Rollup merge of #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````

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -64,7 +64,9 @@ pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
 pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
 pub use self::structural_match::search_for_structural_match_violation;
 pub use self::structural_match::NonStructuralMatchTy;
-pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
+pub use self::util::{
+    elaborate_obligations, elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs,
+};
 pub use self::util::{expand_trait_aliases, TraitAliasExpander};
 pub use self::util::{
     get_vtable_index_of_object_method, impl_item_is_final, predicate_for_trait_def, upcast_choices,

compiler/rustc_typeck/src/impl_wf_check/min_specialization.rs

@@ -74,7 +74,7 @@ use rustc_infer::infer::{InferCtxt, RegionckMode, TyCtxtInferExt};
 use rustc_infer::traits::specialization_graph::Node;
 use rustc_middle::ty::subst::{GenericArg, InternalSubsts, SubstsRef};
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
-use rustc_middle::ty::{self, InstantiatedPredicates, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
 use rustc_span::Span;
 use rustc_trait_selection::traits::{self, translate_substs, wf};
 
@@ -294,13 +294,27 @@ fn check_predicates<'tcx>(
     span: Span,
 ) {
     let tcx = infcx.tcx;
-    let impl1_predicates = tcx.predicates_of(impl1_def_id).instantiate(tcx, impl1_substs);
+    let impl1_predicates: Vec<_> = traits::elaborate_predicates(
+        tcx,
+        tcx.predicates_of(impl1_def_id).instantiate(tcx, impl1_substs).predicates.into_iter(),
+    )
+    .map(|obligation| obligation.predicate)
+    .collect();
+
     let mut impl2_predicates = if impl2_node.is_from_trait() {
         // Always applicable traits have to be always applicable without any
         // assumptions.
-        InstantiatedPredicates::empty()
+        Vec::new()
     } else {
-        tcx.predicates_of(impl2_node.def_id()).instantiate(tcx, impl2_substs)
+        traits::elaborate_predicates(
+            tcx,
+            tcx.predicates_of(impl2_node.def_id())
+                .instantiate(tcx, impl2_substs)
+                .predicates
+                .into_iter(),
+        )
+        .map(|obligation| obligation.predicate)
+        .collect()
     };
     debug!(
         "check_always_applicable(\nimpl1_predicates={:?},\nimpl2_predicates={:?}\n)",
@@ -322,13 +336,12 @@ fn check_predicates<'tcx>(
     // which is sound because we forbid impls like the following
     //
     // impl<D: Debug> AlwaysApplicable for D { }
-    let always_applicable_traits =
-        impl1_predicates.predicates.iter().copied().filter(|&predicate| {
-            matches!(
-                trait_predicate_kind(tcx, predicate),
-                Some(TraitSpecializationKind::AlwaysApplicable)
-            )
-        });
+    let always_applicable_traits = impl1_predicates.iter().copied().filter(|&predicate| {
+        matches!(
+            trait_predicate_kind(tcx, predicate),
+            Some(TraitSpecializationKind::AlwaysApplicable)
+        )
+    });
 
     // Include the well-formed predicates of the type parameters of the impl.
     for arg in tcx.impl_trait_ref(impl1_def_id).unwrap().substs {
@@ -340,18 +353,19 @@ fn check_predicates<'tcx>(
             arg,
             span,
         ) {
-            impl2_predicates
-                .predicates
-                .extend(obligations.into_iter().map(|obligation| obligation.predicate))
+            impl2_predicates.extend(
+                traits::elaborate_obligations(tcx, obligations)
+                    .map(|obligation| obligation.predicate),
+            )
         }
     }
-    impl2_predicates.predicates.extend(
+    impl2_predicates.extend(
         traits::elaborate_predicates(tcx, always_applicable_traits)
             .map(|obligation| obligation.predicate),
     );
 
