capacity(capacity: usize) -> Self {
         Self::with_capacity_in(capacity, Global)
     }
diff --git a/src/test/ui/weak-new-uninhabited-issue-48493.rs b/src/test/ui/weak-new-uninhabited-issue-48493.rs
index 644fc8c248375..39fbf3c9eb4e2 100644
--- a/src/test/ui/weak-new-uninhabited-issue-48493.rs
+++ b/src/test/ui/weak-new-uninhabited-issue-48493.rs
@@ -2,6 +2,6 @@
 
 fn main() {
     enum Void {}
-    std::rc::Weak::<Void>::new();
-    std::sync::Weak::<Void>::new();
+    let _ = std::rc::Weak::<Void>::new();
+    let _ = std::sync::Weak::<Void>::new();
 }

From 5b5c12be1cf2b2531a1cbf7097d2b5102cfaccd8 Mon Sep 17 00:00:00 2001
From: John Kugelman <john@kugelman.name>
Date: Sun, 10 Oct 2021 02:44:26 -0400
Subject: [PATCH 4/8] Add #[must_use] to core and std constructors

---
 library/core/src/alloc/layout.rs         | 1 +
 library/core/src/hash/sip.rs             | 2 ++
 library/core/src/lazy.rs                 | 1 +
 library/core/src/mem/maybe_uninit.rs     | 3 +++
 library/core/src/num/nonzero.rs          | 2 ++
 library/core/src/sync/atomic.rs          | 2 ++
 library/core/src/task/wake.rs            | 1 +
 library/core/src/time.rs                 | 1 +
 library/std/src/collections/hash/map.rs  | 4 ++++
 library/std/src/collections/hash/set.rs  | 2 ++
 library/std/src/ffi/os_str.rs            | 2 ++
 library/std/src/fs.rs                    | 2 ++
 library/std/src/io/mod.rs                | 1 +
 library/std/src/lazy.rs                  | 1 +
 library/std/src/net/addr.rs              | 3 +++
 library/std/src/net/ip.rs                | 2 ++
 library/std/src/os/unix/net/ancillary.rs | 1 +
 library/std/src/path.rs                  | 2 ++
 library/std/src/sync/barrier.rs          | 1 +
 library/std/src/sync/condvar.rs          | 1 +
 library/std/src/sync/once.rs             | 1 +
 21 files changed, 36 insertions(+)

