Auto merge of #84729 - jackh726:rollup-dnm8kg5, r=jackh726

Rollup of 10 pull requests

Successful merges:

 - #84451 (Use flex more consistently)
 - #84590 (Point out that behavior might be switched on 2015 and 2018 too one day)
 - #84682 (Don't rebind in `transitive_bounds_that_define_assoc_type`)
 - #84683 (Minor grammar tweaks for readability to btree internals)
 - #84688 (Remove unnecessary CSS rules for search results)
 - #84690 (Remove unneeded bottom margin on search results)
 - #84692 (Link between std::env::{var, var_os} and std::env::{vars, vars_os})
 - #84705 (make feature recommendations optional)
 - #84706 (Drop alias `reduce` for `fold` - we have a `reduce` function)
 - #84713 (Fix labels for regression issue template)

Failed merges:

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

.github/ISSUE_TEMPLATE/regression.md

@@ -1,7 +1,7 @@
 ---
 name: Regression
 about: Report something that unexpectedly changed between Rust versions.
-labels: C-bug regression-untriaged
+labels: C-bug, regression-untriaged
 ---
 <!--
 Thank you for filing a regression report! 🐛 A regression is something that changed between versions of Rust but was not supposed to.

compiler/rustc_infer/src/traits/util.rs

@@ -305,9 +305,7 @@ pub fn transitive_bounds_that_define_assoc_type<'tcx>(
                     Some(assoc_name),
                 ));
                 for (super_predicate, _) in super_predicates.predicates {
-                    let bound_predicate = super_predicate.kind();
-                    let subst_predicate = super_predicate
-                        .subst_supertrait(tcx, &bound_predicate.rebind(trait_ref.skip_binder()));
+                    let subst_predicate = super_predicate.subst_supertrait(tcx, &trait_ref);
                     if let Some(binder) = subst_predicate.to_opt_poly_trait_ref() {
                         stack.push(binder.value);
                     }

compiler/rustc_middle/src/ty/flags.rs

@@ -59,6 +59,10 @@ impl FlagComputation {
     {
         let mut computation = FlagComputation::new();
 
+        if !value.bound_vars().is_empty() {
+            computation.flags = computation.flags | TypeFlags::HAS_RE_LATE_BOUND;
+        }
+
         f(&mut computation, value.skip_binder());
 
         self.add_flags(computation.flags);

compiler/rustc_resolve/src/diagnostics.rs

@@ -487,7 +487,13 @@ impl<'a> Resolver<'a> {
                         name
                     ));
                 }
-                err.help("use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` to allow generic const expressions");
+
+                if self.session.is_nightly_build() {
+                    err.help(
+                        "use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` \
+                        to allow generic const expressions"
+                    );
+                }
 
                 err
             }

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -315,17 +315,20 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
                         ),
                     )
                 } else {
-                    tcx.sess
-                        .struct_span_err(
-                            hir_ty.span,
-                            &format!(
-                                "{} is forbidden as the type of a const generic parameter",
-                                unsupported_type
-                            ),
-                        )
-                        .note("the only supported types are integers, `bool` and `char`")
-                        .help("more complex types are supported with `#![feature(const_generics)]`")
-                        .emit()
+                    let mut err = tcx.sess.struct_span_err(
+                        hir_ty.span,
+                        &format!(
+                            "{} is forbidden as the type of a const generic parameter",
+                            unsupported_type
+                        ),
+                    );
+                    err.note("the only supported types are integers, `bool` and `char`");
+                    if tcx.sess.is_nightly_build() {
+                        err.help(
+                            "more complex types are supported with `#![feature(const_generics)]`",
+                        );
+                    }
+                    err.emit()
                 }
             };
 

