implement a hack to make traitobject 0.1.0 compile

Author: arielb1

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/traits/mod.rs

@@ -56,6 +56,8 @@ 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

@@ -2260,7 +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.

src/librustc/traits/specialize/mod.rs

@@ -14,11 +14,10 @@ pub mod specialization_graph;
 use hir::def_id::DefId;
 use infer::{InferCtxt, InferOk};
 use lint;
-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;
-use traits::{self, ObligationCause, TraitEngine};
 use traits::select::IntercrateAmbiguityCause;
 use ty::{self, TyCtxt, TypeFoldable};
 use ty::subst::{Subst, Substs};
@@ -27,6 +26,7 @@ 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,
@@ -310,8 +310,9 @@ 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 {
@@ -321,14 +322,20 @@ 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)

src/librustc/traits/specialize/specialization_graph.rs

@@ -58,10 +58,22 @@ struct Children {
     blanket_impls: Vec<DefId>,
 }
 
+#[derive(Copy, Clone, Debug)]
+pub enum FutureCompatOverlapErrorKind {
+    Issue43355,
+    Issue33140,
+}
+
+#[derive(Debug)]
+pub struct FutureCompatOverlapError {
+    pub error: OverlapError,
+    pub kind: FutureCompatOverlapErrorKind
+}
+
 /// The result of attempting to insert an impl into a group of children.
 enum Inserted {
     /// The impl was inserted as a new child in this group of children.
-    BecameNewSibling(Option<OverlapError>),
+    BecameNewSibling(Option<FutureCompatOverlapError>),
 
     /// The impl should replace existing impls [X1, ..], because the impl specializes X1, X2, etc.
     ReplaceChildren(Vec<DefId>),
@@ -162,7 +174,19 @@ impl<'a, 'gcx, 'tcx> Children {
                 impl_def_id,
                 traits::IntercrateMode::Issue43355,
                 |overlap| {
-                    if tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling) {
+                    if let Some(overlap_kind) =
+                        tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling)
+                    {
+                        match overlap_kind {
+                            ty::ImplOverlapKind::Permitted => {}
+                            ty::ImplOverlapKind::Issue33140 => {
+                                last_lint = Some(FutureCompatOverlapError {
+                                    error: overlap_error(overlap),
+                                    kind: FutureCompatOverlapErrorKind::Issue33140
+                                });
+                            }
+                        }
+
                         return Ok((false, false));
                     }
 
@@ -190,13 +214,23 @@ impl<'a, 'gcx, 'tcx> Children {
 
                 replace_children.push(possible_sibling);
             } else {
-                if !tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling) {
+                if let None = tcx.impls_are_allowed_to_overlap(
+                    impl_def_id, possible_sibling)
+                {
+                    // do future-compat checks for overlap. Have issue #33140
+                    // errors overwrite issue #43355 errors when both are present.
+
                     traits::overlapping_impls(
                         tcx,
                         possible_sibling,
                         impl_def_id,
                         traits::IntercrateMode::Fixed,
-                        |overlap| last_lint = Some(overlap_error(overlap)),
+                        |overlap| {
+                            last_lint = Some(FutureCompatOverlapError {
+                                error: overlap_error(overlap),
+                                kind: FutureCompatOverlapErrorKind::Issue43355
+                            });
+                        },
                         || (),
                     );
                 }
@@ -263,7 +297,7 @@ impl<'a, 'gcx, 'tcx> Graph {
     pub fn insert(&mut self,
                   tcx: TyCtxt<'a, 'gcx, 'tcx>,
                   impl_def_id: DefId)
-                  -> Result<Option<OverlapError>, OverlapError> {
+                  -> Result<Option<FutureCompatOverlapError>, OverlapError> {
         assert!(impl_def_id.is_local());
 
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();

src/librustc/ty/mod.rs

@@ -2637,6 +2637,45 @@ impl<'gcx> ::std::ops::Deref for Attributes<'gcx> {
     }
 }
 
