From d15997750211421cc1367faba574b3d9b2dc2432 Mon Sep 17 00:00:00 2001 From: Niko Matsakis Date: Fri, 7 Aug 2015 10:33:18 -0400 Subject: [PATCH] Generalize the outlives rule for projections to handle the new cases; also, generalize VerifyBounds to include OR conditions. --- src/librustc/middle/infer/mod.rs | 8 +- .../middle/infer/region_inference/mod.rs | 193 ++++++-- src/librustc_typeck/check/regionck.rs | 441 +++++++++++++++--- 3 files changed, 541 insertions(+), 101 deletions(-) diff --git a/src/librustc/middle/infer/mod.rs b/src/librustc/middle/infer/mod.rs index da3749979b60..61c166e11d28 100644 --- a/src/librustc/middle/infer/mod.rs +++ b/src/librustc/middle/infer/mod.rs @@ -17,7 +17,7 @@ pub use self::TypeOrigin::*; pub use self::ValuePairs::*; pub use middle::ty::IntVarValue; pub use self::freshen::TypeFreshener; -pub use self::region_inference::GenericKind; +pub use self::region_inference::{GenericKind, VerifyBound}; use middle::free_region::FreeRegionMap; use middle::mem_categorization as mc; @@ -1416,13 +1416,13 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> { origin: SubregionOrigin<'tcx>, kind: GenericKind<'tcx>, a: ty::Region, - bs: Vec) { + bound: VerifyBound) { debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, - bs); + bound); - self.region_vars.verify_generic_bound(origin, kind, a, bs); + self.region_vars.verify_generic_bound(origin, kind, a, bound); } pub fn can_equate<'b,T>(&'b self, a: &T, b: &T) -> UnitResult<'tcx> diff --git a/src/librustc/middle/infer/region_inference/mod.rs b/src/librustc/middle/infer/region_inference/mod.rs index 4b62c7beab00..e8f8dbfbb0e6 100644 --- a/src/librustc/middle/infer/region_inference/mod.rs +++ b/src/librustc/middle/infer/region_inference/mod.rs @@ -64,15 +64,41 @@ pub enum Verify<'tcx> { // outlive `RS`. Therefore verify that `R <= RS[i]` for some // `i`. Inference variables may be involved (but this verification // step doesn't influence inference). - VerifyGenericBound(GenericKind<'tcx>, SubregionOrigin<'tcx>, Region, Vec), + VerifyGenericBound(GenericKind<'tcx>, SubregionOrigin<'tcx>, Region, VerifyBound), } -#[derive(Clone, PartialEq, Eq)] +#[derive(Copy, Clone, PartialEq, Eq)] pub enum GenericKind<'tcx> { Param(ty::ParamTy), Projection(ty::ProjectionTy<'tcx>), } +// When we introduce a verification step, we wish to test that a +// particular region (let's call it `'min`) meets some bound. +// The bound is described the by the following grammar: +#[derive(Debug)] +pub enum VerifyBound { + // B = exists {R} --> some 'r in {R} must outlive 'min + // + // Put another way, the subject value is known to outlive all + // regions in {R}, so if any of those outlives 'min, then the + // bound is met. + AnyRegion(Vec), + + // B = forall {R} --> all 'r in {R} must outlive 'min + // + // Put another way, the subject value is known to outlive some + // region in {R}, so if all of those outlives 'min, then the bound + // is met. + AllRegions(Vec), + + // B = exists {B} --> 'min must meet some bound b in {B} + AnyBound(Vec), + + // B = forall {B} --> 'min must meet all bounds b in {B} + AllBounds(Vec), +} + #[derive(Copy, Clone, PartialEq, Eq, Hash)] pub struct TwoRegions { a: Region, @@ -102,12 +128,11 @@ pub enum RegionResolutionError<'tcx> { /// `o` requires that `a <= b`, but this does not hold ConcreteFailure(SubregionOrigin<'tcx>, Region, Region), - /// `GenericBoundFailure(p, s, a, bs) + /// `GenericBoundFailure(p, s, a) /// /// The parameter/associated-type `p` must be known to outlive the lifetime - /// `a`, but it is only known to outlive `bs` (and none of the - /// regions in `bs` outlive `a`). - GenericBoundFailure(SubregionOrigin<'tcx>, GenericKind<'tcx>, Region, Vec), + /// `a` (but none of the known bounds are sufficient). + GenericBoundFailure(SubregionOrigin<'tcx>, GenericKind<'tcx>, Region), /// `SubSupConflict(v, sub_origin, sub_r, sup_origin, sup_r)`: /// @@ -408,6 +433,14 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> { debug!("RegionVarBindings: add_verify({:?