Begin to implement type system layer of unsafe binders

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -263,7 +263,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                         &self,
                         negative_impls,
                         span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
-                        "negative trait bounds are not yet fully implemented; \
+                        "negative trait bounds are not fully implemented; \
                          use marker types for now"
                     );
                 }

compiler/rustc_borrowck/src/lib.rs

@@ -1602,6 +1602,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     | ty::CoroutineWitness(..)
                     | ty::Never
                     | ty::Tuple(_)
+                    | ty::UnsafeBinder(_)
                     | ty::Alias(_, _)
                     | ty::Param(_)
                     | ty::Bound(_, _)
@@ -1643,6 +1644,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     | ty::Dynamic(_, _, _)
                     | ty::CoroutineWitness(..)
                     | ty::Never
+                    | ty::UnsafeBinder(_)
                     | ty::Alias(_, _)
                     | ty::Param(_)
                     | ty::Bound(_, _)

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -432,6 +432,7 @@ fn push_debuginfo_type_name<'tcx>(
                 push_closure_or_coroutine_name(tcx, def_id, args, qualified, output, visited);
             }
         }
+        ty::UnsafeBinder(_) => todo!("FIXME(unsafe_binders)"),
         ty::Param(_)
         | ty::Error(_)
         | ty::Infer(_)

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -178,7 +178,8 @@ fn const_to_valtree_inner<'tcx>(
         | ty::Closure(..)
         | ty::CoroutineClosure(..)
         | ty::Coroutine(..)
-        | ty::CoroutineWitness(..) => Err(ValTreeCreationError::NonSupportedType(ty)),
+        | ty::CoroutineWitness(..)
+        | ty::UnsafeBinder(_) => Err(ValTreeCreationError::NonSupportedType(ty)),
     }
 }
 
@@ -358,7 +359,10 @@ pub fn valtree_to_const_value<'tcx>(
         | ty::FnPtr(..)
         | ty::Str
         | ty::Slice(_)
-        | ty::Dynamic(..) => bug!("no ValTree should have been created for type {:?}", ty.kind()),
+        | ty::Dynamic(..)
+        | ty::UnsafeBinder(_) => {
+            bug!("no ValTree should have been created for type {:?}", ty.kind())
+        }
     }
 }
 

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -90,6 +90,7 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
             | ty::CoroutineClosure(_, _)
             | ty::Coroutine(_, _)
             | ty::CoroutineWitness(..)
+            | ty::UnsafeBinder(_)
             | ty::Never
             | ty::Tuple(_)
             | ty::Error(_) => ConstValue::from_target_usize(0u64, &tcx),

compiler/rustc_const_eval/src/interpret/stack.rs

@@ -505,6 +505,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 // We don't want to do any queries, so there is not much we can do with ADTs.
                 ty::Adt(..) => false,
 
+                ty::UnsafeBinder(ty) => is_very_trivially_sized(ty.skip_binder()),
+
                 ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => false,
 
                 ty::Infer(ty::TyVar(_)) => false,

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -768,6 +768,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                 // Nothing to check.
                 interp_ok(true)
             }
+            ty::UnsafeBinder(_) => todo!("FIXME(unsafe_binder)"),
             // The above should be all the primitive types. The rest is compound, we
             // check them by visiting their fields/variants.
             ty::Adt(..)

compiler/rustc_const_eval/src/util/type_name.rs

@@ -38,7 +38,8 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
             | ty::FnPtr(..)
             | ty::Never
             | ty::Tuple(_)
-            | ty::Dynamic(_, _, _) => self.pretty_print_type(ty),
+            | ty::Dynamic(_, _, _)
+            | ty::UnsafeBinder(_) => self.pretty_print_type(ty),
 
             // Placeholders (all printed as `_` to uniformize them).
             ty::Param(_) | ty::Bound(..) | ty::Placeholder(_) | ty::Infer(_) | ty::Error(_) => {

compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs

@@ -178,7 +178,8 @@ impl<'tcx> InherentCollect<'tcx> {
             | ty::Ref(..)
             | ty::Never
             | ty::FnPtr(..)
-            | ty::Tuple(..) => self.check_primitive_impl(id, self_ty),
+            | ty::Tuple(..)
+            | ty::UnsafeBinder(_) => self.check_primitive_impl(id, self_ty),
             ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, _) | ty::Param(_) => {
                 Err(self.tcx.dcx().emit_err(errors::InherentNominal { span: item_span }))
             }

