fix for issues #51351 and #52113

src/librustc_mir/borrow_check/nll/region_infer/mod.rs

@@ -1155,8 +1155,8 @@ impl<'gcx, 'tcx> ClosureRegionRequirementsExt<'gcx, 'tcx> for ClosureRegionRequi
         // Extract the values of the free regions in `user_closure_ty`
         // into a vector.  These are the regions that we will be
         // relating to one another.
-        let closure_mapping =
-            &UniversalRegions::closure_mapping(tcx, user_closure_ty, self.num_external_vids);
+        let closure_mapping = &UniversalRegions::closure_mapping(
+            tcx, user_closure_ty, self.num_external_vids, tcx.closure_base_def_id(closure_def_id));
         debug!("apply_requirements: closure_mapping={:?}", closure_mapping);
 
         // Create the predicates.

src/librustc_mir/borrow_check/nll/universal_regions.rs

@@ -270,13 +270,17 @@ impl<'tcx> UniversalRegions<'tcx> {
         tcx: TyCtxt<'_, '_, 'tcx>,
         closure_ty: Ty<'tcx>,
         expected_num_vars: usize,
+        closure_base_def_id: DefId,
     ) -> IndexVec<RegionVid, ty::Region<'tcx>> {
         let mut region_mapping = IndexVec::with_capacity(expected_num_vars);
         region_mapping.push(tcx.types.re_static);
         tcx.for_each_free_region(&closure_ty, |fr| {
             region_mapping.push(fr);
         });
 
+        for_each_late_bound_region_defined_on(
+            tcx, closure_base_def_id, |r| { region_mapping.push(r); });
+
         assert_eq!(
             region_mapping.len(),
             expected_num_vars,
@@ -479,6 +483,20 @@ impl<'cx, 'gcx, 'tcx> UniversalRegionsBuilder<'cx, 'gcx, 'tcx> {
         let mut indices = self.compute_indices(fr_static, defining_ty);
         debug!("build: indices={:?}", indices);
 
+        let closure_base_def_id = self.infcx.tcx.closure_base_def_id(self.mir_def_id);
+
+        // If this is a closure or generator, then the late-bound regions from the enclosing
+        // function are actually external regions to us. For example, here, 'a is not local
+        // to the closure c (although it is local to the fn foo):
+        // fn foo<'a>() {
+        //     let c = || { let x: &'a u32 = ...; }
+        // }
+        if self.mir_def_id != closure_base_def_id {
+            self.infcx.replace_late_bound_regions_with_nll_infer_vars(
+                self.mir_def_id,
+                &mut indices)
+        }
+
         let bound_inputs_and_output = self.compute_inputs_and_output(&indices, defining_ty);
 
         // "Liberate" the late-bound regions. These correspond to
@@ -490,6 +508,14 @@ impl<'cx, 'gcx, 'tcx> UniversalRegionsBuilder<'cx, 'gcx, 'tcx> {
             &bound_inputs_and_output,
             &mut indices,
         );
+        // Converse of above, if this is a function then the late-bound regions declared on its
+        // signature are local to the fn.
+        if self.mir_def_id == closure_base_def_id {
+            self.infcx.replace_late_bound_regions_with_nll_infer_vars(
+                self.mir_def_id,
+                &mut indices);
+        }
+
         let fr_fn_body = self.infcx.next_nll_region_var(FR).to_region_vid();
         let num_universals = self.infcx.num_region_vars();
 
@@ -782,6 +808,13 @@ trait InferCtxtExt<'tcx> {
     ) -> T
     where
         T: TypeFoldable<'tcx>;
+
+
+    fn replace_late_bound_regions_with_nll_infer_vars(
+        &self,
+        mir_def_id: DefId,
+        indices: &mut UniversalRegionIndices<'tcx>
+    );
 }
 
 impl<'cx, 'gcx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'gcx, 'tcx> {
@@ -827,6 +860,28 @@ impl<'cx, 'gcx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'gcx, 'tcx> {
         });
         value
     }
+
+    /// Finds late-bound regions that do not appear in the parameter listing and adds them to the
+    /// indices vector. Typically, we identify late-bound regions as we process the inputs and
+    /// outputs of the closure/function. However, sometimes there are late-bound regions which do
+    /// not appear in the fn parameters but which are nonetheless in scope. The simplest case of
+    /// this are unused functions, like fn foo<'a>() { } (see eg., #51351). Despite not being used,
+    /// users can still reference these regions (e.g., let x: &'a u32 = &22;), so we need to create
+    /// entries for them and store them in the indices map. This code iterates over the complete
+    /// set of late-bound regions and checks for any that we have not yet seen, adding them to the
+    /// inputs vector.
+    fn replace_late_bound_regions_with_nll_infer_vars(
+        &self,
+        mir_def_id: DefId,
+        indices: &mut UniversalRegionIndices<'tcx>,
+    ) {
+        let closure_base_def_id = self.tcx.closure_base_def_id(mir_def_id);
+        for_each_late_bound_region_defined_on(self.tcx, closure_base_def_id, |r| {
+            if !indices.indices.contains_key(&r) {
+                let region_vid = self.next_nll_region_var(FR);
+                indices.insert_late_bound_region(r, region_vid.to_region_vid());
+            }});
+    }
 }
 
