diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/auto_trait.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/auto_trait.rs | 234 |
1 files changed, 98 insertions, 136 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/auto_trait.rs b/compiler/rustc_trait_selection/src/traits/auto_trait.rs index bcdfa4f12..ed34ab95a 100644 --- a/compiler/rustc_trait_selection/src/traits/auto_trait.rs +++ b/compiler/rustc_trait_selection/src/traits/auto_trait.rs @@ -10,7 +10,7 @@ use crate::traits::project::ProjectAndUnifyResult; use rustc_middle::mir::interpret::ErrorHandled; use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable}; use rustc_middle::ty::visit::TypeVisitable; -use rustc_middle::ty::{Region, RegionVid}; +use rustc_middle::ty::{PolyTraitRef, Region, RegionVid}; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; @@ -66,13 +66,13 @@ impl<'tcx> AutoTraitFinder<'tcx> { /// struct Foo<T> { data: Box<T> } /// ``` /// - /// then this might return that Foo<T>: Send if T: Send (encoded in the AutoTraitResult type). - /// The analysis attempts to account for custom impls as well as other complex cases. This - /// result is intended for use by rustdoc and other such consumers. + /// then this might return that `Foo<T>: Send` if `T: Send` (encoded in the AutoTraitResult + /// type). The analysis attempts to account for custom impls as well as other complex cases. + /// This result is intended for use by rustdoc and other such consumers. /// /// (Note that due to the coinductive nature of Send, the full and correct result is actually /// quite simple to generate. That is, when a type has no custom impl, it is Send iff its field - /// types are all Send. So, in our example, we might have that Foo<T>: Send if Box<T>: Send. + /// types are all Send. So, in our example, we might have that `Foo<T>: Send` if `Box<T>: Send`. /// But this is often not the best way to present to the user.) /// /// Warning: The API should be considered highly unstable, and it may be refactored or removed @@ -90,143 +90,105 @@ impl<'tcx> AutoTraitFinder<'tcx> { let trait_pred = ty::Binder::dummy(trait_ref); - let bail_out = tcx.infer_ctxt().enter(|infcx| { - let mut selcx = SelectionContext::new(&infcx); - let result = selcx.select(&Obligation::new( - ObligationCause::dummy(), - orig_env, - trait_pred.to_poly_trait_predicate(), - )); - - match result { - Ok(Some(ImplSource::UserDefined(_))) => { - debug!( - "find_auto_trait_generics({:?}): \ - manual impl found, bailing out", - trait_ref - ); - return true; - } - _ => {} + let infcx = tcx.infer_ctxt().build(); + let mut selcx = SelectionContext::new(&infcx); + for f in [ + PolyTraitRef::to_poly_trait_predicate, + PolyTraitRef::to_poly_trait_predicate_negative_polarity, + ] { + let result = + selcx.select(&Obligation::new(ObligationCause::dummy(), orig_env, f(&trait_pred))); + if let Ok(Some(ImplSource::UserDefined(_))) = result { + debug!( + "find_auto_trait_generics({:?}): \ + manual impl found, bailing out", + trait_ref + ); + // If an explicit impl exists, it always takes priority over an auto impl + return AutoTraitResult::ExplicitImpl; } - - let result = selcx.select(&Obligation::new( - ObligationCause::dummy(), - orig_env, - trait_pred.to_poly_trait_predicate_negative_polarity(), - )); - - match result { - Ok(Some(ImplSource::UserDefined(_))) => { - debug!( - "find_auto_trait_generics({:?}): \ - manual impl found, bailing out", - trait_ref - ); - true - } - _ => false, - } - }); - - // If an explicit impl exists, it always takes priority over an auto impl - if bail_out { - return AutoTraitResult::ExplicitImpl; } - tcx.infer_ctxt().enter(|infcx| { - let mut fresh_preds = FxHashSet::default(); + let infcx = tcx.infer_ctxt().build(); + let mut fresh_preds = FxHashSet::default(); + + // Due to the way projections are handled by SelectionContext, we need to run + // evaluate_predicates twice: once on the original param env, and once on the result of + // the first evaluate_predicates call. + // + // The problem is this: most of rustc, including SelectionContext and traits::project, + // are designed to work with a concrete usage of a type (e.g., Vec<u8> + // fn<T>() { Vec<T> }. This information will generally never change - given + // the 'T' in fn<T>() { ... }, we'll never know anything else about 'T'. + // If we're unable to prove that 'T' implements a particular trait, we're done - + // there's nothing left to do but error out. + // + // However, synthesizing an auto trait impl works differently. Here, we start out with + // a set of initial conditions - the ParamEnv of the struct/enum/union we're dealing + // with - and progressively discover the conditions we need to fulfill for it to + // implement a certain auto trait. This ends up breaking two assumptions made by trait + // selection and projection: + // + // * We can always cache the result of a particular trait selection for the lifetime of + // an InfCtxt + // * Given a projection bound such as '<T as SomeTrait>::SomeItem = K', if 'T: + // SomeTrait' doesn't hold, then we don't need to care about the 'SomeItem = K' + // + // We fix the first assumption by manually clearing out all of the InferCtxt's caches + // in between calls to SelectionContext.select. This allows us to keep all of the + // intermediate types we create bound to the 'tcx lifetime, rather than needing to lift + // them between calls. + // + // We fix the second assumption by reprocessing the result of our first call to + // evaluate_predicates. Using the example of '<T as SomeTrait>::SomeItem = K', our first + // pass will pick up 'T: SomeTrait', but not 'SomeItem = K'. On our second pass, + // traits::project will see that 'T: SomeTrait' is in our ParamEnv, allowing + // SelectionContext to return it back to us. + + let Some((new_env, user_env)) = self.evaluate_predicates( + &infcx, + trait_did, + ty, + orig_env, + orig_env, + &mut fresh_preds, + false, + ) else { + return AutoTraitResult::NegativeImpl; + }; + + let (full_env, full_user_env) = self + .evaluate_predicates(&infcx, trait_did, ty, new_env, user_env, &mut fresh_preds, true) + .unwrap_or_else(|| { + panic!