Auto merge of #102915 - JohnTitor:rollup-5ht99y1, r=JohnTitor

Rollup of 7 pull requests

Successful merges:

 - #102258 (Remove unused variable in float formatting.)
 - #102277 (Consistently write `RwLock`)
 - #102412 (Never panic in `thread::park` and `thread::park_timeout`)
 - #102589 (scoped threads: pass closure through MaybeUninit to avoid invalid dangling references)
 - #102625 (fix backtrace small typo)
 - #102859 (Move lifetime resolution module to rustc_hir_analysis.)
 - #102898 (rustdoc: remove unneeded `<div>` wrapper from sidebar DOM)

Failed merges:

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

compiler/rustc_hir_analysis/src/collect.rs

@@ -46,6 +46,7 @@ use std::iter;
 
 mod generics_of;
 mod item_bounds;
+mod lifetimes;
 mod predicates_of;
 mod type_of;
 
@@ -57,6 +58,7 @@ fn collect_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 }
 
 pub fn provide(providers: &mut Providers) {
+    lifetimes::provide(providers);
     *providers = Providers {
         opt_const_param_of: type_of::opt_const_param_of,
         type_of: type_of::type_of,

compiler/rustc_resolve/src/late/lifetimes.rs → compiler/rustc_hir_analysis/src/collect/lifetimes.rs

@@ -32,8 +32,6 @@ trait RegionExt {
     fn id(&self) -> Option<DefId>;
 
     fn shifted(self, amount: u32) -> Region;
-
-    fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
 }
 
 impl RegionExt for Region {
@@ -69,15 +67,6 @@ impl RegionExt for Region {
             _ => self,
         }
     }
-
-    fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
-        match self {
-            Region::LateBound(debruijn, index, id) => {
-                Region::LateBound(debruijn.shifted_out_to_binder(binder), index, id)
-            }
-            _ => self,
-        }
-    }
 }
 
 /// Maps the id of each lifetime reference to the lifetime decl
@@ -101,8 +90,8 @@ struct NamedRegionMap {
     late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>,
 }
 
-pub(crate) struct LifetimeContext<'a, 'tcx> {
-    pub(crate) tcx: TyCtxt<'tcx>,
+struct LifetimeContext<'a, 'tcx> {
+    tcx: TyCtxt<'tcx>,
     map: &'a mut NamedRegionMap,
     scope: ScopeRef<'a>,
 
@@ -234,7 +223,7 @@ type ScopeRef<'a> = &'a Scope<'a>;
 
 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
 
-pub fn provide(providers: &mut ty::query::Providers) {
+pub(crate) fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers {
         resolve_lifetimes_trait_definition,
         resolve_lifetimes,

compiler/rustc_interface/src/passes.rs

@@ -739,7 +739,6 @@ pub static DEFAULT_QUERY_PROVIDERS: LazyLock<Providers> = LazyLock::new(|| {
     ty::provide(providers);
     traits::provide(providers);
     rustc_passes::provide(providers);
-    rustc_resolve::provide(providers);
     rustc_traits::provide(providers);
     rustc_ty_utils::provide(providers);
     rustc_metadata::provide(providers);

compiler/rustc_resolve/src/late.rs

@@ -34,7 +34,6 @@ use std::collections::{hash_map::Entry, BTreeSet};
 use std::mem::{replace, take};
 
 mod diagnostics;
-pub(crate) mod lifetimes;
 
 type Res = def::Res<NodeId>;
 

compiler/rustc_resolve/src/lib.rs

@@ -42,7 +42,6 @@ use rustc_metadata::creader::{CStore, CrateLoader};
 use rustc_middle::metadata::ModChild;
 use rustc_middle::middle::privacy::AccessLevels;
 use rustc_middle::span_bug;
-use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, DefIdTree, MainDefinition, RegisteredTools, ResolverOutputs};
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::cstore::{CrateStore, CrateStoreDyn, MetadataLoaderDyn};
@@ -2082,7 +2081,3 @@ impl Finalize {
         Finalize { node_id, path_span, root_span, report_private: true }
     }
 }
-
-pub fn provide(providers: &mut Providers) {
-    late::lifetimes::provide(providers);
-}

library/core/src/num/flt2dec/strategy/grisu.rs

@@ -253,7 +253,6 @@ pub fn format_shortest_opt<'a>(
     let delta1frac = delta1 & ((1 << e) - 1);
 
     // render integral parts, while checking for the accuracy at each step.
-    let mut kappa = max_kappa as i16;
     let mut ten_kappa = max_ten_kappa; // 10^kappa
     let mut remainder = plus1int; // digits yet to be rendered
     loop {
@@ -290,12 +289,10 @@ pub fn format_shortest_opt<'a>(
         // the exact number of digits is `max_kappa + 1` as `plus1 < 10^(max_kappa+1)`.
         if i > max_kappa as usize {
             debug_assert_eq!(ten_kappa, 1);
-            debug_assert_eq!(kappa, 0);
             break;
         }
 