 impl<'tcx> UniversalRegionIndices<'tcx> {
@@ -882,3 +937,25 @@ impl<'tcx> FreeRegionRelations<'tcx> for UniversalRegions<'tcx> {
         self.outlives(longer, shorter)
     }
 }
+
+/// Iterates over the late-bound regions defined on fn_def_id and
+/// invokes `f` with the liberated form of each one.
+fn for_each_late_bound_region_defined_on<'tcx>(
+    tcx: TyCtxt<'_, '_, 'tcx>,
+    fn_def_id: DefId,
+    mut f: impl FnMut(ty::Region<'tcx>)
+    ) {
+    if let Some(late_bounds) = tcx.is_late_bound_map(fn_def_id.index) {
+        for late_bound in late_bounds.iter() {
+            let hir_id = HirId{ owner: fn_def_id.index, local_id: *late_bound };
+            let region_node_id = tcx.hir.hir_to_node_id(hir_id);
+            let name = tcx.hir.name(region_node_id).as_interned_str();
+            let region_def_id = tcx.hir.local_def_id(region_node_id);
+            let liberated_region = tcx.mk_region(ty::ReFree(ty::FreeRegion {
+                scope: fn_def_id,
+                bound_region: ty::BoundRegion::BrNamed(region_def_id, name),
+            }));
+            f(liberated_region);
+        }
+    }
+}

src/test/ui/nll/closure-requirements/propagate-approximated-ref.stderr

@@ -20,7 +20,7 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) &'_#2r u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't3)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>))
            ]
-   = note: number of external vids: 3
+   = note: number of external vids: 5
    = note: where '_#1r: '_#2r
 
 error[E0623]: lifetime mismatch

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr

@@ -20,7 +20,7 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) u32>))
            ]
-   = note: number of external vids: 2
+   = note: number of external vids: 4
    = note: where '_#1r: '_#0r
 
 error: borrowed data escapes outside of function

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr

@@ -20,7 +20,7 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't3)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>))
            ]
-   = note: number of external vids: 3
+   = note: number of external vids: 5
    = note: where '_#1r: '_#0r
 
 error: borrowed data escapes outside of function

src/test/ui/nll/closure-requirements/propagate-approximated-val.stderr

@@ -20,7 +20,7 @@ LL | |     });
                i16,
                for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>))
            ]
-   = note: number of external vids: 3
+   = note: number of external vids: 5
    = note: where '_#1r: '_#2r
 
 error[E0623]: lifetime mismatch

src/test/ui/nll/closure-requirements/propagate-despite-same-free-region.stderr

@@ -18,7 +18,7 @@ LL | |         },
                i16,
                for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>))
            ]
-   = note: number of external vids: 3
+   = note: number of external vids: 4
    = note: where '_#1r: '_#2r
 
 note: No external requirements

src/test/ui/nll/closure-requirements/propagate-from-trait-match.stderr

@@ -23,7 +23,7 @@ LL | |     });
                i32,
                extern "rust-call" fn((T,))
            ]
-   = note: number of external vids: 2
+   = note: number of external vids: 3
    = note: where T: '_#1r
 
 error[E0309]: the parameter type `T` may not live long enough

src/test/ui/nll/issue-51351.rs

@@ -0,0 +1,32 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// Regression test for #51351 and #52133: In the case of #51351,
+// late-bound regions (like 'a) that were unused within the arguments of
+// a function were overlooked and could case an ICE. In the case of #52133,
+// LBR defined on the creator function needed to be added to the free regions
+// of the closure, as they were not present in the closure's generic
+// declarations otherwise.
+//
+// compile-pass
+
+#![feature(nll)]
+
+fn creash<'a>() {
+    let x: &'a () = &();
+}
+
+fn produce<'a>() {
+   move || {
+        let x: &'a () = &();
+   };
+}
+
+fn main() {}

