Rollup of 8 pull requests

compiler/rustc_feature/src/removed.rs

@@ -135,6 +135,8 @@ declare_features! (
      Some("removed as it caused some confusion and discussion was inactive for years")),
     /// Lazily evaluate constants. This allows constants to depend on type parameters.
     (removed, lazy_normalization_consts, "1.46.0", Some(72219), Some("superseded by `generic_const_exprs`")),
+    /// Changes `impl Trait` to capture all lifetimes in scope.
+    (removed, lifetime_capture_rules_2024, "1.76.0", None, Some("unnecessary -- use edition 2024 instead")),
     /// Allows using the `#[link_args]` attribute.
     (removed, link_args, "1.53.0", Some(29596),
      Some("removed in favor of using `-C link-arg=ARG` on command line, \

compiler/rustc_feature/src/unstable.rs

@@ -214,8 +214,6 @@ declare_features! (
     (internal, intrinsics, "1.0.0", None),
     /// Allows using `#[lang = ".."]` attribute for linking items to special compiler logic.
     (internal, lang_items, "1.0.0", None),
-    /// Changes `impl Trait` to capture all lifetimes in scope.
-    (unstable, lifetime_capture_rules_2024, "1.76.0", None),
     /// Allows `#[link(..., cfg(..))]`; perma-unstable per #37406
     (internal, link_cfg, "1.14.0", None),
     /// Allows using `?Trait` trait bounds in more contexts.

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -305,21 +305,15 @@ fn generic_param_def_as_bound_arg(param: &ty::GenericParamDef) -> ty::BoundVaria
 }
 
 /// Whether this opaque always captures lifetimes in scope.
-/// Right now, this is all RPITIT and TAITs, and when `lifetime_capture_rules_2024`
-/// is enabled. We don't check the span of the edition, since this is done
-/// on a per-opaque basis to account for nested opaques.
-fn opaque_captures_all_in_scope_lifetimes<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    opaque: &'tcx hir::OpaqueTy<'tcx>,
-) -> bool {
+/// Right now, this is all RPITIT and TAITs, and when the opaque
+/// is coming from a span corresponding to edition 2024.
+fn opaque_captures_all_in_scope_lifetimes<'tcx>(opaque: &'tcx hir::OpaqueTy<'tcx>) -> bool {
     match opaque.origin {
         // if the opaque has the `use<...>` syntax, the user is telling us that they only want
         // to account for those lifetimes, so do not try to be clever.
         _ if opaque.bounds.iter().any(|bound| matches!(bound, hir::GenericBound::Use(..))) => false,
         hir::OpaqueTyOrigin::AsyncFn { .. } | hir::OpaqueTyOrigin::TyAlias { .. } => true,
-        _ if tcx.features().lifetime_capture_rules_2024() || opaque.span.at_least_rust_2024() => {
-            true
-        }
+        _ if opaque.span.at_least_rust_2024() => true,
         hir::OpaqueTyOrigin::FnReturn { in_trait_or_impl, .. } => in_trait_or_impl.is_some(),
     }
 }
@@ -519,8 +513,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
     fn visit_opaque_ty(&mut self, opaque: &'tcx rustc_hir::OpaqueTy<'tcx>) {
         let captures = RefCell::new(FxIndexMap::default());
 
-        let capture_all_in_scope_lifetimes =
-            opaque_captures_all_in_scope_lifetimes(self.tcx, opaque);
+        let capture_all_in_scope_lifetimes = opaque_captures_all_in_scope_lifetimes(opaque);
         if capture_all_in_scope_lifetimes {
             let lifetime_ident = |def_id: LocalDefId| {
                 let name = self.tcx.item_name(def_id.to_def_id());
@@ -2276,7 +2269,7 @@ fn is_late_bound_map(
     }
 
     let mut appears_in_output =
-        AllCollector { tcx, has_fully_capturing_opaque: false, regions: Default::default() };
+        AllCollector { has_fully_capturing_opaque: false, regions: Default::default() };
     intravisit::walk_fn_ret_ty(&mut appears_in_output, &sig.decl.output);
     if appears_in_output.has_fully_capturing_opaque {
         appears_in_output.regions.extend(generics.params.iter().map(|param| param.def_id));
@@ -2289,7 +2282,7 @@ fn is_late_bound_map(
     // Subtle point: because we disallow nested bindings, we can just
     // ignore binders here and scrape up all names we see.
     let mut appears_in_where_clause =
-        AllCollector { tcx, has_fully_capturing_opaque: true, regions: Default::default() };
+        AllCollector { has_fully_capturing_opaque: true, regions: Default::default() };
     appears_in_where_clause.visit_generics(generics);
     debug!(?appears_in_where_clause.regions);
 
