Auto merge of #111933 - matthiaskrgr:rollup-m10k3ts, r=matthiaskrgr

Rollup of 4 pull requests

Successful merges:

 - #95198 (Add slice::{split_,}{first,last}_chunk{,_mut})
 - #109899 (Use apple-m1 as target CPU for aarch64-apple-darwin.)
 - #111624 (Emit diagnostic for privately uninhabited uncovered witnesses.)
 - #111875 (Don't leak the function that is called on drop)

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

compiler/rustc_data_structures/src/lib.rs

@@ -102,21 +102,27 @@ pub mod unord;
 pub use ena::undo_log;
 pub use ena::unify;
 
-pub struct OnDrop<F: Fn()>(pub F);
+/// Returns a structure that calls `f` when dropped.
+pub fn defer<F: FnOnce()>(f: F) -> OnDrop<F> {
+    OnDrop(Some(f))
+}
 
-impl<F: Fn()> OnDrop<F> {
-    /// Forgets the function which prevents it from running.
-    /// Ensure that the function owns no memory, otherwise it will be leaked.
+pub struct OnDrop<F: FnOnce()>(Option<F>);
+
+impl<F: FnOnce()> OnDrop<F> {
+    /// Disables on-drop call.
     #[inline]
-    pub fn disable(self) {
-        std::mem::forget(self);
+    pub fn disable(mut self) {
+        self.0.take();
     }
 }
 
-impl<F: Fn()> Drop for OnDrop<F> {
+impl<F: FnOnce()> Drop for OnDrop<F> {
     #[inline]
     fn drop(&mut self) {
-        (self.0)();
+        if let Some(f) = self.0.take() {
+            f();
+        }
     }
 }
 

compiler/rustc_data_structures/src/owned_slice/tests.rs

@@ -7,8 +7,8 @@ use std::{
 };
 
 use crate::{
+    defer,
     owned_slice::{slice_owned, try_slice_owned, OwnedSlice},
-    OnDrop,
 };
 
 #[test]
@@ -66,7 +66,7 @@ fn boxed() {
 fn drop_drops() {
     let flag = Arc::new(AtomicBool::new(false));
     let flag_prime = Arc::clone(&flag);
-    let d = OnDrop(move || flag_prime.store(true, atomic::Ordering::Relaxed));
+    let d = defer(move || flag_prime.store(true, atomic::Ordering::Relaxed));
 
     let slice = slice_owned(d, |_| &[]);
 

compiler/rustc_interface/src/interface.rs

@@ -3,9 +3,9 @@ use crate::util;
 use rustc_ast::token;
 use rustc_ast::{self as ast, LitKind, MetaItemKind};
 use rustc_codegen_ssa::traits::CodegenBackend;
+use rustc_data_structures::defer;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::Lrc;
-use rustc_data_structures::OnDrop;
 use rustc_errors::registry::Registry;
 use rustc_errors::{ErrorGuaranteed, Handler};
 use rustc_lint::LintStore;
@@ -325,7 +325,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
 
             rustc_span::set_source_map(compiler.sess.parse_sess.clone_source_map(), move || {
                 let r = {
-                    let _sess_abort_error = OnDrop(|| {
+                    let _sess_abort_error = defer(|| {
                         compiler.sess.finish_diagnostics(registry);
                     });
 

compiler/rustc_middle/src/ty/context/tls.rs

@@ -78,7 +78,7 @@ where
 {
     TLV.with(|tlv| {
         let old = tlv.replace(erase(context));
-        let _reset = rustc_data_structures::OnDrop(move || tlv.set(old));
+        let _reset = rustc_data_structures::defer(move || tlv.set(old));
         f()
     })
 }

compiler/rustc_mir_build/messages.ftl

@@ -340,6 +340,8 @@ mir_build_uncovered = {$count ->
         *[other] patterns `{$witness_1}`, `{$witness_2}`, `{$witness_3}` and {$remainder} more
     } not covered
 
