Generalize the outlives rule for projections to handle the new cases;
also, generalize VerifyBounds to include OR conditions.
This commit is contained in:
Niko Matsakis
parent
75ee8f1562
commit
d159977502
@ -17,7 +17,7 @@ pub use self::TypeOrigin::*;
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pub use self::ValuePairs::*;
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pub use middle::ty::IntVarValue;
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pub use self::freshen::TypeFreshener;
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pub use self::region_inference::GenericKind;
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pub use self::region_inference::{GenericKind, VerifyBound};
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use middle::free_region::FreeRegionMap;
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use middle::mem_categorization as mc;
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@ -1416,13 +1416,13 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
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origin: SubregionOrigin<'tcx>,
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kind: GenericKind<'tcx>,
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a: ty::Region,
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bs: Vec<ty::Region>) {
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bound: VerifyBound) {
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debug!("verify_generic_bound({:?}, {:?} <: {:?})",
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kind,
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a,
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bs);
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bound);
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self.region_vars.verify_generic_bound(origin, kind, a, bs);
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self.region_vars.verify_generic_bound(origin, kind, a, bound);
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}
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pub fn can_equate<'b,T>(&'b self, a: &T, b: &T) -> UnitResult<'tcx>
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@ -64,15 +64,41 @@ pub enum Verify<'tcx> {
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// outlive `RS`. Therefore verify that `R <= RS[i]` for some
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// `i`. Inference variables may be involved (but this verification
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// step doesn't influence inference).
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VerifyGenericBound(GenericKind<'tcx>, SubregionOrigin<'tcx>, Region, Vec<Region>),
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VerifyGenericBound(GenericKind<'tcx>, SubregionOrigin<'tcx>, Region, VerifyBound),
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}
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#[derive(Clone, PartialEq, Eq)]
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#[derive(Copy, Clone, PartialEq, Eq)]
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pub enum GenericKind<'tcx> {
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Param(ty::ParamTy),
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Projection(ty::ProjectionTy<'tcx>),
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}
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// When we introduce a verification step, we wish to test that a
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// particular region (let's call it `'min`) meets some bound.
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// The bound is described the by the following grammar:
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#[derive(Debug)]
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pub enum VerifyBound {
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// B = exists {R} --> some 'r in {R} must outlive 'min
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//
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// Put another way, the subject value is known to outlive all
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// regions in {R}, so if any of those outlives 'min, then the
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// bound is met.
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AnyRegion(Vec<Region>),
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// B = forall {R} --> all 'r in {R} must outlive 'min
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//
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// Put another way, the subject value is known to outlive some
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// region in {R}, so if all of those outlives 'min, then the bound
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// is met.
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AllRegions(Vec<Region>),
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// B = exists {B} --> 'min must meet some bound b in {B}
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AnyBound(Vec<VerifyBound>),
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// B = forall {B} --> 'min must meet all bounds b in {B}
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AllBounds(Vec<VerifyBound>),
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}
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#[derive(Copy, Clone, PartialEq, Eq, Hash)]
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pub struct TwoRegions {
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a: Region,
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@ -102,12 +128,11 @@ pub enum RegionResolutionError<'tcx> {
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/// `o` requires that `a <= b`, but this does not hold
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ConcreteFailure(SubregionOrigin<'tcx>, Region, Region),
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/// `GenericBoundFailure(p, s, a, bs)
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/// `GenericBoundFailure(p, s, a)
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///
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/// The parameter/associated-type `p` must be known to outlive the lifetime
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/// `a`, but it is only known to outlive `bs` (and none of the
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/// regions in `bs` outlive `a`).
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GenericBoundFailure(SubregionOrigin<'tcx>, GenericKind<'tcx>, Region, Vec<Region>),
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/// `a` (but none of the known bounds are sufficient).