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

@@ -89,7 +89,7 @@ impl<K, V> LeafNode<K, V> {
 
 /// The underlying representation of internal nodes. As with `LeafNode`s, these should be hidden
 /// behind `BoxedNode`s to prevent dropping uninitialized keys and values. Any pointer to an
-/// `InternalNode` can be directly casted to a pointer to the underlying `LeafNode` portion of the
+/// `InternalNode` can be directly cast to a pointer to the underlying `LeafNode` portion of the
 /// node, allowing code to act on leaf and internal nodes generically without having to even check
 /// which of the two a pointer is pointing at. This property is enabled by the use of `repr(C)`.
 #[repr(C)]
@@ -408,7 +408,7 @@ impl<K, V> NodeRef<marker::Dying, K, V, marker::LeafOrInternal> {
 }
 
 impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
-    /// Temporarily takes out another, mutable reference to the same node. Beware, as
+    /// Temporarily takes out another mutable reference to the same node. Beware, as
     /// this method is very dangerous, doubly so since it may not immediately appear
     /// dangerous.
     ///
@@ -759,7 +759,7 @@ impl<BorrowType, K, V, NodeType, HandleType> PartialEq
 impl<BorrowType, K, V, NodeType, HandleType>
     Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
 {
-    /// Temporarily takes out another, immutable handle on the same location.
+    /// Temporarily takes out another immutable handle on the same location.
     pub fn reborrow(&self) -> Handle<NodeRef<marker::Immut<'_>, K, V, NodeType>, HandleType> {
         // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
         Handle { node: self.node.reborrow(), idx: self.idx, _marker: PhantomData }
@@ -767,7 +767,7 @@ impl<BorrowType, K, V, NodeType, HandleType>
 }
 
 impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
-    /// Temporarily takes out another, mutable handle on the same location. Beware, as
+    /// Temporarily takes out another mutable handle on the same location. Beware, as
     /// this method is very dangerous, doubly so since it may not immediately appear
     /// dangerous.
     ///

library/core/src/iter/traits/iterator.rs

@@ -2133,7 +2133,6 @@ pub trait Iterator {
     /// ```
     ///
     /// [`reduce()`]: Iterator::reduce
-    #[doc(alias = "reduce")]
     #[doc(alias = "inject")]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]

library/std/src/env.rs

@@ -124,6 +124,10 @@ pub fn vars() -> Vars {
 /// variables at the time of this invocation. Modifications to environment
 /// variables afterwards will not be reflected in the returned iterator.
 ///
+/// Note that the returned iterator will not check if the environment variables
+/// are valid Unicode. If you want to panic on invalid UTF-8,
+/// use the [`vars`] function instead.
+///
 /// # Examples
 ///
 /// ```
@@ -180,8 +184,9 @@ impl fmt::Debug for VarsOs {
 ///
 /// # Errors
 ///
-/// * Environment variable is not present
-/// * Environment variable is not valid unicode
+/// Errors if the environment variable is not present.
+/// Errors if the environment variable is not valid Unicode. If this is not desired, consider using
+/// [`var_os`].
 ///
 /// # Panics
 ///
@@ -221,6 +226,10 @@ fn _var(key: &OsStr) -> Result<String, VarError> {
 /// `'='` or the NUL character `'\0'`, or when the value contains the NUL
 /// character.
 ///
+/// Note that the method will not check if the environment variable
+/// is valid Unicode. If you want to have an error on invalid UTF-8,
+/// use the [`var`] function instead.
+///
 /// # Examples
 ///
 /// ```