diff --git a/library/core/src/alloc/layout.rs b/library/core/src/alloc/layout.rs
index ccf6e420de7a9..c98aa38e3df29 100644
--- a/library/core/src/alloc/layout.rs
+++ b/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>();
diff --git a/library/core/src/hash/sip.rs b/library/core/src/hash/sip.rs
index 6178b0af137e8..b9443e30074b0 100644
--- a/library/core/src/hash/sip.rs
+++ b/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) })
     }
diff --git a/library/core/src/lazy.rs b/library/core/src/lazy.rs
index e6bea462fa99a..d109141216aef 100644
--- a/library/core/src/lazy.rs
+++ b/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) }
     }
diff --git a/library/core/src/mem/maybe_uninit.rs b/library/core/src/mem/maybe_uninit.rs
index 9c88a62336161..b9772eaa67813 100644
--- a/library/core/src/mem/maybe_uninit.rs
+++ b/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> {
diff --git a/library/core/src/num/nonzero.rs b/library/core/src/num/nonzero.rs
index e44597279baf2..5b50b13b23e37 100644
--- a/library/core/src/num/nonzero.rs
+++ b/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: $Int) -> Option<Self> {
                     if n != 0 {
diff --git a/library/core/src/sync/atomic.rs b/library/core/src/sync/atomic.rs
index d9de37e9c5197..b07752116e514 100644
--- a/library/core/src/sync/atomic.rs
+++ b/library/core/src/sync/atomic.rs
@@ -290,6 +290,7 @@ impl AtomicBool {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_atomic_new", since = "1.24.0")]
+    #[must_use]
     pub const fn new(v: bool) -> AtomicBool {
         AtomicBool { v: UnsafeCell::new(v as u8) }
     }
@@ -1392,6 +1393,7 @@ macro_rules! atomic_int {
             #[inline]
             #[$stable]
             #[$const_stable]
+            #[must_use]
             pub const fn new(v: $int_type) -> Self {
                 Self {v: UnsafeCell::new(v)}
             }
diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs
index b775e022a54b4..2b540716154a1 100644
--- a/library/core/src/task/wake.rs
+++ b/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 }
     }
diff --git a/library/core/src/time.rs b/library/core/src/time.rs
index d1533b8d67a6b..d2757ef71213f 100644
--- a/library/core/src/time.rs
+++ b/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,
diff --git a/library/std/src/collections/hash/map.rs b/library/std/src/collections/hash/map.rs
index 528bb1bf6e9f9..7fa2e3ed3f6ac 100644
--- a/library/std/src/collections/hash/map.rs
+++ b/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))
     }
diff --git a/library/std/src/collections/hash/set.rs b/library/std/src/collections/hash/set.rs
index dcfe322095082..5804701892e6e 100644
--- a/library/std/src/collections/hash/set.rs
+++ b/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()) }
diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index c305519dd4461..e4ad6cba88046 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/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) }
diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index 726c855c4fd36..85d350729239c 100644
--- a/library/std/src/fs.rs
+++ b/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 }
     }
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 8c71138aa231d..abe29ba0f7caa 100644
--- a/library/std/src/io/mod.rs
+++ b/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))
diff --git a/library/std/src/lazy.rs b/library/std/src/lazy.rs
index 5afdb799f0c74..d7450962359df 100644
--- a/library/std/src/lazy.rs
+++ b/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(),
diff --git a/library/std/src/net/addr.rs b/library/std/src/net/addr.rs
index f4ebcd53a25f7..cd2007cc2cb42 100644
--- a/library/std/src/net/addr.rs
+++ b/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 {
diff --git a/library/std/src/net/ip.rs b/library/std/src/net/ip.rs
index c05a32742ba1e..99922eef61f10 100644
--- a/library/std/src/net/ip.rs
+++ b/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 = [
diff --git a/library/std/src/os/unix/net/ancillary.rs b/library/std/src/os/unix/net/ancillary.rs
index 1f9d42812ecc7..57bb61903c147 100644
--- a/library/std/src/os/unix/net/ancillary.rs
+++ b/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 })
     }
diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index a45ecf6ea8c63..c5476c3d5267b 100644
--- a/library/std/src/path.rs
+++ b/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) }
diff --git a/library/std/src/sync/barrier.rs b/library/std/src/sync/barrier.rs
index a17b82f82e8c2..0e28a2d166f13 100644
--- a/library/std/src/sync/barrier.rs
+++ b/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 }),
diff --git a/library/std/src/sync/condvar.rs b/library/std/src/sync/condvar.rs
index 00a4afc570519..d8aca9651b867 100644
--- a/library/std/src/sync/condvar.rs
+++ b/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() }
     }
diff --git a/library/std/src/sync/once.rs b/library/std/src/sync/once.rs
index a2e935a0cebc4..1710c0053934a 100644
--- a/library/std/src/sync/once.rs
+++ b/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 }
     }

From 9e6e89af697dad4e4505111adef37733cdcbe47e Mon Sep 17 00:00:00 2001
From: Matthew Jasper <mjjasper1@gmail.com>
Date: Sun, 10 Oct 2021 19:59:36 +0100
Subject: [PATCH 5/8] Fix RUSTC_LOG handling

Rustc was incorrectly reading the value of `RUSTC_LOG` as the
environment vairable with the logging configuration, rather than the
logging configuration itself.
---
 compiler/rustc_driver/src/lib.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index 05c7e11cbc29a..9a57ec991444a 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -1259,7 +1259,7 @@ pub fn init_env_logger(env: &str) {
     };
 
     let filter = match std::env::var(env) {
-        Ok(env) => EnvFilter::from_env(env),
+        Ok(env) => EnvFilter::new(env),
         _ => EnvFilter::default().add_directive(filter::Directive::from(LevelFilter::WARN)),
     };
 

From cf2bcd10ed28b169b8df74383c2a35a4ffbdcf40 Mon Sep 17 00:00:00 2001
From: John Kugelman <john@kugelman.name>
Date: Sun, 10 Oct 2021 18:22:40 -0400
Subject: [PATCH 6/8] Add #[must_use] to from_value conversions

