Rollup merge of #72055 - lcnr:predicate-kind, r=nikomatsakis

Intern predicates

Implements the first step of rust-lang/compiler-team#285

Renames `ty::Predicate` to `ty::PredicateKind`, which is now interned.
To ease the transition, `ty::Predicate` is now a struct containing a reference
to `ty::PredicateKind`.

r? @ghost

src/librustc_infer/infer/canonical/query_response.rs

@@ -25,7 +25,7 @@ use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::relate::TypeRelation;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
-use rustc_middle::ty::{self, BoundVar, Const, Ty, TyCtxt};
+use rustc_middle::ty::{self, BoundVar, Const, ToPredicate, Ty, TyCtxt};
 use std::fmt::Debug;
 
 impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
@@ -532,12 +532,14 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
                 cause.clone(),
                 param_env,
                 match k1.unpack() {
-                    GenericArgKind::Lifetime(r1) => ty::Predicate::RegionOutlives(
+                    GenericArgKind::Lifetime(r1) => ty::PredicateKind::RegionOutlives(
                         ty::Binder::bind(ty::OutlivesPredicate(r1, r2)),
-                    ),
-                    GenericArgKind::Type(t1) => {
-                        ty::Predicate::TypeOutlives(ty::Binder::bind(ty::OutlivesPredicate(t1, r2)))
-                    }
+                    )
+                    .to_predicate(self.tcx),
+                    GenericArgKind::Type(t1) => ty::PredicateKind::TypeOutlives(ty::Binder::bind(
+                        ty::OutlivesPredicate(t1, r2),
+                    ))
+                    .to_predicate(self.tcx),
                     GenericArgKind::Const(..) => {
                         // Consts cannot outlive one another, so we don't expect to
                         // ecounter this branch.
@@ -664,9 +666,10 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for QueryTypeRelatingDelegate<'_, 'tcx> {
         self.obligations.push(Obligation {
             cause: self.cause.clone(),
             param_env: self.param_env,
-            predicate: ty::Predicate::RegionOutlives(ty::Binder::dummy(ty::OutlivesPredicate(
+            predicate: ty::PredicateKind::RegionOutlives(ty::Binder::dummy(ty::OutlivesPredicate(
                 sup, sub,
-            ))),
+            )))
+            .to_predicate(self.infcx.tcx),
             recursion_depth: 0,
         });
     }

src/librustc_infer/infer/combine.rs

@@ -39,7 +39,7 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::subst::SubstsRef;
-use rustc_middle::ty::{self, InferConst, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable};
 use rustc_middle::ty::{IntType, UintType};
 use rustc_span::{Span, DUMMY_SP};
 
@@ -307,7 +307,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
             self.obligations.push(Obligation::new(
                 self.trace.cause.clone(),
                 self.param_env,
-                ty::Predicate::WellFormed(b_ty),
+                ty::PredicateKind::WellFormed(b_ty).to_predicate(self.infcx.tcx),
             ));
         }
 
@@ -398,11 +398,15 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         b: &'tcx ty::Const<'tcx>,
     ) {
         let predicate = if a_is_expected {
-            ty::Predicate::ConstEquate(a, b)
+            ty::PredicateKind::ConstEquate(a, b)
         } else {
-            ty::Predicate::ConstEquate(b, a)
+            ty::PredicateKind::ConstEquate(b, a)
         };
-        self.obligations.push(Obligation::new(self.trace.cause.clone(), self.param_env, predicate));
+        self.obligations.push(Obligation::new(
+            self.trace.cause.clone(),
+            self.param_env,
+            predicate.to_predicate(self.tcx()),
+        ));
     }
 }
 

