Use tuple inference for closures

src/librustc_middle/ty/sty.rs

@@ -373,6 +373,11 @@ impl<'tcx> ClosureSubsts<'tcx> {
         self.split().tupled_upvars_ty.expect_ty().tuple_fields()
     }
 
+    #[inline]
+    pub fn upvar_tuple_ty(self) -> Ty<'tcx> {
+        self.split().tupled_upvars_ty.expect_ty()
+    }
+
     /// Returns the closure kind for this closure; may return a type
     /// variable during inference. To get the closure kind during
     /// inference, use `infcx.closure_kind(substs)`.
@@ -488,6 +493,11 @@ impl<'tcx> GeneratorSubsts<'tcx> {
         self.split().tupled_upvars_ty.expect_ty().tuple_fields()
     }
 
+    #[inline]
+    pub fn upvar_tuple_ty(self) -> Ty<'tcx> {
+        self.split().tupled_upvars_ty.expect_ty()
+    }
+
     /// Returns the type representing the resume type of the generator.
     pub fn resume_ty(self) -> Ty<'tcx> {
         self.split().resume_ty.expect_ty()
@@ -630,6 +640,15 @@ impl<'tcx> UpvarSubsts<'tcx> {
         };
         tupled_upvars_ty.expect_ty().tuple_fields()
     }
+
+    #[inline]
+    pub fn upvar_tuple_ty(self) -> Ty<'tcx> {
+        let tupled_upvars_ty = match self {
+            UpvarSubsts::Closure(substs) => substs.as_closure().split().tupled_upvars_ty,
+            UpvarSubsts::Generator(substs) => substs.as_generator().split().tupled_upvars_ty,
+        };
+        tupled_upvars_ty.expect_ty()
+    }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, PartialOrd, Ord, Eq, Hash, RustcEncodable, RustcDecodable)]

src/librustc_trait_selection/opaque_types.rs

@@ -716,24 +716,34 @@ where
             ty::Closure(_, ref substs) => {
                 // Skip lifetime parameters of the enclosing item(s)
 
-                for upvar_ty in substs.as_closure().upvar_tys() {
-                    upvar_ty.visit_with(self);
-                }
+                if !substs.as_closure().is_valid() {
+                    // Not yet resolved.
+                    ty.super_visit_with(self);
+                } else {
+                    for upvar_ty in substs.as_closure().upvar_tys() {
+                        upvar_ty.visit_with(self);
+                    }
 
-                substs.as_closure().sig_as_fn_ptr_ty().visit_with(self);
+                    substs.as_closure().sig_as_fn_ptr_ty().visit_with(self);
+                }
             }
 
             ty::Generator(_, ref substs, _) => {
                 // Skip lifetime parameters of the enclosing item(s)
                 // Also skip the witness type, because that has no free regions.
 
-                for upvar_ty in substs.as_generator().upvar_tys() {
-                    upvar_ty.visit_with(self);
-                }
+                if !substs.as_generator().is_valid() {
+                    // Not yet resolved.
+                    ty.super_visit_with(self);
+                } else {
+                    for upvar_ty in substs.as_generator().upvar_tys() {
+                        upvar_ty.visit_with(self);
+                    }
 
-                substs.as_generator().return_ty().visit_with(self);
-                substs.as_generator().yield_ty().visit_with(self);
-                substs.as_generator().resume_ty().visit_with(self);
+                    substs.as_generator().return_ty().visit_with(self);
+                    substs.as_generator().yield_ty().visit_with(self);
+                    substs.as_generator().resume_ty().visit_with(self);
+                }
             }
             _ => {
                 ty.super_visit_with(self);

src/librustc_trait_selection/traits/query/dropck_outlives.rs

@@ -110,7 +110,12 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         // check if *any* of those are trivial.
         ty::Tuple(ref tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t.expect_ty())),
         ty::Closure(_, ref substs) => {
-            substs.as_closure().upvar_tys().all(|t| trivial_dropck_outlives(tcx, t))
+            if !substs.as_closure().is_valid() {
+                // Not yet resolved.
+                false
+            } else {
+                substs.as_closure().upvar_tys().all(|t| trivial_dropck_outlives(tcx, t))
+            }
         }
 