})", verify); + // skip no-op cases known to be satisfied + match verify { + VerifyGenericBound(_, _, _, VerifyBound::AllBounds(ref bs)) if bs.len() == 0 => { + return; + } + _ => { } + } + let mut verifys = self.verifys.borrow_mut(); let index = verifys.len(); verifys.push(verify); @@ -497,8 +530,8 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> { origin: SubregionOrigin<'tcx>, kind: GenericKind<'tcx>, sub: Region, - sups: Vec) { - self.add_verify(VerifyGenericBound(kind, origin, sub, sups)); + bound: VerifyBound) { + self.add_verify(VerifyGenericBound(kind, origin, sub, bound)); } pub fn lub_regions(&self, @@ -663,12 +696,11 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> { &mut result_set, r, a, b); } - VerifyGenericBound(_, _, a, ref bs) => { - for &b in bs { - consider_adding_bidirectional_edges( - &mut result_set, r, - a, b); - } + VerifyGenericBound(_, _, a, ref bound) => { + bound.for_each_region(&mut |b| { + consider_adding_bidirectional_edges(&mut result_set, r, + a, b) + }); } } } @@ -1258,26 +1290,22 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> { continue; } - debug!("ConcreteFailure: !(sub <= sup): sub={:?}, sup={:?}", - sub, - sup); + debug!("region inference error at {:?}: {:?} <= {:?} is not true", + origin, sub, sup); + errors.push(ConcreteFailure((*origin).clone(), sub, sup)); } - VerifyGenericBound(ref kind, ref origin, sub, ref sups) => { + VerifyGenericBound(ref kind, ref origin, sub, ref bound) => { let sub = normalize(values, sub); - if sups.iter() - .map(|&sup| normalize(values, sup)) - .any(|sup| free_regions.is_subregion_of(self.tcx, sub, sup)) - { + if bound.is_met(self.tcx, free_regions, values, sub) { continue; } - let sups = sups.iter().map(|&sup| normalize(values, sup)) - .collect(); - errors.push( - GenericBoundFailure( - (*origin).clone(), kind.clone(), sub, sups)); + debug!("region inference error at {:?}: verifying {:?} <= {:?}", + origin, sub, bound); + + errors.push(GenericBoundFailure((*origin).clone(), kind.clone(), sub)); } } } @@ -1438,10 +1466,12 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> { if !free_regions.is_subregion_of(self.tcx, lower_bound.region, upper_bound.region) { - debug!("pushing SubSupConflict sub: {:?} sup: {:?}", - lower_bound.region, upper_bound.region); + let origin = (*self.var_origins.borrow())[node_idx.index as usize].clone(); + debug!("region inference error at {:?} for {:?}: \ + SubSupConflict sub: {:?} sup: {:?}", + origin, node_idx, lower_bound.region, upper_bound.region); errors.push(SubSupConflict( - (*self.var_origins.borrow())[node_idx.index as usize].clone(), + origin, lower_bound.origin.clone(), lower_bound.region, upper_bound.origin.clone(), @@ -1484,16 +1514,20 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> { match self.glb_concrete_regions(free_regions, upper_bound_1.region, upper_bound_2.region) { - Ok(_) => {} - Err(_) => { - errors.push(SupSupConflict( - (*self.var_origins.borrow())[node_idx.index as usize].clone(), - upper_bound_1.origin.clone(), - upper_bound_1.region, - upper_bound_2.origin.clone(), - upper_bound_2.region)); - return; - } + Ok(_) => {} + Err(_) => { + let origin = (*self.var_origins.borrow())[node_idx.index as usize].clone(); + debug!("region inference error at {:?} for {:?}: \ + SupSupConflict sub: {:?} sup: {:?}", + origin, node_idx, upper_bound_1.region, upper_bound_2.region); + errors.push(SupSupConflict( + origin, + upper_bound_1.origin.clone(), + upper_bound_1.region, + upper_bound_2.origin.clone(), + upper_bound_2.region)); + return; + } } } } @@ -1676,3 +1710,82 @@ impl<'tcx> GenericKind<'tcx> { } } } + +impl VerifyBound { + fn for_each_region(&self, f: &mut FnMut(ty::Region)) { + match self { + &VerifyBound::AnyRegion(ref rs) | + &VerifyBound::AllRegions(ref rs) => + for &r in rs { f(r); }, + + &VerifyBound::AnyBound(ref bs) | + &VerifyBound::AllBounds(ref bs) => + for b in bs { b.for_each_region(f); }, + } + } + + pub fn must_hold(&self) -> bool { + match self { + &VerifyBound::AnyRegion(ref bs) => bs.contains(&ty::ReStatic), + &VerifyBound::AllRegions(ref bs) => bs.is_empty(), + &VerifyBound::AnyBound(ref bs) => bs.iter().any(|b| b.must_hold()), + &VerifyBound::AllBounds(ref