Rollup merge of #118649 - compiler-errors:coherence-ambig, r=lcnr

matthiaskrgr · web-flow · commit 1974f5cba97b · 2024-01-09T05:33:21.000+01:00
Make inductive cycles in coherence ambiguous always Logical conclusion of #114040 One step after #116493 cc rust-lang/trait-system-refactor-initiative#20 r? lcnr to kick off the FCP after review... maybe we should wait until 1.75 is landed? In that case, I'd still like to get the FCP boxes checked sooner since that'll be near the holidays which means everyone's away.
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
@@ -513,6 +513,11 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, see PR #117984 \
         <https://github.com/rust-lang/rust/pull/117984> for more information",
     );
+    store.register_removed(
+        "coinductive_overlap_in_coherence",
+        "converted into hard error, see PR #118649 \
+         <https://github.com/rust-lang/rust/pull/118649> for more information",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
@@ -26,7 +26,6 @@ declare_lint_pass! {
         BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
         CENUM_IMPL_DROP_CAST,
         COHERENCE_LEAK_CHECK,
-        COINDUCTIVE_OVERLAP_IN_COHERENCE,
         CONFLICTING_REPR_HINTS,
         CONST_EVALUATABLE_UNCHECKED,
         CONST_ITEM_MUTATION,
@@ -4367,45 +4366,6 @@ declare_lint! {
     @feature_gate = sym::type_privacy_lints;
 }
 
-declare_lint! {
-    /// The `coinductive_overlap_in_coherence` lint detects impls which are currently
-    /// considered not overlapping, but may be considered to overlap if support for
-    /// coinduction is added to the trait solver.
-    ///
-    /// ### Example
-    ///
-    /// ```rust,compile_fail
-    /// #![deny(coinductive_overlap_in_coherence)]
-    ///
-    /// trait CyclicTrait {}
-    /// impl<T: CyclicTrait> CyclicTrait for T {}
-    ///
-    /// trait Trait {}
-    /// impl<T: CyclicTrait> Trait for T {}
-    /// // conflicting impl with the above
-    /// impl Trait for u8 {}
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// We have two choices for impl which satisfy `u8: Trait`: the blanket impl
-    /// for generic `T`, and the direct impl for `u8`. These two impls nominally
-    /// overlap, since we can infer `T = u8` in the former impl, but since the where
-    /// clause `u8: CyclicTrait` would end up resulting in a cycle (since it depends
-    /// on itself), the blanket impl is not considered to hold for `u8`. This will
-    /// change in a future release.
-    pub COINDUCTIVE_OVERLAP_IN_COHERENCE,
-    Deny,
-    "impls that are not considered to overlap may be considered to \
-    overlap in the future",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
-        reference: "issue #114040 <https://github.com/rust-lang/rust/issues/114040>",
-    };
-}
-
 declare_lint! {
     /// The `unknown_or_malformed_diagnostic_attributes` lint detects unrecognized or otherwise malformed
     /// diagnostic attributes.
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -10,7 +10,7 @@ use crate::solve::inspect::{InspectGoal, ProofTreeInferCtxtExt, ProofTreeVisitor
 use crate::solve::{deeply_normalize_for_diagnostics, inspect};
 use crate::traits::engine::TraitEngineExt;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
-use crate::traits::select::{IntercrateAmbiguityCause, TreatInductiveCycleAs};
+use crate::traits::select::IntercrateAmbiguityCause;
 use crate::traits::structural_normalize::StructurallyNormalizeExt;
 use crate::traits::NormalizeExt;
 use crate::traits::SkipLeakCheck;
@@ -31,7 +31,6 @@ use rustc_middle::traits::DefiningAnchor;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor};
-use rustc_session::lint::builtin::COINDUCTIVE_OVERLAP_IN_COHERENCE;
 use rustc_span::symbol::sym;
 use rustc_span::DUMMY_SP;
 use std::fmt::Debug;
@@ -197,7 +196,7 @@ fn overlap<'tcx>(
         .intercrate(true)
         .with_next_trait_solver(tcx.next_trait_solver_in_coherence())
         .build();
-    let selcx = &mut SelectionContext::new(&infcx);
+    let selcx = &mut SelectionContext::with_treat_inductive_cycle_as_ambig(&infcx);
     if track_ambiguity_causes.is_yes() {
         selcx.enable_tracking_intercrate_ambiguity_causes();
     }
@@ -224,61 +223,10 @@ fn overlap<'tcx>(
     );
 
