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.

Author: bors

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 {