Auto merge of #45879 - nikomatsakis:nll-kill-cyclic-closures, r=<try>

[WIP] move closure kind, signature into `ClosureSubsts`

Instead of using side-tables, store the closure-kind and signature in the substitutions themselves. This has two key effects:

- It means that the closure's type changes as inference finds out more things, which is very nice.
    - As a result, it avoids the need for the `freshen_closure_like` code (though we still use it for generators).
- It avoids cyclic closures calls.
    - These were never meant to be supported, precisely because they make a lot of the fancy inference that we do much more complicated. However, due to an oversight, it was previously possible -- if challenging -- to create a setup where a closure *directly* called itself (see e.g. #21410).

We have to see what the effect of this change is, though. Needs a crater run. Marking as [WIP] until that has been assessed.

r? @arielb1

src/librustc/dep_graph/dep_node.rs

@@ -498,9 +498,7 @@ define_dep_nodes!( <'tcx>
     [] IsAutoImpl(DefId),
     [] ImplTraitRef(DefId),
     [] ImplPolarity(DefId),
-    [] ClosureKind(DefId),
     [] FnSignature(DefId),
-    [] GenSignature(DefId),
     [] CoerceUnsizedInfo(DefId),
 
     [] ItemVarianceConstraints(DefId),

src/librustc/ich/impls_ty.rs

@@ -236,8 +236,9 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::Predicate<'gcx> {
             ty::Predicate::ObjectSafe(def_id) => {
                 def_id.hash_stable(hcx, hasher);
             }
-            ty::Predicate::ClosureKind(def_id, closure_kind) => {
+            ty::Predicate::ClosureKind(def_id, closure_substs, closure_kind) => {
                 def_id.hash_stable(hcx, hasher);
+                closure_substs.hash_stable(hcx, hasher);
                 closure_kind.hash_stable(hcx, hasher);
             }
             ty::Predicate::ConstEvaluatable(def_id, substs) => {

src/librustc/infer/error_reporting/need_type_info.rs

@@ -125,9 +125,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             // ```
             labels.clear();
             labels.push((pattern.span, format!("consider giving this closure parameter a type")));
-        }
-
-        if let Some(pattern) = local_visitor.found_local_pattern {
+        } else if let Some(pattern) = local_visitor.found_local_pattern {
             if let Some(simple_name) = pattern.simple_name() {
                 labels.push((pattern.span, format!("consider giving `{}` a type", simple_name)));
             } else {

src/librustc/infer/freshen.rs

@@ -43,9 +43,7 @@
 
 use ty::{self, Ty, TyCtxt, TypeFoldable};
 use ty::fold::TypeFolder;
-use ty::subst::Substs;
 use util::nodemap::FxHashMap;
-use hir::def_id::DefId;
 
 use std::collections::hash_map::Entry;
 
@@ -56,7 +54,6 @@ pub struct TypeFreshener<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
     freshen_count: u32,
     freshen_map: FxHashMap<ty::InferTy, Ty<'tcx>>,
-    closure_set: Vec<DefId>,
 }
 
 impl<'a, 'gcx, 'tcx> TypeFreshener<'a, 'gcx, 'tcx> {
@@ -66,7 +63,6 @@ impl<'a, 'gcx, 'tcx> TypeFreshener<'a, 'gcx, 'tcx> {
             infcx,
             freshen_count: 0,
             freshen_map: FxHashMap(),
-            closure_set: vec![],
         }
     }
 
