Rollup of 8 pull requests

compiler/rustc_hir_typeck/src/pat.rs

@@ -690,16 +690,29 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                     BindingMode(def_br, Mutability::Mut)
                 } else {
-                    // `mut` resets binding mode on edition <= 2021
-                    self.typeck_results
+                    // `mut` resets the binding mode on edition <= 2021
+                    *self
+                        .typeck_results
                         .borrow_mut()
                         .rust_2024_migration_desugared_pats_mut()
-                        .insert(pat_info.top_info.hir_id);
+                        .entry(pat_info.top_info.hir_id)
+                        .or_default() |= pat.span.at_least_rust_2024();
                     BindingMode(ByRef::No, Mutability::Mut)
                 }
             }
             BindingMode(ByRef::No, mutbl) => BindingMode(def_br, mutbl),
-            BindingMode(ByRef::Yes(_), _) => user_bind_annot,
+            BindingMode(ByRef::Yes(_), _) => {
+                if matches!(def_br, ByRef::Yes(_)) {
+                    // `ref`/`ref mut` overrides the binding mode on edition <= 2021
+                    *self
+                        .typeck_results
+                        .borrow_mut()
+                        .rust_2024_migration_desugared_pats_mut()
+                        .entry(pat_info.top_info.hir_id)
+                        .or_default() |= pat.span.at_least_rust_2024();
+                }
+                user_bind_annot
+            }
         };
 
         if bm.0 == ByRef::Yes(Mutability::Mut)
@@ -2204,14 +2217,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
         } else {
             // Reset binding mode on old editions
-
             if pat_info.binding_mode != ByRef::No {
                 pat_info.binding_mode = ByRef::No;
-
-                self.typeck_results
+                *self
+                    .typeck_results
                     .borrow_mut()
                     .rust_2024_migration_desugared_pats_mut()
-                    .insert(pat_info.top_info.hir_id);
+                    .entry(pat_info.top_info.hir_id)
+                    .or_default() |= pat.span.at_least_rust_2024();
             }
         }
 
@@ -2262,6 +2275,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 (err, err)
             }
         };
+
         self.check_pat(inner, inner_ty, pat_info);
         ref_ty
     }

compiler/rustc_hir_typeck/src/writeback.rs

@@ -635,7 +635,7 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
 
     #[instrument(skip(self), level = "debug")]
     fn visit_rust_2024_migration_desugared_pats(&mut self, hir_id: hir::HirId) {
-        if self
+        if let Some(is_hard_error) = self
             .fcx
             .typeck_results
             .borrow_mut()
@@ -645,7 +645,9 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
             debug!(
                 "node is a pat whose match ergonomics are desugared by the Rust 2024 migration lint"
             );
-            self.typeck_results.rust_2024_migration_desugared_pats_mut().insert(hir_id);
+            self.typeck_results
+                .rust_2024_migration_desugared_pats_mut()
+                .insert(hir_id, is_hard_error);
         }
     }
 

compiler/rustc_lint_defs/src/builtin.rs

@@ -1651,7 +1651,6 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,edition2021
-    /// #![feature(ref_pat_eat_one_layer_2024)]
     /// #![warn(rust_2024_incompatible_pat)]
     ///
     /// if let Some(&a) = &Some(&0u8) {
@@ -1672,12 +1671,10 @@ declare_lint! {
     pub RUST_2024_INCOMPATIBLE_PAT,
     Allow,
     "detects patterns whose meaning will change in Rust 2024",
-    @feature_gate = ref_pat_eat_one_layer_2024;
-    // FIXME uncomment below upon stabilization
-    /*@future_incompatible = FutureIncompatibleInfo {
+    @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
         reference: "123076",
-    };*/
+    };
 }
 
 declare_lint! {

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -73,9 +73,10 @@ pub struct TypeckResults<'tcx> {
     /// Stores the actual binding mode for all instances of [`BindingMode`].
     pat_binding_modes: ItemLocalMap<BindingMode>,
 
-    /// Top-level patterns whose match ergonomics need to be desugared
-    /// by the Rust 2021 -> 2024 migration lint.
-    rust_2024_migration_desugared_pats: ItemLocalSet,
+    /// Top-level patterns whose match ergonomics need to be desugared by the Rust 2021 -> 2024
+    /// migration lint. The boolean indicates whether the emitted diagnostic should be a hard error
+    /// (if any of the incompatible pattern elements are in edition 2024).
+    rust_2024_migration_desugared_pats: ItemLocalMap<bool>,
 
     /// Stores the types which were implicitly dereferenced in pattern binding modes
     /// for later usage in THIR lowering. For example,
@@ -418,15 +419,15 @@ impl<'tcx> TypeckResults<'tcx> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.pat_adjustments }
     }
 
-    pub fn rust_2024_migration_desugared_pats(&self) -> LocalSetInContext<'_> {
-        LocalSetInContext {
+    pub fn rust_2024_migration_desugared_pats(&self) -> LocalTableInContext<'_, bool> {
+        LocalTableInContext {
             hir_owner: self.hir_owner,
             data: &self.rust_2024_migration_desugared_pats,
         }
     }
 