src/librustc_infer/infer/outlives/mod.rs

@@ -11,17 +11,17 @@ pub fn explicit_outlives_bounds<'tcx>(
     param_env: ty::ParamEnv<'tcx>,
 ) -> impl Iterator<Item = OutlivesBound<'tcx>> + 'tcx {
     debug!("explicit_outlives_bounds()");
-    param_env.caller_bounds.into_iter().filter_map(move |predicate| match predicate {
-        ty::Predicate::Projection(..)
-        | ty::Predicate::Trait(..)
-        | ty::Predicate::Subtype(..)
-        | ty::Predicate::WellFormed(..)
-        | ty::Predicate::ObjectSafe(..)
-        | ty::Predicate::ClosureKind(..)
-        | ty::Predicate::TypeOutlives(..)
-        | ty::Predicate::ConstEvaluatable(..)
-        | ty::Predicate::ConstEquate(..) => None,
-        ty::Predicate::RegionOutlives(ref data) => data
+    param_env.caller_bounds.into_iter().filter_map(move |predicate| match predicate.kind() {
+        ty::PredicateKind::Projection(..)
+        | ty::PredicateKind::Trait(..)
+        | ty::PredicateKind::Subtype(..)
+        | ty::PredicateKind::WellFormed(..)
+        | ty::PredicateKind::ObjectSafe(..)
+        | ty::PredicateKind::ClosureKind(..)
+        | ty::PredicateKind::TypeOutlives(..)
+        | ty::PredicateKind::ConstEvaluatable(..)
+        | ty::PredicateKind::ConstEquate(..) => None,
+        ty::PredicateKind::RegionOutlives(ref data) => data
             .no_bound_vars()
             .map(|ty::OutlivesPredicate(r_a, r_b)| OutlivesBound::RegionSubRegion(r_b, r_a)),
     })

src/librustc_infer/infer/sub.rs

@@ -6,7 +6,7 @@ use crate::traits::Obligation;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::relate::{Cause, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::TyVar;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use std::mem;
 
 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
@@ -100,11 +100,12 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
                 self.fields.obligations.push(Obligation::new(
                     self.fields.trace.cause.clone(),
                     self.fields.param_env,
-                    ty::Predicate::Subtype(ty::Binder::dummy(ty::SubtypePredicate {
+                    ty::PredicateKind::Subtype(ty::Binder::dummy(ty::SubtypePredicate {
                         a_is_expected: self.a_is_expected,
                         a,
                         b,
-                    })),
+                    }))
+                    .to_predicate(self.tcx()),
                 ));
 
                 Ok(a)

src/librustc_infer/traits/engine.rs

@@ -33,7 +33,7 @@ pub trait TraitEngine<'tcx>: 'tcx {
                 cause,
                 recursion_depth: 0,
                 param_env,
-                predicate: trait_ref.without_const().to_predicate(),
+                predicate: trait_ref.without_const().to_predicate(infcx.tcx),
             },
         );
     }

src/librustc_infer/traits/mod.rs

@@ -59,7 +59,7 @@ pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
 
 // `PredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(target_arch = "x86_64")]
-static_assert_size!(PredicateObligation<'_>, 112);
+static_assert_size!(PredicateObligation<'_>, 88);
 
 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;

src/librustc_infer/traits/util.rs

@@ -10,40 +10,49 @@ pub fn anonymize_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
     pred: &ty::Predicate<'tcx>,
 ) -> ty::Predicate<'tcx> {
-    match *pred {
-        ty::Predicate::Trait(ref data, constness) => {
-            ty::Predicate::Trait(tcx.anonymize_late_bound_regions(data), constness)
+    match pred.kind() {
+        &ty::PredicateKind::Trait(ref data, constness) => {
+            ty::PredicateKind::Trait(tcx.anonymize_late_bound_regions(data), constness)
+                .to_predicate(tcx)
         }
 
-        ty::Predicate::RegionOutlives(ref data) => {
-            ty::Predicate::RegionOutlives(tcx.anonymize_late_bound_regions(data))
+        ty::PredicateKind::RegionOutlives(data) => {
+            ty::PredicateKind::RegionOutlives(tcx.anonymize_late_bound_regions(data))
+                .to_predicate(tcx)
         }
 
-        ty::Predicate::TypeOutlives(ref data) => {
-            ty::Predicate::TypeOutlives(tcx.anonymize_late_bound_regions(data))
+        ty::PredicateKind::TypeOutlives(data) => {
+            ty::PredicateKind::TypeOutlives(tcx.anonymize_late_bound_regions(data))
+                .to_predicate(tcx)
         }
 
-        ty::Predicate::Projection(ref data) => {
-            ty::Predicate::Projection(tcx.anonymize_late_bound_regions(data))
+        ty::PredicateKind::Projection(data) => {
+            ty::PredicateKind::Projection(tcx.anonymize_late_bound_regions(data)).to_predicate(tcx)
         }
 