compiler/rustc_hir_analysis/src/coherence/orphan.rs

@@ -225,7 +225,8 @@ pub(crate) fn orphan_check_impl(
             | ty::FnDef(..)
             | ty::FnPtr(..)
             | ty::Never
-            | ty::Tuple(..) => (LocalImpl::Allow, NonlocalImpl::DisallowOther),
+            | ty::Tuple(..)
+            | ty::UnsafeBinder(_) => (LocalImpl::Allow, NonlocalImpl::DisallowOther),
 
             ty::Closure(..)
             | ty::CoroutineClosure(..)

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2318,13 +2318,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     self.lower_fn_ty(hir_ty.hir_id, bf.safety, bf.abi, bf.decl, None, Some(hir_ty)),
                 )
             }
-            hir::TyKind::UnsafeBinder(_binder) => {
-                let guar = self
-                    .dcx()
-                    .struct_span_err(hir_ty.span, "unsafe binders are not yet implemented")
-                    .emit();
-                Ty::new_error(tcx, guar)
-            }
+            hir::TyKind::UnsafeBinder(binder) => Ty::new_unsafe_binder(
+                tcx,
+                ty::Binder::bind_with_vars(
+                    self.lower_ty(binder.inner_ty),
+                    tcx.late_bound_vars(hir_ty.hir_id),
+                ),
+            ),
             hir::TyKind::TraitObject(bounds, lifetime, repr) => {
                 if let Some(guar) = self.prohibit_or_lint_bare_trait_object_ty(hir_ty) {
                     // Don't continue with type analysis if the `dyn` keyword is missing

compiler/rustc_hir_analysis/src/variance/constraints.rs

@@ -322,6 +322,11 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                 self.add_constraints_from_sig(current, sig_tys.with(hdr), variance);
             }
 
+            ty::UnsafeBinder(ty) => {
+                // FIXME(unsafe_binders): This is covariant, right?
+                self.add_constraints_from_ty(current, ty.skip_binder(), variance);
+            }
+
             ty::Error(_) => {
                 // we encounter this when walking the trait references for object
                 // types, where we use Error as the Self type

compiler/rustc_hir_typeck/src/cast.rs

@@ -116,6 +116,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Some(&f) => self.pointer_kind(f, span)?,
             },
 
+            ty::UnsafeBinder(_) => todo!("FIXME(unsafe_binder)"),
+
             // Pointers to foreign types are thin, despite being unsized
             ty::Foreign(..) => Some(PointerKind::Thin),
             // We should really try to normalize here.