src/test/ui/nll/issue-52133.rs

@@ -0,0 +1,50 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+
+#![allow(warnings)]
+#![feature(nll)]
+
+trait Bazinga { }
+impl<F> Bazinga for F { }
+
+fn produce1<'a>(data: &'a u32) -> impl Bazinga + 'a {
+    let x = move || {
+        let _data: &'a u32 = data;
+    };
+    x
+}
+
+fn produce2<'a>(data: &'a mut Vec<&'a u32>, value: &'a u32) -> impl Bazinga + 'a {
+    let x = move || {
+        let value: &'a u32 = value;
+        data.push(value);
+    };
+    x
+}
+
+
+fn produce3<'a, 'b: 'a>(data: &'a mut Vec<&'a u32>, value: &'b u32) -> impl Bazinga + 'a {
+    let x = move || {
+        let value: &'a u32 = value;
+        data.push(value);
+    };
+    x
+}
+
+fn produce_err<'a, 'b: 'a>(data: &'b mut Vec<&'b u32>, value: &'a u32) -> impl Bazinga + 'b {
+    let x = move || { //~ ERROR lifetime mismatch
+        let value: &'a u32 = value;
+        data.push(value);
+    };
+    x
+}
+
+fn main() { }

src/test/ui/nll/issue-52133.stderr

@@ -0,0 +1,11 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/issue-52133.rs:43:9
+   |
+LL | fn produce_err<'a, 'b: 'a>(data: &'b mut Vec<&'b u32>, value: &'a u32) -> impl Bazinga + 'b {
+   |                                  --------------------         ------- these two types are declared with different lifetimes...
+LL |     let x = move || { //~ ERROR lifetime mismatch
+   |         ^ ...but data from `value` flows into `data` here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0623`.

src/test/ui/nll/ty-outlives/projection-no-regions-closure.stderr

@@ -22,7 +22,7 @@ LL |     with_signature(x, |mut y| Box::new(y.next()))
                i32,
                extern "rust-call" fn((std::boxed::Box<T>,)) -> std::boxed::Box<(dyn Anything + '_#2r)>
            ]
-   = note: number of external vids: 3
+   = note: number of external vids: 4
    = note: where <T as std::iter::Iterator>::Item: '_#2r
 
 error[E0309]: the associated type `<T as std::iter::Iterator>::Item` may not live long enough
@@ -62,7 +62,7 @@ LL |     with_signature(x, |mut y| Box::new(y.next()))
                i32,
                extern "rust-call" fn((std::boxed::Box<T>,)) -> std::boxed::Box<(dyn Anything + '_#2r)>
            ]
-   = note: number of external vids: 3
+   = note: number of external vids: 4
    = note: where <T as std::iter::Iterator>::Item: '_#2r
 
 note: No external requirements
@@ -94,7 +94,7 @@ LL |     with_signature(x, |mut y| Box::new(y.next()))
                i32,
                extern "rust-call" fn((std::boxed::Box<T>,)) -> std::boxed::Box<(dyn Anything + '_#3r)>
            ]
-   = note: number of external vids: 4
+   = note: number of external vids: 5
    = note: where <T as std::iter::Iterator>::Item: '_#3r
 
 error[E0309]: the associated type `<T as std::iter::Iterator>::Item` may not live long enough
@@ -136,7 +136,7 @@ LL |     with_signature(x, |mut y| Box::new(y.next()))
                i32,
                extern "rust-call" fn((std::boxed::Box<T>,)) -> std::boxed::Box<(dyn Anything + '_#3r)>
            ]
-   = note: number of external vids: 4
+   = note: number of external vids: 5
    = note: where <T as std::iter::Iterator>::Item: '_#3r
 
 note: No external requirements

src/test/ui/nll/ty-outlives/projection-one-region-closure.stderr

@@ -28,7 +28,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#2r ()>, T))
            ]
-   = note: number of external vids: 3
+   = note: number of external vids: 5
    = note: where T: '_#2r
    = note: where '_#1r: '_#2r
 
@@ -76,7 +76,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#3r ()>, T))
            ]
-   = note: number of external vids: 4
+   = note: number of external vids: 5
    = note: where T: '_#3r
    = note: where '_#2r: '_#3r
 
@@ -125,7 +125,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#3r ()>, T))
            ]
-   = note: number of external vids: 4
+   = note: number of external vids: 5
    = note: where T: '_#3r
    = note: where '_#2r: '_#3r
 
@@ -174,7 +174,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#3r ()>, T))
            ]
-   = note: number of external vids: 4
+   = note: number of external vids: 5
    = note: where T: '_#3r
    = note: where '_#2r: '_#3r