Auto merge of #103227 - lcnr:bye-bye-unevaluated-const, r=oli-obk

stop using `ty::UnevaluatedConst` directly

best reviewed commit by commit.

simplifies #99798 because we now don't have to expand `ty::UnevaluatedConst` to `ty::Const`.
I also remember some other places where using `ty::UnevaluatedConst` directly was annoying and caused issues, though I don't quite remember what they were rn '^^

r? `@oli-obk` cc `@JulianKnodt`

compiler/rustc_hir_analysis/src/check/dropck.rs

@@ -192,7 +192,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
                 (
                     ty::PredicateKind::ConstEvaluatable(a),
                     ty::PredicateKind::ConstEvaluatable(b),
-                ) => tcx.try_unify_abstract_consts(self_param_env.and((a, b))),
+                ) => relator.relate(predicate.rebind(a), predicate.rebind(b)).is_ok(),
                 (
                     ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_a, lt_a)),
                     ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_b, lt_b)),

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1101,8 +1101,6 @@ fn check_type_defn<'tcx, F>(
 
             // Explicit `enum` discriminant values must const-evaluate successfully.
             if let Some(discr_def_id) = variant.explicit_discr {
-                let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());
-
                 let cause = traits::ObligationCause::new(
                     tcx.def_span(discr_def_id),
                     wfcx.body_id,
@@ -1112,10 +1110,7 @@ fn check_type_defn<'tcx, F>(
                     cause,
                     wfcx.param_env,
                     ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(
-                        ty::UnevaluatedConst::new(
+                        ty::Const::from_anon_const(tcx, discr_def_id),
-                            ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
-                            discr_substs,
-                        ),
                     ))
                     .to_predicate(tcx),
                 ));

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -318,10 +318,10 @@ impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
         fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
             let def_id = self.tcx.hir().local_def_id(c.hir_id);
             let ct = ty::Const::from_anon_const(self.tcx, def_id);
-            if let ty::ConstKind::Unevaluated(uv) = ct.kind() {
+            if let ty::ConstKind::Unevaluated(_) = ct.kind() {
                 let span = self.tcx.hir().span(c.hir_id);
                 self.preds.insert((
-                    ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(uv))
+                    ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ct))
                         .to_predicate(self.tcx),
                     span,
                 ));

compiler/rustc_middle/src/lib.rs

@@ -55,6 +55,7 @@
 #![feature(drain_filter)]
 #![feature(intra_doc_pointers)]
 #![feature(yeet_expr)]
+#![feature(result_option_inspect)]
 #![feature(const_option)]
 #![recursion_limit = "512"]
 #![allow(rustc::potential_query_instability)]

compiler/rustc_middle/src/mir/interpret/queries.rs

@@ -4,7 +4,9 @@
 use crate::ty::subst::InternalSubsts;
 use crate::ty::visit::TypeVisitable;
 use crate::ty::{self, query::TyCtxtAt, query::TyCtxtEnsure, TyCtxt};
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
+use rustc_session::lint;
 use rustc_span::{Span, DUMMY_SP};
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -83,7 +85,29 @@ pub fn const_eval_resolve_for_typeck(
         match ty::Instance::resolve_opt_const_arg(self, param_env, ct.def, ct.substs) {
             Ok(Some(instance)) => {
                 let cid = GlobalId { instance, promoted: None };
-                self.const_eval_global_id_for_typeck(param_env, cid, span)
+                self.const_eval_global_id_for_typeck(param_env, cid, span).inspect(|_| {
+                    // We are emitting the lint here instead of in `is_const_evaluatable`
+                    // as we normalize obligations before checking them, and normalization
+                    // uses this function to evaluate this constant.
+                    //
+                    // @lcnr believes that successfully evaluating even though there are
+                    // used generic parameters is a bug of evaluation, so checking for it
+                    // here does feel somewhat sensible.
+                    if !self.features().generic_const_exprs && ct.substs.has_non_region_param() {
+                        assert!(matches!(self.def_kind(ct.def.did), DefKind::AnonConst));
+                        let mir_body = self.mir_for_ctfe_opt_const_arg(ct.def);
+                        if mir_body.is_polymorphic {
+                            let Some(local_def_id) = ct.def.did.as_local() else { return };
+                            self.struct_span_lint_hir(
+                                lint::builtin::CONST_EVALUATABLE_UNCHECKED,
+                                self.hir().local_def_id_to_hir_id(local_def_id),
+                                self.def_span(ct.def.did),
+                                "cannot use constants which depend on generic parameters in types",
+                                |err| err,
+                            )
+                        }
+                    }
+                })
             }
             Ok(None) => Err(ErrorHandled::TooGeneric),
             Err(error_reported) => Err(ErrorHandled::Reported(error_reported)),

