address nits

compiler/rustc_middle/src/query/mod.rs

@@ -704,7 +704,7 @@ rustc_queries! {
     }
 
     query adt_sized_constraint(key: DefId) -> Option<ty::EarlyBinder<Ty<'tcx>>> {
-        desc { |tcx| "computing `Sized` constraint for `{}`", tcx.def_path_str(key) }
+        desc { |tcx| "computing the `Sized` constraint for `{}`", tcx.def_path_str(key) }
     }
 
     query adt_dtorck_constraint(

compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs

@@ -168,10 +168,11 @@ pub(in crate::solve) fn instantiate_constituent_tys_for_sized_trait<'tcx>(
         //   "best effort" optimization and `sized_constraint` may return `Some`, even
         //   if the ADT is sized for all possible args.
         ty::Adt(def, args) => {
-            let sized_crit = def.sized_constraint(ecx.tcx());
-            Ok(sized_crit.map_or_else(Vec::new, |ty| {
-                vec![ty::Binder::dummy(ty.instantiate(ecx.tcx(), args))]
-            }))
+            if let Some(sized_crit) = def.sized_constraint(ecx.tcx()) {
+                Ok(vec![ty::Binder::dummy(sized_crit.instantiate(ecx.tcx(), args))])
+            } else {
+                Ok(vec![])
+            }
         }
     }
 }

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

@@ -2118,11 +2118,14 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             ),
 
             ty::Adt(def, args) => {
-                let sized_crit = def.sized_constraint(self.tcx());
-                // (*) binder moved here
-                Where(obligation.predicate.rebind(
-                    sized_crit.map_or_else(Vec::new, |ty| vec![ty.instantiate(self.tcx(), args)]),
-                ))
+                if let Some(sized_crit) = def.sized_constraint(self.tcx()) {
+                    // (*) binder moved here
+                    Where(
+                        obligation.predicate.rebind(vec![sized_crit.instantiate(self.tcx(), args)]),
+                    )
+                } else {
+                    Where(ty::Binder::dummy(Vec::new()))
+                }
             }
 
             ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => None,

compiler/rustc_ty_utils/src/ty.rs

@@ -39,13 +39,10 @@ fn sized_constraint_for_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'
         Tuple(tys) => tys.last().and_then(|&ty| sized_constraint_for_ty(tcx, ty)),
 
         // recursive case
-        Adt(adt, args) => {
-            let intermediate = adt.sized_constraint(tcx);
-            intermediate.and_then(|intermediate| {
-                let ty = intermediate.instantiate(tcx, args);
-                sized_constraint_for_ty(tcx, ty)
-            })
-        }
+        Adt(adt, args) => adt.sized_constraint(tcx).and_then(|intermediate| {
+            let ty = intermediate.instantiate(tcx, args);
+            sized_constraint_for_ty(tcx, ty)
+        }),
 
         // these can be sized or unsized
         Param(..) | Alias(..) | Error(_) => Some(ty),