closure handling for NLL

src/librustc/ich/impls_mir.rs

@@ -572,3 +572,15 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for mir::Literal<'gcx> {
 }
 
 impl_stable_hash_for!(struct mir::Location { block, statement_index });
+
+impl_stable_hash_for!(struct mir::ClosureRegionRequirements {
+    num_external_vids,
+    outlives_requirements
+});
+
+impl_stable_hash_for!(struct mir::ClosureOutlivesRequirement {
+    free_region,
+    outlived_free_region,
+    blame_span
+});
+

src/librustc/ich/impls_ty.rs

@@ -84,6 +84,16 @@ for ty::RegionKind {
     }
 }
 
+impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::RegionVid {
+    #[inline]
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        use rustc_data_structures::indexed_vec::Idx;
+        self.index().hash_stable(hcx, hasher);
+    }
+}
+
 impl<'gcx> HashStable<StableHashingContext<'gcx>>
 for ty::adjustment::AutoBorrow<'gcx> {
     fn hash_stable<W: StableHasherResult>(&self,

src/librustc/infer/mod.rs

@@ -1062,6 +1062,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.tcx.mk_region(ty::ReVar(self.borrow_region_constraints().new_region_var(origin)))
     }
 
+    /// Number of region variables created so far.
+    pub fn num_region_vars(&self) -> usize {
+        self.borrow_region_constraints().var_origins().len()
+    }
+
     /// Just a convenient wrapper of `next_region_var` for using during NLL.
     pub fn next_nll_region_var(&self, origin: NLLRegionVariableOrigin)
                                -> ty::Region<'tcx> {
@@ -1475,38 +1480,18 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         closure_kind_ty.to_opt_closure_kind()
     }
 
-    /// Obtain the signature of a function or closure.
-    /// For closures, unlike `tcx.fn_sig(def_id)`, this method will
-    /// work during the type-checking of the enclosing function and
-    /// return the closure signature in its partially inferred state.
-    pub fn fn_sig(&self, def_id: DefId) -> ty::PolyFnSig<'tcx> {
-        // Do we have an in-progress set of tables we are inferring?
-        if let Some(tables) = self.in_progress_tables {
-            // Is this a local item?
-            if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
-                // Is it a local *closure*?
-                if self.tcx.is_closure(def_id) {
-                    let hir_id = self.tcx.hir.node_to_hir_id(id);
-                    // Is this local closure contained within the tables we are inferring?
-                    if tables.borrow().local_id_root == Some(DefId::local(hir_id.owner)) {
-                        // if so, extract signature from there.
-                        let closure_ty = tables.borrow().node_id_to_type(hir_id);
-                        let (closure_def_id, closure_substs) = match closure_ty.sty {
-                            ty::TyClosure(closure_def_id, closure_substs) =>
-                                (closure_def_id, closure_substs),
-                            _ =>
-                                bug!("closure with non-closure type: {:?}", closure_ty),
-                        };
-                        assert_eq!(def_id, closure_def_id);
-                        let closure_sig_ty = closure_substs.closure_sig_ty(def_id, self.tcx);
-                        let closure_sig_ty = self.shallow_resolve(&closure_sig_ty);
-                        return closure_sig_ty.fn_sig(self.tcx);
-                    }
-                }
-            }
-        }
-
-        self.tcx.fn_sig(def_id)
+    /// Obtain the signature of a closure.  For closures, unlike
+    /// `tcx.fn_sig(def_id)`, this method will work during the
+    /// type-checking of the enclosing function and return the closure
+    /// signature in its partially inferred state.
+    pub fn closure_sig(
+        &self,
+        def_id: DefId,
+        substs: ty::ClosureSubsts<'tcx>
+    ) -> ty::PolyFnSig<'tcx> {
+        let closure_sig_ty = substs.closure_sig_ty(def_id, self.tcx);
+        let closure_sig_ty = self.shallow_resolve(&closure_sig_ty);
+        closure_sig_ty.fn_sig(self.tcx)
     }
 
     /// Normalizes associated types in `value`, potentially returning

src/librustc/mir/mod.rs

@@ -1789,6 +1789,75 @@ pub struct GeneratorLayout<'tcx> {
     pub fields: Vec<LocalDecl<'tcx>>,
 }
 