compiler/rustc_middle/src/ty/consts.rs

@@ -263,6 +263,10 @@ pub fn eval_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
         self.try_eval_usize(tcx, param_env)
             .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
     }
+
+    pub fn is_ct_infer(self) -> bool {
+        matches!(self.kind(), ty::ConstKind::Infer(_))
+    }
 }
 
 pub fn const_param_default<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Const<'tcx> {

compiler/rustc_middle/src/ty/consts/kind.rs

@@ -15,7 +15,7 @@
 
 /// An unevaluated (potentially generic) constant used in the type-system.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Lift)]
-#[derive(Hash, HashStable)]
+#[derive(Hash, HashStable, TypeFoldable, TypeVisitable)]
 pub struct UnevaluatedConst<'tcx> {
     pub def: ty::WithOptConstParam<DefId>,
     pub substs: SubstsRef<'tcx>,

compiler/rustc_middle/src/ty/flags.rs

@@ -34,12 +34,6 @@ pub fn for_const(c: ty::Const<'_>) -> TypeFlags {
         result.flags
     }
 
-    pub fn for_unevaluated_const(uv: ty::UnevaluatedConst<'_>) -> TypeFlags {
-        let mut result = FlagComputation::new();
-        result.add_unevaluated_const(uv);
-        result.flags
-    }
-
     fn add_flags(&mut self, flags: TypeFlags) {
         self.flags = self.flags | flags;
     }
@@ -256,7 +250,7 @@ fn add_predicate_atom(&mut self, atom: ty::PredicateKind<'_>) {
                 self.add_substs(substs);
             }
             ty::PredicateKind::ConstEvaluatable(uv) => {
-                self.add_unevaluated_const(uv);
+                self.add_const(uv);
             }
             ty::PredicateKind::ConstEquate(expected, found) => {
                 self.add_const(expected);
@@ -289,7 +283,10 @@ fn add_region(&mut self, r: ty::Region<'_>) {
     fn add_const(&mut self, c: ty::Const<'_>) {
         self.add_ty(c.ty());
         match c.kind() {
-            ty::ConstKind::Unevaluated(unevaluated) => self.add_unevaluated_const(unevaluated),
+            ty::ConstKind::Unevaluated(uv) => {
+                self.add_substs(uv.substs);
+                self.add_flags(TypeFlags::HAS_CT_PROJECTION);
+            }
             ty::ConstKind::Infer(infer) => {
                 self.add_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
                 match infer {
@@ -313,11 +310,6 @@ fn add_const(&mut self, c: ty::Const<'_>) {
         }
     }
 
-    fn add_unevaluated_const(&mut self, ct: ty::UnevaluatedConst<'_>) {
-        self.add_substs(ct.substs);
-        self.add_flags(TypeFlags::HAS_CT_PROJECTION);
-    }
-
     fn add_existential_projection(&mut self, projection: &ty::ExistentialProjection<'_>) {
         self.add_substs(projection.substs);
         match projection.term.unpack() {

compiler/rustc_middle/src/ty/fold.rs

@@ -126,13 +126,6 @@ fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
         c.super_fold_with(self)
     }
 
-    fn fold_ty_unevaluated(
-        &mut self,
-        uv: ty::UnevaluatedConst<'tcx>,
-    ) -> ty::UnevaluatedConst<'tcx> {
-        uv.super_fold_with(self)
-    }
-
     fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
         p.super_fold_with(self)
     }
@@ -169,13 +162,6 @@ fn try_fold_const(&mut self, c: ty::Const<'tcx>) -> Result<ty::Const<'tcx>, Self
         c.try_super_fold_with(self)
     }
 
-    fn try_fold_ty_unevaluated(
-        &mut self,
-        c: ty::UnevaluatedConst<'tcx>,
-    ) -> Result<ty::UnevaluatedConst<'tcx>, Self::Error> {
-        c.try_super_fold_with(self)
-    }
-
     fn try_fold_predicate(
         &mut self,
         p: ty::Predicate<'tcx>,
@@ -215,13 +201,6 @@ fn try_fold_const(&mut self, c: ty::Const<'tcx>) -> Result<ty::Const<'tcx>, !> {
         Ok(self.fold_const(c))
     }
 
-    fn try_fold_ty_unevaluated(
-        &mut self,
-        c: ty::UnevaluatedConst<'tcx>,
-    ) -> Result<ty::UnevaluatedConst<'tcx>, !> {
-        Ok(self.fold_ty_unevaluated(c))
-    }
-
     fn try_fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> Result<ty::Predicate<'tcx>, !> {
         Ok(self.fold_predicate(p))
     }

compiler/rustc_middle/src/ty/mod.rs

@@ -683,7 +683,7 @@ pub enum PredicateKind<'tcx> {
     Coerce(CoercePredicate<'tcx>),
 
     /// Constant initializer must evaluate successfully.
-    ConstEvaluatable(ty::UnevaluatedConst<'tcx>),
+    ConstEvaluatable(ty::Const<'tcx>),
 
     /// Constants must be equal. The first component is the const that is expected.
     ConstEquate(Const<'tcx>, Const<'tcx>),

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2702,8 +2702,8 @@ pub struct PrintClosureAsImpl<'tcx> {
                 print_value_path(closure_def_id, &[]),
                 write("` implements the trait `{}`", kind))
             }
-            ty::PredicateKind::ConstEvaluatable(uv) => {
+            ty::PredicateKind::ConstEvaluatable(ct) => {
-                p!("the constant `", print_value_path(uv.def.did, uv.substs), "` can be evaluated")
+                p!("the constant `", print(ct), "` can be evaluated")
             }
             ty::PredicateKind::ConstEquate(c1, c2) => {
                 p!("the constant `", print(c1), "` equals `", print(c2), "`")

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -166,8 +166,8 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
             ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
                 write!(f, "ClosureKind({:?}, {:?}, {:?})", closure_def_id, closure_substs, kind)
             }
-            ty::PredicateKind::ConstEvaluatable(uv) => {
+            ty::PredicateKind::ConstEvaluatable(ct) => {
-                write!(f, "ConstEvaluatable({:?}, {:?})", uv.def, uv.substs)
+                write!(f, "ConstEvaluatable({ct:?})")
             }
             ty::PredicateKind::ConstEquate(c1, c2) => write!(f, "ConstEquate({:?}, {:?})", c1, c2),
             ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
@@ -832,27 +832,6 @@ fn visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<V::B
     }
 }
 
-impl<'tcx> TypeFoldable<'tcx> for ty::UnevaluatedConst<'tcx> {
-    fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
-        folder.try_fold_ty_unevaluated(self)
-    }
-}
-
-impl<'tcx> TypeVisitable<'tcx> for ty::UnevaluatedConst<'tcx> {
-    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
-        visitor.visit_ty_unevaluated(*self)
-    }
-}
-
-impl<'tcx> TypeSuperFoldable<'tcx> for ty::UnevaluatedConst<'tcx> {
-    fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(ty::UnevaluatedConst { def: self.def, substs: self.substs.try_fold_with(folder)? })
-    }
-}
-
 impl<'tcx> TypeSuperVisitable<'tcx> for ty::UnevaluatedConst<'tcx> {
     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.substs.visit_with(visitor)

compiler/rustc_middle/src/ty/subst.rs

@@ -188,6 +188,14 @@ pub fn expect_const(self) -> ty::Const<'tcx> {
             _ => bug!("expected a const, but found another kind"),
         }
     }
+
+    pub fn is_non_region_infer(self) -> bool {
+        match self.unpack() {
+            GenericArgKind::Lifetime(_) => false,
+            GenericArgKind::Type(ty) => ty.is_ty_infer(),
+            GenericArgKind::Const(ct) => ct.is_ct_infer(),
+        }
+    }
 }
 
 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {

compiler/rustc_middle/src/ty/visit.rs

@@ -197,13 +197,6 @@ fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         c.super_visit_with(self)
     }
 
