diff options
| -rw-r--r-- | src/librustc/diagnostics.rs | 48 | ||||
| -rw-r--r-- | src/librustc/infer/anon_types/mod.rs | 188 | ||||
| -rw-r--r-- | src/test/ui/impl-trait/region-escape-via-bound-contravariant.rs | 35 | ||||
| -rw-r--r-- | src/test/ui/impl-trait/region-escape-via-bound.rs | 34 | ||||
| -rw-r--r-- | src/test/ui/impl-trait/region-escape-via-bound.stderr | 20 |
5 files changed, 291 insertions, 34 deletions
diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs index b3a904f2f5f..fad18032592 100644 --- a/src/librustc/diagnostics.rs +++ b/src/librustc/diagnostics.rs @@ -2074,6 +2074,54 @@ a (non-transparent) struct containing a single float, while `Grams` is a transparent wrapper around a float. This can make a difference for the ABI. "##, +E0909: r##" +The `impl Trait` return type captures lifetime parameters that do not +appear within the `impl Trait` itself. + +Erroneous code example: + +```compile-fail,E0909 +use std::cell::Cell; + +trait Trait<'a> { } + +impl Trait<'b> for Cell<&'a u32> { } + +fn foo<'x, 'y>(x: Cell<&'x u32>) -> impl Trait<'y> +where 'x: 'y +{ + x +} +``` + +Here, the function `foo` returns a value of type `Cell<&'x u32>`, +which references the lifetime `'x`. However, the return type is +declared as `impl Trait<'y>` -- this indicates that `foo` returns +"some type that implements `Trait<'y>`", but it also indicates that +the return type **only captures data referencing the lifetime `'y`**. +In this case, though, we are referencing data with lifetime `'x`, so +this function is in error. + +To fix this, you must reference the lifetime `'x` from the return +type. For example, changing the return type to `impl Trait<'y> + 'x` +would work: + +``` +use std::cell::Cell; + +trait Trait<'a> { } + +impl Trait<'b> for Cell<&'a u32> { } + +fn foo<'x, 'y>(x: Cell<&'x u32>) -> impl Trait<'y> + 'x +where 'x: 'y +{ + x +} +``` +"##, + + } diff --git a/src/librustc/infer/anon_types/mod.rs b/src/librustc/infer/anon_types/mod.rs index 6a4f4072f53..93e8745af1b 100644 --- a/src/librustc/infer/anon_types/mod.rs +++ b/src/librustc/infer/anon_types/mod.rs @@ -17,7 +17,7 @@ use traits::{self, PredicateObligation}; use ty::{self, Ty, TyCtxt}; use ty::fold::{BottomUpFolder, TypeFoldable, TypeFolder}; use ty::outlives::Component; -use ty::subst::{Kind, UnpackedKind, Substs}; +use ty::subst::{Kind, Substs, UnpackedKind}; use util::nodemap::DefIdMap; pub type AnonTypeMap<'tcx> = DefIdMap<AnonTypeDecl<'tcx>>; @@ -113,10 +113,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { ) -> InferOk<'tcx, (T, AnonTypeMap<'tcx>)> { debug!( "instantiate_anon_types(value={:?}, parent_def_id={:?}, body_id={:?}, param_env={:?})", - value, - parent_def_id, - body_id, - param_env, + value, parent_def_id, body_id, param_env, ); let mut instantiator = Instantiator { infcx: self, @@ -458,7 +455,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { // Convert the type from the function into a type valid outside // the function, by replacing invalid regions with 'static, // after producing an error for each of them. - let definition_ty = instantiated_ty.fold_with(&mut ReverseMapper { tcx: self.tcx, map }); + let definition_ty = + instantiated_ty.fold_with(&mut ReverseMapper::new( + self.tcx, + self.is_tainted_by_errors(), + def_id, + map, + instantiated_ty, + )); debug!( "infer_anon_definition_from_instantiation: definition_ty={:?}", definition_ty @@ -475,7 +479,49 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { struct ReverseMapper<'cx, 'gcx: 'tcx, 'tcx: 'cx> { tcx: TyCtxt<'cx, 'gcx, 'tcx>, - map: FxHashMap<Kind<'tcx>, Kind<'gcx>> + + /// If errors have already been reported in this fn, we suppress + /// our own errors because they are sometimes derivative. + tainted_by_errors: bool, + + anon_type_def_id: DefId, + map: FxHashMap<Kind<'tcx>, Kind<'gcx>>, + map_missing_regions_to_empty: bool, + + /// initially `Some`, set to `None` once error has been reported + hidden_ty: Option<Ty<'tcx>>, +} + +impl<'cx, 'gcx, 'tcx> ReverseMapper<'cx, 'gcx, 'tcx> { + fn new( + tcx: TyCtxt<'cx, 'gcx, 'tcx>, + tainted_by_errors: bool, + anon_type_def_id: DefId, + map: FxHashMap<Kind<'tcx>, Kind<'gcx>>, + hidden_ty: Ty<'tcx>, + ) -> Self { + Self { + tcx, + tainted_by_errors, + anon_type_def_id, + map, + map_missing_regions_to_empty: false, + hidden_ty: Some(hidden_ty), + } + } + + fn fold_kind_mapping_missing_regions_to_empty(&mut self, kind: Kind<'tcx>) -> Kind<'tcx> { + assert!