Fetch the destructor constness lazily

Author: oli-obk

compiler/rustc_middle/src/ty/adt.rs

@@ -236,7 +236,7 @@ impl<'tcx> rustc_type_ir::inherent::AdtDef<TyCtxt<'tcx>> for AdtDef<'tcx> {
     }
 
     fn destructor(self, tcx: TyCtxt<'tcx>) -> Option<AdtDestructorKind> {
-        Some(match self.destructor(tcx)?.constness {
+        Some(match tcx.constness(self.destructor(tcx)?.did) {
             hir::Constness::Const => AdtDestructorKind::Const,
             hir::Constness::NotConst => AdtDestructorKind::NotConst,
         })

compiler/rustc_middle/src/ty/mod.rs

@@ -1119,8 +1119,6 @@ pub struct PseudoCanonicalInput<'tcx, T> {
 pub struct Destructor {
     /// The `DefId` of the destructor method
     pub did: DefId,
-    /// The constness of the destructor method
-    pub constness: hir::Constness,
 }
 
 // FIXME: consider combining this definition with regular `Destructor`

compiler/rustc_middle/src/ty/util.rs

@@ -414,18 +414,18 @@ impl<'tcx> TyCtxt<'tcx> {
                 continue;
             };
 
-            if let Some((old_item_id, _)) = dtor_candidate {
+            if let Some(old_item_id) = dtor_candidate {
                 self.dcx()
                     .struct_span_err(self.def_span(item_id), "multiple drop impls found")
                     .with_span_note(self.def_span(old_item_id), "other impl here")
                     .delay_as_bug();
             }
 
-            dtor_candidate = Some((*item_id, self.impl_trait_header(impl_did).unwrap().constness));
+            dtor_candidate = Some(*item_id);
         }
 
-        let (did, constness) = dtor_candidate?;
-        Some(ty::Destructor { did, constness })
+        let did = dtor_candidate?;
+        Some(ty::Destructor { did })
     }
 
     /// Calculate the async destructor of a given type.

compiler/rustc_trait_selection/src/traits/effects.rs

@@ -263,7 +263,7 @@ fn evaluate_host_effect_for_destruct_goal<'tcx>(
                 .all_fields()
                 .map(|field| ty::TraitRef::new(tcx, destruct_def_id, [field.ty(tcx, args)]))
                 .collect();
-            match adt_def.destructor(tcx).map(|dtor| dtor.constness) {
+            match adt_def.destructor(tcx).map(|dtor| tcx.constness(dtor.did)) {
                 // `Drop` impl exists, but it's not const. Type cannot be `~const Destruct`.
                 Some(hir::Constness::NotConst) => return Err(EvaluationFailure::NoSolution),
                 // `Drop` impl exists, and it's const. Require `Ty: ~const Drop` to hold.