         // restore invariants
-        kappa -= 1;
         ten_kappa /= 10;
         remainder = r;
     }
@@ -338,7 +335,6 @@ pub fn format_shortest_opt<'a>(
         }
 
         // restore invariants
-        kappa -= 1;
         remainder = r;
     }
 

library/std/src/backtrace.rs

@@ -14,8 +14,8 @@
 //! Backtraces are attempted to be as accurate as possible, but no guarantees
 //! are provided about the exact accuracy of a backtrace. Instruction pointers,
 //! symbol names, filenames, line numbers, etc, may all be incorrect when
-//! reported. Accuracy is attempted on a best-effort basis, however, and bugs
-//! are always welcome to indicate areas of improvement!
+//! reported. Accuracy is attempted on a best-effort basis, however, any bug
+//! reports are always welcome to indicate areas of improvement!
 //!
 //! For most platforms a backtrace with a filename/line number requires that
 //! programs be compiled with debug information. Without debug information
@@ -39,7 +39,7 @@
 //! default. Its behavior is governed by two environment variables:
 //!
 //! * `RUST_LIB_BACKTRACE` - if this is set to `0` then `Backtrace::capture`
-//!   will never capture a backtrace. Any other value this is set to will enable
+//!   will never capture a backtrace. Any other value set will enable
 //!   `Backtrace::capture`.
 //!
 //! * `RUST_BACKTRACE` - if `RUST_LIB_BACKTRACE` is not set, then this variable

library/std/src/sync/rwlock.rs

@@ -167,7 +167,7 @@ impl<T> RwLock<T> {
 }
 
 impl<T: ?Sized> RwLock<T> {
-    /// Locks this rwlock with shared read access, blocking the current thread
+    /// Locks this `RwLock` with shared read access, blocking the current thread
     /// until it can be acquired.
     ///
     /// The calling thread will be blocked until there are no more writers which
@@ -181,9 +181,10 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock.
-    /// The failure will occur immediately after the lock has been acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. The failure will occur immediately after the lock has been
+    /// acquired.
     ///
     /// # Panics
     ///
@@ -215,7 +216,7 @@ impl<T: ?Sized> RwLock<T> {
         }
     }
 
-    /// Attempts to acquire this rwlock with shared read access.
+    /// Attempts to acquire this `RwLock` with shared read access.
     ///
     /// If the access could not be granted at this time, then `Err` is returned.
     /// Otherwise, an RAII guard is returned which will release the shared access
@@ -228,13 +229,13 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return the [`Poisoned`] error if the RwLock is poisoned.
-    /// An RwLock is poisoned whenever a writer panics while holding an exclusive
-    /// lock. `Poisoned` will only be returned if the lock would have otherwise been
-    /// acquired.
+    /// This function will return the [`Poisoned`] error if the `RwLock` is
+    /// poisoned. An `RwLock` is poisoned whenever a writer panics while holding
+    /// an exclusive lock. `Poisoned` will only be returned if the lock would
+    /// have otherwise been acquired.
     ///
-    /// This function will return the [`WouldBlock`] error if the RwLock could not
-    /// be acquired because it was already locked exclusively.
+    /// This function will return the [`WouldBlock`] error if the `RwLock` could
+    /// not be acquired because it was already locked exclusively.
     ///
     /// [`Poisoned`]: TryLockError::Poisoned
     /// [`WouldBlock`]: TryLockError::WouldBlock
@@ -263,20 +264,20 @@ impl<T: ?Sized> RwLock<T> {
         }
     }
 
-    /// Locks this rwlock with exclusive write access, blocking the current
+    /// Locks this `RwLock` with exclusive write access, blocking the current
     /// thread until it can be acquired.
     ///
     /// This function will not return while other writers or other readers
     /// currently have access to the lock.
     ///
-    /// Returns an RAII guard which will drop the write access of this rwlock
+    /// Returns an RAII guard which will drop the write access of this `RwLock`
     /// when dropped.
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock.
-    /// An error will be returned when the lock is acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. An error will be returned when the lock is acquired.
     ///
     /// # Panics
     ///
@@ -303,7 +304,7 @@ impl<T: ?Sized> RwLock<T> {
         }
     }
 
-    /// Attempts to lock this rwlock with exclusive write access.
+    /// Attempts to lock this `RwLock` with exclusive write access.
     ///
     /// If the lock could not be acquired at this time, then `Err` is returned.
     /// Otherwise, an RAII guard is returned which will release the lock when
@@ -316,13 +317,13 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return the [`Poisoned`] error if the RwLock is
-    /// poisoned. An RwLock is poisoned whenever a writer panics while holding
-    /// an exclusive lock. `Poisoned` will only be returned if the lock would have
-    /// otherwise been acquired.
+    /// This function will return the [`Poisoned`] error if the `RwLock` is
+    /// poisoned. An `RwLock` is poisoned whenever a writer panics while holding
+    /// an exclusive lock. `Poisoned` will only be returned if the lock would
+    /// have otherwise been acquired.
     ///
-    /// This function will return the [`WouldBlock`] error if the RwLock could not
-    /// be acquired because it was already locked exclusively.
+    /// This function will return the [`WouldBlock`] error if the `RwLock` could
+    /// not be acquired because it was already locked exclusively.
     ///
     /// [`Poisoned`]: TryLockError::Poisoned
     /// [`WouldBlock`]: TryLockError::WouldBlock
@@ -422,10 +423,10 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. An error will only be returned if the lock would have otherwise
+    /// been acquired.
     ///
     /// # Examples
     ///
@@ -455,10 +456,10 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. An error will only be returned if the lock would have otherwise
+    /// been acquired.
     ///
     /// # Examples
     ///

