Check FnPtr/FnDef built-in fn traits correctly with effects

compiler/rustc_middle/src/traits/select.rs

@@ -153,7 +153,7 @@ pub enum SelectionCandidate<'tcx> {
     /// Implementation of a `Fn`-family trait by one of the anonymous
     /// types generated for a fn pointer type (e.g., `fn(int) -> int`)
     FnPointerCandidate {
-        is_const: bool,
+        fn_host_effect: ty::Const<'tcx>,
     },
 
     TraitAliasCandidate,

compiler/rustc_trait_selection/src/traits/project.rs

@@ -2327,8 +2327,9 @@ fn confirm_fn_pointer_candidate<'cx, 'tcx>(
     obligation: &ProjectionTyObligation<'tcx>,
     nested: Vec<PredicateObligation<'tcx>>,
 ) -> Progress<'tcx> {
+    let tcx = selcx.tcx();
     let fn_type = selcx.infcx.shallow_resolve(obligation.predicate.self_ty());
-    let sig = fn_type.fn_sig(selcx.tcx());
+    let sig = fn_type.fn_sig(tcx);
     let Normalized { value: sig, obligations } = normalize_with_depth(
         selcx,
         obligation.param_env,
@@ -2337,9 +2338,24 @@ fn confirm_fn_pointer_candidate<'cx, 'tcx>(
         sig,
     );
 
-    confirm_callable_candidate(selcx, obligation, sig, util::TupleArgumentsFlag::Yes)
-        .with_addl_obligations(nested)
-        .with_addl_obligations(obligations)
+    let host_effect_param = match *fn_type.kind() {
+        ty::FnDef(def_id, args) => tcx
+            .generics_of(def_id)
+            .host_effect_index
+            .map_or(tcx.consts.true_, |idx| args.const_at(idx)),
+        ty::FnPtr(_) => tcx.consts.true_,
+        _ => unreachable!("only expected FnPtr or FnDef in `confirm_fn_pointer_candidate`"),
+    };
+
+    confirm_callable_candidate(
+        selcx,
+        obligation,
+        sig,
+        util::TupleArgumentsFlag::Yes,
+        host_effect_param,
+    )
+    .with_addl_obligations(nested)
+    .with_addl_obligations(obligations)
 }
 
 fn confirm_closure_candidate<'cx, 'tcx>(
@@ -2362,16 +2378,24 @@ fn confirm_closure_candidate<'cx, 'tcx>(
 
     debug!(?obligation, ?closure_sig, ?obligations, "confirm_closure_candidate");
 
-    confirm_callable_candidate(selcx, obligation, closure_sig, util::TupleArgumentsFlag::No)
-        .with_addl_obligations(nested)
-        .with_addl_obligations(obligations)
+    confirm_callable_candidate(
+        selcx,
+        obligation,
+        closure_sig,
+        util::TupleArgumentsFlag::No,
+        // FIXME(effects): This doesn't handle const closures correctly!
+        selcx.tcx().consts.true_,
+    )
+    .with_addl_obligations(nested)
+    .with_addl_obligations(obligations)
 }
 
 fn confirm_callable_candidate<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionTyObligation<'tcx>,
     fn_sig: ty::PolyFnSig<'tcx>,
     flag: util::TupleArgumentsFlag,
+    fn_host_effect: ty::Const<'tcx>,
 ) -> Progress<'tcx> {
     let tcx = selcx.tcx();
 
@@ -2386,6 +2410,7 @@ fn confirm_callable_candidate<'cx, 'tcx>(
         obligation.predicate.self_ty(),
         fn_sig,
         flag,
+        fn_host_effect,
     )
     .map_bound(|(trait_ref, ret_type)| ty::ProjectionPredicate {
         projection_ty: ty::AliasTy::new(tcx, fn_once_output_def_id, trait_ref.args),

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

@@ -355,17 +355,23 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // Provide an impl, but only for suitable `fn` pointers.
             ty::FnPtr(sig) => {
                 if sig.is_fn_trait_compatible() {
-                    candidates.vec.push(FnPointerCandidate { is_const: false });
+                    candidates
+                        .vec
+                        .push(FnPointerCandidate { fn_host_effect: self.tcx().consts.true_ });
                 }
             }
             // Provide an impl for suitable functions, rejecting `#[target_feature]` functions (RFC 2396).
-            ty::FnDef(def_id, _) => {
-                if self.tcx().fn_sig(def_id).skip_binder().is_fn_trait_compatible()
-                    && self.tcx().codegen_fn_attrs(def_id).target_features.is_empty()
+            ty::FnDef(def_id, args) => {
+                let tcx = self.tcx();
+                if tcx.fn_sig(def_id).skip_binder().is_fn_trait_compatible()
+                    && tcx.codegen_fn_attrs(def_id).target_features.is_empty()
                 {
-                    candidates
-                        .vec
-                        .push(FnPointerCandidate { is_const: self.tcx().is_const_fn(def_id) });
+                    candidates.vec.push(FnPointerCandidate {
+                        fn_host_effect: tcx
+                            .generics_of(def_id)
+                            .host_effect_index
+                            .map_or(tcx.consts.true_, |idx| args.const_at(idx)),
+                    });
                 }
             }
             _ => {}

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

@@ -103,8 +103,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_iterator)
             }
 