@@ -92,88 +88,6 @@ impl<'a, 'gcx, 'tcx> TypeFreshener<'a, 'gcx, 'tcx> {
             }
         }
     }
-
-    fn next_fresh<F>(&mut self,
-                     freshener: F)
-                     -> Ty<'tcx>
-        where F: FnOnce(u32) -> ty::InferTy,
-    {
-        let index = self.freshen_count;
-        self.freshen_count += 1;
-        self.infcx.tcx.mk_infer(freshener(index))
-    }
-
-    fn freshen_closure_like<M, C>(&mut self,
-                                  def_id: DefId,
-                                  substs: ty::ClosureSubsts<'tcx>,
-                                  t: Ty<'tcx>,
-                                  markers: M,
-                                  combine: C)
-                                  -> Ty<'tcx>
-        where M: FnOnce(&mut Self) -> (Ty<'tcx>, Ty<'tcx>),
-              C: FnOnce(&'tcx Substs<'tcx>) -> Ty<'tcx>
-    {
-        let tcx = self.infcx.tcx;
-
-        let closure_in_progress = self.infcx.in_progress_tables.map_or(false, |tables| {
-            tcx.hir.as_local_node_id(def_id).map_or(false, |closure_id| {
-                tables.borrow().local_id_root ==
-                    Some(DefId::local(tcx.hir.node_to_hir_id(closure_id).owner))
-            })
-        });
-
-        if !closure_in_progress {
-            // If this closure belongs to another infcx, its kind etc. were
-            // fully inferred and its signature/kind are exactly what's listed
-            // in its infcx. So we don't need to add the markers for them.
-            return t.super_fold_with(self);
-        }
-
-        // We are encoding a closure in progress. Because we want our freshening
-        // key to contain all inference information needed to make sense of our
-        // value, we need to encode the closure signature and kind. The way
-        // we do that is to add them as 2 variables to the closure substs,
-        // basically because it's there (and nobody cares about adding extra stuff
-        // to substs).
-        //
-        // This means the "freshened" closure substs ends up looking like
-        //     fresh_substs = [PARENT_SUBSTS* ; UPVARS* ; SIG_MARKER ; KIND_MARKER]
-        let (marker_1, marker_2) = if self.closure_set.contains(&def_id) {
-            // We found the closure def-id within its own signature. Just
-            // leave a new freshened type - any matching operations would
-            // have found and compared the exterior closure already to
-            // get here.
-            //
-            // In that case, we already know what the signature would
-            // be - the parent closure on the stack already contains a
-            // "copy" of the signature, so there is no reason to encode
-            // it again for injectivity. Just use a fresh type variable
-            // to make everything comparable.
-            //
-            // For example (closure kinds omitted for clarity)
-            //     t=[closure FOO sig=[closure BAR sig=[closure FOO ..]]]
-            // Would get encoded to
-            //     t=[closure FOO sig=[closure BAR sig=[closure FOO sig=$0]]]
-            //
-            // and we can decode by having
-            //     $0=[closure BAR {sig doesn't exist in decode}]
-            // and get
-            //     t=[closure FOO]
-            //     sig[FOO] = [closure BAR]
-            //     sig[BAR] = [closure FOO]
-            (self.next_fresh(ty::FreshTy), self.next_fresh(ty::FreshTy))
-        } else {
-            self.closure_set.push(def_id);
-            let markers = markers(self);
-            self.closure_set.pop();
-            markers
-        };
-
-        combine(tcx.mk_substs(
-            substs.substs.iter().map(|k| k.fold_with(self)).chain(
-                [marker_1, marker_2].iter().cloned().map(From::from)
-                    )))
-    }
 }
 
 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
@@ -249,51 +163,7 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
                 t
             }
 
-            ty::TyClosure(def_id, substs) => {
-                self.freshen_closure_like(
-                    def_id, substs, t,
-                    |this| {
-                        // HACK: use a "random" integer type to mark the kind. Because
-                        // different closure kinds shouldn't get unified during
-                        // selection, the "subtyping" relationship (where any kind is
-                        // better than no kind) shouldn't  matter here, just that the
-                        // types are different.
-                        let closure_kind = this.infcx.closure_kind(def_id);
-                        let closure_kind_marker = match closure_kind {
-                            None => tcx.types.i8,
-                            Some(ty::ClosureKind::Fn) => tcx.types.i16,
-                            Some(ty::ClosureKind::FnMut) => tcx.types.i32,
-                            Some(ty::ClosureKind::FnOnce) => tcx.types.i64,
-                        };
-
-                        let closure_sig = this.infcx.fn_sig(def_id);
-                        (tcx.mk_fn_ptr(closure_sig.fold_with(this)),
-                         closure_kind_marker)
-                    },
-                    |substs| tcx.mk_closure(def_id, substs)
-                )
-            }
-
-            ty::TyGenerator(def_id, substs, interior) => {
-                self.freshen_closure_like(
-                    def_id, substs, t,
-                    |this| {
-                        let gen_sig = this.infcx.generator_sig(def_id).unwrap();
-                        // FIXME: want to revise this strategy when generator
-                        // signatures can actually contain LBRs.
-                        let sig = this.tcx().no_late_bound_regions(&gen_sig)
-                            .unwrap_or_else(|| {
-                                bug!("late-bound regions in signature of {:?}",
-                                     def_id)
-                            });
-                        (sig.yield_ty, sig.return_ty).fold_with(this)
-                    },
-                    |substs| {
-                        tcx.mk_generator(def_id, ty::ClosureSubsts { substs }, interior)
-                    }
-                )
-            }
-
+            ty::TyGenerator(..) |
             ty::TyBool |
             ty::TyChar |
             ty::TyInt(..) |
@@ -314,6 +184,7 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
             ty::TyProjection(..) |
             ty::TyForeign(..) |
             ty::TyParam(..) |
+            ty::TyClosure(..) |
             ty::TyAnon(..) => {
                 t.super_fold_with(self)
             }