bs) => bs.iter().all(|b| b.must_hold()), + } + } + + pub fn cannot_hold(&self) -> bool { + match self { + &VerifyBound::AnyRegion(ref bs) => bs.is_empty(), + &VerifyBound::AllRegions(ref bs) => bs.contains(&ty::ReEmpty), + &VerifyBound::AnyBound(ref bs) => bs.iter().all(|b| b.cannot_hold()), + &VerifyBound::AllBounds(ref bs) => bs.iter().any(|b| b.cannot_hold()), + } + } + + pub fn or(self, vb: VerifyBound) -> VerifyBound { + if self.must_hold() || vb.cannot_hold() { + self + } else if self.cannot_hold() || vb.must_hold() { + vb + } else { + VerifyBound::AnyBound(vec![self, vb]) + } + } + + pub fn and(self, vb: VerifyBound) -> VerifyBound { + if self.must_hold() && vb.must_hold() { + self + } else if self.cannot_hold() && vb.cannot_hold() { + self + } else { + VerifyBound::AllBounds(vec![self, vb]) + } + } + + fn is_met<'tcx>(&self, + tcx: &ty::ctxt<'tcx>, + free_regions: &FreeRegionMap, + var_values: &Vec, + min: ty::Region) + -> bool { + match self { + &VerifyBound::AnyRegion(ref rs) => + rs.iter() + .map(|&r| normalize(var_values, r)) + .any(|r| free_regions.is_subregion_of(tcx, min, r)), + + &VerifyBound::AllRegions(ref rs) => + rs.iter() + .map(|&r| normalize(var_values, r)) + .all(|r| free_regions.is_subregion_of(tcx, min, r)), + + &VerifyBound::AnyBound(ref bs) => + bs.iter() + .any(|b| b.is_met(tcx, free_regions, var_values, min)), + + &VerifyBound::AllBounds(ref bs) => + bs.iter() + .all(|b| b.is_met(tcx, free_regions, var_values, min)), + } + } +} diff --git a/src/librustc_typeck/check/regionck.rs b/src/librustc_typeck/check/regionck.rs index 925ea1169012..1fed29ec68e7 100644 --- a/src/librustc_typeck/check/regionck.rs +++ b/src/librustc_typeck/check/regionck.rs @@ -568,7 +568,29 @@ fn visit_expr(rcx: &mut Rcx, expr: &ast::Expr) { type_must_outlive(rcx, infer::ExprTypeIsNotInScope(expr_ty, expr.span), expr_ty, ty::ReScope(CodeExtent::from_node_id(expr.id))); - let has_method_map = rcx.fcx.infcx().is_method_call(expr.id); + let method_call = MethodCall::expr(expr.id); + let opt_method_callee = rcx.fcx.inh.tables.borrow().method_map.get(&method_call).cloned(); + let has_method_map = opt_method_callee.is_some(); + + // the region corresponding to this expression + let expr_region = ty::ReScope(CodeExtent::from_node_id(expr.id)); + + // If we are calling a method (either explicitly or via an + // overloaded operator), check that all of the types provided as + // arguments for its type parameters are well-formed, and all the regions + // provided as arguments outlive the call. + if let Some(callee) = opt_method_callee { + let origin = match expr.node { + ast::ExprMethodCall(..) => + infer::ParameterOrigin::MethodCall, + ast::ExprUnary(op, _) if op == ast::UnDeref => + infer::ParameterOrigin::OverloadedDeref, + _ => + infer::ParameterOrigin::OverloadedOperator + }; + + substs_wf_in_scope(rcx, origin, &callee.substs, expr.span, expr_region); + } // Check any autoderefs or autorefs that appear. let adjustment = rcx.fcx.inh.tables.borrow().adjustments.get(&expr.id).map(|a| a.clone()); @@ -639,6 +661,13 @@ fn visit_expr(rcx: &mut Rcx, expr: &ast::Expr) { } match expr.node { + ast::ExprPath(..) => { + rcx.fcx.opt_node_ty_substs(expr.id, |item_substs| { + let origin = infer::ParameterOrigin::Path; + substs_wf_in_scope(rcx, origin, &item_substs.substs, expr.span, expr_region); + }); + } + ast::ExprCall(ref callee, ref args) => { if has_method_map { constrain_call(rcx, expr, Some(&**callee), @@ -949,6 +978,9 @@ fn constrain_autoderefs<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>, debug!("constrain_autoderefs: #{} is overloaded, method={:?