Rollup of 8 pull requests

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -7,7 +7,8 @@ use super::{PatCtxt, PatternError};
 use rustc_arena::TypedArena;
 use rustc_ast::Mutability;
 use rustc_errors::{
-    error_code, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
+    error_code, pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder,
+    ErrorGuaranteed,
 };
 use rustc_hir as hir;
 use rustc_hir::def::*;
@@ -20,7 +21,7 @@ use rustc_session::lint::builtin::{
 };
 use rustc_session::Session;
 use rustc_span::source_map::Spanned;
-use rustc_span::{DesugaringKind, ExpnKind, MultiSpan, Span};
+use rustc_span::{BytePos, DesugaringKind, ExpnKind, MultiSpan, Span};
 
 crate fn check_match(tcx: TyCtxt<'_>, def_id: DefId) {
     let body_id = match def_id.as_local() {
@@ -241,6 +242,9 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
         }
 
         let joined_patterns = joined_uncovered_patterns(&cx, &witnesses);
+
+        let mut bindings = vec![];
+
         let mut err = struct_span_err!(
             self.tcx.sess,
             pat.span,
@@ -257,6 +261,16 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
                 false
             }
             _ => {
+                pat.walk(&mut |pat: &hir::Pat<'_>| {
+                    match pat.kind {
+                        hir::PatKind::Binding(_, _, ident, _) => {
+                            bindings.push(ident);
+                        }
+                        _ => {}
+                    }
+                    true
+                });
+
                 err.span_label(pat.span, pattern_not_covered_label(&witnesses, &joined_patterns));
                 true
             }
@@ -267,13 +281,71 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
                 "`let` bindings require an \"irrefutable pattern\", like a `struct` or \
                  an `enum` with only one variant",
             );
-            if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
-                err.span_suggestion(
-                    span,
-                    "you might want to use `if let` to ignore the variant that isn't matched",
-                    format!("if {} {{ /* */ }}", &snippet[..snippet.len() - 1]),
+            if self.tcx.sess.source_map().span_to_snippet(span).is_ok() {
+                let semi_span = span.shrink_to_hi().with_lo(span.hi() - BytePos(1));
+                let start_span = span.shrink_to_lo();
+                let end_span = semi_span.shrink_to_lo();
+                err.multipart_suggestion(
+                    &format!(
+                        "you might want to use `if let` to ignore the variant{} that {} matched",
+                        pluralize!(witnesses.len()),
+                        match witnesses.len() {
+                            1 => "isn't",
+                            _ => "aren't",
+                        },
+                    ),
+                    vec![
+                        match &bindings[..] {
+                            [] => (start_span, "if ".to_string()),
+                            [binding] => (start_span, format!("let {} = if ", binding)),
+                            bindings => (
+                                start_span,
+                                format!(
+                                    "let ({}) = if ",
+                                    bindings
+                                        .iter()
+                                        .map(|ident| ident.to_string())
+                                        .collect::<Vec<_>>()
+                                        .join(", ")
+                                ),
+                            ),
+                        },
+                        match &bindings[..] {
+                            [] => (semi_span, " { todo!() }".to_string()),
+                            [binding] => {
+                                (end_span, format!(" {{ {} }} else {{ todo!() }}", binding))
+                            }
+                            bindings => (
+                                end_span,
+                                format!(
+                                    " {{ ({}) }} else {{ todo!() }}",
+                                    bindings
+                                        .iter()
+                                        .map(|ident| ident.to_string())
+                                        .collect::<Vec<_>>()
+                                        .join(", ")
+                                ),
+                            ),
+                        },
+                    ],
                     Applicability::HasPlaceholders,
                 );
+                if !bindings.is_empty() && cx.tcx.sess.is_nightly_build() {
+                    err.span_suggestion_verbose(
+                        semi_span.shrink_to_lo(),
+                        &format!(
+                            "alternatively, on nightly, you might want to use \
+                             `#![feature(let_else)]` to handle the variant{} that {} matched",
+                            pluralize!(witnesses.len()),
+                            match witnesses.len() {
+                                1 => "isn't",
+                                _ => "aren't",
+                            },
+                        ),
+                        " else { todo!() }".to_string(),
+                        Applicability::HasPlaceholders,
+                    );
+                }
             }
             err.note(
                 "for more information, visit \

library/alloc/src/collections/vec_deque/iter.rs

@@ -1,5 +1,6 @@
 use core::fmt;
 use core::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
+use core::mem::MaybeUninit;
 use core::ops::Try;
 
 use super::{count, wrap_index, RingSlices};
@@ -12,7 +13,7 @@ use super::{count, wrap_index, RingSlices};
 /// [`iter`]: super::VecDeque::iter
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Iter<'a, T: 'a> {
-    pub(crate) ring: &'a [T],
+    pub(crate) ring: &'a [MaybeUninit<T>],
     pub(crate) tail: usize,
     pub(crate) head: usize,
 }
@@ -44,7 +45,10 @@ impl<'a, T> Iterator for Iter<'a, T> {
         }
         let tail = self.tail;
         self.tail = wrap_index(self.tail.wrapping_add(1), self.ring.len());
-        unsafe { Some(self.ring.get_unchecked(tail)) }
+        // Safety:
+        // - `self.tail` in a ring buffer is always a valid index.
+        // - `self.head` and `self.tail` equality is checked above.
+        unsafe { Some(self.ring.get_unchecked(tail).assume_init_ref()) }
     }
 
