Auto merge of #58583 - varkor:const-generics-ty, r=oli-obk

Add const generics to ty (and transitive dependencies)

Split out from #53645. This work is a collaborative effort with @yodaldevoid.

There are a number of stubs. Some I plan to leave for the next PRs (e.g. `infer` and `rustdoc`). Others I can either fix up in this PR, or as follow ups (which would avoid the time-consuming rebasing).

It was a little hard to split this up, as so much depends on ty and friends. Apologies for the large diff.

r? @eddyb

src/librustc/ich/impls_ty.rs

@@ -74,6 +74,7 @@ for ty::subst::UnpackedKind<'gcx> {
         match self {
             ty::subst::UnpackedKind::Lifetime(lt) => lt.hash_stable(hcx, hasher),
             ty::subst::UnpackedKind::Type(ty) => ty.hash_stable(hcx, hasher),
+            ty::subst::UnpackedKind::Const(ct) => ct.hash_stable(hcx, hasher),
         }
     }
 }
@@ -134,6 +135,15 @@ impl<'a> HashStable<StableHashingContext<'a>> for ty::RegionVid {
     }
 }
 
+impl<'gcx, 'tcx> HashStable<StableHashingContext<'gcx>> for ty::ConstVid<'tcx> {
+    #[inline]
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        self.index.hash_stable(hcx, hasher);
+    }
+}
+
 impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::BoundVar {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,
@@ -297,6 +307,14 @@ impl<'a> HashStable<StableHashingContext<'a>> for ty::VariantFlags {
     }
 }
 
+impl_stable_hash_for!(
+    impl<'tcx> for enum ty::InferConst<'tcx> [ ty::InferConst ] {
+        Var(vid),
+        Fresh(i),
+        Canonical(debruijn, var),
+    }
+);
+
 impl_stable_hash_for!(enum ty::VariantDiscr {
     Explicit(def_id),
     Relative(distance)
@@ -310,11 +328,14 @@ impl_stable_hash_for!(struct ty::FieldDef {
 
 impl_stable_hash_for!(
     impl<'tcx> for enum mir::interpret::ConstValue<'tcx> [ mir::interpret::ConstValue ] {
+        Param(param),
+        Infer(infer),
         Scalar(val),
         Slice(a, b),
         ByRef(ptr, alloc),
     }
 );
+
 impl_stable_hash_for!(struct crate::mir::interpret::RawConst<'tcx> {
     alloc_id,
     ty,
@@ -518,6 +539,7 @@ impl_stable_hash_for!(struct ty::GenericParamDef {
 impl_stable_hash_for!(enum ty::GenericParamDefKind {
     Lifetime,
     Type { has_default, object_lifetime_default, synthetic },
+    Const,
 });
 
 impl_stable_hash_for!(
@@ -736,6 +758,11 @@ for ty::FloatVid
     }
 }
 
+impl_stable_hash_for!(struct ty::ParamConst {
+    index,
+    name
+});
+
 impl_stable_hash_for!(struct ty::ParamTy {
     idx,
     name

src/librustc/infer/canonical/mod.rs

@@ -443,6 +443,9 @@ impl<'tcx> CanonicalVarValues<'tcx> {
                     UnpackedKind::Lifetime(..) => tcx.mk_region(
                         ty::ReLateBound(ty::INNERMOST, ty::BoundRegion::BrAnon(i))
                     ).into(),
+                    UnpackedKind::Const(..) => {
+                        unimplemented!() // FIXME(const_generics)
+                    }
                 })
                 .collect()
         }

src/librustc/infer/canonical/query_response.rs

@@ -315,6 +315,10 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
                     obligations.extend(ok.into_obligations());
                 }
 
+                (UnpackedKind::Const(..), UnpackedKind::Const(..)) => {
+                    unimplemented!() // FIXME(const_generics)
+                }
+
                 _ => {
                     bug!(
                         "kind mismatch, cannot unify {:?} and {:?}",
@@ -473,6 +477,9 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
                         opt_values[br.assert_bound_var()] = Some(*original_value);
                     }
                 }
+                UnpackedKind::Const(..) => {
+                    unimplemented!() // FIXME(const_generics)
+                }
             }
         }
 
@@ -568,6 +575,11 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
                                 ty::OutlivesPredicate(t1, r2)
                             )
                         ),
+                        UnpackedKind::Const(..) => {
+                            // Consts cannot outlive one another, so we don't expect to
+                            // ecounter this branch.
+                            span_bug!(cause.span, "unexpected const outlives {:?}", constraint);
+                        }
                     }
                 )
             })
@@ -602,6 +614,9 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
                         obligations
                             .extend(self.at(cause, param_env).eq(v1, v2)?.into_obligations());
                     }
+                    (UnpackedKind::Const(..), UnpackedKind::Const(..)) => {
+                        unimplemented!() // FIXME(const_generics)
+                    }
                     _ => {
                         bug!("kind mismatch, cannot unify {:?} and {:?}", value1, value2,);
                     }

src/librustc/infer/combine.rs

@@ -449,7 +449,7 @@ impl<'cx, 'gcx, 'tcx> TypeRelation<'cx, 'gcx, 'tcx> for Generalizer<'cx, 'gcx, '
 
