Allow the elaborator to only filter to real supertraits

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1663,39 +1663,45 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
  })
  });
 
- let existential_projections = projection_bounds.iter().map(|(bound, _)| {
- bound.map_bound(|mut b| {
- assert_eq!(b.projection_ty.self_ty(), dummy_self);
-
- // Like for trait refs, verify that `dummy_self` did not leak inside default type
- // parameters.
- let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
- if arg.walk().any(|arg| arg == dummy_self.into()) {
- return true;
+ let existential_projections = projection_bounds
+ .iter()
+ // We filter out traits that don't have `Self` as their self type above,
+ // we need to do the same for projections.
+ .filter(|(bound, _)| bound.skip_binder().self_ty() == dummy_self)
+ .map(|(bound, _)| {
+ bound.map_bound(|mut b| {
+ assert_eq!(b.projection_ty.self_ty(), dummy_self);
+
+ // Like for trait refs, verify that `dummy_self` did not leak inside default type
+ // parameters.
+ let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
+ if arg.walk().any(|arg| arg == dummy_self.into()) {
+ return true;
+ }
+ false
+ });
+ if references_self {
+ let guar = tcx.sess.delay_span_bug(
+ span,
+ "trait object projection bounds reference `Self`",
+ );
+ let substs: Vec<_> = b
+ .projection_ty
+ .substs
+ .iter()
+ .map(|arg| {
+ if arg.walk().any(|arg| arg == dummy_self.into()) {
+ return tcx.ty_error(guar).into();
+ }
+ arg
+ })
+ .collect();
+ b.projection_ty.substs = tcx.mk_substs(&substs);
  }
- false
- });
- if references_self {
- let guar = tcx
- .sess
- .delay_span_bug(span, "trait object projection bounds reference `Self`");
- let substs: Vec<_> = b
- .projection_ty
- .substs
- .iter()
- .map(|arg| {
- if arg.walk().any(|arg| arg == dummy_self.into()) {
- return tcx.ty_error(guar).into();
- }
- arg
- })
- .collect();
- b.projection_ty.substs = tcx.mk_substs(&substs);
- }
 
- ty::ExistentialProjection::erase_self_ty(tcx, b)
- })
- });
+  ty::ExistentialProjection::erase_self_ty(tcx, b)
+  })
+  });
 
  let regular_trait_predicates = existential_trait_refs
  .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));

compiler/rustc_hir_typeck/src/closure.rs

@@ -210,7 +210,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  // and we want to keep inference generally in the same order of
  // the registered obligations.
  predicates.rev(),
- ) {
+ )
+ // We only care about self bounds
+ .filter_only_self()
+ {
  debug!(?pred);
  let bound_predicate = pred.kind();
 

compiler/rustc_infer/src/traits/util.rs

@@ -69,6 +69,7 @@ impl<'tcx> Extend<ty::Predicate<'tcx>> for PredicateSet<'tcx> {
 pub struct Elaborator<'tcx, O> {
  stack: Vec<O>,
  visited: PredicateSet<'tcx>,
+ only_self: bool,
 }
 
 /// Describes how to elaborate an obligation into a sub-obligation.
@@ -170,7 +171,8 @@ pub fn elaborate<'tcx, O: Elaboratable<'tcx>>(
  tcx: TyCtxt<'tcx>,
  obligations: impl IntoIterator<Item = O>,
 ) -> Elaborator<'tcx, O> {
- let mut elaborator = Elaborator { stack: Vec::new(), visited: PredicateSet::new(tcx) };
+ let mut elaborator =
+ Elaborator { stack: Vec::new(), visited: PredicateSet::new(tcx), only_self: false };
  elaborator.extend_deduped(obligations);
  elaborator
 }
@@ -185,14 +187,25 @@ impl<'tcx, O: Elaboratable<'tcx>> Elaborator<'tcx, O> {
  self.stack.extend(obligations.into_iter().filter(|o| self.visited.insert(o.predicate())));
  }
 
+ /// Filter to only the supertraits of trait predicates, i.e. only the predicates
+ /// that have `Self` as their self type, instead of all implied predicates.
+ pub fn filter_only_self(mut self) -> Self {
+ self.only_self = true;
+ self
+ }
+
  fn elaborate(&mut self, elaboratable: &O) {
  let tcx = self.visited.tcx;
 
  let bound_predicate = elaboratable.predicate().kind();
  match bound_predicate.skip_binder() {
  ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
- // Get predicates declared on the trait.
- let predicates = tcx.implied_predicates_of(data.def_id());
+ // Get predicates implied by the trait, or only super predicates if we only care about self predicates.
+ let predicates = if self.only_self {
+ tcx.super_predicates_of(data.def_id())
+ } else {
+ tcx.implied_predicates_of(data.def_id())
+ };
 
