Auto merge of #55323 - nikomatsakis:nll-ICE-55219-and-55241, r=pnkfelix

introduce type-op for user-type ascription in NLL

Handle user-type ascription in a type operator, which gives us a lot more flexibility around the order in which we resolve things.

r? @pnkfelix

Fixes #55219
Fixes #55241

src/librustc/dep_graph/dep_node.rs

@@ -72,8 +72,9 @@ use std::hash::Hash;
 use syntax_pos::symbol::InternedString;
 use traits;
 use traits::query::{
-    CanonicalProjectionGoal, CanonicalTyGoal, CanonicalTypeOpEqGoal, CanonicalTypeOpSubtypeGoal,
-    CanonicalPredicateGoal, CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpNormalizeGoal,
+    CanonicalProjectionGoal, CanonicalTyGoal, CanonicalTypeOpAscribeUserTypeGoal,
+    CanonicalTypeOpEqGoal, CanonicalTypeOpSubtypeGoal, CanonicalPredicateGoal,
+    CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpNormalizeGoal,
 };
 use ty::{TyCtxt, FnSig, Instance, InstanceDef,
          ParamEnv, ParamEnvAnd, Predicate, PolyFnSig, PolyTraitRef, Ty};
@@ -654,6 +655,7 @@ define_dep_nodes!( <'tcx>
     [] ImpliedOutlivesBounds(CanonicalTyGoal<'tcx>),
     [] DropckOutlives(CanonicalTyGoal<'tcx>),
     [] EvaluateObligation(CanonicalPredicateGoal<'tcx>),
+    [] TypeOpAscribeUserType(CanonicalTypeOpAscribeUserTypeGoal<'tcx>),
     [] TypeOpEq(CanonicalTypeOpEqGoal<'tcx>),
     [] TypeOpSubtype(CanonicalTypeOpSubtypeGoal<'tcx>),
     [] TypeOpProvePredicate(CanonicalTypeOpProvePredicateGoal<'tcx>),

src/librustc/infer/at.rs

@@ -142,6 +142,28 @@ impl<'a, 'gcx, 'tcx> At<'a, 'gcx, 'tcx> {
         self.trace(expected, actual).eq(&expected, &actual)
     }
 
+    pub fn relate<T>(
+        self,
+        expected: T,
+        variance: ty::Variance,
+        actual: T,
+    ) -> InferResult<'tcx, ()>
+        where T: ToTrace<'tcx>
+    {
+        match variance {
+            ty::Variance::Covariant => self.sub(expected, actual),
+            ty::Variance::Invariant => self.eq(expected, actual),
+            ty::Variance::Contravariant => self.sup(expected, actual),
+
+            // We could make this make sense but it's not readily
+            // exposed and I don't feel like dealing with it. Note
+            // that bivariance in general does a bit more than just
+            // *nothing*, it checks that the types are the same
+            // "modulo variance" basically.
+            ty::Variance::Bivariant => panic!("Bivariant given to `relate()`"),
+        }
+    }
+
     /// Compute the least-upper-bound, or mutual supertype, of two
     /// values. The order of the arguments doesn't matter, but since
     /// this can result in an error (e.g., if asked to compute LUB of

src/librustc/mir/mod.rs

@@ -2438,6 +2438,14 @@ EnumTypeFoldableImpl! {
     }
 }
 
+EnumLiftImpl! {
+    impl<'a, 'tcx> Lift<'tcx> for UserTypeAnnotation<'a> {
+        type Lifted = UserTypeAnnotation<'tcx>;
+        (UserTypeAnnotation::Ty)(ty),
+        (UserTypeAnnotation::TypeOf)(def, substs),
+    }
+}
+
 newtype_index! {
     pub struct Promoted {
         DEBUG_FORMAT = "promoted[{}]"

src/librustc/traits/query/mod.rs

@@ -34,6 +34,9 @@ pub type CanonicalTyGoal<'tcx> = Canonical<'tcx, ty::ParamEnvAnd<'tcx, Ty<'tcx>>
 pub type CanonicalPredicateGoal<'tcx> =
     Canonical<'tcx, ty::ParamEnvAnd<'tcx, ty::Predicate<'tcx>>>;
 
