Auto merge of rust-lang#72036 - Dylan-DPC:rollup-ca8b0ql, r=Dylan-DPC

Rollup of 8 pull requests

Successful merges:

 - rust-lang#70834 (Add core::future::{pending,ready})
 - rust-lang#71839 (Make BTreeMap::new and BTreeSet::new const)
 - rust-lang#71890 (Simplify the error Registry methods a little)
 - rust-lang#71942 (Shrink `LocalDecl`)
 - rust-lang#71947 (Dead-code pass highlights too much of impl functions)
 - rust-lang#71981 (Fix `strip-priv-imports` pass name in the rustdoc documentation)
 - rust-lang#72018 (Fix canonicalization links)
 - rust-lang#72031 (Better documentation for io::Read::read() return value)

Failed merges:

r? @ghost

Author: bors

Diff for: src/doc/rustdoc/src/passes.md

@@ -17,7 +17,7 @@ By default, rustdoc will run some passes, namely:
 * `collapse-docs`
 * `unindent-comments`
 
-However, `strip-private` implies `strip-private-imports`, and so effectively,
+However, `strip-private` implies `strip-priv-imports`, and so effectively,
 all passes are run by default.
 
 ## `strip-hidden`

Diff for: src/liballoc/collections/btree/map.rs

@@ -556,7 +556,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// map.insert(1, "a");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> BTreeMap<K, V> {
+    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    pub const fn new() -> BTreeMap<K, V> {
         BTreeMap { root: None, length: 0 }
     }
 

Diff for: src/liballoc/collections/btree/set.rs

@@ -309,7 +309,8 @@ impl<T: Ord> BTreeSet<T> {
     /// let mut set: BTreeSet<i32> = BTreeSet::new();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> BTreeSet<T> {
+    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    pub const fn new() -> BTreeSet<T> {
         BTreeSet { map: BTreeMap::new() }
     }
 

Diff for: src/liballoc/lib.rs

@@ -82,6 +82,7 @@
 #![feature(cfg_sanitize)]
 #![feature(cfg_target_has_atomic)]
 #![feature(coerce_unsized)]
+#![feature(const_btree_new)]
 #![feature(const_generic_impls_guard)]
 #![feature(const_generics)]
 #![feature(const_in_array_repeat_expressions)]

Diff for: src/libcore/future/mod.rs

@@ -10,9 +10,17 @@ use crate::{
 };
 
 mod future;
+mod pending;
+mod ready;
+
 #[stable(feature = "futures_api", since = "1.36.0")]
 pub use self::future::Future;
 
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+pub use pending::{pending, Pending};
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+pub use ready::{ready, Ready};
+
 /// This type is needed because:
 ///
 /// a) Generators cannot implement `for<'a, 'b> Generator<&'a mut Context<'b>>`, so we need to pass

Diff for: src/libcore/future/pending.rs

@@ -0,0 +1,57 @@
+use crate::future::Future;
+use crate::marker;
+use crate::pin::Pin;
+use crate::task::{Context, Poll};
+
+/// Creates a future which never resolves, representing a computation that never
+/// finishes.
+///
+/// This `struct` is created by the [`pending`] function. See its
+/// documentation for more.
+///
+/// [`pending`]: fn.pending.html
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Pending<T> {
+    _data: marker::PhantomData<T>,
+}
+
+/// Creates a future which never resolves, representing a computation that never
+/// finishes.
+///
+/// # Examples
+///
+/// ```no_run
+/// #![feature(future_readiness_fns)]
+/// use core::future;
+///
+/// # async fn run() {
+/// let future = future::pending();
+/// let () = future.await;
+/// unreachable!();
+/// # }
+/// ```
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+pub fn pending<T>() -> Pending<T> {
+    Pending { _data: marker::PhantomData }
+}
+
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+impl<T> Future for Pending<T> {
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<T> {
+        Poll::Pending
+    }
+}
+
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+impl<T> Unpin for Pending<T> {}
+
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+impl<T> Clone for Pending<T> {
+    fn clone(&self) -> Self {
+        pending()
+    }
+}

Diff for: src/libcore/future/ready.rs

@@ -0,0 +1,45 @@
+use crate::future::Future;
+use crate::pin::Pin;
+use crate::task::{Context, Poll};
+
+/// Creates a future that is immediately ready with a value.
+///
+/// This `struct` is created by the [`ready`] function. See its
+/// documentation for more.
+///
+/// [`ready`]: fn.ready.html
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+#[derive(Debug, Clone)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Ready<T>(Option<T>);
+
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+impl<T> Unpin for Ready<T> {}
+
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+impl<T> Future for Ready<T> {
+    type Output = T;
+
+    #[inline]
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
+        Poll::Ready(self.0.take().expect("Ready polled after completion"))
+    }
+}
+
+/// Creates a future that is immediately ready with a value.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(future_readiness_fns)]
+/// use core::future;
+///
+/// # async fn run() {
+/// let a = future::ready(1);
+/// assert_eq!(a.await, 1);
+/// # }
+/// ```
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+pub fn ready<T>(t: T) -> Ready<T> {
+    Ready(Some(t))
+}