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GenericBoundFailure(SubregionOrigin<'tcx>, GenericKind<'tcx>, Region),
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/// `SubSupConflict(v, sub_origin, sub_r, sup_origin, sup_r)`:
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///
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@ -408,6 +433,14 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
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debug!("RegionVarBindings: add_verify({:?})",
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verify);
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// skip no-op cases known to be satisfied
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match verify {
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VerifyGenericBound(_, _, _, VerifyBound::AllBounds(ref bs)) if bs.len() == 0 => {
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return;
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}
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_ => { }
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}
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let mut verifys = self.verifys.borrow_mut();
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let index = verifys.len();
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verifys.push(verify);
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@ -497,8 +530,8 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
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origin: SubregionOrigin<'tcx>,
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kind: GenericKind<'tcx>,
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sub: Region,
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sups: Vec<Region>) {
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self.add_verify(VerifyGenericBound(kind, origin, sub, sups));
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bound: VerifyBound) {
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self.add_verify(VerifyGenericBound(kind, origin, sub, bound));
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}
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pub fn lub_regions(&self,
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@ -663,12 +696,11 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
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&mut result_set, r,
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a, b);
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}
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VerifyGenericBound(_, _, a, ref bs) => {
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for &b in bs {
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consider_adding_bidirectional_edges(
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&mut result_set, r,
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a, b);
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}
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VerifyGenericBound(_, _, a, ref bound) => {
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bound.for_each_region(&mut |b| {
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consider_adding_bidirectional_edges(&mut result_set, r,
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a, b)
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});
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}
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}
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}
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@ -1258,26 +1290,22 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
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continue;
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}
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debug!("ConcreteFailure: !(sub <= sup): sub={:?}, sup={:?}",
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sub,
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sup);
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debug!("region inference error at {:?}: {:?} <= {:?} is not true",
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origin, sub, sup);
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errors.push(ConcreteFailure((*origin).clone(), sub, sup));
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}
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VerifyGenericBound(ref kind, ref origin, sub, ref sups) => {
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VerifyGenericBound(ref kind, ref origin, sub, ref bound) => {
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let sub = normalize(values, sub);
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if sups.iter()
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.map(|&sup| normalize(values, sup))
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.any(|sup| free_regions.is_subregion_of(self.tcx, sub, sup))
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{
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if bound.is_met(self.tcx, free_regions, values, sub) {
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continue;
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}
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let sups = sups.iter().map(|&sup| normalize(values, sup))
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.collect();
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errors.push(
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GenericBoundFailure(
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(*origin).clone(), kind.clone(), sub, sups));
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debug!("region inference error at {:?}: verifying {:?} <= {:?}",
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origin, sub, bound);
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errors.push(GenericBoundFailure((*origin).clone(), kind.clone(), sub));
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}
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}
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}
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@ -1438,10 +1466,12 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
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if !free_regions.is_subregion_of(self.tcx,
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lower_bound.region,
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upper_bound.region) {
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debug!("pushing SubSupConflict sub: {:?} sup: {:?}",
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lower_bound.region, upper_bound.region);
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let origin = (*self.var_origins.borrow())[node_idx.index as usize].clone();
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debug!("region inference error at {:?} for {:?}: \
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SubSupConflict sub: {:?} sup: {:?}",
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origin, node_idx, lower_bound.region, upper_bound.region);
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errors.push(SubSupConflict(
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(*self.var_origins.borrow())[node_idx.index as usize].clone(),
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origin,
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lower_bound.origin.clone(),
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lower_bound.region,
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upper_bound.origin.clone(),
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@ -1484,16 +1514,20 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
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match self.glb_concrete_regions(free_regions,
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upper_bound_1.region,
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upper_bound_2.region) {
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Ok(_) => {}
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Err(_) => {
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errors.push(SupSupConflict(
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(*self.var_origins.borrow())[node_idx.index as usize].clone(),
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upper_bound_1.origin.clone(),
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upper_bound_1.region,
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upper_bound_2.origin.clone(),
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upper_bound_2.region));
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return;
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}
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Ok(_) => {}
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Err(_) => {
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let origin = (*self.var_origins.borrow())[node_idx.index as usize].clone();
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debug!("region inference error at {:?} for {:?}: \
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SupSupConflict sub: {:?} sup: {:?}",