+pub type CanonicalTypeOpAscribeUserTypeGoal<'tcx> =
+    Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::ascribe_user_type::AscribeUserType<'tcx>>>;
+
 pub type CanonicalTypeOpEqGoal<'tcx> =
     Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::eq::Eq<'tcx>>>;
 

src/librustc/traits/query/type_op/ascribe_user_type.rs

@@ -0,0 +1,77 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use infer::canonical::{Canonical, Canonicalized, CanonicalizedQueryResponse, QueryResponse};
+use traits::query::Fallible;
+use hir::def_id::DefId;
+use ty::{self, ParamEnvAnd, Ty, TyCtxt};
+use ty::subst::UserSubsts;
+
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+pub struct AscribeUserType<'tcx> {
+    pub mir_ty: Ty<'tcx>,
+    pub variance: ty::Variance,
+    pub def_id: DefId,
+    pub user_substs: UserSubsts<'tcx>,
+}
+
+impl<'tcx> AscribeUserType<'tcx> {
+    pub fn new(
+        mir_ty: Ty<'tcx>,
+        variance: ty::Variance,
+        def_id: DefId,
+        user_substs: UserSubsts<'tcx>,
+    ) -> Self {
+        AscribeUserType { mir_ty, variance, def_id, user_substs }
+    }
+}
+
+impl<'gcx: 'tcx, 'tcx> super::QueryTypeOp<'gcx, 'tcx> for AscribeUserType<'tcx> {
+    type QueryResponse = ();
+
+    fn try_fast_path(
+        _tcx: TyCtxt<'_, 'gcx, 'tcx>,
+        _key: &ParamEnvAnd<'tcx, Self>,
+    ) -> Option<Self::QueryResponse> {
+        None
+    }
+
+    fn perform_query(
+        tcx: TyCtxt<'_, 'gcx, 'tcx>,
+        canonicalized: Canonicalized<'gcx, ParamEnvAnd<'tcx, Self>>,
+    ) -> Fallible<CanonicalizedQueryResponse<'gcx, ()>> {
+        tcx.type_op_ascribe_user_type(canonicalized)
+    }
+
+    fn shrink_to_tcx_lifetime(
+        v: &'a CanonicalizedQueryResponse<'gcx, ()>,
+    ) -> &'a Canonical<'tcx, QueryResponse<'tcx, ()>> {
+        v
+    }
+}
+
+BraceStructTypeFoldableImpl! {
+    impl<'tcx> TypeFoldable<'tcx> for AscribeUserType<'tcx> {
+        mir_ty, variance, def_id, user_substs
+    }
+}
+
+BraceStructLiftImpl! {
+    impl<'a, 'tcx> Lift<'tcx> for AscribeUserType<'a> {
+        type Lifted = AscribeUserType<'tcx>;
+        mir_ty, variance, def_id, user_substs
+    }
+}
+
+impl_stable_hash_for! {
+    struct AscribeUserType<'tcx> {
+        mir_ty, variance, def_id, user_substs
+    }
+}

src/librustc/traits/query/type_op/mod.rs

@@ -20,6 +20,7 @@ use traits::ObligationCause;
 use ty::fold::TypeFoldable;
 use ty::{Lift, ParamEnvAnd, TyCtxt};
 
+pub mod ascribe_user_type;
 pub mod custom;
 pub mod eq;
 pub mod implied_outlives_bounds;

src/librustc/ty/mod.rs

@@ -330,7 +330,7 @@ impl Visibility {
     }
 }
 
-#[derive(Clone, PartialEq, RustcDecodable, RustcEncodable, Copy)]
+#[derive(Copy, Clone, PartialEq, Eq, RustcDecodable, RustcEncodable, Hash)]
 pub enum Variance {
     Covariant,      // T<A> <: T<B> iff A <: B -- e.g., function return type
     Invariant,      // T<A> <: T<B> iff B == A -- e.g., type of mutable cell

