Use tuple inference

Use shallow_resolve and is_valid to check if tuple has been resolved
Check upvars_mentioned instead of substs to coerce closure to fnptr

Co-authored-by: Aman Arora <me@aman-arora.com>
Co-authored-by: Jenny Wills <wills.jenniferg@gmail.com>

compiler/rustc_middle/src/ty/outlives.rs

@@ -96,15 +96,25 @@ fn compute_components(
             }
 
             ty::Closure(_, ref substs) => {
-                for upvar_ty in substs.as_closure().upvar_tys() {
-                    compute_components(tcx, upvar_ty, out, visited);
+                if substs.as_closure().is_valid() {
+                    for upvar_ty in substs.as_closure().upvar_tys() {
+                        compute_components(tcx, upvar_ty, out, visited);
+                    }
+                } else {
+                    let tupled_ty = substs.as_closure().tupled_upvars_ty();
+                    compute_components(tcx, tupled_ty, out, visited);
                 }
             }
 
             ty::Generator(_, ref substs, _) => {
                 // Same as the closure case
-                for upvar_ty in substs.as_generator().upvar_tys() {
-                    compute_components(tcx, upvar_ty, out, visited);
+                if substs.as_generator().is_valid() {
+                    for upvar_ty in substs.as_generator().upvar_tys() {
+                        compute_components(tcx, upvar_ty, out, visited);
+                    }
+                } else {
+                    let tupled_ty = substs.as_generator().tupled_upvars_ty();
+                    compute_components(tcx, tupled_ty, out, visited);
                 }
 
                 // We ignore regions in the generator interior as we don't

compiler/rustc_middle/src/ty/sty.rs

@@ -656,6 +656,14 @@ impl<'tcx> UpvarSubsts<'tcx> {
         };
         tupled_upvars_ty.expect_ty().tuple_fields()
     }
+
+    #[inline]
+    pub fn tupled_upvars_ty(self) -> Ty<'tcx> {
+        match self {
+            UpvarSubsts::Closure(substs) => substs.as_closure().tupled_upvars_ty(),
+            UpvarSubsts::Generator(substs) => substs.as_generator().tupled_upvars_ty(),
+        }
+    }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, PartialOrd, Ord, Eq, Hash, TyEncodable, TyDecodable)]

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -440,6 +440,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
             for required_region in required_region_bounds {
                 concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
+                    infcx: self,
                     op: |r| self.sub_regions(infer::CallReturn(span), required_region, r),
                 });
             }
@@ -508,6 +509,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             }
         }
         concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
+            infcx: self,
             op: |r| self.sub_regions(infer::CallReturn(span), least_region, r),
         });
     }
@@ -542,6 +544,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         );
 
         concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
+            infcx: self,
             op: |r| {
                 self.member_constraint(
                     opaque_type_def_id,
@@ -682,11 +685,12 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 //
 // We ignore any type parameters because impl trait values are assumed to
 // capture all the in-scope type parameters.
-struct ConstrainOpaqueTypeRegionVisitor<OP> {
+struct ConstrainOpaqueTypeRegionVisitor<'cx, 'tcx, OP> {
+    infcx: &'cx InferCtxt<'cx, 'tcx>,
     op: OP,
 }
 
-impl<'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<OP>
+impl<'cx, 'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<'cx, 'tcx, OP>
 where
     OP: FnMut(ty::Region<'tcx>),
 {
@@ -716,24 +720,36 @@ 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);
-                }
+                let ty = self.infcx.shallow_resolve(substs.as_closure().tupled_upvars_ty());
+                if let ty::Infer(ty::TyVar(_)) = ty.kind() {
+                    // 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);
-                }
+                let ty = self.infcx.shallow_resolve(substs.as_generator().tupled_upvars_ty());
+                if let ty::Infer(ty::TyVar(_)) = ty.kind() {
+                    // 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);

compiler/rustc_trait_selection/src/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, _) => {

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1678,7 +1678,13 @@ 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().tupled_upvars_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(..) => {
@@ -1747,11 +1753,31 @@ 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().tupled_upvars_ty());
+                if let ty::Infer(ty::TyVar(_)) = ty.kind() {
+                    // The inference variable will be replaced by a tuple once capture analysis
+                    // completes. If the tuple meets a bound, so do all the elements within it.
+                    vec![ty]
+                } 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 upvar_tys_resolved =
+                    self.infcx.shallow_resolve(substs.as_generator().tupled_upvars_ty());
+
+                if let ty::Infer(ty::TyVar(_)) = upvar_tys_resolved.kind() {
+                    // The inference variable will be replaced by a tuple once capture analysis
+                    // completes, if the tuple meets a bound, so do all the elements within it.
+                    let witness_resolved =
+                        self.infcx.shallow_resolve(substs.as_generator().witness());
+                    vec![upvar_tys_resolved, witness_resolved]
+                } else {
+                    let witness = substs.as_generator().witness();
+                    substs.as_generator().upvar_tys().chain(iter::once(witness)).collect()
+                }
             }
 
             ty::GeneratorWitness(types) => {

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -530,10 +530,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     // 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());
-                    }
+                    self.compute(substs.as_closure().tupled_upvars_ty().into());
                 }
 
                 ty::FnPtr(_) => {

compiler/rustc_traits/src/dropck_outlives.rs

@@ -210,12 +210,20 @@ fn dtorck_constraint_for_ty<'tcx>(
             Ok::<_, NoSolution>(())
         })?,
 
