From b966d1cf1ef8e2569bf23171d09bff2243c9b4b4 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Oct 2021 13:23:00 +0000
Subject: [PATCH 01/12] Prepare for more ParamEnv flags

---
 compiler/rustc_middle/src/ty/mod.rs | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index cf47da157d19f..f799465107348 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1216,23 +1216,28 @@ pub struct ParamEnv<'tcx> {
     /// want `Reveal::All`.
     ///
     /// Note: This is packed, use the reveal() method to access it.
-    packed: CopyTaggedPtr<&'tcx List<Predicate<'tcx>>, traits::Reveal, true>,
+    packed: CopyTaggedPtr<&'tcx List<Predicate<'tcx>>, ParamTag, true>,
 }
 
-unsafe impl rustc_data_structures::tagged_ptr::Tag for traits::Reveal {
+#[derive(Copy, Clone)]
+struct ParamTag {
+    reveal: traits::Reveal,
+}
+
+unsafe impl rustc_data_structures::tagged_ptr::Tag for ParamTag {
     const BITS: usize = 1;
     #[inline]
     fn into_usize(self) -> usize {
         match self {
-            traits::Reveal::UserFacing => 0,
-            traits::Reveal::All => 1,
+            Self { reveal: traits::Reveal::UserFacing } => 0,
+            Self { reveal: traits::Reveal::All } => 1,
         }
     }
     #[inline]
     unsafe fn from_usize(ptr: usize) -> Self {
         match ptr {
-            0 => traits::Reveal::UserFacing,
-            1 => traits::Reveal::All,
+            0 => Self { reveal: traits::Reveal::UserFacing },
+            1 => Self { reveal: traits::Reveal::All },
             _ => std::hint::unreachable_unchecked(),
         }
     }
@@ -1282,7 +1287,7 @@ impl<'tcx> ParamEnv<'tcx> {
 
     #[inline]
     pub fn reveal(self) -> traits::Reveal {
-        self.packed.tag()
+        self.packed.tag().reveal
     }
 
     /// Construct a trait environment with no where-clauses in scope
@@ -1300,11 +1305,11 @@ impl<'tcx> ParamEnv<'tcx> {
     /// Construct a trait environment with the given set of predicates.
     #[inline]
     pub fn new(caller_bounds: &'tcx List<Predicate<'tcx>>, reveal: Reveal) -> Self {
-        ty::ParamEnv { packed: CopyTaggedPtr::new(caller_bounds, reveal) }
+        ty::ParamEnv { packed: CopyTaggedPtr::new(caller_bounds, ParamTag { reveal }) }
     }
 
     pub fn with_user_facing(mut self) -> Self {
-        self.packed.set_tag(Reveal::UserFacing);
+        self.packed.set_tag(ParamTag { reveal: Reveal::UserFacing, ..self.packed.tag() });
         self
     }
 
@@ -1318,7 +1323,7 @@ impl<'tcx> ParamEnv<'tcx> {
     /// will be normalized to their underlying types.
     /// See PR #65989 and issue #65918 for more details
     pub fn with_reveal_all_normalized(self, tcx: TyCtxt<'tcx>) -> Self {
-        if self.packed.tag() == traits::Reveal::All {
+        if self.packed.tag().reveal == traits::Reveal::All {
             return self;
         }
 

From 8e84aa921d18365f81bc9004026ae66f3e5f16ce Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Oct 2021 14:56:00 +0000
Subject: [PATCH 02/12] Add constness to ParamEnv

This now causes a lot of queries to be executed twice, as reveal_all forces NotConst
---
 compiler/rustc_middle/src/hir/map/mod.rs      | 25 ++++++---
 compiler/rustc_middle/src/ty/mod.rs           | 51 ++++++++++++++-----
 .../rustc_middle/src/ty/structural_impls.rs   |  2 +-
 .../src/traits/auto_trait.rs                  |  7 ++-
 .../rustc_trait_selection/src/traits/mod.rs   | 20 ++++++--
 .../src/traits/object_safety.rs               |  6 ++-
 compiler/rustc_ty_utils/src/ty.rs             | 36 +++++++++----
 .../rustc_typeck/src/check/compare_method.rs  | 20 ++++++--
 8 files changed, 126 insertions(+), 41 deletions(-)

diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index fad7e875fa1c0..90e8a98b5e398 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -446,18 +446,30 @@ impl<'hir> Map<'hir> {
     ///
     /// Panics if `LocalDefId` does not have an associated body.
     pub fn body_owner_kind(&self, id: HirId) -> BodyOwnerKind {
+        match self.opt_body_owner_kind(id) {
+            Ok(kind) => kind,
+            Err(node) => bug!("{:#?} is not a body node", node),
+        }
+    }
+
+    /// Returns the `BodyOwnerKind` of this `LocalDefId`.
+    ///
+    /// Returns the `Node` if `LocalDefId` does not have an associated body.
+    pub fn opt_body_owner_kind(&self, id: HirId) -> Result<BodyOwnerKind, Node<'_>> {
         match self.get(id) {
             Node::Item(&Item { kind: ItemKind::Const(..), .. })
             | Node::TraitItem(&TraitItem { kind: TraitItemKind::Const(..), .. })
             | Node::ImplItem(&ImplItem { kind: ImplItemKind::Const(..), .. })
-            | Node::AnonConst(_) => BodyOwnerKind::Const,
+            | Node::AnonConst(_) => Ok(BodyOwnerKind::Const),
             Node::Ctor(..)
             | Node::Item(&Item { kind: ItemKind::Fn(..), .. })
             | Node::TraitItem(&TraitItem { kind: TraitItemKind::Fn(..), .. })
-            | Node::ImplItem(&ImplItem { kind: ImplItemKind::Fn(..), .. }) => BodyOwnerKind::Fn,
-            Node::Item(&Item { kind: ItemKind::Static(_, m, _), .. }) => BodyOwnerKind::Static(m),
-            Node::Expr(&Expr { kind: ExprKind::Closure(..), .. }) => BodyOwnerKind::Closure,
-            node => bug!("{:#?} is not a body node", node),
+            | Node::ImplItem(&ImplItem { kind: ImplItemKind::Fn(..), .. }) => Ok(BodyOwnerKind::Fn),
+            Node::Item(&Item { kind: ItemKind::Static(_, m, _), .. }) => {
+                Ok(BodyOwnerKind::Static(m))
+            }
+            Node::Expr(&Expr { kind: ExprKind::Closure(..), .. }) => Ok(BodyOwnerKind::Closure),
+            node => Err(node),
         }
     }
 
@@ -466,7 +478,8 @@ impl<'hir> Map<'hir> {
     /// Panics if `LocalDefId` does not have an associated body.
     ///
     /// This should only be used for determining the context of a body, a return
-    /// value of `Some` does not always suggest that the owner of the body is `const`.
+    /// value of `Some` does not always suggest that the owner of the body is `const`,
+    /// just that it has to be checked as if it were.
     pub fn body_const_context(&self, did: LocalDefId) -> Option<ConstContext> {
         let hir_id = self.local_def_id_to_hir_id(did);
         let ccx = match self.body_owner_kind(hir_id) {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index f799465107348..a76cb4c4c528c 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1222,22 +1222,27 @@ pub struct ParamEnv<'tcx> {
 #[derive(Copy, Clone)]
 struct ParamTag {
     reveal: traits::Reveal,
+    constness: hir::Constness,
 }
 
 unsafe impl rustc_data_structures::tagged_ptr::Tag for ParamTag {
-    const BITS: usize = 1;
+    const BITS: usize = 2;
     #[inline]
     fn into_usize(self) -> usize {
         match self {
-            Self { reveal: traits::Reveal::UserFacing } => 0,
-            Self { reveal: traits::Reveal::All } => 1,
+            Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::NotConst } => 0,
+            Self { reveal: traits::Reveal::All, constness: hir::Constness::NotConst } => 1,
+            Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::Const } => 2,
+            Self { reveal: traits::Reveal::All, constness: hir::Constness::Const } => 3,
         }
     }
     #[inline]
     unsafe fn from_usize(ptr: usize) -> Self {
         match ptr {
-            0 => Self { reveal: traits::Reveal::UserFacing },
-            1 => Self { reveal: traits::Reveal::All },
+            0 => Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::NotConst },
+            1 => Self { reveal: traits::Reveal::All, constness: hir::Constness::NotConst },
+            2 => Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::Const },
+            3 => Self { reveal: traits::Reveal::All, constness: hir::Constness::Const },
             _ => std::hint::unreachable_unchecked(),
         }
     }
@@ -1248,6 +1253,7 @@ impl<'tcx> fmt::Debug for ParamEnv<'tcx> {
         f.debug_struct("ParamEnv")
             .field("caller_bounds", &self.caller_bounds())
             .field("reveal", &self.reveal())
+            .field("constness", &self.constness())
             .finish()
     }
 }
@@ -1256,17 +1262,23 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for ParamEnv<'tcx> {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         self.caller_bounds().hash_stable(hcx, hasher);
         self.reveal().hash_stable(hcx, hasher);
+        self.constness().hash_stable(hcx, hasher);
     }
 }
 
 impl<'tcx> TypeFoldable<'tcx> for ParamEnv<'tcx> {
     fn super_fold_with<F: ty::fold::TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
-        ParamEnv::new(self.caller_bounds().fold_with(folder), self.reveal().fold_with(folder))
+        ParamEnv::new(
+            self.caller_bounds().fold_with(folder),
+            self.reveal().fold_with(folder),
+            self.constness().fold_with(folder),
+        )
     }
 
     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.caller_bounds().visit_with(visitor)?;
-        self.reveal().visit_with(visitor)
+        self.reveal().visit_with(visitor)?;
+        self.constness().visit_with(visitor)
     }
 }
 
@@ -1277,7 +1289,7 @@ impl<'tcx> ParamEnv<'tcx> {
     /// type-checking.
     #[inline]
     pub fn empty() -> Self {
-        Self::new(List::empty(), Reveal::UserFacing)
+        Self::new(List::empty(), Reveal::UserFacing, hir::Constness::NotConst)
     }
 
     #[inline]
@@ -1290,6 +1302,11 @@ impl<'tcx> ParamEnv<'tcx> {
         self.packed.tag().reveal
     }
 
+    #[inline]
+    pub fn constness(self) -> hir::Constness {
+        self.packed.tag().constness
+    }
+
     /// Construct a trait environment with no where-clauses in scope
     /// where the values of all `impl Trait` and other hidden types
     /// are revealed. This is suitable for monomorphized, post-typeck
@@ -1299,13 +1316,17 @@ impl<'tcx> ParamEnv<'tcx> {
     /// or invoke `param_env.with_reveal_all()`.
     #[inline]
     pub fn reveal_all() -> Self {
-        Self::new(List::empty(), Reveal::All)
+        Self::new(List::empty(), Reveal::All, hir::Constness::NotConst)
     }
 
     /// Construct a trait environment with the given set of predicates.
     #[inline]
-    pub fn new(caller_bounds: &'tcx List<Predicate<'tcx>>, reveal: Reveal) -> Self {
-        ty::ParamEnv { packed: CopyTaggedPtr::new(caller_bounds, ParamTag { reveal }) }
+    pub fn new(
+        caller_bounds: &'tcx List<Predicate<'tcx>>,
+        reveal: Reveal,
+        constness: hir::Constness,
+    ) -> Self {
+        ty::ParamEnv { packed: CopyTaggedPtr::new(caller_bounds, ParamTag { reveal, constness }) }
     }
 
     pub fn with_user_facing(mut self) -> Self {
@@ -1327,13 +1348,17 @@ impl<'tcx> ParamEnv<'tcx> {
             return self;
         }
 
-        ParamEnv::new(tcx.normalize_opaque_types(self.caller_bounds()), Reveal::All)
+        ParamEnv::new(
+            tcx.normalize_opaque_types(self.caller_bounds()),
+            Reveal::All,
+            self.constness(),
+        )
     }
 
     /// Returns this same environment but with no caller bounds.
     #[inline]
     pub fn without_caller_bounds(self) -> Self {
-        Self::new(List::empty(), self.reveal())
+        Self::new(List::empty(), self.reveal(), self.constness())
     }
 