+mir_build_privately_uninhabited = pattern `{$witness_1}` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
+
 mir_build_pattern_not_covered = refutable pattern in {$origin}
     .pattern_ty = the matched value is of type `{$pattern_ty}`
 

compiler/rustc_mir_build/src/errors.rs

@@ -781,6 +781,8 @@ pub(crate) struct PatternNotCovered<'s, 'tcx> {
     pub interpreted_as_const: Option<InterpretedAsConst>,
     #[subdiagnostic]
     pub adt_defined_here: Option<AdtDefinedHere<'tcx>>,
+    #[note(mir_build_privately_uninhabited)]
+    pub witness_1_is_privately_uninhabited: Option<()>,
     #[note(mir_build_pattern_ty)]
     pub _p: (),
     pub pattern_ty: Ty<'tcx>,

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

@@ -479,12 +479,30 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
             AdtDefinedHere { adt_def_span, ty, variants }
         };
 
+        // Emit an extra note if the first uncovered witness is
+        // visibly uninhabited anywhere in the current crate.
+        let witness_1_is_privately_uninhabited =
+            if cx.tcx.features().exhaustive_patterns
+                && let Some(witness_1) = witnesses.get(0)
+                && let ty::Adt(adt, substs) = witness_1.ty().kind()
+                && adt.is_enum()
+                && let Constructor::Variant(variant_index) = witness_1.ctor()
+            {
+                let variant = adt.variant(*variant_index);
+                let inhabited = variant.inhabited_predicate(cx.tcx, *adt).subst(cx.tcx, substs);
+                assert!(inhabited.apply(cx.tcx, cx.param_env, cx.module));
+                !inhabited.apply_ignore_module(cx.tcx, cx.param_env)
+            } else {
+                false
+            };
+
         self.error = Err(self.tcx.sess.emit_err(PatternNotCovered {
             span: pat.span,
             origin,
             uncovered: Uncovered::new(pat.span, &cx, witnesses),
             inform,
             interpreted_as_const,
+            witness_1_is_privately_uninhabited: witness_1_is_privately_uninhabited.then_some(()),
             _p: (),
             pattern_ty,
             let_suggestion,

compiler/rustc_query_system/src/query/job.rs

@@ -22,7 +22,7 @@ use {
     rustc_data_structures::fx::FxHashSet,
     rustc_data_structures::sync::Lock,
     rustc_data_structures::sync::Lrc,
-    rustc_data_structures::{jobserver, OnDrop},
+    rustc_data_structures::{defer, jobserver},
     rustc_span::DUMMY_SP,
     std::iter,
     std::process,
@@ -530,7 +530,7 @@ fn remove_cycle<D: DepKind>(
 /// all active queries for cycles before finally resuming all the waiters at once.
 #[cfg(parallel_compiler)]
 pub fn deadlock<D: DepKind>(query_map: QueryMap<D>, registry: &rayon_core::Registry) {
-    let on_panic = OnDrop(|| {
+    let on_panic = defer(|| {
         eprintln!("deadlock handler panicked, aborting process");
         process::abort();
     });

compiler/rustc_target/src/spec/aarch64_apple_darwin.rs

@@ -4,7 +4,7 @@ use crate::spec::{FramePointer, SanitizerSet, Target, TargetOptions};
 pub fn target() -> Target {
     let arch = Arch::Arm64;
     let mut base = opts("macos", arch);
-    base.cpu = "apple-a14".into();
+    base.cpu = "apple-m1".into();
     base.max_atomic_width = Some(128);
 
     // FIXME: The leak sanitizer currently fails the tests, see #88132.

library/core/src/slice/mod.rs

@@ -319,6 +319,264 @@ impl<T> [T] {
         if let [.., last] = self { Some(last) } else { None }
     }
 