-        ty::Predicate::WellFormed(data) => ty::Predicate::WellFormed(data),
+        &ty::PredicateKind::WellFormed(data) => {
+            ty::PredicateKind::WellFormed(data).to_predicate(tcx)
+        }
 
-        ty::Predicate::ObjectSafe(data) => ty::Predicate::ObjectSafe(data),
+        &ty::PredicateKind::ObjectSafe(data) => {
+            ty::PredicateKind::ObjectSafe(data).to_predicate(tcx)
+        }
 
-        ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
-            ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind)
+        &ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
+            ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind).to_predicate(tcx)
         }
 
-        ty::Predicate::Subtype(ref data) => {
-            ty::Predicate::Subtype(tcx.anonymize_late_bound_regions(data))
+        ty::PredicateKind::Subtype(data) => {
+            ty::PredicateKind::Subtype(tcx.anonymize_late_bound_regions(data)).to_predicate(tcx)
         }
 
-        ty::Predicate::ConstEvaluatable(def_id, substs) => {
-            ty::Predicate::ConstEvaluatable(def_id, substs)
+        &ty::PredicateKind::ConstEvaluatable(def_id, substs) => {
+            ty::PredicateKind::ConstEvaluatable(def_id, substs).to_predicate(tcx)
         }
 
-        ty::Predicate::ConstEquate(c1, c2) => ty::Predicate::ConstEquate(c1, c2),
+        ty::PredicateKind::ConstEquate(c1, c2) => {
+            ty::PredicateKind::ConstEquate(c1, c2).to_predicate(tcx)
+        }
     }
 }
 
@@ -99,14 +108,14 @@ pub fn elaborate_trait_ref<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_ref: ty::PolyTraitRef<'tcx>,
 ) -> Elaborator<'tcx> {
-    elaborate_predicates(tcx, std::iter::once(trait_ref.without_const().to_predicate()))
+    elaborate_predicates(tcx, std::iter::once(trait_ref.without_const().to_predicate(tcx)))
 }
 
 pub fn elaborate_trait_refs<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_refs: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
 ) -> Elaborator<'tcx> {
-    let predicates = trait_refs.map(|trait_ref| trait_ref.without_const().to_predicate());
+    let predicates = trait_refs.map(|trait_ref| trait_ref.without_const().to_predicate(tcx));
     elaborate_predicates(tcx, predicates)
 }
 
@@ -145,8 +154,8 @@ impl Elaborator<'tcx> {
 
     fn elaborate(&mut self, obligation: &PredicateObligation<'tcx>) {
         let tcx = self.visited.tcx;
-        match obligation.predicate {
-            ty::Predicate::Trait(ref data, _) => {
+        match obligation.predicate.kind() {
+            ty::PredicateKind::Trait(ref data, _) => {
                 // Get predicates declared on the trait.
                 let predicates = tcx.super_predicates_of(data.def_id());
 
@@ -167,36 +176,36 @@ impl Elaborator<'tcx> {
 
                 self.stack.extend(obligations);
             }
-            ty::Predicate::WellFormed(..) => {
+            ty::PredicateKind::WellFormed(..) => {
                 // Currently, we do not elaborate WF predicates,
                 // although we easily could.
             }
-            ty::Predicate::ObjectSafe(..) => {
+            ty::PredicateKind::ObjectSafe(..) => {
                 // Currently, we do not elaborate object-safe
                 // predicates.
             }
-            ty::Predicate::Subtype(..) => {
+            ty::PredicateKind::Subtype(..) => {
                 // Currently, we do not "elaborate" predicates like `X <: Y`,
                 // though conceivably we might.
             }
-            ty::Predicate::Projection(..) => {
+            ty::PredicateKind::Projection(..) => {
                 // Nothing to elaborate in a projection predicate.
             }
-            ty::Predicate::ClosureKind(..) => {
+            ty::PredicateKind::ClosureKind(..) => {
                 // Nothing to elaborate when waiting for a closure's kind to be inferred.
             }
-            ty::Predicate::ConstEvaluatable(..) => {
+            ty::PredicateKind::ConstEvaluatable(..) => {
                 // Currently, we do not elaborate const-evaluatable
                 // predicates.
             }
-            ty::Predicate::ConstEquate(..) => {
+            ty::PredicateKind::ConstEquate(..) => {
                 // Currently, we do not elaborate const-equate
                 // predicates.
             }
-            ty::Predicate::RegionOutlives(..) => {
+            ty::PredicateKind::RegionOutlives(..) => {
                 // Nothing to elaborate from `'a: 'b`.
             }
-            ty::Predicate::TypeOutlives(ref data) => {
+            ty::PredicateKind::TypeOutlives(ref data) => {
                 // We know that `T: 'a` for some type `T`. We can
                 // often elaborate this. For example, if we know that
                 // `[U]: 'a`, that implies that `U: 'a`. Similarly, if
@@ -228,15 +237,15 @@ impl Elaborator<'tcx> {
                                 if r.is_late_bound() {
                                     None
                                 } else {
-                                    Some(ty::Predicate::RegionOutlives(ty::Binder::dummy(
+                                    Some(ty::PredicateKind::RegionOutlives(ty::Binder::dummy(
                                         ty::OutlivesPredicate(r, r_min),
                                     )))
                                 }
                             }
 
