More assertions, tests, and miri coverage

compiler/rustc_codegen_ssa/src/meth.rs

@@ -80,6 +80,8 @@ fn dyn_trait_in_self<'tcx>(
         if let GenericArgKind::Type(ty) = arg.unpack()
             && let ty::Dynamic(data, _, _) = ty.kind()
         {
+            // FIXME(arbitrary_self_types): This is likely broken for receivers which
+            // have a "non-self" trait objects as a generic argument.
             return data
                 .principal()
                 .map(|principal| tcx.instantiate_bound_regions_with_erased(principal));

compiler/rustc_const_eval/src/interpret/call.rs

@@ -5,6 +5,7 @@ use std::borrow::Cow;
 
 use either::{Left, Right};
 use rustc_abi::{self as abi, ExternAbi, FieldIdx, Integer, VariantIdx};
+use rustc_hir::def_id::DefId;
 use rustc_middle::ty::layout::{FnAbiOf, IntegerExt, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, AdtDef, Instance, Ty, VariantDef};
 use rustc_middle::{bug, mir, span_bug};
@@ -693,25 +694,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 trace!("Virtual call dispatches to {fn_inst:#?}");
                 // We can also do the lookup based on `def_id` and `dyn_ty`, and check that that
                 // produces the same result.
-                if cfg!(debug_assertions) {
-                    let tcx = *self.tcx;
-
-                    let trait_def_id = tcx.trait_of_item(def_id).unwrap();
-                    let virtual_trait_ref =
-                        ty::TraitRef::from_method(tcx, trait_def_id, instance.args);
-                    let existential_trait_ref =
-                        ty::ExistentialTraitRef::erase_self_ty(tcx, virtual_trait_ref);
-                    let concrete_trait_ref = existential_trait_ref.with_self_ty(tcx, dyn_ty);
-
-                    let concrete_method = Instance::expect_resolve_for_vtable(
-                        tcx,
-                        self.typing_env,
-                        def_id,
-                        instance.args.rebase_onto(tcx, trait_def_id, concrete_trait_ref.args),
-                        self.cur_span(),
-                    );
-                    assert_eq!(fn_inst, concrete_method);
-                }
+                self.assert_virtual_instance_matches_concrete(dyn_ty, def_id, instance, fn_inst);
 
                 // Adjust receiver argument. Layout can be any (thin) ptr.
                 let receiver_ty = Ty::new_mut_ptr(self.tcx.tcx, dyn_ty);
@@ -744,6 +727,30 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         }
     }
 
+    fn assert_virtual_instance_matches_concrete(
+        &self,
+        dyn_ty: Ty<'tcx>,
+        def_id: DefId,
+        virtual_instance: ty::Instance<'tcx>,
+        concrete_instance: ty::Instance<'tcx>,
+    ) {
+        let tcx = *self.tcx;
+
+        let trait_def_id = tcx.trait_of_item(def_id).unwrap();
+        let virtual_trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, virtual_instance.args);
+        let existential_trait_ref = ty::ExistentialTraitRef::erase_self_ty(tcx, virtual_trait_ref);
+        let concrete_trait_ref = existential_trait_ref.with_self_ty(tcx, dyn_ty);
+
+        let concrete_method = Instance::expect_resolve_for_vtable(
+            tcx,
+            self.typing_env,
+            def_id,
+            virtual_instance.args.rebase_onto(tcx, trait_def_id, concrete_trait_ref.args),
+            self.cur_span(),
+        );
+        assert_eq!(concrete_instance, concrete_method);
+    }
+
     /// Initiate a tail call to this function -- popping the current stack frame, pushing the new
     /// stack frame and initializing the arguments.
     pub(super) fn init_fn_tail_call(