}", i, method); + let origin = infer::ParameterOrigin::OverloadedDeref; + substs_wf_in_scope(rcx, origin, method.substs, deref_expr.span, r_deref_expr); + // Treat overloaded autoderefs as if an AutoRef adjustment // was applied on the base type, as that is always the case. let fn_sig = method.ty.fn_sig(); @@ -1250,6 +1282,9 @@ fn link_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, let mut borrow_cmt = borrow_cmt; let mut borrow_kind = borrow_kind; + let origin = infer::DataBorrowed(borrow_cmt.ty, span); + type_must_outlive(rcx, origin, borrow_cmt.ty, *borrow_region); + loop { debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})", borrow_region, @@ -1449,74 +1484,371 @@ fn link_reborrowed_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, } } -/// Ensures that all borrowed data reachable via `ty` outlives `region`. -pub fn type_must_outlive<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>, - origin: infer::SubregionOrigin<'tcx>, - ty: Ty<'tcx>, - region: ty::Region) +/// Checks that the values provided for type/region arguments in a given +/// expression are well-formed and in-scope. +pub fn substs_wf_in_scope<'a,'tcx>(rcx: &mut Rcx<'a,'tcx>, + origin: infer::ParameterOrigin, + substs: &Substs<'tcx>, + expr_span: Span, + expr_region: ty::Region) { + debug!("substs_wf_in_scope(substs={:?}, \ + expr_region={:?}, \ + origin={:?}, \ + expr_span={:?})", + substs, expr_region, origin, expr_span); + + let origin = infer::ParameterInScope(origin, expr_span); + + for ®ion in substs.regions() { + rcx.fcx.mk_subr(origin.clone(), expr_region, region); + } + + for &ty in &substs.types { + let ty = rcx.resolve_type(ty); + type_must_outlive(rcx, origin.clone(), ty, expr_region); + } +} + +/// Ensures that type is well-formed in `region`, which implies (among +/// other things) that all borrowed data reachable via `ty` outlives +/// `region`. +pub fn type_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, + origin: infer::SubregionOrigin<'tcx>, + ty: Ty<'tcx>, + region: ty::Region) { + let ty = rcx.resolve_type(ty); + debug!("type_must_outlive(ty={:?}, region={:?})", ty, region); - let implications = implicator::implications(rcx.fcx.infcx(), rcx.body_id, - ty, region, origin.span()); - for implication in implications { - debug!("implication: {:?}", implication); - match implication { - implicator::Implication::RegionSubRegion(None, r_a, r_b) => { - rcx.fcx.mk_subr(origin.clone(), r_a, r_b); + assert!(!ty.has_escaping_regions()); + + let components = outlives::components(rcx.infcx(), ty); + components_must_outlive(rcx, origin, components, region); +} + +fn components_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, + origin: infer::SubregionOrigin<'tcx>, + components: Vec>, + region: ty::Region) +{ + for component in components { + let origin = origin.clone(); + match component { + outlives::Component::Region(region1) => { + rcx.fcx.mk_subr(origin, region, region1); } - implicator::Implication::RegionSubRegion(Some(ty), r_a, r_b) => { - let o1 = infer::ReferenceOutlivesReferent(ty, origin.span()); - rcx.fcx.mk_subr(o1, r_a, r_b); + outlives::Component::Param(param_ty) => { + param_ty_must_outlive(rcx, origin, region, param_ty); } - implicator::Implication::RegionSubGeneric(None, r_a, ref generic_b) => { - generic_must_outlive(rcx, origin.clone(), r_a, generic_b); + outlives::Component::Projection(projection_ty) => { + projection_must_outlive(rcx, origin, region, projection_ty); } - implicator::Implication::RegionSubGeneric(Some(ty), r_a, ref generic_b) => { - let o1 = infer::ReferenceOutlivesReferent(ty, origin.span()); - generic_must_outlive(rcx, o1, r_a, generic_b); + outlives::Component::EscapingProjection(subcomponents) => { + components_must_outlive(rcx, origin, subcomponents, region); } - implicator::Implication::Predicate(def_id, predicate) => { - let cause = traits::ObligationCause::new(origin.span(), - rcx.body_id, - traits::ItemObligation(def_id)); - let obligation = traits::Obligation::new(cause, predicate); - rcx.fcx.register_predicate(obligation); + outlives::Component::UnresolvedInferenceVariable(_) => { + // ignore this, we presume it will yield an error + // later, since if a type variable is not resolved by + // this point it never will be + } + outlives::Component::RFC1214(subcomponents) => { + let suborigin = infer::RFC1214Subregion(Rc::new(origin)); + components_must_outlive(rcx, suborigin, subcomponents, region); } } } } -fn generic_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, - origin: infer::SubregionOrigin<'tcx>, - region: ty::Region, - generic: &GenericKind<'tcx>) { - let param_env = &rcx.fcx.inh.infcx.parameter_environment; +/// Checks that all data reachable via `ty` *strictly* outlives `scope`. +/// This is used by dropck. +/// +/// CAUTION: It is mostly but not entirely equivalent to `T:'parent` +/// where `'parent` is the parent of `scope`. The difference is subtle +/// and has to do with trait objects, primarily. In particular, if you +/// have `Foo<'y>+'z`, then we require that `'z:'parent` but not +/// `'y:'parent` (same with lifetimes appearing in fn arguments). This +/// is because there is no actual reference to the trait object that +/// outlives `scope`, so we don't need to require that the type could +/// be named outside `scope`. Because trait objects are always +/// considered "suspicious" by dropck, if we don't add this special +/// case, you wind up with some kind of annoying and odd limitations +/// that crop up +/// `src/test/compile-fail/regions-early-bound-trait-param.rs`. +/// Basically there we have `&'foo Trait<'foo>+'bar`, and thus forcing +/// `'foo` to outlive `'parent` also forces the borrow to outlive +/// `'parent`, which is longer than should be necessary. The existence +/// of this "the same but different" predicate is somewhat bothersome +/// and questionable. +pub fn type_strictly_outlives<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>, + origin: infer::SubregionOrigin<'tcx>, + ty: Ty<'tcx>, + scope: CodeExtent) +{ + debug!("type_strictly_outlives(ty={:?}, scope={:?})", + ty, scope); - debug!("param_must_outlive(region={:?}, generic={:?})", - region, - generic); + let span = origin.span(); - // To start, collect bounds from user: - let mut param_bounds = rcx.tcx().required_region_bounds(generic.to_ty(rcx.tcx()), - param_env.caller_bounds.clone()); + let parent_region = + match rcx.tcx().region_maps.opt_encl_scope(scope) { + Some(parent_scope) => ty::ReScope(parent_scope), + None => rcx.tcx().sess.span_bug( + span, &format!("no enclosing scope found for scope: {:?}", + scope)), + }; - // In the case of a projection T::Foo, we may be able to extract bounds from the trait def: - match *generic { - GenericKind::Param(..) => { } - GenericKind::Projection(ref projection_ty) => { - param_bounds.push_all( - &projection_bounds(rcx, origin.span(), projection_ty)); + type_must_outlive(rcx, origin, ty, parent_region); +} + +fn param_ty_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, + origin: infer::SubregionOrigin<'tcx>, + region: ty::Region, + param_ty: ty::ParamTy) { + debug!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})", + region, param_ty, origin); + + let verify_bound = param_bound(rcx, param_ty); + let generic = GenericKind::Param(param_ty); + rcx.fcx.infcx().verify_generic_bound(origin, generic, region, verify_bound); +} + +fn projection_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, + origin: infer::SubregionOrigin<'tcx>, + region: ty::Region, + projection_ty: ty::ProjectionTy<'tcx>) { + debug!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})", + region, projection_ty, origin); + + // This is a particularly thorny situation for inference, and for + // now we don't have a complete solution, we just do the best we + // can. The problem is that there are multiple ways for `>::Foo: 'r` to be satisfied: + // + // 1. If `Pi: 'r` forall i, it is satisfied. + // 2. If there is a suitable where-clause, it can be satisfied. + // 3. The trait declaration may declare `'static` bounds on `Foo` as well. + // + // The fact that there are so many options here makes this thorny. + // In the case of parameter relations like `T: 'r`, it's somewhat + // simpler, because checking such a relation does not affect + // inference. This is true because the region bounds we can + // derive for `T` never involve region variables -- they are + // always free regions. The only place a region variable can come + // is on the RHS, and in that case, the smaller the region, the + // better. This means that our current inference, which always + // infers the smallest region it can, can just be used, and we'll + // know what the smallest value