("Failed to fully process: {:?} {:?} {:?}", ty, trait_did, orig_env) + }); - // Due to the way projections are handled by SelectionContext, we need to run - // evaluate_predicates twice: once on the original param env, and once on the result of - // the first evaluate_predicates call. - // - // The problem is this: most of rustc, including SelectionContext and traits::project, - // are designed to work with a concrete usage of a type (e.g., Vec<u8> - // fn<T>() { Vec<T> }. This information will generally never change - given - // the 'T' in fn<T>() { ... }, we'll never know anything else about 'T'. - // If we're unable to prove that 'T' implements a particular trait, we're done - - // there's nothing left to do but error out. - // - // However, synthesizing an auto trait impl works differently. Here, we start out with - // a set of initial conditions - the ParamEnv of the struct/enum/union we're dealing - // with - and progressively discover the conditions we need to fulfill for it to - // implement a certain auto trait. This ends up breaking two assumptions made by trait - // selection and projection: - // - // * We can always cache the result of a particular trait selection for the lifetime of - // an InfCtxt - // * Given a projection bound such as '<T as SomeTrait>::SomeItem = K', if 'T: - // SomeTrait' doesn't hold, then we don't need to care about the 'SomeItem = K' - // - // We fix the first assumption by manually clearing out all of the InferCtxt's caches - // in between calls to SelectionContext.select. This allows us to keep all of the - // intermediate types we create bound to the 'tcx lifetime, rather than needing to lift - // them between calls. - // - // We fix the second assumption by reprocessing the result of our first call to - // evaluate_predicates. Using the example of '<T as SomeTrait>::SomeItem = K', our first - // pass will pick up 'T: SomeTrait', but not 'SomeItem = K'. On our second pass, - // traits::project will see that 'T: SomeTrait' is in our ParamEnv, allowing - // SelectionContext to return it back to us. - - let Some((new_env, user_env)) = self.evaluate_predicates( - &infcx, - trait_did, - ty, - orig_env, - orig_env, - &mut fresh_preds, - false, - ) else { - return AutoTraitResult::NegativeImpl; - }; - - let (full_env, full_user_env) = self - .evaluate_predicates( - &infcx, - trait_did, - ty, - new_env, - user_env, - &mut fresh_preds, - true, - ) - .unwrap_or_else(|| { - panic!("Failed to fully process: {:?} {:?} {:?}", ty, trait_did, orig_env) - }); - - debug!( - "find_auto_trait_generics({:?}): fulfilling \ - with {:?}", - trait_ref, full_env - ); - infcx.clear_caches(); - - // At this point, we already have all of the bounds we need. FulfillmentContext is used - // to store all of the necessary region/lifetime bounds in the InferContext, as well as - // an additional sanity check. - let errors = - super::fully_solve_bound(&infcx, ObligationCause::dummy(), full_env, ty, trait_did); - if !errors.is_empty() { - panic!("Unable to fulfill trait {:?} for '{:?}': {:?}", trait_did, ty, errors); - } + debug!( + "find_auto_trait_generics({:?}): fulfilling \ + with {:?}", + trait_ref, full_env + ); + infcx.clear_caches(); + + // At this point, we already have all of the bounds we need. FulfillmentContext is used + // to store all of the necessary region/lifetime bounds in the InferContext, as well as + // an additional sanity check. + let errors = + super::fully_solve_bound(&infcx, ObligationCause::dummy(), full_env, ty, trait_did); + if !errors.is_empty() { + panic!("Unable to fulfill trait {:?} for '{:?}': {:?}", trait_did, ty, errors); + } - infcx.process_registered_region_obligations(&Default::default(), full_env); + infcx.process_registered_region_obligations(&Default::default(), full_env); - let region_data = infcx - .inner - .borrow_mut() - .unwrap_region_constraints() - .region_constraint_data() - .clone(); + let region_data = + infcx.inner.borrow_mut().unwrap_region_constraints().region_constraint_data().clone(); - let vid_to_region = self.map_vid_to_region(®ion_data); + let vid_to_region = self.map_vid_to_region(®ion_data); - let info = AutoTraitInfo { full_user_env, region_data, vid_to_region }; + let info = AutoTraitInfo { full_user_env, region_data, vid_to_region }; - AutoTraitResult::PositiveImpl(auto_trait_callback(info)) - }) + AutoTraitResult::PositiveImpl(auto_trait_callback(info)) } } @@ -272,7 +234,7 @@ impl<'tcx> AutoTraitFinder<'tcx> { /// user. fn evaluate_predicates( &self, - infcx: &InferCtxt<'_, 'tcx>, + infcx: &InferCtxt<'tcx>, trait_did: DefId, ty: Ty<'tcx>, param_env: ty::ParamEnv<'tcx>, @@ -834,7 +796,7 @@ impl<'tcx> AutoTraitFinder<'tcx> { let reported = tcx.sess.emit_err(UnableToConstructConstantValue { span: tcx.def_span(def_id), - unevaluated: unevaluated.expand(), + unevaluated: unevaluated, }); Err(ErrorHandled::Reported(reported)) } @@ -877,7 +839,7 @@ impl<'tcx> AutoTraitFinder<'tcx> { pub fn clean_pred( &self, - infcx: &InferCtxt<'_, 'tcx>, + infcx: &InferCtxt<'tcx>, p: ty::Predicate<'tcx>, ) -> ty::Predicate<'tcx> { infcx.freshen(p) |