     if overlap_mode.use_implicit_negative() {
-        for mode in [TreatInductiveCycleAs::Ambig, TreatInductiveCycleAs::Recur] {
-            if let Some(failing_obligation) = selcx.with_treat_inductive_cycle_as(mode, |selcx| {
-                impl_intersection_has_impossible_obligation(selcx, &obligations)
-            }) {
-                if matches!(mode, TreatInductiveCycleAs::Recur) {
-                    let first_local_impl = impl1_header
-                        .impl_def_id
-                        .as_local()
-                        .or(impl2_header.impl_def_id.as_local())
-                        .expect("expected one of the impls to be local");
-                    infcx.tcx.struct_span_lint_hir(
-                        COINDUCTIVE_OVERLAP_IN_COHERENCE,
-                        infcx.tcx.local_def_id_to_hir_id(first_local_impl),
-                        infcx.tcx.def_span(first_local_impl),
-                        format!(
-                            "implementations {} will conflict in the future",
-                            match impl1_header.trait_ref {
-                                Some(trait_ref) => {
-                                    let trait_ref = infcx.resolve_vars_if_possible(trait_ref);
-                                    format!(
-                                        "of `{}` for `{}`",
-                                        trait_ref.print_trait_sugared(),
-                                        trait_ref.self_ty()
-                                    )
-                                }
-                                None => format!(
-                                    "for `{}`",
-                                    infcx.resolve_vars_if_possible(impl1_header.self_ty)
-                                ),
-                            },
-                        ),
-                        |lint| {
-                            lint.note(
-                                "impls that are not considered to overlap may be considered to \
-                                overlap in the future",
-                            )
-                            .span_label(
-                                infcx.tcx.def_span(impl1_header.impl_def_id),
-                                "the first impl is here",
-                            )
-                            .span_label(
-                                infcx.tcx.def_span(impl2_header.impl_def_id),
-                                "the second impl is here",
-                            );
-                            lint.note(format!(
-                                "`{}` may be considered to hold in future releases, \
-                                    causing the impls to overlap",
-                                infcx.resolve_vars_if_possible(failing_obligation.predicate)
-                            ));
-                        },
-                    );
-                }
-
-                return None;
-            }
+        if let Some(_failing_obligation) =
+            impl_intersection_has_impossible_obligation(selcx, &obligations)
+        {
+            return None;
         }
     }
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -239,20 +239,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
     }
 
-    // Sets the `TreatInductiveCycleAs` mode temporarily in the selection context
-    pub fn with_treat_inductive_cycle_as<T>(
-        &mut self,
-        treat_inductive_cycle: TreatInductiveCycleAs,
-        f: impl FnOnce(&mut Self) -> T,
-    ) -> T {
+    pub fn with_treat_inductive_cycle_as_ambig(
+        infcx: &'cx InferCtxt<'tcx>,
+    ) -> SelectionContext<'cx, 'tcx> {
         // Should be executed in a context where caching is disabled,
         // otherwise the cache is poisoned with the temporary result.
-        assert!(self.is_intercrate());
-        let treat_inductive_cycle =
-            std::mem::replace(&mut self.treat_inductive_cycle, treat_inductive_cycle);
-        let value = f(self);
-        self.treat_inductive_cycle = treat_inductive_cycle;
-        value
+        assert!(infcx.intercrate);
+        SelectionContext {
+            treat_inductive_cycle: TreatInductiveCycleAs::Ambig,
+            ..SelectionContext::new(infcx)
+        }
     }
 
     pub fn with_query_mode(
diff --git a/tests/ui/coherence/warn-when-cycle-is-error-in-coherence.rs b/tests/ui/coherence/warn-when-cycle-is-error-in-coherence.rs
@@ -1,18 +1,15 @@
-#![deny(coinductive_overlap_in_coherence)]
-
 use std::borrow::Borrow;
 use std::cmp::Ordering;
 use std::marker::PhantomData;
 
