attempt to make a minimal example work

3 files changed, 24 insertions, 16 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index c54d901e9b1..a5635ccfec4 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -254,18 +254,23 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // touch bound regions, they just capture the in-scope
         // type/region parameters
         match *obligation.self_ty().skip_binder().kind() {
-            ty::Closure(_, closure_substs) => {
+            ty::Closure(def_id, closure_substs) => {
+                let is_const = self.tcx().is_const_fn_raw(def_id);
                 debug!(?kind, ?obligation, "assemble_unboxed_candidates");
                 match self.infcx.closure_kind(closure_substs) {
                     Some(closure_kind) => {
                         debug!(?closure_kind, "assemble_unboxed_candidates");
                         if closure_kind.extends(kind) {
-                            candidates.vec.push(ClosureCandidate);
+                            candidates.vec.push(ClosureCandidate {
+                                is_const,
+                            });
                         }
                     }
                     None => {
                         debug!("assemble_unboxed_candidates: closure_kind not yet known");
-                        candidates.vec.push(ClosureCandidate);
+                        candidates.vec.push(ClosureCandidate {
+                            is_const,
+                        });
                     }
                 }
             }
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 15526b34ed2..a41d10f1043 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -84,7 +84,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplSource::Object(data)
             }
 
-            ClosureCandidate => {
+            ClosureCandidate { .. } => {
                 let vtable_closure = self.confirm_closure_candidate(obligation)?;
                 ImplSource::Closure(vtable_closure)
             }
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 3f14491f803..25a294b5401 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1365,15 +1365,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     // const param
                     ParamCandidate(trait_pred) if trait_pred.is_const_if_const() => {}
                     // const projection
-                    ProjectionCandidate(_, ty::BoundConstness::ConstIfConst) => {}
+                    ProjectionCandidate(_, ty::BoundConstness::ConstIfConst)
                     // auto trait impl
-                    AutoImplCandidate => {}
+                    | AutoImplCandidate
                     // generator / future, this will raise error in other places
                     // or ignore error with const_async_blocks feature
-                    GeneratorCandidate => {}
-                    FutureCandidate => {}
+                    | GeneratorCandidate
+                    | FutureCandidate
                     // FnDef where the function is const
-                    FnPointerCandidate { is_const: true } => {}
+                    | FnPointerCandidate { is_const: true }
+                    | ConstDestructCandidate(_)
+                    | ClosureCandidate { is_const: true } => {}
+
                     FnPointerCandidate { is_const: false } => {
                         if let ty::FnDef(def_id, _) = obligation.self_ty().skip_binder().kind() && tcx.trait_of_item(*def_id).is_some() {
                             // Trait methods are not seen as const unless the trait is implemented as const.
@@ -1382,7 +1385,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                             continue
                         }
                     }
-                    ConstDestructCandidate(_) => {}
+
                     _ => {
                         // reject all other types of candidates
                         continue;
@@ -1844,7 +1847,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             (
                 ParamCandidate(ref cand),
                 ImplCandidate(..)
-                | ClosureCandidate
+                | ClosureCandidate { .. }
                 | GeneratorCandidate
                 | FutureCandidate
                 | FnPointerCandidate { .. }
@@ -1863,7 +1866,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
             (
                 ImplCandidate(_)
-                | ClosureCandidate
+                | ClosureCandidate { .. }
                 | GeneratorCandidate
                 | FutureCandidate
                 | FnPointerCandidate { .. }
@@ -1894,7 +1897,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             (
                 ObjectCandidate(_) | ProjectionCandidate(..),
                 ImplCandidate(..)
-                | ClosureCandidate
+                | ClosureCandidate { .. }
                 | GeneratorCandidate
                 | FutureCandidate
                 | FnPointerCandidate { .. }
@@ -1907,7 +1910,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             (
                 ImplCandidate(..)
-                | ClosureCandidate
+                | ClosureCandidate { .. }
                 | GeneratorCandidate
                 | FutureCandidate
                 | FnPointerCandidate { .. }
@@ -1989,7 +1992,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // Everything else is ambiguous
             (
                 ImplCandidate(_)
-                | ClosureCandidate
+                | ClosureCandidate { .. }
                 | GeneratorCandidate
                 | FutureCandidate
                 | FnPointerCandidate { .. }
@@ -1999,7 +2002,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 | BuiltinCandidate { has_nested: true }
                 | TraitAliasCandidate,
                 ImplCandidate(_)
-                | ClosureCandidate
+                | ClosureCandidate { .. }
                 | GeneratorCandidate
                 | FutureCandidate
                 | FnPointerCandidate { .. }