+#[derive(Debug, PartialEq, Eq)]
+pub enum ImplOverlapKind {
+    /// These impls are always allowed to overlap.
+    Permitted,
+    /// These impls are allowed to overlap, but that raises
+    /// an issue #33140 future-compatibility warning.
+    ///
+    /// Some background: in Rust 1.0, the trait-object types `Send + Sync` (today's
+    /// `dyn Send + Sync`) and `Sync + Send` (now `dyn Sync + Send`) were different.
+    ///
+    /// The widely-used version 0.1.0 of the crate `traitobject` had accidentally relied
+    /// that difference, making what reduces to the following set of impls:
+    ///
+    /// ```
+    /// trait Trait {}
+    /// impl Trait for dyn Send + Sync {}
+    /// impl Trait for dyn Sync + Send {}
+    /// ```
+    ///
+    /// Obviously, once we made these types be identical, that code causes a coherence
+    /// error and a fairly big headache for us. However, luckily for us, the trait
+    /// `Trait` used in this case is basically a marker trait, and therefore having
+    /// overlapping impls for it is sound.
+    ///
+    /// To handle this, we basically regard the trait as a marker trait, with an additional
+    /// future-compatibility warning. To avoid accidentally "stabilizing" this feature,
+    /// it has the following restrictions:
+    ///
+    /// 1. The trait must indeed be a marker-like trait (i.e., no items), and must be
+    /// positive impls.
+    /// 2. The trait-ref of both impls must be equal.
+    /// 3. The trait-ref of both impls must be a trait object type consisting only of
+    /// marker traits.
+    /// 4. Neither of the impls can have any where-clauses.
+    ///
+    /// Once `traitobject` 0.1.0 is no longer an active concern, this hack can be removed.
+    Issue33140
+}
+
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     pub fn body_tables(self, body: hir::BodyId) -> &'gcx TypeckTables<'gcx> {
         self.typeck_tables_of(self.hir().body_owner_def_id(body))
@@ -2788,8 +2827,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
     /// Returns `true` if the impls are the same polarity and the trait either
     /// has no items or is annotated #[marker] and prevents item overrides.
-    pub fn impls_are_allowed_to_overlap(self, def_id1: DefId, def_id2: DefId) -> bool {
-        if self.features().overlapping_marker_traits {
+    pub fn impls_are_allowed_to_overlap(self, def_id1: DefId, def_id2: DefId)
+                                        -> Option<ImplOverlapKind>
+    {
+        let is_legit = if self.features().overlapping_marker_traits {
             let trait1_is_empty = self.impl_trait_ref(def_id1)
                 .map_or(false, |trait_ref| {
                     self.associated_item_def_ids(trait_ref.def_id).is_empty()
@@ -2811,6 +2852,29 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                 && is_marker_impl(def_id2)
         } else {
             false
+        };
+
+        if is_legit {
+            debug!("impls_are_allowed_to_overlap({:?}, {:?}) = Some(Permitted)",
+                  def_id1, def_id2);
+            Some(ImplOverlapKind::Permitted)
+        } else {
+            if let Some(self_ty1) = self.issue33140_self_ty(def_id1) {
+                if let Some(self_ty2) = self.issue33140_self_ty(def_id2) {
+                    if self_ty1 == self_ty2 {
+                        debug!("impls_are_allowed_to_overlap({:?}, {:?}) - issue #33140 HACK",
+                               def_id1, def_id2);
+                        return Some(ImplOverlapKind::Issue33140);
+                    } else {
+                        debug!("impls_are_allowed_to_overlap({:?}, {:?}) - found {:?} != {:?}",
+                              def_id1, def_id2, self_ty1, self_ty2);
+                    }
+                }
+            }
+
+            debug!("impls_are_allowed_to_overlap({:?}, {:?}) = None",
+                  def_id1, def_id2);
+            None
         }
     }
 
@@ -3203,6 +3267,59 @@ fn instance_def_size_estimate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     }
 }
 
+/// If `def_id` is an issue 33140 hack impl, return its self type. Otherwise
+/// return None.
+///
+/// See ImplOverlapKind::Issue33140 for more details.
+fn issue33140_self_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                def_id: DefId)
+                                -> Option<Ty<'tcx>>
+{
+    debug!("issue33140_self_ty({:?})", def_id);
+
+    let trait_ref = tcx.impl_trait_ref(def_id).unwrap_or_else(|| {
+        bug!("issue33140_self_ty called on inherent impl {:?}", def_id)
+    });
+
+    debug!("issue33140_self_ty({:?}), trait-ref={:?}", def_id, trait_ref);
+
+    let is_marker_like =
+        tcx.impl_polarity(def_id) == hir::ImplPolarity::Positive &&
+        tcx.associated_item_def_ids(trait_ref.def_id).is_empty();
+
+    // Check whether these impls would be ok for a marker trait.
+    if !is_marker_like {
+        debug!("issue33140_self_ty - not marker-like!");
+        return None;
+    }
+
+    // impl must be `impl Trait for dyn Marker1 + Marker2 + ...`
+    if trait_ref.substs.len() != 1 {
+        debug!("issue33140_self_ty - impl has substs!");
+        return None;
+    }
+
+    let predicates = tcx.predicates_of(def_id);
+    if predicates.parent.is_some() || !predicates.predicates.is_empty() {
+        debug!("issue33140_self_ty - impl has predicates {:?}!", predicates);
+        return None;
+    }
+
+    let self_ty = trait_ref.self_ty();
+    let self_ty_matches = match self_ty.sty {
+        ty::Dynamic(ref data, ty::ReStatic) => data.principal().is_none(),
+        _ => false
+    };
+
+    if self_ty_matches {
+        debug!("issue33140_self_ty - MATCHES!");
+        Some(self_ty)
+    } else {
+        debug!("issue33140_self_ty - non-matching self type");
+        None
+    }
+}
+
 pub fn provide(providers: &mut ty::query::Providers<'_>) {
     context::provide(providers);
     erase_regions::provide(providers);
@@ -3221,6 +3338,7 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
         crate_hash,
         trait_impls_of: trait_def::trait_impls_of_provider,
         instance_def_size_estimate,
+        issue33140_self_ty,
         ..*providers
     };
 }

src/librustc/ty/query/mod.rs

@@ -202,6 +202,8 @@ define_queries! { <'tcx>
 
         [] fn impl_trait_ref: ImplTraitRef(DefId) -> Option<ty::TraitRef<'tcx>>,
         [] fn impl_polarity: ImplPolarity(DefId) -> hir::ImplPolarity,
+
+        [] fn issue33140_self_ty: Issue33140SelfTy(DefId) -> Option<ty::Ty<'tcx>>,
     },
 
     TypeChecking {

src/librustc/ty/query/plumbing.rs

@@ -1275,6 +1275,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
         DepKind::AdtDefOfItem => { force!(adt_def, def_id!()); }
         DepKind::ImplTraitRef => { force!(impl_trait_ref, def_id!()); }
         DepKind::ImplPolarity => { force!(impl_polarity, def_id!()); }
+        DepKind::Issue33140SelfTy => { force!(issue33140_self_ty, def_id!()); }
         DepKind::FnSignature => { force!(fn_sig, def_id!()); }
         DepKind::CoerceUnsizedInfo => { force!(coerce_unsized_info, def_id!()); }
         DepKind::ItemVariances => { force!(variances_of, def_id!()); }