-            FnPointerCandidate { is_const } => {
-                let data = self.confirm_fn_pointer_candidate(obligation, is_const)?;
+            FnPointerCandidate { fn_host_effect } => {
+                let data = self.confirm_fn_pointer_candidate(obligation, fn_host_effect)?;
                 ImplSource::Builtin(BuiltinImplSource::Misc, data)
             }
 
@@ -653,8 +653,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     fn confirm_fn_pointer_candidate(
         &mut self,
         obligation: &PolyTraitObligation<'tcx>,
-        // FIXME(effects)
-        _is_const: bool,
+        fn_host_effect: ty::Const<'tcx>,
     ) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
         debug!(?obligation, "confirm_fn_pointer_candidate");
 
@@ -675,6 +674,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             self_ty,
             sig,
             util::TupleArgumentsFlag::Yes,
+            fn_host_effect,
         )
         .map_bound(|(trait_ref, _)| trait_ref);
 
@@ -860,7 +860,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             bug!("closure candidate for non-closure {:?}", obligation);
         };
 
-        let trait_ref = self.closure_trait_ref_unnormalized(obligation, args);
+        let trait_ref =
+            self.closure_trait_ref_unnormalized(obligation, args, self.tcx().consts.true_);
         let nested = self.confirm_poly_trait_refs(obligation, trait_ref)?;
 
         debug!(?closure_def_id, ?trait_ref, ?nested, "confirm closure candidate obligations");

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

@@ -1865,7 +1865,9 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             }
 
             // Drop otherwise equivalent non-const fn pointer candidates
-            (FnPointerCandidate { .. }, FnPointerCandidate { is_const: false }) => DropVictim::Yes,
+            (FnPointerCandidate { .. }, FnPointerCandidate { fn_host_effect }) => {
+                DropVictim::drop_if(*fn_host_effect == self.tcx().consts.true_)
+            }
 
             (
                 ParamCandidate(ref other_cand),
@@ -2660,6 +2662,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         &mut self,
         obligation: &PolyTraitObligation<'tcx>,
         args: GenericArgsRef<'tcx>,
+        fn_host_effect: ty::Const<'tcx>,
     ) -> ty::PolyTraitRef<'tcx> {
         let closure_sig = args.as_closure().sig();
 
@@ -2680,6 +2683,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             self_ty,
             closure_sig,
             util::TupleArgumentsFlag::No,
+            fn_host_effect,
         )
         .map_bound(|(trait_ref, _)| trait_ref)
     }

compiler/rustc_trait_selection/src/traits/util.rs

@@ -264,13 +264,26 @@ pub fn closure_trait_ref_and_return_type<'tcx>(
     self_ty: Ty<'tcx>,
     sig: ty::PolyFnSig<'tcx>,
     tuple_arguments: TupleArgumentsFlag,
+    fn_host_effect: ty::Const<'tcx>,
 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
     assert!(!self_ty.has_escaping_bound_vars());
     let arguments_tuple = match tuple_arguments {
         TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
         TupleArgumentsFlag::Yes => Ty::new_tup(tcx, sig.skip_binder().inputs()),
     };
-    let trait_ref = ty::TraitRef::new(tcx, fn_trait_def_id, [self_ty, arguments_tuple]);
+    let trait_ref = if tcx.generics_of(fn_trait_def_id).host_effect_index.is_some() {
+        ty::TraitRef::new(
+            tcx,
+            fn_trait_def_id,
+            [
+                ty::GenericArg::from(self_ty),
+                ty::GenericArg::from(arguments_tuple),
+                ty::GenericArg::from(fn_host_effect),
+            ],
+        )
+    } else {
+        ty::TraitRef::new(tcx, fn_trait_def_id, [self_ty, arguments_tuple])
+    };
     sig.map_bound(|sig| (trait_ref, sig.output()))
 }
 

tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs

@@ -1,12 +1,13 @@
 // check-pass
 
 #![crate_type = "lib"]
-#![feature(no_core, lang_items, unboxed_closures, auto_traits, intrinsics, rustc_attrs)]
+#![feature(no_core, lang_items, unboxed_closures, auto_traits, intrinsics, rustc_attrs, staged_api)]
 #![feature(fundamental)]
 #![feature(const_trait_impl, effects, const_mut_refs)]
 #![allow(internal_features)]
 #![no_std]
 #![no_core]
+#![stable(feature = "minicore", since = "1.0.0")]
 
 #[lang = "sized"]
 trait Sized {}
@@ -82,6 +83,7 @@ trait FnMut<Args: Tuple>: ~const FnOnce<Args> {
 #[lang = "fn_once"]
 #[rustc_paren_sugar]
 trait FnOnce<Args: Tuple> {
+    #[lang = "fn_once_output"]
     type Output;
 
     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
@@ -93,7 +95,7 @@ struct ConstFnMutClosure<CapturedData, Function> {
 }
 
 #[lang = "tuple_trait"]
-pub trait Tuple {}
+trait Tuple {}
 
 macro_rules! impl_fn_mut_tuple {
     ($($var:ident)*) => {
@@ -509,3 +511,12 @@ trait StructuralPartialEq {}
 trait StructuralEq {}
 
 const fn drop<T: ~const Destruct>(_: T) {}
+
+extern "rust-intrinsic" {
+    #[rustc_const_stable(feature = "const_eval_select", since = "1.0.0")]
+    fn const_eval_select<ARG: Tuple, F, G, RET>(
+        arg: ARG,
+        called_in_const: F,
+        called_at_rt: G,
+    ) -> RET;
+}