Overlap inherent impls

compiler/rustc_middle/src/hir/mod.rs

@@ -7,10 +7,10 @@ pub mod nested_filter;
 pub mod place;
 
 use crate::ty::query::Providers;
-use crate::ty::TyCtxt;
+use crate::ty::{ImplSubject, TyCtxt};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_hir::def_id::LocalDefId;
+use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::*;
 use rustc_query_system::ich::StableHashingContext;
 use rustc_span::DUMMY_SP;
@@ -54,6 +54,12 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn parent_module(self, id: HirId) -> LocalDefId {
         self.parent_module_from_def_id(id.owner)
     }
+
+    pub fn impl_header(self, def_id: DefId) -> ImplSubject<'tcx> {
+        self.impl_trait_ref(def_id)
+            .map(ImplSubject::Trait)
+            .unwrap_or_else(|| ImplSubject::Inherent(self.type_of(def_id)))
+    }
 }
 
 pub fn provide(providers: &mut Providers) {

compiler/rustc_middle/src/ty/mod.rs

@@ -172,6 +172,12 @@ pub struct ImplHeader<'tcx> {
     pub predicates: Vec<Predicate<'tcx>>,
 }
 
+#[derive(Debug)]
+pub enum ImplSubject<'tcx> {
+    Trait(TraitRef<'tcx>),
+    Inherent(Ty<'tcx>),
+}
+
 #[derive(
     Copy,
     Clone,

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -17,15 +17,17 @@ use crate::traits::{
 use rustc_errors::Diagnostic;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_hir::CRATE_HIR_ID;
+use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::{util, TraitEngine};
 use rustc_middle::traits::specialization_graph::OverlapMode;
 use rustc_middle::ty::fast_reject::{self, TreatParams};
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::subst::Subst;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::DUMMY_SP;
+use std::fmt::Debug;
 use std::iter;
 
 /// Whether we do the orphan check relative to this crate or
@@ -300,60 +302,85 @@ fn negative_impl<'cx, 'tcx>(
     debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
     let tcx = selcx.infcx().tcx;
 
-    // create a parameter environment corresponding to a (placeholder) instantiation of impl1
-    let impl1_env = tcx.param_env(impl1_def_id);
-    let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap();
-
     // Create an infcx, taking the predicates of impl1 as assumptions:
     tcx.infer_ctxt().enter(|infcx| {
-        // Normalize the trait reference. The WF rules ought to ensure
-        // that this always succeeds.
-        let impl1_trait_ref = match traits::fully_normalize(
-            &infcx,
-            FulfillmentContext::new(),
-            ObligationCause::dummy(),
-            impl1_env,
-            impl1_trait_ref,
-        ) {
-            Ok(impl1_trait_ref) => impl1_trait_ref,
-            Err(err) => {
-                bug!("failed to fully normalize {:?}: {:?}", impl1_trait_ref, err);
+        // create a parameter environment corresponding to a (placeholder) instantiation of impl1
+        let impl1_env = tcx.param_env(impl1_def_id);
+
+        match tcx.impl_header(impl1_def_id) {
+            ImplSubject::Trait(impl1_trait_ref) => {
+                // Normalize the trait reference. The WF rules ought to ensure
+                // that this always succeeds.
+                let impl1_trait_ref = match traits::fully_normalize(
+                    &infcx,
+                    FulfillmentContext::new(),
+                    ObligationCause::dummy(),
+                    impl1_env,
+                    impl1_trait_ref,
+                ) {
+                    Ok(impl1_trait_ref) => impl1_trait_ref,
+                    Err(err) => {
+                        bug!("failed to fully normalize {:?}: {:?}", impl1_trait_ref, err);
+                    }
+                };
+
+                // Attempt to prove that impl2 applies, given all of the above.
+                let selcx = &mut SelectionContext::new(&infcx);
+                let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
+                let (impl2_trait_ref, obligations) =
+                    impl_trait_ref_and_oblig(selcx, impl1_env, impl2_def_id, impl2_substs);
+
+                !equate(
+                    &infcx,
+                    impl1_env,
+                    impl1_def_id,
+                    impl1_trait_ref,
+                    impl2_trait_ref,
+                    obligations,
+                )
             }
-        };
+            ImplSubject::Inherent(ty1) => {
+                let ty2 = tcx.type_of(impl2_def_id);
+                !equate(&infcx, impl1_env, impl1_def_id, ty1, ty2, iter::empty())
+            }
+        }
+    })
+}
 
