Auto merge of #121078 - oli-obk:rollup-p11zsav, r=oli-obk

Rollup of 13 pull requests

Successful merges:

 - #116387 (Additional doc links and explanation of `Wake`.)
 - #118738 (Netbsd10 update)
 - #118890 (Clarify the lifetimes of allocations returned by the `Allocator` trait)
 - #120498 (Uplift `TypeVisitableExt` into `rustc_type_ir`)
 - #120530 (Be less confident when `dyn` suggestion is not checked for object safety)
 - #120915 (Fix suggestion span for `?Sized` when param type has default)
 - #121015 (Optimize `delayed_bug` handling.)
 - #121024 (implement `Default` for `AsciiChar`)
 - #121039 (Correctly compute adjustment casts in GVN)
 - #121045 (Fix two UI tests with incorrect directive / invalid revision)
 - #121049 (Do not point at `#[allow(_)]` as the reason for compat lint triggering)
 - #121071 (Use fewer delayed bugs.)
 - #121073 (Fix typos in `OneLock` doc)

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

4 files changed, 29 insertions, 6 deletions

diff --git a/library/core/src/alloc/mod.rs b/library/core/src/alloc/mod.rs
index 78091c01729..1c8e6676544 100644
--- a/library/core/src/alloc/mod.rs
+++ b/library/core/src/alloc/mod.rs
@@ -95,8 +95,10 @@ impl fmt::Display for AllocError {
 /// # Safety
 ///
 /// * Memory blocks returned from an allocator that are [*currently allocated*] must point to
-///   valid memory and retain their validity while they are [*currently allocated*] and at
-///   least one of the instance and all of its clones has not been dropped.
+///   valid memory and retain their validity while they are [*currently allocated*] and the shorter
+///   of:
+///   - the borrow-checker lifetime of the allocator type itself.
+///   - as long as at least one of the instance and all of its clones has not been dropped.
 ///
 /// * copying, cloning, or moving the allocator must not invalidate memory blocks returned from this
 ///   allocator. A copied or cloned allocator must behave like the same allocator, and
@@ -114,6 +116,10 @@ pub unsafe trait Allocator {
     /// The returned block may have a larger size than specified by `layout.size()`, and may or may
     /// not have its contents initialized.
     ///
+    /// The returned block of memory remains valid as long as it is [*currently allocated*] and the shorter of:
+    ///   - the borrow-checker lifetime of the allocator type itself.
+    ///   - as long as at the allocator and all its clones has not been dropped.
+    ///
     /// # Errors
     ///
     /// Returning `Err` indicates that either memory is exhausted or `layout` does not meet
diff --git a/library/core/src/ascii/ascii_char.rs b/library/core/src/ascii/ascii_char.rs
index 5f758af1624..34a05ac3888 100644
--- a/library/core/src/ascii/ascii_char.rs
+++ b/library/core/src/ascii/ascii_char.rs
@@ -58,7 +58,7 @@ use crate::mem::transmute;
 #[unstable(feature = "ascii_char", issue = "110998")]
 #[repr(u8)]
 pub enum AsciiChar {
-    /// U+0000
+    /// U+0000 (The default variant)
     #[unstable(feature = "ascii_char_variants", issue = "110998")]
     Null = 0,
     /// U+0001
diff --git a/library/core/src/default.rs b/library/core/src/default.rs
index 16618b38769..a1303fcd821 100644
--- a/library/core/src/default.rs
+++ b/library/core/src/default.rs
@@ -2,6 +2,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use crate::ascii::Char as AsciiChar;
+
 /// A trait for giving a type a useful default value.
 ///
 /// Sometimes, you want to fall back to some kind of default value, and
@@ -158,6 +160,7 @@ macro_rules! default_impl {
 default_impl! { (), (), "Returns the default value of `()`" }
 default_impl! { bool, false, "Returns the default value of `false`" }
 default_impl! { char, '\x00', "Returns the default value of `\\x00`" }
+default_impl! { AsciiChar, AsciiChar::Null, "Returns the default value of `Null`" }
 
 default_impl! { usize, 0, "Returns the default value of `0`" }
 default_impl! { u8, 0, "Returns the default value of `0`" }
diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs
index 09f3f2f02ea..b9895f7edea 100644
--- a/library/core/src/task/wake.rs
+++ b/library/core/src/task/wake.rs
@@ -9,10 +9,14 @@ use crate::ptr;
 /// A `RawWaker` allows the implementor of a task executor to create a [`Waker`]
 /// or a [`LocalWaker`] which provides customized wakeup behavior.
 ///
-/// [vtable]: https://en.wikipedia.org/wiki/Virtual_method_table
-///
 /// It consists of a data pointer and a [virtual function pointer table (vtable)][vtable]
 /// that customizes the behavior of the `RawWaker`.
+///
+/// `RawWaker`s are unsafe to use.
+/// Implementing the [`Wake`] trait is a safe alternative that requires memory allocation.
+///
+/// [vtable]: https://en.wikipedia.org/wiki/Virtual_method_table
+/// [`Wake`]: ../../alloc/task/trait.Wake.html
 #[derive(PartialEq, Debug)]
 #[stable(feature = "futures_api", since = "1.36.0")]
 pub struct RawWaker {
@@ -355,8 +359,12 @@ impl<'a> ContextBuilder<'a> {
 /// of `*waker = new_waker.clone()`, as the former will avoid cloning the waker
 /// unnecessarily if the two wakers [wake the same task](Self::will_wake).
 ///
+/// Constructing a `Waker` from a [`RawWaker`] is unsafe.
+/// Implementing the [`Wake`] trait is a safe alternative that requires memory allocation.
+///
 /// [`Future::poll()`]: core::future::Future::poll
 /// [`Poll::Pending`]: core::task::Poll::Pending
+/// [`Wake`]: ../../alloc/task/trait.Wake.html
 #[cfg_attr(not(doc), repr(transparent))] // work around https://github.com/rust-lang/rust/issues/66401
 #[stable(feature = "futures_api", since = "1.36.0")]
 pub struct Waker {
@@ -438,9 +446,15 @@ impl Waker {
 
     /// Creates a new `Waker` from [`RawWaker`].
     ///
+    /// # Safety
+    ///
     /// The behavior of the returned `Waker` is undefined if the contract defined
     /// in [`RawWaker`]'s and [`RawWakerVTable`]'s documentation is not upheld.
-    /// Therefore this method is unsafe.
+    ///
+    /// (Authors wishing to avoid unsafe code may implement the [`Wake`] trait instead, at the
+    /// cost of a required heap allocation.)
+    ///
+    /// [`Wake`]: ../../alloc/task/trait.Wake.html
     #[inline]
     #[must_use]
     #[stable(feature = "futures_api", since = "1.36.0")]