Rollup merge of rust-lang#89413 - matthewjasper:spec-marker-fix, r=nikomatsakis

Correctly handle supertraits for min_specialization

Supertraits of specialization markers could circumvent checks for
min_specialization. Elaborating predicates prevents this.

r? ````@nikomatsakis````

Author: workingjubilee

alloc/src/vec/into_iter.rs

@@ -266,14 +266,21 @@ unsafe impl<T, A: Allocator> TrustedLen for IntoIter<T, A> {}
 
 #[doc(hidden)]
 #[unstable(issue = "none", feature = "std_internals")]
+#[rustc_unsafe_specialization_marker]
+pub trait NonDrop {}
+
 // T: Copy as approximation for !Drop since get_unchecked does not advance self.ptr
 // and thus we can't implement drop-handling
-//
+#[unstable(issue = "none", feature = "std_internals")]
+impl<T: Copy> NonDrop for T {}
+
+#[doc(hidden)]
+#[unstable(issue = "none", feature = "std_internals")]
 // TrustedRandomAccess (without NoCoerce) must not be implemented because
-// subtypes/supertypes of `T` might not be `Copy`
+// subtypes/supertypes of `T` might not be `NonDrop`
 unsafe impl<T, A: Allocator> TrustedRandomAccessNoCoerce for IntoIter<T, A>
 where
-    T: Copy,
+    T: NonDrop,
 {
     const MAY_HAVE_SIDE_EFFECT: bool = false;
 }

alloc/src/vec/source_iter_marker.rs

@@ -6,24 +6,14 @@ use super::{AsIntoIter, InPlaceDrop, SpecFromIter, SpecFromIterNested, Vec};
 
 /// Specialization marker for collecting an iterator pipeline into a Vec while reusing the
 /// source allocation, i.e. executing the pipeline in place.
-///
-/// The SourceIter parent trait is necessary for the specializing function to access the allocation
-/// which is to be reused. But it is not sufficient for the specialization to be valid. See
-/// additional bounds on the impl.
 #[rustc_unsafe_specialization_marker]
-pub(super) trait SourceIterMarker: SourceIter<Source: AsIntoIter> {}
+pub(super) trait InPlaceIterableMarker {}
 
-// The std-internal SourceIter/InPlaceIterable traits are only implemented by chains of
-// Adapter<Adapter<Adapter<IntoIter>>> (all owned by core/std). Additional bounds
-// on the adapter implementations (beyond `impl<I: Trait> Trait for Adapter<I>`) only depend on other
-// traits already marked as specialization traits (Copy, TrustedRandomAccess, FusedIterator).
-// I.e. the marker does not depend on lifetimes of user-supplied types. Modulo the Copy hole, which
-// several other specializations already depend on.
-impl<T> SourceIterMarker for T where T: SourceIter<Source: AsIntoIter> + InPlaceIterable {}
+impl<T> InPlaceIterableMarker for T where T: InPlaceIterable {}
 
 impl<T, I> SpecFromIter<T, I> for Vec<T>
 where
-    I: Iterator<Item = T> + SourceIterMarker,
+    I: Iterator<Item = T> + SourceIter<Source: AsIntoIter> + InPlaceIterableMarker,
 {
     default fn from_iter(mut iterator: I) -> Self {
         // Additional requirements which cannot expressed via trait bounds. We rely on const eval

core/src/iter/adapters/enumerate.rs

@@ -249,14 +249,14 @@ impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}
 unsafe impl<I> TrustedLen for Enumerate<I> where I: TrustedLen {}
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, I: Iterator> SourceIter for Enumerate<I>
+unsafe impl<I> SourceIter for Enumerate<I>
 where
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }

core/src/iter/adapters/filter.rs

@@ -135,15 +135,14 @@ where
 impl<I: FusedIterator, P> FusedIterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {}
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, P, I: Iterator> SourceIter for Filter<I, P>
+unsafe impl<P, I> SourceIter for Filter<I, P>
 where
-    P: FnMut(&I::Item) -> bool,
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }

core/src/iter/adapters/filter_map.rs

@@ -129,15 +129,14 @@ where
 impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F> where F: FnMut(I::Item) -> Option<B> {}
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, B, I: Iterator, F> SourceIter for FilterMap<I, F>
+unsafe impl<I, F> SourceIter for FilterMap<I, F>
 where
-    F: FnMut(I::Item) -> Option<B>,
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }

core/src/iter/adapters/inspect.rs

@@ -149,15 +149,14 @@ where
 impl<I: FusedIterator, F> FusedIterator for Inspect<I, F> where F: FnMut(&I::Item) {}
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, I: Iterator, F> SourceIter for Inspect<I, F>
+unsafe impl<I, F> SourceIter for Inspect<I, F>
 where
-    F: FnMut(&I::Item),
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }

core/src/iter/adapters/map.rs

@@ -201,15 +201,14 @@ where
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, B, I: Iterator, F> SourceIter for Map<I, F>
+unsafe impl<I, F> SourceIter for Map<I, F>
 where
-    F: FnMut(I::Item) -> B,
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }

core/src/iter/adapters/map_while.rs

@@ -80,15 +80,14 @@ where
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, B, I: Iterator, P> SourceIter for MapWhile<I, P>
+unsafe impl<I, P> SourceIter for MapWhile<I, P>
 where
-    P: FnMut(I::Item) -> Option<B>,
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }

core/src/iter/adapters/mod.rs

@@ -92,9 +92,10 @@ pub use self::zip::zip;
 /// [`as_inner`]: SourceIter::as_inner
 #[unstable(issue = "none", feature = "inplace_iteration")]
 #[doc(hidden)]
+#[rustc_specialization_trait]
 pub unsafe trait SourceIter {
     /// A source stage in an iterator pipeline.
-    type Source: Iterator;
+    type Source;
 
     /// Retrieve the source of an iterator pipeline.
     ///
@@ -200,14 +201,14 @@ where
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, I, E> SourceIter for ResultShunt<'_, I, E>
+unsafe impl<I, E> SourceIter for ResultShunt<'_, I, E>
 where
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut Self::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }

core/src/iter/adapters/peekable.rs

@@ -321,14 +321,14 @@ impl<I: Iterator> Peekable<I> {
 unsafe impl<I> TrustedLen for Peekable<I> where I: TrustedLen {}
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, I: Iterator> SourceIter for Peekable<I>
+unsafe impl<I: Iterator> SourceIter for Peekable<I>
 where
-    I: SourceIter<Source = S>,
+    I: SourceIter,
 {
-    type Source = S;
+    type Source = I::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }