add values for associated items of UnalignedField

Author: BennoLossin

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1555,6 +1555,17 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
             }
         });
         (metadata_ty.into(), obligations)
+    } else if tcx.is_lang_item(trait_def_id, LangItem::UnalignedField) {
+        let &ty::Field(container, field_path) = self_ty.kind() else {
+            bug!("only `field_of!()` can implement `UnalignedField`")
+        };
+        if tcx.is_lang_item(item_def_id, LangItem::UnalignedFieldBase) {
+            (container.into(), PredicateObligations::new())
+        } else if tcx.is_lang_item(item_def_id, LangItem::UnalignedFieldType) {
+            (field_path.field_ty(tcx, container).into(), PredicateObligations::new())
+        } else {
+            bug!("unexpected associated type {:?} in `UnalignedField`", obligation.predicate);
+        }
     } else {
         bug!("unexpected builtin trait with associated type: {:?}", obligation.predicate);
     };

compiler/rustc_ty_utils/src/instance.rs

@@ -256,7 +256,23 @@ fn resolve_associated_item<'tcx>(
             }
         }
         traits::ImplSource::Builtin(BuiltinImplSource::Misc | BuiltinImplSource::Trivial, _) => {
-            if tcx.is_lang_item(trait_ref.def_id, LangItem::Clone) {
+            if tcx.is_lang_item(trait_ref.def_id, LangItem::UnalignedField) {
+                if tcx.is_lang_item(trait_item_id, LangItem::UnalignedFieldOFFSET) {
+                    let self_ty = trait_ref.self_ty();
+                    match self_ty.kind() {
+                        ty::Field(_, _) => {}
+                        _ => bug!("expected field representing type, found {self_ty}"),
+                    }
+                    Some(Instance {
+                        def: ty::InstanceKind::Item(
+                            tcx.lang_items().get(LangItem::UnalignedFieldOFFSET).unwrap(),
+                        ),
+                        args: rcvr_args,
+                    })
+                } else {
+                    bug!("unexpected associated associated item")
+                }
+            } else if tcx.is_lang_item(trait_ref.def_id, LangItem::Clone) {
                 // FIXME(eddyb) use lang items for methods instead of names.
                 let name = tcx.item_name(trait_item_id);
                 if name == sym::clone {