for `'r` is when it's done. We can + // then compare that to the regions in the LHS, which are already + // as big as possible, and we're all done. + // + // Projections can in fact be this simple as well. In particular, + // if the parameters `P0..Pn` do not involve any region variables, + // that's the same situation. + // + // Where things get thorny is when region variables are involved, + // because in that case relating `Pi: 'r` may influence the + // inference process, since it could cause `'r` to be inferred to + // a larger value. But the problem is that if we add that as a + // constraint into our dataflow graph, we've essentially committed + // to using option 1 (above) to show that `>::Foo: 'r` is satisfied, and it may be that + // Option 1 does not apply, but Option 2 or 3 does. But we can't + // know that now. + // + // For now we choose to accept this. It's a conservative choice, + // so we can move to a more sophisticated inference model later. + // And it's sometimes possible to workaround by introducing + // explicit type parameters or type annotations. But it ain't + // great! + + let declared_bounds = projection_declared_bounds(rcx, origin.span(), projection_ty); + + debug!("projection_must_outlive: declared_bounds={:?}", + declared_bounds); + + // If we know that the projection outlives 'static, then we're done here. + if declared_bounds.contains(&ty::ReStatic) { + return; + } + + // Determine whether any of regions that appear in the projection + // were declared as bounds by the user. This is typically a situation + // like this: + // + // trait Foo<'a> { + // type Bar: 'a; + // } + // + // where we are checking `>: '_#1r`. In such a + // case, if we use the conservative rule, we will check that + // BOTH of the following hold: + // + // T: _#1r + // _#0r: _#1r + // + // This is overkill, since the declared bounds tell us that the + // the latter is sufficient. + let intersection_bounds: Vec<_> = + projection_ty.trait_ref.substs.regions() + .iter() + .filter(|r| declared_bounds.contains(r)) + .collect(); + let intersection_bounds_needs_infer = + intersection_bounds.iter() + .any(|r| r.needs_infer()); + if intersection_bounds_needs_infer { + // If the upper bound(s) (`_#0r` in the above example) are + // region variables, then introduce edges into the inference + // graph, because we need to ensure that `_#0r` is inferred to + // something big enough. But if the upper bound has no + // inference, then fallback (below) to the verify path, where + // we just check after the fact that it was big enough. This + // is more flexible, because it only requires that there + // exists SOME intersection bound that is big enough, whereas + // this path requires that ALL intersection bounds be big + // enough. + debug!("projection_must_outlive: intersection_bounds={:?}", + intersection_bounds); + for &r in intersection_bounds { + rcx.fcx.mk_subr(origin.clone(), region, r); + } + return; + } + + // If there are no intersection bounds, but there are still + // inference variables involves, then fallback to the most + // conservative rule, where we require all components of the + // projection outlive the bound. + if + intersection_bounds.is_empty() && ( + projection_ty.trait_ref.substs.types.iter().any(|t| t.needs_infer()) || + projection_ty.trait_ref.substs.regions().iter().any(|r| r.needs_infer())) + { + debug!("projection_must_outlive: fallback to rule #1"); + + for &component_ty in &projection_ty.trait_ref.substs.types { + type_must_outlive(rcx, origin.clone(), component_ty, region); + } + + for &r in projection_ty.trait_ref.substs.regions() { + rcx.fcx.mk_subr(origin.clone(), region, r); + } + + return; + } + + // Inform region inference that this generic must be properly + // bounded. + let verify_bound = projection_bound(rcx, origin.span(), declared_bounds, projection_ty); + let generic = GenericKind::Projection(projection_ty); + rcx.fcx.infcx().verify_generic_bound(origin, generic.clone(), region, verify_bound); +} + +fn type_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, span: Span, ty: Ty<'tcx>) -> VerifyBound { + match ty.sty { + ty::TyParam(p) => { + param_bound(rcx, p) + } + ty::TyProjection(data) => { + let declared_bounds = projection_declared_bounds(rcx, span, data); + projection_bound(rcx, span, declared_bounds, data) + } + _ => { + recursive_type_bound(rcx, span, ty) } } +} + +fn param_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, param_ty: ty::ParamTy) -> VerifyBound { + let param_env = &rcx.infcx().parameter_environment; + + debug!