         ty::Adt(def, _) => {

src/librustc_trait_selection/traits/select/mod.rs

@@ -1632,7 +1632,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             ty::Closure(_, substs) => {
                 // (*) binder moved here
-                Where(ty::Binder::bind(substs.as_closure().upvar_tys().collect()))
+                let ty = self.infcx.shallow_resolve(substs.as_closure().upvar_tuple_ty());
+                if let ty::Infer(ty::TyVar(_)) = ty.kind {
+                    // Not yet resolved.
+                    Ambiguous
+                } else {
+                    Where(ty::Binder::bind(substs.as_closure().upvar_tys().collect()))
+                }
             }
 
             ty::Adt(..) | ty::Projection(..) | ty::Param(..) | ty::Opaque(..) => {
@@ -1701,11 +1707,27 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 tys.iter().map(|k| k.expect_ty()).collect()
             }
 
-            ty::Closure(_, ref substs) => substs.as_closure().upvar_tys().collect(),
+            ty::Closure(_, ref substs) => {
+                let ty = self.infcx.shallow_resolve(substs.as_closure().upvar_tuple_ty());
+                if let ty::Infer(ty::TyVar(_)) = ty.kind {
+                    // Not yet resolved.
+                    warn!("asked to assemble constituent types of unexpected type: {:?}", t);
+                    Vec::new()
+                } else {
+                    substs.as_closure().upvar_tys().collect()
+                }
+            }
 
             ty::Generator(_, ref substs, _) => {
-                let witness = substs.as_generator().witness();
-                substs.as_generator().upvar_tys().chain(iter::once(witness)).collect()
+                let ty = self.infcx.shallow_resolve(substs.as_generator().upvar_tuple_ty());
+                if let ty::Infer(ty::TyVar(_)) = ty.kind {
+                    // Not yet resolved.
+                    warn!("asked to assemble constituent types of unexpected type: {:?}", t);
+                    Vec::new()
+                } else {
+                    let witness = substs.as_generator().witness();
+                    substs.as_generator().upvar_tys().chain(iter::once(witness)).collect()
+                }
             }
 
             ty::GeneratorWitness(types) => {

src/librustc_trait_selection/traits/wf.rs

@@ -521,10 +521,17 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     // are not directly inspecting closure types
                     // anyway, except via auto trait matching (which
                     // only inspects the upvar types).
-                    walker.skip_current_subtree(); // subtree handled below
-                    for upvar_ty in substs.as_closure().upvar_tys() {
-                        // FIXME(eddyb) add the type to `walker` instead of recursing.
-                        self.compute(upvar_ty.into());
+                    let ty = self.infcx.shallow_resolve(substs.as_closure().upvar_tuple_ty());
+                    if let ty::Infer(ty::TyVar(_)) = ty.kind {
+                        // Not yet resolved.
+                        walker.skip_current_subtree();
+                        self.compute(ty.into());
+                    } else {
+                        walker.skip_current_subtree(); // subtree handled below
+                        for upvar_ty in substs.as_closure().upvar_tys() {
+                            // FIXME(eddyb) add the type to `walker` instead of recursing.
+                            self.compute(upvar_ty.into());
+                        }
                     }
                 }
 

src/librustc_typeck/check/closure.rs

@@ -81,19 +81,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.tcx.closure_base_def_id(expr_def_id.to_def_id()),
         );
 