     /// Creates a suitable environment in which to perform trait
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index d6069395474ab..4b7f142905096 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -480,7 +480,7 @@ impl<'a, 'tcx> Lift<'tcx> for ty::ParamEnv<'a> {
     type Lifted = ty::ParamEnv<'tcx>;
     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
         tcx.lift(self.caller_bounds())
-            .map(|caller_bounds| ty::ParamEnv::new(caller_bounds, self.reveal()))
+            .map(|caller_bounds| ty::ParamEnv::new(caller_bounds, self.reveal(), self.constness()))
     }
 }
 
diff --git a/compiler/rustc_trait_selection/src/traits/auto_trait.rs b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
index 6452b520452d6..8f6dd717249f7 100644
--- a/compiler/rustc_trait_selection/src/traits/auto_trait.rs
+++ b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
@@ -368,12 +368,17 @@ impl AutoTraitFinder<'tcx> {
                 computed_preds.clone().chain(user_computed_preds.iter().cloned()),
             )
             .map(|o| o.predicate);
-            new_env = ty::ParamEnv::new(tcx.mk_predicates(normalized_preds), param_env.reveal());
+            new_env = ty::ParamEnv::new(
+                tcx.mk_predicates(normalized_preds),
+                param_env.reveal(),
+                param_env.constness(),
+            );
         }
 
         let final_user_env = ty::ParamEnv::new(
             tcx.mk_predicates(user_computed_preds.into_iter()),
             user_env.reveal(),
+            user_env.constness(),
         );
         debug!(
             "evaluate_nested_obligations(ty={:?}, trait_did={:?}): succeeded with '{:?}' \
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 428873b8d3dda..65dd0e7f537f2 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -310,8 +310,11 @@ pub fn normalize_param_env_or_error<'tcx>(
 
     debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
 
-    let elaborated_env =
-        ty::ParamEnv::new(tcx.intern_predicates(&predicates), unnormalized_env.reveal());
+    let elaborated_env = ty::ParamEnv::new(
+        tcx.intern_predicates(&predicates),
+        unnormalized_env.reveal(),
+        unnormalized_env.constness(),
+    );
 
     // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
     // normalization expects its param-env to be already normalized, which means we have
@@ -363,8 +366,11 @@ pub fn normalize_param_env_or_error<'tcx>(
     // predicates here anyway. Keeping them here anyway because it seems safer.
     let outlives_env: Vec<_> =
         non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
-    let outlives_env =
-        ty::ParamEnv::new(tcx.intern_predicates(&outlives_env), unnormalized_env.reveal());
+    let outlives_env = ty::ParamEnv::new(
+        tcx.intern_predicates(&outlives_env),
+        unnormalized_env.reveal(),
+        unnormalized_env.constness(),
+    );
     let outlives_predicates = match do_normalize_predicates(
         tcx,
         region_context,
@@ -384,7 +390,11 @@ pub fn normalize_param_env_or_error<'tcx>(
     let mut predicates = non_outlives_predicates;
     predicates.extend(outlives_predicates);
     debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
-    ty::ParamEnv::new(tcx.intern_predicates(&predicates), unnormalized_env.reveal())
+    ty::ParamEnv::new(
+        tcx.intern_predicates(&predicates),
+        unnormalized_env.reveal(),
+        unnormalized_env.constness(),
+    )
 }
 
 pub fn fully_normalize<'a, 'tcx, T>(
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index afc546540d2e2..616efffd999ec 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -698,7 +698,11 @@ fn receiver_is_dispatchable<'tcx>(
             .chain(array::IntoIter::new([unsize_predicate, trait_predicate]))
             .collect();
 
-        ty::ParamEnv::new(tcx.intern_predicates(&caller_bounds), param_env.reveal())
+        ty::ParamEnv::new(
+            tcx.intern_predicates(&caller_bounds),
+            param_env.reveal(),
+            param_env.constness(),
+        )
     };
 
     // Receiver: DispatchFromDyn<Receiver[Self => U]>
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index bc77c94809eb5..dbac232753e3d 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -274,15 +274,33 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
         predicates.extend(environment);
     }
 
-    let unnormalized_env =
-        ty::ParamEnv::new(tcx.intern_predicates(&predicates), traits::Reveal::UserFacing);
-
-    let body_id = def_id
-        .as_local()
-        .map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
-        .map_or(hir::CRATE_HIR_ID, |id| {
-            tcx.hir().maybe_body_owned_by(id).map_or(id, |body| body.hir_id)
-        });
+    let local_did = def_id.as_local();
+    let hir_id = local_did.map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
+
+    let constness = match hir_id {
+        Some(hir_id) => match tcx.hir().opt_body_owner_kind(hir_id) {
+            Err(hir::Node::Item(&hir::Item {
+                kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
+                ..
+            })) => constness,
+            Err(_) => hir::Constness::NotConst,
+            Ok(_) => match tcx.hir().body_const_context(local_did.unwrap()) {
+                Some(_) => hir::Constness::Const,
+                None => hir::Constness::NotConst,
+            },
+        },
+        None => hir::Constness::NotConst,
+    };
+
+    let unnormalized_env = ty::ParamEnv::new(
+        tcx.intern_predicates(&predicates),
+        traits::Reveal::UserFacing,
+        constness,
+    );
+
+    let body_id = hir_id.map_or(hir::CRATE_HIR_ID, |id| {
+        tcx.hir().maybe_body_owned_by(id).map_or(id, |body| body.hir_id)
+    });
     let cause = traits::ObligationCause::misc(tcx.def_span(def_id), body_id);
     traits::normalize_param_env_or_error(tcx, def_id, unnormalized_env, cause)
 }
diff --git a/compiler/rustc_typeck/src/check/compare_method.rs b/compiler/rustc_typeck/src/check/compare_method.rs
index d5b631df058ae..f3d5d87353fb8 100644
--- a/compiler/rustc_typeck/src/check/compare_method.rs
+++ b/compiler/rustc_typeck/src/check/compare_method.rs
@@ -209,8 +209,11 @@ fn compare_predicate_entailment<'tcx>(
     // The key step here is to update the caller_bounds's predicates to be
     // the new hybrid bounds we computed.
     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
-    let param_env =
-        ty::ParamEnv::new(tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing);
+    let param_env = ty::ParamEnv::new(
+        tcx.intern_predicates(&hybrid_preds.predicates),
+        Reveal::UserFacing,
+        hir::Constness::NotConst,
+    );
     let param_env = traits::normalize_param_env_or_error(
         tcx,
         impl_m.def_id,
@@ -1183,8 +1186,11 @@ fn compare_type_predicate_entailment<'tcx>(
     debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
 
     let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
-    let param_env =
-        ty::ParamEnv::new(tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing);
+    let param_env = ty::ParamEnv::new(
+        tcx.intern_predicates(&hybrid_preds.predicates),
+        Reveal::UserFacing,
+        hir::Constness::NotConst,
+    );
     let param_env = traits::normalize_param_env_or_error(
         tcx,
         impl_ty.def_id,
@@ -1368,7 +1374,11 @@ pub fn check_type_bounds<'tcx>(
                 .to_predicate(tcx),
             ),
         };
-        ty::ParamEnv::new(tcx.intern_predicates(&predicates), Reveal::UserFacing)
+        ty::ParamEnv::new(
+            tcx.intern_predicates(&predicates),
+            Reveal::UserFacing,
+            param_env.constness(),
+        )
     };
     debug!(?normalize_param_env);
 

From 8c0edcafab274cea701d69acb6260f832a3fa775 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Oct 2021 15:24:29 +0000
Subject: [PATCH 03/12] Static items are also const

---
 compiler/rustc_hir/src/hir.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 6f25715fbecc4..ac3575e769eec 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -3242,6 +3242,7 @@ impl<'hir> Node<'hir> {
             | Node::Item(Item { kind: ItemKind::Impl(Impl { constness, .. }), .. }) => *constness,
 
             Node::Item(Item { kind: ItemKind::Const(..), .. })
+            | Node::Item(Item { kind: ItemKind::Static(..), .. })
             | Node::TraitItem(TraitItem { kind: TraitItemKind::Const(..), .. })
             | Node::ImplItem(ImplItem { kind: ImplItemKind::Const(..), .. }) => Constness::Const,
 

From ffd46d000431d19f1f6ff9ad2966e6db6382dcb7 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Oct 2021 15:28:26 +0000
Subject: [PATCH 04/12] Re-use `constness_for_typeck` instead of rolling it
 ourselves

---
 compiler/rustc_middle/src/hir/map/mod.rs | 22 +++++-----------------
 compiler/rustc_ty_utils/src/ty.rs        | 12 +-----------
 2 files changed, 6 insertions(+), 28 deletions(-)

diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 90e8a98b5e398..ca1b5466126b9 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -446,30 +446,18 @@ impl<'hir> Map<'hir> {
     ///
     /// Panics if `LocalDefId` does not have an associated body.
     pub fn body_owner_kind(&self, id: HirId) -> BodyOwnerKind {
-        match self.opt_body_owner_kind(id) {
-            Ok(kind) => kind,
-            Err(node) => bug!("{:#?} is not a body node", node),
-        }
-    }
-
-    /// Returns the `BodyOwnerKind` of this `LocalDefId`.
-    ///
-    /// Returns the `Node` if `LocalDefId` does not have an associated body.
-    pub fn opt_body_owner_kind(&self, id: HirId) -> Result<BodyOwnerKind, Node<'_>> {
         match self.get(id) {
             Node::Item(&Item { kind: ItemKind::Const(..), .. })
             | Node::TraitItem(&TraitItem { kind: TraitItemKind::Const(..), .. })
             | Node::ImplItem(&ImplItem { kind: ImplItemKind::Const(..), .. })
-            | Node::AnonConst(_) => Ok(BodyOwnerKind::Const),
+            | Node::AnonConst(_) => BodyOwnerKind::Const,
             Node::Ctor(..)
             | Node::Item(&Item { kind: ItemKind::Fn(..), .. })
             | Node::TraitItem(&TraitItem { kind: TraitItemKind::Fn(..), .. })
-            | Node::ImplItem(&ImplItem { kind: ImplItemKind::Fn(..), .. }) => Ok(BodyOwnerKind::Fn),
-            Node::Item(&Item { kind: ItemKind::Static(_, m, _), .. }) => {
-                Ok(BodyOwnerKind::Static(m))
-            }
-            Node::Expr(&Expr { kind: ExprKind::Closure(..), .. }) => Ok(BodyOwnerKind::Closure),
-            node => Err(node),
+            | Node::ImplItem(&ImplItem { kind: ImplItemKind::Fn(..), .. }) => BodyOwnerKind::Fn,
+            Node::Item(&Item { kind: ItemKind::Static(_, m, _), .. }) => BodyOwnerKind::Static(m),
+            Node::Expr(&Expr { kind: ExprKind::Closure(..), .. }) => BodyOwnerKind::Closure,
+            node => bug!("{:#?} is not a body node", node),
         }
     }
 
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index dbac232753e3d..aa766344860a5 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -278,17 +278,7 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
     let hir_id = local_did.map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
 
     let constness = match hir_id {
-        Some(hir_id) => match tcx.hir().opt_body_owner_kind(hir_id) {
-            Err(hir::Node::Item(&hir::Item {
-                kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
-                ..
-            })) => constness,
-            Err(_) => hir::Constness::NotConst,
-            Ok(_) => match tcx.hir().body_const_context(local_did.unwrap()) {
-                Some(_) => hir::Constness::Const,
-                None => hir::Constness::NotConst,
-            },
-        },
+        Some(hir_id) => tcx.hir().get(hir_id).constness_for_typeck(),
         None => hir::Constness::NotConst,
     };
 

From fce93cb7cb915833e1bac643ba3668cb9cfb94dd Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 25 Oct 2021 12:48:58 +0000
Subject: [PATCH 05/12] Fixup add const to param env

