Rollup merge of rust-lang#55687 - alexreg:fix-24010, r=scalexm

Take supertraits into account when calculating associated types

Fixes rust-lang#24010 and rust-lang#23856. Applies to trait aliases too.

As a by-product, this PR also makes repeated bindings of the same associated item in the same definition a hard error. This was previously a warning with a note about it becoming a hard error in the future. See rust-lang#50589 for more info.

I talked about this with @nikomatsakis recently, but only very superficially, so this shouldn't stop anyone from assigning it to themself to review and r+.

N.B. The "WIP" commits represent imperfect attempts to solve the problem just for trait objects, but I've left them in for reference for the sake of whomever is reviewing this.

CC @carllerche @theemathas @durka @mbrubeck

Author: pietroalbini

src/librustc/diagnostics.rs

@@ -2134,7 +2134,7 @@ static X: u32 = 42;
 
 
 register_diagnostics! {
-//  E0006 // merged with E0005
+//  E0006, // merged with E0005
 //  E0101, // replaced with E0282
 //  E0102, // replaced with E0282
 //  E0134,
@@ -2183,9 +2183,7 @@ register_diagnostics! {
     E0657, // `impl Trait` can only capture lifetimes bound at the fn level
     E0687, // in-band lifetimes cannot be used in `fn`/`Fn` syntax
     E0688, // in-band lifetimes cannot be mixed with explicit lifetime binders
-
     E0697, // closures cannot be static
-
     E0707, // multiple elided lifetimes used in arguments of `async fn`
     E0708, // `async` non-`move` closures with arguments are not currently supported
     E0709, // multiple different lifetimes used in arguments of `async fn`

src/librustc/hir/mod.rs

@@ -506,9 +506,9 @@ pub enum TraitBoundModifier {
 }
 
 /// The AST represents all type param bounds as types.
-/// typeck::collect::compute_bounds matches these against
-/// the "special" built-in traits (see middle::lang_items) and
-/// detects Copy, Send and Sync.
+/// `typeck::collect::compute_bounds` matches these against
+/// the "special" built-in traits (see `middle::lang_items`) and
+/// detects `Copy`, `Send` and `Sync`.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub enum GenericBound {
     Trait(PolyTraitRef, TraitBoundModifier),

src/librustc/lint/builtin.rs

@@ -300,12 +300,6 @@ declare_lint! {
     "detects labels that are never used"
 }
 
-declare_lint! {
-    pub DUPLICATE_ASSOCIATED_TYPE_BINDINGS,
-    Warn,
-    "warns about duplicate associated type bindings in generics"
-}
-
 declare_lint! {
     pub DUPLICATE_MACRO_EXPORTS,
     Deny,
@@ -418,7 +412,6 @@ impl LintPass for HardwiredLints {
             ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
             UNSTABLE_NAME_COLLISIONS,
             IRREFUTABLE_LET_PATTERNS,
-            DUPLICATE_ASSOCIATED_TYPE_BINDINGS,
             DUPLICATE_MACRO_EXPORTS,
             INTRA_DOC_LINK_RESOLUTION_FAILURE,
             MISSING_DOC_CODE_EXAMPLES,

src/librustc/traits/mod.rs

@@ -50,11 +50,8 @@ 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::engine::{TraitEngine, TraitEngineExt};
-pub use self::util::elaborate_predicates;
-pub use self::util::supertraits;
-pub use self::util::Supertraits;
-pub use self::util::supertrait_def_ids;
-pub use self::util::SupertraitDefIds;
+pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
+pub use self::util::{supertraits, supertrait_def_ids, Supertraits, SupertraitDefIds};
 pub use self::util::transitive_bounds;
 
 #[allow(dead_code)]

src/librustc/traits/util.rs

@@ -333,7 +333,7 @@ impl<I> FilterToTraits<I> {
     }
 }
 
-impl<'tcx,I:Iterator<Item = ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
+impl<'tcx, I: Iterator<Item = ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
     type Item = ty::PolyTraitRef<'tcx>;
 
