Auto merge of #91354 - fee1-dead:const_env, r=spastorino

Cleanup: Eliminate ConstnessAnd

This is almost a behaviour-free change and purely a refactoring. "almost" because we appear to be using the wrong ParamEnv somewhere already, and this is now exposed by failing a test using the unstable `~const` feature.

We most definitely need to review all `without_const` and at some point should probably get rid of many of them by using `TraitPredicate` instead of `TraitRef`.

This is a continuation of #90274.

r? `@oli-obk`

cc `@spastorino` `@ecstatic-morse`

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -31,7 +31,7 @@ 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};

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;
@@ -215,6 +216,7 @@ 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;
@@ -249,6 +251,7 @@ 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

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)
     }

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -817,8 +817,7 @@ 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)
                     });
 

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)
         });
         !matches!(

compiler/rustc_hir/src/hir.rs

@@ -3230,31 +3230,6 @@ impl<'hir> Node<'hir> {
         }
     }
 
-    /// Returns `Constness::Const` when this node is a const fn/impl/item.
-    pub fn constness_for_typeck(&self) -> Constness {
-        match self {
-            Node::Item(Item {
-                kind: ItemKind::Fn(FnSig { header: FnHeader { constness, .. }, .. }, ..),
-                ..
-            })
-            | Node::TraitItem(TraitItem {
-                kind: TraitItemKind::Fn(FnSig { header: FnHeader { constness, .. }, .. }, ..),
-                ..
-            })
-            | Node::ImplItem(ImplItem {
-                kind: ImplItemKind::Fn(FnSig { header: FnHeader { constness, .. }, .. }, ..),
-                ..
-            })
-            | Node::Item(Item { kind: ItemKind::Impl(Impl { constness, .. }), .. }) => *constness,
-
-            Node::Item(Item { kind: ItemKind::Const(..), .. })
-            | Node::TraitItem(TraitItem { kind: TraitItemKind::Const(..), .. })
-            | Node::ImplItem(ImplItem { kind: ImplItemKind::Const(..), .. }) => Constness::Const,
-
-            _ => Constness::NotConst,
-        }
-    }
-
     pub fn as_owner(self) -> Option<OwnerNode<'hir>> {
         match self {
             Node::Item(i) => Some(OwnerNode::Item(i)),

compiler/rustc_infer/src/traits/engine.rs

@@ -1,9 +1,8 @@
 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};
+use rustc_middle::ty::{self, ToPredicate, Ty};
 
 use super::FulfillmentError;
 use super::{ObligationCause, PredicateObligation};
@@ -48,26 +47,9 @@ pub trait TraitEngine<'tcx>: 'tcx {
 
     fn select_all_or_error(&mut self, infcx: &InferCtxt<'_, 'tcx>) -> Vec<FulfillmentError<'tcx>>;
 
-    fn select_all_with_constness_or_error(
-        &mut self,
-        infcx: &InferCtxt<'_, 'tcx>,
-        _constness: hir::Constness,
-    ) -> Vec<FulfillmentError<'tcx>> {
-        self.select_all_or_error(infcx)
-    }
-
     fn select_where_possible(&mut self, infcx: &InferCtxt<'_, 'tcx>)
     -> 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,
-    ) -> 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>;

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);

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;
 use rustc_span::Span;
 
@@ -328,8 +328,8 @@ 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));
                     }
                 }
 
@@ -362,8 +362,8 @@ 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

compiler/rustc_middle/src/hir/map/mod.rs

@@ -474,7 +474,8 @@ 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) {

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())

compiler/rustc_middle/src/traits/select.rs

@@ -12,14 +12,12 @@ 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>>,
 >;
 
-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
@@ -103,7 +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),
 

compiler/rustc_middle/src/traits/util.rs

@@ -26,9 +26,9 @@ impl<'tcx> Elaborator<'tcx> {
             .predicates
             .into_iter()
             .flat_map(|(pred, _)| {
-                pred.subst_supertrait(self.tcx, &trait_ref).to_opt_poly_trait_ref()
+                pred.subst_supertrait(self.tcx, &trait_ref).to_opt_poly_trait_pred()
             })
-            .map(|t| t.value)
+            .map(|t| t.map_bound(|pred| pred.trait_ref))
             .filter(|supertrait_ref| self.visited.insert(*supertrait_ref));
 
         self.stack.extend(supertrait_refs);