-    fn visit_ty_unevaluated(
-        &mut self,
-        uv: ty::UnevaluatedConst<'tcx>,
-    ) -> ControlFlow<Self::BreakTy> {
-        uv.super_visit_with(self)
-    }
-
     fn visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
         p.super_visit_with(self)
     }
@@ -592,21 +585,6 @@ fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         }
     }
 
-    #[inline]
-    #[instrument(level = "trace", ret)]
-    fn visit_ty_unevaluated(
-        &mut self,
-        uv: ty::UnevaluatedConst<'tcx>,
-    ) -> ControlFlow<Self::BreakTy> {
-        let flags = FlagComputation::for_unevaluated_const(uv);
-        trace!(r.flags=?flags);
-        if flags.intersects(self.flags) {
-            ControlFlow::Break(FoundFlags)
-        } else {
-            ControlFlow::CONTINUE
-        }
-    }
-
     #[inline]
     #[instrument(level = "trace", ret)]
     fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {

compiler/rustc_middle/src/ty/walk.rs

@@ -112,6 +112,22 @@ pub fn walk(self) -> TypeWalker<'tcx> {
     }
 }
 
+impl<'tcx> ty::Const<'tcx> {
+    /// Iterator that walks `self` and any types reachable from
+    /// `self`, in depth-first order. Note that just walks the types
+    /// that appear in `self`, it does not descend into the fields of
+    /// structs or variants. For example:
+    ///
+    /// ```text
+    /// isize => { isize }
+    /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
+    /// [isize] => { [isize], isize }
+    /// ```
+    pub fn walk(self) -> TypeWalker<'tcx> {
+        TypeWalker::new(self.into())
+    }
+}
+
 /// We push `GenericArg`s on the stack in reverse order so as to
 /// maintain a pre-order traversal. As of the time of this
 /// writing, the fact that the traversal is pre-order is not

compiler/rustc_privacy/src/lib.rs

@@ -159,34 +159,12 @@ fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<V::
                 ty.visit_with(self)
             }
             ty::PredicateKind::RegionOutlives(..) => ControlFlow::CONTINUE,
-            ty::PredicateKind::ConstEvaluatable(uv)
+            ty::PredicateKind::ConstEvaluatable(ct) => ct.visit_with(self),
-                if self.def_id_visitor.tcx().features().generic_const_exprs =>
-            {
-                let tcx = self.def_id_visitor.tcx();
-                if let Ok(Some(ct)) = AbstractConst::new(tcx, uv) {
-                    self.visit_abstract_const_expr(tcx, ct)?;
-                }
-                ControlFlow::CONTINUE
-            }
             ty::PredicateKind::WellFormed(arg) => arg.visit_with(self),
             _ => bug!("unexpected predicate: {:?}", predicate),
         }
     }
 
-    fn visit_abstract_const_expr(
-        &mut self,
-        tcx: TyCtxt<'tcx>,
-        ct: AbstractConst<'tcx>,
-    ) -> ControlFlow<V::BreakTy> {
-        walk_abstract_const(tcx, ct, |node| match node.root(tcx) {
-            ACNode::Leaf(leaf) => self.visit_const(leaf),
-            ACNode::Cast(_, _, ty) => self.visit_ty(ty),
-            ACNode::Binop(..) | ACNode::UnaryOp(..) | ACNode::FunctionCall(_, _) => {
-                ControlFlow::CONTINUE
-            }
-        })
-    }
-
     fn visit_predicates(
         &mut self,
         predicates: ty::GenericPredicates<'tcx>,
@@ -309,9 +287,16 @@ fn visit_const(&mut self, c: Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         self.visit_ty(c.ty())?;
         let tcx = self.def_id_visitor.tcx();
         if let Ok(Some(ct)) = AbstractConst::from_const(tcx, c) {
-            self.visit_abstract_const_expr(tcx, ct)?;
+            walk_abstract_const(tcx, ct, |node| match node.root(tcx) {
+                ACNode::Leaf(leaf) => self.visit_const(leaf),
+                ACNode::Cast(_, _, ty) => self.visit_ty(ty),
+                ACNode::Binop(..) | ACNode::UnaryOp(..) | ACNode::FunctionCall(_, _) => {
+                    ControlFlow::CONTINUE
+                }
+            })
+        } else {
+            ControlFlow::CONTINUE
         }
-        ControlFlow::CONTINUE
     }
 }
 

compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -9,14 +9,12 @@
 //! `thir_abstract_const` which can then be checked for structural equality with other
 //! generic constants mentioned in the `caller_bounds` of the current environment.
 use rustc_errors::ErrorGuaranteed;
-use rustc_hir::def::DefKind;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::abstract_const::{
     walk_abstract_const, AbstractConst, FailureKind, Node, NotConstEvaluatable,
 };
 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
-use rustc_session::lint;
 use rustc_span::Span;
 
 use std::iter;
@@ -161,11 +159,20 @@ pub fn try_unify_abstract_consts<'tcx>(
 #[instrument(skip(infcx), level = "debug")]
 pub fn is_const_evaluatable<'tcx>(
     infcx: &InferCtxt<'tcx>,
-    uv: ty::UnevaluatedConst<'tcx>,
+    ct: ty::Const<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     span: Span,
 ) -> Result<(), NotConstEvaluatable> {
     let tcx = infcx.tcx;
+    let uv = match ct.kind() {
+        ty::ConstKind::Unevaluated(uv) => uv,
+        ty::ConstKind::Param(_)
+        | ty::ConstKind::Bound(_, _)
+        | ty::ConstKind::Placeholder(_)
+        | ty::ConstKind::Value(_)
+        | ty::ConstKind::Error(_) => return Ok(()),
+        ty::ConstKind::Infer(_) => return Err(NotConstEvaluatable::MentionsInfer),
+    };
 
     if tcx.features().generic_const_exprs {
         if let Some(ct) = AbstractConst::new(tcx, uv)? {
@@ -253,25 +260,7 @@ pub fn is_const_evaluatable<'tcx>(
                 Err(NotConstEvaluatable::Error(reported))
             }
             Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)),
-            Ok(_) => {
+            Ok(_) => Ok(()),
-                if uv.substs.has_non_region_param() {
-                    assert!(matches!(infcx.tcx.def_kind(uv.def.did), DefKind::AnonConst));
-                    let mir_body = infcx.tcx.mir_for_ctfe_opt_const_arg(uv.def);
-
-                    if mir_body.is_polymorphic {
-                        let Some(local_def_id) = uv.def.did.as_local() else { return Ok(()) };
-                        tcx.struct_span_lint_hir(
-                            lint::builtin::CONST_EVALUATABLE_UNCHECKED,
-                            tcx.hir().local_def_id_to_hir_id(local_def_id),
-                            span,
-                            "cannot use constants which depend on generic parameters in types",
-                            |err| err
-                        )
-                    }
-                }
-
-                Ok(())
-            },
         }
     }
 }
@@ -285,7 +274,7 @@ fn satisfied_from_param_env<'tcx>(
     for pred in param_env.caller_bounds() {
         match pred.kind().skip_binder() {
             ty::PredicateKind::ConstEvaluatable(uv) => {
-                if let Some(b_ct) = AbstractConst::new(tcx, uv)? {
+                if let Some(b_ct) = AbstractConst::from_const(tcx, uv)? {
                     let const_unify_ctxt = ConstUnifyCtxt { tcx, param_env };
 
                     // Try to unify with each subtree in the AbstractConst to allow for

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

@@ -1304,7 +1304,10 @@ fn report_selection_error(
                 }
 
                 match obligation.predicate.kind().skip_binder() {
-                    ty::PredicateKind::ConstEvaluatable(uv) => {
+                    ty::PredicateKind::ConstEvaluatable(ct) => {
+                        let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
+                            bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
+                        };
                         let mut err =
                             self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
                         let const_span = self.tcx.def_span(uv.def.did);
@@ -2368,7 +2371,7 @@ fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
                 if predicate.references_error() || self.is_tainted_by_errors() {
                     return;
                 }
-                let subst = data.substs.iter().find(|g| g.has_non_region_infer());
+                let subst = data.walk().find(|g| g.is_non_region_infer());
                 if let Some(subst) = subst {
                     let err = self.emit_inference_failure_err(
                         body_id,

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -476,9 +476,7 @@ fn process_obligation(
                         Err(NotConstEvaluatable::MentionsInfer) => {
                             pending_obligation.stalled_on.clear();
                             pending_obligation.stalled_on.extend(
-                                uv.substs
+                                uv.walk().filter_map(TyOrConstInferVar::maybe_from_generic_arg),
-                                    .iter()
-                                    .filter_map(TyOrConstInferVar::maybe_from_generic_arg),
                             );
                             ProcessResult::Unchanged
                         }