library/std/src/primitive_docs.rs

@@ -553,8 +553,10 @@ mod prim_pointer {}
 /// # Editions
 ///
 /// Prior to Rust 1.53, arrays did not implement `IntoIterator` by value, so the method call
-/// `array.into_iter()` auto-referenced into a slice iterator. That behavior is preserved in the
-/// 2015 and 2018 editions of Rust for compatability, ignoring `IntoIterator` by value.
+/// `array.into_iter()` auto-referenced into a slice iterator. Right now, the old behavior
+/// is preserved in the 2015 and 2018 editions of Rust for compatibility, ignoring
+/// `IntoIterator` by value. In the future, the behavior on the 2015 and 2018 edition
+/// might be made consistent to the behavior of later editions.
 ///
 #[cfg_attr(bootstrap, doc = "```rust,edition2018,ignore")]
 #[cfg_attr(not(bootstrap), doc = "```rust,edition2018")]
@@ -601,6 +603,49 @@ mod prim_pointer {}
 /// }
 /// ```
 ///
+/// Future language versions might start treating the `array.into_iter()`
+/// syntax on editions 2015 and 2018 the same as on edition 2021. So code using
+/// those older editions should still be written with this change in mind, to
+/// prevent breakage in the future. The safest way to accomplish this is to
+/// avoid the `into_iter` syntax on those editions. If an edition update is not
+/// viable/desired, there are multiple alternatives:
+/// * use `iter`, equivalent to the old behavior, creating references
+/// * use [`array::IntoIter`], equivalent to the post-2021 behavior (Rust 1.51+)
+/// * replace `for ... in array.into_iter() {` with `for ... in array {`,
+///   equivalent to the post-2021 behavior (Rust 1.53+)
+///
+#[cfg_attr(bootstrap, doc = "```rust,edition2018,ignore")]
+#[cfg_attr(not(bootstrap), doc = "```rust,edition2018")]
+/// use std::array::IntoIter;
+///
+/// let array: [i32; 3] = [0; 3];
+///
+/// // This iterates by reference:
+/// for item in array.iter() {
+///     let x: &i32 = item;
+///     println!("{}", x);
+/// }
+///
+/// // This iterates by value:
+/// for item in IntoIter::new(array) {
+///     let x: i32 = item;
+///     println!("{}", x);
+/// }
+///
+/// // This iterates by value:
+/// for item in array {
+///     let x: i32 = item;
+///     println!("{}", x);
+/// }
+///
+/// // IntoIter can also start a chain.
+/// // This iterates by value:
+/// for item in IntoIter::new(array).enumerate() {
+///     let (i, x): (usize, i32) = item;
+///     println!("array[{}] = {}", i, x);
+/// }
+/// ```
+///
 /// [slice]: prim@slice
 /// [`Debug`]: fmt::Debug
 /// [`Hash`]: hash::Hash

src/librustdoc/html/static/rustdoc.css

@@ -117,9 +117,12 @@ h4:not(.method):not(.type):not(.tymethod):not(.associatedconstant) {
 }
 h1.fqn {
 	display: flex;
-	width: 100%;
 	border-bottom: 1px dashed;
 	margin-top: 0;
+
+	/* workaround to keep flex from breaking below 700 px width due to the float: right on the nav
+	   above the h1 */
+	padding-left: 1px;
 }
 h1.fqn > .in-band > a:hover {
 	text-decoration: underline;
@@ -385,17 +388,9 @@ nav.sub {
 	position: relative;
 }
 
-#results {
-	position: absolute;
-	right: 0;
-	left: 0;
-	overflow: auto;
-}
-
 #results > table {
 	width: 100%;
 	table-layout: fixed;
-	margin-bottom: 40px;
 }
 
 .content pre.line-numbers {
@@ -453,20 +448,14 @@ nav.sub {
 }
 
 .content .out-of-band {
-	float: right;
+	flex-grow: 0;
+	text-align: right;
 	font-size: 23px;
 	margin: 0px;
-	padding: 0px;
+	padding: 0 0 0 12px;
 	font-weight: normal;
 }
 
-h1.fqn > .out-of-band {
-	float: unset;
-	flex: 1;
-	text-align: right;
-	margin-left: 8px;
-}
-
 h3.impl > .out-of-band {
 	font-size: 21px;
 }
@@ -486,6 +475,7 @@ h4 > code, h3 > code, .invisible > code {
 }
 
 .content .in-band {
+	flex-grow: 1;
 	margin: 0px;
 	padding: 0px;
 }
@@ -1484,10 +1474,6 @@ h4 > .notable-traits {
 		display: none !important;
 	}
 
-	h1.fqn {
-		overflow: initial;
-	}
-
 	.theme-picker {
 		left: 10px;
 		top: 54px;

src/test/ui/lifetimes/issue-83737-erasing-bound-vars.rs

@@ -0,0 +1,14 @@
+// build-pass
+// compile-flags: --edition 2018
+// compile-flags: --crate-type rlib
+
+use std::future::Future;
+
+async fn handle<F>(slf: &F)
+where
+    F: Fn(&()) -> Box<dyn for<'a> Future<Output = ()> + Unpin>,
+{
+    (slf)(&()).await;
+}
+
+fn main() {}

src/test/ui/lifetimes/issue-84604.rs

@@ -0,0 +1,9 @@
+// run-pass
+// compile-flags: -Zsymbol-mangling-version=v0
+
+pub fn f<T: ?Sized>() {}
+pub trait Frob<T: ?Sized> {}
+fn main() {
+    f::<dyn Frob<str>>();
+    f::<dyn for<'a> Frob<str>>();
+}