Auto merge of #131275 - workingjubilee:rollup-4yxqio3, r=workingjubilee

Rollup of 9 pull requests

Successful merges:

 - #129517 (Compute array length from type for unconditional panic lint. )
 - #130367 (Check elaborated projections from dyn don't mention unconstrained late bound lifetimes)
 - #130403 (Stabilize `const_slice_from_raw_parts_mut`)
 - #130633 (Add support for reborrowing pinned method receivers)
 - #131105 (update `Literal`'s intro)
 - #131194 (Fix needless_lifetimes in stable_mir)
 - #131260 (rustdoc: cleaner errors on disambiguator/namespace mismatches)
 - #131267 (Stabilize `BufRead::skip_until`)
 - #131273 (Account for `impl Trait {` when `impl Trait for Type {` was intended)

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

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -13,6 +13,7 @@ use rustc_middle::ty::{
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::error_reporting::traits::report_dyn_incompatibility;
 use rustc_trait_selection::traits::{self, hir_ty_lowering_dyn_compatibility_violations};
+use rustc_type_ir::elaborate::ClauseWithSupertraitSpan;
 use smallvec::{SmallVec, smallvec};
 use tracing::{debug, instrument};
 
@@ -124,16 +125,19 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             .into_iter()
             .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()));
 
-        for (base_trait_ref, span) in regular_traits_refs_spans {
+        for (base_trait_ref, original_span) in regular_traits_refs_spans {
             let base_pred: ty::Predicate<'tcx> = base_trait_ref.upcast(tcx);
-            for pred in traits::elaborate(tcx, [base_pred]).filter_only_self() {
+            for ClauseWithSupertraitSpan { pred, original_span, supertrait_span } in
+                traits::elaborate(tcx, [ClauseWithSupertraitSpan::new(base_pred, original_span)])
+                    .filter_only_self()
+            {
                 debug!("observing object predicate `{pred:?}`");
 
                 let bound_predicate = pred.kind();
                 match bound_predicate.skip_binder() {
                     ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
                         let pred = bound_predicate.rebind(pred);
-                        associated_types.entry(span).or_default().extend(
+                        associated_types.entry(original_span).or_default().extend(
                             tcx.associated_items(pred.def_id())
                                 .in_definition_order()
                                 .filter(|item| item.kind == ty::AssocKind::Type)
@@ -172,8 +176,14 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         // the discussion in #56288 for alternatives.
                         if !references_self {
                             // Include projections defined on supertraits.
-                            projection_bounds.push((pred, span));
+                            projection_bounds.push((pred, original_span));
                         }
+
+                        self.check_elaborated_projection_mentions_input_lifetimes(
+                            pred,
+                            original_span,
+                            supertrait_span,
+                        );
                     }
                     _ => (),
                 }
@@ -360,6 +370,56 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         Ty::new_dynamic(tcx, existential_predicates, region_bound, representation)
     }
+
+    /// Check that elaborating the principal of a trait ref doesn't lead to projections
+    /// that are unconstrained. This can happen because an otherwise unconstrained
+    /// *type variable* can be substituted with a type that has late-bound regions. See
+    /// `elaborated-predicates-unconstrained-late-bound.rs` for a test.
+    fn check_elaborated_projection_mentions_input_lifetimes(
+        &self,
+        pred: ty::PolyProjectionPredicate<'tcx>,
+        span: Span,
+        supertrait_span: Span,
+    ) {
+        let tcx = self.tcx();
+
+        // Find any late-bound regions declared in `ty` that are not
+        // declared in the trait-ref or assoc_item. These are not well-formed.
+        //
+        // Example:
+        //
+        //     for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
+        //     for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
+        let late_bound_in_projection_term =
+            tcx.collect_constrained_late_bound_regions(pred.map_bound(|pred| pred.projection_term));
+        let late_bound_in_term =
+            tcx.collect_referenced_late_bound_regions(pred.map_bound(|pred| pred.term));
+        debug!(?late_bound_in_projection_term);
+        debug!(?late_bound_in_term);
+
+        // FIXME: point at the type params that don't have appropriate lifetimes:
+        // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
+        //                         ----  ----     ^^^^^^^
+        // NOTE(associated_const_equality): This error should be impossible to trigger
+        //                                  with associated const equality constraints.
+        self.validate_late_bound_regions(
+            late_bound_in_projection_term,
+            late_bound_in_term,
+            |br_name| {
+                let item_name = tcx.item_name(pred.projection_def_id());
+                struct_span_code_err!(
+                    self.dcx(),
+                    span,
+                    E0582,
+                    "binding for associated type `{}` references {}, \
+                             which does not appear in the trait input types",
+                    item_name,
+                    br_name
+                )
+                .with_span_label(supertrait_span, "due to this supertrait")
+            },
+        );
+    }
 }
 