                             let origin = *variables.var_origin(vid);
                             let new_var_id = variables.new_var(self.for_universe, false, origin);
-                            let u = self.tcx().mk_var(new_var_id);
+                            let u = self.tcx().mk_ty_var(new_var_id);
                             debug!("generalize: replacing original vid={:?} with new={:?}",
                                    vid, u);
                             return Ok(u);

src/librustc/infer/error_reporting/mod.rs

@@ -691,17 +691,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     ) -> SubstsRef<'tcx> {
         let generics = self.tcx.generics_of(def_id);
         let mut num_supplied_defaults = 0;
-        let mut type_params = generics
-            .params
-            .iter()
-            .rev()
-            .filter_map(|param| match param.kind {
-                ty::GenericParamDefKind::Lifetime => None,
-                ty::GenericParamDefKind::Type { has_default, .. } => {
-                    Some((param.def_id, has_default))
-                }
-            })
-            .peekable();
+        let mut type_params = generics.params.iter().rev().filter_map(|param| match param.kind {
+            ty::GenericParamDefKind::Lifetime => None,
+            ty::GenericParamDefKind::Type { has_default, .. } => Some((param.def_id, has_default)),
+            ty::GenericParamDefKind::Const => None, // FIXME(const_generics:defaults)
+        }).peekable();
         let has_default = {
             let has_default = type_params.peek().map(|(_, has_default)| has_default);
             *has_default.unwrap_or(&false)

src/librustc/infer/mod.rs

@@ -656,7 +656,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         type_variables
             .unsolved_variables()
             .into_iter()
-            .map(|t| self.tcx.mk_var(t))
+            .map(|t| self.tcx.mk_ty_var(t))
             .chain(
                 (0..int_unification_table.len())
                     .map(|i| ty::IntVid { index: i as u32 })
@@ -981,7 +981,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
-        self.tcx.mk_var(self.next_ty_var_id(false, origin))
+        self.tcx.mk_ty_var(self.next_ty_var_id(false, origin))
     }
 
     pub fn next_ty_var_in_universe(
@@ -992,11 +992,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         let vid = self.type_variables
             .borrow_mut()
             .new_var(universe, false, origin);
-        self.tcx.mk_var(vid)
+        self.tcx.mk_ty_var(vid)
     }
 
     pub fn next_diverging_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
-        self.tcx.mk_var(self.next_ty_var_id(true, origin))
+        self.tcx.mk_ty_var(self.next_ty_var_id(true, origin))
     }
 
     pub fn next_int_var_id(&self) -> IntVid {
@@ -1081,7 +1081,10 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     TypeVariableOrigin::TypeParameterDefinition(span, param.name),
                 );
 
-                self.tcx.mk_var(ty_var_id).into()
+                self.tcx.mk_ty_var(ty_var_id).into()
+            }
+            GenericParamDefKind::Const { .. } => {
+                unimplemented!() // FIXME(const_generics)
             }
         }
     }

src/librustc/infer/nll_relate/mod.rs

@@ -310,7 +310,7 @@ where
             ty::Projection(projection_ty)
                 if D::normalization() == NormalizationStrategy::Lazy =>
             {
-                return Ok(self.relate_projection_ty(projection_ty, self.infcx.tcx.mk_var(vid)));
+                return Ok(self.relate_projection_ty(projection_ty, self.infcx.tcx.mk_ty_var(vid)));
             }
 
             _ => (),
@@ -764,7 +764,7 @@ where
                             // the universe `_universe`.
                             let new_var_id = variables.new_var(self.universe, false, origin);
 
-                            let u = self.tcx().mk_var(new_var_id);
+                            let u = self.tcx().mk_ty_var(new_var_id);
                             debug!(
                                 "generalize: replacing original vid={:?} with new={:?}",
                                 vid,

src/librustc/infer/opaque_types/mod.rs

@@ -381,10 +381,15 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         substs,
                         item_def_id: _,
                     }) => {
-                        for r in substs.regions() {
-                            bound_region(r);
+                        for k in substs {
+                            match k.unpack() {
+                                UnpackedKind::Lifetime(lt) => bound_region(lt),
+                                UnpackedKind::Type(ty) => types.push(ty),
+                                UnpackedKind::Const(_) => {
+                                    // Const parameters don't impose constraints.
+                                }
+                            }
                         }
-                        types.extend(substs.types());
                     }
 