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -414,35 +414,33 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
                 // Sanity-check that `supertrait_vtable_slot` in this type's vtable indeed produces
                 // our destination trait.
-                if cfg!(debug_assertions) {
-                    let vptr_entry_idx =
-                        self.tcx.supertrait_vtable_slot((src_pointee_ty, dest_pointee_ty));
-                    let vtable_entries = self.vtable_entries(data_a.principal(), ty);
-                    if let Some(entry_idx) = vptr_entry_idx {
-                        let Some(&ty::VtblEntry::TraitVPtr(upcast_trait_ref)) =
-                            vtable_entries.get(entry_idx)
-                        else {
-                            span_bug!(
-                                self.cur_span(),
-                                "invalid vtable entry index in {} -> {} upcast",
-                                src_pointee_ty,
-                                dest_pointee_ty
-                            );
-                        };
-                        let erased_trait_ref =
-                            ty::ExistentialTraitRef::erase_self_ty(*self.tcx, upcast_trait_ref);
-                        assert!(data_b.principal().is_some_and(|b| self.eq_in_param_env(
-                            erased_trait_ref,
-                            self.tcx.instantiate_bound_regions_with_erased(b)
-                        )));
-                    } else {
-                        // In this case codegen would keep using the old vtable. We don't want to do
-                        // that as it has the wrong trait. The reason codegen can do this is that
-                        // one vtable is a prefix of the other, so we double-check that.
-                        let vtable_entries_b = self.vtable_entries(data_b.principal(), ty);
-                        assert!(&vtable_entries[..vtable_entries_b.len()] == vtable_entries_b);
+                let vptr_entry_idx =
+                    self.tcx.supertrait_vtable_slot((src_pointee_ty, dest_pointee_ty));
+                let vtable_entries = self.vtable_entries(data_a.principal(), ty);
+                if let Some(entry_idx) = vptr_entry_idx {
+                    let Some(&ty::VtblEntry::TraitVPtr(upcast_trait_ref)) =
+                        vtable_entries.get(entry_idx)
+                    else {
+                        span_bug!(
+                            self.cur_span(),
+                            "invalid vtable entry index in {} -> {} upcast",
+                            src_pointee_ty,
+                            dest_pointee_ty
+                        );
                     };
-                }
+                    let erased_trait_ref =
+                        ty::ExistentialTraitRef::erase_self_ty(*self.tcx, upcast_trait_ref);
+                    assert!(data_b.principal().is_some_and(|b| self.eq_in_param_env(
+                        erased_trait_ref,
+                        self.tcx.instantiate_bound_regions_with_erased(b)
+                    )));
+                } else {
+                    // In this case codegen would keep using the old vtable. We don't want to do
+                    // that as it has the wrong trait. The reason codegen can do this is that
+                    // one vtable is a prefix of the other, so we double-check that.
+                    let vtable_entries_b = self.vtable_entries(data_b.principal(), ty);
+                    assert!(&vtable_entries[..vtable_entries_b.len()] == vtable_entries_b);
+                };
 
                 // Get the destination trait vtable and return that.
                 let new_vptr = self.get_vtable_ptr(ty, data_b)?;

compiler/rustc_trait_selection/src/traits/vtable.rs

@@ -2,8 +2,6 @@ use std::fmt::Debug;
 use std::ops::ControlFlow;
 
 use rustc_hir::def_id::DefId;
-use rustc_infer::infer::TyCtxtInferExt;
-use rustc_infer::traits::ObligationCause;
 use rustc_infer::traits::util::PredicateSet;
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
@@ -14,7 +12,7 @@ use rustc_span::DUMMY_SP;
 use smallvec::{SmallVec, smallvec};
 use tracing::debug;
 
-use crate::traits::{ObligationCtxt, impossible_predicates, is_vtable_safe_method};
+use crate::traits::{impossible_predicates, is_vtable_safe_method};
 
 #[derive(Clone, Debug)]
 pub enum VtblSegment<'tcx> {
@@ -228,6 +226,11 @@ fn vtable_entries<'tcx>(
     trait_ref: ty::TraitRef<'tcx>,
 ) -> &'tcx [VtblEntry<'tcx>] {
     debug_assert!(!trait_ref.has_non_region_infer() && !trait_ref.has_non_region_param());
+    debug_assert_eq!(
+        tcx.normalize_erasing_regions(ty::TypingEnv::fully_monomorphized(), trait_ref),
+        trait_ref,
+        "vtable trait ref should be normalized"
+    );
 
     debug!("vtable_entries({:?})", trait_ref);
 
