change is_subtype to relate_types

9 files changed, 74 insertions, 25 deletions

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 0b2fc9bf559..ed36ca6a29b 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -716,14 +716,11 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 }
                 PlaceTy::from_ty(fty)
             }
-            ProjectionElem::Subtype(_) => {
-                let guard = span_mirbug_and_err!(
-                    self,
-                    place,
-                    "ProjectionElem::Subtype shouldn't exist in borrowck"
-                );
-                PlaceTy::from_ty(Ty::new_error(tcx, guard))
-            }
+            ProjectionElem::Subtype(_) => PlaceTy::from_ty(Ty::new_error_with_message(
+                tcx,
+                self.last_span,
+                "ProjectionElem::Subtype shouldn't exist in borrowck",
+            )),
             ProjectionElem::OpaqueCast(ty) => {
                 let ty = self.sanitize_type(place, ty);
                 let ty = self.cx.normalize(ty, location);
@@ -2564,7 +2561,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     }
                 }
                 ProjectionElem::Field(..)
-                | ProjectionElem::Subtype(..)
                 | ProjectionElem::Downcast(..)
                 | ProjectionElem::OpaqueCast(..)
                 | ProjectionElem::Index(..)
@@ -2572,6 +2568,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 | ProjectionElem::Subslice { .. } => {
                     // other field access
                 }
+                ProjectionElem::Subtype(_) => {
+                    bug!("ProjectionElem::Subtype shouldn't exist in borrowck")
+                }
             }
         }
     }
diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
index a13d3a0e115..0a451dad9d2 100644
--- a/compiler/rustc_codegen_cranelift/src/base.rs
+++ b/compiler/rustc_codegen_cranelift/src/base.rs
@@ -876,7 +876,7 @@ pub(crate) fn codegen_place<'tcx>(
                 cplace = cplace.place_deref(fx);
             }
             PlaceElem::OpaqueCast(ty) => bug!("encountered OpaqueCast({ty}) in codegen"),
-            PlaceElem::Subtype(ty) => cplace = cplace.place_transmute_type(fx, ty),
+            PlaceElem::Subtype(ty) => cplace = cplace.place_transmute_type(fx, fx.monomorphize(ty)),
             PlaceElem::Field(field, _ty) => {
                 cplace = cplace.place_field(fx, field);
             }
diff --git a/compiler/rustc_codegen_cranelift/src/value_and_place.rs b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
index 34cde0a0e78..09033cfb23f 100644
--- a/compiler/rustc_codegen_cranelift/src/value_and_place.rs
+++ b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
@@ -674,12 +674,14 @@ impl<'tcx> CPlace<'tcx> {
         }
     }
 
+    /// Used for `ProjectionElem::Subtype`, ty has to be monomorphized before
+    /// passed on.
     pub(crate) fn place_transmute_type(
         self,
         fx: &mut FunctionCx<'_, '_, 'tcx>,
         ty: Ty<'tcx>,
     ) -> CPlace<'tcx> {
-        CPlace { inner: self.inner, layout: fx.layout_of(fx.monomorphize(ty)) }
+        CPlace { inner: self.inner, layout: fx.layout_of(ty) }
     }
 
