diff options
| -rw-r--r-- | src/librustc/infer/combine.rs | 10 | ||||
| -rw-r--r-- | src/librustc/infer/equate.rs | 3 | ||||
| -rw-r--r-- | src/librustc/traits/select.rs | 35 | ||||
| -rw-r--r-- | src/librustdoc/clean/blanket_impl.rs | 11 | ||||
| -rw-r--r-- | src/test/rustdoc/issue-55001.rs | 31 |
5 files changed, 87 insertions, 3 deletions
diff --git a/src/librustc/infer/combine.rs b/src/librustc/infer/combine.rs index de8f57ee796..0ee03bc4c6e 100644 --- a/src/librustc/infer/combine.rs +++ b/src/librustc/infer/combine.rs @@ -251,6 +251,7 @@ impl<'infcx, 'gcx, 'tcx> CombineFields<'infcx, 'gcx, 'tcx> { dir: RelationDir) -> RelateResult<'tcx, Generalization<'tcx>> { + debug!("generalize(ty={:?}, for_vid={:?}, dir={:?}", ty, for_vid, dir); // Determine the ambient variance within which `ty` appears. // The surrounding equation is: // @@ -273,8 +274,15 @@ impl<'infcx, 'gcx, 'tcx> CombineFields<'infcx, 'gcx, 'tcx> { root_ty: ty, }; - let ty = generalize.relate(&ty, &ty)?; + let ty = match generalize.relate(&ty, &ty) { + Ok(ty) => ty, + Err(e) => { + debug!("generalize: failure {:?}", e); + return Err(e); + } + }; let needs_wf = generalize.needs_wf; + debug!("generalize: success {{ {:?}, {:?} }}", ty, needs_wf); Ok(Generalization { ty, needs_wf }) } } diff --git a/src/librustc/infer/equate.rs b/src/librustc/infer/equate.rs index 854960492c9..c7b5ddb8341 100644 --- a/src/librustc/infer/equate.rs +++ b/src/librustc/infer/equate.rs @@ -74,6 +74,9 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx> let infcx = self.fields.infcx; let a = infcx.type_variables.borrow_mut().replace_if_possible(a); let b = infcx.type_variables.borrow_mut().replace_if_possible(b); + + debug!("{}.tys: replacements ({:?}, {:?})", self.tag(), a, b); + match (&a.sty, &b.sty) { (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => { infcx.type_variables.borrow_mut().equate(a_id, b_id); diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs index 49f37179354..2ea16823cc6 100644 --- a/src/librustc/traits/select.rs +++ b/src/librustc/traits/select.rs @@ -1522,6 +1522,33 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> { .map(|v| v.get(tcx)) } + /// Determines whether can we safely cache the result + /// of selecting an obligation. This is almost always 'true', + /// except when dealing with certain ParamCandidates. + /// + /// Ordinarily, a ParamCandidate will contain no inference variables, + /// since it was usually produced directly from a DefId. However, + /// certain cases (currently only librustdoc's blanket impl finder), + /// a ParamEnv may be explicitly constructed with inference types. + /// When this is the case, we do *not* want to cache the resulting selection + /// candidate. This is due to the fact that it might not always be possible + /// to equate the obligation's trait ref and the candidate's trait ref, + /// if more constraints end up getting added to an inference variable. + /// + /// Because of this, we always want to re-run the full selection + /// process for our obligation the next time we see it, since + /// we might end up picking a different SelectionCandidate (or none at all) + fn can_cache_candidate(&self, + result: &SelectionResult<'tcx, SelectionCandidate<'tcx>> + ) -> bool { + match result { + Ok(Some(SelectionCandidate::ParamCandidate(trait_ref))) => { + !trait_ref.skip_binder().input_types().any(|t| t.walk().any(|t_| t_.is_ty_infer())) + }, + _ => true + } + } + fn insert_candidate_cache( &mut self, param_env: ty::ParamEnv<'tcx>, @@ -1531,6 +1558,14 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> { ) { let tcx = self.tcx(); let trait_ref = cache_fresh_trait_pred.skip_binder().trait_ref; + + if !self.can_cache_candidate(&candidate) { + debug!