Diff for: src/librustc_errors/registry.rs

@@ -10,12 +10,12 @@ pub struct Registry {
 
 impl Registry {
     pub fn new(long_descriptions: &[(&'static str, Option<&'static str>)]) -> Registry {
-        Registry { long_descriptions: long_descriptions.iter().cloned().collect() }
+        Registry { long_descriptions: long_descriptions.iter().copied().collect() }
     }
 
     /// This will panic if an invalid error code is passed in
     pub fn find_description(&self, code: &str) -> Option<&'static str> {
-        self.try_find_description(code).unwrap()
+        self.long_descriptions[code]
     }
     /// Returns `InvalidErrorCode` if the code requested does not exist in the
     /// registry. Otherwise, returns an `Option` where `None` means the error
@@ -24,9 +24,6 @@ impl Registry {
         &self,
         code: &str,
     ) -> Result<Option<&'static str>, InvalidErrorCode> {
-        if !self.long_descriptions.contains_key(code) {
-            return Err(InvalidErrorCode);
-        }
-        Ok(*self.long_descriptions.get(code).unwrap())
+        self.long_descriptions.get(code).copied().ok_or(InvalidErrorCode)
     }
 }

Diff for: src/librustc_infer/infer/canonical/canonicalizer.rs

@@ -3,7 +3,7 @@
 //! For an overview of what canonicalization is and how it fits into
 //! rustc, check out the [chapter in the rustc dev guide][c].
 //!
-//! [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html
+//! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html
 
 use crate::infer::canonical::{
     Canonical, CanonicalTyVarKind, CanonicalVarInfo, CanonicalVarKind, Canonicalized,
@@ -35,7 +35,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     /// To get a good understanding of what is happening here, check
     /// out the [chapter in the rustc dev guide][c].
     ///
-    /// [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html#canonicalizing-the-query
+    /// [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html#canonicalizing-the-query
     pub fn canonicalize_query<V>(
         &self,
         value: &V,
@@ -79,7 +79,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     /// To get a good understanding of what is happening here, check
     /// out the [chapter in the rustc dev guide][c].
     ///
-    /// [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html#canonicalizing-the-query-result
+    /// [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html#canonicalizing-the-query-result
     pub fn canonicalize_response<V>(&self, value: &V) -> Canonicalized<'tcx, V>
     where
         V: TypeFoldable<'tcx>,

Diff for: src/librustc_infer/infer/canonical/mod.rs

@@ -19,7 +19,7 @@
 //! For a more detailed look at what is happening here, check
 //! out the [chapter in the rustc dev guide][c].
 //!
-//! [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html
+//! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html
 
 use crate::infer::{ConstVariableOrigin, ConstVariableOriginKind};
 use crate::infer::{InferCtxt, RegionVariableOrigin, TypeVariableOrigin, TypeVariableOriginKind};

Diff for: src/librustc_infer/infer/canonical/query_response.rs

@@ -5,7 +5,7 @@
 //! For an overview of what canonicaliation is and how it fits into
 //! rustc, check out the [chapter in the rustc dev guide][c].
 //!
-//! [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html
+//! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html
 
 use crate::infer::canonical::substitute::{substitute_value, CanonicalExt};
 use crate::infer::canonical::{
@@ -154,7 +154,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     /// To get a good understanding of what is happening here, check
     /// out the [chapter in the rustc dev guide][c].
     ///
-    /// [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html#processing-the-canonicalized-query-result
+    /// [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html#processing-the-canonicalized-query-result
     pub fn instantiate_query_response_and_region_obligations<R>(
         &self,
         cause: &ObligationCause<'tcx>,

Diff for: src/librustc_infer/infer/canonical/substitute.rs

@@ -4,7 +4,7 @@
 //! For an overview of what canonicalization is and how it fits into
 //! rustc, check out the [chapter in the rustc dev guide][c].
 //!
-//! [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html
+//! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html
 
 use crate::infer::canonical::{Canonical, CanonicalVarValues};
 use rustc_middle::ty::fold::TypeFoldable;

Diff for: src/librustc_middle/infer/canonical.rs

@@ -19,7 +19,7 @@
 //! For a more detailed look at what is happening here, check
 //! out the [chapter in the rustc dev guide][c].
 //!
-//! [c]: https://rustc-dev-guide.rust-lang.org/traits/canonicalization.html
+//! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html
 
 use crate::infer::MemberConstraint;
 use crate::ty::subst::GenericArg;