Implement impl_subject_and_oblig instead of repeating the impls

Author: spastorino

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -7,7 +7,7 @@
 use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::{CombinedSnapshot, InferOk, RegionckMode};
 use crate::traits::select::IntercrateAmbiguityCause;
-use crate::traits::util::{impl_trait_ref_and_oblig, inherent_impl_and_oblig};
+use crate::traits::util::impl_subject_and_oblig;
 use crate::traits::SkipLeakCheck;
 use crate::traits::{
     self, FulfillmentContext, Normalized, Obligation, ObligationCause, PredicateObligation,
@@ -316,36 +316,14 @@ fn negative_impl<'cx, 'tcx>(
             Err(err) => bug!("failed to fully normalize {:?}: {:?}", impl1_def_id, err),
         };
 
-        let (subject2, obligations) =
-            impl_subject_and_obligations(&infcx, impl_env, subject1, impl2_def_id);
-
-        !equate(&infcx, impl_env, impl1_def_id, subject1, subject2, obligations)
-    })
-}
-
-fn impl_subject_and_obligations<'cx, 'tcx>(
-    infcx: &InferCtxt<'cx, 'tcx>,
-    impl_env: ty::ParamEnv<'tcx>,
-    subject1: ImplSubject<'tcx>,
-    impl2_def_id: DefId,
-) -> (ImplSubject<'tcx>, Box<dyn Iterator<Item = PredicateObligation<'tcx>> + 'tcx>) {
-    if let ImplSubject::Trait(_) = subject1 {
         // 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, impl_env, impl2_def_id, impl2_substs);
-
-        (ImplSubject::Trait(impl2_trait_ref), Box::new(obligations))
-    } else {
-        // 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_ty, obligations) =
-            inherent_impl_and_oblig(selcx, impl_env, impl2_def_id, impl2_substs);
+        let (subject2, obligations) =
+            impl_subject_and_oblig(selcx, impl_env, impl2_def_id, impl2_substs);
 
-        (ImplSubject::Inherent(impl2_ty), Box::new(obligations))
-    }
+        !equate(&infcx, impl_env, impl1_def_id, subject1, subject2, obligations)
+    })
 }
 
 fn equate<'cx, 'tcx>(

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

@@ -20,12 +20,12 @@ use rustc_errors::{struct_span_err, EmissionGuarantee};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::lint::LintDiagnosticBuilder;
 use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, ImplSubject, TyCtxt};
 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::impl_trait_ref_and_oblig;
+use super::util;
 use super::{FulfillmentContext, SelectionContext};
 
 /// Information pertinent to an overlapping impl error.
@@ -186,18 +186,20 @@ fn fulfill_implication<'a, 'tcx>(
         param_env, source_trait_ref, target_impl
     );
 
+    let source_trait = ImplSubject::Trait(source_trait_ref);
+
     let selcx = &mut SelectionContext::new(&infcx);
     let target_substs = infcx.fresh_substs_for_item(DUMMY_SP, target_impl);
-    let (target_trait_ref, obligations) =
-        impl_trait_ref_and_oblig(selcx, param_env, target_impl, target_substs);
+    let (target_trait, obligations) =
+        util::impl_subject_and_oblig(selcx, param_env, target_impl, target_substs);
 
     // do the impls unify? If not, no specialization.
     let Ok(InferOk { obligations: more_obligations, .. }) =
-        infcx.at(&ObligationCause::dummy(), param_env).eq(source_trait_ref, target_trait_ref)
+        infcx.at(&ObligationCause::dummy(), param_env).eq(source_trait, target_trait)
     else {
         debug!(
             "fulfill_implication: {:?} does not unify with {:?}",
-            source_trait_ref, target_trait_ref
+            source_trait, target_trait
         );
         return Err(());
     };
@@ -225,7 +227,7 @@ fn fulfill_implication<'a, 'tcx>(
             [] => {
                 debug!(
                     "fulfill_implication: an impl for {:?} specializes {:?}",
-                    source_trait_ref, target_trait_ref
+                    source_trait, target_trait
                 );
 
