Fix lifetime elision region accounting

This merges accumulate_regions_in_type with ty_fold::collect_regions.
Fixes #26638

Author: Ariel Ben-Yehuda

src/librustc/middle/infer/higher_ranked/mod.rs

@@ -359,7 +359,7 @@ fn fold_regions_in<'tcx, T, F>(tcx: &ty::ctxt<'tcx>,
     where T: TypeFoldable<'tcx>,
           F: FnMut(ty::Region, ty::DebruijnIndex) -> ty::Region,
 {
-    unbound_value.fold_with(&mut ty_fold::RegionFolder::new(tcx, &mut |region, current_depth| {
+    ty_fold::fold_regions(tcx, unbound_value, &mut false, |region, current_depth| {
         // we should only be encountering "escaping" late-bound regions here,
         // because the ones at the current level should have been replaced
         // with fresh variables
@@ -369,7 +369,7 @@ fn fold_regions_in<'tcx, T, F>(tcx: &ty::ctxt<'tcx>,
         });
 
         fldr(region, ty::DebruijnIndex::new(current_depth))
-    }))
+    })
 }
 
 impl<'a,'tcx> InferCtxtExt for InferCtxt<'a,'tcx> {
@@ -437,11 +437,10 @@ impl<'a,'tcx> InferCtxtExt for InferCtxt<'a,'tcx> {
         let escaping_types =
             self.type_variables.borrow().types_escaping_snapshot(&snapshot.type_snapshot);
 
-        let escaping_region_vars: FnvHashSet<_> =
-            escaping_types
-            .iter()
-            .flat_map(|&t| ty_fold::collect_regions(self.tcx, &t))
-            .collect();
+        let mut escaping_region_vars = FnvHashSet();
+        for ty in &escaping_types {
+            ty_fold::collect_regions(self.tcx, ty, &mut escaping_region_vars);
+        }
 
         region_vars.retain(|&region_vid| {
             let r = ty::ReInfer(ty::ReVar(region_vid));
@@ -649,7 +648,7 @@ pub fn plug_leaks<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
     // binder is that we encountered in `value`. The caller is
     // responsible for ensuring that (a) `value` contains at least one
     // binder and (b) that binder is the one we want to use.
-    let result = ty_fold::fold_regions(infcx.tcx, &value, |r, current_depth| {
+    let result = ty_fold::fold_regions(infcx.tcx, &value, &mut false, |r, current_depth| {
         match inv_skol_map.get(&r) {
             None => r,
             Some(br) => {

src/librustc/middle/ty.rs

@@ -1713,6 +1713,16 @@ impl Region {
             _ => false,
         }
     }
+
+    /// Returns the depth of `self` from the (1-based) binding level `depth`
+    pub fn from_depth(&self, depth: u32) -> Region {
+        match *self {
+            ty::ReLateBound(debruijn, r) => ty::ReLateBound(DebruijnIndex {
+                depth: debruijn.depth - (depth - 1)
+            }, r),
+            r => r
+        }
+    }
 }
 
 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash,
@@ -6783,60 +6793,6 @@ pub enum ExplicitSelfCategory {
     ByBoxExplicitSelfCategory,
 }
 
-impl<'tcx> TyS<'tcx> {
-    /// Pushes all the lifetimes in the given type onto the given list. A
-    /// "lifetime in a type" is a lifetime specified by a reference or a lifetime
-    /// in a list of type substitutions. This does *not* traverse into nominal
-    /// types, nor does it resolve fictitious types.
-    pub fn accumulate_lifetimes_in_type(&self, accumulator: &mut Vec<ty::Region>) {
-        for ty in self.walk() {
-            match ty.sty {
-                TyRef(region, _) => {
-                    accumulator.push(*region)
-                }
-                TyTrait(ref t) => {
-                    accumulator.push_all(t.principal.0.substs.regions().as_slice());
-                }
-                TyEnum(_, substs) |
-                TyStruct(_, substs) => {
-                    accum_substs(accumulator, substs);
-                }
-                TyClosure(_, substs) => {
-                    accum_substs(accumulator, substs);
-                }
-                TyBool |
-                TyChar |
-                TyInt(_) |
-                TyUint(_) |
-                TyFloat(_) |
-                TyBox(_) |
-                TyStr |
-                TyArray(_, _) |
-                TySlice(_) |
-                TyRawPtr(_) |
-                TyBareFn(..) |
-                TyTuple(_) |
-                TyProjection(_) |
-                TyParam(_) |
-                TyInfer(_) |
-                TyError => {
-                }
-            }
-        }
-
-        fn accum_substs(accumulator: &mut Vec<Region>, substs: &Substs) {
-            match substs.regions {
-                subst::ErasedRegions => {}
-                subst::NonerasedRegions(ref regions) => {
-                    for region in regions {
-                        accumulator.push(*region)
-                    }
-                }
-            }
-        }
-    }
-}
-
 /// A free variable referred to in a function.
 #[derive(Copy, Clone, RustcEncodable, RustcDecodable)]
 pub struct Freevar {
@@ -6917,7 +6873,8 @@ impl<'tcx> ctxt<'tcx> {
         where T: TypeFoldable<'tcx>
     {
         let bound0_value = bound2_value.skip_binder().skip_binder();
-        let value = ty_fold::fold_regions(self, bound0_value, |region, current_depth| {
+        let value = ty_fold::fold_regions(self, bound0_value, &mut false,
+                                          |region, current_depth| {
             match region {
                 ty::ReLateBound(debruijn, br) if debruijn.depth >= current_depth => {
                     // should be true if no escaping regions from bound2_value

