mir borrowck: cleanup late-bound region handling

Author: lcnr

compiler/rustc_borrowck/src/renumber.rs

@@ -34,7 +34,6 @@ pub(crate) enum RegionCtxt {
     Location(Location),
     TyContext(TyContext),
     Free(Symbol),
-    Bound(Symbol),
     LateBound(Symbol),
     Existential(Option<Symbol>),
     Placeholder(Symbol),

compiler/rustc_borrowck/src/universal_regions.rs

@@ -467,15 +467,13 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 self.infcx.tcx.local_parent(self.mir_def),
                 |r| {
                     debug!(?r);
-                    if !indices.indices.contains_key(&r) {
-                        let region_vid = {
-                            let name = r.get_name_or_anon();
-                            self.infcx.next_nll_region_var(FR, || RegionCtxt::LateBound(name))
-                        };
-
-                        debug!(?region_vid);
-                        indices.insert_late_bound_region(r, region_vid.as_var());
-                    }
+                    let region_vid = {
+                        let name = r.get_name_or_anon();
+                        self.infcx.next_nll_region_var(FR, || RegionCtxt::LateBound(name))
+                    };
+
+                    debug!(?region_vid);
+                    indices.insert_late_bound_region(r, region_vid.as_var());
                 },
             );
 
@@ -484,21 +482,17 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
             self.infcx.num_region_vars()
         };
 
-        // "Liberate" the late-bound regions. These correspond to
-        // "local" free regions.
+        // Converse of above, if this is a function/closure then the late-bound regions declared
+        // on its signature are local.
+        //
+        // We manually loop over `bound_inputs_and_output` instead of using
+        // `for_each_late_bound_region_in_item` as we may need to add the otherwise
+        // implicit `ClosureEnv` region.
         let bound_inputs_and_output = self.compute_inputs_and_output(&indices, defining_ty);
-
-        let inputs_and_output = self.infcx.replace_bound_regions_with_nll_infer_vars(
-            FR,
-            self.mir_def,
-            bound_inputs_and_output,
-            &mut indices,
-        );
-        // Converse of above, if this is a function/closure then the late-bound regions declared on its
-        // signature are local.
-        for_each_late_bound_region_in_item(self.infcx.tcx, self.mir_def, |r| {
-            debug!(?r);
-            if !indices.indices.contains_key(&r) {
+        for (idx, bound_var) in bound_inputs_and_output.bound_vars().iter().enumerate() {
+            if let ty::BoundVariableKind::Region(kind) = bound_var {
+                let kind = ty::LateParamRegionKind::from_bound(ty::BoundVar::from_usize(idx), kind);
+                let r = ty::Region::new_late_param(self.infcx.tcx, self.mir_def.to_def_id(), kind);
                 let region_vid = {
                     let name = r.get_name_or_anon();
                     self.infcx.next_nll_region_var(FR, || RegionCtxt::LateBound(name))
@@ -507,7 +501,12 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 debug!(?region_vid);
                 indices.insert_late_bound_region(r, region_vid.as_var());
             }
-        });
+        }
+        let inputs_and_output = self.infcx.replace_bound_regions_with_nll_infer_vars(
+            self.mir_def,
+            bound_inputs_and_output,
+            &indices,
+        );
 
