make incoherent_auto_trait_objects a hard error

Author: lcnr

compiler/rustc_lint_defs/src/builtin.rs

@@ -1426,41 +1426,6 @@ declare_lint! {
     };
 }
 
-declare_lint! {
-    /// The `order_dependent_trait_objects` lint detects a trait coherency
-    /// violation that would allow creating two trait impls for the same
-    /// dynamic trait object involving marker traits.
-    ///
-    /// ### Example
-    ///
-    /// ```rust,compile_fail
-    /// pub trait Trait {}
-    ///
-    /// impl Trait for dyn Send + Sync { }
-    /// impl Trait for dyn Sync + Send { }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// A previous bug caused the compiler to interpret traits with different
-    /// orders (such as `Send + Sync` and `Sync + Send`) as distinct types
-    /// when they were intended to be treated the same. This allowed code to
-    /// define separate trait implementations when there should be a coherence
-    /// error. This is a [future-incompatible] lint to transition this to a
-    /// hard error in the future. See [issue #56484] for more details.
-    ///
-    /// [issue #56484]: https://github.com/rust-lang/rust/issues/56484
-    /// [future-incompatible]: ../index.md#future-incompatible-lints
-    pub ORDER_DEPENDENT_TRAIT_OBJECTS,
-    Deny,
-    "trait-object types were treated as different depending on marker-trait order",
-    @future_incompatible = FutureIncompatibleInfo {
-        reference: "issue #56484 <https://github.com/rust-lang/rust/issues/56484>",
-    };
-}
-
 declare_lint! {
     /// The `coherence_leak_check` lint detects conflicting implementations of
     /// a trait that are only distinguished by the old leak-check code.
@@ -3302,7 +3267,6 @@ declare_lint_pass! {
         PATTERNS_IN_FNS_WITHOUT_BODY,
         MISSING_FRAGMENT_SPECIFIER,
         LATE_BOUND_LIFETIME_ARGUMENTS,
-        ORDER_DEPENDENT_TRAIT_OBJECTS,
         COHERENCE_LEAK_CHECK,
         DEPRECATED,
         UNUSED_UNSAFE,

compiler/rustc_middle/src/query/mod.rs

@@ -722,10 +722,6 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    query issue33140_self_ty(key: DefId) -> Option<ty::Ty<'tcx>> {
-        desc { |tcx| "computing Self type wrt issue #33140 `{}`", tcx.def_path_str(key) }
-    }
-
     /// Maps a `DefId` of a type to a list of its inherent impls.
     /// Contains implementations of methods that are inherent to a type.
     /// Methods in these implementations don't need to be exported.

compiler/rustc_middle/src/ty/mod.rs

@@ -2109,45 +2109,9 @@ impl<'tcx> FieldDef {
 
 pub type Attributes<'tcx> = impl Iterator<Item = &'tcx ast::Attribute>;
 #[derive(Debug, PartialEq, Eq)]
-pub enum ImplOverlapKind {
-    /// These impls are always allowed to overlap.
-    Permitted {
-        /// Whether or not the impl is permitted due to the trait being a `#[marker]` trait
-        marker: bool,
-    },
-    /// These impls are allowed to overlap, but that raises
-    /// an issue #33140 future-compatibility warning.
-    ///
-    /// Some background: in Rust 1.0, the trait-object types `Send + Sync` (today's
-    /// `dyn Send + Sync`) and `Sync + Send` (now `dyn Sync + Send`) were different.
-    ///
-    /// The widely-used version 0.1.0 of the crate `traitobject` had accidentally relied
-    /// that difference, making what reduces to the following set of impls:
-    ///
-    /// ```compile_fail,(E0119)
-    /// trait Trait {}
-    /// impl Trait for dyn Send + Sync {}
-    /// impl Trait for dyn Sync + Send {}
-    /// ```
-    ///
-    /// Obviously, once we made these types be identical, that code causes a coherence
-    /// error and a fairly big headache for us. However, luckily for us, the trait
-    /// `Trait` used in this case is basically a marker trait, and therefore having
-    /// overlapping impls for it is sound.
-    ///
-    /// To handle this, we basically regard the trait as a marker trait, with an additional
-    /// future-compatibility warning. To avoid accidentally "stabilizing" this feature,
-    /// it has the following restrictions:
-    ///
-    /// 1. The trait must indeed be a marker-like trait (i.e., no items), and must be
-    /// positive impls.
-    /// 2. The trait-ref of both impls must be equal.
-    /// 3. The trait-ref of both impls must be a trait object type consisting only of
-    /// marker traits.
-    /// 4. Neither of the impls can have any where-clauses.
-    ///
-    /// Once `traitobject` 0.1.0 is no longer an active concern, this hack can be removed.
-    Issue33140,
+pub struct PermittedImplOverlap {
+    /// Whether or not the impl is permitted due to the trait being a `#[marker]` trait
+    pub marker: bool,
 }
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -2229,13 +2193,13 @@ impl<'tcx> TyCtxt<'tcx> {
         self,
         def_id1: DefId,
         def_id2: DefId,
-    ) -> Option<ImplOverlapKind> {
+    ) -> Option<PermittedImplOverlap> {
         // If either trait impl references an error, they're allowed to overlap,
         // as one of them essentially doesn't exist.
         if self.impl_trait_ref(def_id1).map_or(false, |tr| tr.references_error())
             || self.impl_trait_ref(def_id2).map_or(false, |tr| tr.references_error())
         {
-            return Some(ImplOverlapKind::Permitted { marker: false });
+            return Some(PermittedImplOverlap { marker: false });
         }
 