@@ -305,6 +308,11 @@ fn vtable_entries<'tcx>(
 // for `Supertrait`'s methods in the vtable of `Subtrait`.
 pub(crate) fn first_method_vtable_slot<'tcx>(tcx: TyCtxt<'tcx>, key: ty::TraitRef<'tcx>) -> usize {
     debug_assert!(!key.has_non_region_infer() && !key.has_non_region_param());
+    debug_assert_eq!(
+        tcx.normalize_erasing_regions(ty::TypingEnv::fully_monomorphized(), key),
+        key,
+        "vtable trait ref should be normalized"
+    );
 
     let ty::Dynamic(source, _, _) = *key.self_ty().kind() else {
         bug!();
@@ -323,11 +331,9 @@ pub(crate) fn first_method_vtable_slot<'tcx>(tcx: TyCtxt<'tcx>, key: ty::TraitRe
                     vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
                 }
                 VtblSegment::TraitOwnEntries { trait_ref: vtable_principal, emit_vptr } => {
-                    if trait_refs_are_compatible(
-                        tcx,
-                        ty::ExistentialTraitRef::erase_self_ty(tcx, vtable_principal),
-                        target_principal,
-                    ) {
+                    if ty::ExistentialTraitRef::erase_self_ty(tcx, vtable_principal)
+                        == target_principal
+                    {
                         return ControlFlow::Break(vptr_offset);
                     }
 
@@ -358,6 +364,12 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
     ),
 ) -> Option<usize> {
     debug_assert!(!key.has_non_region_infer() && !key.has_non_region_param());
+    debug_assert_eq!(
+        tcx.normalize_erasing_regions(ty::TypingEnv::fully_monomorphized(), key),
+        key,
+        "upcasting trait refs should be normalized"
+    );
+
     let (source, target) = key;
 
     // If the target principal is `None`, we can just return `None`.
@@ -384,11 +396,9 @@ pub(crate) fn supertrait_vtable_slot<'tcx>(
                 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,
-                        ty::ExistentialTraitRef::erase_self_ty(tcx, vtable_principal),
-                        target_principal,
-                    ) {
+                    if ty::ExistentialTraitRef::erase_self_ty(tcx, vtable_principal)
+                        == target_principal
+                    {
                         if emit_vptr {
                             return ControlFlow::Break(Some(vptr_offset));
                         } else {
@@ -408,27 +418,6 @@ 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>,
-    vtable_principal: ty::ExistentialTraitRef<'tcx>,
-    target_principal: ty::ExistentialTraitRef<'tcx>,
-) -> bool {
-    if vtable_principal.def_id != target_principal.def_id {
-        return false;
-    }
-
-    let (infcx, param_env) =
-        tcx.infer_ctxt().build_with_typing_env(ty::TypingEnv::fully_monomorphized());
-    let ocx = ObligationCtxt::new(&infcx);
-    let source_principal = ocx.normalize(&ObligationCause::dummy(), param_env, vtable_principal);
-    let target_principal = ocx.normalize(&ObligationCause::dummy(), param_env, target_principal);
-    let Ok(()) = ocx.eq(&ObligationCause::dummy(), param_env, 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,

src/tools/miri/tests/pass/dyn-upcast.rs

@@ -10,6 +10,8 @@ fn main() {
     replace_vptr();
     vtable_nop_cast();
     drop_principal();
+    modulo_binder();
+    modulo_assoc();
 }
 
 fn vtable_nop_cast() {
@@ -482,3 +484,53 @@ fn drop_principal() {
     println!("before");
     drop(y);
 }
+
+// Test for <https://github.com/rust-lang/rust/issues/135316>.
+fn modulo_binder() {
+    trait Supertrait<T> {
+        fn _print_numbers(&self, mem: &[usize; 100]) {
+            println!("{mem:?}");
+        }
+    }
+    impl<T> Supertrait<T> for () {}
+
+    trait Trait<T, U>: Supertrait<T> + Supertrait<U> {
+        fn say_hello(&self, _: &usize) {
+            println!("Hello!");
+        }
+    }
+    impl<T, U> Trait<T, U> for () {}
+
+    (&() as &'static dyn for<'a> Trait<&'static (), &'a ()>
+        as &'static dyn Trait<&'static (), &'static ()>)
+        .say_hello(&0);
+}
+
+// Test for <https://github.com/rust-lang/rust/issues/135315>.
+fn modulo_assoc() {
+    trait Supertrait<T> {
+        fn _print_numbers(&self, mem: &[usize; 100]) {
+            println!("{mem:?}");
+        }
+    }
+    impl<T> Supertrait<T> for () {}
+
+    trait Identity {
+        type Selff;
+    }
+    impl<Selff> Identity for Selff {
+        type Selff = Selff;
+    }
+
+    trait Middle<T>: Supertrait<()> + Supertrait<T> {
+        fn say_hello(&self, _: &usize) {
+            println!("Hello!");
+        }
+    }
+    impl<T> Middle<T> for () {}
+
+    trait Trait: Middle<<() as Identity>::Selff> {}
+    impl Trait for () {}
+
+    (&() as &dyn Trait as &dyn Middle<()>).say_hello(&0);
+}

