Auto merge of #56837 - arielb1:nonprincipal-trait-objects, r=nikomats…

…akis

Add support for trait-objects without a principal

The hard-error version of #56481 - should be merged after we do something about the `traitobject` crate.

Fixes #33140.
Fixes #57057.

r? @nikomatsakis

src/librustc/dep_graph/dep_node.rs

@@ -492,6 +492,7 @@ define_dep_nodes!( <'tcx>
     [] AdtDefOfItem(DefId),
     [] ImplTraitRef(DefId),
     [] ImplPolarity(DefId),
+    [] Issue33140SelfTy(DefId),
     [] FnSignature(DefId),
     [] CoerceUnsizedInfo(DefId),
 

src/librustc/infer/combine.rs

@@ -337,10 +337,6 @@ impl<'cx, 'gcx, 'tcx> TypeRelation<'cx, 'gcx, 'tcx> for Generalizer<'cx, 'gcx, '
         self.infcx.tcx
     }
 
-    fn trait_object_mode(&self) -> relate::TraitObjectMode {
-        self.infcx.trait_object_mode()
-    }
-
     fn tag(&self) -> &'static str {
         "Generalizer"
     }

src/librustc/infer/equate.rs

@@ -29,10 +29,6 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
 
     fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
 
-    fn trait_object_mode(&self) -> relate::TraitObjectMode {
-        self.fields.infcx.trait_object_mode()
-    }
-
     fn a_is_expected(&self) -> bool { self.a_is_expected }
 
     fn relate_item_substs(&mut self,

src/librustc/infer/glb.rs

@@ -5,7 +5,7 @@ use super::Subtype;
 
 use traits::ObligationCause;
 use ty::{self, Ty, TyCtxt};
-use ty::relate::{self, Relate, RelateResult, TypeRelation};
+use ty::relate::{Relate, RelateResult, TypeRelation};
 
 /// "Greatest lower bound" (common subtype)
 pub struct Glb<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
@@ -26,10 +26,6 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
 {
     fn tag(&self) -> &'static str { "Glb" }
 
-    fn trait_object_mode(&self) -> relate::TraitObjectMode {
-        self.fields.infcx.trait_object_mode()
-    }
-
     fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
 
     fn a_is_expected(&self) -> bool { self.a_is_expected }

src/librustc/infer/lub.rs

@@ -5,7 +5,7 @@ use super::Subtype;
 
 use traits::ObligationCause;
 use ty::{self, Ty, TyCtxt};
-use ty::relate::{self, Relate, RelateResult, TypeRelation};
+use ty::relate::{Relate, RelateResult, TypeRelation};
 
 /// "Least upper bound" (common supertype)
 pub struct Lub<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
@@ -26,10 +26,6 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
 {
     fn tag(&self) -> &'static str { "Lub" }
 
-    fn trait_object_mode(&self) -> relate::TraitObjectMode {
-        self.fields.infcx.trait_object_mode()
-    }
-
     fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
 
     fn a_is_expected(&self) -> bool { self.a_is_expected }

src/librustc/infer/mod.rs

@@ -25,7 +25,7 @@ use syntax_pos::{self, Span};
 use traits::{self, ObligationCause, PredicateObligations, TraitEngine};
 use ty::error::{ExpectedFound, TypeError, UnconstrainedNumeric};
 use ty::fold::TypeFoldable;
-use ty::relate::{RelateResult, TraitObjectMode};
+use ty::relate::RelateResult;
 use ty::subst::{Kind, Substs};
 use ty::{self, GenericParamDefKind, Ty, TyCtxt, CtxtInterners};
 use ty::{FloatVid, IntVid, TyVid};
@@ -171,9 +171,6 @@ pub struct InferCtxt<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
     // This flag is true while there is an active snapshot.
     in_snapshot: Cell<bool>,
 