("insert_candidate_cache(trait_ref={:?}, candidate={:?} -\ + candidate is not cacheable", trait_ref, candidate); + return; + + } + if self.can_use_global_caches(param_env) { if let Err(Overflow) = candidate { // Don't cache overflow globally; we only produce this diff --git a/src/librustdoc/clean/blanket_impl.rs b/src/librustdoc/clean/blanket_impl.rs index b6bc8d603d5..57c7e2afd62 100644 --- a/src/librustdoc/clean/blanket_impl.rs +++ b/src/librustdoc/clean/blanket_impl.rs @@ -50,6 +50,7 @@ impl<'a, 'tcx, 'rcx, 'cstore> BlanketImplFinder <'a, 'tcx, 'rcx, 'cstore> { name: Option<String>, ) -> Vec<Item> where F: Fn(DefId) -> Def { + debug!("get_blanket_impls(def_id={:?}, ...)", def_id); let mut impls = Vec::new(); if self.cx .tcx @@ -78,6 +79,8 @@ impl<'a, 'tcx, 'rcx, 'cstore> BlanketImplFinder <'a, 'tcx, 'rcx, 'cstore> { } self.cx.tcx.for_each_relevant_impl(trait_def_id, ty, |impl_def_id| { self.cx.tcx.infer_ctxt().enter(|infcx| { + debug!("get_blanet_impls: Considering impl for trait '{:?}' {:?}", + trait_def_id, impl_def_id); let t_generics = infcx.tcx.generics_of(impl_def_id); let trait_ref = infcx.tcx.impl_trait_ref(impl_def_id) .expect("Cannot get impl trait"); @@ -104,8 +107,8 @@ impl<'a, 'tcx, 'rcx, 'cstore> BlanketImplFinder <'a, 'tcx, 'rcx, 'cstore> { drop(obligations); debug!( - "invoking predicate_may_hold: {:?}", - trait_ref, + "invoking predicate_may_hold: param_env={:?}, trait_ref={:?}, ty={:?}", + param_env, trait_ref, ty ); let may_apply = match infcx.evaluate_obligation( &traits::Obligation::new( @@ -117,6 +120,10 @@ impl<'a, 'tcx, 'rcx, 'cstore> BlanketImplFinder <'a, 'tcx, 'rcx, 'cstore> { Ok(eval_result) => eval_result.may_apply(), Err(traits::OverflowError) => true, // overflow doesn't mean yes *or* no }; + debug!("get_blanket_impls: found applicable impl: {}\ + for trait_ref={:?}, ty={:?}", + may_apply, trait_ref, ty); + if !may_apply { return } diff --git a/src/test/rustdoc/issue-55001.rs b/src/test/rustdoc/issue-55001.rs new file mode 100644 index 00000000000..f6c7f9a3d08 --- /dev/null +++ b/src/test/rustdoc/issue-55001.rs @@ -0,0 +1,31 @@ +// Regression test for issue #55001. Previously, we would incorrectly +// cache certain trait selection results when checking for blanket impls, +// resulting in an ICE when we tried to confirm the cached ParamCandidate +// against an obligation. + +pub struct DefaultAllocator; +pub struct Standard; +pub struct Inner; + +pub trait Rand {} + +pub trait Distribution<T> {} +pub trait Allocator<N> {} + +impl<T> Rand for T where Standard: Distribution<T> {} + +impl<A> Distribution<Point<A>> for Standard +where +DefaultAllocator: Allocator<A>, +Standard: Distribution<A> {} + +impl Distribution<Inner> for Standard {} + + +pub struct Point<N> +where DefaultAllocator: Allocator<N> +{ + field: N +} + +fn main() {} |