---
 src/test/ui/infinite/infinite-struct.stderr             | 2 +-
 src/test/ui/infinite/infinite-tag-type-recursion.stderr | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/test/ui/infinite/infinite-struct.stderr b/src/test/ui/infinite/infinite-struct.stderr
index 369645f9030fb..383e13fd4b09d 100644
--- a/src/test/ui/infinite/infinite-struct.stderr
+++ b/src/test/ui/infinite/infinite-struct.stderr
@@ -19,7 +19,7 @@ LL | struct Take(Take);
    | ^^^^^^^^^^^^^^^^^^
    |
    = note: ...which immediately requires computing drop-check constraints for `Take` again
-   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: Take } }`
+   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing, constness: NotConst }, value: Take } }`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/infinite/infinite-tag-type-recursion.stderr b/src/test/ui/infinite/infinite-tag-type-recursion.stderr
index 61b5e94677526..1802c7599a3b5 100644
--- a/src/test/ui/infinite/infinite-tag-type-recursion.stderr
+++ b/src/test/ui/infinite/infinite-tag-type-recursion.stderr
@@ -18,7 +18,7 @@ LL | enum MList { Cons(isize, MList), Nil }
    | ^^^^^^^^^^
    |
    = note: ...which immediately requires computing drop-check constraints for `MList` again
-   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: MList } }`
+   = note: cycle used when computing dropck types for `Canonical { max_universe: U0, variables: [], value: ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing, constness: NotConst }, value: MList } }`
 
 error: aborting due to 2 previous errors
 

From 3193cf7ce2741969a8580ed6d4bfbd53f0b4b049 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Oct 2021 16:07:37 +0000
Subject: [PATCH 06/12] Use the constness from the param env instead of having
 a separate dimension for it

This breaks a ~const test that will be fixed in a follow up commit of this PR
---
 .../src/transform/check_consts/check.rs       |  3 +-
 .../src/transform/check_consts/qualifs.rs     |  3 +-
 compiler/rustc_infer/src/traits/engine.rs     | 18 --------
 compiler/rustc_infer/src/traits/mod.rs        | 10 +++++
 .../src/traits/fulfill.rs                     | 40 +-----------------
 .../src/traits/select/candidate_assembly.rs   |  2 +-
 .../src/traits/select/mod.rs                  | 41 +------------------
 .../rustc_typeck/src/check/compare_method.rs  | 12 +-----
 .../rustc_typeck/src/check/fn_ctxt/_impl.rs   | 11 +----
 compiler/rustc_typeck/src/check/inherited.rs  | 14 -------
 .../rfc-2632-const-trait-impl/assoc-type.rs   |  4 +-
 .../assoc-type.stderr                         | 20 ---------
 12 files changed, 23 insertions(+), 155 deletions(-)
 delete mode 100644 src/test/ui/rfc-2632-const-trait-impl/assoc-type.stderr

diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index 85f37c813d85d..05ce442dc3c11 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -859,8 +859,7 @@ impl Visitor<'tcx> for Checker<'mir, 'tcx> {
                     );
 
                     let implsrc = tcx.infer_ctxt().enter(|infcx| {
-                        let mut selcx =
-                            SelectionContext::with_constness(&infcx, hir::Constness::Const);
+                        let mut selcx = SelectionContext::new(&infcx);
                         selcx.select(&obligation)
                     });
 
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
index aa42f8936f32c..5acf94dbcbad4 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
@@ -3,7 +3,6 @@
 //! See the `Qualif` trait for more info.
 
 use rustc_errors::ErrorReported;
-use rustc_hir as hir;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, subst::SubstsRef, AdtDef, Ty};
@@ -167,7 +166,7 @@ impl Qualif for NeedsNonConstDrop {
         );
 
         let implsrc = cx.tcx.infer_ctxt().enter(|infcx| {
-            let mut selcx = SelectionContext::with_constness(&infcx, hir::Constness::Const);
+            let mut selcx = SelectionContext::new(&infcx);
             selcx.select(&obligation)
         });
         match implsrc {
diff --git a/compiler/rustc_infer/src/traits/engine.rs b/compiler/rustc_infer/src/traits/engine.rs
index dce4a87b04118..5f9a66ea10845 100644
--- a/compiler/rustc_infer/src/traits/engine.rs
+++ b/compiler/rustc_infer/src/traits/engine.rs
@@ -1,7 +1,6 @@
 use crate::infer::InferCtxt;
 use crate::traits::Obligation;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, ToPredicate, Ty, WithConstness};
 
@@ -51,28 +50,11 @@ pub trait TraitEngine<'tcx>: 'tcx {
         infcx: &InferCtxt<'_, 'tcx>,
     ) -> Result<(), Vec<FulfillmentError<'tcx>>>;
 
-    fn select_all_with_constness_or_error(
-        &mut self,
-        infcx: &InferCtxt<'_, 'tcx>,
-        _constness: hir::Constness,
-    ) -> Result<(), Vec<FulfillmentError<'tcx>>> {
-        self.select_all_or_error(infcx)
-    }
-
     fn select_where_possible(
         &mut self,
         infcx: &InferCtxt<'_, 'tcx>,
     ) -> Result<(), Vec<FulfillmentError<'tcx>>>;
 
-    // FIXME(fee1-dead) this should not provide a default body for chalk as chalk should be updated
-    fn select_with_constness_where_possible(
-        &mut self,
-        infcx: &InferCtxt<'_, 'tcx>,
-        _constness: hir::Constness,
-    ) -> Result<(), Vec<FulfillmentError<'tcx>>> {
-        self.select_where_possible(infcx)
-    }
-
     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>>;
 
     fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships>;
diff --git a/compiler/rustc_infer/src/traits/mod.rs b/compiler/rustc_infer/src/traits/mod.rs
index e8622b3c819d2..7e30f859dae4e 100644
--- a/compiler/rustc_infer/src/traits/mod.rs
+++ b/compiler/rustc_infer/src/traits/mod.rs
@@ -69,6 +69,16 @@ impl PredicateObligation<'tcx> {
     }
 }
 
+impl TraitObligation<'tcx> {
+    /// Returns `true` if the trait predicate is considered `const` in its ParamEnv.
+    pub fn is_const(&self) -> bool {
+        match (self.predicate.skip_binder().constness, self.param_env.constness()) {
+            (ty::BoundConstness::ConstIfConst, hir::Constness::Const) => true,
+            _ => false,
+        }
+    }
+}
+
 // `PredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 static_assert_size!(PredicateObligation<'_>, 32);
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 465d1465d5d35..241df9cc132b1 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -4,7 +4,6 @@ use rustc_data_structures::obligation_forest::ProcessResult;
 use rustc_data_structures::obligation_forest::{Error, ForestObligation, Outcome};
 use rustc_data_structures::obligation_forest::{ObligationForest, ObligationProcessor};
 use rustc_errors::ErrorReported;
-use rustc_hir as hir;
 use rustc_infer::traits::{SelectionError, TraitEngine, TraitEngineExt as _, TraitObligation};
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::thir::abstract_const::NotConstEvaluatable;
@@ -238,22 +237,6 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
         if errors.is_empty() { Ok(()) } else { Err(errors) }
     }
 
-    fn select_all_with_constness_or_error(
-        &mut self,
-        infcx: &InferCtxt<'_, 'tcx>,
-        constness: rustc_hir::Constness,
-    ) -> Result<(), Vec<FulfillmentError<'tcx>>> {
-        self.select_with_constness_where_possible(infcx, constness)?;
-
-        let errors: Vec<_> = self
-            .predicates
-            .to_errors(CodeAmbiguity)
-            .into_iter()
-            .map(to_fulfillment_error)
-            .collect();
-        if errors.is_empty() { Ok(()) } else { Err(errors) }
-    }
-
     fn select_where_possible(
         &mut self,
         infcx: &InferCtxt<'_, 'tcx>,
@@ -262,15 +245,6 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
         self.select(&mut selcx)
     }
 
-    fn select_with_constness_where_possible(
-        &mut self,
-        infcx: &InferCtxt<'_, 'tcx>,
-        constness: hir::Constness,
-    ) -> Result<(), Vec<FulfillmentError<'tcx>>> {
-        let mut selcx = SelectionContext::with_constness(infcx, constness);
-        self.select(&mut selcx)
-    }
-
     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
         self.predicates.map_pending_obligations(|o| o.obligation.clone())
     }
@@ -687,12 +661,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
         if obligation.predicate.is_known_global() {
             // no type variables present, can use evaluation for better caching.
             // FIXME: consider caching errors too.
-            //
-            // If the predicate is considered const, then we cannot use this because
-            // it will cause false negatives in the ui tests.
-            if !self.selcx.is_predicate_const(obligation.predicate)
-                && infcx.predicate_must_hold_considering_regions(obligation)
-            {
+            if infcx.predicate_must_hold_considering_regions(obligation) {
                 debug!(
                     "selecting trait at depth {} evaluated to holds",
                     obligation.recursion_depth
@@ -746,12 +715,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
         if obligation.predicate.is_global(tcx) {
             // no type variables present, can use evaluation for better caching.
             // FIXME: consider caching errors too.
-            //
-            // If the predicate is considered const, then we cannot use this because
-            // it will cause false negatives in the ui tests.
-            if !self.selcx.is_predicate_const(obligation.predicate)
-                && self.selcx.infcx().predicate_must_hold_considering_regions(obligation)
-            {
+            if self.selcx.infcx().predicate_must_hold_considering_regions(obligation) {
                 return ProcessResult::Changed(vec![]);
             } else {
                 tracing::debug!("Does NOT hold: {:?}", obligation);
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index 1d0c54f86dea8..dc81542fd6746 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -303,7 +303,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             } else if lang_items.drop_trait() == Some(def_id)
                 && obligation.predicate.skip_binder().constness == ty::BoundConstness::ConstIfConst
             {
-                if self.is_in_const_context {
+                if obligation.param_env.constness() == hir::Constness::Const {
                     self.assemble_const_drop_candidates(obligation, &mut candidates)?;
                 } else {
                     debug!("passing ~const Drop bound; in non-const context");
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 1b26e38fe0e4d..43ee67cbf7e0e 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -128,9 +128,6 @@ pub struct SelectionContext<'cx, 'tcx> {
     /// and a negative impl
     allow_negative_impls: bool,
 
-    /// Are we in a const context that needs `~const` bounds to be const?
-    is_in_const_context: bool,
-
     /// The mode that trait queries run in, which informs our error handling
     /// policy. In essence, canonicalized queries need their errors propagated
     /// rather than immediately reported because we do not have accurate spans.
@@ -222,7 +219,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             intercrate: false,
             intercrate_ambiguity_causes: None,
             allow_negative_impls: false,
-            is_in_const_context: false,
             query_mode: TraitQueryMode::Standard,
         }
     }
@@ -234,7 +230,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             intercrate: true,
             intercrate_ambiguity_causes: None,
             allow_negative_impls: false,
-            is_in_const_context: false,
             query_mode: TraitQueryMode::Standard,
         }
     }
@@ -250,7 +245,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             intercrate: false,
             intercrate_ambiguity_causes: None,
             allow_negative_impls,
-            is_in_const_context: false,
             query_mode: TraitQueryMode::Standard,
         }
     }
@@ -266,26 +260,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             intercrate: false,
             intercrate_ambiguity_causes: None,
             allow_negative_impls: false,
-            is_in_const_context: false,
             query_mode,
         }
     }
 
-    pub fn with_constness(
-        infcx: &'cx InferCtxt<'cx, 'tcx>,
-        constness: hir::Constness,
-    ) -> SelectionContext<'cx, 'tcx> {
-        SelectionContext {
-            infcx,
-            freshener: infcx.freshener_keep_static(),
-            intercrate: false,
-            intercrate_ambiguity_causes: None,
-            allow_negative_impls: false,
-            is_in_const_context: matches!(constness, hir::Constness::Const),
-            query_mode: TraitQueryMode::Standard,
-        }
-    }
-
     /// Enables tracking of intercrate ambiguity causes. These are
     /// used in coherence to give improved diagnostics. We don't do
     /// this until we detect a coherence error because it can lead to
@@ -318,23 +296,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         self.intercrate
     }
 