                 // Now resolve the *substitution* we built for the target earlier, replacing
@@ -237,8 +239,8 @@ fn fulfill_implication<'a, 'tcx>(
                 debug!(
                     "fulfill_implication: for impls on {:?} and {:?}, \
                      could not fulfill: {:?} given {:?}",
-                    source_trait_ref,
-                    target_trait_ref,
+                    source_trait,
+                    target_trait,
                     errors,
                     param_env.caller_bounds()
                 );

compiler/rustc_trait_selection/src/traits/util.rs

@@ -6,7 +6,7 @@ use smallvec::SmallVec;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::{GenericArg, Subst, SubstsRef};
-use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, ImplSubject, ToPredicate, Ty, TyCtxt, TypeFoldable};
 
 use super::{Normalized, Obligation, ObligationCause, PredicateObligation, SelectionContext};
 pub use rustc_infer::traits::{self, util::*};
@@ -190,19 +190,19 @@ impl Iterator for SupertraitDefIds<'_> {
 // Other
 ///////////////////////////////////////////////////////////////////////////
 
-/// Instantiate all bound parameters of the impl with the given substs,
-/// returning the resulting trait ref and all obligations that arise.
+/// Instantiate all bound parameters of the impl subject with the given substs,
+/// returning the resulting subject and all obligations that arise.
 /// The obligations are closed under normalization.
-pub fn impl_trait_ref_and_oblig<'a, 'tcx>(
+pub fn impl_subject_and_oblig<'a, 'tcx>(
     selcx: &mut SelectionContext<'a, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     impl_def_id: DefId,
     impl_substs: SubstsRef<'tcx>,
-) -> (ty::TraitRef<'tcx>, impl Iterator<Item = PredicateObligation<'tcx>>) {
-    let impl_trait_ref = selcx.tcx().impl_trait_ref(impl_def_id).unwrap();
-    let impl_trait_ref = impl_trait_ref.subst(selcx.tcx(), impl_substs);
-    let Normalized { value: impl_trait_ref, obligations: normalization_obligations1 } =
-        super::normalize(selcx, param_env, ObligationCause::dummy(), impl_trait_ref);
+) -> (ImplSubject<'tcx>, impl Iterator<Item = PredicateObligation<'tcx>>) {
+    let subject = selcx.tcx().impl_subject(impl_def_id);
+    let subject = subject.subst(selcx.tcx(), impl_substs);
+    let Normalized { value: subject, obligations: normalization_obligations1 } =
+        super::normalize(selcx, param_env, ObligationCause::dummy(), subject);
 
     let predicates = selcx.tcx().predicates_of(impl_def_id);
     let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
@@ -215,35 +215,7 @@ pub fn impl_trait_ref_and_oblig<'a, 'tcx>(
         .chain(normalization_obligations1.into_iter())
         .chain(normalization_obligations2.into_iter());
 
-    (impl_trait_ref, impl_obligations)
-}
-
-/// Instantiate all bound parameters of the impl with the given substs,
-/// returning the resulting trait ref and all obligations that arise.
-/// The obligations are closed under normalization.
-pub fn inherent_impl_and_oblig<'a, 'tcx>(
-    selcx: &mut SelectionContext<'a, 'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    impl_def_id: DefId,
-    impl_substs: SubstsRef<'tcx>,
-) -> (Ty<'tcx>, impl Iterator<Item = PredicateObligation<'tcx>>) {
-    let ty = selcx.tcx().type_of(impl_def_id);
-    let ty = ty.subst(selcx.tcx(), impl_substs);
-    let Normalized { value: ty, obligations: normalization_obligations1 } =
-        super::normalize(selcx, param_env, ObligationCause::dummy(), ty);
-
-    let predicates = selcx.tcx().predicates_of(impl_def_id);
-    let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
-    let Normalized { value: predicates, obligations: normalization_obligations2 } =
-        super::normalize(selcx, param_env, ObligationCause::dummy(), predicates);
-    let impl_obligations =
-        predicates_for_generics(ObligationCause::dummy(), 0, param_env, predicates);
-
-    let impl_obligations = impl_obligations
-        .chain(normalization_obligations1.into_iter())
-        .chain(normalization_obligations2.into_iter());
-
-    (ty, impl_obligations)
+    (subject, impl_obligations)
 }
 
 pub fn predicates_for_generics<'tcx>(