-    for predicate in impl1_predicates.predicates {
-        if !impl2_predicates.predicates.contains(&predicate) {
+    for predicate in impl1_predicates {
+        if !impl2_predicates.contains(&predicate) {
             check_specialization_on(tcx, predicate, span)
         }
     }

library/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;
 }

library/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

library/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) }
     }

library/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) }
     }

library/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) }
     }

library/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) }
     }

library/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) }
     }

library/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) }
     }

library/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) }
     }

library/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) }
     }

library/core/src/iter/adapters/scan.rs

@@ -90,15 +90,14 @@ where
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<St, F, B, S: Iterator, I: Iterator> SourceIter for Scan<I, St, F>
+unsafe impl<St, F, I> SourceIter for Scan<I, St, F>
 where
-    I: SourceIter<Source = S>,
-    F: FnMut(&mut St, I::Item) -> Option<B>,
+    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) }
     }

library/core/src/iter/adapters/skip.rs

@@ -222,14 +222,14 @@ where
 impl<I> FusedIterator for Skip<I> where I: FusedIterator {}
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, I: Iterator> SourceIter for Skip<I>
+unsafe impl<I> SourceIter for Skip<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) }
     }

library/core/src/iter/adapters/skip_while.rs

@@ -105,15 +105,14 @@ where
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, P, I: Iterator> SourceIter for SkipWhile<I, P>
+unsafe impl<P, I> SourceIter for SkipWhile<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) }
     }

library/core/src/iter/adapters/take.rs

@@ -130,14 +130,14 @@ where
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, I: Iterator> SourceIter for Take<I>
+unsafe impl<I> SourceIter for Take<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) }
     }

library/core/src/iter/adapters/take_while.rs

@@ -118,15 +118,14 @@ where
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S: Iterator, P, I: Iterator> SourceIter for TakeWhile<I, P>
+unsafe impl<P, I> SourceIter for TakeWhile<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) }
     }

library/core/src/iter/adapters/zip.rs

@@ -414,16 +414,14 @@ where
 // Arbitrarily selects the left side of the zip iteration as extractable "source"
 // it would require negative trait bounds to be able to try both
 #[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<S, A, B> SourceIter for Zip<A, B>
+unsafe impl<A, B> SourceIter for Zip<A, B>
 where
-    A: SourceIter<Source = S>,
-    B: Iterator,
-    S: Iterator,
+    A: SourceIter,
 {
-    type Source = S;
+    type Source = A::Source;
 
     #[inline]
-    unsafe fn as_inner(&mut self) -> &mut S {
+    unsafe fn as_inner(&mut self) -> &mut A::Source {
         // SAFETY: unsafe function forwarding to unsafe function with the same requirements
         unsafe { SourceIter::as_inner(&mut self.a) }
     }

src/test/ui/specialization/min_specialization/spec-marker-supertraits.rs

@@ -0,0 +1,29 @@
+// Check that supertraits cannot be used to work around min_specialization
+// limitations.
+
+#![feature(min_specialization)]
+#![feature(rustc_attrs)]
+
+trait HasMethod {
+    fn method(&self);
+}
+
+#[rustc_unsafe_specialization_marker]
+trait Marker: HasMethod {}
+
+trait Spec {
+    fn spec_me(&self);
+}
+
+impl<T> Spec for T {
+    default fn spec_me(&self) {}
+}
+
+impl<T: Marker> Spec for T {
+    //~^ ERROR cannot specialize on trait `HasMethod`
+    fn spec_me(&self) {
+        self.method();
+    }
+}
+
+fn main() {}

src/test/ui/specialization/min_specialization/spec-marker-supertraits.stderr

@@ -0,0 +1,13 @@
+error: cannot specialize on trait `HasMethod`
+  --> $DIR/spec-marker-supertraits.rs:22:1
+   |
+LL | / impl<T: Marker> Spec for T {
+LL | |
+LL | |     fn spec_me(&self) {
+LL | |         self.method();
+LL | |     }
+LL | | }
+   | |_^
+
+error: aborting due to previous error
+