---
 library/alloc/src/str.rs            | 1 +
 library/alloc/src/string.rs         | 1 +
 library/core/src/alloc/layout.rs    | 1 +
 library/core/src/char/convert.rs    | 3 +++
 library/core/src/char/methods.rs    | 5 ++++-
 library/core/src/num/f32.rs         | 4 ++++
 library/core/src/num/f64.rs         | 4 ++++
 library/core/src/num/int_macros.rs  | 5 +++++
 library/core/src/num/saturating.rs  | 2 ++
 library/core/src/num/uint_macros.rs | 5 +++++
 library/core/src/num/wrapping.rs    | 2 ++
 library/core/src/str/converts.rs    | 2 ++
 library/core/src/str/lossy.rs       | 2 ++
 library/core/src/task/wake.rs       | 2 ++
 library/core/src/time.rs            | 6 ++++++
 library/std/src/ffi/c_str.rs        | 5 +++++
 library/std/src/io/error.rs         | 1 +
 17 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
index 2900d01d9bdae..ac7f230445656 100644
--- a/library/alloc/src/str.rs
+++ b/library/alloc/src/str.rs
@@ -595,6 +595,7 @@ impl str {
 /// assert_eq!("☺", &*smile);
 /// ```
 #[stable(feature = "str_box_extras", since = "1.20.0")]
+#[must_use]
 #[inline]
 pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
     unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index d88b8e398985a..0c383b8bdb6c6 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -761,6 +761,7 @@ impl String {
     /// assert_eq!("💖", sparkle_heart);
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
         String { vec: bytes }
diff --git a/library/core/src/alloc/layout.rs b/library/core/src/alloc/layout.rs
index ccf6e420de7a9..8086dd357306e 100644
--- a/library/core/src/alloc/layout.rs
+++ b/library/core/src/alloc/layout.rs
@@ -94,6 +94,7 @@ impl Layout {
     /// [`Layout::from_size_align`].
     #[stable(feature = "alloc_layout", since = "1.28.0")]
     #[rustc_const_stable(feature = "alloc_layout", since = "1.36.0")]
+    #[must_use]
     #[inline]
     pub const unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Self {
         // SAFETY: the caller must ensure that `align` is greater than zero.
diff --git a/library/core/src/char/convert.rs b/library/core/src/char/convert.rs
index 7a0ec32cc61a9..72921414fb3f2 100644
--- a/library/core/src/char/convert.rs
+++ b/library/core/src/char/convert.rs
@@ -48,6 +48,7 @@ use super::MAX;
 /// assert_eq!(None, c);
 /// ```
 #[doc(alias = "chr")]
+#[must_use]
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn from_u32(i: u32) -> Option<char> {
@@ -88,6 +89,7 @@ pub fn from_u32(i: u32) -> Option<char> {
 /// assert_eq!('❤', c);
 /// ```
 #[inline]
+#[must_use]
 #[stable(feature = "char_from_unchecked", since = "1.5.0")]
 pub unsafe fn from_u32_unchecked(i: u32) -> char {
     // SAFETY: the caller must guarantee that `i` is a valid char value.
@@ -319,6 +321,7 @@ impl fmt::Display for CharTryFromError {
 /// let c = char::from_digit(1, 37);
 /// ```
 #[inline]
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn from_digit(num: u32, radix: u32) -> Option<char> {
     if radix > 36 {
diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index b3af1f1ffb592..07ac08f45c79f 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -136,6 +136,7 @@ impl char {
     /// assert_eq!(None, c);
     /// ```
     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+    #[must_use]
     #[inline]
     pub fn from_u32(i: u32) -> Option<char> {
         super::convert::from_u32(i)
@@ -177,6 +178,7 @@ impl char {
     /// assert_eq!('❤', c);
     /// ```
     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+    #[must_use]
     #[inline]
     pub unsafe fn from_u32_unchecked(i: u32) -> char {
         // SAFETY: the safety contract must be upheld by the caller.
@@ -230,9 +232,10 @@ impl char {
     /// use std::char;
     ///
     /// // this panics
-    /// char::from_digit(1, 37);
+    /// let _c = char::from_digit(1, 37);
     /// ```
     #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+    #[must_use]
     #[inline]
     pub fn from_digit(num: u32, radix: u32) -> Option<char> {
         super::convert::from_digit(num, radix)
diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index c47a2e8b05c4b..fd82be33d1abd 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -786,6 +786,7 @@ impl f32 {
     /// ```
     #[stable(feature = "float_bits_conv", since = "1.20.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_bits(v: u32) -> Self {
         // SAFETY: `u32` is a plain old datatype so we can always transmute from it
@@ -864,6 +865,7 @@ impl f32 {
     /// ```
     #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_be_bytes(bytes: [u8; 4]) -> Self {
         Self::from_bits(u32::from_be_bytes(bytes))
@@ -879,6 +881,7 @@ impl f32 {
     /// ```
     #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_le_bytes(bytes: [u8; 4]) -> Self {
         Self::from_bits(u32::from_le_bytes(bytes))
@@ -905,6 +908,7 @@ impl f32 {
     /// ```
     #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self {
         Self::from_bits(u32::from_ne_bytes(bytes))
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index cfcc08b9addeb..e7dec62c04ead 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -800,6 +800,7 @@ impl f64 {
     /// ```
     #[stable(feature = "float_bits_conv", since = "1.20.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_bits(v: u64) -> Self {
         // SAFETY: `u64` is a plain old datatype so we can always transmute from it
@@ -878,6 +879,7 @@ impl f64 {
     /// ```
     #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_be_bytes(bytes: [u8; 8]) -> Self {
         Self::from_bits(u64::from_be_bytes(bytes))
@@ -893,6 +895,7 @@ impl f64 {
     /// ```
     #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_le_bytes(bytes: [u8; 8]) -> Self {
         Self::from_bits(u64::from_le_bytes(bytes))
@@ -919,6 +922,7 @@ impl f64 {
     /// ```
     #[stable(feature = "float_to_from_bytes", since = "1.40.0")]
     #[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+    #[must_use]
     #[inline]
     pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self {
         Self::from_bits(u64::from_ne_bytes(bytes))
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
