Handle const generics in typeck

Co-Authored-By: Gabriel Smith <yodaldevoid@users.noreply.github.com>

src/librustc_typeck/check/closure.rs

@@ -99,11 +99,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         let substs = base_substs.extend_to(self.tcx,expr_def_id, |param, _| {
             match param.kind {
                 GenericParamDefKind::Lifetime => {
-                    span_bug!(expr.span, "closure has region param")
+                    span_bug!(expr.span, "closure has lifetime param")
                 }
-                GenericParamDefKind::Type {..} => {
-                    self.infcx
-                        .next_ty_var(TypeVariableOrigin::ClosureSynthetic(expr.span)).into()
+                GenericParamDefKind::Type { .. } => {
+                    self.infcx.next_ty_var(TypeVariableOrigin::ClosureSynthetic(expr.span)).into()
+                }
+                GenericParamDefKind::Const => {
+                    span_bug!(expr.span, "closure has const param")
                 }
             }
         });

src/librustc_typeck/check/dropck.rs

@@ -313,6 +313,9 @@ pub fn check_safety_of_destructor_if_necessary<'a, 'gcx, 'tcx>(
         match kind.unpack() {
             UnpackedKind::Lifetime(r) => rcx.sub_regions(origin(), parent_scope, r),
             UnpackedKind::Type(ty) => rcx.type_must_outlive(origin(), ty, parent_scope),
+            UnpackedKind::Const(_) => {
+                // Generic consts don't add constraints.
+            }
         }
     }
     Ok(())

src/librustc_typeck/check/method/confirm.rs

@@ -341,6 +341,9 @@ impl<'a, 'gcx, 'tcx> ConfirmContext<'a, 'gcx, 'tcx> {
                     (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
                         self.to_ty(ty).into()
                     }
+                    (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
+                        self.to_const(&ct.value, self.tcx.type_of(param.def_id)).into()
+                    }
                     _ => unreachable!(),
                 }
             },

src/librustc_typeck/check/method/mod.rs

@@ -283,8 +283,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         // Construct a trait-reference `self_ty : Trait<input_tys>`
         let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
             match param.kind {
-                GenericParamDefKind::Lifetime => {}
-                GenericParamDefKind::Type {..} => {
+                GenericParamDefKind::Lifetime | GenericParamDefKind::Const => {}
+                GenericParamDefKind::Type { .. } => {
                     if param.index == 0 {
                         return self_ty.into();
                     } else if let Some(ref input_types) = opt_input_types {

src/librustc_typeck/check/method/probe.rs

@@ -1528,7 +1528,10 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
                             // `impl_self_ty()` for an explanation.
                             self.tcx.types.re_erased.into()
                         }
-                        GenericParamDefKind::Type {..} => self.var_for_def(self.span, param),
+                        GenericParamDefKind::Type { .. }
+                        | GenericParamDefKind::Const => {
+                            self.var_for_def(self.span, param)
+                        }
                     }
                 }
             });
@@ -1545,10 +1548,13 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
         InternalSubsts::for_item(self.tcx, def_id, |param, _| {
             match param.kind {
                 GenericParamDefKind::Lifetime => self.tcx.types.re_erased.into(),
-                GenericParamDefKind::Type {..} => {
+                GenericParamDefKind::Type { .. } => {
                     self.next_ty_var(TypeVariableOrigin::SubstitutionPlaceholder(
                         self.tcx.def_span(def_id))).into()
                 }
+                GenericParamDefKind::Const { .. } => {
+                    unimplemented!() // FIXME(const_generics)
+                }
             }
         })
     }

src/librustc_typeck/check/mod.rs

@@ -2437,6 +2437,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         ty
     }
 
+    pub fn to_const(&self, ast_c: &hir::AnonConst, ty: Ty<'tcx>) -> &'tcx ty::LazyConst<'tcx> {
+        AstConv::ast_const_to_const(self, ast_c, ty)
+    }
+
     // If the type given by the user has free regions, save it for later, since
     // NLL would like to enforce those. Also pass in types that involve
     // projections, since those can resolve to `'static` bounds (modulo #54940,
@@ -5501,6 +5505,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
                         self.to_ty(ty).into()
                     }
+                    (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
+                        self.to_const(&ct.value, self.tcx.type_of(param.def_id)).into()
+                    }
                     _ => unreachable!(),
                 }
             },
@@ -5528,6 +5535,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             self.var_for_def(span, param)
                         }
                     }
+                    GenericParamDefKind::Const => {
+                        // FIXME(const_generics:defaults)
+                        // No const parameters were provided, we have to infer them.
+                        self.var_for_def(span, param)
+                    }
                 }
             },
         );
@@ -5685,11 +5697,19 @@ pub fn check_bounds_are_used<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                        generics: &ty::Generics,
                                        ty: Ty<'tcx>) {
     let own_counts = generics.own_counts();
-    debug!("check_bounds_are_used(n_tps={}, ty={:?})", own_counts.types, ty);
+    debug!(
+        "check_bounds_are_used(n_tys={}, n_cts={}, ty={:?})",
+        own_counts.types,
+        own_counts.consts,
+        ty
+    );
+
+    // FIXME(const_generics): we probably want to check the bounds for const parameters too.
 