 #[derive(PartialEq, Default)]
+//~^ ERROR conflicting implementations of trait `PartialEq<Interval<_>>` for type `Interval<_>`
 pub(crate) struct Interval<T>(PhantomData<T>);
 
 // This impl overlaps with the `derive` unless we reject the nested
 // `Interval<?1>: PartialOrd<Interval<?1>>` candidate which results
-// in a - currently inductive - cycle.
+// in a -- currently inductive -- cycle.
 impl<T, Q> PartialEq<Q> for Interval<T>
-//~^ ERROR implementations of `PartialEq<Interval<_>>` for `Interval<_>` will conflict in the future
-//~| WARN this was previously accepted by the compiler but is being phased out
 where
     T: Borrow<Q>,
     Q: ?Sized + PartialOrd,
diff --git a/tests/ui/coherence/warn-when-cycle-is-error-in-coherence.stderr b/tests/ui/coherence/warn-when-cycle-is-error-in-coherence.stderr
@@ -1,51 +1,17 @@
-error: implementations of `PartialEq<Interval<_>>` for `Interval<_>` will conflict in the future
-  --> $DIR/warn-when-cycle-is-error-in-coherence.rs:13:1
+error[E0119]: conflicting implementations of trait `PartialEq<Interval<_>>` for type `Interval<_>`
+  --> $DIR/warn-when-cycle-is-error-in-coherence.rs:5:10
    |
 LL |   #[derive(PartialEq, Default)]
-   |            --------- the second impl is here
+   |            ^^^^^^^^^ conflicting implementation for `Interval<_>`
 ...
 LL | / impl<T, Q> PartialEq<Q> for Interval<T>
-LL | |
-LL | |
 LL | | where
 LL | |     T: Borrow<Q>,
 LL | |     Q: ?Sized + PartialOrd,
-   | |___________________________^ the first impl is here
+   | |___________________________- first implementation here
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #114040 <https://github.com/rust-lang/rust/issues/114040>
-   = note: impls that are not considered to overlap may be considered to overlap in the future
-   = note: `Interval<_>: PartialOrd` may be considered to hold in future releases, causing the impls to overlap
-note: the lint level is defined here
-  --> $DIR/warn-when-cycle-is-error-in-coherence.rs:1:9
-   |
-LL | #![deny(coinductive_overlap_in_coherence)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 
-Future incompatibility report: Future breakage diagnostic:
-error: implementations of `PartialEq<Interval<_>>` for `Interval<_>` will conflict in the future
-  --> $DIR/warn-when-cycle-is-error-in-coherence.rs:13:1
-   |
-LL |   #[derive(PartialEq, Default)]
-   |            --------- the second impl is here
-...
-LL | / impl<T, Q> PartialEq<Q> for Interval<T>
-LL | |
-LL | |
-LL | | where
-LL | |     T: Borrow<Q>,
-LL | |     Q: ?Sized + PartialOrd,
-   | |___________________________^ the first impl is here
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #114040 <https://github.com/rust-lang/rust/issues/114040>
-   = note: impls that are not considered to overlap may be considered to overlap in the future
-   = note: `Interval<_>: PartialOrd` may be considered to hold in future releases, causing the impls to overlap
-note: the lint level is defined here
-  --> $DIR/warn-when-cycle-is-error-in-coherence.rs:1:9
-   |
-LL | #![deny(coinductive_overlap_in_coherence)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
+For more information about this error, try `rustc --explain E0119`.
