Rollup of 8 pull requests

compiler/rustc_codegen_ssa/messages.ftl

@@ -31,7 +31,7 @@ codegen_ssa_cpu_required = target requires explicitly specifying a cpu with `-C
 codegen_ssa_create_temp_dir = couldn't create a temp dir: {$error}
 
 codegen_ssa_dlltool_fail_import_library =
-    Dlltool could not create import library with {$dlltool_path} {$dlltool_args}:
+    dlltool could not create import library with {$dlltool_path} {$dlltool_args}:
     {$stdout}
     {$stderr}
 

compiler/rustc_passes/messages.ftl

@@ -75,7 +75,7 @@ passes_const_stable_not_stable =
     .label = attribute specified here
 
 passes_custom_mir_incompatible_dialect_and_phase =
-    The {$dialect} dialect is not compatible with the {$phase} phase
+    the {$dialect} dialect is not compatible with the {$phase} phase
     .dialect_span = this dialect...
     .phase_span = ... is not compatible with this phase
 

compiler/rustc_span/src/hygiene.rs

@@ -46,6 +46,8 @@ use crate::symbol::{Symbol, kw, sym};
 use crate::{DUMMY_SP, HashStableContext, Span, SpanDecoder, SpanEncoder, with_session_globals};
 
 /// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
+///
+/// See <https://rustc-dev-guide.rust-lang.org/macro-expansion.html> for more explanation.
 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub struct SyntaxContext(u32);
 
@@ -61,7 +63,10 @@ pub type SyntaxContextKey = (SyntaxContext, ExpnId, Transparency);
 
 #[derive(Clone, Copy, Debug)]
 struct SyntaxContextData {
+    /// The last macro expansion in the chain.
+    /// (Here we say the most deeply nested macro expansion is the "outermost" expansion.)
     outer_expn: ExpnId,
+    /// Transparency of the last macro expansion
     outer_transparency: Transparency,
     parent: SyntaxContext,
     /// This context, but with all transparent and semi-opaque expansions filtered away.
@@ -450,11 +455,13 @@ impl HygieneData {
         self.syntax_context_data[ctxt.0 as usize].opaque_and_semiopaque
     }
 
+    /// See [`SyntaxContextData::outer_expn`]
     #[inline]
     fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
         self.syntax_context_data[ctxt.0 as usize].outer_expn
     }
 
+    /// The last macro expansion and its Transparency
     #[inline]
     fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
         let data = &self.syntax_context_data[ctxt.0 as usize];
@@ -900,6 +907,7 @@ impl SyntaxContext {
         HygieneData::with(|data| data.normalize_to_macro_rules(self))
     }
 
+    /// See [`SyntaxContextData::outer_expn`]
     #[inline]
     pub fn outer_expn(self) -> ExpnId {
         HygieneData::with(|data| data.outer_expn(self))
@@ -912,6 +920,7 @@ impl SyntaxContext {
         HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
     }
 
+    /// See [`HygieneData::outer_mark`]
     #[inline]
     fn outer_mark(self) -> (ExpnId, Transparency) {
         HygieneData::with(|data| data.outer_mark(self))
@@ -982,19 +991,20 @@ impl Span {
 #[derive(Clone, Debug, Encodable, Decodable, HashStable_Generic)]
 pub struct ExpnData {
     // --- The part unique to each expansion.
-    /// The kind of this expansion - macro or compiler desugaring.
     pub kind: ExpnKind,
-    /// The expansion that produced this expansion.
+    /// The expansion that contains the definition of the macro for this expansion.
     pub parent: ExpnId,
-    /// The location of the actual macro invocation or syntax sugar , e.g.
-    /// `let x = foo!();` or `if let Some(y) = x {}`
+    /// The span of the macro call which produced this expansion.
+    ///
+    /// This span will typically have a different `ExpnData` and `call_site`.
+    /// This recursively traces back through any macro calls which expanded into further
+    /// macro calls, until the "source call-site" is reached at the root SyntaxContext.
+    /// For example, if `food!()` expands to `fruit!()` which then expands to `grape`,
+    /// then the call-site of `grape` is `fruit!()` and the call-site of `fruit!()`
+    /// is `food!()`.
     ///
-    /// This may recursively refer to other macro invocations, e.g., if
-    /// `foo!()` invoked `bar!()` internally, and there was an
-    /// expression inside `bar!`; the call_site of the expression in
-    /// the expansion would point to the `bar!` invocation; that
-    /// call_site span would have its own ExpnData, with the call_site
-    /// pointing to the `foo!` invocation.
+    /// For a desugaring expansion, this is the span of the expression or node that was
+    /// desugared.
     pub call_site: Span,
     /// Used to force two `ExpnData`s to have different `Fingerprint`s.
     /// Due to macro expansion, it's possible to end up with two `ExpnId`s