-    // The TraitObjectMode used here,
-    trait_object_mode: TraitObjectMode,
-
     // A set of constraints that regionck must validate. Each
     // constraint has the form `T:'a`, meaning "some type `T` must
     // outlive the lifetime 'a". These constraints derive from
@@ -465,7 +462,6 @@ pub struct InferCtxtBuilder<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
     arena: SyncDroplessArena,
     interners: Option<CtxtInterners<'tcx>>,
     fresh_tables: Option<RefCell<ty::TypeckTables<'tcx>>>,
-    trait_object_mode: TraitObjectMode,
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
@@ -475,7 +471,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             arena: SyncDroplessArena::default(),
             interners: None,
             fresh_tables: None,
-            trait_object_mode: TraitObjectMode::NoSquash,
         }
     }
 }
@@ -488,12 +483,6 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
         self
     }
 
-    pub fn with_trait_object_mode(mut self, mode: TraitObjectMode) -> Self {
-        debug!("with_trait_object_mode: setting mode to {:?}", mode);
-        self.trait_object_mode = mode;
-        self
-    }
-
     /// Given a canonical value `C` as a starting point, create an
     /// inference context that contains each of the bound values
     /// within instantiated as a fresh variable. The `f` closure is
@@ -520,7 +509,6 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
     pub fn enter<R>(&'tcx mut self, f: impl for<'b> FnOnce(InferCtxt<'b, 'gcx, 'tcx>) -> R) -> R {
         let InferCtxtBuilder {
             global_tcx,
-            trait_object_mode,
             ref arena,
             ref mut interners,
             ref fresh_tables,
@@ -532,7 +520,6 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
             f(InferCtxt {
                 tcx,
                 in_progress_tables,
-                trait_object_mode,
                 projection_cache: Default::default(),
                 type_variables: RefCell::new(type_variable::TypeVariableTable::new()),
                 int_unification_table: RefCell::new(ut::UnificationTable::new()),
@@ -614,10 +601,6 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.in_snapshot.get()
     }
 
-    pub fn trait_object_mode(&self) -> TraitObjectMode {
-        self.trait_object_mode
-    }
-
     pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
         t.fold_with(&mut self.freshener())
     }

src/librustc/infer/nll_relate/mod.rs

@@ -372,13 +372,6 @@ where
         self.infcx.tcx
     }
 
-    fn trait_object_mode(&self) -> relate::TraitObjectMode {
-        // squashing should only be done in coherence, not NLL
-        assert_eq!(self.infcx.trait_object_mode(),
-                   relate::TraitObjectMode::NoSquash);
-        relate::TraitObjectMode::NoSquash
-    }
-
     fn tag(&self) -> &'static str {
         "nll::subtype"
     }
@@ -693,13 +686,6 @@ where
         self.infcx.tcx
     }
 
-    fn trait_object_mode(&self) -> relate::TraitObjectMode {
-        // squashing should only be done in coherence, not NLL
-        assert_eq!(self.infcx.trait_object_mode(),
-                   relate::TraitObjectMode::NoSquash);
-        relate::TraitObjectMode::NoSquash
-    }
-
     fn tag(&self) -> &'static str {
         "nll::generalizer"
     }

src/librustc/infer/sub.rs

@@ -5,7 +5,7 @@ use traits::Obligation;
 use ty::{self, Ty, TyCtxt};
 use ty::TyVar;
 use ty::fold::TypeFoldable;
-use ty::relate::{self, Cause, Relate, RelateResult, TypeRelation};
+use ty::relate::{Cause, Relate, RelateResult, TypeRelation};
 use std::mem;
 
 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
@@ -33,10 +33,6 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
     for Sub<'combine, 'infcx, 'gcx, 'tcx>
 {
     fn tag(&self) -> &'static str { "Sub" }
-    fn trait_object_mode(&self) -> relate::TraitObjectMode {
-        self.fields.infcx.trait_object_mode()
-    }
-
     fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.infcx.tcx }
     fn a_is_expected(&self) -> bool { self.a_is_expected }
 

src/librustc/traits/coherence.rs

@@ -11,7 +11,6 @@ use traits::{self, Normalized, SelectionContext, Obligation, ObligationCause};
 use traits::IntercrateMode;
 use traits::select::IntercrateAmbiguityCause;
 use ty::{self, Ty, TyCtxt};
-use ty::relate::TraitObjectMode;
 use ty::fold::TypeFoldable;
 use ty::subst::Subst;
 