         let (unnormalized_output_ty, mut unnormalized_input_tys) =
             inputs_and_output.split_last().unwrap();
@@ -832,10 +831,9 @@ impl<'tcx> BorrowckInferCtxt<'tcx> {
     #[instrument(level = "debug", skip(self, indices))]
     fn replace_bound_regions_with_nll_infer_vars<T>(
         &self,
-        origin: NllRegionVariableOrigin,
         all_outlive_scope: LocalDefId,
         value: ty::Binder<'tcx, T>,
-        indices: &mut UniversalRegionIndices<'tcx>,
+        indices: &UniversalRegionIndices<'tcx>,
     ) -> T
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
@@ -845,18 +843,7 @@ impl<'tcx> BorrowckInferCtxt<'tcx> {
             let kind = ty::LateParamRegionKind::from_bound(br.var, br.kind);
             let liberated_region =
                 ty::Region::new_late_param(self.tcx, all_outlive_scope.to_def_id(), kind);
-            let region_vid = {
-                let name = match br.kind.get_name() {
-                    Some(name) => name,
-                    _ => sym::anon,
-                };
-
-                self.next_nll_region_var(origin, || RegionCtxt::Bound(name))
-            };
-
-            indices.insert_late_bound_region(liberated_region, region_vid.as_var());
-            debug!(?liberated_region, ?region_vid);
-            region_vid
+            ty::Region::new_var(self.tcx, indices.to_region_vid(liberated_region))
         });
         value
     }
@@ -870,7 +857,7 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
     /// well. These are used for error reporting.
     fn insert_late_bound_region(&mut self, r: ty::Region<'tcx>, vid: ty::RegionVid) {
         debug!("insert_late_bound_region({:?}, {:?})", r, vid);
-        self.indices.insert(r, vid);
+        assert_eq!(self.indices.insert(r, vid), None);
     }
 
     /// Converts `r` into a local inference variable: `r` can either

tests/ui/closures/binder/nested-closures-regions.stderr

@@ -9,7 +9,7 @@ LL |     for<'a> || -> () { for<'c> |_: &'a ()| -> () {}; };
                extern "rust-call" fn((&(),)),
                (),
            ]
-   = note: late-bound region is '?4
+   = note: late-bound region is '?3
    = note: late-bound region is '?2
    = note: number of external vids: 3
    = note: where '?1: '?2
@@ -26,7 +26,7 @@ LL |     for<'a> || -> () { for<'c> |_: &'a ()| -> () {}; };
                extern "rust-call" fn(()),
                (),
            ]
-   = note: late-bound region is '?2
+   = note: late-bound region is '?1
 
 note: no external requirements
   --> $DIR/nested-closures-regions.rs:7:1

tests/ui/nll/closure-requirements/escape-argument-callee.stderr

@@ -17,7 +17,7 @@ LL |         let mut closure = expect_sig(|p, y| *p = y);
    |                                       -  -  ^^^^^^ assignment requires that `'1` must outlive `'2`
    |                                       |  |
    |                                       |  has type `&'1 i32`
-   |                                       has type `&'?2 mut &'2 i32`
+   |                                       has type `&'?1 mut &'2 i32`
 
 note: no external requirements
   --> $DIR/escape-argument-callee.rs:20:1

tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr

@@ -20,7 +20,7 @@ LL |     foo(cell, |cell_a, cell_x| {
 LL |         cell_a.set(cell_x.get()); // forces 'x: 'a, error in closure
    |         ^^^^^^^^^^^^^^^^^^^^^^^^ `cell_x` escapes the closure body here
    |
-   = note: requirement occurs because of the type `Cell<&'?8 u32>`, which makes the generic argument `&'?8 u32` invariant
+   = note: requirement occurs because of the type `Cell<&'?9 u32>`, which makes the generic argument `&'?9 u32` invariant
    = note: the struct `Cell<T>` is invariant over the parameter `T`
    = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 

tests/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr

@@ -16,9 +16,9 @@ error: lifetime may not live long enough
   --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:37:9
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
-   |                                                ---------  - has type `&'?7 Cell<&'1 u32>`
+   |                                                ---------  - has type `&'?6 Cell<&'1 u32>`
    |                                                |
-   |                                                has type `&'?5 Cell<&'2 &'?1 u32>`
+   |                                                has type `&'?4 Cell<&'2 &'?1 u32>`
 LL |         // Only works if 'x: 'y:
 LL |         demand_y(x, y, x.get())
    |         ^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`

tests/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr

@@ -16,9 +16,9 @@ error: lifetime may not live long enough
   --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:41:9
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
-   |                                                ----------  ---------- has type `&'?8 Cell<&'2 &'?2 u32>`
+   |                                                ----------  ---------- has type `&'?7 Cell<&'2 &'?2 u32>`
    |                                                |
-   |                                                has type `&'?6 Cell<&'1 &'?1 u32>`
+   |                                                has type `&'?5 Cell<&'1 &'?1 u32>`
 LL |         // Only works if 'x: 'y:
 LL |         demand_y(x, y, x.get())
    |         ^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`