compiler/rustc_span/src/lib.rs

@@ -710,8 +710,8 @@ impl Span {
         if !ctxt.is_root() { ctxt.outer_expn_data().call_site.source_callsite() } else { self }
     }
 
-    /// The `Span` for the tokens in the previous macro expansion from which `self` was generated,
-    /// if any.
+    /// Returns the call-site span of the last macro expansion which produced this `Span`.
+    /// (see [`ExpnData::call_site`]). Returns `None` if this is not an expansion.
     pub fn parent_callsite(self) -> Option<Span> {
         let ctxt = self.ctxt();
         (!ctxt.is_root()).then(|| ctxt.outer_expn_data().call_site)

library/core/src/ffi/va_list.rs

@@ -202,18 +202,23 @@ mod sealed {
     impl<T> Sealed for *const T {}
 }
 
-/// Trait which permits the allowed types to be used with [`VaListImpl::arg`].
+/// Types that are valid to read using [`VaListImpl::arg`].
 ///
 /// # Safety
 ///
-/// This trait must only be implemented for types that C passes as varargs without implicit promotion.
+/// The standard library implements this trait for primitive types that are
+/// expected to have a variable argument application-binary interface (ABI) on all
+/// platforms.
 ///
-/// In C varargs, integers smaller than [`c_int`] and floats smaller than [`c_double`]
-/// are implicitly promoted to [`c_int`] and [`c_double`] respectively. Implementing this trait for
-/// types that are subject to this promotion rule is invalid.
+/// When C passes variable arguments, integers smaller than [`c_int`] and floats smaller
+/// than [`c_double`] are implicitly promoted to [`c_int`] and [`c_double`] respectively.
+/// Implementing this trait for types that are subject to this promotion rule is invalid.
 ///
 /// [`c_int`]: core::ffi::c_int
 /// [`c_double`]: core::ffi::c_double
+// We may unseal this trait in the future, but currently our `va_arg` implementations don't support
+// types with an alignment larger than 8, or with a non-scalar layout. Inline assembly can be used
+// to accept unsupported types in the meantime.
 pub unsafe trait VaArgSafe: sealed::Sealed {}
 
 // i8 and i16 are implicitly promoted to c_int in C, and cannot implement `VaArgSafe`.
@@ -233,7 +238,19 @@ unsafe impl<T> VaArgSafe for *mut T {}
 unsafe impl<T> VaArgSafe for *const T {}
 
 impl<'f> VaListImpl<'f> {
-    /// Advance to the next arg.
+    /// Advance to and read the next variable argument.
+    ///
+    /// # Safety
+    ///
+    /// This function is only sound to call when the next variable argument:
+    ///
+    /// - has a type that is ABI-compatible with the type `T`
+    /// - has a value that is a properly initialized value of type `T`
+    ///
+    /// Calling this function with an incompatible type, an invalid value, or when there
+    /// are no more variable arguments, is unsound.
+    ///
+    /// [valid]: https://doc.rust-lang.org/nightly/nomicon/what-unsafe-does.html
     #[inline]
     pub unsafe fn arg<T: VaArgSafe>(&mut self) -> T {
         // SAFETY: the caller must uphold the safety contract for `va_arg`.

library/std/src/keyword_docs.rs

@@ -1257,6 +1257,108 @@ mod ref_keyword {}
 /// [`async`]: ../std/keyword.async.html
 mod return_keyword {}
 