@@ -55,7 +54,6 @@ pub fn overlapping_impls<'gcx, F1, F2, R>(
     impl1_def_id: DefId,
     impl2_def_id: DefId,
     intercrate_mode: IntercrateMode,
-    trait_object_mode: TraitObjectMode,
     on_overlap: F1,
     no_overlap: F2,
 ) -> R
@@ -66,14 +64,12 @@ where
     debug!("overlapping_impls(\
            impl1_def_id={:?}, \
            impl2_def_id={:?},
-           intercrate_mode={:?},
-           trait_object_mode={:?})",
+           intercrate_mode={:?})",
            impl1_def_id,
            impl2_def_id,
-           intercrate_mode,
-           trait_object_mode);
+           intercrate_mode);
 
-    let overlaps = tcx.infer_ctxt().with_trait_object_mode(trait_object_mode).enter(|infcx| {
+    let overlaps = tcx.infer_ctxt().enter(|infcx| {
         let selcx = &mut SelectionContext::intercrate(&infcx, intercrate_mode);
         overlap(selcx, impl1_def_id, impl2_def_id).is_some()
     });
@@ -85,7 +81,7 @@ where
     // In the case where we detect an error, run the check again, but
     // this time tracking intercrate ambuiguity causes for better
     // diagnostics. (These take time and can lead to false errors.)
-    tcx.infer_ctxt().with_trait_object_mode(trait_object_mode).enter(|infcx| {
+    tcx.infer_ctxt().enter(|infcx| {
         let selcx = &mut SelectionContext::intercrate(&infcx, intercrate_mode);
         selcx.enable_tracking_intercrate_ambiguity_causes();
         on_overlap(overlap(selcx, impl1_def_id, impl2_def_id).unwrap())
@@ -510,7 +506,13 @@ fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
         ty::Adt(def, _) => def_id_is_local(def.did, in_crate),
         ty::Foreign(did) => def_id_is_local(did, in_crate),
 
-        ty::Dynamic(ref tt, ..) => def_id_is_local(tt.principal().def_id(), in_crate),
+        ty::Dynamic(ref tt, ..) => {
+            if let Some(principal) = tt.principal() {
+                def_id_is_local(principal.def_id(), in_crate)
+            } else {
+                false
+            }
+        }
 
         ty::Error => true,
 

src/librustc/traits/error_reporting.rs

@@ -447,7 +447,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     {
         let simp = fast_reject::simplify_type(self.tcx,
                                               trait_ref.skip_binder().self_ty(),
-                                              true,);
+                                              true);
         let all_impls = self.tcx.all_impls(trait_ref.def_id());
 
         match simp {

src/librustc/traits/select.rs

@@ -33,7 +33,7 @@ use infer::{InferCtxt, InferOk, TypeFreshener};
 use middle::lang_items;
 use mir::interpret::GlobalId;
 use ty::fast_reject;
-use ty::relate::{TypeRelation, TraitObjectMode};
+use ty::relate::TypeRelation;
 use ty::subst::{Subst, Substs};
 use ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable};
 
@@ -1416,13 +1416,6 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             return false;
         }
 
-        // Same idea as the above, but for alt trait object modes. These
-        // should only be used in intercrate mode - better safe than sorry.
-        if self.infcx.trait_object_mode() != TraitObjectMode::NoSquash {
-            bug!("using squashing TraitObjectMode outside of intercrate mode? param_env={:?}",
-                 param_env);
-        }
-
         // Otherwise, we can use the global cache.
         true
     }
@@ -2016,7 +2009,12 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                         return;
                     }
 