         match (self.impl_polarity(def_id1), self.impl_polarity(def_id2)) {
@@ -2245,7 +2209,7 @@ impl<'tcx> TyCtxt<'tcx> {
                     "impls_are_allowed_to_overlap({:?}, {:?}) = Some(Permitted) (reservations)",
                     def_id1, def_id2
                 );
-                return Some(ImplOverlapKind::Permitted { marker: false });
+                return Some(PermittedImplOverlap { marker: false });
             }
             (ImplPolarity::Positive, ImplPolarity::Negative)
             | (ImplPolarity::Negative, ImplPolarity::Positive) => {
@@ -2273,25 +2237,8 @@ impl<'tcx> TyCtxt<'tcx> {
                 "impls_are_allowed_to_overlap({:?}, {:?}) = Some(Permitted) (marker overlap)",
                 def_id1, def_id2
             );
-            Some(ImplOverlapKind::Permitted { marker: true })
+            Some(PermittedImplOverlap { marker: true })
         } else {
-            if let Some(self_ty1) = self.issue33140_self_ty(def_id1) {
-                if let Some(self_ty2) = self.issue33140_self_ty(def_id2) {
-                    if self_ty1 == self_ty2 {
-                        debug!(
-                            "impls_are_allowed_to_overlap({:?}, {:?}) - issue #33140 HACK",
-                            def_id1, def_id2
-                        );
-                        return Some(ImplOverlapKind::Issue33140);
-                    } else {
-                        debug!(
-                            "impls_are_allowed_to_overlap({:?}, {:?}) - found {:?} != {:?}",
-                            def_id1, def_id2, self_ty1, self_ty2
-                        );
-                    }
-                }
-            }
-
             debug!("impls_are_allowed_to_overlap({:?}, {:?}) = None", def_id1, def_id2);
             None
         }

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -63,7 +63,6 @@ pub use self::project::{normalize, normalize_projection_type, normalize_to};
 pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
-pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
 pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
 pub use self::structural_match::{
     search_for_adt_const_param_violation, search_for_structural_match_violation,

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1752,7 +1752,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
                 if other.evaluation.must_apply_considering_regions() {
                     match tcx.impls_are_allowed_to_overlap(other_def, victim_def) {
-                        Some(ty::ImplOverlapKind::Permitted { marker: true }) => {
+                        Some(ty::PermittedImplOverlap { marker: true }) => {
                             // Subtle: If the predicate we are evaluating has inference
                             // variables, do *not* allow discarding candidates due to
                             // marker trait impls.

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -15,14 +15,13 @@ use specialization_graph::GraphExt;
 use crate::errors::NegativePositiveConflict;
 use crate::infer::{InferCtxt, InferOk, TyCtxtInferExt};
 use crate::traits::select::IntercrateAmbiguityCause;
-use crate::traits::{self, coherence, FutureCompatOverlapErrorKind, ObligationCause};
+use crate::traits::{self, coherence, ObligationCause};
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_errors::{struct_span_err, EmissionGuarantee, LintDiagnosticBuilder};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::ty::{self, ImplSubject, TyCtxt};
 use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_session::lint::builtin::COHERENCE_LEAK_CHECK;
-use rustc_session::lint::builtin::ORDER_DEPENDENT_TRAIT_OBJECTS;
 use rustc_span::{Span, DUMMY_SP};
 
 use super::util;
@@ -260,9 +259,9 @@ pub(super) fn specialization_graph_provider(
             let insert_result = sg.insert(tcx, impl_def_id.to_def_id(), overlap_mode);
             // Report error if there was one.
             let (overlap, used_to_be_allowed) = match insert_result {
-                Err(overlap) => (Some(overlap), None),
-                Ok(Some(overlap)) => (Some(overlap.error), Some(overlap.kind)),
-                Ok(None) => (None, None),
+                Err(overlap) => (Some(overlap), false),
+                Ok(Some(overlap)) => (Some(overlap.error), overlap.used_to_be_allowed),
+                Ok(None) => (None, false),
             };
 