+    /// Returns the first `N` elements of the slice, or `None` if it has fewer than `N` elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let u = [10, 40, 30];
+    /// assert_eq!(Some(&[10, 40]), u.first_chunk::<2>());
+    ///
+    /// let v: &[i32] = &[10];
+    /// assert_eq!(None, v.first_chunk::<2>());
+    ///
+    /// let w: &[i32] = &[];
+    /// assert_eq!(Some(&[]), w.first_chunk::<0>());
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn first_chunk<const N: usize>(&self) -> Option<&[T; N]> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   and do not let the reference outlive the slice.
+            Some(unsafe { &*(self.as_ptr() as *const [T; N]) })
+        }
+    }
+
+    /// Returns a mutable reference to the first `N` elements of the slice,
+    /// or `None` if it has fewer than `N` elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some(first) = x.first_chunk_mut::<2>() {
+    ///     first[0] = 5;
+    ///     first[1] = 4;
+    /// }
+    /// assert_eq!(x, &[5, 4, 2]);
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   do not let the reference outlive the slice,
+            //   and require exclusive access to the entire slice to mutate the chunk.
+            Some(unsafe { &mut *(self.as_mut_ptr() as *mut [T; N]) })
+        }
+    }
+
+    /// Returns the first `N` elements of the slice and the remainder,
+    /// or `None` if it has fewer than `N` elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let x = &[0, 1, 2];
+    ///
+    /// if let Some((first, elements)) = x.split_first_chunk::<2>() {
+    ///     assert_eq!(first, &[0, 1]);
+    ///     assert_eq!(elements, &[2]);
+    /// }
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We manually verified the bounds of the split.
+            let (first, tail) = unsafe { self.split_at_unchecked(N) };
+
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   and do not let the references outlive the slice.
+            Some((unsafe { &*(first.as_ptr() as *const [T; N]) }, tail))
+        }
+    }
+
+    /// Returns a mutable reference to the first `N` elements of the slice and the remainder,
+    /// or `None` if it has fewer than `N` elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some((first, elements)) = x.split_first_chunk_mut::<2>() {
+    ///     first[0] = 3;
+    ///     first[1] = 4;
+    ///     elements[0] = 5;
+    /// }
+    /// assert_eq!(x, &[3, 4, 5]);
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn split_first_chunk_mut<const N: usize>(
+        &mut self,
+    ) -> Option<(&mut [T; N], &mut [T])> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We manually verified the bounds of the split.
+            let (first, tail) = unsafe { self.split_at_mut_unchecked(N) };
+
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   do not let the reference outlive the slice,
+            //   and enforce exclusive mutability of the chunk by the split.
+            Some((unsafe { &mut *(first.as_mut_ptr() as *mut [T; N]) }, tail))
+        }
+    }
+
+    /// Returns the last `N` elements of the slice and the remainder,
+    /// or `None` if it has fewer than `N` elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let x = &[0, 1, 2];
+    ///
+    /// if let Some((last, elements)) = x.split_last_chunk::<2>() {
+    ///     assert_eq!(last, &[1, 2]);
+    ///     assert_eq!(elements, &[0]);
+    /// }
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn split_last_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We manually verified the bounds of the split.
+            let (init, last) = unsafe { self.split_at_unchecked(self.len() - N) };
+
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   and do not let the references outlive the slice.
+            Some((unsafe { &*(last.as_ptr() as *const [T; N]) }, init))
+        }
+    }
+
+    /// Returns the last and all the rest of the elements of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some((last, elements)) = x.split_last_chunk_mut::<2>() {
+    ///     last[0] = 3;
+    ///     last[1] = 4;
+    ///     elements[0] = 5;
+    /// }
+    /// assert_eq!(x, &[5, 3, 4]);
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn split_last_chunk_mut<const N: usize>(
+        &mut self,
+    ) -> Option<(&mut [T; N], &mut [T])> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We manually verified the bounds of the split.
+            let (init, last) = unsafe { self.split_at_mut_unchecked(self.len() - N) };
+
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   do not let the reference outlive the slice,
+            //   and enforce exclusive mutability of the chunk by the split.
+            Some((unsafe { &mut *(last.as_mut_ptr() as *mut [T; N]) }, init))
+        }
+    }
+
+    /// Returns the last element of the slice, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let u = [10, 40, 30];
+    /// assert_eq!(Some(&[40, 30]), u.last_chunk::<2>());
+    ///
+    /// let v: &[i32] = &[10];
+    /// assert_eq!(None, v.last_chunk::<2>());
+    ///
+    /// let w: &[i32] = &[];
+    /// assert_eq!(Some(&[]), w.last_chunk::<0>());
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn last_chunk<const N: usize>(&self) -> Option<&[T; N]> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We manually verified the bounds of the slice.
+            // FIXME: Without const traits, we need this instead of `get_unchecked`.
+            let last = unsafe { self.split_at_unchecked(self.len() - N).1 };
+
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   and do not let the references outlive the slice.
+            Some(unsafe { &*(last.as_ptr() as *const [T; N]) })
+        }
+    }
+
+    /// Returns a mutable pointer to the last item in the slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_first_last_chunk)]
+    ///
+    /// let x = &mut [0, 1, 2];
+    ///
+    /// if let Some(last) = x.last_chunk_mut::<2>() {
+    ///     last[0] = 10;
+    ///     last[1] = 20;
+    /// }
+    /// assert_eq!(x, &[0, 10, 20]);
+    /// ```
+    #[unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[rustc_const_unstable(feature = "slice_first_last_chunk", issue = "111774")]
+    #[inline]
+    pub const fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]> {
+        if self.len() < N {
+            None
+        } else {
+            // SAFETY: We manually verified the bounds of the slice.
+            // FIXME: Without const traits, we need this instead of `get_unchecked`.
+            let last = unsafe { self.split_at_mut_unchecked(self.len() - N).1 };
+
+            // SAFETY: We explicitly check for the correct number of elements,
+            //   do not let the reference outlive the slice,
+            //   and require exclusive access to the entire slice to mutate the chunk.
+            Some(unsafe { &mut *(last.as_mut_ptr() as *mut [T; N]) })
+        }
+    }
+
     /// Returns a reference to an element or subslice depending on the type of
     /// index.
     ///

