add predicate evaluation logic

Author: BoxyUwU

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -9,8 +9,8 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_middle::ty::subst::InternalSubsts;
-use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{GenericPredicates, ToPredicate};
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{Span, DUMMY_SP};
 
@@ -151,7 +151,8 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
     trace!(?generics);
 
     // Collect the predicates that were written inline by the user on each
-    // type parameter (e.g., `<T: Foo>`).
+    // type parameter (e.g., `<T: Foo>`). Also add `ConstArgHasType` predicates
+    // for each const parameter.
     for param in ast_generics.params {
         match param.kind {
             // We already dealt with early bound lifetimes above.
@@ -175,7 +176,19 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
                 trace!(?predicates);
             }
             GenericParamKind::Const { .. } => {
-                // Bounds on const parameters are currently not possible.
+                let name = param.name.ident().name;
+                let param_const = ty::ParamConst::new(index, name);
+
+                let ct_ty = tcx.type_of(param.def_id.to_def_id()).subst_identity();
+
+                let ct = tcx.mk_const(param_const, ct_ty);
+
+                let predicate = ty::Binder::dummy(ty::PredicateKind::Clause(
+                    ty::Clause::ConstArgHasType(ct, ct_ty),
+                ))
+                .to_predicate(tcx);
+                predicates.insert((predicate, param.span));
+
                 index += 1;
             }
         }
@@ -439,7 +452,9 @@ pub(super) fn explicit_predicates_of<'tcx>(
             let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
             let parent_def_id = tcx.hir().get_parent_item(hir_id);
 
-            if tcx.hir().opt_const_param_default_param_def_id(hir_id).is_some() {
+            if let Some(defaulted_param_def_id) =
+                tcx.hir().opt_const_param_default_param_def_id(hir_id)
+            {
                 // In `generics_of` we set the generics' parent to be our parent's parent which means that
                 // we lose out on the predicates of our actual parent if we dont return those predicates here.
                 // (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
@@ -452,7 +467,39 @@ pub(super) fn explicit_predicates_of<'tcx>(
                 //
                 // In the above code we want the anon const to have predicates in its param env for `T: Trait`
                 // and we would be calling `explicit_predicates_of(Foo)` here
-                return tcx.explicit_predicates_of(parent_def_id);
+                let parent_preds = tcx.explicit_predicates_of(parent_def_id);
+
+                // If we dont filter out `ConstArgHasType` predicates then every single defaulted const parameter
+                // will ICE because of #106994. FIXME(generic_const_exprs): remove this when a more general solution
+                // to #106994 is implemented.
+                let filtered_predicates = parent_preds
+                    .predicates
+                    .into_iter()
+                    .filter(|(pred, _)| {
+                        if let ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, _)) =
+                            pred.kind().skip_binder()
+                        {
+                            match ct.kind() {
+                                ty::ConstKind::Param(param_const) => {
+                                    let defaulted_param_idx = tcx
+                                        .generics_of(parent_def_id)
+                                        .param_def_id_to_index[&defaulted_param_def_id.to_def_id()];
+                                    param_const.index < defaulted_param_idx
+                                }
+                                _ => bug!(
+                                    "`ConstArgHasType` in `predicates_of`\
+                                 that isn't a `Param` const"
+                                ),
+                            }
+                        } else {
+                            true
+                        }
+                    })
+                    .cloned();
+                return GenericPredicates {
+                    parent: parent_preds.parent,
+                    predicates: { tcx.arena.alloc_from_iter(filtered_predicates) },
+                };
             }
 
             let parent_def_kind = tcx.def_kind(parent_def_id);

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -496,6 +496,16 @@ fn check_specialization_on<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
                 )
                 .emit();
         }
+        ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..)) => {
+            // FIXME(min_specialization), FIXME(const_generics):
+            // It probably isn't right to allow _every_ `ConstArgHasType` but I am somewhat unsure
+            // about the actual rules that would be sound. Can't just always error here because otherwise
+            // std/core doesn't even compile as they have `const N: usize` in some specializing impls.
+            //
+            // While we do not support constructs like `<T, const N: T>` there is probably no risk of
+            // soundness bugs, but when we support generic const parameter types this will need to be
+            // revisited.
+        }
         _ => {
             tcx.sess
                 .struct_span_err(span, &format!("cannot specialize on predicate `{}`", predicate))

compiler/rustc_privacy/src/lib.rs

@@ -159,9 +159,21 @@ where
                 _region,
             ))) => ty.visit_with(self),
             ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..)) => ControlFlow::Continue(()),
+            ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => {
+                ct.visit_with(self)?;
+                ty.visit_with(self)
+            }
             ty::PredicateKind::ConstEvaluatable(ct) => ct.visit_with(self),
             ty::PredicateKind::WellFormed(arg) => arg.visit_with(self),
-            _ => bug!("unexpected predicate: {:?}", predicate),
+
+            ty::PredicateKind::ObjectSafe(_)
+            | ty::PredicateKind::ClosureKind(_, _, _)
+            | ty::PredicateKind::Subtype(_)
+            | ty::PredicateKind::Coerce(_)
+            | ty::PredicateKind::ConstEquate(_, _)
+            | ty::PredicateKind::TypeWellFormedFromEnv(_)
+            | ty::PredicateKind::Ambiguous
+            | ty::PredicateKind::AliasEq(_, _) => bug!("unexpected predicate: {:?}", predicate),
         }
     }
 