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origin, node_idx, upper_bound_1.region, upper_bound_2.region);
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errors.push(SupSupConflict(
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origin,
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upper_bound_1.origin.clone(),
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upper_bound_1.region,
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upper_bound_2.origin.clone(),
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upper_bound_2.region));
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return;
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}
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}
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}
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}
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@ -1676,3 +1710,82 @@ impl<'tcx> GenericKind<'tcx> {
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}
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}
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}
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impl VerifyBound {
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fn for_each_region(&self, f: &mut FnMut(ty::Region)) {
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match self {
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&VerifyBound::AnyRegion(ref rs) |
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&VerifyBound::AllRegions(ref rs) =>
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for &r in rs { f(r); },
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&VerifyBound::AnyBound(ref bs) |
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&VerifyBound::AllBounds(ref bs) =>
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for b in bs { b.for_each_region(f); },
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}
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}
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pub fn must_hold(&self) -> bool {
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match self {
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&VerifyBound::AnyRegion(ref bs) => bs.contains(&ty::ReStatic),
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&VerifyBound::AllRegions(ref bs) => bs.is_empty(),
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&VerifyBound::AnyBound(ref bs) => bs.iter().any(|b| b.must_hold()),
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&VerifyBound::AllBounds(ref bs) => bs.iter().all(|b| b.must_hold()),
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}
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}
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pub fn cannot_hold(&self) -> bool {
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match self {
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&VerifyBound::AnyRegion(ref bs) => bs.is_empty(),
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&VerifyBound::AllRegions(ref bs) => bs.contains(&ty::ReEmpty),
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&VerifyBound::AnyBound(ref bs) => bs.iter().all(|b| b.cannot_hold()),
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&VerifyBound::AllBounds(ref bs) => bs.iter().any(|b| b.cannot_hold()),
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}
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}
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pub fn or(self, vb: VerifyBound) -> VerifyBound {
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if self.must_hold() || vb.cannot_hold() {
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self
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} else if self.cannot_hold() || vb.must_hold() {
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vb
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} else {
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VerifyBound::AnyBound(vec![self, vb])
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}
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}
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pub fn and(self, vb: VerifyBound) -> VerifyBound {
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if self.must_hold() && vb.must_hold() {
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self
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} else if self.cannot_hold() && vb.cannot_hold() {
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self
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} else {
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VerifyBound::AllBounds(vec![self, vb])
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}
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}
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fn is_met<'tcx>(&self,
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tcx: &ty::ctxt<'tcx>,
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free_regions: &FreeRegionMap,
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var_values: &Vec<VarValue>,
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min: ty::Region)
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-> bool {
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match self {
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&VerifyBound::AnyRegion(ref rs) =>
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rs.iter()
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.map(|&r| normalize(var_values, r))
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.any(|r| free_regions.is_subregion_of(tcx, min, r)),
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&VerifyBound::AllRegions(ref rs) =>
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rs.iter()
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.map(|&r| normalize(var_values, r))
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.all(|r| free_regions.is_subregion_of(tcx, min, r)),
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&VerifyBound::AnyBound(ref bs) =>
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bs.iter()
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.any(|b| b.is_met(tcx, free_regions, var_values, min)),
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&VerifyBound::AllBounds(ref bs) =>
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bs.iter()
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.all(|b| b.is_met(tcx, free_regions, var_values, min)),
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}
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}
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}
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@ -568,7 +568,29 @@ fn visit_expr(rcx: &mut Rcx, expr: &ast::Expr) {
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type_must_outlive(rcx, infer::ExprTypeIsNotInScope(expr_ty, expr.span),
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expr_ty, ty::ReScope(CodeExtent::from_node_id(expr.id)));
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let has_method_map = rcx.fcx.infcx().is_method_call(expr.id);
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let method_call = MethodCall::expr(expr.id);
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let opt_method_callee = rcx.fcx.inh.tables.borrow().method_map.get(&method_call).cloned();
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let has_method_map = opt_method_callee.is_some();
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// the region corresponding to this expression
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let expr_region = ty::ReScope(CodeExtent::from_node_id(expr.id));
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// If we are calling a method (either explicitly or via an
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// overloaded operator), check that all of the types provided as
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// arguments for its type parameters are well-formed, and all the regions
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// provided as arguments outlive the call.
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if let Some(callee) = opt_method_callee {
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let origin = match expr.node {
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ast::ExprMethodCall(..) =>
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infer::ParameterOrigin::MethodCall,
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ast::ExprUnary(op, _) if op == ast::UnDeref =>
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infer::ParameterOrigin::OverloadedDeref,
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_ =>
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infer::ParameterOrigin::OverloadedOperator
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};
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substs_wf_in_scope(rcx, origin, &callee.substs, expr.span, expr_region);
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}
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// Check any autoderefs or autorefs that appear.