+#[doc(keyword = "become")]
+//
+/// Perform a tail-call of a function.
+///
+/// <div class="warning">
+///
+/// `feature(explicit_tail_calls)` is currently incomplete and may not work properly.
+/// </div>
+///
+/// When tail calling a function, instead of its stack frame being added to the
+/// stack, the stack frame of the caller is directly replaced with the callee's.
+/// This means that as long as a loop in a call graph only uses tail calls, the
+/// stack growth will be bounded.
+///
+/// This is useful for writing functional-style code (since it prevents recursion
+/// from exhausting resources) or for code optimization (since a tail call
+/// *might* be cheaper than a normal call, tail calls can be used in a similar
+/// manner to computed goto).
+///
+/// Example of using `become` to implement functional-style `fold`:
+/// ```
+/// #![feature(explicit_tail_calls)]
+/// #![expect(incomplete_features)]
+///
+/// fn fold<T: Copy, S>(slice: &[T], init: S, f: impl Fn(S, T) -> S) -> S {
+///     match slice {
+///         // without `become`, on big inputs this could easily overflow the
+///         // stack. using a tail call guarantees that the stack will not grow unboundedly
+///         [first, rest @ ..] => become fold(rest, f(init, *first), f),
+///         [] => init,
+///     }
+/// }
+/// ```
+///
+/// Compilers can already perform "tail call optimization" -- they can replace normal
+/// calls with tail calls, although there are no guarantees that this will be done.
+/// However, to perform TCO, the call needs to be the last thing that happens
+/// in the functions and be returned from it. This requirement is often broken
+/// by drop code for locals, which is run after computing the return expression:
+///
+/// ```
+/// fn example() {
+///     let string = "meow".to_owned();
+///     println!("{string}");
+///     return help(); // this is *not* the last thing that happens in `example`...
+/// }
+///
+/// // ... because it is desugared to this:
+/// fn example_desugared() {
+///     let string = "meow".to_owned();
+///     println!("{string}");
+///     let tmp = help();
+///     drop(string);
+///     return tmp;
+/// }
+///
+/// fn help() {}
+/// ```
+///
+/// For this reason, `become` also changes the drop order, such that locals are
+/// dropped *before* evaluating the call.
+///
+/// In order to guarantee that the compiler can perform a tail call, `become`
+/// currently has these requirements:
+/// 1. callee and caller must have the same ABI, arguments, and return type
+/// 2. callee and caller must not have varargs
+/// 3. caller must not be marked with `#[track_caller]`
+///    - callee is allowed to be marked with `#[track_caller]` as otherwise
+///      adding `#[track_caller]` would be a breaking change. if callee is
+///      marked with `#[track_caller]` a tail call is not guaranteed.
+/// 4. callee and caller cannot be a closure
+///    (unless it's coerced to a function pointer)
+///
+/// It is possible to tail-call a function pointer:
+/// ```
+/// #![feature(explicit_tail_calls)]
+/// #![expect(incomplete_features)]
+///
+/// #[derive(Copy, Clone)]
+/// enum Inst { Inc, Dec }
+///
+/// fn dispatch(stream: &[Inst], state: u32) -> u32 {
+///     const TABLE: &[fn(&[Inst], u32) -> u32] = &[increment, decrement];
+///     match stream {
+///         [inst, rest @ ..] => become TABLE[*inst as usize](rest, state),
+///         [] => state,
+///     }
+/// }
+///
+/// fn increment(stream: &[Inst], state: u32) -> u32 {
+///     become dispatch(stream, state + 1)
+/// }
+///
+/// fn decrement(stream: &[Inst], state: u32) -> u32 {
+///     become dispatch(stream, state - 1)
+/// }
+///
+/// let program = &[Inst::Inc, Inst::Inc, Inst::Dec, Inst::Inc];
+/// assert_eq!(dispatch(program, 0), 2);
+/// ```
+mod become_keyword {}
+
 #[doc(keyword = "self")]
 //
 /// The receiver of a method, or the current module.

library/std/src/lib.rs

@@ -284,7 +284,6 @@
 #![feature(core_float_math)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
-#![feature(derive_const)]
 #![feature(doc_cfg)]
 #![feature(doc_cfg_hide)]
 #![feature(doc_masked)]
@@ -332,11 +331,7 @@
 #![feature(cfg_select)]
 #![feature(char_internals)]
 #![feature(clone_to_uninit)]
-#![feature(const_cmp)]
 #![feature(const_convert)]
-#![feature(const_ops)]
-#![feature(const_option_ops)]
-#![feature(const_try)]
 #![feature(core_intrinsics)]
 #![feature(core_io_borrowed_buf)]
 #![feature(drop_guard)]