-    /// Returns `true` if the trait predicate is considerd `const` to this selection context.
-    pub fn is_trait_predicate_const(&self, pred: ty::TraitPredicate<'_>) -> bool {
-        match pred.constness {
-            ty::BoundConstness::ConstIfConst if self.is_in_const_context => true,
-            _ => false,
-        }
-    }
-
-    /// Returns `true` if the predicate is considered `const` to
-    /// this selection context.
-    pub fn is_predicate_const(&self, pred: ty::Predicate<'_>) -> bool {
-        match pred.kind().skip_binder() {
-            ty::PredicateKind::Trait(pred) => self.is_trait_predicate_const(pred),
-            _ => false,
-        }
-    }
-
     ///////////////////////////////////////////////////////////////////////////
     // Selection
     //
@@ -1141,7 +1102,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         for candidate in candidates {
             // Respect const trait obligations
-            if self.is_trait_predicate_const(obligation.predicate.skip_binder()) {
+            if obligation.is_const() {
                 match candidate {
                     // const impl
                     ImplCandidate(def_id)
diff --git a/compiler/rustc_typeck/src/check/compare_method.rs b/compiler/rustc_typeck/src/check/compare_method.rs
index f3d5d87353fb8..15bf18ce670a1 100644
--- a/compiler/rustc_typeck/src/check/compare_method.rs
+++ b/compiler/rustc_typeck/src/check/compare_method.rs
@@ -1387,13 +1387,7 @@ pub fn check_type_bounds<'tcx>(
         impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
 
     tcx.infer_ctxt().enter(move |infcx| {
-        let constness = impl_ty
-            .container
-            .impl_def_id()
-            .map(|did| tcx.impl_constness(did))
-            .unwrap_or(hir::Constness::NotConst);
-
-        let inh = Inherited::with_constness(infcx, impl_ty.def_id.expect_local(), constness);
+        let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
         let infcx = &inh.infcx;
         let mut selcx = traits::SelectionContext::new(&infcx);
 
@@ -1436,9 +1430,7 @@ pub fn check_type_bounds<'tcx>(
 
         // Check that all obligations are satisfied by the implementation's
         // version.
-        if let Err(ref errors) =
-            inh.fulfillment_cx.borrow_mut().select_all_with_constness_or_error(&infcx, constness)
-        {
+        if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
             infcx.report_fulfillment_errors(errors, None, false);
             return Err(ErrorReported);
         }
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
index 41e43321a8f0a..8cac6d5eef8c4 100644
--- a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
@@ -643,11 +643,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     #[instrument(skip(self), level = "debug")]
     pub(in super::super) fn select_all_obligations_or_error(&self) {
-        if let Err(errors) = self
-            .fulfillment_cx
-            .borrow_mut()
-            .select_all_with_constness_or_error(&self, self.inh.constness)
-        {
+        if let Err(errors) = self.fulfillment_cx.borrow_mut().select_all_or_error(&self) {
             self.report_fulfillment_errors(&errors, self.inh.body_id, false);
         }
     }
@@ -658,10 +654,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         fallback_has_occurred: bool,
         mutate_fulfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
     ) {
-        let result = self
-            .fulfillment_cx
-            .borrow_mut()
-            .select_with_constness_where_possible(self, self.inh.constness);
+        let result = self.fulfillment_cx.borrow_mut().select_where_possible(self);
         if let Err(mut errors) = result {
             mutate_fulfillment_errors(&mut errors);
             self.report_fulfillment_errors(&errors, self.inh.body_id, fallback_has_occurred);
diff --git a/compiler/rustc_typeck/src/check/inherited.rs b/compiler/rustc_typeck/src/check/inherited.rs
index f7552c1f4eb0c..bf52e77504331 100644
--- a/compiler/rustc_typeck/src/check/inherited.rs
+++ b/compiler/rustc_typeck/src/check/inherited.rs
@@ -53,9 +53,6 @@ pub struct Inherited<'a, 'tcx> {
     pub(super) deferred_generator_interiors:
         RefCell<Vec<(hir::BodyId, Ty<'tcx>, hir::GeneratorKind)>>,
 
-    /// Reports whether this is in a const context.
-    pub(super) constness: hir::Constness,
-
     pub(super) body_id: Option<hir::BodyId>,
 
     /// Whenever we introduce an adjustment from `!` into a type variable,
@@ -102,16 +99,6 @@ impl<'tcx> InheritedBuilder<'tcx> {
 
 impl Inherited<'a, 'tcx> {
     pub(super) fn new(infcx: InferCtxt<'a, 'tcx>, def_id: LocalDefId) -> Self {
-        let tcx = infcx.tcx;
-        let item_id = tcx.hir().local_def_id_to_hir_id(def_id);
-        Self::with_constness(infcx, def_id, tcx.hir().get(item_id).constness_for_typeck())
-    }
-
-    pub(super) fn with_constness(
-        infcx: InferCtxt<'a, 'tcx>,
-        def_id: LocalDefId,
-        constness: hir::Constness,
-    ) -> Self {
         let tcx = infcx.tcx;
         let item_id = tcx.hir().local_def_id_to_hir_id(def_id);
         let body_id = tcx.hir().maybe_body_owned_by(item_id);
@@ -128,7 +115,6 @@ impl Inherited<'a, 'tcx> {
             deferred_cast_checks: RefCell::new(Vec::new()),
             deferred_generator_interiors: RefCell::new(Vec::new()),
             diverging_type_vars: RefCell::new(Default::default()),
-            constness,
             body_id,
         }
     }
diff --git a/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs b/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs
index 228b5ed71e80a..c65adc9178479 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs
@@ -1,6 +1,6 @@
 // FIXME(fee1-dead): this should have a better error message
 #![feature(const_trait_impl)]
-
+// check-pass
 struct NonConstAdd(i32);
 
 impl std::ops::Add for NonConstAdd {
@@ -29,3 +29,5 @@ impl const Baz for NonConstAdd {
 }
 
 fn main() {}
+
+// TODO: this test should not pass
\ No newline at end of file
diff --git a/src/test/ui/rfc-2632-const-trait-impl/assoc-type.stderr b/src/test/ui/rfc-2632-const-trait-impl/assoc-type.stderr
deleted file mode 100644
index b894092205e43..0000000000000
--- a/src/test/ui/rfc-2632-const-trait-impl/assoc-type.stderr
+++ /dev/null
@@ -1,20 +0,0 @@
-error[E0277]: cannot add `NonConstAdd` to `NonConstAdd`
-  --> $DIR/assoc-type.rs:19:5
-   |
-LL |     type Bar = NonConstAdd;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^ no implementation for `NonConstAdd + NonConstAdd`
-   |
-   = help: the trait `Add` is not implemented for `NonConstAdd`
-note: required by a bound in `Foo::Bar`
-  --> $DIR/assoc-type.rs:15:15
-   |
-LL |     type Bar: ~const std::ops::Add;
-   |               ^^^^^^^^^^^^^^^^^^^^ required by this bound in `Foo::Bar`
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
-   |
-LL | impl const Foo for NonConstAdd where NonConstAdd: Add {
-   |                                ++++++++++++++++++++++
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0277`.

From 104593fbe831b4ff02f419744096a623b317941a Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 25 Oct 2021 13:28:09 +0000
Subject: [PATCH 07/12] Fixup

---
 src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs b/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs
index c65adc9178479..321cea0d4154a 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/assoc-type.rs
@@ -17,7 +17,7 @@ trait Foo {
 
 impl const Foo for NonConstAdd {
     type Bar = NonConstAdd;
-    //~^ ERROR
+    //TODO: ~^ ERROR
 }
 
 trait Baz {
@@ -28,6 +28,4 @@ impl const Baz for NonConstAdd {
     type Qux = NonConstAdd; // OK
 }
 
-fn main() {}
-
-// TODO: this test should not pass
\ No newline at end of file
+fn main() {}
\ No newline at end of file

From cde1f6ae4b7e1b866c575a779ddb1431a1184b57 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Thu, 21 Oct 2021 18:12:19 +0000
Subject: [PATCH 08/12] Prefer TraitPredicate over ConstnessAnd<TraitRef>

---
 compiler/rustc_middle/src/traits/select.rs    |  2 +-
 .../src/traits/select/mod.rs                  | 33 +++++--------------
 2 files changed, 10 insertions(+), 25 deletions(-)

diff --git a/compiler/rustc_middle/src/traits/select.rs b/compiler/rustc_middle/src/traits/select.rs
index 560660517f34b..621bc0c5786c3 100644
--- a/compiler/rustc_middle/src/traits/select.rs
+++ b/compiler/rustc_middle/src/traits/select.rs
@@ -12,7 +12,7 @@ use rustc_hir::def_id::DefId;
 use rustc_query_system::cache::Cache;
 
 pub type SelectionCache<'tcx> = Cache<
-    (ty::ConstnessAnd<ty::ParamEnvAnd<'tcx, ty::TraitRef<'tcx>>>, ty::ImplPolarity),
+    ty::ParamEnvAnd<'tcx, ty::TraitPredicate<'tcx>>,
     SelectionResult<'tcx, SelectionCandidate<'tcx>>,
 >;
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 43ee67cbf7e0e..9fda75a2b8d5d 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1231,19 +1231,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             return None;
         }
         let tcx = self.tcx();
-        let pred = &cache_fresh_trait_pred.skip_binder();
-        let trait_ref = pred.trait_ref;
+        let pred = cache_fresh_trait_pred.skip_binder();
         if self.can_use_global_caches(param_env) {
-            if let Some(res) = tcx
-                .selection_cache
-                .get(&(param_env.and(trait_ref).with_constness(pred.constness), pred.polarity), tcx)
-            {
+            if let Some(res) = tcx.selection_cache.get(&param_env.and(pred), tcx) {
                 return Some(res);
             }
         }
-        self.infcx
-            .selection_cache
-            .get(&(param_env.and(trait_ref).with_constness(pred.constness), pred.polarity), tcx)
+        self.infcx.selection_cache.get(&param_env.and(pred), tcx)
     }
 
     /// Determines whether can we safely cache the result
@@ -1288,36 +1282,27 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     ) {
         let tcx = self.tcx();
         let pred = cache_fresh_trait_pred.skip_binder();
-        let trait_ref = pred.trait_ref;
 
         if !self.can_cache_candidate(&candidate) {
-            debug!(?trait_ref, ?candidate, "insert_candidate_cache - candidate is not cacheable");
+            debug!(?pred, ?candidate, "insert_candidate_cache - candidate is not cacheable");
             return;
         }
 
         if self.can_use_global_caches(param_env) {
             if let Err(Overflow) = candidate {
                 // Don't cache overflow globally; we only produce this in certain modes.
-            } else if !trait_ref.needs_infer() {
+            } else if !pred.needs_infer() {
                 if !candidate.needs_infer() {
-                    debug!(?trait_ref, ?candidate, "insert_candidate_cache global");
+                    debug!(?pred, ?candidate, "insert_candidate_cache global");
                     // This may overwrite the cache with the same value.
-                    tcx.selection_cache.insert(
-                        (param_env.and(trait_ref).with_constness(pred.constness), pred.polarity),
-                        dep_node,
-                        candidate,
-                    );
+                    tcx.selection_cache.insert(param_env.and(pred), dep_node, candidate);
                     return;
                 }
             }
         }
 
-        debug!(?trait_ref, ?candidate, "insert_candidate_cache local");
-        self.infcx.selection_cache.insert(
-            (param_env.and(trait_ref).with_constness(pred.constness), pred.polarity),
-            dep_node,
-            candidate,
-        );
+        debug!(?pred, ?candidate, "insert_candidate_cache local");
+        self.infcx.selection_cache.insert(param_env.and(pred), dep_node, candidate);
     }
 
     /// Matches a predicate against the bounds of its self type.