-    pub fn rust_2024_migration_desugared_pats_mut(&mut self) -> LocalSetInContextMut<'_> {
-        LocalSetInContextMut {
+    pub fn rust_2024_migration_desugared_pats_mut(&mut self) -> LocalTableInContextMut<'_, bool> {
+        LocalTableInContextMut {
             hir_owner: self.hir_owner,
             data: &mut self.rust_2024_migration_desugared_pats,
         }

compiler/rustc_mir_build/messages.ftl

@@ -265,7 +265,7 @@ mir_build_pointer_pattern = function pointers and raw pointers not derived from
 
 mir_build_privately_uninhabited = pattern `{$witness_1}` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
 
-mir_build_rust_2024_incompatible_pat = the semantics of this pattern will change in edition 2024
+mir_build_rust_2024_incompatible_pat = patterns are not allowed to reset the default binding mode in edition 2024
 
 mir_build_rustc_box_attribute_error = `#[rustc_box]` attribute used incorrectly
     .attributes = no other attributes may be applied

compiler/rustc_mir_build/src/errors.rs

@@ -983,6 +983,8 @@ pub(crate) struct Rust2024IncompatiblePat {
 
 pub(crate) struct Rust2024IncompatiblePatSugg {
     pub(crate) suggestion: Vec<(Span, String)>,
+    /// Whether the incompatibility is a hard error because a relevant span is in edition 2024.
+    pub(crate) is_hard_error: bool,
 }
 
 impl Subdiagnostic for Rust2024IncompatiblePatSugg {

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -25,6 +25,7 @@ use tracing::{debug, instrument};
 
 pub(crate) use self::check_match::check_match;
 use crate::errors::*;
+use crate::fluent_generated as fluent;
 use crate::thir::util::UserAnnotatedTyHelpers;
 
 struct PatCtxt<'a, 'tcx> {
@@ -48,18 +49,28 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
         typeck_results,
         rust_2024_migration_suggestion: typeck_results
             .rust_2024_migration_desugared_pats()
-            .contains(pat.hir_id)
-            .then_some(Rust2024IncompatiblePatSugg { suggestion: Vec::new() }),
+            .get(pat.hir_id)
+            .map(|&is_hard_error| Rust2024IncompatiblePatSugg {
+                suggestion: Vec::new(),
+                is_hard_error,
+            }),
     };
     let result = pcx.lower_pattern(pat);
     debug!("pat_from_hir({:?}) = {:?}", pat, result);
     if let Some(sugg) = pcx.rust_2024_migration_suggestion {
-        tcx.emit_node_span_lint(
-            lint::builtin::RUST_2024_INCOMPATIBLE_PAT,
-            pat.hir_id,
-            pat.span,
-            Rust2024IncompatiblePat { sugg },
-        );
+        if sugg.is_hard_error {
+            let mut err =
+                tcx.dcx().struct_span_err(pat.span, fluent::mir_build_rust_2024_incompatible_pat);
+            err.subdiagnostic(sugg);
+            err.emit();
+        } else {
+            tcx.emit_node_span_lint(
+                lint::builtin::RUST_2024_INCOMPATIBLE_PAT,
+                pat.hir_id,
+                pat.span,
+                Rust2024IncompatiblePat { sugg },
+            );
+        }
     }
     result
 }

compiler/rustc_monomorphize/src/partitioning.rs

@@ -119,6 +119,7 @@ use rustc_middle::util::Providers;
 use rustc_session::CodegenUnits;
 use rustc_session::config::{DumpMonoStatsFormat, SwitchWithOptPath};
 use rustc_span::symbol::Symbol;
+use rustc_target::spec::SymbolVisibility;
 use tracing::debug;
 
 use crate::collector::{self, MonoItemCollectionStrategy, UsageMap};
@@ -904,6 +905,11 @@ fn mono_item_visibility<'tcx>(
 }
 
 fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibility {
+    // Fast-path to avoid expensive query call below
+    if tcx.sess.default_visibility() == SymbolVisibility::Interposable {
+        return Visibility::Default;
+    }
+
     let export_level = if is_generic {
         // Generic functions never have export-level C.
         SymbolExportLevel::Rust
@@ -913,6 +919,7 @@ fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibilit
             _ => SymbolExportLevel::Rust,
         }
     };
+
     match export_level {
         // C-export level items remain at `Default` to allow C code to
         // access and interpose them.

compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs

@@ -6,6 +6,7 @@ use derive_where::derive_where;
 use rustc_type_ir::fold::TypeFoldable;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::solve::inspect;
 use rustc_type_ir::visit::TypeVisitableExt as _;
 use rustc_type_ir::{self as ty, Interner, Upcast as _, elaborate};
 use tracing::{debug, instrument};
@@ -288,6 +289,25 @@ where
         let Ok(normalized_self_ty) =
             self.structurally_normalize_ty(goal.param_env, goal.predicate.self_ty())
         else {
+            // FIXME: We register a fake candidate when normalization fails so that
+            // we can point at the reason for *why*. I'm tempted to say that this
+            // is the wrong way to do this, though.
+            let result =
+                self.probe(|&result| inspect::ProbeKind::RigidAlias { result }).enter(|this| {
+                    let normalized_ty = this.next_ty_infer();
+                    let alias_relate_goal = Goal::new(
+                        this.cx(),
+                        goal.param_env,
+                        ty::PredicateKind::AliasRelate(
+                            goal.predicate.self_ty().into(),
+                            normalized_ty.into(),
+                            ty::AliasRelationDirection::Equate,
+                        ),
+                    );
+                    this.add_goal(GoalSource::AliasWellFormed, alias_relate_goal);
+                    this.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
+                });
+            assert_eq!(result, Err(NoSolution));
             return vec![];
         };
 