(!self.map_missing_regions_to_empty); + self.map_missing_regions_to_empty = true; + let kind = kind.fold_with(self); + self.map_missing_regions_to_empty = false; + kind + } + + fn fold_kind_normally(&mut self, kind: Kind<'tcx>) -> Kind<'tcx> { + assert!(!self.map_missing_regions_to_empty); + kind.fold_with(self) + } } impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for ReverseMapper<'cx, 'gcx, 'tcx> { @@ -484,33 +530,105 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for ReverseMapper<'cx, 'gcx, 'tcx> } fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { - // ignore bound regions that appear in the type (e.g., this - // would ignore `'r` in a type like `for<'r> fn(&'r u32)`. - if let ty::ReLateBound(..) = *r { - return r; + match r { + // ignore bound regions that appear in the type (e.g., this + // would ignore `'r` in a type like `for<'r> fn(&'r u32)`. + ty::ReLateBound(..) => return r, + + // ignore `'static`, as that can appear anywhere + ty::ReStatic => return r, + + _ => { } } match self.map.get(&r.into()).map(|k| k.unpack()) { Some(UnpackedKind::Lifetime(r1)) => r1, Some(u) => panic!("region mapped to unexpected kind: {:?}", u), None => { - // No mapping was found. This means that it is either a - // disallowed lifetime, which will be caught by regionck, - // or it is a region in a non-upvar closure generic, which - // is explicitly allowed. If that surprises you, read on. + if !self.map_missing_regions_to_empty && !self.tainted_by_errors { + if let Some(hidden_ty) = self.hidden_ty.take() { + let span = self.tcx.def_span(self.anon_type_def_id); + let mut err = struct_span_err!( + self.tcx.sess, + span, + E0909, + "hidden type for `impl Trait` captures lifetime that \ + does not appear in bounds", + ); + + // Assuming regionck succeeded, then we must + // be capturing *some* region from the fn + // header, and hence it must be free, so it's + // ok to invoke this fn (which doesn't accept + // all regions, and would ICE if an + // inappropriate region is given). We check + // `is_tainted_by_errors` by errors above, so + // we don't get in here unless regionck + // succeeded. (Note also that if regionck + // failed, then the regions we are attempting + // to map here may well be giving errors + // *because* the constraints were not + // satisfiable.) + self.tcx.note_and_explain_free_region( + &mut err, + &format!("hidden type `{}` captures ", hidden_ty), + r, + "" + ); + + err.emit(); + } + } + self.tcx.types.re_empty + }, + } + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + match ty.sty { + ty::TyClosure(def_id, substs) => { + // I am a horrible monster and I pray for death. When + // we encounter a closure here, it is always a closure + // from within the function that we are currently + // type-checking -- one that is now being encapsulated + // in an existential abstract type. Ideally, we would + // go through the types/lifetimes that it references + // and treat them just like we would any other type, + // which means we would error out if we find any + // reference to a type/region that is not in the + // "reverse map". // - // The case of closure is a somewhat subtle (read: hacky) - // consideration. The problem is that our closure types - // currently include all the lifetime parameters declared - // on the enclosing function, even if they are unused by - // the closure itself. We can't readily filter them out, + // **However,** in the case of closures, there is a + // somewhat subtle (read: hacky) consideration. The + // problem is that our closure types currently include + // all the lifetime parameters declared on the + // enclosing function, even if they are unused by the + // closure itself. We can't readily filter them out, // so here we replace those values with `'empty`. This // can't really make a difference to the rest of the - // compiler; those regions are ignored for the outlives - // relation, and hence don't affect trait selection or - // auto traits, and they are erased during trans. - self.tcx.types.re_empty + // compiler; those regions are ignored for the + // outlives relation, and hence don't affect trait + // selection or auto traits, and they are erased + // during trans. + + let generics = self.tcx.generics_of(def_id); + let parent_len = generics.parent_count(); + let substs = self.tcx.mk_substs(substs.substs.iter().enumerate().map( + |(index, &kind)| { + if index < parent_len { + // Accommodate missing regions in the parent kinds... + self.fold_kind_mapping_missing_regions_to_empty(kind) + } else { + // ...but not elsewhere. + self.fold_kind_normally(kind) + } + }, + )); + + self.tcx.mk_closure(def_id, ty::ClosureSubsts { substs }) } + + _ => ty.super_fold_with(self), } } } @@ -573,12 +691,13 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> { return self.fold_anon_ty(ty, def_id, substs); } - debug!