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

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)
     }