     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {

src/librustc/ty/mod.rs

@@ -294,7 +294,7 @@ impl Visibility {
         }
     }
 
-    /// Returns true if an item with this visibility is accessible from the given block.
+    /// Returns `true` if an item with this visibility is accessible from the given block.
     pub fn is_accessible_from<T: DefIdTree>(self, module: DefId, tree: T) -> bool {
         let restriction = match self {
             // Public items are visible everywhere.
@@ -309,7 +309,7 @@ impl Visibility {
         tree.is_descendant_of(module, restriction)
     }
 
-    /// Returns true if this visibility is at least as accessible as the given visibility
+    /// Returns `true` if this visibility is at least as accessible as the given visibility
     pub fn is_at_least<T: DefIdTree>(self, vis: Visibility, tree: T) -> bool {
         let vis_restriction = match vis {
             Visibility::Public => return self == Visibility::Public,
@@ -320,7 +320,7 @@ impl Visibility {
         self.is_accessible_from(vis_restriction, tree)
     }
 
-    // Returns true if this item is visible anywhere in the local crate.
+    // Returns `true` if this item is visible anywhere in the local crate.
     pub fn is_visible_locally(self) -> bool {
         match self {
             Visibility::Public => true,
@@ -451,7 +451,7 @@ bitflags! {
         // FIXME: Rename this to the actual property since it's used for generators too
         const HAS_TY_CLOSURE     = 1 << 9;
 
-        // true if there are "names" of types and regions and so forth
+        // `true` if there are "names" of types and regions and so forth
         // that are local to a particular fn
         const HAS_FREE_LOCAL_NAMES    = 1 << 10;
 
@@ -544,14 +544,14 @@ impl<'tcx> TyS<'tcx> {
     pub fn is_primitive_ty(&self) -> bool {
         match self.sty {
             TyKind::Bool |
-                TyKind::Char |
-                TyKind::Int(_) |
-                TyKind::Uint(_) |
-                TyKind::Float(_) |
-                TyKind::Infer(InferTy::IntVar(_)) |
-                TyKind::Infer(InferTy::FloatVar(_)) |
-                TyKind::Infer(InferTy::FreshIntTy(_)) |
-                TyKind::Infer(InferTy::FreshFloatTy(_)) => true,
+            TyKind::Char |
+            TyKind::Int(_) |
+            TyKind::Uint(_) |
+            TyKind::Float(_) |
+            TyKind::Infer(InferTy::IntVar(_)) |
+            TyKind::Infer(InferTy::FloatVar(_)) |
+            TyKind::Infer(InferTy::FreshIntTy(_)) |
+            TyKind::Infer(InferTy::FreshFloatTy(_)) => true,
             TyKind::Ref(_, x, _) => x.is_primitive_ty(),
             _ => false,
         }
@@ -953,7 +953,7 @@ impl<'a, 'gcx, 'tcx> Generics {
                 _ => bug!("expected lifetime parameter, but found another generic parameter")
             }
         } else {
-            tcx.generics_of(self.parent.expect("parent_count>0 but no parent?"))
+            tcx.generics_of(self.parent.expect("parent_count > 0 but no parent?"))
                .region_param(param, tcx)
         }
     }
@@ -970,7 +970,7 @@ impl<'a, 'gcx, 'tcx> Generics {
                 _ => bug!("expected type parameter, but found another generic parameter")
             }
         } else {
-            tcx.generics_of(self.parent.expect("parent_count>0 but no parent?"))
+            tcx.generics_of(self.parent.expect("parent_count > 0 but no parent?"))
                .type_param(param, tcx)
         }
     }
@@ -993,6 +993,7 @@ impl<'a, 'gcx, 'tcx> GenericPredicates<'tcx> {
         self.instantiate_into(tcx, &mut instantiated, substs);
         instantiated
     }
+
     pub fn instantiate_own(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, substs: &Substs<'tcx>)
                            -> InstantiatedPredicates<'tcx> {
         InstantiatedPredicates {
@@ -1041,15 +1042,15 @@ impl<'a, 'gcx, 'tcx> GenericPredicates<'tcx> {
 