     if own_counts.types == 0 {
         return;
     }
+
     // Make a vector of booleans initially false, set to true when used.
     let mut types_used = vec![false; own_counts.types];
 

src/librustc_typeck/constrained_type_params.rs

@@ -1,6 +1,7 @@
 use rustc::ty::{self, Ty, TyCtxt};
 use rustc::ty::fold::{TypeFoldable, TypeVisitor};
 use rustc::util::nodemap::FxHashSet;
+use rustc::mir::interpret::ConstValue;
 use syntax::source_map::Span;
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
@@ -14,6 +15,10 @@ impl From<ty::EarlyBoundRegion> for Parameter {
     fn from(param: ty::EarlyBoundRegion) -> Self { Parameter(param.index) }
 }
 
+impl From<ty::ParamConst> for Parameter {
+    fn from(param: ty::ParamConst) -> Self { Parameter(param.index) }
+}
+
 /// Returns the set of parameters constrained by the impl header.
 pub fn parameters_for_impl<'tcx>(impl_self_ty: Ty<'tcx>,
                                  impl_trait_ref: Option<ty::TraitRef<'tcx>>)
@@ -72,6 +77,16 @@ impl<'tcx> TypeVisitor<'tcx> for ParameterCollector {
         }
         false
     }
+
+    fn visit_const(&mut self, c: &'tcx ty::LazyConst<'tcx>) -> bool {
+        if let ty::LazyConst::Evaluated(ty::Const {
+            val: ConstValue::Param(data),
+            ..
+        }) = c {
+            self.parameters.push(Parameter::from(*data));
+        }
+        false
+    }
 }
 
 pub fn identify_constrained_type_params<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>,

src/librustc_typeck/impl_wf_check.rs

@@ -120,7 +120,7 @@ fn enforce_impl_params_are_constrained<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     for param in &impl_generics.params {
         match param.kind {
             // Disallow ANY unconstrained type parameters.
-            ty::GenericParamDefKind::Type {..} => {
+            ty::GenericParamDefKind::Type { .. } => {
                 let param_ty = ty::ParamTy::for_def(param);
                 if !input_parameters.contains(&ctp::Parameter::from(param_ty)) {
                     report_unused_parameter(tcx,
@@ -139,6 +139,15 @@ fn enforce_impl_params_are_constrained<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                             &param.name.to_string());
                 }
             }
+            ty::GenericParamDefKind::Const => {
+                let param_ct = ty::ParamConst::for_def(param);
+                if !input_parameters.contains(&ctp::Parameter::from(param_ct)) {
+                    report_unused_parameter(tcx,
+                                           tcx.def_span(param.def_id),
+                                           "const",
+                                           &param_ct.to_string());
+                }
+            }
         }
     }
 

src/librustc_typeck/outlives/mod.rs

@@ -98,14 +98,22 @@ fn inferred_outlives_crate<'tcx>(
         .map(|(&def_id, set)| {
             let vec: Vec<ty::Predicate<'tcx>> = set
                 .iter()
-                .map(
+                .filter_map(
                     |ty::OutlivesPredicate(kind1, region2)| match kind1.unpack() {
-                        UnpackedKind::Type(ty1) => ty::Predicate::TypeOutlives(ty::Binder::bind(
-                            ty::OutlivesPredicate(ty1, region2),
-                        )),
-                        UnpackedKind::Lifetime(region1) => ty::Predicate::RegionOutlives(
-                            ty::Binder::bind(ty::OutlivesPredicate(region1, region2)),
-                        ),
+                        UnpackedKind::Type(ty1) => {
+                            Some(ty::Predicate::TypeOutlives(ty::Binder::bind(
+                                ty::OutlivesPredicate(ty1, region2)
+                            )))
+                        }
+                        UnpackedKind::Lifetime(region1) => {
+                            Some(ty::Predicate::RegionOutlives(
+                                ty::Binder::bind(ty::OutlivesPredicate(region1, region2))
+                            ))
+                        }
+                        UnpackedKind::Const(_) => {
+                            // Generic consts don't impose any constraints.
+                            None
+                        }
                     },
                 ).collect();
             (def_id, Lrc::new(vec))

src/librustc_typeck/outlives/utils.rs

@@ -118,6 +118,10 @@ pub fn insert_outlives_predicate<'tcx>(
             }
             required_predicates.insert(ty::OutlivesPredicate(kind, outlived_region));
         }
+
+        UnpackedKind::Const(_) => {
+            // Generic consts don't impose any constraints.
+        }
     }
 }