("instantiate_anon_types_in_map: \ - encountered anon with wrong parent \ - def_id={:?} \ - anon_parent_def_id={:?}", - def_id, - anon_parent_def_id); + debug!( + "instantiate_anon_types_in_map: \ + encountered anon with wrong parent \ + def_id={:?} \ + anon_parent_def_id={:?}", + def_id, anon_parent_def_id + ); } } @@ -598,8 +717,7 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> { debug!( "instantiate_anon_types: TyAnon(def_id={:?}, substs={:?})", - def_id, - substs + def_id, substs ); // Use the same type variable if the exact same TyAnon appears more @@ -608,8 +726,10 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> { return anon_defn.concrete_ty; } let span = tcx.def_span(def_id); - let ty_var = infcx.next_ty_var(ty::UniverseIndex::ROOT, - TypeVariableOrigin::TypeInference(span)); + let ty_var = infcx.next_ty_var( + ty::UniverseIndex::ROOT, + TypeVariableOrigin::TypeInference(span), + ); let predicates_of = tcx.predicates_of(def_id); let bounds = predicates_of.instantiate(tcx, substs); diff --git a/src/test/ui/impl-trait/region-escape-via-bound-contravariant.rs b/src/test/ui/impl-trait/region-escape-via-bound-contravariant.rs new file mode 100644 index 00000000000..416bdae5178 --- /dev/null +++ b/src/test/ui/impl-trait/region-escape-via-bound-contravariant.rs @@ -0,0 +1,35 @@ +// Copyright 2016 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 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// In contrast to `region-escape-via-bound-invariant`, in this case we +// *can* return a value of type `&'x u32`, even though `'x` does not +// appear in the bounds. This is because `&` is contravariant, and so +// we are *actually* returning a `&'y u32`. +// +// See https://github.com/rust-lang/rust/issues/46541 for more details. + +// run-pass + +#![allow(dead_code)] +#![feature(conservative_impl_trait)] +#![feature(in_band_lifetimes)] +#![feature(nll)] + +trait Trait<'a> { } + +impl Trait<'b> for &'a u32 { } + +fn foo(x: &'x u32) -> impl Trait<'y> +where 'x: 'y +{ + x +} + +fn main() { } diff --git a/src/test/ui/impl-trait/region-escape-via-bound.rs b/src/test/ui/impl-trait/region-escape-via-bound.rs new file mode 100644 index 00000000000..38c18ce6104 --- /dev/null +++ b/src/test/ui/impl-trait/region-escape-via-bound.rs @@ -0,0 +1,34 @@ +// Copyright 2016 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 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// Test that we do not allow the region `'x` to escape in the impl +// trait **even though** `'y` escapes, which outlives `'x`. +// +// See https://github.com/rust-lang/rust/issues/46541 for more details. + +#![allow(dead_code)] +#![feature(conservative_impl_trait)] +#![feature(in_band_lifetimes)] +#![feature(nll)] + +use std::cell::Cell; + +trait Trait<'a> { } + +impl Trait<'b> for Cell<&'a u32> { } + +fn foo(x: Cell<&'x u32>) -> impl Trait<'y> + //~^ ERROR hidden type for `impl Trait` captures lifetime that does not appear in bounds [E0909] +where 'x: 'y +{ + x +} + +fn main() { } diff --git a/src/test/ui/impl-trait/region-escape-via-bound.stderr b/src/test/ui/impl-trait/region-escape-via-bound.stderr new file mode 100644 index 00000000000..5659fee9bed --- /dev/null +++ b/src/test/ui/impl-trait/region-escape-via-bound.stderr @@ -0,0 +1,20 @@ +error[E0909]: hidden type for `impl Trait` captures lifetime that does not appear in bounds + --> $DIR/region-escape-via-bound.rs:27:29 + | +LL | fn foo(x: Cell<&'x u32>) -> impl Trait<'y> + | ^^^^^^^^^^^^^^ + | +note: hidden type `std::cell::Cell<&'x u32>` captures the lifetime 'x as defined on the function body at 27:1 + --> $DIR/region-escape-via-bound.rs:27:1 + | +LL | / fn foo(x: Cell<&'x u32>) -> impl Trait<'y> +LL | | //~^ ERROR hidden type for `impl Trait` captures lifetime that does not appear in bounds [E0909] +LL | | where 'x: 'y +LL | | { +LL | | x +LL | | } + | |_^ + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0909`. |