 #[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub enum Predicate<'tcx> {
-    /// Corresponds to `where Foo : Bar<A,B,C>`. `Foo` here would be
+    /// Corresponds to `where Foo: Bar<A,B,C>`. `Foo` here would be
     /// the `Self` type of the trait reference and `A`, `B`, and `C`
     /// would be the type parameters.
     Trait(PolyTraitPredicate<'tcx>),
 
-    /// where `'a : 'b`
+    /// where `'a: 'b`
     RegionOutlives(PolyRegionOutlivesPredicate<'tcx>),
 
-    /// where `T : 'a`
+    /// where `T: 'a`
     TypeOutlives(PolyTypeOutlivesPredicate<'tcx>),
 
     /// where `<T as TraitRef>::Name == X`, approximately.
@@ -1062,7 +1063,7 @@ pub enum Predicate<'tcx> {
     /// trait must be object-safe
     ObjectSafe(DefId),
 
-    /// No direct syntax. May be thought of as `where T : FnFoo<...>`
+    /// No direct syntax. May be thought of as `where T: FnFoo<...>`
     /// for some substitutions `...` and `T` being a closure type.
     /// Satisfied (or refuted) once we know the closure's kind.
     ClosureKind(DefId, ClosureSubsts<'tcx>, ClosureKind),
@@ -1111,11 +1112,11 @@ impl<'a, 'gcx, 'tcx> Predicate<'tcx> {
         //
         // Let's start with an easy case. Consider two traits:
         //
-        //     trait Foo<'a> : Bar<'a,'a> { }
+        //     trait Foo<'a>: Bar<'a,'a> { }
         //     trait Bar<'b,'c> { }
         //
-        // Now, if we have a trait reference `for<'x> T : Foo<'x>`, then
-        // we can deduce that `for<'x> T : Bar<'x,'x>`. Basically, if we
+        // Now, if we have a trait reference `for<'x> T: Foo<'x>`, then
+        // we can deduce that `for<'x> T: Bar<'x,'x>`. Basically, if we
         // knew that `Foo<'x>` (for any 'x) then we also know that
         // `Bar<'x,'x>` (for any 'x). This more-or-less falls out from
         // normal substitution.
@@ -1128,21 +1129,21 @@ impl<'a, 'gcx, 'tcx> Predicate<'tcx> {
         //
         // Another example to be careful of is this:
         //
-        //     trait Foo1<'a> : for<'b> Bar1<'a,'b> { }
+        //     trait Foo1<'a>: for<'b> Bar1<'a,'b> { }
         //     trait Bar1<'b,'c> { }
         //
-        // Here, if we have `for<'x> T : Foo1<'x>`, then what do we know?
-        // The answer is that we know `for<'x,'b> T : Bar1<'x,'b>`. The
+        // Here, if we have `for<'x> T: Foo1<'x>`, then what do we know?
+        // The answer is that we know `for<'x,'b> T: Bar1<'x,'b>`. The
         // reason is similar to the previous example: any impl of
-        // `T:Foo1<'x>` must show that `for<'b> T : Bar1<'x, 'b>`.  So
+        // `T:Foo1<'x>` must show that `for<'b> T: Bar1<'x, 'b>`.  So
         // basically we would want to collapse the bound lifetimes from
         // the input (`trait_ref`) and the supertraits.
         //
         // To achieve this in practice is fairly straightforward. Let's
         // consider the more complicated scenario:
         //
-        // - We start out with `for<'x> T : Foo1<'x>`. In this case, `'x`
-        //   has a De Bruijn index of 1. We want to produce `for<'x,'b> T : Bar1<'x,'b>`,
+        // - We start out with `for<'x> T: Foo1<'x>`. In this case, `'x`
+        //   has a De Bruijn index of 1. We want to produce `for<'x,'b> T: Bar1<'x,'b>`,
         //   where both `'x` and `'b` would have a DB index of 1.
         //   The substitution from the input trait-ref is therefore going to be
         //   `'a => 'x` (where `'x` has a DB index of 1).
@@ -1194,6 +1195,7 @@ impl<'a, 'gcx, 'tcx> Predicate<'tcx> {
 pub struct TraitPredicate<'tcx> {
     pub trait_ref: TraitRef<'tcx>
 }
+
 pub type PolyTraitPredicate<'tcx> = ty::Binder<TraitPredicate<'tcx>>;
 