     pub(crate) fn place_field(
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index 94a5cc67d31..af7dfbef2ff 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -13,7 +13,7 @@ use rustc_middle::ty::layout::{
     self, FnAbiError, FnAbiOfHelpers, FnAbiRequest, LayoutError, LayoutOf, LayoutOfHelpers,
     TyAndLayout,
 };
-use rustc_middle::ty::{self, GenericArgsRef, ParamEnv, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, GenericArgsRef, ParamEnv, Ty, TyCtxt, TypeFoldable, Variance};
 use rustc_mir_dataflow::storage::always_storage_live_locals;
 use rustc_session::Limit;
 use rustc_span::Span;
@@ -384,7 +384,7 @@ pub(super) fn mir_assign_valid_types<'tcx>(
     // all normal lifetimes are erased, higher-ranked types with their
     // late-bound lifetimes are still around and can lead to type
     // differences.
-    if util::is_subtype(tcx, param_env, src.ty, dest.ty) {
+    if util::relate_types(tcx, param_env, Variance::Covariant, src.ty, dest.ty) {
         // Make sure the layout is equal, too -- just to be safe. Miri really
         // needs layout equality. For performance reason we skip this check when
         // the types are equal. Equal types *can* have different layouts when
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 6a5a3628617..4711f7b47cc 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -7,7 +7,7 @@ use rustc_infer::traits::Reveal;
 use rustc_middle::mir::interpret::Scalar;
 use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
-use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeVisitableExt, Variance};
 use rustc_mir_dataflow::impls::MaybeStorageLive;
 use rustc_mir_dataflow::storage::always_storage_live_locals;
 use rustc_mir_dataflow::{Analysis, ResultsCursor};
@@ -16,7 +16,7 @@ use rustc_target::spec::abi::Abi;
 
 use crate::util::is_within_packed;
 
-use crate::util::is_subtype;
+use crate::util::relate_types;
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 enum EdgeKind {
@@ -604,7 +604,15 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             return true;
         }
 
-        return crate::util::is_subtype(self.tcx, self.param_env, src, dest);
+        // After borrowck subtyping should be fully explicit via
+        // `Subtype` projections.
+        let variance = if self.mir_phase >= MirPhase::Runtime(RuntimePhase::Initial) {
+            Variance::Invariant
+        } else {
+            Variance::Covariant
+        };
+
+        crate::util::relate_types(self.tcx, self.param_env, variance, src, dest)
     }
 }
 
@@ -756,9 +764,10 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 }
             }
             ProjectionElem::Subtype(ty) => {
-                if !is_subtype(
+                if !relate_types(
                     self.tcx,
                     self.param_env,
+                    Variance::Covariant,
                     ty,
                     place_ref.ty(&self.body.local_decls, self.tcx).ty,
                 ) {
diff --git a/compiler/rustc_const_eval/src/util/compare_types.rs b/compiler/rustc_const_eval/src/util/compare_types.rs
index 83376c8e992..dd4c67e8d6b 100644
--- a/compiler/rustc_const_eval/src/util/compare_types.rs
+++ b/compiler/rustc_const_eval/src/util/compare_types.rs
@@ -5,7 +5,7 @@
 
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::traits::{DefiningAnchor, ObligationCause};
-use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
+use rustc_middle::ty::{ParamEnv, Ty, TyCtxt, Variance};
 use rustc_trait_selection::traits::ObligationCtxt;
 
 /// Returns whether the two types are equal up to subtyping.
@@ -24,16 +24,22 @@ pub fn is_equal_up_to_subtyping<'tcx>(
     }
 
     // Check for subtyping in either direction.
-    is_subtype(tcx, param_env, src, dest) || is_subtype(tcx, param_env, dest, src)
+    relate_types(tcx, param_env, Variance::Covariant, src, dest)
+        || relate_types(tcx, param_env, Variance::Covariant, dest, src)
 }
 