+/// After we borrow check a closure, we are left with various
+/// requirements that we have inferred between the free regions that
+/// appear in the closure's signature or on its field types.  These
+/// requirements are then verified and proved by the closure's
+/// creating function. This struct encodes those requirements.
+///
+/// The requirements are listed as being between various
+/// `RegionVid`. The 0th region refers to `'static`; subsequent region
+/// vids refer to the free regions that appear in the closure (or
+/// generator's) type, in order of appearance. (This numbering is
+/// actually defined by the `UniversalRegions` struct in the NLL
+/// region checker. See for example
+/// `UniversalRegions::closure_mapping`.) Note that we treat the free
+/// regions in the closure's type "as if" they were erased, so their
+/// precise identity is not important, only their position.
+///
+/// Example: If type check produces a closure with the closure substs:
+///
+/// ```
+/// ClosureSubsts = [
+///     i8,                                  // the "closure kind"
+///     for<'x> fn(&'a &'x u32) -> &'x u32,  // the "closure signature"
+///     &'a String,                          // some upvar
+/// ]
+/// ```
+///
+/// here, there is one unique free region (`'a`) but it appears
+/// twice. We would "renumber" each occurence to a unique vid, as follows:
+///
+/// ```
+/// ClosureSubsts = [
+///     i8,                                  // the "closure kind"
+///     for<'x> fn(&'1 &'x u32) -> &'x u32,  // the "closure signature"
+///     &'2 String,                          // some upvar
+/// ]
+/// ```
+///
+/// Now the code might impose a requirement like `'1: '2`. When an
+/// instance of the closure is created, the corresponding free regions
+/// can be extracted from its type and constrained to have the given
+/// outlives relationship.
+#[derive(Clone, Debug)]
+pub struct ClosureRegionRequirements {
+    /// The number of external regions defined on the closure.  In our
+    /// example above, it would be 3 -- one for `'static`, then `'1`
+    /// and `'2`. This is just used for a sanity check later on, to
+    /// make sure that the number of regions we see at the callsite
+    /// matches.
+    pub num_external_vids: usize,
+
+    /// Requirements between the various free regions defined in
+    /// indices.
+    pub outlives_requirements: Vec<ClosureOutlivesRequirement>,
+}
+
+/// Indicates an outlives constraint between two free-regions declared
+/// on the closure.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ClosureOutlivesRequirement {
+    // This region ...
+    pub free_region: ty::RegionVid,
+
+    // .. must outlive this one.
+    pub outlived_free_region: ty::RegionVid,
+
+    // If not, report an error here.
+    pub blame_span: Span,
+}
+
 /*
  * TypeFoldable implementations for MIR types
  */

src/librustc/traits/project.rs

@@ -1339,26 +1339,27 @@ fn confirm_closure_candidate<'cx, 'gcx, 'tcx>(
     vtable: VtableClosureData<'tcx, PredicateObligation<'tcx>>)
     -> Progress<'tcx>
 {
-    let closure_typer = selcx.closure_typer();
-    let closure_type = closure_typer.fn_sig(vtable.closure_def_id)
-        .subst(selcx.tcx(), vtable.substs.substs);
+    let tcx = selcx.tcx();
+    let infcx = selcx.infcx();
+    let closure_sig_ty = vtable.substs.closure_sig_ty(vtable.closure_def_id, tcx);
+    let closure_sig = infcx.shallow_resolve(&closure_sig_ty).fn_sig(tcx);
     let Normalized {
-        value: closure_type,
+        value: closure_sig,
         obligations
     } = normalize_with_depth(selcx,
                              obligation.param_env,
                              obligation.cause.clone(),
                              obligation.recursion_depth+1,
-                             &closure_type);
+                             &closure_sig);
 
-    debug!("confirm_closure_candidate: obligation={:?},closure_type={:?},obligations={:?}",
+    debug!("confirm_closure_candidate: obligation={:?},closure_sig={:?},obligations={:?}",
            obligation,
-           closure_type,
+           closure_sig,
            obligations);
 
     confirm_callable_candidate(selcx,
                                obligation,
-                               closure_type,
+                               closure_sig,
                                util::TupleArgumentsFlag::No)
         .with_addl_obligations(vtable.nested)
         .with_addl_obligations(obligations)

src/librustc/traits/select.rs

@@ -3183,8 +3183,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                                       substs: ty::ClosureSubsts<'tcx>)
                                       -> ty::PolyTraitRef<'tcx>
     {
-        let closure_type = self.infcx.fn_sig(closure_def_id)
-            .subst(self.tcx(), substs.substs);
+        let closure_type = self.infcx.closure_sig(closure_def_id, substs);
         let ty::Binder((trait_ref, _)) =
             self.tcx().closure_trait_ref_and_return_type(obligation.predicate.def_id(),
                                                          obligation.predicate.0.self_ty(), // (1)

src/librustc/ty/instance.rs

@@ -10,7 +10,7 @@
 
 use hir::def_id::DefId;
 use ty::{self, Ty, TypeFoldable, Substs, TyCtxt};
-use ty::subst::{Kind, Subst};
+use ty::subst::Kind;
 use traits;
 use syntax::abi::Abi;
 use util::ppaux;
@@ -311,7 +311,7 @@ fn fn_once_adapter_instance<'a, 'tcx>(
     let self_ty = tcx.mk_closure_from_closure_substs(
         closure_did, substs);
 
-    let sig = tcx.fn_sig(closure_did).subst(tcx, substs.substs);
+    let sig = substs.closure_sig(closure_did, tcx);
     let sig = tcx.erase_late_bound_regions_and_normalize(&sig);
     assert_eq!(sig.inputs().len(), 1);
     let substs = tcx.mk_substs([

src/librustc/ty/maps/mod.rs

@@ -190,8 +190,10 @@ define_maps! { <'tcx>
     [] fn coherent_trait: coherent_trait_dep_node((CrateNum, DefId)) -> (),
 