  let obligations =
  predicates.predicates.iter().enumerate().map(|(index, &(mut pred, span))| {
@@ -350,18 +363,16 @@ pub fn supertraits<'tcx>(
  tcx: TyCtxt<'tcx>,
  trait_ref: ty::PolyTraitRef<'tcx>,
 ) -> impl Iterator<Item = ty::PolyTraitRef<'tcx>> {
- let pred: ty::Predicate<'tcx> = trait_ref.to_predicate(tcx);
- FilterToTraits::new(elaborate(tcx, [pred]))
+ elaborate(tcx, [trait_ref.to_predicate(tcx)]).filter_only_self().filter_to_traits()
 }
 
 pub fn transitive_bounds<'tcx>(
  tcx: TyCtxt<'tcx>,
  trait_refs: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
 ) -> impl Iterator<Item = ty::PolyTraitRef<'tcx>> {
- FilterToTraits::new(elaborate(
- tcx,
- trait_refs.map(|trait_ref| -> ty::Predicate<'tcx> { trait_ref.to_predicate(tcx) }),
- ))
+ elaborate(tcx, trait_refs.map(|trait_ref| trait_ref.to_predicate(tcx)))
+ .filter_only_self()
+ .filter_to_traits()
 }
 
 /// A specialized variant of `elaborate` that only elaborates trait references that may
@@ -402,18 +413,18 @@ pub fn transitive_bounds_that_define_assoc_type<'tcx>(
 // Other
 ///////////////////////////////////////////////////////////////////////////
 
+impl<'tcx> Elaborator<'tcx, ty::Predicate<'tcx>> {
+ fn filter_to_traits(self) -> FilterToTraits<Self> {
+ FilterToTraits { base_iterator: self }
+ }
+}
+
 /// A filter around an iterator of predicates that makes it yield up
 /// just trait references.
 pub struct FilterToTraits<I> {
  base_iterator: I,
 }
 
-impl<I> FilterToTraits<I> {
- fn new(base: I) -> FilterToTraits<I> {
- FilterToTraits { base_iterator: base }
- }
-}
-
 impl<'tcx, I: Iterator<Item = ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
  type Item = ty::PolyTraitRef<'tcx>;
 

compiler/rustc_lint/src/unused.rs

@@ -255,6 +255,8 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
  ty::Adt(def, _) => is_def_must_use(cx, def.did(), span),
  ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, .. }) => {
  elaborate(cx.tcx, cx.tcx.explicit_item_bounds(def).iter().cloned())
+ // We only care about self bounds for the impl-trait
+ .filter_only_self()
  .find_map(|(pred, _span)| {
  // We only look at the `DefId`, so it is safe to skip the binder here.
  if let ty::PredicateKind::Clause(ty::Clause::Trait(

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -498,7 +498,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
  let tcx = self.tcx();
  let own_bounds: FxIndexSet<_> =
  bounds.iter().map(|bound| bound.with_self_ty(tcx, self_ty)).collect();
- for assumption in elaborate(tcx, own_bounds.iter().copied()) {
+ for assumption in elaborate(tcx, own_bounds.iter().copied())
+ // we only care about bounds that match the `Self` type
+ .filter_only_self()
+ {
  // FIXME: Predicates are fully elaborated in the object type's existential bounds
  // list. We want to only consider these pre-elaborated projections, and not other
  // projection predicates that we reach by elaborating the principal trait ref,

tests/ui/traits/alias/dont-elaborate-non-self.stderr

@@ -0,0 +1,20 @@
+error[E0277]: the size for values of type `(dyn Fn() -> Fut + 'static)` cannot be known at compilation time
+ --> $DIR/dont-elaborate-non-self.rs:7:11
+ |
+LL | fn f<Fut>(a: dyn F<Fut>) {}
+ | ^ doesn't have a size known at compile-time
+ |
+ = help: the trait `Sized` is not implemented for `(dyn Fn() -> Fut + 'static)`
+ = help: unsized fn params are gated as an unstable feature
+help: you can use `impl Trait` as the argument type
+ |
+LL | fn f<Fut>(a: impl F<Fut>) {}
+ | ~~~~
+help: function arguments must have a statically known size, borrowed types always have a known size
+ |
+LL | fn f<Fut>(a: &dyn F<Fut>) {}
+ | +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/trait-upcasting/alias-where-clause-isnt-supertrait.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+ --> $DIR/alias-where-clause-isnt-supertrait.rs:27:5
+ |
+LL | fn test(x: &dyn C) -> &dyn B {
+ | ------ expected `&dyn B` because of return type
+LL | x
+ | ^ expected trait `B`, found trait `C`
+ |
+ = note: expected reference `&dyn B`
+ found reference `&dyn C`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.