                             Component::Param(p) => {
                                 let ty = tcx.mk_ty_param(p.index, p.name);
-                                Some(ty::Predicate::TypeOutlives(ty::Binder::dummy(
+                                Some(ty::PredicateKind::TypeOutlives(ty::Binder::dummy(
                                     ty::OutlivesPredicate(ty, r_min),
                                 )))
                             }
@@ -250,8 +259,9 @@ impl Elaborator<'tcx> {
                                 None
                             }
                         })
-                        .filter(|p| visited.insert(p))
-                        .map(|p| predicate_obligation(p, None)),
+                        .map(|predicate_kind| predicate_kind.to_predicate(tcx))
+                        .filter(|predicate| visited.insert(predicate))
+                        .map(|predicate| predicate_obligation(predicate, None)),
                 );
             }
         }
@@ -317,7 +327,7 @@ 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 ty::Predicate::Trait(data, _) = obligation.predicate {
+            if let ty::PredicateKind::Trait(data, _) = obligation.predicate.kind() {
                 return Some(data.to_poly_trait_ref());
             }
         }

src/librustc_lint/builtin.rs

@@ -1202,13 +1202,13 @@ declare_lint_pass!(
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TrivialConstraints {
     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'tcx>) {
         use rustc_middle::ty::fold::TypeFoldable;
-        use rustc_middle::ty::Predicate::*;
+        use rustc_middle::ty::PredicateKind::*;
 
         if cx.tcx.features().trivial_bounds {
             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
             let predicates = cx.tcx.predicates_of(def_id);
             for &(predicate, span) in predicates.predicates {
-                let predicate_kind_name = match predicate {
+                let predicate_kind_name = match predicate.kind() {
                     Trait(..) => "Trait",
                     TypeOutlives(..) |
                     RegionOutlives(..) => "Lifetime",
@@ -1497,8 +1497,8 @@ impl ExplicitOutlivesRequirements {
     ) -> Vec<ty::Region<'tcx>> {
         inferred_outlives
             .iter()
-            .filter_map(|(pred, _)| match pred {
-                ty::Predicate::RegionOutlives(outlives) => {
+            .filter_map(|(pred, _)| match pred.kind() {
+                ty::PredicateKind::RegionOutlives(outlives) => {
                     let outlives = outlives.skip_binder();
                     match outlives.0 {
                         ty::ReEarlyBound(ebr) if ebr.index == index => Some(outlives.1),
@@ -1516,8 +1516,8 @@ impl ExplicitOutlivesRequirements {
     ) -> Vec<ty::Region<'tcx>> {
         inferred_outlives
             .iter()
-            .filter_map(|(pred, _)| match pred {
-                ty::Predicate::TypeOutlives(outlives) => {
+            .filter_map(|(pred, _)| match pred.kind() {
+                ty::PredicateKind::TypeOutlives(outlives) => {
                     let outlives = outlives.skip_binder();
                     outlives.0.is_param(index).then_some(outlives.1)
                 }

src/librustc_lint/unused.rs

@@ -146,7 +146,9 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
                 ty::Opaque(def, _) => {
                     let mut has_emitted = false;
                     for (predicate, _) in cx.tcx.predicates_of(def).predicates {
-                        if let ty::Predicate::Trait(ref poly_trait_predicate, _) = predicate {
+                        if let ty::PredicateKind::Trait(ref poly_trait_predicate, _) =
+                            predicate.kind()
+                        {
                             let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
                             let def_id = trait_ref.def_id;
                             let descr_pre =