Auto merge of #56481 - arielb1:dynamic-order, r=nikomatsakis

add coherence future-compat warnings for marker-only trait objects

The future-compat warnings break code that assumes that `dyn Send + Sync !=
dyn Sync + Send`, and are the first step in making them equal. cc #33140.

Note: this lint should be made to default-warn before we merge. It is deny only for the crater run.

r? @nikomatsakis / @scalexm . cc @Centril & @alexreg.

src/librustc/infer/combine.rs

@@ -347,6 +347,10 @@ 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

@@ -39,6 +39,10 @@ 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

@@ -15,7 +15,7 @@ use super::Subtype;
 
 use traits::ObligationCause;
 use ty::{self, Ty, TyCtxt};
-use ty::relate::{Relate, RelateResult, TypeRelation};
+use ty::relate::{self, Relate, RelateResult, TypeRelation};
 
 /// "Greatest lower bound" (common subtype)
 pub struct Glb<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
@@ -36,6 +36,10 @@ 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

@@ -15,7 +15,7 @@ use super::Subtype;
 
 use traits::ObligationCause;
 use ty::{self, Ty, TyCtxt};
-use ty::relate::{Relate, RelateResult, TypeRelation};
+use ty::relate::{self, Relate, RelateResult, TypeRelation};
 
 /// "Least upper bound" (common supertype)
 pub struct Lub<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
@@ -36,6 +36,10 @@ 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

@@ -35,7 +35,7 @@ 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;
+use ty::relate::{RelateResult, TraitObjectMode};
 use ty::subst::{Kind, Substs};
 use ty::{self, GenericParamDefKind, Ty, TyCtxt};
 use ty::{FloatVid, IntVid, TyVid};
@@ -182,6 +182,9 @@ 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
@@ -472,6 +475,7 @@ pub struct InferCtxtBuilder<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
     global_tcx: TyCtxt<'a, 'gcx, 'gcx>,
     arena: SyncDroplessArena,
     fresh_tables: Option<RefCell<ty::TypeckTables<'tcx>>>,
+    trait_object_mode: TraitObjectMode,
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
@@ -480,6 +484,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             global_tcx: self,
             arena: SyncDroplessArena::default(),
             fresh_tables: None,
+            trait_object_mode: TraitObjectMode::NoSquash,
         }
     }
 }
@@ -492,6 +497,12 @@ 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
@@ -518,6 +529,7 @@ 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 fresh_tables,
         } = *self;
@@ -526,6 +538,7 @@ 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()),
@@ -607,6 +620,10 @@ 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

@@ -382,6 +382,13 @@ 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"
     }
@@ -696,6 +703,13 @@ 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

@@ -15,7 +15,7 @@ use traits::Obligation;
 use ty::{self, Ty, TyCtxt};
 use ty::TyVar;
 use ty::fold::TypeFoldable;
-use ty::relate::{Cause, Relate, RelateResult, TypeRelation};
+use ty::relate::{self, Cause, Relate, RelateResult, TypeRelation};
 use std::mem;
 
 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
@@ -43,6 +43,10 @@ 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/lint/builtin.rs

@@ -208,6 +208,12 @@ declare_lint! {
     "potentially-conflicting impls were erroneously allowed"
 }
 
+declare_lint! {
+    pub ORDER_DEPENDENT_TRAIT_OBJECTS,
+    Deny,
+    "trait-object types were treated as different depending on marker-trait order"
+}
+
 declare_lint! {
     pub BAD_REPR,
     Warn,
@@ -412,6 +418,7 @@ impl LintPass for HardwiredLints {
             PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
             LATE_BOUND_LIFETIME_ARGUMENTS,
             INCOHERENT_FUNDAMENTAL_IMPLS,
+            ORDER_DEPENDENT_TRAIT_OBJECTS,
             DEPRECATED,
             UNUSED_UNSAFE,
             UNUSED_MUT,

src/librustc/traits/coherence.rs

@@ -20,6 +20,7 @@ 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;
 
@@ -52,6 +53,7 @@ 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
@@ -62,12 +64,14 @@ where
     debug!("overlapping_impls(\
            impl1_def_id={:?}, \
            impl2_def_id={:?},
-           intercrate_mode={:?})",
+           intercrate_mode={:?},
+           trait_object_mode={:?})",
            impl1_def_id,
            impl2_def_id,
-           intercrate_mode);
+           intercrate_mode,
+           trait_object_mode);
 