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -25,7 +25,7 @@ use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::Obligation;
 use rustc_middle::infer::canonical::Certainty as OldCertainty;
 use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData};
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::ty::{
     CoercePredicate, RegionOutlivesPredicate, SubtypePredicate, ToPredicate, TypeOutlivesPredicate,
 };
@@ -290,8 +290,8 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
                 ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => {
                     self.compute_region_outlives_goal(Goal { param_env, predicate })
                 }
-                ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..)) => {
-                    unimplemented!()
+                ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => {
+                    self.compute_const_arg_has_type_goal(Goal { param_env, predicate: (ct, ty) })
                 }
                 ty::PredicateKind::Subtype(predicate) => {
                     self.compute_subtype_goal(Goal { param_env, predicate })
@@ -474,6 +474,16 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
             }
         }
     }
+
+    #[instrument(level = "debug", skip(self), ret)]
+    fn compute_const_arg_has_type_goal(
+        &mut self,
+        goal: Goal<'tcx, (ty::Const<'tcx>, Ty<'tcx>)>,
+    ) -> QueryResult<'tcx> {
+        let (ct, ty) = goal.predicate;
+        let nested_goals = self.infcx.eq(goal.param_env, ct.ty(), ty)?;
+        self.evaluate_all_and_make_canonical_response(nested_goals)
+    }
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {

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

@@ -1283,9 +1283,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         "AliasEq predicate should never be the predicate cause of a SelectionError"
                     ),
 
-                    ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..)) => {
-                        // FIXME: don't know how selection error works so unsure when this is reachable (if it is)
-                        unimplemented!()
+                    ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => {
+                        self.tcx.sess.struct_span_err(
+                            span,
+                            &format!("the constant `{}` is not of type `{}`", ct, ty),
+                        )
                     }
                 }
             }

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -601,8 +601,18 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 ty::PredicateKind::AliasEq(..) => {
                     bug!("AliasEq is only used for new solver")
                 }
-                ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..)) => {
-                    unimplemented!()
+                ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => {
+                    match self
+                        .selcx
+                        .infcx
+                        .at(&obligation.cause, obligation.param_env)
+                        .eq(ct.ty(), ty)
+                    {
+                        Ok(inf_ok) => ProcessResult::Changed(mk_pending(inf_ok.into_obligations())),
+                        Err(_) => ProcessResult::Error(FulfillmentErrorCode::CodeSelectionError(
+                            SelectionError::Unimplemented,
+                        )),
+                    }
                 }
             },
         }

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

@@ -993,8 +993,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     bug!("AliasEq is only used for new solver")
                 }
                 ty::PredicateKind::Ambiguous => Ok(EvaluatedToAmbig),
-                ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..)) => {
-                    unimplemented!()
+                ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => {
+                    match self.infcx.at(&obligation.cause, obligation.param_env).eq(ct.ty(), ty) {
+                        Ok(inf_ok) => self.evaluate_predicates_recursively(
+                            previous_stack,
+                            inf_ok.into_obligations(),
+                        ),
+                        Err(_) => Ok(EvaluatedToErr),
+                    }
                 }
             }
         })

tests/ui/const-generics/nested-type.min.stderr

@@ -1,3 +1,11 @@
+error[E0015]: cannot call non-const fn `Foo::{constant#0}::Foo::<17>::value` in constants
+  --> $DIR/nested-type.rs:15:5
+   |
+LL |     Foo::<17>::value()
+   |     ^^^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+
 error: `[u8; {
            struct Foo<const N: usize>;
 
@@ -24,5 +32,6 @@ LL | | }]>;
    = note: the only supported types are integers, `bool` and `char`
    = help: more complex types are supported with `#![feature(adt_const_params)]`
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0015`.

tests/ui/const-generics/nested-type.rs

@@ -13,7 +13,7 @@ struct Foo<const N: [u8; { //[min]~ ERROR `[u8; _]` is forbidden
     }
 
     Foo::<17>::value()
-    //[full]~^ ERROR cannot call non-const fn
+    //~^ ERROR cannot call non-const fn
 }]>;
 
 fn main() {}