 /// Returns whether `src` is a subtype of `dest`, i.e. `src <: dest`.
 ///
+/// For almost all of the use cases variance should be `Covariant`,
+/// in `MirPhase` >= `MirPhase::Runtime(RuntimePhase::Initial` variance should
+/// be `Invariant`.
+///
 /// This mostly ignores opaque types as it can be used in constraining contexts
 /// while still computing the final underlying type.
-pub fn is_subtype<'tcx>(
+pub fn relate_types<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
+    variance: Variance,
     src: Ty<'tcx>,
     dest: Ty<'tcx>,
 ) -> bool {
@@ -48,7 +54,7 @@ pub fn is_subtype<'tcx>(
     let cause = ObligationCause::dummy();
     let src = ocx.normalize(&cause, param_env, src);
     let dest = ocx.normalize(&cause, param_env, dest);
-    match ocx.sub(&cause, param_env, src, dest) {
+    match ocx.relate(&cause, param_env, variance, src, dest) {
         Ok(()) => {}
         Err(_) => return false,
     };
diff --git a/compiler/rustc_const_eval/src/util/mod.rs b/compiler/rustc_const_eval/src/util/mod.rs
index 0aef7fa469e..040b3071e6f 100644
--- a/compiler/rustc_const_eval/src/util/mod.rs
+++ b/compiler/rustc_const_eval/src/util/mod.rs
@@ -7,7 +7,7 @@ mod type_name;
 
 pub use self::alignment::{is_disaligned, is_within_packed};
 pub use self::check_validity_requirement::check_validity_requirement;
-pub use self::compare_types::{is_equal_up_to_subtyping, is_subtype};
+pub use self::compare_types::{is_equal_up_to_subtyping, relate_types};
 pub use self::type_name::type_name;
 
 /// Classify whether an operator is "left-homogeneous", i.e., the LHS has the
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index ebd61f8ad95..b53e0852c09 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -218,7 +218,13 @@ impl<'tcx> Inliner<'tcx> {
         // Normally, this shouldn't be required, but trait normalization failure can create a
         // validation ICE.
         let output_type = callee_body.return_ty();
-        if !util::is_subtype(self.tcx, self.param_env, output_type, destination_ty) {
+        if !util::relate_types(
+            self.tcx,
+            self.param_env,
+            ty::Variance::Covariant,
+            output_type,
+            destination_ty,
+        ) {
             trace!(?output_type, ?destination_ty);
             return Err("failed to normalize return type");
         }
@@ -248,7 +254,13 @@ impl<'tcx> Inliner<'tcx> {
                 self_arg_ty.into_iter().chain(arg_tuple_tys).zip(callee_body.args_iter())
             {
                 let input_type = callee_body.local_decls[input].ty;
-                if !util::is_subtype(self.tcx, self.param_env, input_type, arg_ty) {
+                if !util::relate_types(
+                    self.tcx,
+                    self.param_env,
+                    ty::Variance::Covariant,
+                    input_type,
+                    arg_ty,
+                ) {
                     trace!(?arg_ty, ?input_type);
                     return Err("failed to normalize tuple argument type");
                 }
@@ -257,7 +269,13 @@ impl<'tcx> Inliner<'tcx> {
             for (arg, input) in args.iter().zip(callee_body.args_iter()) {
                 let input_type = callee_body.local_decls[input].ty;
                 let arg_ty = arg.ty(&caller_body.local_decls, self.tcx);
-                if !util::is_subtype(self.tcx, self.param_env, input_type, arg_ty) {
+                if !util::relate_types(
+                    self.tcx,
+                    self.param_env,
+                    ty::Variance::Covariant,
+                    input_type,
+                    arg_ty,
+                ) {
                     trace!(?arg_ty, ?input_type);
                     return Err("failed to normalize argument type");
                 }
diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index 820973dc090..015e38b2ac0 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -23,6 +23,7 @@ use rustc_middle::traits::query::NoSolution;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::TypeFoldable;
+use rustc_middle::ty::Variance;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::config::TraitSolver;
 
@@ -156,6 +157,20 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
             .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
     }
 
+    pub fn relate<T: ToTrace<'tcx>>(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        variance: Variance,
+        expected: T,
+        actual: T,
+    ) -> Result<(), TypeError<'tcx>> {
+        self.infcx
+            .at(cause, param_env)
+            .relate(DefineOpaqueTypes::Yes, expected, variance, actual)
+            .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
+    }
+
     /// Checks whether `expected` is a supertype of `actual`: `expected :> actual`.
     pub fn sup<T: ToTrace<'tcx>>(
         &self,