compiler/rustc_hir_typeck/src/expr.rs

@@ -574,8 +574,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.check_expr_index(base, idx, expr, brackets_span)
             }
             ExprKind::Yield(value, _) => self.check_expr_yield(value, expr),
-            ExprKind::UnsafeBinderCast(kind, expr, ty) => {
-                self.check_expr_unsafe_binder_cast(kind, expr, ty, expected)
+            ExprKind::UnsafeBinderCast(kind, inner_expr, ty) => {
+                self.check_expr_unsafe_binder_cast(expr.span, kind, inner_expr, ty, expected)
             }
             ExprKind::Err(guar) => Ty::new_error(tcx, guar),
         }
@@ -1649,14 +1649,94 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     fn check_expr_unsafe_binder_cast(
         &self,
-        _kind: hir::UnsafeBinderCastKind,
-        expr: &'tcx hir::Expr<'tcx>,
-        _hir_ty: Option<&'tcx hir::Ty<'tcx>>,
-        _expected: Expectation<'tcx>,
+        span: Span,
+        kind: hir::UnsafeBinderCastKind,
+        inner_expr: &'tcx hir::Expr<'tcx>,
+        hir_ty: Option<&'tcx hir::Ty<'tcx>>,
+        expected: Expectation<'tcx>,
     ) -> Ty<'tcx> {
-        let guar =
-            self.dcx().struct_span_err(expr.span, "unsafe binders are not yet implemented").emit();
-        Ty::new_error(self.tcx, guar)
+        self.dcx().span_err(inner_expr.span, "unsafe binder casts are not fully implemented");
+
+        match kind {
+            hir::UnsafeBinderCastKind::Wrap => {
+                let ascribed_ty =
+                    hir_ty.map(|hir_ty| self.lower_ty_saving_user_provided_ty(hir_ty));
+                let expected_ty = expected.only_has_type(self);
+                let binder_ty = match (ascribed_ty, expected_ty) {
+                    (Some(ascribed_ty), Some(expected_ty)) => {
+                        self.demand_eqtype(inner_expr.span, expected_ty, ascribed_ty);
+                        expected_ty
+                    }
+                    (Some(ty), None) | (None, Some(ty)) => ty,
+                    // This will always cause a structural resolve error, but we do it
+                    // so we don't need to manually report an E0282 both on this codepath
+                    // and in the others; it all happens in `structurally_resolve_type`.
+                    (None, None) => self.next_ty_var(inner_expr.span),
+                };
+
+                let binder_ty = self.structurally_resolve_type(inner_expr.span, binder_ty);
+                let hint_ty = match *binder_ty.kind() {
+                    ty::UnsafeBinder(binder) => self.instantiate_binder_with_fresh_vars(
+                        inner_expr.span,
+                        infer::BoundRegionConversionTime::HigherRankedType,
+                        binder.into(),
+                    ),
+                    ty::Error(e) => Ty::new_error(self.tcx, e),
+                    _ => {
+                        let guar = self
+                            .dcx()
+                            .struct_span_err(
+                                hir_ty.map_or(span, |hir_ty| hir_ty.span),
+                                format!(
+                                    "`wrap_binder!()` can only wrap into unsafe binder, not {}",
+                                    binder_ty.sort_string(self.tcx)
+                                ),
+                            )
+                            .with_note("unsafe binders are the only valid output of wrap")
+                            .emit();
+                        Ty::new_error(self.tcx, guar)
+                    }
+                };
+
+                self.check_expr_has_type_or_error(inner_expr, hint_ty, |_| {});
+
+                binder_ty
+            }
+            hir::UnsafeBinderCastKind::Unwrap => {
+                let ascribed_ty =
+                    hir_ty.map(|hir_ty| self.lower_ty_saving_user_provided_ty(hir_ty));
+                let hint_ty = ascribed_ty.unwrap_or_else(|| self.next_ty_var(inner_expr.span));
+                // FIXME(unsafe_binders): coerce here if needed?
+                let binder_ty = self.check_expr_has_type_or_error(inner_expr, hint_ty, |_| {});
+
+                // Unwrap the binder. This will be ambiguous if it's an infer var, and will error
+                // if it's not an unsafe binder.
+                let binder_ty = self.structurally_resolve_type(inner_expr.span, binder_ty);
+                match *binder_ty.kind() {
+                    ty::UnsafeBinder(binder) => self.instantiate_binder_with_fresh_vars(
+                        inner_expr.span,
+                        infer::BoundRegionConversionTime::HigherRankedType,
+                        binder.into(),
+                    ),
+                    ty::Error(e) => Ty::new_error(self.tcx, e),
+                    _ => {
+                        let guar = self
+                            .dcx()
+                            .struct_span_err(
+                                hir_ty.map_or(inner_expr.span, |hir_ty| hir_ty.span),
+                                format!(
+                                    "expected unsafe binder, found {} as input of \
+                                    `unwrap_binder!()`",
+                                    binder_ty.sort_string(self.tcx)
+                                ),
+                            )
+                            .with_note("only an unsafe binder type can be unwrapped")
+                            .emit();
+                        Ty::new_error(self.tcx, guar)
+                    }
+                }
+            }
+        }
     }
 
     fn check_expr_array(

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -441,6 +441,7 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
             | ty::FnDef(..)
             | ty::FnPtr(..)
             | ty::Dynamic(..)
+            | ty::UnsafeBinder(_)
             | ty::Never
             | ty::Tuple(..)
             | ty::Alias(..)

compiler/rustc_lint/src/types.rs

@@ -1284,6 +1284,8 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                 FfiSafe
             }
 
+            ty::UnsafeBinder(_) => todo!("FIXME(unsafe_binder)"),
+
             ty::Param(..)
             | ty::Alias(ty::Projection | ty::Inherent | ty::Weak, ..)
             | ty::Infer(..)