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -837,24 +837,14 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
             }
         }
 
-        fn visit_ty_unevaluated(
+        fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-            &mut self,
-            uv: ty::UnevaluatedConst<'tcx>,
-        ) -> ControlFlow<Self::BreakTy> {
             // Constants can only influence object safety if they reference `Self`.
             // This is only possible for unevaluated constants, so we walk these here.
             //
-            // If `AbstractConst::new` returned an error we already failed compilation
+            // If `AbstractConst::from_const` returned an error we already failed compilation
             // so we don't have to emit an additional error here.
-            //
-            // We currently recurse into abstract consts here but do not recurse in
-            // `is_const_evaluatable`. This means that the object safety check is more
-            // liberal than the const eval check.
-            //
-            // This shouldn't really matter though as we can't really use any
-            // constants which are not considered const evaluatable.
             use rustc_middle::ty::abstract_const::Node;
-            if let Ok(Some(ct)) = AbstractConst::new(self.tcx, uv) {
+            if let Ok(Some(ct)) = AbstractConst::from_const(self.tcx, ct) {
                 walk_abstract_const(self.tcx, ct, |node| match node.root(self.tcx) {
                     Node::Leaf(leaf) => self.visit_const(leaf),
                     Node::Cast(_, _, ty) => self.visit_ty(ty),
@@ -863,7 +853,7 @@ fn visit_ty_unevaluated(
                     }
                 })
             } else {
-                ControlFlow::CONTINUE
+                ct.super_visit_with(self)
             }
         }
     }

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -148,13 +148,8 @@ pub fn predicate_obligations<'tcx>(
             wf.compute(a.into());
             wf.compute(b.into());
         }
-        ty::PredicateKind::ConstEvaluatable(uv) => {
+        ty::PredicateKind::ConstEvaluatable(ct) => {
-            let obligations = wf.nominal_obligations(uv.def.did, uv.substs);
+            wf.compute(ct.into());
-            wf.out.extend(obligations);
-
-            for arg in uv.substs.iter() {
-                wf.compute(arg);
-            }
         }
         ty::PredicateKind::ConstEquate(c1, c2) => {
             wf.compute(c1.into());
@@ -476,14 +471,14 @@ fn compute(&mut self, arg: GenericArg<'tcx>) {
                 // obligations are handled by the parent (e.g. `ty::Ref`).
                 GenericArgKind::Lifetime(_) => continue,
 
-                GenericArgKind::Const(constant) => {
+                GenericArgKind::Const(ct) => {
-                    match constant.kind() {
+                    match ct.kind() {
                         ty::ConstKind::Unevaluated(uv) => {
                             let obligations = self.nominal_obligations(uv.def.did, uv.substs);
                             self.out.extend(obligations);
 
                             let predicate =
-                                ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(uv))
+                                ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ct))
                                     .to_predicate(self.tcx());
                             let cause = self.cause(traits::WellFormed(None));
                             self.out.push(traits::Obligation::with_depth(
@@ -500,7 +495,7 @@ fn compute(&mut self, arg: GenericArg<'tcx>) {
                                 cause,
                                 self.recursion_depth,
                                 self.param_env,
-                                ty::Binder::dummy(ty::PredicateKind::WellFormed(constant.into()))
+                                ty::Binder::dummy(ty::PredicateKind::WellFormed(ct.into()))
                                     .to_predicate(self.tcx()),
                             ));
                         }

src/test/ui/const-generics/generic_const_exprs/dependence_lint.full.stderr

@@ -1,5 +1,5 @@
 error: generic parameters may not be used in const operations
-  --> $DIR/dependence_lint.rs:13:32
+  --> $DIR/dependence_lint.rs:14:32
    |
 LL |     let _: [u8; size_of::<*mut T>()]; // error on stable, error with gce
    |                                ^ cannot perform const operation using `T`
@@ -8,7 +8,7 @@ LL |     let _: [u8; size_of::<*mut T>()]; // error on stable, error with gce
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/dependence_lint.rs:20:37
+  --> $DIR/dependence_lint.rs:21:37
    |
 LL |     let _: [u8; if true { size_of::<T>() } else { 3 }]; // error on stable, error with gce
    |                                     ^ cannot perform const operation using `T`
@@ -17,7 +17,7 @@ LL |     let _: [u8; if true { size_of::<T>() } else { 3 }]; // error on stable,
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 warning: cannot use constants which depend on generic parameters in types
-  --> $DIR/dependence_lint.rs:9:9
+  --> $DIR/dependence_lint.rs:10:9
    |
 LL |     [0; size_of::<*mut T>()]; // lint on stable, error with `generic_const_exprs`
    |         ^^^^^^^^^^^^^^^^^^^
@@ -27,7 +27,7 @@ LL |     [0; size_of::<*mut T>()]; // lint on stable, error with `generic_const_
    = note: `#[warn(const_evaluatable_unchecked)]` on by default
 