From 63ce5c190e35af26bbbd484470eb9fc768351a85 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 25 Oct 2021 14:04:15 +0000
Subject: [PATCH 09/12] Replace `ConstnessAnd<TraitRef>` with `TraitPredicate`
 which conveys the same information

---
 compiler/rustc_middle/src/traits/select.rs    |   6 +-
 .../src/traits/select/mod.rs                  | 109 +++++++-----------
 2 files changed, 45 insertions(+), 70 deletions(-)

diff --git a/compiler/rustc_middle/src/traits/select.rs b/compiler/rustc_middle/src/traits/select.rs
index 621bc0c5786c3..ff711bff86f61 100644
--- a/compiler/rustc_middle/src/traits/select.rs
+++ b/compiler/rustc_middle/src/traits/select.rs
@@ -16,10 +16,8 @@ pub type SelectionCache<'tcx> = Cache<
     SelectionResult<'tcx, SelectionCandidate<'tcx>>,
 >;
 
-pub type EvaluationCache<'tcx> = Cache<
-    (ty::ParamEnvAnd<'tcx, ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>>, ty::ImplPolarity),
-    EvaluationResult,
->;
+pub type EvaluationCache<'tcx> =
+    Cache<ty::ParamEnvAnd<'tcx, ty::PolyTraitPredicate<'tcx>>, EvaluationResult>;
 
 /// The selection process begins by considering all impls, where
 /// clauses, and so forth that might resolve an obligation. Sometimes
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 9fda75a2b8d5d..7f020437158a5 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -39,7 +39,6 @@ use rustc_middle::ty::fast_reject;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::relate::TypeRelation;
 use rustc_middle::ty::subst::{GenericArgKind, Subst, SubstsRef};
-use rustc_middle::ty::WithConstness;
 use rustc_middle::ty::{self, PolyProjectionPredicate, ToPolyTraitRef, ToPredicate};
 use rustc_middle::ty::{Ty, TyCtxt, TypeFoldable};
 use rustc_span::symbol::sym;
@@ -138,9 +137,9 @@ pub struct SelectionContext<'cx, 'tcx> {
 struct TraitObligationStack<'prev, 'tcx> {
     obligation: &'prev TraitObligation<'tcx>,
 
-    /// The trait ref from `obligation` but "freshened" with the
+    /// The trait predicate from `obligation` but "freshened" with the
     /// selection-context's freshener. Used to check for recursion.
-    fresh_trait_ref: ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>,
+    fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
 
     /// Starts out equal to `depth` -- if, during evaluation, we
     /// encounter a cycle, then we will set this flag to the minimum
@@ -676,20 +675,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
 
         let stack = self.push_stack(previous_stack, &obligation);
-        let fresh_trait_ref = stack.fresh_trait_ref;
+        let fresh_trait_pred = stack.fresh_trait_pred;
 
-        debug!(?fresh_trait_ref);
+        debug!(?fresh_trait_pred);
 
-        if let Some(result) = self.check_evaluation_cache(
-            obligation.param_env,
-            fresh_trait_ref,
-            obligation.polarity(),
-        ) {
+        if let Some(result) = self.check_evaluation_cache(obligation.param_env, fresh_trait_pred) {
             debug!(?result, "CACHE HIT");
             return Ok(result);
         }
 
-        if let Some(result) = stack.cache().get_provisional(fresh_trait_ref) {
+        if let Some(result) = stack.cache().get_provisional(fresh_trait_pred) {
             debug!(?result, "PROVISIONAL CACHE HIT");
             stack.update_reached_depth(result.reached_depth);
             return Ok(result.result);
@@ -714,19 +709,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let reached_depth = stack.reached_depth.get();
         if reached_depth >= stack.depth {
             debug!(?result, "CACHE MISS");
-            self.insert_evaluation_cache(
-                obligation.param_env,
-                fresh_trait_ref,
-                obligation.polarity(),
-                dep_node,
-                result,
-            );
+            self.insert_evaluation_cache(obligation.param_env, fresh_trait_pred, dep_node, result);
 
-            stack.cache().on_completion(stack.dfn, |fresh_trait_ref, provisional_result| {
+            stack.cache().on_completion(stack.dfn, |fresh_trait_pred, provisional_result| {
                 self.insert_evaluation_cache(
                     obligation.param_env,
-                    fresh_trait_ref,
-                    obligation.polarity(),
+                    fresh_trait_pred,
                     dep_node,
                     provisional_result.max(result),
                 );
@@ -736,10 +724,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             debug!(
                 "caching provisionally because {:?} \
                  is a cycle participant (at depth {}, reached depth {})",
-                fresh_trait_ref, stack.depth, reached_depth,
+                fresh_trait_pred, stack.depth, reached_depth,
             );
 
-            stack.cache().insert_provisional(stack.dfn, reached_depth, fresh_trait_ref, result);
+            stack.cache().insert_provisional(stack.dfn, reached_depth, fresh_trait_pred, result);
         }
 
         Ok(result)
@@ -773,7 +761,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .skip(1) // Skip top-most frame.
             .find(|prev| {
                 stack.obligation.param_env == prev.obligation.param_env
-                    && stack.fresh_trait_ref == prev.fresh_trait_ref
+                    && stack.fresh_trait_pred == prev.fresh_trait_pred
             })
             .map(|stack| stack.depth)
         {
@@ -836,7 +824,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // terms of `Fn` etc, but we could probably make this more
         // precise still.
         let unbound_input_types =
-            stack.fresh_trait_ref.value.skip_binder().substs.types().any(|ty| ty.is_fresh());
+            stack.fresh_trait_pred.skip_binder().trait_ref.substs.types().any(|ty| ty.is_fresh());
 
         if stack.obligation.polarity() != ty::ImplPolarity::Negative {
             // This check was an imperfect workaround for a bug in the old
@@ -874,8 +862,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             && stack.iter().skip(1).any(|prev| {
                 stack.obligation.param_env == prev.obligation.param_env
                     && self.match_fresh_trait_refs(
-                        stack.fresh_trait_ref,
-                        prev.fresh_trait_ref,
+                        stack.fresh_trait_pred,
+                        prev.fresh_trait_pred,
                         prev.obligation.param_env,
                     )
             })
@@ -953,7 +941,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // not just the lifetime choice for this particular (non-erased)
         // predicate.
         // See issue #80691
-        if stack.fresh_trait_ref.has_erased_regions() {
+        if stack.fresh_trait_pred.has_erased_regions() {
             result = result.max(EvaluatedToOkModuloRegions);
         }
 
@@ -964,8 +952,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     fn check_evaluation_cache(
         &self,
         param_env: ty::ParamEnv<'tcx>,
-        trait_ref: ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>,
-        polarity: ty::ImplPolarity,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> Option<EvaluationResult> {
         // Neither the global nor local cache is aware of intercrate
         // mode, so don't do any caching. In particular, we might
@@ -977,19 +964,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let tcx = self.tcx();
         if self.can_use_global_caches(param_env) {
-            if let Some(res) = tcx.evaluation_cache.get(&(param_env.and(trait_ref), polarity), tcx)
-            {
+            if let Some(res) = tcx.evaluation_cache.get(&param_env.and(trait_pred), tcx) {
                 return Some(res);
             }
         }
-        self.infcx.evaluation_cache.get(&(param_env.and(trait_ref), polarity), tcx)
+        self.infcx.evaluation_cache.get(&param_env.and(trait_pred), tcx)
     }
 
     fn insert_evaluation_cache(
         &mut self,
         param_env: ty::ParamEnv<'tcx>,
-        trait_ref: ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>,
-        polarity: ty::ImplPolarity,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
         dep_node: DepNodeIndex,
         result: EvaluationResult,
     ) {
@@ -1008,23 +993,19 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
 
         if self.can_use_global_caches(param_env) {
-            if !trait_ref.needs_infer() {
-                debug!(?trait_ref, ?result, "insert_evaluation_cache global");
+            if !trait_pred.needs_infer() {
+                debug!(?trait_pred, ?result, "insert_evaluation_cache global");
                 // This may overwrite the cache with the same value
                 // FIXME: Due to #50507 this overwrites the different values
                 // This should be changed to use HashMapExt::insert_same
                 // when that is fixed
-                self.tcx().evaluation_cache.insert(
-                    (param_env.and(trait_ref), polarity),
-                    dep_node,
-                    result,
-                );
+                self.tcx().evaluation_cache.insert(param_env.and(trait_pred), dep_node, result);
                 return;
             }
         }
 
-        debug!(?trait_ref, ?result, "insert_evaluation_cache");
-        self.infcx.evaluation_cache.insert((param_env.and(trait_ref), polarity), dep_node, result);
+        debug!(?trait_pred, ?result, "insert_evaluation_cache");
+        self.infcx.evaluation_cache.insert(param_env.and(trait_pred), dep_node, result);
     }
 
     /// For various reasons, it's possible for a subobligation
@@ -2157,8 +2138,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
     fn match_fresh_trait_refs(
         &self,
-        previous: ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>,
-        current: ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>,
+        previous: ty::PolyTraitPredicate<'tcx>,
+        current: ty::PolyTraitPredicate<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> bool {
         let mut matcher = ty::_match::Match::new(self.tcx(), param_env);
@@ -2170,17 +2151,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         previous_stack: TraitObligationStackList<'o, 'tcx>,
         obligation: &'o TraitObligation<'tcx>,
     ) -> TraitObligationStack<'o, 'tcx> {
-        let fresh_trait_ref = obligation
-            .predicate
-            .to_poly_trait_ref()
-            .fold_with(&mut self.freshener)
-            .with_constness(obligation.predicate.skip_binder().constness);
+        let fresh_trait_pred = obligation.predicate.fold_with(&mut self.freshener);
 
         let dfn = previous_stack.cache.next_dfn();
         let depth = previous_stack.depth() + 1;
         TraitObligationStack {
             obligation,
-            fresh_trait_ref,
+            fresh_trait_pred,
             reached_depth: Cell::new(depth),
             previous: previous_stack,
             dfn,
@@ -2374,7 +2351,7 @@ impl<'o, 'tcx> TraitObligationStack<'o, 'tcx> {
         debug!(reached_depth, "update_reached_depth");
         let mut p = self;
         while reached_depth < p.depth {
-            debug!(?p.fresh_trait_ref, "update_reached_depth: marking as cycle participant");
+            debug!(?p.fresh_trait_pred, "update_reached_depth: marking as cycle participant");
             p.reached_depth.set(p.reached_depth.get().min(reached_depth));
             p = p.previous.head.unwrap();
         }
@@ -2453,7 +2430,7 @@ struct ProvisionalEvaluationCache<'tcx> {
     /// - then we determine that `E` is in error -- we will then clear
     ///   all cache values whose DFN is >= 4 -- in this case, that
     ///   means the cached value for `F`.
-    map: RefCell<FxHashMap<ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>, ProvisionalEvaluation>>,
+    map: RefCell<FxHashMap<ty::PolyTraitPredicate<'tcx>, ProvisionalEvaluation>>,
 }
 
 /// A cache value for the provisional cache: contains the depth-first
@@ -2485,28 +2462,28 @@ impl<'tcx> ProvisionalEvaluationCache<'tcx> {
     /// `reached_depth` (from the returned value).
     fn get_provisional(
         &self,
-        fresh_trait_ref: ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>,
+        fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> Option<ProvisionalEvaluation> {
         debug!(
-            ?fresh_trait_ref,
+            ?fresh_trait_pred,
             "get_provisional = {:#?}",
-            self.map.borrow().get(&fresh_trait_ref),
+            self.map.borrow().get(&fresh_trait_pred),
         );
-        Some(*self.map.borrow().get(&fresh_trait_ref)?)
+        Some(*self.map.borrow().get(&fresh_trait_pred)?)
     }
 
     /// Insert a provisional result into the cache. The result came
     /// from the node with the given DFN. It accessed a minimum depth
-    /// of `reached_depth` to compute. It evaluated `fresh_trait_ref`
+    /// of `reached_depth` to compute. It evaluated `fresh_trait_pred`
     /// and resulted in `result`.
     fn insert_provisional(
         &self,
         from_dfn: usize,
         reached_depth: usize,
-        fresh_trait_ref: ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>,
+        fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
         result: EvaluationResult,
     ) {
-        debug!(?from_dfn, ?fresh_trait_ref, ?result, "insert_provisional");
+        debug!(?from_dfn, ?fresh_trait_pred, ?result, "insert_provisional");
 
         let mut map = self.map.borrow_mut();
 
@@ -2530,7 +2507,7 @@ impl<'tcx> ProvisionalEvaluationCache<'tcx> {
             }
         }
 
-        map.insert(fresh_trait_ref, ProvisionalEvaluation { from_dfn, reached_depth, result });
+        map.insert(fresh_trait_pred, ProvisionalEvaluation { from_dfn, reached_depth, result });
     }
 
     /// Invoked when the node with dfn `dfn` does not get a successful
@@ -2581,16 +2558,16 @@ impl<'tcx> ProvisionalEvaluationCache<'tcx> {
     fn on_completion(
         &self,
         dfn: usize,
-        mut op: impl FnMut(ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>, EvaluationResult),
+        mut op: impl FnMut(ty::PolyTraitPredicate<'tcx>, EvaluationResult),
     ) {
         debug!(?dfn, "on_completion");
 