 fn replace_dummy_self_with_error<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(

compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs

@@ -108,17 +108,20 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let tcx = self.tcx();
         let parent_id = tcx.hir().get_parent_item(self_ty.hir_id).def_id;
         if let hir::Node::Item(hir::Item {
-            kind:
-                hir::ItemKind::Impl(hir::Impl {
-                    self_ty: impl_self_ty,
-                    of_trait: Some(of_trait_ref),
-                    generics,
-                    ..
-                }),
+            kind: hir::ItemKind::Impl(hir::Impl { self_ty: impl_self_ty, of_trait, generics, .. }),
             ..
         }) = tcx.hir_node_by_def_id(parent_id)
             && self_ty.hir_id == impl_self_ty.hir_id
         {
+            let Some(of_trait_ref) = of_trait else {
+                diag.span_suggestion_verbose(
+                    impl_self_ty.span.shrink_to_hi(),
+                    "you might have intended to implement this trait for a given type",
+                    format!(" for /* Type */"),
+                    Applicability::HasPlaceholders,
+                );
+                return;
+            };
             if !of_trait_ref.trait_def_id().is_some_and(|def_id| def_id.is_local()) {
                 return;
             }

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -235,6 +235,23 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                     target,
                 });
             }
+
+            Some(probe::AutorefOrPtrAdjustment::ReborrowPin(mutbl)) => {
+                let region = self.next_region_var(infer::Autoref(self.span));
+
+                target = match target.kind() {
+                    ty::Adt(pin, args) if self.tcx.is_lang_item(pin.did(), hir::LangItem::Pin) => {
+                        let inner_ty = match args[0].expect_ty().kind() {
+                            ty::Ref(_, ty, _) => *ty,
+                            _ => bug!("Expected a reference type for argument to Pin"),
+                        };
+                        Ty::new_pinned_ref(self.tcx, region, inner_ty, mutbl)
+                    }
+                    _ => bug!("Cannot adjust receiver type for reborrowing pin of {target:?}"),
+                };
+
+                adjustments.push(Adjustment { kind: Adjust::ReborrowPin(region, mutbl), target });
+            }
             None => {}
         }
 

compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs

@@ -121,16 +121,27 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             mutbl.ref_prefix_str()
                         }
                         Some(probe::AutorefOrPtrAdjustment::ToConstPtr) | None => "",
+                        Some(probe::AutorefOrPtrAdjustment::ReborrowPin(mutbl)) => match mutbl {
+                            hir::Mutability::Mut => "Pin<&mut ",
+                            hir::Mutability::Not => "Pin<&",
+                        },
                     };
                     if let Ok(self_expr) = self.sess().source_map().span_to_snippet(self_expr.span)
                     {
-                        let self_adjusted = if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
+                        let mut self_adjusted =
+                            if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
+                                pick.autoref_or_ptr_adjustment
+                            {
+                                format!("{derefs}{self_expr} as *const _")
+                            } else {
+                                format!("{autoref}{derefs}{self_expr}")
+                            };
+
+                        if let Some(probe::AutorefOrPtrAdjustment::ReborrowPin(_)) =
                             pick.autoref_or_ptr_adjustment
                         {
-                            format!("{derefs}{self_expr} as *const _")
-                        } else {
-                            format!("{autoref}{derefs}{self_expr}")
-                        };
+                            self_adjusted.push('>');
+                        }
 