("param_bound(param_ty={:?})", + param_ty); + + let mut param_bounds = declared_generic_bounds_from_env(rcx, GenericKind::Param(param_ty)); // Add in the default bound of fn body that applies to all in // scope type parameters: param_bounds.push(param_env.implicit_region_bound); - // Finally, collect regions we scraped from the well-formedness + VerifyBound::AnyRegion(param_bounds) +} + +fn projection_declared_bounds<'a, 'tcx>(rcx: &Rcx<'a,'tcx>, + span: Span, + projection_ty: ty::ProjectionTy<'tcx>) + -> Vec +{ + // First assemble bounds from where clauses and traits. + + let mut declared_bounds = + declared_generic_bounds_from_env(rcx, GenericKind::Projection(projection_ty)); + + declared_bounds.push_all( + &declared_projection_bounds_from_trait(rcx, span, projection_ty)); + + declared_bounds +} + +fn projection_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, + span: Span, + declared_bounds: Vec, + projection_ty: ty::ProjectionTy<'tcx>) + -> VerifyBound { + debug!("projection_bound(declared_bounds={:?}, projection_ty={:?})", + declared_bounds, projection_ty); + + // see the extensive comment in projection_must_outlive + + // this routine is not invoked in this case + assert!( + !projection_ty.trait_ref.substs.types.iter().any(|t| t.needs_infer()) && + !projection_ty.trait_ref.substs.regions().iter().any(|r| r.needs_infer())); + + let ty = rcx.tcx().mk_projection(projection_ty.trait_ref, projection_ty.item_name); + let recursive_bound = recursive_type_bound(rcx, span, ty); + + VerifyBound::AnyRegion(declared_bounds).or(recursive_bound) +} + +fn recursive_type_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, + span: Span, + ty: Ty<'tcx>) + -> VerifyBound { + let mut bounds = vec![]; + + for subty in ty.walk_shallow() { + bounds.push(type_bound(rcx, span, subty)); + } + + let mut regions = ty.regions(); + regions.retain(|r| !r.is_bound()); // ignore late-bound regions + bounds.push(VerifyBound::AllRegions(ty.regions())); + + // remove bounds that must hold, since they are not interesting + bounds.retain(|b| !b.must_hold()); + + if bounds.len() == 1 { + bounds.pop().unwrap() + } else { + VerifyBound::AllBounds(bounds) + } +} + +fn declared_generic_bounds_from_env<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, + generic: GenericKind<'tcx>) + -> Vec +{ + let param_env = &rcx.infcx().parameter_environment; + + // To start, collect bounds from user: + let mut param_bounds = rcx.tcx().required_region_bounds(generic.to_ty(rcx.tcx()), + param_env.caller_bounds.clone()); + + // Next, collect regions we scraped from the well-formedness // constraints in the fn signature. To do that, we walk the list // of known relations from the fn ctxt. // @@ -1527,27 +1859,22 @@ fn generic_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, // The problem is that the type of `x` is `&'a A`. To be // well-formed, then, A must be lower-generic by `'a`, but we // don't know that this holds from first principles. - for &(ref r, ref p) in &rcx.region_bound_pairs { + for &(r, p) in &rcx.region_bound_pairs { debug!("generic={:?} p={:?}", generic, p); if generic == p { - param_bounds.push(*r); + param_bounds.push(r); } } - // Inform region inference that this generic must be properly - // bounded. - rcx.fcx.infcx().verify_generic_bound(origin, - generic.clone(), - region, - param_bounds); + param_bounds } -fn projection_bounds<'a,'tcx>(rcx: &Rcx<'a, 'tcx>, - span: Span, - projection_ty: &ty::ProjectionTy<'tcx>) - -> Vec +fn declared_projection_bounds_from_trait<'a,'tcx>(rcx: &Rcx<'a, 'tcx>, + span: Span, + projection_ty: ty::ProjectionTy<'tcx>) + -> Vec { let fcx = rcx.fcx; let tcx = fcx.tcx();