compiler/rustc_middle/src/ty/context.rs

@@ -471,7 +471,8 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
             | ty::CoroutineClosure(..)
             | ty::Coroutine(_, _)
             | ty::Never
-            | ty::Tuple(_) => {
+            | ty::Tuple(_)
+            | ty::UnsafeBinder(_) => {
                 let simp = ty::fast_reject::simplify_type(
                     tcx,
                     self_ty,
@@ -2295,6 +2296,7 @@ impl<'tcx> TyCtxt<'tcx> {
                     Ref,
                     FnDef,
                     FnPtr,
+                    UnsafeBinder,
                     Placeholder,
                     Coroutine,
                     CoroutineWitness,

compiler/rustc_middle/src/ty/error.rs

@@ -191,6 +191,7 @@ impl<'tcx> Ty<'tcx> {
                 _ => "fn item".into(),
             },
             ty::FnPtr(..) => "fn pointer".into(),
+            ty::UnsafeBinder(_) => "unsafe binder".into(),
             ty::Dynamic(..) => "trait object".into(),
             ty::Closure(..) | ty::CoroutineClosure(..) => "closure".into(),
             ty::Coroutine(def_id, ..) => {

compiler/rustc_middle/src/ty/flags.rs

@@ -253,6 +253,12 @@ impl FlagComputation {
             &ty::FnPtr(sig_tys, _) => self.bound_computation(sig_tys, |computation, sig_tys| {
                 computation.add_tys(sig_tys.inputs_and_output);
             }),
+
+            &ty::UnsafeBinder(bound_ty) => {
+                self.bound_computation(bound_ty.into(), |computation, ty| {
+                    computation.add_ty(ty);
+                })
+            }
         }
     }
 

compiler/rustc_middle/src/ty/layout.rs

@@ -816,6 +816,11 @@ where
                     bug!("TyAndLayout::field({:?}): not applicable", this)
                 }
 
+                ty::UnsafeBinder(bound_ty) => {
+                    let ty = tcx.instantiate_bound_regions_with_erased(bound_ty.into());
+                    field_ty_or_layout(TyAndLayout { ty, ..this }, cx, i)
+                }
+
                 // Potentially-wide pointers.
                 ty::Ref(_, pointee, _) | ty::RawPtr(pointee, _) => {
                     assert!(i < this.fields.count());

compiler/rustc_middle/src/ty/print/mod.rs

@@ -291,6 +291,7 @@ fn characteristic_def_id_of_type_cached<'a>(
         | ty::Uint(_)
         | ty::Str
         | ty::FnPtr(..)
+        | ty::UnsafeBinder(_)
         | ty::Alias(..)
         | ty::Placeholder(..)
         | ty::Param(_)

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -695,6 +695,10 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                 }
             }
             ty::FnPtr(ref sig_tys, hdr) => p!(print(sig_tys.with(hdr))),
+            ty::UnsafeBinder(ref bound_ty) => {
+                // FIXME(unsafe_binders): Make this print `unsafe<>` rather than `for<>`.
+                self.wrap_binder(bound_ty, |ty, cx| cx.pretty_print_type(*ty))?;
+            }
             ty::Infer(infer_ty) => {
                 if self.should_print_verbose() {
                     p!(write("{:?}", ty.kind()));

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -393,6 +393,7 @@ impl<'tcx> TypeSuperFoldable<TyCtxt<'tcx>> for Ty<'tcx> {
             ty::Tuple(ts) => ty::Tuple(ts.try_fold_with(folder)?),
             ty::FnDef(def_id, args) => ty::FnDef(def_id, args.try_fold_with(folder)?),
             ty::FnPtr(sig_tys, hdr) => ty::FnPtr(sig_tys.try_fold_with(folder)?, hdr),
+            ty::UnsafeBinder(f) => ty::UnsafeBinder(f.try_fold_with(folder)?),
             ty::Ref(r, ty, mutbl) => {
                 ty::Ref(r.try_fold_with(folder)?, ty.try_fold_with(folder)?, mutbl)
             }
@@ -443,6 +444,7 @@ impl<'tcx> TypeSuperVisitable<TyCtxt<'tcx>> for Ty<'tcx> {
             ty::Tuple(ts) => ts.visit_with(visitor),
             ty::FnDef(_, args) => args.visit_with(visitor),
             ty::FnPtr(ref sig_tys, _) => sig_tys.visit_with(visitor),
+            ty::UnsafeBinder(ref f) => f.visit_with(visitor),
             ty::Ref(r, ty, _) => {
                 try_visit!(r.visit_with(visitor));
                 ty.visit_with(visitor)