index 12dda61400f2a..7ef2d5c40034d 100644
--- a/library/core/src/num/int_macros.rs
+++ b/library/core/src/num/int_macros.rs
@@ -282,6 +282,7 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
         #[rustc_const_stable(feature = "const_int_conversions", since = "1.32.0")]
+        #[must_use]
         #[inline]
         pub const fn from_be(x: Self) -> Self {
             #[cfg(target_endian = "big")]
@@ -313,6 +314,7 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
         #[rustc_const_stable(feature = "const_int_conversions", since = "1.32.0")]
+        #[must_use]
         #[inline]
         pub const fn from_le(x: Self) -> Self {
             #[cfg(target_endian = "little")]
@@ -2620,6 +2622,7 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
         #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+        #[must_use]
         #[inline]
         pub const fn from_be_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
             Self::from_be(Self::from_ne_bytes(bytes))
@@ -2650,6 +2653,7 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
         #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+        #[must_use]
         #[inline]
         pub const fn from_le_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
             Self::from_le(Self::from_ne_bytes(bytes))
@@ -2691,6 +2695,7 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
         #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+        #[must_use]
         // SAFETY: const sound because integers are plain old datatypes so we can always
         // transmute to them
         #[inline]
diff --git a/library/core/src/num/saturating.rs b/library/core/src/num/saturating.rs
index f6dd3603c4914..cf8cf79fe46e0 100644
--- a/library/core/src/num/saturating.rs
+++ b/library/core/src/num/saturating.rs
@@ -644,6 +644,7 @@ macro_rules! saturating_int_impl {
             /// }
             /// ```
             #[inline]
+            #[must_use]
             #[unstable(feature = "saturating_int_impl", issue = "87920")]
             pub const fn from_be(x: Self) -> Self {
                 Saturating(<$t>::from_be(x.0))
@@ -671,6 +672,7 @@ macro_rules! saturating_int_impl {
             /// }
             /// ```
             #[inline]
+            #[must_use]
             #[unstable(feature = "saturating_int_impl", issue = "87920")]
             pub const fn from_le(x: Self) -> Self {
                 Saturating(<$t>::from_le(x.0))
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
index 25cd582bb67d7..eb03be2a62ae9 100644
--- a/library/core/src/num/uint_macros.rs
+++ b/library/core/src/num/uint_macros.rs
@@ -285,6 +285,7 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
         #[rustc_const_stable(feature = "const_math", since = "1.32.0")]
+        #[must_use]
         #[inline(always)]
         pub const fn from_be(x: Self) -> Self {
             #[cfg(target_endian = "big")]
@@ -317,6 +318,7 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
         #[rustc_const_stable(feature = "const_math", since = "1.32.0")]
+        #[must_use]
         #[inline(always)]
         pub const fn from_le(x: Self) -> Self {
             #[cfg(target_endian = "little")]
@@ -2278,6 +2280,7 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
         #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+        #[must_use]
         #[inline]
         pub const fn from_be_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
             Self::from_be(Self::from_ne_bytes(bytes))
@@ -2308,6 +2311,7 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
         #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+        #[must_use]
         #[inline]
         pub const fn from_le_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
             Self::from_le(Self::from_ne_bytes(bytes))
@@ -2349,6 +2353,7 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_to_from_bytes", since = "1.32.0")]
         #[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+        #[must_use]
         // SAFETY: const sound because integers are plain old datatypes so we can always
         // transmute to them
         #[inline]
diff --git a/library/core/src/num/wrapping.rs b/library/core/src/num/wrapping.rs
index b078cdf5479d7..cca83661b7ea6 100644
--- a/library/core/src/num/wrapping.rs
+++ b/library/core/src/num/wrapping.rs
@@ -638,6 +638,7 @@ macro_rules! wrapping_int_impl {
             /// }
             /// ```
             #[inline]
+            #[must_use]
             #[unstable(feature = "wrapping_int_impl", issue = "32463")]
             pub const fn from_be(x: Self) -> Self {
                 Wrapping(<$t>::from_be(x.0))
@@ -665,6 +666,7 @@ macro_rules! wrapping_int_impl {
             /// }
             /// ```
             #[inline]
+            #[must_use]
             #[unstable(feature = "wrapping_int_impl", issue = "32463")]
             pub const fn from_le(x: Self) -> Self {
                 Wrapping(<$t>::from_le(x.0))
diff --git a/library/core/src/str/converts.rs b/library/core/src/str/converts.rs
index da6ef1b6678c6..ed9f49f159611 100644
--- a/library/core/src/str/converts.rs
+++ b/library/core/src/str/converts.rs
@@ -155,6 +155,7 @@ pub fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error> {
 /// assert_eq!("💖", sparkle_heart);
 /// ```
 #[inline]
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_stable(feature = "const_str_from_utf8_unchecked", since = "1.55.0")]
 pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str {
@@ -181,6 +182,7 @@ pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str {
 /// assert_eq!("💖", heart);
 /// ```
 #[inline]
+#[must_use]
 #[stable(feature = "str_mut_extras", since = "1.20.0")]
 pub unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str {
     // SAFETY: the caller must guarantee that the bytes `v`
diff --git a/library/core/src/str/lossy.rs b/library/core/src/str/lossy.rs
index 720a35bbc8f2c..d3c9d21c3c756 100644
--- a/library/core/src/str/lossy.rs
+++ b/library/core/src/str/lossy.rs
@@ -12,10 +12,12 @@ pub struct Utf8Lossy {
 }
 
