Introduce DeepRejectCtxt::substs_refs_may_unify.

It factors out a repeated code pattern.

Author: nnethercote

compiler/rustc_middle/src/ty/fast_reject.rs

@@ -1,6 +1,6 @@
 use crate::mir::Mutability;
 use crate::ty::subst::GenericArgKind;
-use crate::ty::{self, Ty, TyCtxt, TypeVisitableExt};
+use crate::ty::{self, SubstsRef, Ty, TyCtxt, TypeVisitableExt};
 use rustc_hir::def_id::DefId;
 use std::fmt::Debug;
 use std::hash::Hash;
@@ -188,6 +188,15 @@ pub struct DeepRejectCtxt {
 }
 
 impl DeepRejectCtxt {
+    pub fn substs_refs_may_unify<'tcx>(
+        self,
+        obligation_substs: SubstsRef<'tcx>,
+        impl_substs: SubstsRef<'tcx>,
+    ) -> bool {
+        iter::zip(obligation_substs, impl_substs)
+            .all(|(obl, imp)| self.generic_args_may_unify(obl, imp))
+    }
+
     pub fn generic_args_may_unify<'tcx>(
         self,
         obligation_arg: ty::GenericArg<'tcx>,
@@ -258,9 +267,7 @@ impl DeepRejectCtxt {
             },
             ty::Adt(obl_def, obl_substs) => match k {
                 &ty::Adt(impl_def, impl_substs) => {
-                    obl_def == impl_def
-                        && iter::zip(obl_substs, impl_substs)
-                            .all(|(obl, imp)| self.generic_args_may_unify(obl, imp))
+                    obl_def == impl_def && self.substs_refs_may_unify(obl_substs, impl_substs)
                 }
                 _ => false,
             },

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -17,7 +17,6 @@ use rustc_middle::ty::ProjectionPredicate;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::ty::{ToPredicate, TypeVisitableExt};
 use rustc_span::{sym, DUMMY_SP};
-use std::iter;
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {
     #[instrument(level = "debug", skip(self), ret)]
@@ -144,9 +143,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
         let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
         let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup };
-        if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs)
-            .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
-        {
+        if !drcx.substs_refs_may_unify(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs) {
             return Err(NoSolution);
         }
 

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -1,7 +1,5 @@
 //! Dealing with trait goals, i.e. `T: Trait<'a, U>`.
 
-use std::iter;
-
 use super::{assembly, EvalCtxt, SolverMode};
 use rustc_hir::def_id::DefId;
 use rustc_hir::LangItem;
@@ -41,9 +39,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
 
         let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup };
-        if iter::zip(goal.predicate.trait_ref.substs, impl_trait_ref.skip_binder().substs)
-            .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
-        {
+        if !drcx.substs_refs_may_unify(
+            goal.predicate.trait_ref.substs,
+            impl_trait_ref.skip_binder().substs,
+        ) {
             return Err(NoSolution);
         }
 

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -79,8 +79,9 @@ pub fn overlapping_impls(
     let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
     let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
     let may_overlap = match (impl1_ref, impl2_ref) {
-        (Some(a), Some(b)) => iter::zip(a.skip_binder().substs, b.skip_binder().substs)
-            .all(|(arg1, arg2)| drcx.generic_args_may_unify(arg1, arg2)),
+        (Some(a), Some(b)) => {
+            drcx.substs_refs_may_unify(a.skip_binder().substs, b.skip_binder().substs)
+        }
         (None, None) => {
             let self_ty1 = tcx.type_of(impl1_def_id).skip_binder();
             let self_ty2 = tcx.type_of(impl2_def_id).skip_binder();

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

@@ -2542,8 +2542,10 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         // substitution if we find that any of the input types, when
         // simplified, do not match.
         let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup };
-        iter::zip(obligation.predicate.skip_binder().trait_ref.substs, impl_trait_ref.substs)
-            .any(|(obl, imp)| !drcx.generic_args_may_unify(obl, imp))
+        !drcx.substs_refs_may_unify(
+            obligation.predicate.skip_binder().trait_ref.substs,
+            impl_trait_ref.substs,
+        )
     }
 
     /// Normalize `where_clause_trait_ref` and try to match it against