diff --git a/src/librustc/traits/auto_trait.rs b/src/librustc/traits/auto_trait.rs index c3cca149c2c57..a0237348ea690 100644 --- a/src/librustc/traits/auto_trait.rs +++ b/src/librustc/traits/auto_trait.rs @@ -334,7 +334,12 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> { continue; } - let result = select.select(&Obligation::new(dummy_cause.clone(), new_env, pred)); + // Call infcx.resolve_type_vars_if_possible to see if we can + // get rid of any inference variables. + let obligation = infcx.resolve_type_vars_if_possible( + &Obligation::new(dummy_cause.clone(), new_env, pred) + ); + let result = select.select(&obligation); match &result { &Ok(Some(ref vtable)) => { @@ -369,7 +374,7 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> { } &Ok(None) => {} &Err(SelectionError::Unimplemented) => { - if self.is_of_param(pred.skip_binder().trait_ref.substs) { + if self.is_param_no_infer(pred.skip_binder().trait_ref.substs) { already_visited.remove(&pred); self.add_user_pred( &mut user_computed_preds, @@ -631,18 +636,28 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> { finished_map } - pub fn is_of_param(&self, substs: &Substs<'_>) -> bool { - if substs.is_noop() { - return false; - } + fn is_param_no_infer(&self, substs: &Substs<'_>) -> bool { + return self.is_of_param(substs.type_at(0)) && + !substs.types().any(|t| t.has_infer_types()); + } - return match substs.type_at(0).sty { + pub fn is_of_param(&self, ty: Ty<'_>) -> bool { + return match ty.sty { ty::Param(_) => true, - ty::Projection(p) => self.is_of_param(p.substs), + ty::Projection(p) => self.is_of_param(p.self_ty()), _ => false, }; } + fn is_self_referential_projection(&self, p: ty::PolyProjectionPredicate<'_>) -> bool { + match p.ty().skip_binder().sty { + ty::Projection(proj) if proj == p.skip_binder().projection_ty => { + true + }, + _ => false + } + } + pub fn evaluate_nested_obligations< 'b, 'c, @@ -661,28 +676,77 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> { ) -> bool { let dummy_cause = ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID); - for (obligation, predicate) in nested - .filter(|o| o.recursion_depth == 1) + for (obligation, mut predicate) in nested .map(|o| (o.clone(), o.predicate.clone())) { let is_new_pred = fresh_preds.insert(self.clean_pred(select.infcx(), predicate.clone())); + // Resolve any inference variables that we can, to help selection succeed + predicate = select.infcx().resolve_type_vars_if_possible(&predicate); + + // We only add a predicate as a user-displayable bound if + // it involves a generic parameter, and doesn't contain + // any inference variables. + // + // Displaying a bound involving a concrete type (instead of a generic + // parameter) would be pointless, since it's always true + // (e.g. u8: Copy) + // Displaying an inference variable is impossible, since they're + // an internal compiler detail without a defined visual representation + // + // We check this by calling is_of_param on the relevant types + // from the various possible predicates match &predicate { &ty::Predicate::Trait(ref p) => { - let substs = &p.skip_binder().trait_ref.substs; + if self.is_param_no_infer(p.skip_binder().trait_ref.substs) + && !only_projections + && is_new_pred { - if self.is_of_param(substs) && !only_projections && is_new_pred { self.add_user_pred(computed_preds, predicate); } predicates.push_back(p.clone()); } &ty::Predicate::Projection(p) => { - // If the projection isn't all type vars, then - // we don't want to add it as a bound - if self.is_of_param(p.skip_binder().projection_ty.substs) && is_new_pred { - self.add_user_pred(computed_preds, predicate); - } else { + debug!("evaluate_nested_obligations: examining projection predicate {:?}", + predicate); + + // As described above, we only want to display + // bounds which include a generic parameter but don't include + // an inference variable. + // Additionally, we check if we've seen this predicate before, + // to avoid rendering duplicate bounds to the user. + if self.is_param_no_infer(p.skip_binder().projection_ty.substs) + && !p.ty().skip_binder().is_ty_infer() + && is_new_pred { + debug!("evaluate_nested_obligations: adding projection predicate\ + to computed_preds: {:?}", predicate); + + // Under unusual circumstances, we can end up with a self-refeential + // projection predicate. For example: + // ::Value == ::Value + // Not only is displaying this to the user pointless, + // having it in the ParamEnv will cause an issue if we try to call + // poly_project_and_unify_type on the predicate, since this kind of + // predicate will normally never end up in a ParamEnv. + // + // For these reasons, we ignore these weird predicates, + // ensuring that we're able to properly synthesize an auto trait impl + if self.is_self_referential_projection(p) { + debug!("evaluate_nested_obligations: encountered a projection + predicate equating a type with itself! Skipping"); + + } else { + self.add_user_pred(computed_preds, predicate); + } + } + + // We can only call poly_project_and_unify_type when our predicate's + // Ty is an inference variable - otherwise, there won't be anything to + // unify + if p.ty().skip_binder().is_ty_infer() { + debug!("Projecting and unifying projection predicate {:?}", + predicate); match poly_project_and_unify_type(select, &obligation.with(p.clone())) { Err(e) => { debug!( diff --git a/src/test/rustdoc/issue-50159.rs b/src/test/rustdoc/issue-50159.rs new file mode 100644 index 0000000000000..3055c72162452 --- /dev/null +++ b/src/test/rustdoc/issue-50159.rs @@ -0,0 +1,31 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + + +pub trait Signal { + type Item; +} + +pub trait Signal2 { + type Item2; +} + +impl Signal2 for B where B: Signal { + type Item2 = C; +} + +// @has issue_50159/struct.Switch.html +// @has - '//code' 'impl Send for Switch where ::Item: Send' +// @has - '//code' 'impl Sync for Switch where ::Item: Sync' +// @count - '//*[@id="implementations-list"]/*[@class="impl"]' 0 +// @count - '//*[@id="synthetic-implementations-list"]/*[@class="impl"]' 2 +pub struct Switch { + pub inner: ::Item2, +} diff --git a/src/test/rustdoc/synthetic_auto/self-referential.rs b/src/test/rustdoc/synthetic_auto/self-referential.rs new file mode 100644 index 0000000000000..516a3c9a516ab --- /dev/null +++ b/src/test/rustdoc/synthetic_auto/self-referential.rs @@ -0,0 +1,40 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// Some unusual code minimized from +// https://github.com/sile/handy_async/tree/7b619b762c06544fc67792c8ff8ebc24a88fdb98 + +pub trait Pattern { + type Value; +} + +pub struct Constrain(A, B, C); + +impl Pattern for Constrain + where A: Pattern, + B: Pattern, + C: Pattern, +{ + type Value = A::Value; +} + +pub struct Wrapper(T); + +impl Pattern for Wrapper { + type Value = T; +} + + +// @has self_referential/struct.WriteAndThen.html +// @has - '//*[@id="synthetic-implementations-list"]/*[@class="impl"]//*/code' "impl Send for \ +// WriteAndThen where ::Value: Send" +pub struct WriteAndThen(pub P1::Value,pub > as Pattern>::Value) + where P1: Pattern; +