-        for (fresh_trait_ref, eval) in
+        for (fresh_trait_pred, eval) in
             self.map.borrow_mut().drain_filter(|_k, eval| eval.from_dfn >= dfn)
         {
-            debug!(?fresh_trait_ref, ?eval, "on_completion");
+            debug!(?fresh_trait_pred, ?eval, "on_completion");
 
-            op(fresh_trait_ref, eval.result);
+            op(fresh_trait_pred, eval.result);
         }
     }
 }

From 3be778657f54bd14496a653b41eac7048b421417 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 25 Oct 2021 14:29:54 +0000
Subject: [PATCH 10/12] Avoid storing the ImplPolarity and Constness next to a
 TraitRef and use TraitPredicate instead

---
 compiler/rustc_infer/src/traits/util.rs       |  8 ++--
 compiler/rustc_middle/src/traits/select.rs    |  2 +-
 compiler/rustc_middle/src/ty/mod.rs           |  6 +--
 .../rustc_trait_selection/src/traits/mod.rs   | 13 ++++--
 .../src/traits/select/candidate_assembly.rs   | 10 +++--
 .../src/traits/select/confirmation.rs         | 14 ++++---
 .../src/traits/select/mod.rs                  | 41 +++++++++----------
 .../src/traits/specialize/mod.rs              |  6 +--
 .../rustc_trait_selection/src/traits/util.rs  |  8 ++--
 .../rustc_trait_selection/src/traits/wf.rs    |  5 ++-
 compiler/rustc_typeck/src/astconv/mod.rs      |  2 +-
 11 files changed, 61 insertions(+), 54 deletions(-)

diff --git a/compiler/rustc_infer/src/traits/util.rs b/compiler/rustc_infer/src/traits/util.rs
index c839f824d1c9c..f82999f12c25d 100644
--- a/compiler/rustc_infer/src/traits/util.rs
+++ b/compiler/rustc_infer/src/traits/util.rs
@@ -311,8 +311,8 @@ pub fn transitive_bounds_that_define_assoc_type<'tcx>(
                 ));
                 for (super_predicate, _) in super_predicates.predicates {
                     let subst_predicate = super_predicate.subst_supertrait(tcx, &trait_ref);
-                    if let Some(binder) = subst_predicate.to_opt_poly_trait_ref() {
-                        stack.push(binder.value);
+                    if let Some(binder) = subst_predicate.to_opt_poly_trait_pred() {
+                        stack.push(binder.map_bound(|t| t.trait_ref));
                     }
                 }
 
@@ -345,8 +345,8 @@ impl<'tcx, I: Iterator<Item = PredicateObligation<'tcx>>> Iterator for FilterToT
 
     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
         while let Some(obligation) = self.base_iterator.next() {
-            if let Some(data) = obligation.predicate.to_opt_poly_trait_ref() {
-                return Some(data.value);
+            if let Some(data) = obligation.predicate.to_opt_poly_trait_pred() {
+                return Some(data.map_bound(|t| t.trait_ref));
             }
         }
         None
diff --git a/compiler/rustc_middle/src/traits/select.rs b/compiler/rustc_middle/src/traits/select.rs
index ff711bff86f61..71ee00c602a3d 100644
--- a/compiler/rustc_middle/src/traits/select.rs
+++ b/compiler/rustc_middle/src/traits/select.rs
@@ -101,7 +101,7 @@ pub enum SelectionCandidate<'tcx> {
         /// `false` if there are no *further* obligations.
         has_nested: bool,
     },
-    ParamCandidate((ty::ConstnessAnd<ty::PolyTraitRef<'tcx>>, ty::ImplPolarity)),
+    ParamCandidate(ty::PolyTraitPredicate<'tcx>),
     ImplCandidate(DefId),
     AutoImplCandidate(DefId),
 
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index a76cb4c4c528c..1f34b9cd1898c 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -880,12 +880,10 @@ impl<'tcx> ToPredicate<'tcx> for PolyProjectionPredicate<'tcx> {
 }
 
 impl<'tcx> Predicate<'tcx> {
-    pub fn to_opt_poly_trait_ref(self) -> Option<ConstnessAnd<PolyTraitRef<'tcx>>> {
+    pub fn to_opt_poly_trait_pred(self) -> Option<PolyTraitPredicate<'tcx>> {
         let predicate = self.kind();
         match predicate.skip_binder() {
-            PredicateKind::Trait(t) => {
-                Some(ConstnessAnd { constness: t.constness, value: predicate.rebind(t.trait_ref) })
-            }
+            PredicateKind::Trait(t) => Some(predicate.rebind(t)),
             PredicateKind::Projection(..)
             | PredicateKind::Subtype(..)
             | PredicateKind::Coerce(..)
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 65dd0e7f537f2..3a9970fdfa737 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -572,14 +572,17 @@ fn prepare_vtable_segments<'tcx, T>(
                     .predicates
                     .into_iter()
                     .filter_map(move |(pred, _)| {
-                        pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_ref()
+                        pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
                     });
 
                 'diving_in_skip_visited_traits: loop {
                     if let Some(next_super_trait) = direct_super_traits_iter.next() {
                         if visited.insert(next_super_trait.to_predicate(tcx)) {
+                            // We're throwing away potential constness of super traits here.
+                            // FIXME: handle ~const super traits
+                            let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
                             stack.push((
-                                next_super_trait.value,
+                                next_super_trait,
                                 emit_vptr_on_new_entry,
                                 Some(direct_super_traits_iter),
                             ));
@@ -611,7 +614,11 @@ fn prepare_vtable_segments<'tcx, T>(
                     if let Some(siblings) = siblings_opt {
                         if let Some(next_inner_most_trait_ref) = siblings.next() {
                             if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
-                                *inner_most_trait_ref = next_inner_most_trait_ref.value;
+                                // We're throwing away potential constness of super traits here.
+                                // FIXME: handle ~const super traits
+                                let next_inner_most_trait_ref =
+                                    next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
+                                *inner_most_trait_ref = next_inner_most_trait_ref;
                                 *emit_vptr = emit_vptr_on_new_entry;
                                 break 'exiting_out;
                             } else {
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index dc81542fd6746..2b96e5f97265b 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -383,17 +383,19 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .param_env
             .caller_bounds()
             .iter()
-            .filter_map(|o| o.to_opt_poly_trait_ref());
+            .filter_map(|o| o.to_opt_poly_trait_pred());
 
         // Micro-optimization: filter out predicates relating to different traits.
         let matching_bounds =
-            all_bounds.filter(|p| p.value.def_id() == stack.obligation.predicate.def_id());
+            all_bounds.filter(|p| p.def_id() == stack.obligation.predicate.def_id());
 
         // Keep only those bounds which may apply, and propagate overflow if it occurs.
         for bound in matching_bounds {
-            let wc = self.evaluate_where_clause(stack, bound.value)?;
+            // FIXME(oli-obk): it is suspicious that we are dropping the constness and
+            // polarity here.
+            let wc = self.evaluate_where_clause(stack, bound.map_bound(|t| t.trait_ref))?;
             if wc.may_apply() {
-                candidates.vec.push(ParamCandidate((bound, stack.obligation.polarity())));
+                candidates.vec.push(ParamCandidate(bound));
             }
         }
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 84721922c8dd7..4d4d11c0ab50e 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -58,8 +58,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
 
             ParamCandidate(param) => {
-                let obligations = self.confirm_param_candidate(obligation, param.0.value);
-                Ok(ImplSource::Param(obligations, param.0.constness))
+                let obligations =
+                    self.confirm_param_candidate(obligation, param.map_bound(|t| t.trait_ref));
+                Ok(ImplSource::Param(obligations, param.skip_binder().constness))
             }
 
             ImplCandidate(impl_def_id) => {
@@ -139,7 +140,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             let trait_predicate = self.infcx.shallow_resolve(obligation.predicate);
             let placeholder_trait_predicate =
-                self.infcx().replace_bound_vars_with_placeholders(trait_predicate);
+                self.infcx().replace_bound_vars_with_placeholders(trait_predicate).trait_ref;
             let placeholder_self_ty = placeholder_trait_predicate.self_ty();
             let placeholder_trait_predicate = ty::Binder::dummy(placeholder_trait_predicate);
             let (def_id, substs) = match *placeholder_self_ty.kind() {
@@ -150,8 +151,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             let candidate_predicate = tcx.item_bounds(def_id)[idx].subst(tcx, substs);
             let candidate = candidate_predicate
-                .to_opt_poly_trait_ref()
-                .expect("projection candidate is not a trait predicate");
+                .to_opt_poly_trait_pred()
+                .expect("projection candidate is not a trait predicate")
+                .map_bound(|t| t.trait_ref);
             let mut obligations = Vec::new();
             let candidate = normalize_with_depth_to(
                 self,
@@ -165,7 +167,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             obligations.extend(self.infcx.commit_if_ok(|_| {
                 self.infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .sup(placeholder_trait_predicate.to_poly_trait_ref(), candidate.value)
+                    .sup(placeholder_trait_predicate, candidate)
                     .map(|InferOk { obligations, .. }| obligations)
                     .map_err(|_| Unimplemented)
             })?);
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 7f020437158a5..294b10942285e 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1089,10 +1089,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     ImplCandidate(def_id)
                         if tcx.impl_constness(def_id) == hir::Constness::Const => {}
                     // const param
-                    ParamCandidate((
-                        ty::ConstnessAnd { constness: ty::BoundConstness::ConstIfConst, .. },
-                        _,
-                    )) => {}
+                    ParamCandidate(trait_pred)
+                        if trait_pred.skip_binder().constness
+                            == ty::BoundConstness::ConstIfConst => {}
                     // auto trait impl
                     AutoImplCandidate(..) => {}
                     // generator, this will raise error in other places
@@ -1474,8 +1473,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // Check if a bound would previously have been removed when normalizing
         // the param_env so that it can be given the lowest priority. See
         // #50825 for the motivation for this.
-        let is_global =
-            |cand: &ty::PolyTraitRef<'_>| cand.is_known_global() && !cand.has_late_bound_regions();
+        let is_global = |cand: &ty::PolyTraitPredicate<'_>| {
+            cand.is_known_global() && !cand.has_late_bound_regions()
+        };
 
         // (*) Prefer `BuiltinCandidate { has_nested: false }`, `PointeeCandidate`,
         // and `DiscriminantKindCandidate` to anything else.
@@ -1506,25 +1506,22 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 | ConstDropCandidate,
             ) => false,
 
-            (
-                ParamCandidate((other, other_polarity)),
-                ParamCandidate((victim, victim_polarity)),
-            ) => {
-                let same_except_bound_vars = other.value.skip_binder()
-                    == victim.value.skip_binder()
-                    && other.constness == victim.constness
-                    && other_polarity == victim_polarity
-                    && !other.value.skip_binder().has_escaping_bound_vars();
+            (ParamCandidate(other), ParamCandidate(victim)) => {
+                let same_except_bound_vars = other.skip_binder().trait_ref
+                    == victim.skip_binder().trait_ref
+                    && other.skip_binder().constness == victim.skip_binder().constness
+                    && other.skip_binder().polarity == victim.skip_binder().polarity
+                    && !other.skip_binder().trait_ref.has_escaping_bound_vars();
                 if same_except_bound_vars {
                     // See issue #84398. In short, we can generate multiple ParamCandidates which are
                     // the same except for unused bound vars. Just pick the one with the fewest bound vars
                     // or the current one if tied (they should both evaluate to the same answer). This is
                     // probably best characterized as a "hack", since we might prefer to just do our
                     // best to *not* create essentially duplicate candidates in the first place.
-                    other.value.bound_vars().len() <= victim.value.bound_vars().len()
-                } else if other.value == victim.value
-                    && victim.constness == ty::BoundConstness::NotConst
-                    && other_polarity == victim_polarity
+                    other.bound_vars().len() <= victim.bound_vars().len()
+                } else if other.skip_binder().trait_ref == victim.skip_binder().trait_ref
+                    && victim.skip_binder().constness == ty::BoundConstness::NotConst
+                    && other.skip_binder().polarity == victim.skip_binder().polarity
                 {
                     // Drop otherwise equivalent non-const candidates in favor of const candidates.
                     true
@@ -1554,11 +1551,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 | TraitAliasCandidate(..)
                 | ObjectCandidate(_)
                 | ProjectionCandidate(_),
-            ) => !is_global(&cand.0.value),
+            ) => !is_global(cand),
             (ObjectCandidate(_) | ProjectionCandidate(_), ParamCandidate(ref cand)) => {
                 // Prefer these to a global where-clause bound
                 // (see issue #50825).
-                is_global(&cand.0.value)
+                is_global(cand)
             }
             (
                 ImplCandidate(_)
@@ -1574,7 +1571,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             ) => {
                 // Prefer these to a global where-clause bound
                 // (see issue #50825).
-                is_global(&cand.0.value) && other.evaluation.must_apply_modulo_regions()
+                is_global(cand) && other.evaluation.must_apply_modulo_regions()
             }
 
