Extract trait_refs_are_compatible, make it instantiate binders

2 files changed, 64 insertions, 28 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index de1d4ef15ac..d562692c1a8 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -9,12 +9,13 @@ use rustc_infer::infer::canonical::{
     Canonical, CanonicalQueryResponse, CanonicalVarValues, QueryResponse,
 };
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
-use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk, RegionResolutionError};
+use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk, RegionResolutionError, TypeTrace};
 use rustc_macros::extension;
 use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, Upcast, Variance};
+use rustc_type_ir::relate::Relate;
 
 use super::{FromSolverError, FulfillmentContext, ScrubbedTraitError, TraitEngine};
 use crate::error_reporting::InferCtxtErrorExt;
@@ -133,6 +134,20 @@ where
             .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
     }
 
+    pub fn eq_trace<T: Relate<TyCtxt<'tcx>>>(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        trace: TypeTrace<'tcx>,
+        expected: T,
+        actual: T,
+    ) -> Result<(), TypeError<'tcx>> {
+        self.infcx
+            .at(cause, param_env)
+            .eq_trace(DefineOpaqueTypes::Yes, trace, expected, actual)
+            .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
+    }
+
     /// Checks whether `expected` is a subtype of `actual`: `expected <: actual`.
     pub fn sub<T: ToTrace<'tcx>>(
         &self,
diff --git a/compiler/rustc_trait_selection/src/traits/vtable.rs b/compiler/rustc_trait_selection/src/traits/vtable.rs
index 5aed55ef2d2..4f13524706b 100644
--- a/compiler/rustc_trait_selection/src/traits/vtable.rs
+++ b/compiler/rustc_trait_selection/src/traits/vtable.rs
@@ -2,6 +2,7 @@ use std::fmt::Debug;
 use std::ops::ControlFlow;
 
 use rustc_hir::def_id::DefId;
+use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::{BoundRegionConversionTime, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
 use rustc_infer::traits::util::PredicateSet;
@@ -24,6 +25,8 @@ pub enum VtblSegment<'tcx> {
 }
 
 /// Prepare the segments for a vtable
+// FIXME: This should take a `PolyExistentialTraitRef`, since we don't care
+// about our `Self` type here.
 pub fn prepare_vtable_segments<'tcx, T>(
     tcx: TyCtxt<'tcx>,
     trait_ref: ty::PolyTraitRef<'tcx>,
@@ -385,7 +388,7 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
     let ty::Dynamic(target, _, _) = *target.kind() else {
         bug!();
     };
-    let target_principal = target.principal()?.with_self_ty(tcx, tcx.types.trait_object_dummy_self);
+    let target_principal = target.principal()?;
 
     // Given that we have a target principal, it is a bug for there not to be a source principal.
     let ty::Dynamic(source, _, _) = *source.kind() else {
@@ -394,29 +397,6 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
     let source_principal =
         source.principal().unwrap().with_self_ty(tcx, tcx.types.trait_object_dummy_self);
 
-    let infcx = tcx.infer_ctxt().build();
-    let param_env = ty::ParamEnv::reveal_all();
-    let trait_refs_are_compatible =
-        |source: ty::PolyTraitRef<'tcx>, target: ty::PolyTraitRef<'tcx>| {
-            infcx.probe(|_| {
-                let ocx = ObligationCtxt::new(&infcx);
-                let source = ocx.normalize(&ObligationCause::dummy(), param_env, source);
-                let target = ocx.normalize(&ObligationCause::dummy(), param_env, target);
-                infcx.enter_forall(target, |target| {
-                    let source = infcx.instantiate_binder_with_fresh_vars(
-                        DUMMY_SP,
-                        BoundRegionConversionTime::HigherRankedType,
-                        source,
-                    );
-                    let Ok(()) = ocx.eq(&ObligationCause::dummy(), param_env, target, source)
-                    else {
-                        return false;
-                    };
-                    ocx.select_all_or_error().is_empty()
-                })
-            })
-        };
-
     let vtable_segment_callback = {
         let mut vptr_offset = 0;
         move |segment| {
@@ -424,9 +404,15 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
                 VtblSegment::MetadataDSA => {
                     vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
                 }
-                VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
-                    vptr_offset += tcx.own_existential_vtable_entries(trait_ref.def_id()).len();
-                    if trait_refs_are_compatible(trait_ref, target_principal) {
+                VtblSegment::TraitOwnEntries { trait_ref: vtable_principal, emit_vptr } => {
+                    vptr_offset +=
+                        tcx.own_existential_vtable_entries(vtable_principal.def_id()).len();
+                    if trait_refs_are_compatible(
+                        tcx,
+                        vtable_principal
+                            .map_bound(|t| ty::ExistentialTraitRef::erase_self_ty(tcx, t)),
+                        target_principal,
+                    ) {
                         if emit_vptr {
                             return ControlFlow::Break(Some(vptr_offset));
                         } else {
@@ -446,6 +432,41 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
     prepare_vtable_segments(tcx, source_principal, vtable_segment_callback).unwrap()
 }
 
+fn trait_refs_are_compatible<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    hr_vtable_principal: ty::PolyExistentialTraitRef<'tcx>,
+    hr_target_principal: ty::PolyExistentialTraitRef<'tcx>,
+) -> bool {
+    if hr_vtable_principal.def_id() != hr_target_principal.def_id() {
+        return false;
+    }
+
+    let infcx = tcx.infer_ctxt().build();
+    let param_env = ty::ParamEnv::reveal_all();
+    let ocx = ObligationCtxt::new(&infcx);
+    let hr_source_principal =
+        ocx.normalize(&ObligationCause::dummy(), param_env, hr_vtable_principal);
+    let hr_target_principal =
+        ocx.normalize(&ObligationCause::dummy(), param_env, hr_target_principal);
+    infcx.enter_forall(hr_target_principal, |target_principal| {
+        let source_principal = infcx.instantiate_binder_with_fresh_vars(
+            DUMMY_SP,
+            BoundRegionConversionTime::HigherRankedType,
+            hr_source_principal,
+        );
+        let Ok(()) = ocx.eq_trace(
+            &ObligationCause::dummy(),
+            param_env,
+            ToTrace::to_trace(&ObligationCause::dummy(), hr_target_principal, hr_source_principal),
+            target_principal,
+            source_principal,
+        ) else {
+            return false;
+        };
+        ocx.select_all_or_error().is_empty()
+    })
+}
+
 pub(super) fn provide(providers: &mut Providers) {
     *providers = Providers {
         own_existential_vtable_entries,