 impl<'tcx> TraitPredicate<'tcx> {
@@ -1218,7 +1220,7 @@ impl<'tcx> PolyTraitPredicate<'tcx> {
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
-pub struct OutlivesPredicate<A,B>(pub A, pub B); // `A : B`
+pub struct OutlivesPredicate<A,B>(pub A, pub B); // `A: B`
 pub type PolyOutlivesPredicate<A,B> = ty::Binder<OutlivesPredicate<A,B>>;
 pub type RegionOutlivesPredicate<'tcx> = OutlivesPredicate<ty::Region<'tcx>,
                                                            ty::Region<'tcx>>;
@@ -1238,11 +1240,11 @@ pub type PolySubtypePredicate<'tcx> = ty::Binder<SubtypePredicate<'tcx>>;
 /// This kind of predicate has no *direct* correspondent in the
 /// syntax, but it roughly corresponds to the syntactic forms:
 ///
-/// 1. `T : TraitRef<..., Item=Type>`
+/// 1. `T: TraitRef<..., Item=Type>`
 /// 2. `<T as TraitRef<...>>::Item == Type` (NYI)
 ///
 /// In particular, form #1 is "desugared" to the combination of a
-/// normal trait predicate (`T : TraitRef<...>`) and one of these
+/// normal trait predicate (`T: TraitRef<...>`) and one of these
 /// predicates. Form #2 is a broader form in that it also permits
 /// equality between arbitrary types. Processing an instance of
 /// Form #2 eventually yields one of these `ProjectionPredicate`
@@ -1256,14 +1258,14 @@ pub struct ProjectionPredicate<'tcx> {
 pub type PolyProjectionPredicate<'tcx> = Binder<ProjectionPredicate<'tcx>>;
 
 impl<'tcx> PolyProjectionPredicate<'tcx> {
-    /// Returns the def-id of the associated item being projected.
+    /// Returns the `DefId` of the associated item being projected.
     pub fn item_def_id(&self) -> DefId {
         self.skip_binder().projection_ty.item_def_id
     }
 
     pub fn to_poly_trait_ref(&self, tcx: TyCtxt<'_, '_, '_>) -> PolyTraitRef<'tcx> {
-        // Note: unlike with TraitRef::to_poly_trait_ref(),
-        // self.0.trait_ref is permitted to have escaping regions.
+        // Note: unlike with `TraitRef::to_poly_trait_ref()`,
+        // `self.0.trait_ref` is permitted to have escaping regions.
         // This is because here `self` has a `Binder` and so does our
         // return value, so we are preserving the number of binding
         // levels.
@@ -1274,12 +1276,12 @@ impl<'tcx> PolyProjectionPredicate<'tcx> {
         self.map_bound(|predicate| predicate.ty)
     }
 
-    /// The DefId of the TraitItem for the associated type.
+    /// The `DefId` of the `TraitItem` for the associated type.
     ///
-    /// Note that this is not the DefId of the TraitRef containing this
-    /// associated type, which is in tcx.associated_item(projection_def_id()).container.
+    /// Note that this is not the `DefId` of the `TraitRef` containing this
+    /// associated type, which is in `tcx.associated_item(projection_def_id()).container`.
     pub fn projection_def_id(&self) -> DefId {
-        // ok to skip binder since trait def-id does not care about regions
+        // okay to skip binder since trait def-id does not care about regions
         self.skip_binder().projection_ty.item_def_id
     }
 }
@@ -1515,14 +1517,14 @@ impl UniverseIndex {
         UniverseIndex::from_u32(self.private.checked_add(1).unwrap())
     }
 