                     Component::EscapingProjection(more_components) => {

src/librustc/infer/outlives/obligations.rs

@@ -67,6 +67,7 @@ use crate::hir;
 use crate::traits::ObligationCause;
 use crate::ty::outlives::Component;
 use crate::ty::{self, Region, Ty, TyCtxt, TypeFoldable};
+use crate::ty::subst::UnpackedKind;
 
 impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
     /// Registers that the given region obligation must be resolved
@@ -430,13 +431,18 @@ where
         if approx_env_bounds.is_empty() && trait_bounds.is_empty() && needs_infer {
             debug!("projection_must_outlive: no declared bounds");
 
-            for component_ty in projection_ty.substs.types() {
-                self.type_must_outlive(origin.clone(), component_ty, region);
-            }
-
-            for r in projection_ty.substs.regions() {
-                self.delegate
-                    .push_sub_region_constraint(origin.clone(), region, r);
+            for k in projection_ty.substs {
+                match k.unpack() {
+                    UnpackedKind::Lifetime(lt) => {
+                        self.delegate.push_sub_region_constraint(origin.clone(), region, lt);
+                    }
+                    UnpackedKind::Type(ty) => {
+                        self.type_must_outlive(origin.clone(), ty, region);
+                    }
+                    UnpackedKind::Const(_) => {
+                        // Const parameters don't impose constraints.
+                    }
+                }
             }
 
             return;

src/librustc/middle/resolve_lifetime.rs

@@ -1974,7 +1974,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
                                     object_lifetime_default,
                                     ..
                                 } => Some(object_lifetime_default),
-                                GenericParamDefKind::Lifetime => None,
+                                GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
                             })
                             .collect()
                     })

src/librustc/mir/interpret/value.rs

@@ -1,6 +1,6 @@
 use std::fmt;
 
-use crate::ty::{Ty, layout::{HasDataLayout, Size}};
+use crate::ty::{Ty, InferConst, ParamConst, layout::{HasDataLayout, Size}};
 
 use super::{EvalResult, Pointer, PointerArithmetic, Allocation, AllocId, sign_extend, truncate};
 
@@ -17,6 +17,12 @@ pub struct RawConst<'tcx> {
 /// match the `LocalState` optimizations for easy conversions between `Value` and `ConstValue`.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, RustcEncodable, RustcDecodable, Hash)]
 pub enum ConstValue<'tcx> {
+    /// A const generic parameter.
+    Param(ParamConst),
+
+    /// Infer the value of the const.
+    Infer(InferConst<'tcx>),
+
     /// Used only for types with `layout::abi::Scalar` ABI and ZSTs.
     ///
     /// Not using the enum `Value` to encode that this must not be `Undef`.
@@ -43,6 +49,8 @@ impl<'tcx> ConstValue<'tcx> {
     #[inline]
     pub fn try_to_scalar(&self) -> Option<Scalar> {
         match *self {
+            ConstValue::Param(_) |
+            ConstValue::Infer(_) |
             ConstValue::ByRef(..) |
             ConstValue::Slice(..) => None,
             ConstValue::Scalar(val) => Some(val),

src/librustc/traits/error_reporting.rs

@@ -389,7 +389,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         for param in generics.params.iter() {
             let value = match param.kind {
-                GenericParamDefKind::Type {..} => {
+                GenericParamDefKind::Type { .. } |
+                GenericParamDefKind::Const => {
                     trait_ref.substs[param.index as usize].to_string()
                 },
                 GenericParamDefKind::Lifetime => continue,

src/librustc/traits/mod.rs

@@ -1010,7 +1010,8 @@ fn vtable_methods<'a, 'tcx>(
                     InternalSubsts::for_item(tcx, def_id, |param, _|
                         match param.kind {
                             GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
-                            GenericParamDefKind::Type {..} => {
+                            GenericParamDefKind::Type { .. } |
+                            GenericParamDefKind::Const => {
                                 trait_ref.substs[param.index as usize]
                             }
                         }

src/librustc/traits/object_safety.rs

@@ -310,7 +310,8 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
         }
 
         // We can't monomorphize things like `fn foo<A>(...)`.
-        if self.generics_of(method.def_id).own_counts().types != 0 {
+        let own_counts = self.generics_of(method.def_id).own_counts();
+        if own_counts.types + own_counts.consts != 0 {
             return Some(MethodViolationCode::Generic);
         }
 

src/librustc/traits/on_unimplemented.rs

@@ -280,7 +280,8 @@ impl<'a, 'gcx, 'tcx> OnUnimplementedFormatString {
         let generics = tcx.generics_of(trait_ref.def_id);
         let generic_map = generics.params.iter().filter_map(|param| {
             let value = match param.kind {
-                GenericParamDefKind::Type {..} => {
+                GenericParamDefKind::Type { .. } |
+                GenericParamDefKind::Const => {
                     trait_ref.substs[param.index as usize].to_string()
                 },
                 GenericParamDefKind::Lifetime => return None