             if let Some(overlap) = overlap {
@@ -286,7 +285,7 @@ fn report_overlap_conflict(
     tcx: TyCtxt<'_>,
     overlap: OverlapError,
     impl_def_id: LocalDefId,
-    used_to_be_allowed: Option<FutureCompatOverlapErrorKind>,
+    used_to_be_allowed: bool,
     sg: &mut specialization_graph::Graph,
 ) {
     let impl_polarity = tcx.impl_polarity(impl_def_id.to_def_id());
@@ -342,7 +341,7 @@ fn report_conflicting_impls(
     tcx: TyCtxt<'_>,
     overlap: OverlapError,
     impl_def_id: LocalDefId,
-    used_to_be_allowed: Option<FutureCompatOverlapErrorKind>,
+    used_to_be_allowed: bool,
     sg: &mut specialization_graph::Graph,
 ) {
     let impl_span = tcx.def_span(impl_def_id);
@@ -353,21 +352,16 @@ fn report_conflicting_impls(
     fn decorate<G: EmissionGuarantee>(
         tcx: TyCtxt<'_>,
         overlap: OverlapError,
-        used_to_be_allowed: Option<FutureCompatOverlapErrorKind>,
         impl_span: Span,
         err: LintDiagnosticBuilder<'_, G>,
     ) -> G {
         let msg = format!(
-            "conflicting implementations of trait `{}`{}{}",
+            "conflicting implementations of trait `{}`{}",
             overlap.trait_desc,
             overlap
                 .self_desc
                 .clone()
                 .map_or_else(String::new, |ty| { format!(" for type `{}`", ty) }),
-            match used_to_be_allowed {
-                Some(FutureCompatOverlapErrorKind::Issue33140) => ": (E0119)",
-                _ => "",
-            }
         );
         let mut err = err.build(&msg);
         match tcx.span_of_impl(overlap.with_impl) {
@@ -401,39 +395,25 @@ fn report_conflicting_impls(
         err.emit()
     }
 
-    match used_to_be_allowed {
-        None => {
-            let reported = if overlap.with_impl.is_local()
-                || tcx.orphan_check_impl(impl_def_id).is_ok()
-            {
-                let err = struct_span_err!(tcx.sess, impl_span, E0119, "");
-                Some(decorate(
-                    tcx,
-                    overlap,
-                    used_to_be_allowed,
-                    impl_span,
-                    LintDiagnosticBuilder::new(err),
-                ))
-            } else {
-                Some(tcx.sess.delay_span_bug(impl_span, "impl should have failed the orphan check"))
-            };
-            sg.has_errored = reported;
-        }
-        Some(kind) => {
-            let lint = match kind {
-                FutureCompatOverlapErrorKind::Issue33140 => ORDER_DEPENDENT_TRAIT_OBJECTS,
-                FutureCompatOverlapErrorKind::LeakCheck => COHERENCE_LEAK_CHECK,
-            };
-            tcx.struct_span_lint_hir(
-                lint,
-                tcx.hir().local_def_id_to_hir_id(impl_def_id),
-                impl_span,
-                |ldb| {
-                    decorate(tcx, overlap, used_to_be_allowed, impl_span, ldb);
-                },
-            );
-        }
-    };
+    if used_to_be_allowed {
+        tcx.struct_span_lint_hir(
+            COHERENCE_LEAK_CHECK,
+            tcx.hir().local_def_id_to_hir_id(impl_def_id),
+            impl_span,
+            |ldb| {
+                decorate(tcx, overlap, impl_span, ldb);
+            },
+        );
+    } else {
+        let reported = if overlap.with_impl.is_local() || tcx.orphan_check_impl(impl_def_id).is_ok()
+        {
+            let err = struct_span_err!(tcx.sess, impl_span, E0119, "");
+            Some(decorate(tcx, overlap, impl_span, LintDiagnosticBuilder::new(err)))
+        } else {
+            Some(tcx.sess.delay_span_bug(impl_span, "impl should have failed the orphan check"))
+        };
+        sg.has_errored = reported;
+    }
 }
 
 /// Recovers the "impl X for Y" signature from `impl_def_id` and returns it as a

compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs

@@ -8,16 +8,10 @@ use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
 
 pub use rustc_middle::traits::specialization_graph::*;
 
-#[derive(Copy, Clone, Debug)]
-pub enum FutureCompatOverlapErrorKind {
-    Issue33140,
-    LeakCheck,
-}
-
 #[derive(Debug)]
 pub struct FutureCompatOverlapError {
     pub error: OverlapError,
-    pub kind: FutureCompatOverlapErrorKind,
+    pub used_to_be_allowed: bool,
 }
 
 /// The result of attempting to insert an impl into a group of children.
@@ -146,10 +140,7 @@ impl ChildrenExt<'_> for Children {
                 if should_err {
                     Err(error)
                 } else {
-                    *last_lint = Some(FutureCompatOverlapError {
-                        error,
-                        kind: FutureCompatOverlapErrorKind::LeakCheck,
-                    });
+                    *last_lint = Some(FutureCompatOverlapError { error, used_to_be_allowed: true });
 
                     Ok((false, false))
                 }
@@ -167,13 +158,7 @@ impl ChildrenExt<'_> for Children {
                         tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling)
                     {
                         match overlap_kind {
-                            ty::ImplOverlapKind::Permitted { marker: _ } => {}
-                            ty::ImplOverlapKind::Issue33140 => {
-                                *last_lint_mut = Some(FutureCompatOverlapError {
-                                    error: create_overlap_error(overlap),
-                                    kind: FutureCompatOverlapErrorKind::Issue33140,
-                                });
-                            }
+                            ty::PermittedImplOverlap { marker: _ } => {}
                         }
 
                         return Ok((false, false));