             (ProjectionCandidate(i), ProjectionCandidate(j))
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index f9867f0671e59..a37beceba31c2 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -500,9 +500,9 @@ crate fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Option<St
         Vec::with_capacity(predicates.len() + types_without_default_bounds.len());
 
     for (p, _) in predicates {
-        if let Some(poly_trait_ref) = p.to_opt_poly_trait_ref() {
-            if Some(poly_trait_ref.value.def_id()) == sized_trait {
-                types_without_default_bounds.remove(poly_trait_ref.value.self_ty().skip_binder());
+        if let Some(poly_trait_ref) = p.to_opt_poly_trait_pred() {
+            if Some(poly_trait_ref.def_id()) == sized_trait {
+                types_without_default_bounds.remove(poly_trait_ref.self_ty().skip_binder());
                 continue;
             }
         }
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index ed49abbbedc92..027028b09a361 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -124,8 +124,8 @@ impl<'tcx> TraitAliasExpander<'tcx> {
 
         let items = predicates.predicates.iter().rev().filter_map(|(pred, span)| {
             pred.subst_supertrait(tcx, &trait_ref)
-                .to_opt_poly_trait_ref()
-                .map(|trait_ref| item.clone_and_push(trait_ref.value, *span))
+                .to_opt_poly_trait_pred()
+                .map(|trait_ref| item.clone_and_push(trait_ref.map_bound(|t| t.trait_ref), *span))
         });
         debug!("expand_trait_aliases: items={:?}", items.clone());
 
@@ -181,8 +181,8 @@ impl Iterator for SupertraitDefIds<'tcx> {
             predicates
                 .predicates
                 .iter()
-                .filter_map(|(pred, _)| pred.to_opt_poly_trait_ref())
-                .map(|trait_ref| trait_ref.value.def_id())
+                .filter_map(|(pred, _)| pred.to_opt_poly_trait_pred())
+                .map(|trait_ref| trait_ref.def_id())
                 .filter(|&super_def_id| visited.insert(super_def_id)),
         );
         Some(def_id)
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index cb47ba9c360da..dbf078952de00 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -298,9 +298,10 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
 
         let extend = |obligation: traits::PredicateObligation<'tcx>| {
             let mut cause = cause.clone();
-            if let Some(parent_trait_ref) = obligation.predicate.to_opt_poly_trait_ref() {
+            if let Some(parent_trait_ref) = obligation.predicate.to_opt_poly_trait_pred() {
                 let derived_cause = traits::DerivedObligationCause {
-                    parent_trait_ref: parent_trait_ref.value,
+                    // TODO: sus
+                    parent_trait_ref: parent_trait_ref.map_bound(|t| t.trait_ref),
                     parent_code: Lrc::new(obligation.cause.code.clone()),
                 };
                 cause.make_mut().code =
diff --git a/compiler/rustc_typeck/src/astconv/mod.rs b/compiler/rustc_typeck/src/astconv/mod.rs
index da751f2075399..b532a6b118f06 100644
--- a/compiler/rustc_typeck/src/astconv/mod.rs
+++ b/compiler/rustc_typeck/src/astconv/mod.rs
@@ -1588,7 +1588,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 traits::transitive_bounds_that_define_assoc_type(
                     tcx,
                     predicates.iter().filter_map(|(p, _)| {
-                        p.to_opt_poly_trait_ref().map(|trait_ref| trait_ref.value)
+                        Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
                     }),
                     assoc_name,
                 )

From afbac7547c526c3e7141aedcbc44a257eb3818db Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 25 Oct 2021 15:58:41 +0000
Subject: [PATCH 11/12] Completely remove ConstnessAnd

---
 compiler/rustc_borrowck/src/type_check/mod.rs |  2 +-
 compiler/rustc_infer/src/traits/engine.rs     |  2 +-
 compiler/rustc_infer/src/traits/util.rs       |  2 +-
 compiler/rustc_middle/src/ty/mod.rs           | 40 ++++---------------
 compiler/rustc_middle/src/ty/relate.rs        | 13 ------
 compiler/rustc_middle/src/ty/sty.rs           |  4 +-
 .../rustc_trait_selection/src/autoderef.rs    |  2 +-
 compiler/rustc_trait_selection/src/infer.rs   |  1 -
 .../src/traits/error_reporting/mod.rs         |  2 +-
 .../src/traits/error_reporting/suggestions.rs |  2 +-
 .../rustc_trait_selection/src/traits/mod.rs   |  3 +-
 .../src/traits/object_safety.rs               |  2 +-
 .../src/traits/project.rs                     |  2 +-
 .../src/traits/select/candidate_assembly.rs   |  2 +-
 .../src/traits/select/confirmation.rs         |  2 +-
 .../rustc_trait_selection/src/traits/util.rs  |  2 +-
 .../rustc_trait_selection/src/traits/wf.rs    |  2 +-
 compiler/rustc_ty_utils/src/ty.rs             |  4 +-
 compiler/rustc_typeck/src/bounds.rs           |  2 +-
 compiler/rustc_typeck/src/check/method/mod.rs |  2 +-
 .../rustc_typeck/src/check/method/probe.rs    |  2 +-
 .../rustc_typeck/src/check/method/suggest.rs  |  2 +-
 compiler/rustc_typeck/src/check/wfcheck.rs    |  4 +-
 compiler/rustc_typeck/src/collect.rs          |  2 +-
 24 files changed, 29 insertions(+), 74 deletions(-)

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 7e69e710d6868..e316115fec9cd 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -30,7 +30,7 @@ use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef, UserSubsts};
 use rustc_middle::ty::{
     self, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, OpaqueTypeKey, RegionVid,
-    ToPredicate, Ty, TyCtxt, UserType, UserTypeAnnotationIndex, WithConstness,
+    ToPredicate, Ty, TyCtxt, UserType, UserTypeAnnotationIndex,
 };
 use rustc_span::def_id::CRATE_DEF_ID;
 use rustc_span::{Span, DUMMY_SP};
diff --git a/compiler/rustc_infer/src/traits/engine.rs b/compiler/rustc_infer/src/traits/engine.rs
index 5f9a66ea10845..36031e3219829 100644
--- a/compiler/rustc_infer/src/traits/engine.rs
+++ b/compiler/rustc_infer/src/traits/engine.rs
@@ -2,7 +2,7 @@ use crate::infer::InferCtxt;
 use crate::traits::Obligation;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::{self, ToPredicate, Ty, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty};
 
 use super::FulfillmentError;
 use super::{ObligationCause, PredicateObligation};
diff --git a/compiler/rustc_infer/src/traits/util.rs b/compiler/rustc_infer/src/traits/util.rs
index f82999f12c25d..a19c6839e41d1 100644
--- a/compiler/rustc_infer/src/traits/util.rs
+++ b/compiler/rustc_infer/src/traits/util.rs
@@ -3,7 +3,7 @@ use smallvec::smallvec;
 use crate::infer::outlives::components::{push_outlives_components, Component};
 use crate::traits::{Obligation, ObligationCause, PredicateObligation};
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
-use rustc_middle::ty::{self, ToPredicate, TyCtxt, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, TyCtxt};
 use rustc_span::symbol::Ident;
 
 pub fn anonymize_predicate<'tcx>(
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 1f34b9cd1898c..312395b7d6b82 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -841,20 +841,6 @@ impl ToPredicate<'tcx> for Binder<'tcx, PredicateKind<'tcx>> {
     }
 }
 
-impl<'tcx> ToPredicate<'tcx> for ConstnessAnd<PolyTraitRef<'tcx>> {
-    fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        self.value
-            .map_bound(|trait_ref| {
-                PredicateKind::Trait(ty::TraitPredicate {
-                    trait_ref,
-                    constness: self.constness,
-                    polarity: ty::ImplPolarity::Positive,
-                })
-            })
-            .to_predicate(tcx)
-    }
-}
-
 impl<'tcx> ToPredicate<'tcx> for PolyTraitPredicate<'tcx> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
         self.map_bound(PredicateKind::Trait).to_predicate(tcx)
@@ -1386,33 +1372,23 @@ impl<'tcx> ParamEnv<'tcx> {
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TypeFoldable)]
-pub struct ConstnessAnd<T> {
-    pub constness: BoundConstness,
-    pub value: T,
-}
-
 // FIXME(ecstaticmorse): Audit all occurrences of `without_const().to_predicate(tcx)` to ensure that
 // the constness of trait bounds is being propagated correctly.
-pub trait WithConstness: Sized {
-    #[inline]
-    fn with_constness(self, constness: BoundConstness) -> ConstnessAnd<Self> {
-        ConstnessAnd { constness, value: self }
-    }
-
+impl PolyTraitRef<'tcx> {
     #[inline]
-    fn with_const_if_const(self) -> ConstnessAnd<Self> {
-        self.with_constness(BoundConstness::ConstIfConst)
+    pub fn with_constness(self, constness: BoundConstness) -> PolyTraitPredicate<'tcx> {
+        self.map_bound(|trait_ref| ty::TraitPredicate {
+            trait_ref,
+            constness,
+            polarity: ty::ImplPolarity::Positive,
+        })
     }
-
     #[inline]
-    fn without_const(self) -> ConstnessAnd<Self> {
+    pub fn without_const(self) -> PolyTraitPredicate<'tcx> {
         self.with_constness(BoundConstness::NotConst)
     }
 }
 
-impl<T> WithConstness for T {}
-
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TypeFoldable)]
 pub struct ParamEnvAnd<'tcx, T> {
     pub param_env: ParamEnv<'tcx>,
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index 8b20e1eec9a86..034df983ffcab 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -214,19 +214,6 @@ impl<'tcx> Relate<'tcx> for ty::BoundConstness {
     }
 }
 
-impl<'tcx, T: Relate<'tcx>> Relate<'tcx> for ty::ConstnessAnd<T> {
-    fn relate<R: TypeRelation<'tcx>>(
-        relation: &mut R,
-        a: ty::ConstnessAnd<T>,
-        b: ty::ConstnessAnd<T>,
-    ) -> RelateResult<'tcx, ty::ConstnessAnd<T>> {
-        Ok(ty::ConstnessAnd {
-            constness: relation.relate(a.constness, b.constness)?,
-            value: relation.relate(a.value, b.value)?,
-        })
-    }
-}
-
 impl<'tcx> Relate<'tcx> for ast::Unsafety {
     fn relate<R: TypeRelation<'tcx>>(
         relation: &mut R,
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 874de3366d792..d985b4ab9345d 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -8,9 +8,7 @@ use crate::infer::canonical::Canonical;
 use crate::ty::fold::ValidateBoundVars;
 use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
 use crate::ty::InferTy::{self, *};
-use crate::ty::{
-    self, AdtDef, DefIdTree, Discr, Ty, TyCtxt, TypeFlags, TypeFoldable, WithConstness,
-};
+use crate::ty::{self, AdtDef, DefIdTree, Discr, Ty, TyCtxt, TypeFlags, TypeFoldable};
 use crate::ty::{DelaySpanBugEmitted, List, ParamEnv, TyS};
 use polonius_engine::Atom;
 use rustc_data_structures::captures::Captures;
diff --git a/compiler/rustc_trait_selection/src/autoderef.rs b/compiler/rustc_trait_selection/src/autoderef.rs
index 53afe4ca068c4..c6158bde00e10 100644
--- a/compiler/rustc_trait_selection/src/autoderef.rs
+++ b/compiler/rustc_trait_selection/src/autoderef.rs
@@ -3,7 +3,7 @@ use crate::traits::{self, TraitEngine};
 use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_infer::infer::InferCtxt;
-use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt, WithConstness};
+use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt};
 use rustc_middle::ty::{ToPredicate, TypeFoldable};
 use rustc_session::{DiagnosticMessageId, Limit};
 use rustc_span::def_id::LOCAL_CRATE;
diff --git a/compiler/rustc_trait_selection/src/infer.rs b/compiler/rustc_trait_selection/src/infer.rs
index 70816b5722b2d..f135f0c1b13d2 100644
--- a/compiler/rustc_trait_selection/src/infer.rs
+++ b/compiler/rustc_trait_selection/src/infer.rs
@@ -9,7 +9,6 @@ use rustc_middle::infer::canonical::{Canonical, CanonicalizedQueryResponse, Quer
 use rustc_middle::traits::query::Fallible;
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::ToPredicate;
-use rustc_middle::ty::WithConstness;
 use rustc_middle::ty::{self, Ty, TypeFoldable};
 use rustc_span::{Span, DUMMY_SP};
 