 warning: cannot use constants which depend on generic parameters in types
-  --> $DIR/dependence_lint.rs:16:9
+  --> $DIR/dependence_lint.rs:17:9
    |
 LL |     [0; if false { size_of::<T>() } else { 3 }]; // lint on stable, error with gce
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/test/ui/const-generics/generic_const_exprs/dependence_lint.gce.stderr

@@ -1,5 +1,5 @@
 error: overly complex generic constant
-  --> $DIR/dependence_lint.rs:16:9
+  --> $DIR/dependence_lint.rs:17:9
    |
 LL |     [0; if false { size_of::<T>() } else { 3 }]; // lint on stable, error with gce
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ control flow is not supported in generic constants
@@ -7,7 +7,7 @@ LL |     [0; if false { size_of::<T>() } else { 3 }]; // lint on stable, error w
    = help: consider moving this anonymous constant into a `const` function
 
 error: overly complex generic constant
-  --> $DIR/dependence_lint.rs:20:17
+  --> $DIR/dependence_lint.rs:21:17
    |
 LL |     let _: [u8; if true { size_of::<T>() } else { 3 }]; // error on stable, error with gce
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ control flow is not supported in generic constants
@@ -15,7 +15,7 @@ LL |     let _: [u8; if true { size_of::<T>() } else { 3 }]; // error on stable,
    = help: consider moving this anonymous constant into a `const` function
 
 error: unconstrained generic constant
-  --> $DIR/dependence_lint.rs:13:12
+  --> $DIR/dependence_lint.rs:14:12
    |
 LL |     let _: [u8; size_of::<*mut T>()]; // error on stable, error with gce
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -23,7 +23,7 @@ LL |     let _: [u8; size_of::<*mut T>()]; // error on stable, error with gce
    = help: try adding a `where` bound using this expression: `where [(); size_of::<*mut T>()]:`
 
 error: unconstrained generic constant
-  --> $DIR/dependence_lint.rs:9:9
+  --> $DIR/dependence_lint.rs:10:9
    |
 LL |     [0; size_of::<*mut T>()]; // lint on stable, error with `generic_const_exprs`
    |         ^^^^^^^^^^^^^^^^^^^

src/test/ui/const-generics/generic_const_exprs/dependence_lint.rs

@@ -1,4 +1,5 @@
 // revisions: full gce
+// compile-flags: -Zdeduplicate-diagnostics=yes
 
 #![cfg_attr(gce, feature(generic_const_exprs))]
 #![allow(incomplete_features)]

src/test/ui/const-generics/generic_const_exprs/function-call.rs

@@ -1,4 +1,5 @@
 // check-pass
+// compile-flags: -Zdeduplicate-diagnostics=yes
 
 const fn foo<T>() -> usize {
     // We might instead branch on `std::mem::size_of::<*mut T>() < 8` here,

src/test/ui/const-generics/generic_const_exprs/function-call.stderr

@@ -1,5 +1,5 @@
 warning: cannot use constants which depend on generic parameters in types
-  --> $DIR/function-call.rs:14:17
+  --> $DIR/function-call.rs:15:17
    |
 LL |     let _ = [0; foo::<T>()];
    |                 ^^^^^^^^^^

src/test/ui/const-generics/min_const_generics/complex-expression.rs

@@ -1,3 +1,4 @@
+// compile-flags: -Zdeduplicate-diagnostics=yes
 use std::mem::size_of;
 