-        let tupled_upvars_ty =
-            self.tcx.mk_tup(self.tcx.upvars_mentioned(expr_def_id).iter().flat_map(|upvars| {
-                upvars.iter().map(|(&var_hir_id, _)| {
-                    // Create type variables (for now) to represent the transformed
-                    // types of upvars. These will be unified during the upvar
-                    // inference phase (`upvar.rs`).
-                    self.infcx.next_ty_var(TypeVariableOrigin {
-                        // FIXME(eddyb) distinguish upvar inference variables from the rest.
-                        kind: TypeVariableOriginKind::ClosureSynthetic,
-                        span: self.tcx.hir().span(var_hir_id),
-                    })
-                })
-            }));
+        let tupled_upvars_ty = self.infcx.next_ty_var(TypeVariableOrigin {
+            // FIXME(eddyb) distinguish upvar inference variables from the rest.
+            kind: TypeVariableOriginKind::ClosureSynthetic,
+            span: self.tcx.hir().span(expr.hir_id),
+        });
 
         if let Some(GeneratorTypes { resume_ty, yield_ty, interior, movability }) = generator_types
         {

src/librustc_typeck/check/coercion.rs

@@ -39,6 +39,7 @@ use crate::astconv::AstConv;
 use crate::check::FnCtxt;
 use rustc_errors::{struct_span_err, DiagnosticBuilder};
 use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::{Coercion, InferOk, InferResult};
 use rustc_middle::ty::adjustment::{
@@ -221,11 +222,11 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 // unsafe qualifier.
                 self.coerce_from_fn_pointer(a, a_f, b)
             }
-            ty::Closure(_, substs_a) => {
+            ty::Closure(closure_def_id_a, substs_a) => {
                 // Non-capturing closures are coercible to
                 // function pointers or unsafe function pointers.
                 // It cannot convert closures that require unsafe.
-                self.coerce_closure_to_fn(a, substs_a, b)
+                self.coerce_closure_to_fn(a, closure_def_id_a, substs_a, b)
             }
             _ => {
                 // Otherwise, just use unification rules.
@@ -762,6 +763,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
     fn coerce_closure_to_fn(
         &self,
         a: Ty<'tcx>,
+        closure_def_id_a: DefId,
         substs_a: SubstsRef<'tcx>,
         b: Ty<'tcx>,
     ) -> CoerceResult<'tcx> {
@@ -772,7 +774,15 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         let b = self.shallow_resolve(b);
 
         match b.kind {
-            ty::FnPtr(fn_ty) if substs_a.as_closure().upvar_tys().next().is_none() => {
+            // At this point we haven't done capture analysis, which means
+            // that the ClosureSubsts just contains an inference variable instead
+            // of tuple of captured types.
+            //
+            // All we care here is if any variable is being captured and not the exact paths,
+            // so we check `upvars_mentioned` for root variables being captured.
+            ty::FnPtr(fn_ty)
+                if self.tcx.upvars_mentioned(closure_def_id_a.expect_local()).is_none() =>
+            {
                 // We coerce the closure, which has fn type
                 //     `extern "rust-call" fn((arg0,arg1,...)) -> _`
                 // to
@@ -907,7 +917,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let (a_sig, b_sig) = {
             let is_capturing_closure = |ty| {
                 if let &ty::Closure(_, substs) = ty {
-                    substs.as_closure().upvar_tys().next().is_some()
+                    let ty = self.infcx.shallow_resolve(substs.as_closure().upvar_tuple_ty());
+                    if let ty::Infer(ty::TyVar(_)) = ty.kind {
+                        substs.as_closure().upvar_tys().next().is_some()
+                    } else {
+                        false
+                    }
                 } else {
                     false
                 }

src/librustc_typeck/check/upvar.rs

@@ -201,9 +201,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
             closure_hir_id, substs, final_upvar_tys
         );
-        for (upvar_ty, final_upvar_ty) in substs.upvar_tys().zip(final_upvar_tys) {
-            self.demand_suptype(span, upvar_ty, final_upvar_ty);
-        }
+
+        // Build a tuple (U0..Un) of the final upvar types U0..Un
+        // and unify the upvar tupe type in the closure with it:
+        let final_upvar_tuple_type = self.tcx.mk_tup(final_upvar_tys.iter());
+        self.demand_suptype(span, substs.upvar_tuple_ty(), final_upvar_tuple_type);
 
         // If we are also inferred the closure kind here,
         // process any deferred resolutions.