@@ -2455,23 +2448,21 @@ fn is_late_bound_map(
         }
     }
 
-    struct AllCollector<'tcx> {
-        tcx: TyCtxt<'tcx>,
+    struct AllCollector {
         has_fully_capturing_opaque: bool,
         regions: FxHashSet<LocalDefId>,
     }
 
-    impl<'v> Visitor<'v> for AllCollector<'v> {
-        fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
+    impl<'tcx> Visitor<'tcx> for AllCollector {
+        fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
             if let hir::LifetimeName::Param(def_id) = lifetime_ref.res {
                 self.regions.insert(def_id);
             }
         }
 
-        fn visit_opaque_ty(&mut self, opaque: &'v hir::OpaqueTy<'v>) {
+        fn visit_opaque_ty(&mut self, opaque: &'tcx hir::OpaqueTy<'tcx>) {
             if !self.has_fully_capturing_opaque {
-                self.has_fully_capturing_opaque =
-                    opaque_captures_all_in_scope_lifetimes(self.tcx, opaque);
+                self.has_fully_capturing_opaque = opaque_captures_all_in_scope_lifetimes(opaque);
             }
             intravisit::walk_opaque_ty(self, opaque);
         }

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -1,4 +1,4 @@
-use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
+use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::struct_span_code_err;
 use rustc_hir as hir;
@@ -58,9 +58,9 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             }
         }
 
-        let (trait_bounds, mut projection_bounds) =
+        let (elaborated_trait_bounds, elaborated_projection_bounds) =
             traits::expand_trait_aliases(tcx, user_written_bounds.iter().copied());
-        let (regular_traits, mut auto_traits): (Vec<_>, Vec<_>) = trait_bounds
+        let (regular_traits, mut auto_traits): (Vec<_>, Vec<_>) = elaborated_trait_bounds
             .into_iter()
             .partition(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()));
 
@@ -103,37 +103,89 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             }
         }
 
+        // Map the projection bounds onto a key that makes it easy to remove redundant
+        // bounds that are constrained by supertraits of the principal def id.
+        //
+        // Also make sure we detect conflicting bounds from expanding a trait alias and
+        // also specifying it manually, like:
+        // ```
+        // type Alias = Trait<Assoc = i32>;
+        // let _: &dyn Alias<Assoc = u32> = /* ... */;
+        // ```
+        let mut projection_bounds = FxIndexMap::default();
+        for (proj, proj_span) in elaborated_projection_bounds {
+            let key = (
+                proj.skip_binder().projection_term.def_id,
+                tcx.anonymize_bound_vars(
+                    proj.map_bound(|proj| proj.projection_term.trait_ref(tcx)),
+                ),
+            );
+            if let Some((old_proj, old_proj_span)) =
+                projection_bounds.insert(key, (proj, proj_span))
+                && tcx.anonymize_bound_vars(proj) != tcx.anonymize_bound_vars(old_proj)
+            {
+                let item = tcx.item_name(proj.item_def_id());
+                self.dcx()
+                    .struct_span_err(
+                        span,
+                        format!(
+                            "conflicting associated type bounds for `{item}` when \
+                            expanding trait alias"
+                        ),
+                    )
+                    .with_span_label(
+                        old_proj_span,
+                        format!("`{item}` is specified to be `{}` here", old_proj.term()),
+                    )
+                    .with_span_label(
+                        proj_span,
+                        format!("`{item}` is specified to be `{}` here", proj.term()),
+                    )
+                    .emit();
+            }
+        }
+
         let principal_trait = regular_traits.into_iter().next();
 