-    let overlaps = tcx.infer_ctxt().enter(|infcx| {
+    let overlaps = tcx.infer_ctxt().with_trait_object_mode(trait_object_mode).enter(|infcx| {
         let selcx = &mut SelectionContext::intercrate(&infcx, intercrate_mode);
         overlap(selcx, impl1_def_id, impl2_def_id).is_some()
     });
@@ -79,7 +83,7 @@ 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().enter(|infcx| {
+    tcx.infer_ctxt().with_trait_object_mode(trait_object_mode).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())

src/librustc/traits/error_reporting.rs

@@ -459,7 +459,7 @@ 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/mod.rs

@@ -64,6 +64,8 @@ pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
 pub use self::specialize::{OverlapError, specialization_graph, translate_substs};
 pub use self::specialize::find_associated_item;
+pub use self::specialize::specialization_graph::FutureCompatOverlapError;
+pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
 pub use self::engine::{TraitEngine, TraitEngineExt};
 pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
 pub use self::util::{supertraits, supertrait_def_ids, transitive_bounds,

src/librustc/traits/select.rs

@@ -44,7 +44,7 @@ use infer::{InferCtxt, InferOk, TypeFreshener};
 use middle::lang_items;
 use mir::interpret::GlobalId;
 use ty::fast_reject;
-use ty::relate::TypeRelation;
+use ty::relate::{TypeRelation, TraitObjectMode};
 use ty::subst::{Subst, Substs};
 use ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable};
 
@@ -1501,6 +1501,13 @@ 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
     }
@@ -3699,7 +3706,8 @@ 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());
+        let mut matcher = ty::_match::Match::new(
+            self.tcx(), self.infcx.trait_object_mode());
         matcher.relate(previous, current).is_ok()
     }
 

src/librustc/traits/specialize/mod.rs

@@ -24,10 +24,10 @@ pub mod specialization_graph;
 use hir::def_id::DefId;
 use infer::{InferCtxt, InferOk};
 use lint;
+use traits::{self, FutureCompatOverlapErrorKind, ObligationCause, TraitEngine};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lrc;
 use syntax_pos::DUMMY_SP;
-use traits::{self, ObligationCause, TraitEngine};
 use traits::select::IntercrateAmbiguityCause;
 use ty::{self, TyCtxt, TypeFoldable};
 use ty::subst::{Subst, Substs};
@@ -36,6 +36,7 @@ use super::{SelectionContext, FulfillmentContext};
 use super::util::impl_trait_ref_and_oblig;
 
 /// Information pertinent to an overlapping impl error.
+#[derive(Debug)]
 pub struct OverlapError {
     pub with_impl: DefId,
     pub trait_desc: String,
@@ -318,8 +319,9 @@ pub(super) fn specialization_graph_provider<'a, 'tcx>(
             let insert_result = sg.insert(tcx, impl_def_id);
             // Report error if there was one.
             let (overlap, used_to_be_allowed) = match insert_result {
-                Err(overlap) => (Some(overlap), false),
-                Ok(opt_overlap) => (opt_overlap, true)
+                Err(overlap) => (Some(overlap), None),
+                Ok(Some(overlap)) => (Some(overlap.error), Some(overlap.kind)),
+                Ok(None) => (None, None)
             };
 
             if let Some(overlap) = overlap {
@@ -329,14 +331,20 @@ pub(super) fn specialization_graph_provider<'a, 'tcx>(
                         String::new(), |ty| {
                             format!(" for type `{}`", ty)
                         }),
-                    if used_to_be_allowed { " (E0119)" } else { "" }
+                    if used_to_be_allowed.is_some() { " (E0119)" } else { "" }
                 );
                 let impl_span = tcx.sess.source_map().def_span(
                     tcx.span_of_impl(impl_def_id).unwrap()
                 );
-                let mut err = if used_to_be_allowed {
+                let mut err = if let Some(kind) = used_to_be_allowed {
+                    let lint = match kind {
+                        FutureCompatOverlapErrorKind::Issue43355 =>
+                            lint::builtin::INCOHERENT_FUNDAMENTAL_IMPLS,
+                        FutureCompatOverlapErrorKind::Issue33140 =>
+                            lint::builtin::ORDER_DEPENDENT_TRAIT_OBJECTS,
+                    };
                     tcx.struct_span_lint_node(
-                        lint::builtin::INCOHERENT_FUNDAMENTAL_IMPLS,
+                        lint,
                         tcx.hir().as_local_node_id(impl_def_id).unwrap(),
                         impl_span,
                         &msg)