-        // Attempt to prove that impl2 applies, given all of the above.
-        let selcx = &mut SelectionContext::new(&infcx);
-        let impl2_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl2_def_id);
-        let (impl2_trait_ref, obligations) =
-            impl_trait_ref_and_oblig(selcx, impl1_env, impl2_def_id, impl2_substs);
-
-        // do the impls unify? If not, not disjoint.
-        let Ok(InferOk { obligations: more_obligations, .. }) = infcx
-            .at(&ObligationCause::dummy(), impl1_env)
-            .eq(impl1_trait_ref, impl2_trait_ref)
-        else {
+fn equate<'cx, 'tcx, T: Debug + ToTrace<'tcx>>(
+    infcx: &InferCtxt<'cx, 'tcx>,
+    impl1_env: ty::ParamEnv<'tcx>,
+    impl1_def_id: DefId,
+    impl1: T,
+    impl2: T,
+    obligations: impl Iterator<Item = PredicateObligation<'tcx>>,
+) -> bool {
+    // do the impls unify? If not, not disjoint.
+    let Ok(InferOk { obligations: more_obligations, .. }) = infcx
+        .at(&ObligationCause::dummy(), impl1_env)
+        .eq(impl1, impl2) else {
             debug!(
                 "explicit_disjoint: {:?} does not unify with {:?}",
-                impl1_trait_ref, impl2_trait_ref
+                impl1, impl2
             );
-            return false;
+            return true;
         };
 
-        let opt_failing_obligation = obligations
-            .into_iter()
-            .chain(more_obligations)
-            .find(|o| negative_impl_exists(selcx, impl1_env, impl1_def_id, o));
+    let selcx = &mut SelectionContext::new(&infcx);
+    let opt_failing_obligation = obligations
+        .into_iter()
+        .chain(more_obligations)
+        .find(|o| negative_impl_exists(selcx, impl1_env, impl1_def_id, o));
 
-        if let Some(failing_obligation) = opt_failing_obligation {
-            debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
-            true
-        } else {
-            false
-        }
-    })
+    if let Some(failing_obligation) = opt_failing_obligation {
+        debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
+        false
+    } else {
+        true
+    }
 }
 
-/// Try to prove that a negative impl exist for the given obligation and their super predicates.
+/// Try to prove that a negative impl exist for the given obligation and its super predicates.
 #[instrument(level = "debug", skip(selcx))]
 fn negative_impl_exists<'cx, 'tcx>(
     selcx: &SelectionContext<'cx, 'tcx>,
@@ -367,7 +394,7 @@ fn negative_impl_exists<'cx, 'tcx>(
         return true;
     }
 
-    // Try to prove a negative obligation exist for super predicates
+    // Try to prove a negative obligation exists for super predicates
     for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
         if resolve_negative_obligation(infcx, param_env, region_context, &o) {
             return true;

src/test/ui/coherence/coherence-negative-inherent.rs

@@ -0,0 +1,22 @@
+// check-pass
+
+#![feature(negative_impls)]
+#![feature(rustc_attrs)]
+#![feature(with_negative_coherence)]
+
+#[rustc_strict_coherence]
+trait Foo {}
+
+impl !Foo for u32 {}
+
+struct MyStruct<T>(T);
+
+impl<T: Foo> MyStruct<T> {
+    fn method(&self) {}
+}
+
+impl MyStruct<u32> {
+    fn method(&self) {}
+}
+
+fn main() {}