     #[inline]
@@ -58,8 +62,13 @@ impl<'a, T> Iterator for Iter<'a, T> {
         F: FnMut(Acc, Self::Item) -> Acc,
     {
         let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
-        accum = front.iter().fold(accum, &mut f);
-        back.iter().fold(accum, &mut f)
+        // Safety:
+        // - `self.head` and `self.tail` in a ring buffer are always valid indices.
+        // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
+        unsafe {
+            accum = MaybeUninit::slice_assume_init_ref(front).iter().fold(accum, &mut f);
+            MaybeUninit::slice_assume_init_ref(back).iter().fold(accum, &mut f)
+        }
     }
 
     fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R
@@ -70,17 +79,19 @@ impl<'a, T> Iterator for Iter<'a, T> {
     {
         let (mut iter, final_res);
         if self.tail <= self.head {
-            // single slice self.ring[self.tail..self.head]
-            iter = self.ring[self.tail..self.head].iter();
+            // Safety: single slice self.ring[self.tail..self.head] is initialized.
+            iter = unsafe { MaybeUninit::slice_assume_init_ref(&self.ring[self.tail..self.head]) }
+                .iter();
             final_res = iter.try_fold(init, &mut f);
         } else {
-            // two slices: self.ring[self.tail..], self.ring[..self.head]
+            // Safety: two slices: self.ring[self.tail..], self.ring[..self.head] both are initialized.
             let (front, back) = self.ring.split_at(self.tail);
-            let mut back_iter = back.iter();
+
+            let mut back_iter = unsafe { MaybeUninit::slice_assume_init_ref(back).iter() };
             let res = back_iter.try_fold(init, &mut f);
             let len = self.ring.len();
             self.tail = (self.ring.len() - back_iter.len()) & (len - 1);
-            iter = front[..self.head].iter();
+            iter = unsafe { MaybeUninit::slice_assume_init_ref(&front[..self.head]).iter() };
             final_res = iter.try_fold(res?, &mut f);
         }
         self.tail = self.head - iter.len();
@@ -109,7 +120,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
         // that is in bounds.
         unsafe {
             let idx = wrap_index(self.tail.wrapping_add(idx), self.ring.len());
-            self.ring.get_unchecked(idx)
+            self.ring.get_unchecked(idx).assume_init_ref()
         }
     }
 }
@@ -122,16 +133,24 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
             return None;
         }
         self.head = wrap_index(self.head.wrapping_sub(1), self.ring.len());
-        unsafe { Some(self.ring.get_unchecked(self.head)) }
+        // Safety:
+        // - `self.head` in a ring buffer is always a valid index.
+        // - `self.head` and `self.tail` equality is checked above.
+        unsafe { Some(self.ring.get_unchecked(self.head).assume_init_ref()) }
     }
 
     fn rfold<Acc, F>(self, mut accum: Acc, mut f: F) -> Acc
     where
         F: FnMut(Acc, Self::Item) -> Acc,
     {
         let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
-        accum = back.iter().rfold(accum, &mut f);
-        front.iter().rfold(accum, &mut f)
+        // Safety:
+        // - `self.head` and `self.tail` in a ring buffer are always valid indices.
+        // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
+        unsafe {
+            accum = MaybeUninit::slice_assume_init_ref(back).iter().rfold(accum, &mut f);
+            MaybeUninit::slice_assume_init_ref(front).iter().rfold(accum, &mut f)
+        }
     }
 
     fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R
@@ -142,16 +161,20 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
     {
         let (mut iter, final_res);
         if self.tail <= self.head {
-            // single slice self.ring[self.tail..self.head]
-            iter = self.ring[self.tail..self.head].iter();
+            // Safety: single slice self.ring[self.tail..self.head] is initialized.
+            iter = unsafe {
+                MaybeUninit::slice_assume_init_ref(&self.ring[self.tail..self.head]).iter()
+            };
             final_res = iter.try_rfold(init, &mut f);
         } else {
-            // two slices: self.ring[self.tail..], self.ring[..self.head]
+            // Safety: two slices: self.ring[self.tail..], self.ring[..self.head] both are initialized.
             let (front, back) = self.ring.split_at(self.tail);
-            let mut front_iter = front[..self.head].iter();
+
+            let mut front_iter =
+                unsafe { MaybeUninit::slice_assume_init_ref(&front[..self.head]).iter() };
             let res = front_iter.try_rfold(init, &mut f);
             self.head = front_iter.len();
-            iter = back.iter();
+            iter = unsafe { MaybeUninit::slice_assume_init_ref(back).iter() };
             final_res = iter.try_rfold(res?, &mut f);
         }
         self.head = self.tail + iter.len();