-        let mut needed_associated_types = FxIndexSet::default();
-        if let Some((principal_trait, spans)) = &principal_trait {
-            let pred: ty::Predicate<'tcx> = (*principal_trait).upcast(tcx);
-            for ClauseWithSupertraitSpan { pred, supertrait_span } in traits::elaborate(
+        let mut needed_associated_types = vec![];
+        if let Some((principal_trait, ref spans)) = principal_trait {
+            let principal_trait = principal_trait.map_bound(|trait_pred| {
+                assert_eq!(trait_pred.polarity, ty::PredicatePolarity::Positive);
+                trait_pred.trait_ref
+            });
+
+            for ClauseWithSupertraitSpan { clause, supertrait_span } in traits::elaborate(
                 tcx,
-                [ClauseWithSupertraitSpan::new(pred, *spans.last().unwrap())],
+                [ClauseWithSupertraitSpan::new(
+                    ty::TraitRef::identity(tcx, principal_trait.def_id()).upcast(tcx),
+                    *spans.last().unwrap(),
+                )],
             )
             .filter_only_self()
             {
-                debug!("observing object predicate `{pred:?}`");
+                let clause = clause.instantiate_supertrait(tcx, principal_trait);
+                debug!("observing object predicate `{clause:?}`");
 
-                let bound_predicate = pred.kind();
+                let bound_predicate = clause.kind();
                 match bound_predicate.skip_binder() {
-                    ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
+                    ty::ClauseKind::Trait(pred) => {
                         // FIXME(negative_bounds): Handle this correctly...
                         let trait_ref =
                             tcx.anonymize_bound_vars(bound_predicate.rebind(pred.trait_ref));
                         needed_associated_types.extend(
-                            tcx.associated_items(trait_ref.def_id())
+                            tcx.associated_items(pred.trait_ref.def_id)
                                 .in_definition_order()
+                                // We only care about associated types.
                                 .filter(|item| item.kind == ty::AssocKind::Type)
+                                // No RPITITs -- even with `async_fn_in_dyn_trait`, they are implicit.
                                 .filter(|item| !item.is_impl_trait_in_trait())
                                 // If the associated type has a `where Self: Sized` bound,
                                 // we do not need to constrain the associated type.
                                 .filter(|item| !tcx.generics_require_sized_self(item.def_id))
                                 .map(|item| (item.def_id, trait_ref)),
                         );
                     }
-                    ty::PredicateKind::Clause(ty::ClauseKind::Projection(pred)) => {
+                    ty::ClauseKind::Projection(pred) => {
                         let pred = bound_predicate.rebind(pred);
                         // A `Self` within the original bound will be instantiated with a
                         // `trait_object_dummy_self`, so check for that.
@@ -161,8 +213,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
                         // the discussion in #56288 for alternatives.
                         if !references_self {
-                            // Include projections defined on supertraits.
-                            projection_bounds.push((pred, supertrait_span));
+                            let key = (
+                                pred.skip_binder().projection_term.def_id,
+                                tcx.anonymize_bound_vars(
+                                    pred.map_bound(|proj| proj.projection_term.trait_ref(tcx)),
+                                ),
+                            );
+                            if !projection_bounds.contains_key(&key) {
+                                projection_bounds.insert(key, (pred, supertrait_span));
+                            }
                         }
 
                         self.check_elaborated_projection_mentions_input_lifetimes(
@@ -182,12 +241,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // types that we expect to be provided by the user, so the following loop
         // removes all the associated types that have a corresponding `Projection`
         // clause, either from expanding trait aliases or written by the user.
-        for &(projection_bound, span) in &projection_bounds {
+        for &(projection_bound, span) in projection_bounds.values() {
             let def_id = projection_bound.item_def_id();
-            let trait_ref = tcx.anonymize_bound_vars(
-                projection_bound.map_bound(|p| p.projection_term.trait_ref(tcx)),
-            );
-            needed_associated_types.swap_remove(&(def_id, trait_ref));
             if tcx.generics_require_sized_self(def_id) {
                 tcx.emit_node_span_lint(
                     UNUSED_ASSOCIATED_TYPE_BOUNDS,
@@ -198,9 +253,22 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             }
         }
 
+        let mut missing_assoc_types = FxIndexSet::default();
+        let projection_bounds: Vec<_> = needed_associated_types
+            .into_iter()
+            .filter_map(|key| {
+                if let Some(assoc) = projection_bounds.get(&key) {
+                    Some(*assoc)
+                } else {
+                    missing_assoc_types.insert(key);
+                    None
+                }
+            })
+            .collect();
+
         if let Err(guar) = self.check_for_required_assoc_tys(
             principal_trait.as_ref().map_or(smallvec![], |(_, spans)| spans.clone()),
-            needed_associated_types,
+            missing_assoc_types,
             potential_assoc_types,
             hir_bounds,
         ) {
@@ -266,7 +334,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             })
         });
 