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 8396e3263f9a4..3063317299a13 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -24,7 +24,7 @@ use rustc_middle::ty::error::ExpectedFound;
 use rustc_middle::ty::fold::TypeFolder;
 use rustc_middle::ty::{
     self, fast_reject, AdtKind, SubtypePredicate, ToPolyTraitRef, ToPredicate, Ty, TyCtxt,
-    TypeFoldable, WithConstness,
+    TypeFoldable,
 };
 use rustc_session::DiagnosticMessageId;
 use rustc_span::symbol::{kw, sym};
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index b4fd851f45636..d2699dd6e1c8e 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -21,7 +21,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node};
 use rustc_middle::ty::{
     self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind, DefIdTree,
-    Infer, InferTy, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
+    Infer, InferTy, ToPredicate, Ty, TyCtxt, TypeFoldable,
 };
 use rustc_middle::ty::{TypeAndMut, TypeckResults};
 use rustc_session::Limit;
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 3a9970fdfa737..448475cb972e8 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -33,8 +33,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
 use rustc_middle::ty::{
-    self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry, WithConstness,
-    COMMON_VTABLE_ENTRIES,
+    self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry, COMMON_VTABLE_ENTRIES,
 };
 use rustc_span::{sym, Span};
 use smallvec::SmallVec;
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 616efffd999ec..412f7923fb586 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -18,7 +18,7 @@ use rustc_errors::FatalError;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::{GenericArg, InternalSubsts, Subst};
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeVisitor, WithConstness};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeVisitor};
 use rustc_middle::ty::{Predicate, ToPredicate};
 use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
 use rustc_span::symbol::Symbol;
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index db8a6d9620495..a3285d17bc32c 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -27,7 +27,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::resolve::OpportunisticRegionResolver;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::subst::Subst;
-use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use rustc_span::symbol::sym;
 
 use std::collections::BTreeMap;
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index 2b96e5f97265b..1a2765f3af076 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -11,7 +11,7 @@ use rustc_infer::traits::TraitEngine;
 use rustc_infer::traits::{Obligation, SelectionError, TraitObligation};
 use rustc_lint_defs::builtin::DEREF_INTO_DYN_SUPERTRAIT;
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::{self, ToPredicate, Ty, TypeFoldable, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TypeFoldable};
 use rustc_target::spec::abi::Abi;
 
 use crate::traits;
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 4d4d11c0ab50e..abed019483a55 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -13,7 +13,7 @@ use rustc_infer::infer::InferOk;
 use rustc_infer::infer::LateBoundRegionConversionTime::HigherRankedType;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef};
 use rustc_middle::ty::{self, Ty};
-use rustc_middle::ty::{ToPolyTraitRef, ToPredicate, WithConstness};
+use rustc_middle::ty::{ToPolyTraitRef, ToPredicate};
 use rustc_span::def_id::DefId;
 
 use crate::traits::project::{normalize_with_depth, normalize_with_depth_to};
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 027028b09a361..24ef352b86650 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/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, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable};
 
 use super::{Normalized, Obligation, ObligationCause, PredicateObligation, SelectionContext};
 pub use rustc_infer::traits::util::*;
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index dbf078952de00..357c3a6f8b5e9 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -6,7 +6,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
-use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable};
 use rustc_span::Span;
 
 use std::iter;
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index aa766344860a5..783377f7c749a 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -2,9 +2,7 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::ty::subst::Subst;
-use rustc_middle::ty::{
-    self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt, WithConstness,
-};
+use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
 use rustc_span::Span;
 use rustc_trait_selection::traits;
 
diff --git a/compiler/rustc_typeck/src/bounds.rs b/compiler/rustc_typeck/src/bounds.rs
index 24474e163b9da..8bc3a48e5b506 100644
--- a/compiler/rustc_typeck/src/bounds.rs
+++ b/compiler/rustc_typeck/src/bounds.rs
@@ -1,7 +1,7 @@
 //! Bounds are restrictions applied to some types after they've been converted into the
 //! `ty` form from the HIR.
 
-use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use rustc_span::Span;
 
 /// Collects together a list of type bounds. These lists of bounds occur in many places
diff --git a/compiler/rustc_typeck/src/check/method/mod.rs b/compiler/rustc_typeck/src/check/method/mod.rs
index f0f2470e80a8c..c2c976d7a9f65 100644
--- a/compiler/rustc_typeck/src/check/method/mod.rs
+++ b/compiler/rustc_typeck/src/check/method/mod.rs
@@ -21,7 +21,7 @@ use rustc_infer::infer::{self, InferOk};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
 use rustc_middle::ty::GenericParamDefKind;
-use rustc_middle::ty::{self, ToPredicate, Ty, TypeFoldable, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TypeFoldable};
 use rustc_span::symbol::Ident;
 use rustc_span::Span;
 use rustc_trait_selection::traits;
diff --git a/compiler/rustc_typeck/src/check/method/probe.rs b/compiler/rustc_typeck/src/check/method/probe.rs
index 6eeb28e32f1e9..4bb8690053bf3 100644
--- a/compiler/rustc_typeck/src/check/method/probe.rs
+++ b/compiler/rustc_typeck/src/check/method/probe.rs
@@ -21,7 +21,7 @@ use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
 use rustc_middle::middle::stability;
 use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::GenericParamDefKind;
-use rustc_middle::ty::{self, ParamEnvAnd, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
+use rustc_middle::ty::{self, ParamEnvAnd, ToPredicate, Ty, TyCtxt, TypeFoldable};
 use rustc_session::lint;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::lev_distance::{find_best_match_for_name, lev_distance};
diff --git a/compiler/rustc_typeck/src/check/method/suggest.rs b/compiler/rustc_typeck/src/check/method/suggest.rs
index 183ebc559ae42..9cd2110c00473 100644
--- a/compiler/rustc_typeck/src/check/method/suggest.rs
+++ b/compiler/rustc_typeck/src/check/method/suggest.rs
@@ -12,7 +12,7 @@ use rustc_hir::{ExprKind, Node, QPath};
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_middle::ty::fast_reject::simplify_type;
 use rustc_middle::ty::print::with_crate_prefix;
-use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable};
 use rustc_span::lev_distance;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{source_map, FileName, MultiSpan, Span};
diff --git a/compiler/rustc_typeck/src/check/wfcheck.rs b/compiler/rustc_typeck/src/check/wfcheck.rs
index 30aab38b1eb85..361c4d534a82a 100644
--- a/compiler/rustc_typeck/src/check/wfcheck.rs
+++ b/compiler/rustc_typeck/src/check/wfcheck.rs
@@ -14,9 +14,7 @@ use rustc_hir::ItemKind;
 use rustc_middle::hir::map as hir_map;
 use rustc_middle::ty::subst::{InternalSubsts, Subst};
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
-use rustc_middle::ty::{
-    self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
-};
+use rustc_middle::ty::{self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable};
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::Span;
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index df7f2aea9c3ac..8ba255373f337 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -41,7 +41,7 @@ use rustc_middle::ty::subst::InternalSubsts;
 use rustc_middle::ty::util::Discr;
 use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{self, AdtKind, Const, DefIdTree, Ty, TyCtxt};
-use rustc_middle::ty::{ReprOptions, ToPredicate, WithConstness};
+use rustc_middle::ty::{ReprOptions, ToPredicate};
 use rustc_session::lint;
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};

From 764aac2789cc470c05706de660a6cce8832e2c2b Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 25 Oct 2021 16:49:39 +0000
Subject: [PATCH 12/12] Always use const param envs for const eval.

Nothing else makes sense, and there is no "danger" in doing so, as it only does something if there are const bounds, which are unstable. This used to happen implicitly via the inferctxt before, which was much more fragile.
---
 compiler/rustc_const_eval/src/const_eval/eval_queries.rs | 3 +++
 compiler/rustc_const_eval/src/interpret/eval_context.rs  | 1 +
 compiler/rustc_hir/src/hir.rs                            | 1 +
 compiler/rustc_middle/src/mir/interpret/queries.rs       | 2 ++
 compiler/rustc_middle/src/ty/mod.rs                      | 5 +++++
 5 files changed, 12 insertions(+)

diff --git a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
index 57af0ff071433..338a09691893a 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -7,6 +7,7 @@ use crate::interpret::{
 };
 
 use rustc_errors::ErrorReported;
+use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::ErrorHandled;
@@ -214,6 +215,7 @@ pub fn eval_to_const_value_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
+    assert!(key.param_env.constness() == hir::Constness::Const);
     // see comment in eval_to_allocation_raw_provider for what we're doing here
     if key.param_env.reveal() == Reveal::All {
         let mut key = key;
@@ -248,6 +250,7 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
+    assert!(key.param_env.constness() == hir::Constness::Const);
     // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
     // reporting the same error twice here. To resolve this, we check whether we can evaluate the
     // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index cf084faade8cc..6206deb211533 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -918,6 +918,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         } else {
             self.param_env
         };
+        let param_env = param_env.with_const();
         let val = self.tcx.eval_to_allocation_raw(param_env.and(gid))?;
         self.raw_const_to_mplace(val)
     }
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index ac3575e769eec..ace7071c7ea0d 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -3244,6 +3244,7 @@ impl<'hir> Node<'hir> {
             Node::Item(Item { kind: ItemKind::Const(..), .. })
             | Node::Item(Item { kind: ItemKind::Static(..), .. })
             | Node::TraitItem(TraitItem { kind: TraitItemKind::Const(..), .. })
+            | Node::AnonConst(_)
             | Node::ImplItem(ImplItem { kind: ImplItemKind::Const(..), .. }) => Constness::Const,
 
             _ => Constness::NotConst,
diff --git a/compiler/rustc_middle/src/mir/interpret/queries.rs b/compiler/rustc_middle/src/mir/interpret/queries.rs
index c63613ae3af29..f983185563315 100644
--- a/compiler/rustc_middle/src/mir/interpret/queries.rs
+++ b/compiler/rustc_middle/src/mir/interpret/queries.rs
@@ -64,6 +64,7 @@ impl<'tcx> TyCtxt<'tcx> {
         cid: GlobalId<'tcx>,
         span: Option<Span>,
     ) -> EvalToConstValueResult<'tcx> {
+        let param_env = param_env.with_const();
         // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
         // improve caching of queries.
         let inputs = self.erase_regions(param_env.and(cid));
@@ -92,6 +93,7 @@ impl<'tcx> TyCtxt<'tcx> {
         gid: GlobalId<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> Result<&'tcx mir::Allocation, ErrorHandled> {
+        let param_env = param_env.with_const();
         trace!("eval_to_allocation: Need to compute {:?}", gid);
         let raw_const = self.eval_to_allocation_raw(param_env.and(gid))?;
         Ok(self.global_alloc(raw_const.alloc_id).unwrap_memory())
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 312395b7d6b82..3f96c83c5134b 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1318,6 +1318,11 @@ impl<'tcx> ParamEnv<'tcx> {
         self
     }
 
+    pub fn with_const(mut self) -> Self {
+        self.packed.set_tag(ParamTag { constness: hir::Constness::Const, ..self.packed.tag() });
+        self
+    }
+
     /// Returns a new parameter environment with the same clauses, but
     /// which "reveals" the true results of projections in all cases
     /// (even for associated types that are specializable). This is