                         lint.span_suggestion(
                             sp,
@@ -400,6 +411,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let autoref = match pick.autoref_or_ptr_adjustment {
             Some(probe::AutorefOrPtrAdjustment::Autoref { mutbl, .. }) => mutbl.ref_prefix_str(),
             Some(probe::AutorefOrPtrAdjustment::ToConstPtr) | None => "",
+            Some(probe::AutorefOrPtrAdjustment::ReborrowPin(mutbl)) => match mutbl {
+                hir::Mutability::Mut => "Pin<&mut ",
+                hir::Mutability::Not => "Pin<&",
+            },
         };
 
         let (expr_text, precise) = if let Some(expr_text) = expr
@@ -412,14 +427,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ("(..)".to_string(), false)
         };
 
-        let adjusted_text = if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
+        let mut adjusted_text = if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
             pick.autoref_or_ptr_adjustment
         {
             format!("{derefs}{expr_text} as *const _")
         } else {
             format!("{autoref}{derefs}{expr_text}")
         };
 
+        if let Some(probe::AutorefOrPtrAdjustment::ReborrowPin(_)) = pick.autoref_or_ptr_adjustment
+        {
+            adjusted_text.push('>');
+        }
+
         (adjusted_text, precise)
     }
 }

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -136,7 +136,7 @@ enum ProbeResult {
 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
 #[derive(Debug, PartialEq, Copy, Clone)]
 pub(crate) enum AutorefOrPtrAdjustment {
-    /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
+    /// Receiver has type `T`, add `&` or `&mut` (if `T` is `mut`), and maybe also "unsize" it.
     /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
     Autoref {
         mutbl: hir::Mutability,
@@ -147,13 +147,17 @@ pub(crate) enum AutorefOrPtrAdjustment {
     },
     /// Receiver has type `*mut T`, convert to `*const T`
     ToConstPtr,
+
+    /// Reborrow a `Pin<&mut T>` or `Pin<&T>`.
+    ReborrowPin(hir::Mutability),
 }
 
 impl AutorefOrPtrAdjustment {
     fn get_unsize(&self) -> bool {
         match self {
             AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
             AutorefOrPtrAdjustment::ToConstPtr => false,
+            AutorefOrPtrAdjustment::ReborrowPin(_) => false,
         }
     }
 }
@@ -1103,6 +1107,13 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                                 unstable_candidates.as_deref_mut(),
                             )
                         })
+                        .or_else(|| {
+                            self.pick_reborrow_pin_method(
+                                step,
+                                self_ty,
+                                unstable_candidates.as_deref_mut(),
+                            )
+                        })
                     })
             })
     }
@@ -1127,13 +1138,28 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             r.map(|mut pick| {
                 pick.autoderefs = step.autoderefs;
 
-                // Insert a `&*` or `&mut *` if this is a reference type:
-                if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
-                    pick.autoderefs += 1;
-                    pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
-                        mutbl,
-                        unsize: pick.autoref_or_ptr_adjustment.is_some_and(|a| a.get_unsize()),
-                    })
+                match *step.self_ty.value.value.kind() {
+                    // Insert a `&*` or `&mut *` if this is a reference type:
+                    ty::Ref(_, _, mutbl) => {
+                        pick.autoderefs += 1;
+                        pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
+                            mutbl,
+                            unsize: pick.autoref_or_ptr_adjustment.is_some_and(|a| a.get_unsize()),
+                        })
+                    }
+
+                    ty::Adt(def, args)
+                        if self.tcx.features().pin_ergonomics
+                            && self.tcx.is_lang_item(def.did(), hir::LangItem::Pin) =>
+                    {
+                        // make sure this is a pinned reference (and not a `Pin<Box>` or something)
+                        if let ty::Ref(_, _, mutbl) = args[0].expect_ty().kind() {
+                            pick.autoref_or_ptr_adjustment =
+                                Some(AutorefOrPtrAdjustment::ReborrowPin(*mutbl));
+                        }
+                    }
+
+                    _ => (),
                 }
 
                 pick
@@ -1164,6 +1190,43 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         })
     }
 