-        let existential_projections = projection_bounds.iter().map(|(bound, _)| {
+        let existential_projections = projection_bounds.into_iter().map(|(bound, _)| {
             bound.map_bound(|mut b| {
                 assert_eq!(b.projection_term.self_ty(), dummy_self);
 
@@ -291,12 +359,16 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             })
         });
 
-        let auto_trait_predicates = auto_traits.into_iter().map(|(trait_pred, _)| {
-            assert_eq!(trait_pred.polarity(), ty::PredicatePolarity::Positive);
-            assert_eq!(trait_pred.self_ty().skip_binder(), dummy_self);
+        let mut auto_trait_predicates: Vec<_> = auto_traits
+            .into_iter()
+            .map(|(trait_pred, _)| {
+                assert_eq!(trait_pred.polarity(), ty::PredicatePolarity::Positive);
+                assert_eq!(trait_pred.self_ty().skip_binder(), dummy_self);
 
-            ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_pred.def_id()))
-        });
+                ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_pred.def_id()))
+            })
+            .collect();
+        auto_trait_predicates.dedup();
 
         // N.b. principal, projections, auto traits
         // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
@@ -306,7 +378,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             .chain(auto_trait_predicates)
             .collect::<SmallVec<[_; 8]>>();
         v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
-        v.dedup();
         let existential_predicates = tcx.mk_poly_existential_predicates(&v);
 
         // Use explicitly-specified region bound, unless the bound is missing.

compiler/rustc_lint/src/impl_trait_overcaptures.rs

@@ -86,8 +86,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
-    /// # #![feature(lifetime_capture_rules_2024)]
+    /// ```rust,edition2024,compile_fail
     /// # #![deny(impl_trait_redundant_captures)]
     /// fn test<'a>(x: &'a i32) -> impl Sized + use<'a> { x }
     /// ```
@@ -268,8 +267,7 @@ where
             && parent == self.parent_def_id
         {
             let opaque_span = self.tcx.def_span(opaque_def_id);
-            let new_capture_rules = opaque_span.at_least_rust_2024()
-                || self.tcx.features().lifetime_capture_rules_2024();
+            let new_capture_rules = opaque_span.at_least_rust_2024();
             if !new_capture_rules
                 && !opaque.bounds.iter().any(|bound| matches!(bound, hir::GenericBound::Use(..)))
             {

compiler/rustc_middle/src/mir/visit.rs

@@ -1364,13 +1364,13 @@ impl PlaceContext {
         matches!(self, PlaceContext::MutatingUse(MutatingUseContext::Drop))
     }
 
-    /// Returns `true` if this place context represents a borrow.
+    /// Returns `true` if this place context represents a borrow, excluding fake borrows
+    /// (which are an artifact of borrowck and not actually borrows in runtime MIR).
     pub fn is_borrow(self) -> bool {
         matches!(
             self,
-            PlaceContext::NonMutatingUse(
-                NonMutatingUseContext::SharedBorrow | NonMutatingUseContext::FakeBorrow
-            ) | PlaceContext::MutatingUse(MutatingUseContext::Borrow)
+            PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
+                | PlaceContext::MutatingUse(MutatingUseContext::Borrow)
         )
     }
 

compiler/rustc_middle/src/traits/mod.rs

@@ -12,7 +12,7 @@ use std::borrow::Cow;
 use std::hash::{Hash, Hasher};
 use std::sync::Arc;
 
-use rustc_errors::{Applicability, Diag, EmissionGuarantee};
+use rustc_errors::{Applicability, Diag, EmissionGuarantee, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::HirId;
 use rustc_hir::def_id::DefId;
@@ -996,4 +996,7 @@ pub enum CodegenObligationError {
     /// but was included during typeck due to the trivial_bounds feature.
     Unimplemented,
     FulfillmentError,
+    /// The selected impl has unconstrained generic parameters. This will emit an error
+    /// during impl WF checking.
+    UnconstrainedParam(ErrorGuaranteed),
 }