src/tools/miri/tests/pass/dyn-upcast.stdout

@@ -2,3 +2,5 @@ before
 goodbye
 before
 goodbye
+Hello!
+Hello!

tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder-vtable.rs

@@ -1,5 +1,7 @@
 #![feature(rustc_attrs)]
 
+// Test for <https://github.com/rust-lang/rust/issues/135316>.
+
 trait Supertrait<T> {
     fn _print_numbers(&self, mem: &[usize; 100]) {
     }

tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder-vtable.stderr

@@ -5,7 +5,7 @@ error: vtable entries: [
            Method(<dyn for<'a> Trait<&(), &'a ()> as Supertrait<&()>>::_print_numbers - shim(reify)),
            Method(<dyn for<'a> Trait<&(), &'a ()> as Trait<&(), &()>>::say_hello - shim(reify)),
        ]
-  --> $DIR/multiple-supertraits-modulo-binder-vtable.rs:18:1
+  --> $DIR/multiple-supertraits-modulo-binder-vtable.rs:20:1
    |
 LL | type First = dyn for<'a> Trait<&'static (), &'a ()>;
    | ^^^^^^^^^^
@@ -17,7 +17,7 @@ error: vtable entries: [
            Method(<dyn Trait<&(), &()> as Supertrait<&()>>::_print_numbers - shim(reify)),
            Method(<dyn Trait<&(), &()> as Trait<&(), &()>>::say_hello - shim(reify)),
        ]
-  --> $DIR/multiple-supertraits-modulo-binder-vtable.rs:22:1
+  --> $DIR/multiple-supertraits-modulo-binder-vtable.rs:24:1
    |
 LL | type Second = dyn Trait<&'static (), &'static ()>;
    | ^^^^^^^^^^^

tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-binder.rs

@@ -1,6 +1,8 @@
 //@ run-pass
 //@ check-run-results
 
+// Test for <https://github.com/rust-lang/rust/issues/135316>.
+
 #![feature(trait_upcasting)]
 
 trait Supertrait<T> {

tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-normalization-vtable.rs

@@ -1,7 +1,8 @@
 #![feature(rustc_attrs)]
-
 #![feature(trait_upcasting)]
 
+// Test for <https://github.com/rust-lang/rust/issues/135315>.
+
 trait Supertrait<T> {
     fn _print_numbers(&self, mem: &[usize; 100]) {
         println!("{mem:?}");

tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-normalization-vtable.stderr

@@ -5,7 +5,7 @@ error: vtable entries: [
            Method(<() as Supertrait<()>>::_print_numbers),
            Method(<() as Middle<()>>::say_hello),
        ]
-  --> $DIR/multiple-supertraits-modulo-normalization-vtable.rs:29:1
+  --> $DIR/multiple-supertraits-modulo-normalization-vtable.rs:30:1
    |
 LL | impl Trait for () {}
    | ^^^^^^^^^^^^^^^^^
@@ -17,7 +17,7 @@ error: vtable entries: [
            Method(<dyn Middle<()> as Supertrait<()>>::_print_numbers - shim(reify)),
            Method(<dyn Middle<()> as Middle<()>>::say_hello - shim(reify)),
        ]
-  --> $DIR/multiple-supertraits-modulo-normalization-vtable.rs:33:1
+  --> $DIR/multiple-supertraits-modulo-normalization-vtable.rs:34:1
    |
 LL | type Virtual = dyn Middle<()>;
    | ^^^^^^^^^^^^

tests/ui/traits/trait-upcasting/multiple-supertraits-modulo-normalization.rs

@@ -3,6 +3,8 @@
 
 #![feature(trait_upcasting)]
 
+// Test for <https://github.com/rust-lang/rust/issues/135315>.
+
 trait Supertrait<T> {
     fn _print_numbers(&self, mem: &[usize; 100]) {
         println!("{mem:?}");