 impl Utf8Lossy {
+    #[must_use]
     pub fn from_str(s: &str) -> &Utf8Lossy {
         Utf8Lossy::from_bytes(s.as_bytes())
     }
 
+    #[must_use]
     pub fn from_bytes(bytes: &[u8]) -> &Utf8Lossy {
         // SAFETY: Both use the same memory layout, and UTF-8 correctness isn't required.
         unsafe { mem::transmute(bytes) }
diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs
index b775e022a54b4..e1bbdfaef8016 100644
--- a/library/core/src/task/wake.rs
+++ b/library/core/src/task/wake.rs
@@ -158,6 +158,7 @@ pub struct Context<'a> {
 impl<'a> Context<'a> {
     /// Create a new `Context` from a `&Waker`.
     #[stable(feature = "futures_api", since = "1.36.0")]
+    #[must_use]
     #[inline]
     pub fn from_waker(waker: &'a Waker) -> Self {
         Context { waker, _marker: PhantomData }
@@ -251,6 +252,7 @@ impl Waker {
     /// in [`RawWaker`]'s and [`RawWakerVTable`]'s documentation is not upheld.
     /// Therefore this method is unsafe.
     #[inline]
+    #[must_use]
     #[stable(feature = "futures_api", since = "1.36.0")]
     pub unsafe fn from_raw(waker: RawWaker) -> Waker {
         Waker { waker }
diff --git a/library/core/src/time.rs b/library/core/src/time.rs
index d1533b8d67a6b..d57c959820d8d 100644
--- a/library/core/src/time.rs
+++ b/library/core/src/time.rs
@@ -203,6 +203,7 @@ impl Duration {
     /// assert_eq!(0, duration.subsec_nanos());
     /// ```
     #[stable(feature = "duration", since = "1.3.0")]
+    #[must_use]
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_secs(secs: u64) -> Duration {
@@ -222,6 +223,7 @@ impl Duration {
     /// assert_eq!(569_000_000, duration.subsec_nanos());
     /// ```
     #[stable(feature = "duration", since = "1.3.0")]
+    #[must_use]
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_millis(millis: u64) -> Duration {
@@ -244,6 +246,7 @@ impl Duration {
     /// assert_eq!(2000, duration.subsec_nanos());
     /// ```
     #[stable(feature = "duration_from_micros", since = "1.27.0")]
+    #[must_use]
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_micros(micros: u64) -> Duration {
@@ -266,6 +269,7 @@ impl Duration {
     /// assert_eq!(123, duration.subsec_nanos());
     /// ```
     #[stable(feature = "duration_extras", since = "1.27.0")]
+    #[must_use]
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_nanos(nanos: u64) -> Duration {
@@ -692,6 +696,7 @@ impl Duration {
     /// assert_eq!(dur, Duration::new(2, 700_000_000));
     /// ```
     #[stable(feature = "duration_float", since = "1.38.0")]
+    #[must_use]
     #[inline]
     #[rustc_const_unstable(feature = "duration_consts_2", issue = "72440")]
     pub const fn from_secs_f64(secs: f64) -> Duration {
@@ -753,6 +758,7 @@ impl Duration {
     /// assert_eq!(dur, Duration::new(2, 700_000_000));
     /// ```
     #[stable(feature = "duration_float", since = "1.38.0")]
+    #[must_use]
     #[inline]
     #[rustc_const_unstable(feature = "duration_consts_2", issue = "72440")]
     pub const fn from_secs_f32(secs: f32) -> Duration {
diff --git a/library/std/src/ffi/c_str.rs b/library/std/src/ffi/c_str.rs
index fe1f28f00c403..e290350993d73 100644
--- a/library/std/src/ffi/c_str.rs
+++ b/library/std/src/ffi/c_str.rs
@@ -425,6 +425,7 @@ impl CString {
     ///     let c_string = CString::from_vec_unchecked(raw);
     /// }
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
         v.reserve_exact(1);
@@ -476,6 +477,7 @@ impl CString {
     ///     let c_string = CString::from_raw(raw);
     /// }
     /// ```
+    #[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `CString`"]
     #[stable(feature = "cstr_memory", since = "1.4.0")]
     pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
         // SAFETY: This is called with a pointer that was obtained from a call
@@ -701,6 +703,7 @@ impl CString {
     ///     unsafe { CString::from_vec_unchecked(b"abc".to_vec()) }
     /// );
     /// ```
+    #[must_use]
     #[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
     pub unsafe fn from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
         Self { inner: v.into_boxed_slice() }
@@ -1162,6 +1165,7 @@ impl CStr {
     /// }
     /// # }
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
         // SAFETY: The caller has provided a pointer that points to a valid C
@@ -1244,6 +1248,7 @@ impl CStr {
     /// }
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
     #[rustc_const_unstable(feature = "const_cstr_unchecked", issue = "none")]
     pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs
index 51666c0a3c7f1..57b5c28430f1e 100644
--- a/library/std/src/io/error.rs
+++ b/library/std/src/io/error.rs
@@ -473,6 +473,7 @@ impl Error {
     /// # }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
     #[inline]
     pub fn from_raw_os_error(code: i32) -> Error {
         Error { repr: Repr::Os(code) }