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -983,7 +983,7 @@ where
             hidden_ty,
             &mut goals,
         );
-        self.add_goals(GoalSource::Misc, goals);
+        self.add_goals(GoalSource::AliasWellFormed, goals);
     }
 
     // Do something for each opaque/hidden pair defined with `def_id` in the

compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs

@@ -15,7 +15,7 @@ use crate::solve::assembly::{self, Candidate};
 use crate::solve::inspect::ProbeKind;
 use crate::solve::{
     BuiltinImplSource, CandidateSource, Certainty, EvalCtxt, Goal, GoalSource, MaybeCause,
-    NoSolution, QueryResult,
+    NoSolution, QueryResult, Reveal,
 };
 
 impl<D, I> EvalCtxt<'_, D>
@@ -37,10 +37,61 @@ where
         match normalize_result {
             Ok(res) => Ok(res),
             Err(NoSolution) => {
-                let Goal { param_env, predicate: NormalizesTo { alias, term } } = goal;
-                self.relate_rigid_alias_non_alias(param_env, alias, ty::Invariant, term)?;
-                self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                self.probe(|&result| ProbeKind::RigidAlias { result }).enter(|this| {
+                    let Goal { param_env, predicate: NormalizesTo { alias, term } } = goal;
+                    this.add_rigid_constraints(param_env, alias)?;
+                    this.relate_rigid_alias_non_alias(param_env, alias, ty::Invariant, term)?;
+                    this.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                })
+            }
+        }
+    }
+
+    /// Register any obligations that are used to validate that an alias should be
+    /// treated as rigid.
+    ///
+    /// An alias may be considered rigid if it fails normalization, but we also don't
+    /// want to consider aliases that are not well-formed to be rigid simply because
+    /// they fail normalization.
+    ///
+    /// For example, some `<T as Trait>::Assoc` where `T: Trait` does not hold, or an
+    /// opaque type whose hidden type doesn't actually satisfy the opaque item bounds.
+    fn add_rigid_constraints(
+        &mut self,
+        param_env: I::ParamEnv,
+        rigid_alias: ty::AliasTerm<I>,
+    ) -> Result<(), NoSolution> {
+        let cx = self.cx();
+        match rigid_alias.kind(cx) {
+            // Projections are rigid only if their trait ref holds,
+            // and the GAT where-clauses hold.
+            ty::AliasTermKind::ProjectionTy | ty::AliasTermKind::ProjectionConst => {
+                let trait_ref = rigid_alias.trait_ref(cx);
+                self.add_goal(GoalSource::AliasWellFormed, Goal::new(cx, param_env, trait_ref));
+                Ok(())
+            }
+            ty::AliasTermKind::OpaqueTy => {
+                match param_env.reveal() {
+                    // In user-facing mode, paques are only rigid if we may not define it.
+                    Reveal::UserFacing => {
+                        if rigid_alias
+                            .def_id
+                            .as_local()
+                            .is_some_and(|def_id| self.can_define_opaque_ty(def_id))
+                        {
+                            Err(NoSolution)
+                        } else {
+                            Ok(())
+                        }
+                    }
+                    // Opaques are never rigid in reveal-all mode.
+                    Reveal::All => Err(NoSolution),
+                }
             }
+            // FIXME(generic_const_exprs): we would need to support generic consts here
+            ty::AliasTermKind::UnevaluatedConst => Err(NoSolution),
+            // Inherent and weak types are never rigid. This type must not be well-formed.
+            ty::AliasTermKind::WeakTy | ty::AliasTermKind::InherentTy => Err(NoSolution),
         }
     }
 
@@ -124,6 +175,7 @@ where
                     ecx.instantiate_normalizes_to_term(goal, assumption_projection_pred.term);
 
                     // Add GAT where clauses from the trait's definition
+                    // FIXME: We don't need these, since these are the type's own WF obligations.
                     ecx.add_goals(
                         GoalSource::Misc,
                         cx.own_predicates_of(goal.predicate.def_id())
@@ -179,7 +231,8 @@ where
                 .map(|pred| goal.with(cx, pred));
             ecx.add_goals(GoalSource::ImplWhereBound, where_clause_bounds);
 
-            // Add GAT where clauses from the trait's definition
+            // Add GAT where clauses from the trait's definition.
+            // FIXME: We don't need these, since these are the type's own WF obligations.
             ecx.add_goals(
                 GoalSource::Misc,
                 cx.own_predicates_of(goal.predicate.def_id())