-    /// True if `self` can name a name from `other` -- in other words,
+    /// Returns `true` if `self` can name a name from `other` -- in other words,
     /// if the set of names in `self` is a superset of those in
     /// `other` (`self >= other`).
     pub fn can_name(self, other: UniverseIndex) -> bool {
         self.private >= other.private
     }
 
-    /// True if `self` cannot name some names from `other` -- in other
+    /// Returns `true` if `self` cannot name some names from `other` -- in other
     /// words, if the set of names in `self` is a strict subset of
     /// those in `other` (`self < other`).
     pub fn cannot_name(self, other: UniverseIndex) -> bool {
@@ -1574,7 +1576,7 @@ impl<'tcx> ParamEnv<'tcx> {
     /// are revealed. This is suitable for monomorphized, post-typeck
     /// environments like codegen or doing optimizations.
     ///
-    /// NB. If you want to have predicates in scope, use `ParamEnv::new`,
+    /// N.B. If you want to have predicates in scope, use `ParamEnv::new`,
     /// or invoke `param_env.with_reveal_all()`.
     pub fn reveal_all() -> Self {
         Self::new(List::empty(), Reveal::All)
@@ -1979,14 +1981,14 @@ impl ReprOptions {
         self.int.unwrap_or(attr::SignedInt(ast::IntTy::Isize))
     }
 
-    /// Returns true if this `#[repr()]` should inhabit "smart enum
+    /// Returns `true` if this `#[repr()]` should inhabit "smart enum
     /// layout" optimizations, such as representing `Foo<&T>` as a
     /// single pointer.
     pub fn inhibit_enum_layout_opt(&self) -> bool {
         self.c() || self.int.is_some()
     }
 
-    /// Returns true if this `#[repr()]` should inhibit struct field reordering
+    /// Returns `true` if this `#[repr()]` should inhibit struct field reordering
     /// optimizations, such as with repr(C) or repr(packed(1)).
     pub fn inhibit_struct_field_reordering_opt(&self) -> bool {
         !(self.flags & ReprFlags::IS_UNOPTIMISABLE).is_empty() || (self.pack == 1)
@@ -2089,7 +2091,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         self.flags.intersects(AdtFlags::IS_FUNDAMENTAL)
     }
 
-    /// Returns true if this is PhantomData<T>.
+    /// Returns `true` if this is PhantomData<T>.
     #[inline]
     pub fn is_phantom_data(&self) -> bool {
         self.flags.intersects(AdtFlags::IS_PHANTOM_DATA)
@@ -2105,7 +2107,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         self.flags.intersects(AdtFlags::IS_RC)
     }
 
-    /// Returns true if this is Box<T>.
+    /// Returns `true` if this is Box<T>.
     #[inline]
     pub fn is_box(&self) -> bool {
         self.flags.intersects(AdtFlags::IS_BOX)
@@ -2422,7 +2424,7 @@ impl<'a, 'tcx> ClosureKind {
         }
     }
 
-    /// True if this a type that impls this closure kind
+    /// Returns `true` if this a type that impls this closure kind
     /// must also implement `other`.
     pub fn extends(self, other: ty::ClosureKind) -> bool {
         match (self, other) {
@@ -2475,7 +2477,7 @@ impl<'tcx> TyS<'tcx> {
     ///
     /// Note: prefer `ty.walk()` where possible.
     pub fn maybe_walk<F>(&'tcx self, mut f: F)
-        where F : FnMut(Ty<'tcx>) -> bool
+        where F: FnMut(Ty<'tcx>) -> bool
     {
         let mut walker = self.walk();
         while let Some(ty) = walker.next() {
@@ -2678,7 +2680,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             as Box<dyn Iterator<Item = AssociatedItem> + 'a>
     }
 
-    /// Returns true if the impls are the same polarity and the trait either
+    /// 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 {
@@ -2802,7 +2804,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         attr::contains_name(&self.get_attrs(did), attr)
     }
 
-    /// Returns true if this is an `auto trait`.
+    /// Returns `true` if this is an `auto trait`.
     pub fn trait_is_auto(self, trait_def_id: DefId) -> bool {
         self.trait_def(trait_def_id).has_auto_impl
     }