     [] fn borrowck: BorrowCheck(DefId) -> Rc<BorrowCheckResult>,
-    // FIXME: shouldn't this return a `Result<(), BorrowckErrors>` instead?
-    [] fn mir_borrowck: MirBorrowCheck(DefId) -> (),
+
+    /// Borrow checks the function body. If this is a closure, returns
+    /// additional requirements that the closure's creator must verify.
+    [] fn mir_borrowck: MirBorrowCheck(DefId) -> Option<mir::ClosureRegionRequirements>,
 
     /// Gets a complete map from all types to their inherent impls.
     /// Not meant to be used directly outside of coherence.

src/librustc/ty/sty.rs

@@ -356,13 +356,17 @@ impl<'tcx> ClosureSubsts<'tcx> {
     /// Returns the closure kind for this closure; only usable outside
     /// of an inference context, because in that context we know that
     /// there are no type variables.
+    ///
+    /// If you have an inference context, use `infcx.closure_kind()`.
     pub fn closure_kind(self, def_id: DefId, tcx: TyCtxt<'_, 'tcx, 'tcx>) -> ty::ClosureKind {
         self.split(def_id, tcx).closure_kind_ty.to_opt_closure_kind().unwrap()
     }
 
     /// Extracts the signature from the closure; only usable outside
     /// of an inference context, because in that context we know that
     /// there are no type variables.
+    ///
+    /// If you have an inference context, use `infcx.closure_sig()`.
     pub fn closure_sig(self, def_id: DefId, tcx: TyCtxt<'_, 'tcx, 'tcx>) -> ty::PolyFnSig<'tcx> {
         match self.closure_sig_ty(def_id, tcx).sty {
             ty::TyFnPtr(sig) => sig,
@@ -646,6 +650,17 @@ impl<'tcx> PolyExistentialTraitRef<'tcx> {
 pub struct Binder<T>(pub T);
 
 impl<T> Binder<T> {
+    /// Wraps `value` in a binder, asserting that `value` does not
+    /// contain any bound regions that would be bound by the
+    /// binder. This is commonly used to 'inject' a value T into a
+    /// different binding level.
+    pub fn dummy<'tcx>(value: T) -> Binder<T>
+        where T: TypeFoldable<'tcx>
+    {
+        assert!(!value.has_escaping_regions());
+        Binder(value)
+    }
+
     /// Skips the binder and returns the "bound" value. This is a
     /// risky thing to do because it's easy to get confused about
     /// debruijn indices and the like. It is usually better to
@@ -700,6 +715,32 @@ impl<T> Binder<T> {
             Some(self.skip_binder().clone())
         }
     }
+
+    /// Given two things that have the same binder level,
+    /// and an operation that wraps on their contents, execute the operation
+    /// and then wrap its result.
+    ///
+    /// `f` should consider bound regions at depth 1 to be free, and
+    /// anything it produces with bound regions at depth 1 will be
+    /// bound in the resulting return value.
+    pub fn fuse<U,F,R>(self, u: Binder<U>, f: F) -> Binder<R>
+        where F: FnOnce(T, U) -> R
+    {
+        ty::Binder(f(self.0, u.0))
+    }
+
+    /// Split the contents into two things that share the same binder
+    /// level as the original, returning two distinct binders.
+    ///
+    /// `f` should consider bound regions at depth 1 to be free, and
+    /// anything it produces with bound regions at depth 1 will be
+    /// bound in the resulting return values.
+    pub fn split<U,V,F>(self, f: F) -> (Binder<U>, Binder<V>)
+        where F: FnOnce(T) -> (U, V)
+    {
+        let (u, v) = f(self.0);
+        (ty::Binder(u), ty::Binder(v))
+    }
 }
 
 /// Represents the projection of an associated type. In explicit UFCS
@@ -799,6 +840,9 @@ impl<'tcx> PolyFnSig<'tcx> {
     pub fn input(&self, index: usize) -> ty::Binder<Ty<'tcx>> {
         self.map_bound_ref(|fn_sig| fn_sig.inputs()[index])
     }
+    pub fn inputs_and_output(&self) -> ty::Binder<&'tcx Slice<Ty<'tcx>>> {
+        self.map_bound_ref(|fn_sig| fn_sig.inputs_and_output)
+    }
     pub fn output(&self) -> ty::Binder<Ty<'tcx>> {
         self.map_bound_ref(|fn_sig| fn_sig.output().clone())
     }

src/librustc_driver/driver.rs

@@ -1069,7 +1069,7 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(control: &CompileController,
 
         time(time_passes,
              "MIR borrow checking",
-             || for def_id in tcx.body_owners() { tcx.mir_borrowck(def_id) });
+             || for def_id in tcx.body_owners() { tcx.mir_borrowck(def_id); });
 
         time(time_passes,
              "MIR effect checking",