 fn test<const N: usize>() {}

src/test/ui/const-generics/min_const_generics/complex-expression.stderr

@@ -1,5 +1,5 @@
 error: generic parameters may not be used in const operations
-  --> $DIR/complex-expression.rs:9:38
+  --> $DIR/complex-expression.rs:10:38
    |
 LL | struct Break0<const N: usize>([u8; { N + 1 }]);
    |                                      ^ cannot perform const operation using `N`
@@ -8,7 +8,7 @@ LL | struct Break0<const N: usize>([u8; { N + 1 }]);
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/complex-expression.rs:12:40
+  --> $DIR/complex-expression.rs:13:40
    |
 LL | struct Break1<const N: usize>([u8; { { N } }]);
    |                                        ^ cannot perform const operation using `N`
@@ -17,7 +17,7 @@ LL | struct Break1<const N: usize>([u8; { { N } }]);
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/complex-expression.rs:16:17
+  --> $DIR/complex-expression.rs:17:17
    |
 LL |     let _: [u8; N + 1];
    |                 ^ cannot perform const operation using `N`
@@ -26,7 +26,7 @@ LL |     let _: [u8; N + 1];
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/complex-expression.rs:21:17
+  --> $DIR/complex-expression.rs:22:17
    |
 LL |     let _ = [0; N + 1];
    |                 ^ cannot perform const operation using `N`
@@ -35,7 +35,7 @@ LL |     let _ = [0; N + 1];
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/complex-expression.rs:25:45
+  --> $DIR/complex-expression.rs:26:45
    |
 LL | struct BreakTy0<T>(T, [u8; { size_of::<*mut T>() }]);
    |                                             ^ cannot perform const operation using `T`
@@ -44,7 +44,7 @@ LL | struct BreakTy0<T>(T, [u8; { size_of::<*mut T>() }]);
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/complex-expression.rs:28:47
+  --> $DIR/complex-expression.rs:29:47
    |
 LL | struct BreakTy1<T>(T, [u8; { { size_of::<*mut T>() } }]);
    |                                               ^ cannot perform const operation using `T`
@@ -53,7 +53,7 @@ LL | struct BreakTy1<T>(T, [u8; { { size_of::<*mut T>() } }]);
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/complex-expression.rs:32:32
+  --> $DIR/complex-expression.rs:33:32
    |
 LL |     let _: [u8; size_of::<*mut T>() + 1];
    |                                ^ cannot perform const operation using `T`
@@ -62,7 +62,7 @@ LL |     let _: [u8; size_of::<*mut T>() + 1];
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 warning: cannot use constants which depend on generic parameters in types
-  --> $DIR/complex-expression.rs:37:17
+  --> $DIR/complex-expression.rs:38:17
    |
 LL |     let _ = [0; size_of::<*mut T>() + 1];
    |                 ^^^^^^^^^^^^^^^^^^^^^^^

src/test/ui/const-generics/min_const_generics/const-evaluatable-unchecked.rs

@@ -1,4 +1,5 @@
 // check-pass
+// compile-flags: -Zdeduplicate-diagnostics=yes
 #![allow(dead_code)]
 
 fn foo<T>() {

src/test/ui/const-generics/min_const_generics/const-evaluatable-unchecked.stderr

@@ -1,5 +1,5 @@
 warning: cannot use constants which depend on generic parameters in types
-  --> $DIR/const-evaluatable-unchecked.rs:5:9
+  --> $DIR/const-evaluatable-unchecked.rs:6:9
    |
 LL |     [0; std::mem::size_of::<*mut T>()];
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -9,7 +9,7 @@ LL |     [0; std::mem::size_of::<*mut T>()];
    = note: `#[warn(const_evaluatable_unchecked)]` on by default
 
 warning: cannot use constants which depend on generic parameters in types
-  --> $DIR/const-evaluatable-unchecked.rs:16:21
+  --> $DIR/const-evaluatable-unchecked.rs:17:21
    |
 LL |         let _ = [0; Self::ASSOC];
    |                     ^^^^^^^^^^^
@@ -18,7 +18,7 @@ LL |         let _ = [0; Self::ASSOC];
    = note: for more information, see issue #76200 <https://github.com/rust-lang/rust/issues/76200>
 
 warning: cannot use constants which depend on generic parameters in types
-  --> $DIR/const-evaluatable-unchecked.rs:28:21
+  --> $DIR/const-evaluatable-unchecked.rs:29:21
    |
 LL |         let _ = [0; Self::ASSOC];
    |                     ^^^^^^^^^^^