From 687cc5d4a67bf059233b8a606befae83167f3a5a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lauren=C8=9Biu=20Nicola?= <lnicola@dend.ro>
Date: Mon, 11 Oct 2021 10:01:39 +0300
Subject: [PATCH 7/8] :arrow_up: rust-analyzer

---
 src/tools/rust-analyzer | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/tools/rust-analyzer b/src/tools/rust-analyzer
index 4b7675fcc30d3..ed4b312fa777e 160000
--- a/src/tools/rust-analyzer
+++ b/src/tools/rust-analyzer
@@ -1 +1 @@
-Subproject commit 4b7675fcc30d3e2c05eafc68a5724db66b58142c
+Subproject commit ed4b312fa777ebb39ba1348fe3df574c441a485e

From 4bd7e965b23e979e6afbda5640f0bd68e9ed50ec Mon Sep 17 00:00:00 2001
From: Stefan Schindler <dns2utf8@estada.ch>
Date: Mon, 11 Oct 2021 00:38:56 +0200
Subject: [PATCH 8/8] Cleanup .item-table CSS

---
 src/librustdoc/html/static/css/rustdoc.css | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index cea3452780e6f..962af66368d3b 100644
--- a/src/librustdoc/html/static/css/rustdoc.css
+++ b/src/librustdoc/html/static/css/rustdoc.css
@@ -772,7 +772,7 @@ h2.small-section-header > .anchor {
 .block a.current.crate { font-weight: 500; }
 
 .item-table {
-	display: table-row;
+	display: table;
 }
 .item-row {
 	display: table-row;