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let adjustment = rcx.fcx.inh.tables.borrow().adjustments.get(&expr.id).map(|a| a.clone());
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@ -639,6 +661,13 @@ fn visit_expr(rcx: &mut Rcx, expr: &ast::Expr) {
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}
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match expr.node {
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ast::ExprPath(..) => {
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rcx.fcx.opt_node_ty_substs(expr.id, |item_substs| {
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let origin = infer::ParameterOrigin::Path;
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substs_wf_in_scope(rcx, origin, &item_substs.substs, expr.span, expr_region);
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});
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}
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ast::ExprCall(ref callee, ref args) => {
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if has_method_map {
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constrain_call(rcx, expr, Some(&**callee),
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@ -949,6 +978,9 @@ fn constrain_autoderefs<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
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debug!("constrain_autoderefs: #{} is overloaded, method={:?}",
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i, method);
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let origin = infer::ParameterOrigin::OverloadedDeref;
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substs_wf_in_scope(rcx, origin, method.substs, deref_expr.span, r_deref_expr);
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// Treat overloaded autoderefs as if an AutoRef adjustment
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// was applied on the base type, as that is always the case.
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let fn_sig = method.ty.fn_sig();
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@ -1250,6 +1282,9 @@ fn link_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
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let mut borrow_cmt = borrow_cmt;
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let mut borrow_kind = borrow_kind;
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let origin = infer::DataBorrowed(borrow_cmt.ty, span);
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type_must_outlive(rcx, origin, borrow_cmt.ty, *borrow_region);
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loop {
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debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
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borrow_region,
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@ -1449,74 +1484,371 @@ fn link_reborrowed_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
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}
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}
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/// Ensures that all borrowed data reachable via `ty` outlives `region`.
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pub fn type_must_outlive<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
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origin: infer::SubregionOrigin<'tcx>,
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ty: Ty<'tcx>,
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region: ty::Region)
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/// Checks that the values provided for type/region arguments in a given
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/// expression are well-formed and in-scope.
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pub fn substs_wf_in_scope<'a,'tcx>(rcx: &mut Rcx<'a,'tcx>,
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origin: infer::ParameterOrigin,
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substs: &Substs<'tcx>,
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expr_span: Span,
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expr_region: ty::Region) {
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debug!("substs_wf_in_scope(substs={:?}, \
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expr_region={:?}, \
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origin={:?}, \
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expr_span={:?})",
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substs, expr_region, origin, expr_span);
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let origin = infer::ParameterInScope(origin, expr_span);
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for ®ion in substs.regions() {
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rcx.fcx.mk_subr(origin.clone(), expr_region, region);
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}
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for &ty in &substs.types {
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let ty = rcx.resolve_type(ty);
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type_must_outlive(rcx, origin.clone(), ty, expr_region);
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}
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}
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/// Ensures that type is well-formed in `region`, which implies (among
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/// other things) that all borrowed data reachable via `ty` outlives
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/// `region`.
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pub fn type_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
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origin: infer::SubregionOrigin<'tcx>,
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ty: Ty<'tcx>,
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region: ty::Region)
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{
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let ty = rcx.resolve_type(ty);
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debug!("type_must_outlive(ty={:?}, region={:?})",
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ty,
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region);
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let implications = implicator::implications(rcx.fcx.infcx(), rcx.body_id,
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ty, region, origin.span());
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for implication in implications {
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debug!("implication: {:?}", implication);
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match implication {
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implicator::Implication::RegionSubRegion(None, r_a, r_b) => {
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rcx.fcx.mk_subr(origin.clone(), r_a, r_b);
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assert!(!ty.has_escaping_regions());
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let components = outlives::components(rcx.infcx(), ty);
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components_must_outlive(rcx, origin, components, region);
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}
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|
||||
fn components_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
|
||||
origin: infer::SubregionOrigin<'tcx>,
|
||||
components: Vec<outlives::Component<'tcx>>,
|
||||
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 `<P0 as
|
||||
// TraitRef<P1..Pn>>::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 `<P0 as
|
||||
// Trait<P1..Pn>>::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 `<T as Foo<'_#0r>>: '_#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<ty::Region>
|
||||
{
|
||||
// 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<ty::Region>,
|
||||
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<ty::Region>
|
||||
{
|
||||
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<ty::Region>
|
||||
fn declared_projection_bounds_from_trait<'a,'tcx>(rcx: &Rcx<'a, 'tcx>,
|
||||
span: Span,
|
||||
projection_ty: ty::ProjectionTy<'tcx>)
|
||||
-> Vec<ty::Region>
|
||||
{
|
||||
let fcx = rcx.fcx;
|
||||
let tcx = fcx.tcx();
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user