library/std/src/sync/nonpoison/condvar.rs

@@ -198,11 +198,10 @@ impl Condvar {
     /// the system time. This function is susceptible to spurious wakeups.
     /// Condition variables normally have a boolean predicate associated with
     /// them, and the predicate must always be checked each time this function
-    /// returns to protect against spurious wakeups. Additionally, it is
-    /// typically desirable for the timeout to not exceed some duration in
-    /// spite of spurious wakes, thus the sleep-duration is decremented by the
-    /// amount slept. Alternatively, use the `wait_timeout_while` method
-    /// to wait with a timeout while a predicate is true.
+    /// returns to protect against spurious wakeups.  Furthermore, since the timeout
+    /// is given relative to the moment this function is called, it needs to be adjusted
+    /// when this function is called in a loop. The [`wait_timeout_while`] method
+    /// lets you wait with a timeout while a predicate is true, taking care of all these concerns.
     ///
     /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
     /// known to have elapsed.

library/std/src/sync/poison/condvar.rs

@@ -269,11 +269,10 @@ impl Condvar {
     /// the system time. This function is susceptible to spurious wakeups.
     /// Condition variables normally have a boolean predicate associated with
     /// them, and the predicate must always be checked each time this function
-    /// returns to protect against spurious wakeups. Additionally, it is
-    /// typically desirable for the timeout to not exceed some duration in
-    /// spite of spurious wakes, thus the sleep-duration is decremented by the
-    /// amount slept. Alternatively, use the `wait_timeout_while` method
-    /// to wait with a timeout while a predicate is true.
+    /// returns to protect against spurious wakeups. Furthermore, since the timeout
+    /// is given relative to the moment this function is called, it needs to be adjusted
+    /// when this function is called in a loop. The [`wait_timeout_while`] method
+    /// lets you wait with a timeout while a predicate is true, taking care of all these concerns.
     ///
     /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
     /// known to have elapsed.

library/std/src/sys/pal/hermit/time.rs

@@ -25,15 +25,8 @@ impl Timespec {
         Timespec { t: timespec { tv_sec, tv_nsec } }
     }
 
-    #[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
-    const fn sub_timespec(&self, other: &Timespec) -> Result<Duration, Duration> {
-        // FIXME: const PartialOrd
-        let mut cmp = self.t.tv_sec - other.t.tv_sec;
-        if cmp == 0 {
-            cmp = self.t.tv_nsec as i64 - other.t.tv_nsec as i64;
-        }
-
-        if cmp >= 0 {
+    fn sub_timespec(&self, other: &Timespec) -> Result<Duration, Duration> {
+        if self >= other {
             Ok(if self.t.tv_nsec >= other.t.tv_nsec {
                 Duration::new(
                     (self.t.tv_sec - other.t.tv_sec) as u64,
@@ -53,22 +46,20 @@ impl Timespec {
         }
     }
 
-    #[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
-    const fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
+    fn checked_add_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = self.t.tv_sec.checked_add_unsigned(other.as_secs())?;
 
         // Nano calculations can't overflow because nanos are <1B which fit
         // in a u32.
-        let mut nsec = other.subsec_nanos() + self.t.tv_nsec as u32;
-        if nsec >= NSEC_PER_SEC as u32 {
-            nsec -= NSEC_PER_SEC as u32;
+        let mut nsec = other.subsec_nanos() + u32::try_from(self.t.tv_nsec).unwrap();
+        if nsec >= NSEC_PER_SEC.try_into().unwrap() {
+            nsec -= u32::try_from(NSEC_PER_SEC).unwrap();
             secs = secs.checked_add(1)?;
         }
         Some(Timespec { t: timespec { tv_sec: secs, tv_nsec: nsec as _ } })
     }
 
-    #[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
-    const fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
+    fn checked_sub_duration(&self, other: &Duration) -> Option<Timespec> {
         let mut secs = self.t.tv_sec.checked_sub_unsigned(other.as_secs())?;
 
         // Similar to above, nanos can't overflow.
@@ -222,18 +213,15 @@ impl SystemTime {
         SystemTime(time)
     }
 
-    #[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
-    pub const fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
+    pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
         self.0.sub_timespec(&other.0)
     }
 
-    #[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
-    pub const fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
         Some(SystemTime(self.0.checked_add_duration(other)?))
     }
 
-    #[rustc_const_unstable(feature = "const_system_time", issue = "144517")]
-    pub const fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
         Some(SystemTime(self.0.checked_sub_duration(other)?))
     }
 }