src/librustc/middle/ty_fold.rs

@@ -44,7 +44,7 @@ use std::rc::Rc;
 use syntax::abi;
 use syntax::ast;
 use syntax::owned_slice::OwnedSlice;
-use util::nodemap::FnvHashMap;
+use util::nodemap::{FnvHashMap, FnvHashSet};
 
 ///////////////////////////////////////////////////////////////////////////
 // Two generic traits
@@ -783,38 +783,51 @@ impl<'a, 'tcx, F> TypeFolder<'tcx> for BottomUpFolder<'a, 'tcx, F> where
 
 pub struct RegionFolder<'a, 'tcx: 'a> {
     tcx: &'a ty::ctxt<'tcx>,
+    skipped_regions: &'a mut bool,
     current_depth: u32,
     fld_r: &'a mut (FnMut(ty::Region, u32) -> ty::Region + 'a),
 }
 
 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
-    pub fn new<F>(tcx: &'a ty::ctxt<'tcx>, fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
+    pub fn new<F>(tcx: &'a ty::ctxt<'tcx>,
+                  skipped_regions: &'a mut bool,
+                  fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
         where F : FnMut(ty::Region, u32) -> ty::Region
     {
         RegionFolder {
             tcx: tcx,
+            skipped_regions: skipped_regions,
             current_depth: 1,
             fld_r: fld_r,
         }
     }
 }
 
-pub fn collect_regions<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> Vec<ty::Region>
+/// Collects the free and escaping regions in `value` into `region_set`. Returns
+/// whether any late-bound regions were skipped
+pub fn collect_regions<'tcx,T>(tcx: &ty::ctxt<'tcx>,
+                               value: &T,
+                               region_set: &mut FnvHashSet<ty::Region>) -> bool
     where T : TypeFoldable<'tcx>
 {
-    let mut vec = Vec::new();
-    fold_regions(tcx, value, |r, _| { vec.push(r); r });
-    vec
+    let mut have_bound_regions = false;
+    fold_regions(tcx, value, &mut have_bound_regions,
+                 |r, d| { region_set.insert(r.from_depth(d)); r });
+    have_bound_regions
 }
 
+/// Folds the escaping and free regions in `value` using `f`, and
+/// sets `skipped_regions` to true if any late-bound region was found
+/// and skipped.
 pub fn fold_regions<'tcx,T,F>(tcx: &ty::ctxt<'tcx>,
                               value: &T,
+                              skipped_regions: &mut bool,
                               mut f: F)
                               -> T
     where F : FnMut(ty::Region, u32) -> ty::Region,
           T : TypeFoldable<'tcx>,
 {
-    value.fold_with(&mut RegionFolder::new(tcx, &mut f))
+    value.fold_with(&mut RegionFolder::new(tcx, skipped_regions, &mut f))
 }
 
 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
@@ -834,6 +847,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
             ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
                 debug!("RegionFolder.fold_region({:?}) skipped bound region (current depth={})",
                        r, self.current_depth);
+                *self.skipped_regions = true;
                 r
             }
             _ => {
@@ -989,7 +1003,7 @@ pub fn shift_regions<'tcx, T:TypeFoldable<'tcx>>(tcx: &ty::ctxt<'tcx>,
     debug!("shift_regions(value={:?}, amount={})",
            value, amount);
 
-    value.fold_with(&mut RegionFolder::new(tcx, &mut |region, _current_depth| {
+    value.fold_with(&mut RegionFolder::new(tcx, &mut false, &mut |region, _current_depth| {
         shift_region(region, amount)
     }))
 }

src/librustc/middle/ty_walk.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 //! An iterator over the type substructure.
+//! WARNING: this does not keep track of the region depth.
 
 use middle::ty::{self, Ty};
 use std::iter::Iterator;