src/librustc/ty/query/config.rs

@@ -14,8 +14,9 @@ use hir::def_id::{CrateNum, DefId, DefIndex};
 use mir::interpret::GlobalId;
 use traits;
 use traits::query::{
-    CanonicalPredicateGoal, CanonicalProjectionGoal, CanonicalTyGoal, CanonicalTypeOpEqGoal,
-    CanonicalTypeOpNormalizeGoal, CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpSubtypeGoal,
+    CanonicalPredicateGoal, CanonicalProjectionGoal, CanonicalTyGoal,
+    CanonicalTypeOpAscribeUserTypeGoal, CanonicalTypeOpEqGoal, CanonicalTypeOpNormalizeGoal,
+    CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpSubtypeGoal,
 };
 use ty::{self, ParamEnvAnd, Ty, TyCtxt};
 use ty::subst::Substs;
@@ -115,6 +116,15 @@ impl<'tcx> QueryDescription<'tcx> for queries::evaluate_obligation<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription<'tcx> for queries::type_op_ascribe_user_type<'tcx> {
+    fn describe(
+        _tcx: TyCtxt<'_, '_, '_>,
+        goal: CanonicalTypeOpAscribeUserTypeGoal<'tcx>,
+    ) -> Cow<'static, str> {
+        format!("evaluating `type_op_ascribe_user_type` `{:?}`", goal).into()
+    }
+}
+
 impl<'tcx> QueryDescription<'tcx> for queries::type_op_eq<'tcx> {
     fn describe(_tcx: TyCtxt<'_, '_, '_>, goal: CanonicalTypeOpEqGoal<'tcx>) -> Cow<'static, str> {
         format!("evaluating `type_op_eq` `{:?}`", goal).into()

src/librustc/ty/query/mod.rs

@@ -34,9 +34,12 @@ use mir::interpret::GlobalId;
 use session::{CompileResult, CrateDisambiguator};
 use session::config::OutputFilenames;
 use traits::{self, Vtable};
-use traits::query::{CanonicalPredicateGoal, CanonicalProjectionGoal,
-                    CanonicalTyGoal, CanonicalTypeOpEqGoal, CanonicalTypeOpSubtypeGoal,
-                    CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpNormalizeGoal, NoSolution};
+use traits::query::{
+    CanonicalPredicateGoal, CanonicalProjectionGoal,
+    CanonicalTyGoal, CanonicalTypeOpAscribeUserTypeGoal, CanonicalTypeOpEqGoal,
+    CanonicalTypeOpSubtypeGoal, CanonicalTypeOpProvePredicateGoal,
+    CanonicalTypeOpNormalizeGoal, NoSolution,
+};
 use traits::query::dropck_outlives::{DtorckConstraint, DropckOutlivesResult};
 use traits::query::normalize::NormalizationResult;
 use traits::query::outlives_bounds::OutlivesBound;
@@ -589,6 +592,14 @@ define_queries! { <'tcx>
             CanonicalPredicateGoal<'tcx>
         ) -> Result<traits::EvaluationResult, traits::OverflowError>,
 
+        /// Do not call this query directly: part of the `Eq` type-op
+        [] fn type_op_ascribe_user_type: TypeOpAscribeUserType(
+            CanonicalTypeOpAscribeUserTypeGoal<'tcx>
+        ) -> Result<
+            Lrc<Canonical<'tcx, canonical::QueryResponse<'tcx, ()>>>,
+            NoSolution,
+        >,
+
         /// Do not call this query directly: part of the `Eq` type-op
         [] fn type_op_eq: TypeOpEq(
             CanonicalTypeOpEqGoal<'tcx>

src/librustc/ty/query/plumbing.rs

@@ -1079,6 +1079,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
         DepKind::ImpliedOutlivesBounds |
         DepKind::DropckOutlives |
         DepKind::EvaluateObligation |
+        DepKind::TypeOpAscribeUserType |
         DepKind::TypeOpEq |
         DepKind::TypeOpSubtype |
         DepKind::TypeOpProvePredicate |

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -42,7 +42,7 @@ use rustc::traits::query::type_op::custom::CustomTypeOp;
 use rustc::traits::query::{Fallible, NoSolution};
 use rustc::traits::{ObligationCause, PredicateObligations};
 use rustc::ty::fold::TypeFoldable;
-use rustc::ty::subst::{Subst, Substs, UnpackedKind, UserSelfTy, UserSubsts};
+use rustc::ty::subst::{Subst, Substs, UnpackedKind};
 use rustc::ty::{self, RegionVid, ToPolyTraitRef, Ty, TyCtxt, TyKind};
 use std::rc::Rc;
 use std::{fmt, iter};
@@ -975,126 +975,43 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
         locations: Locations,
         category: ConstraintCategory,
     ) -> Fallible<()> {
-        let tcx = self.tcx();
-
         debug!(
-            "relate_type_and_user_type(a={:?}, v={:?}, b={:?}, locations={:?})",
-            a, v, user_ty, locations
+            "relate_type_and_user_type(a={:?}, v={:?}, user_ty={:?}, locations={:?})",
+            a, v, user_ty, locations,
         );
 