library/alloc/src/collections/vec_deque/mod.rs

@@ -12,7 +12,7 @@ use core::fmt;
 use core::hash::{Hash, Hasher};
 use core::iter::{repeat_with, FromIterator};
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop};
+use core::mem::{self, ManuallyDrop, MaybeUninit};
 use core::ops::{Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
 use core::slice;
@@ -181,16 +181,28 @@ impl<T, A: Allocator> VecDeque<T, A> {
         }
     }
 
-    /// Turn ptr into a slice
+    /// Turn ptr into a slice, since the elements of the backing buffer may be uninitialized,
+    /// we will return a slice of [`MaybeUninit<T>`].
+    ///
+    /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and
+    /// incorrect usage of this method.
+    ///
+    /// [zeroed]: mem::MaybeUninit::zeroed
     #[inline]
-    unsafe fn buffer_as_slice(&self) -> &[T] {
-        unsafe { slice::from_raw_parts(self.ptr(), self.cap()) }
+    unsafe fn buffer_as_slice(&self) -> &[MaybeUninit<T>] {
+        unsafe { slice::from_raw_parts(self.ptr() as *mut MaybeUninit<T>, self.cap()) }
     }
 
-    /// Turn ptr into a mut slice
+    /// Turn ptr into a mut slice, since the elements of the backing buffer may be uninitialized,
+    /// we will return a slice of [`MaybeUninit<T>`].
+    ///
+    /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and
+    /// incorrect usage of this method.
+    ///
+    /// [zeroed]: mem::MaybeUninit::zeroed
     #[inline]
-    unsafe fn buffer_as_mut_slice(&mut self) -> &mut [T] {
-        unsafe { slice::from_raw_parts_mut(self.ptr(), self.cap()) }
+    unsafe fn buffer_as_mut_slice(&mut self) -> &mut [MaybeUninit<T>] {
+        unsafe { slice::from_raw_parts_mut(self.ptr() as *mut MaybeUninit<T>, self.cap()) }
     }
 
     /// Moves an element out of the buffer
@@ -1055,9 +1067,13 @@ impl<T, A: Allocator> VecDeque<T, A> {
     #[inline]
     #[stable(feature = "deque_extras_15", since = "1.5.0")]
     pub fn as_slices(&self) -> (&[T], &[T]) {
+        // Safety:
+        // - `self.head` and `self.tail` in a ring buffer are always valid indices.
+        // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
         unsafe {
             let buf = self.buffer_as_slice();
-            RingSlices::ring_slices(buf, self.head, self.tail)
+            let (front, back) = RingSlices::ring_slices(buf, self.head, self.tail);
+            (MaybeUninit::slice_assume_init_ref(front), MaybeUninit::slice_assume_init_ref(back))
         }
     }
 
@@ -1089,11 +1105,15 @@ impl<T, A: Allocator> VecDeque<T, A> {
     #[inline]
     #[stable(feature = "deque_extras_15", since = "1.5.0")]
     pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
+        // Safety:
+        // - `self.head` and `self.tail` in a ring buffer are always valid indices.
+        // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
         unsafe {
             let head = self.head;
             let tail = self.tail;
             let buf = self.buffer_as_mut_slice();
-            RingSlices::ring_slices(buf, head, tail)
+            let (front, back) = RingSlices::ring_slices(buf, head, tail);
+            (MaybeUninit::slice_assume_init_mut(front), MaybeUninit::slice_assume_init_mut(back))
         }
     }
 
@@ -2327,7 +2347,14 @@ impl<T, A: Allocator> VecDeque<T, A> {
         if self.is_contiguous() {
             let tail = self.tail;
             let head = self.head;
-            return unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 };
+            // Safety:
+            // - `self.head` and `self.tail` in a ring buffer are always valid indices.
+            // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
+            return unsafe {
+                MaybeUninit::slice_assume_init_mut(
+                    RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0,
+                )
+            };
         }
 
         let buf = self.buf.ptr();
@@ -2413,7 +2440,14 @@ impl<T, A: Allocator> VecDeque<T, A> {
 
         let tail = self.tail;
         let head = self.head;
-        unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 }
+        // Safety:
+        // - `self.head` and `self.tail` in a ring buffer are always valid indices.
+        // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized.
+        unsafe {
+            MaybeUninit::slice_assume_init_mut(
+                RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0,
+            )
+        }
     }
 
     /// Rotates the double-ended queue `mid` places to the left.