Auto merge of #98588 - b-naber:valtrees-cleanup, r=lcnr

Use only ty::Unevaluated<'tcx, ()> in type system

r? `@lcnr`

3 files changed, 49 insertions, 31 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index f6c4f7dd112..29c745a0886 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -564,8 +564,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 throw_inval!(AlreadyReported(reported))
             }
             ty::ConstKind::Unevaluated(uv) => {
+                // NOTE: We evaluate to a `ValTree` here as a check to ensure
+                // we're working with valid constants, even though we never need it.
                 let instance = self.resolve(uv.def, uv.substs)?;
-                Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into())
+                let cid = GlobalId { instance, promoted: None };
+                let _valtree = self
+                    .tcx
+                    .eval_to_valtree(self.param_env.and(cid))?
+                    .unwrap_or_else(|| bug!("unable to create ValTree for {:?}", uv));
+
+                Ok(self.eval_to_allocation(cid)?.into())
             }
             ty::ConstKind::Bound(..) | ty::ConstKind::Infer(..) => {
                 span_bug!(self.cur_span(), "const_to_op: Unexpected ConstKind {:?}", c)
@@ -586,6 +594,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         match val {
             mir::ConstantKind::Ty(ct) => self.const_to_op(*ct, layout),
             mir::ConstantKind::Val(val, ty) => self.const_val_to_op(*val, *ty, layout),
+            mir::ConstantKind::Unevaluated(uv, _) => {
+                let instance = self.resolve(uv.def, uv.substs)?;
+                Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into())
+            }
         }
     }
 
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 45dadcfff2e..6c73ef5a8fa 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
@@ -346,31 +346,43 @@ where
     };
 
     // Check the qualifs of the value of `const` items.
-    if let Some(ct) = constant.literal.const_for_ty() {
-        if let ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs: _, promoted }) = ct.kind()
-        {
-            // Use qualifs of the type for the promoted. Promoteds in MIR body should be possible
-            // only for `NeedsNonConstDrop` with precise drop checking. This is the only const
-            // check performed after the promotion. Verify that with an assertion.
-            assert!(promoted.is_none() || Q::ALLOW_PROMOTED);
-            // Don't peek inside trait associated constants.
-            if promoted.is_none() && cx.tcx.trait_of_item(def.did).is_none() {
-                let qualifs = if let Some((did, param_did)) = def.as_const_arg() {
-                    cx.tcx.at(constant.span).mir_const_qualif_const_arg((did, param_did))
-                } else {
-                    cx.tcx.at(constant.span).mir_const_qualif(def.did)
-                };
-
-                if !Q::in_qualifs(&qualifs) {
-                    return false;
-                }
+    // FIXME(valtrees): check whether const qualifs should behave the same
+    // way for type and mir constants.
+    let uneval = match constant.literal {
+        ConstantKind::Ty(ct) if matches!(ct.kind(), ty::ConstKind::Unevaluated(_)) => {
+            let ty::ConstKind::Unevaluated(uv) = ct.kind() else { unreachable!() };
 
-                // Just in case the type is more specific than
-                // the definition, e.g., impl associated const
-                // with type parameters, take it into account.
+            Some(uv.expand())
+        }
+        ConstantKind::Ty(_) => None,
+        ConstantKind::Unevaluated(uv, _) => Some(uv),
+        ConstantKind::Val(..) => None,
+    };
+
+    if let Some(ty::Unevaluated { def, substs: _, promoted }) = uneval {
+        // Use qualifs of the type for the promoted. Promoteds in MIR body should be possible
+        // only for `NeedsNonConstDrop` with precise drop checking. This is the only const
+        // check performed after the promotion. Verify that with an assertion.
+        assert!(promoted.is_none() || Q::ALLOW_PROMOTED);
+
+        // Don't peek inside trait associated constants.
+        if promoted.is_none() && cx.tcx.trait_of_item(def.did).is_none() {
+            let qualifs = if let Some((did, param_did)) = def.as_const_arg() {
+                cx.tcx.at(constant.span).mir_const_qualif_const_arg((did, param_did))
+            } else {
+                cx.tcx.at(constant.span).mir_const_qualif(def.did)
+            };
+
+            if !Q::in_qualifs(&qualifs) {
+                return false;
             }
+
+            // Just in case the type is more specific than
+            // the definition, e.g., impl associated const
+            // with type parameters, take it into account.
         }
     }
+
     // Otherwise use the qualifs of the type.
     Q::in_any_value_of_ty(cx, constant.literal.ty())
 }
diff --git a/compiler/rustc_const_eval/src/transform/promote_consts.rs b/compiler/rustc_const_eval/src/transform/promote_consts.rs
index f5ba408bee0..f7a7cc88a52 100644
--- a/compiler/rustc_const_eval/src/transform/promote_consts.rs
+++ b/compiler/rustc_const_eval/src/transform/promote_consts.rs
@@ -840,21 +840,15 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                 promoted.span = span;
                 promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span);
                 let substs = tcx.erase_regions(InternalSubsts::identity_for_item(tcx, def.did));
-                let _const = tcx.mk_const(ty::ConstS {
-                    ty,
-                    kind: ty::ConstKind::Unevaluated(ty::Unevaluated {
-                        def,
-                        substs,
-                        promoted: Some(promoted_id),
-                    }),
-                });
+                let uneval = ty::Unevaluated { def, substs, promoted: Some(promoted_id) };
 
                 Operand::Constant(Box::new(Constant {
                     span,
                     user_ty: None,
-                    literal: ConstantKind::from_const(_const, tcx),
+                    literal: ConstantKind::Unevaluated(uneval, ty),
                 }))
             };
+
             let blocks = self.source.basic_blocks.as_mut();
             let local_decls = &mut self.source.local_decls;
             let loc = candidate.location;