src/librustc/infer/mod.rs

@@ -1338,26 +1338,17 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         !traits::type_known_to_meet_bound(self, param_env, ty, copy_def_id, span)
     }
 
+    /// Obtains the latest type of the given closure; this may be a
+    /// closure in the current function, in which case its
+    /// `ClosureKind` may not yet be known.
     pub fn closure_kind(&self,
-                        def_id: DefId)
+                        closure_def_id: DefId,
+                        closure_substs: ty::ClosureSubsts<'tcx>)
                         -> Option<ty::ClosureKind>
     {
-        if let Some(tables) = self.in_progress_tables {
-            if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
-                let hir_id = self.tcx.hir.node_to_hir_id(id);
-                return tables.borrow()
-                             .closure_kinds()
-                             .get(hir_id)
-                             .cloned()
-                             .map(|(kind, _)| kind);
-            }
-        }
-
-        // During typeck, ALL closures are local. But afterwards,
-        // during trans, we see closure ids from other traits.
-        // That may require loading the closure data out of the
-        // cstore.
-        Some(self.tcx.closure_kind(def_id))
+        let closure_kind_ty = closure_substs.closure_kind_ty(closure_def_id, self.tcx);
+        let closure_kind_ty = self.shallow_resolve(&closure_kind_ty);
+        closure_kind_ty.to_opt_closure_kind()
     }
 
     /// Obtain the signature of a function or closure.
@@ -1368,27 +1359,22 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         if let Some(tables) = self.in_progress_tables {
             if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
                 let hir_id = self.tcx.hir.node_to_hir_id(id);
-                if let Some(&ty) = tables.borrow().closure_tys().get(hir_id) {
-                    return ty;
-                }
+                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)
     }
-
-    pub fn generator_sig(&self, def_id: DefId) -> Option<ty::PolyGenSig<'tcx>> {
-        if let Some(tables) = self.in_progress_tables {
-            if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
-                let hir_id = self.tcx.hir.node_to_hir_id(id);
-                if let Some(&ty) = tables.borrow().generator_sigs().get(hir_id) {
-                    return ty.map(|t| ty::Binder(t));
-                }
-            }
-        }
-
-        self.tcx.generator_sig(def_id)
-    }
 }
 
 impl<'a, 'gcx, 'tcx> TypeTrace<'tcx> {

src/librustc/infer/type_variable.rs

@@ -56,7 +56,10 @@ pub enum TypeVariableOrigin {
     NormalizeProjectionType(Span),
     TypeInference(Span),
     TypeParameterDefinition(Span, ast::Name),
-    TransformedUpvar(Span),
+
+    /// one of the upvars or closure kind parameters in a `ClosureSubsts`
+    /// (before it has been determined)
+    ClosureSynthetic(Span),
     SubstitutionPlaceholder(Span),
     AutoDeref(Span),
     AdjustmentType(Span),

src/librustc/lib.rs

@@ -49,13 +49,15 @@
 #![feature(inclusive_range_syntax)]
 #![cfg_attr(windows, feature(libc))]
 #![feature(macro_vis_matcher)]
+#![feature(match_default_bindings)]
 #![feature(never_type)]
 #![feature(nonzero)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_patterns)]
 #![feature(specialization)]
 #![feature(unboxed_closures)]
+#![feature(underscore_lifetimes)]
 #![feature(trace_macros)]
 #![feature(test)]
 #![feature(const_atomic_bool_new)]