library/std/src/thread/mod.rs

@@ -160,7 +160,7 @@ use crate::ffi::{CStr, CString};
 use crate::fmt;
 use crate::io;
 use crate::marker::PhantomData;
-use crate::mem;
+use crate::mem::{self, forget};
 use crate::num::NonZeroU64;
 use crate::num::NonZeroUsize;
 use crate::panic;
@@ -499,13 +499,40 @@ impl Builder {
         let output_capture = crate::io::set_output_capture(None);
         crate::io::set_output_capture(output_capture.clone());
 
+        // Pass `f` in `MaybeUninit` because actually that closure might *run longer than the lifetime of `F`*.
+        // See <https://github.com/rust-lang/rust/issues/101983> for more details.
+        // To prevent leaks we use a wrapper that drops its contents.
+        #[repr(transparent)]
+        struct MaybeDangling<T>(mem::MaybeUninit<T>);
+        impl<T> MaybeDangling<T> {
+            fn new(x: T) -> Self {
+                MaybeDangling(mem::MaybeUninit::new(x))
+            }
+            fn into_inner(self) -> T {
+                // SAFETY: we are always initiailized.
+                let ret = unsafe { self.0.assume_init_read() };
+                // Make sure we don't drop.
+                mem::forget(self);
+                ret
+            }
+        }
+        impl<T> Drop for MaybeDangling<T> {
+            fn drop(&mut self) {
+                // SAFETY: we are always initiailized.
+                unsafe { self.0.assume_init_drop() };
+            }
+        }
+
+        let f = MaybeDangling::new(f);
         let main = move || {
             if let Some(name) = their_thread.cname() {
                 imp::Thread::set_name(name);
             }
 
             crate::io::set_output_capture(output_capture);
 
+            // SAFETY: we constructed `f` initialized.
+            let f = f.into_inner();
             // SAFETY: the stack guard passed is the one for the current thread.
             // This means the current thread's stack and the new thread's stack
             // are properly set and protected from each other.
@@ -518,6 +545,12 @@ impl Builder {
             // same `JoinInner` as this closure meaning the mutation will be
             // safe (not modify it and affect a value far away).
             unsafe { *their_packet.result.get() = Some(try_result) };
+            // Here `their_packet` gets dropped, and if this is the last `Arc` for that packet that
+            // will call `decrement_num_running_threads` and therefore signal that this thread is
+            // done.
+            drop(their_packet);
+            // Here, the lifetime `'a` and even `'scope` can end. `main` keeps running for a bit
+            // after that before returning itself.
         };
 
         if let Some(scope_data) = &my_packet.scope {
@@ -851,10 +884,22 @@ pub fn sleep(dur: Duration) {
     imp::Thread::sleep(dur)
 }
 
+/// Used to ensure that `park` and `park_timeout` do not unwind, as that can
+/// cause undefined behaviour if not handled correctly (see #102398 for context).
+struct PanicGuard;
+
+impl Drop for PanicGuard {
+    fn drop(&mut self) {
+        rtabort!("an irrecoverable error occurred while synchronizing threads")
+    }
+}
+
 /// Blocks unless or until the current thread's token is made available.
 ///
 /// A call to `park` does not guarantee that the thread will remain parked
-/// forever, and callers should be prepared for this possibility.
+/// forever, and callers should be prepared for this possibility. However,
+/// it is guaranteed that this function will not panic (it may abort the
+/// process if the implementation encounters some rare errors).
 ///
 /// # park and unpark
 ///
@@ -939,10 +984,13 @@ pub fn sleep(dur: Duration) {
 /// [`thread::park_timeout`]: park_timeout
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn park() {
+    let guard = PanicGuard;
     // SAFETY: park_timeout is called on the parker owned by this thread.
     unsafe {
         current().inner.as_ref().parker().park();
     }
+    // No panic occurred, do not abort.
+    forget(guard);
 }
 
 /// Use [`park_timeout`].
@@ -1003,10 +1051,13 @@ pub fn park_timeout_ms(ms: u32) {
 /// ```
 #[stable(feature = "park_timeout", since = "1.4.0")]
 pub fn park_timeout(dur: Duration) {
+    let guard = PanicGuard;
     // SAFETY: park_timeout is called on the parker owned by this thread.
     unsafe {
         current().inner.as_ref().parker().park_timeout(dur);
     }
+    // No panic occurred, do not abort.
+    forget(guard);
 }
 
 ////////////////////////////////////////////////////////////////////////////////