-        ty::Closure(_, substs) => rustc_data_structures::stack::ensure_sufficient_stack(|| {
-            for ty in substs.as_closure().upvar_tys() {
-                dtorck_constraint_for_ty(tcx, span, for_ty, depth + 1, ty, constraints)?;
+        ty::Closure(_, substs) => {
+            if !substs.as_closure().is_valid() {
+                // By the time this code runs, all type variables ought to
+                // be fully resolved.
+                return Err(NoSolution);
             }
-            Ok::<_, NoSolution>(())
-        })?,
+
+            rustc_data_structures::stack::ensure_sufficient_stack(|| {
+                for ty in substs.as_closure().upvar_tys() {
+                    dtorck_constraint_for_ty(tcx, span, for_ty, depth + 1, ty, constraints)?;
+                }
+                Ok::<_, NoSolution>(())
+            })?
+        }
 
         ty::Generator(_, substs, _movability) => {
             // rust-lang/rust#49918: types can be constructed, stored
@@ -241,6 +249,12 @@ fn dtorck_constraint_for_ty<'tcx>(
             // derived from lifetimes attached to the upvars and resume
             // argument, and we *do* incorporate those here.
 
+            if !substs.as_generator().is_valid() {
+                // By the time this code runs, all type variables ought to
+                // be fully resolved.
+                return Err(NoSolution);
+            }
+
             constraints.outlives.extend(
                 substs
                     .as_generator()

compiler/rustc_typeck/src/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
         {

compiler/rustc_typeck/src/check/coercion.rs

@@ -39,6 +39,7 @@ use crate::astconv::AstConv;
 use crate::check::FnCtxt;
 use rustc_errors::{struct_span_err, Applicability, 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 +774,18 @@ 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())
+                    .map_or(true, |u| u.is_empty()) =>
+            {
                 // We coerce the closure, which has fn type
                 //     `extern "rust-call" fn((arg0,arg1,...)) -> _`
                 // to
@@ -906,8 +919,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // Function items or non-capturing closures of differing IDs or InternalSubsts.
         let (a_sig, b_sig) = {
             let is_capturing_closure = |ty| {
-                if let &ty::Closure(_, substs) = ty {
-                    substs.as_closure().upvar_tys().next().is_some()
+                if let &ty::Closure(closure_def_id, _substs) = ty {
+                    self.tcx.upvars_mentioned(closure_def_id.expect_local()).is_some()
                 } else {
                     false
                 }

compiler/rustc_typeck/src/check/upvar.rs

@@ -202,9 +202,11 @@ 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_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
+        self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
 
         // If we are also inferred the closure kind here,
         // process any deferred resolutions.

src/test/ui/async-await/issue-70818.stderr

@@ -1,17 +1,21 @@
-error: future cannot be sent between threads safely
+error[E0277]: `U` cannot be sent between threads safely
   --> $DIR/issue-70818.rs:4:38
    |
 LL | fn foo<T: Send, U>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + Send {
-   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `U` cannot be sent between threads safely
 LL |
 LL |     async { (ty, ty1) }
    |     ------------------- this returned value is of type `impl Future`
+   | 
+  ::: $SRC_DIR/core/src/future/mod.rs:LL:COL
    |
-note: captured value is not `Send`
-  --> $DIR/issue-70818.rs:6:18
+LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
+   |                                           ------------------------------- within this `impl Future`
    |
-LL |     async { (ty, ty1) }
-   |                  ^^^ has type `U` which is not `Send`
+   = note: required because it appears within the type `(T, U)`
+   = note: required because it appears within the type `[static generator@$DIR/issue-70818.rs:6:11: 6:24 _]`
+   = note: required because it appears within the type `from_generator::GenFuture<[static generator@$DIR/issue-70818.rs:6:11: 6:24 _]>`
+   = note: required because it appears within the type `impl Future`
    = note: the return type of a function must have a statically known size
 help: consider restricting type parameter `U`
    |
@@ -20,3 +24,4 @@ LL | fn foo<T: Send, U: Send>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + S
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/closures/closure-move-sync.stderr

@@ -11,6 +11,7 @@ LL |     F: Send + 'static,
    |
    = help: the trait `Sync` is not implemented for `std::sync::mpsc::Receiver<()>`
    = note: required because of the requirements on the impl of `Send` for `&std::sync::mpsc::Receiver<()>`
+   = note: required because it appears within the type `(&std::sync::mpsc::Receiver<()>,)`
    = note: required because it appears within the type `[closure@$DIR/closure-move-sync.rs:6:27: 9:6]`
 
 error[E0277]: `Sender<()>` cannot be shared between threads safely
@@ -26,6 +27,7 @@ LL |     F: Send + 'static,
    |
    = help: the trait `Sync` is not implemented for `Sender<()>`
    = note: required because of the requirements on the impl of `Send` for `&Sender<()>`
+   = note: required because it appears within the type `(&Sender<()>,)`
    = note: required because it appears within the type `[closure@$DIR/closure-move-sync.rs:18:19: 18:42]`
 
 error: aborting due to 2 previous errors