-                    data.principal().with_self_ty(self.tcx(), self_ty)
+                    if let Some(principal) = data.principal() {
+                        principal.with_self_ty(self.tcx(), self_ty)
+                    } else {
+                        // Only auto-trait bounds exist.
+                        return;
+                    }
                 }
                 ty::Infer(ty::TyVar(_)) => {
                     debug!("assemble_candidates_from_object_ty: ambiguous");
@@ -2108,7 +2106,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 //
                 // We always upcast when we can because of reason
                 // #2 (region bounds).
-                data_a.principal().def_id() == data_b.principal().def_id()
+                data_a.principal_def_id() == data_b.principal_def_id()
                     && data_b.auto_traits()
                     // All of a's auto traits need to be in b's auto traits.
                     .all(|b| data_a.auto_traits().any(|a| a == b))
@@ -2262,7 +2260,8 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                         ImplCandidate(victim_def) => {
                             let tcx = self.tcx().global_tcx();
                             return tcx.specializes((other_def, victim_def))
-                                || tcx.impls_are_allowed_to_overlap(other_def, victim_def);
+                                || tcx.impls_are_allowed_to_overlap(
+                                    other_def, victim_def).is_some();
                         }
                         ParamCandidate(ref cand) => {
                             // Prefer the impl to a global where clause candidate.
@@ -2919,7 +2918,10 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         let self_ty = self.infcx
             .shallow_resolve(*obligation.self_ty().skip_binder());
         let poly_trait_ref = match self_ty.sty {
-            ty::Dynamic(ref data, ..) => data.principal().with_self_ty(self.tcx(), self_ty),
+            ty::Dynamic(ref data, ..) =>
+                data.principal().unwrap_or_else(|| {
+                    span_bug!(obligation.cause.span, "object candidate with no principal")
+                }).with_self_ty(self.tcx(), self_ty),
             _ => span_bug!(obligation.cause.span, "object candidate with non-object"),
         };
 
@@ -3222,8 +3224,9 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             (&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => {
                 // See assemble_candidates_for_unsizing for more info.
                 let existential_predicates = data_a.map_bound(|data_a| {
-                    let iter = iter::once(ty::ExistentialPredicate::Trait(data_a.principal()))
-                        .chain(
+                    let iter =
+                        data_a.principal().map(|x| ty::ExistentialPredicate::Trait(x))
+                        .into_iter().chain(
                             data_a
                                 .projection_bounds()
                                 .map(|x| ty::ExistentialPredicate::Projection(x)),
@@ -3260,7 +3263,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             // T -> Trait.
             (_, &ty::Dynamic(ref data, r)) => {
                 let mut object_dids = data.auto_traits()
-                    .chain(iter::once(data.principal().def_id()));
+                    .chain(data.principal_def_id());
                 if let Some(did) = object_dids.find(|did| !tcx.is_object_safe(*did)) {
                     return Err(TraitNotObjectSafe(did));
                 }
@@ -3571,8 +3574,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         previous: &ty::PolyTraitRef<'tcx>,
         current: &ty::PolyTraitRef<'tcx>,
     ) -> bool {
-        let mut matcher = ty::_match::Match::new(
-            self.tcx(), self.infcx.trait_object_mode());
+        let mut matcher = ty::_match::Match::new(self.tcx());
         matcher.relate(previous, current).is_ok()
     }
 

src/librustc/traits/specialize/mod.rs

@@ -14,8 +14,7 @@ pub mod specialization_graph;
 use hir::def_id::DefId;
 use infer::{InferCtxt, InferOk};
 use lint;
-use traits::{self, FutureCompatOverlapErrorKind, ObligationCause, TraitEngine};
-use traits::coherence;
+use traits::{self, coherence, FutureCompatOverlapErrorKind, ObligationCause, TraitEngine};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lrc;
 use syntax_pos::DUMMY_SP;