+    /// Looks for applicable methods if we reborrow a `Pin<&mut T>` as a `Pin<&T>`.
+    #[instrument(level = "debug", skip(self, step, unstable_candidates))]
+    fn pick_reborrow_pin_method(
+        &self,
+        step: &CandidateStep<'tcx>,
+        self_ty: Ty<'tcx>,
+        unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
+    ) -> Option<PickResult<'tcx>> {
+        if !self.tcx.features().pin_ergonomics {
+            return None;
+        }
+
+        // make sure self is a Pin<&mut T>
+        let inner_ty = match self_ty.kind() {
+            ty::Adt(def, args) if self.tcx.is_lang_item(def.did(), hir::LangItem::Pin) => {
+                match args[0].expect_ty().kind() {
+                    ty::Ref(_, ty, hir::Mutability::Mut) => *ty,
+                    _ => {
+                        return None;
+                    }
+                }
+            }
+            _ => return None,
+        };
+
+        let region = self.tcx.lifetimes.re_erased;
+        let autopin_ty = Ty::new_pinned_ref(self.tcx, region, inner_ty, hir::Mutability::Not);
+        self.pick_method(autopin_ty, unstable_candidates).map(|r| {
+            r.map(|mut pick| {
+                pick.autoderefs = step.autoderefs;
+                pick.autoref_or_ptr_adjustment =
+                    Some(AutorefOrPtrAdjustment::ReborrowPin(hir::Mutability::Not));
+                pick
+            })
+        })
+    }
+
     /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
     /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
     /// autorefs would require dereferencing the pointer, which is not safe.

compiler/rustc_middle/src/ty/predicate.rs

@@ -179,6 +179,10 @@ pub struct Clause<'tcx>(
 );
 
 impl<'tcx> rustc_type_ir::inherent::Clause<TyCtxt<'tcx>> for Clause<'tcx> {
+    fn as_predicate(self) -> Predicate<'tcx> {
+        self.as_predicate()
+    }
+
     fn instantiate_supertrait(self, tcx: TyCtxt<'tcx>, trait_ref: ty::PolyTraitRef<'tcx>) -> Self {
         self.instantiate_supertrait(tcx, trait_ref)
     }

compiler/rustc_middle/src/ty/sty.rs

@@ -584,6 +584,16 @@ impl<'tcx> Ty<'tcx> {
         Ty::new_ref(tcx, r, ty, hir::Mutability::Not)
     }
 
+    pub fn new_pinned_ref(
+        tcx: TyCtxt<'tcx>,
+        r: Region<'tcx>,
+        ty: Ty<'tcx>,
+        mutbl: ty::Mutability,
+    ) -> Ty<'tcx> {
+        let pin = tcx.adt_def(tcx.require_lang_item(LangItem::Pin, None));
+        Ty::new_adt(tcx, pin, tcx.mk_args(&[Ty::new_ref(tcx, r, ty, mutbl).into()]))
+    }
+
     #[inline]
     pub fn new_ptr(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, mutbl: ty::Mutability) -> Ty<'tcx> {
         Ty::new(tcx, ty::RawPtr(ty, mutbl))

compiler/rustc_mir_transform/src/known_panics_lint.rs

@@ -600,13 +600,15 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             }
 
             Len(place) => {
-                let len = match self.get_const(place)? {
-                    Value::Immediate(src) => src.len(&self.ecx).discard_err()?,
-                    Value::Aggregate { fields, .. } => fields.len() as u64,
-                    Value::Uninit => match place.ty(self.local_decls(), self.tcx).ty.kind() {
-                        ty::Array(_, n) => n.try_eval_target_usize(self.tcx, self.param_env)?,
-                        _ => return None,
-                    },
+                let len = if let ty::Array(_, n) = place.ty(self.local_decls(), self.tcx).ty.kind()
+                {
+                    n.try_eval_target_usize(self.tcx, self.param_env)?
+                } else {
+                    match self.get_const(place)? {
+                        Value::Immediate(src) => src.len(&self.ecx).discard_err()?,
+                        Value::Aggregate { fields, .. } => fields.len() as u64,
+                        Value::Uninit => return None,
+                    }
                 };
                 ImmTy::from_scalar(Scalar::from_target_usize(len, self), layout).into()
             }