-        // The `TypeRelating` code assumes that "unresolved inference
-        // variables" appear in the "a" side, so flip `Contravariant`
-        // ambient variance to get the right relationship.
-        let v1 = ty::Contravariant.xform(v);
-
         match user_ty {
             UserTypeAnnotation::Ty(canonical_ty) => {
                 let (ty, _) = self.infcx
                     .instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_ty);
 
-                self.relate_types(ty, v1, a, locations, category)?;
+                // The `TypeRelating` code assumes that "unresolved inference
+                // variables" appear in the "a" side, so flip `Contravariant`
+                // ambient variance to get the right relationship.
+                let v1 = ty::Contravariant.xform(v);
 
-                self.prove_predicate(ty::Predicate::WellFormed(ty), locations, category);
+                self.relate_types(ty, v1, a, locations, category)?;
             }
             UserTypeAnnotation::TypeOf(def_id, canonical_substs) => {
                 let (
-                    UserSubsts {
-                        substs,
-                        user_self_ty,
-                    },
+                    user_substs,
                     _,
                 ) = self.infcx
                     .instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_substs);
 
-                let ty = self.tcx().type_of(def_id);
-                let ty = ty.subst(tcx, substs);
-                let ty = self.normalize(ty, locations);
-
-                self.relate_types(ty, v1, a, locations, category)?;
-
-                if let Some(UserSelfTy {
-                    impl_def_id,
-                    self_ty,
-                }) = user_self_ty
-                {
-                    let impl_self_ty = tcx.type_of(impl_def_id);
-                    let impl_self_ty = impl_self_ty.subst(tcx, &substs);
-                    let impl_self_ty = self.normalize(impl_self_ty, locations);
-
-                    // There may be type variables in `substs` and hence
-                    // in `impl_self_ty`, but they should all have been
-                    // resolved to some fixed value during the first call
-                    // to `relate`, above. Therefore, if we use
-                    // `resolve_type_vars_if_possible` we should get to
-                    // something without type variables. This is important
-                    // because the `b` type in `relate_with_variance`
-                    // below is not permitted to have inference variables.
-                    let impl_self_ty = self.infcx.resolve_type_vars_if_possible(&impl_self_ty);
-                    assert!(!impl_self_ty.has_infer_types());
-
-                    self.eq_types(self_ty, impl_self_ty, locations, category)?;
-
-                    self.prove_predicate(
-                        ty::Predicate::WellFormed(impl_self_ty),
-                        locations,
-                        category,
-                    );
-                }
-
-                // Prove the predicates coming along with `def_id`.
-                //
-                // Also, normalize the `instantiated_predicates`
-                // because otherwise we wind up with duplicate "type
-                // outlives" error messages.
-                let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
-                let instantiated_predicates = self.fold_to_region_vid(instantiated_predicates);
-                self.normalize_and_prove_instantiated_predicates(
-                    instantiated_predicates,
+                self.fully_perform_op(
                     locations,
-                );
-
-                // In addition to proving the predicates, we have to
-                // prove that `ty` is well-formed -- this is because
-                // the WF of `ty` is predicated on the substs being
-                // well-formed, and we haven't proven *that*. We don't
-                // want to prove the WF of types from  `substs` directly because they
-                // haven't been normalized.
-                //
-                // FIXME(nmatsakis): Well, perhaps we should normalize
-                // them?  This would only be relevant if some input
-                // type were ill-formed but did not appear in `ty`,
-                // which...could happen with normalization...
-                self.prove_predicate(ty::Predicate::WellFormed(ty), locations, category);
+                    category,
+                    self.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
+                        a, v, def_id, user_substs,
+                    )),
+                )?;
             }
         }
 
         Ok(())
     }
 
-    /// Replace all free regions in `value` with their NLL `RegionVid`
-    /// equivalents; if not in NLL, does nothing. This is never
-    /// particularly necessary -- we'll do it lazilly as we process
-    /// the value anyway -- but in some specific cases it is useful to
-    /// normalize so we can suppress duplicate error messages.
-    fn fold_to_region_vid<T>(&self, value: T) -> T
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        if let Some(borrowck_context) = &self.borrowck_context {
-            self.tcx().fold_regions(&value, &mut false, |r, _debruijn| {
-                if r.has_free_regions() {
-                    self.tcx().mk_region(ty::RegionKind::ReVar(
-                        borrowck_context.universal_regions.to_region_vid(r),
-                    ))
-                } else {
-                    r
-                }
-            })
-        } else {
-            value
-        }
-    }
-
     fn eq_opaque_type_and_type(
         &mut self,
         revealed_ty: Ty<'tcx>,