tests/ui/never_type/exhaustive_patterns.stderr

@@ -14,6 +14,7 @@ LL | enum Either<A, B> {
 LL |     A(A),
 LL |     B(inner::Wrapper<B>),
    |     - not covered
+   = note: pattern `Either::B(_)` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
    = note: the matched value is of type `Either<(), !>`
 help: you might want to use `if let` to ignore the variant that isn't matched
    |

tests/ui/uninhabited/uninhabited-irrefutable.rs

@@ -16,7 +16,9 @@ struct NotSoSecretlyEmpty {
 }
 
 enum Foo {
+    //~^ NOTE `Foo` defined here
     A(foo::SecretlyEmpty),
+    //~^ NOTE not covered
     B(foo::NotSoSecretlyEmpty),
     C(NotSoSecretlyEmpty),
     D(u32, u32),
@@ -27,4 +29,9 @@ fn main() {
     let Foo::D(_y, _z) = x;
     //~^ ERROR refutable pattern in local binding
     //~| `Foo::A(_)` not covered
+    //~| NOTE `let` bindings require an "irrefutable pattern"
+    //~| NOTE for more information
+    //~| NOTE pattern `Foo::A(_)` is currently uninhabited
+    //~| NOTE the matched value is of type `Foo`
+    //~| HELP you might want to use `let else`
 }

tests/ui/uninhabited/uninhabited-irrefutable.stderr

@@ -1,5 +1,5 @@
 error[E0005]: refutable pattern in local binding
-  --> $DIR/uninhabited-irrefutable.rs:27:9
+  --> $DIR/uninhabited-irrefutable.rs:29:9
    |
 LL |     let Foo::D(_y, _z) = x;
    |         ^^^^^^^^^^^^^^ pattern `Foo::A(_)` not covered
@@ -11,8 +11,10 @@ note: `Foo` defined here
    |
 LL | enum Foo {
    |      ^^^
+LL |
 LL |     A(foo::SecretlyEmpty),
    |     - not covered
+   = note: pattern `Foo::A(_)` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
    = note: the matched value is of type `Foo`
 help: you might want to use `let else` to handle the variant that isn't matched
    |