src/librustc/middle/mem_categorization.rs

@@ -750,10 +750,19 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
 
         let kind = match self.node_ty(fn_hir_id)?.sty {
             ty::TyGenerator(..) => ty::ClosureKind::FnOnce,
-            ty::TyClosure(..) => {
-                match self.tables.closure_kinds().get(fn_hir_id) {
-                    Some(&(kind, _)) => kind,
-                    None => span_bug!(span, "missing closure kind"),
+            ty::TyClosure(closure_def_id, closure_substs) => {
+                match self.infcx {
+                    // During upvar inference we may not know the
+                    // closure kind, just use the LATTICE_BOTTOM value.
+                    Some(infcx) =>
+                        infcx.closure_kind(closure_def_id, closure_substs)
+                             .unwrap_or(ty::ClosureKind::LATTICE_BOTTOM),
+
+                    None =>
+                        self.tcx.global_tcx()
+                                .lift(&closure_substs)
+                                .expect("no inference cx, but inference variables in closure ty")
+                                .closure_kind(closure_def_id, self.tcx.global_tcx()),
                 }
             }
             ref t => span_bug!(span, "unexpected type for fn in mem_categorization: {:?}", t),

src/librustc/traits/error_reporting.rs

@@ -661,8 +661,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                                             violations)
                     }
 
-                    ty::Predicate::ClosureKind(closure_def_id, kind) => {
-                        let found_kind = self.closure_kind(closure_def_id).unwrap();
+                    ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
+                        let found_kind = self.closure_kind(closure_def_id, closure_substs).unwrap();
                         let closure_span = self.tcx.hir.span_if_local(closure_def_id).unwrap();
                         let node_id = self.tcx.hir.as_local_node_id(closure_def_id).unwrap();
                         let mut err = struct_span_err!(
@@ -681,14 +681,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         if let Some(tables) = self.in_progress_tables {
                             let tables = tables.borrow();
                             let closure_hir_id = self.tcx.hir.node_to_hir_id(node_id);
-                            match tables.closure_kinds().get(closure_hir_id) {
-                                Some(&(ty::ClosureKind::FnOnce, Some((span, name)))) => {
-                                    err.span_note(span, &format!(
+                            match (found_kind, tables.closure_kind_origins().get(closure_hir_id)) {
+                                (ty::ClosureKind::FnOnce, Some((span, name))) => {
+                                    err.span_note(*span, &format!(
                                         "closure is `FnOnce` because it moves the \
                                          variable `{}` out of its environment", name));
                                 },
-                                Some(&(ty::ClosureKind::FnMut, Some((span, name)))) => {
-                                    err.span_note(span, &format!(
+                                (ty::ClosureKind::FnMut, Some((span, name))) => {
+                                    err.span_note(*span, &format!(
                                         "closure is `FnMut` because it mutates the \
                                          variable `{}` here", name));
                                 },

src/librustc/traits/fulfill.rs

@@ -491,8 +491,8 @@ fn process_predicate<'a, 'gcx, 'tcx>(
             }
         }
 
-        ty::Predicate::ClosureKind(closure_def_id, kind) => {
-            match selcx.infcx().closure_kind(closure_def_id) {
+        ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
+            match selcx.infcx().closure_kind(closure_def_id, closure_substs) {
                 Some(closure_kind) => {
                     if closure_kind.extends(kind) {
                         Ok(Some(vec![]))

src/librustc/traits/project.rs

@@ -1264,8 +1264,7 @@ fn confirm_generator_candidate<'cx, 'gcx, 'tcx>(
     vtable: VtableGeneratorData<'tcx, PredicateObligation<'tcx>>)
     -> Progress<'tcx>
 {
-    let gen_sig = selcx.infcx().generator_sig(vtable.closure_def_id).unwrap()
-        .subst(selcx.tcx(), vtable.substs.substs);
+    let gen_sig = vtable.substs.generator_poly_sig(vtable.closure_def_id, selcx.tcx());
     let Normalized {
         value: gen_sig,
         obligations