remove impl Field for fields of packed structs

Author: BennoLossin

compiler/rustc_middle/src/ty/adt.rs

@@ -247,6 +247,10 @@ impl<'tcx> rustc_type_ir::inherent::AdtDef<TyCtxt<'tcx>> for AdtDef<'tcx> {
             hir::Constness::NotConst => AdtDestructorKind::NotConst,
         })
     }
+
+    fn is_packed(self) -> bool {
+        self.repr().packed()
+    }
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, HashStable, TyEncodable, TyDecodable)]

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -1,5 +1,7 @@
 //! Dealing with trait goals, i.e. `T: Trait<'a, U>`.
 
+use std::ops::ControlFlow;
+
 use rustc_type_ir::data_structures::IndexSet;
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
@@ -852,9 +854,23 @@ where
         }
 
         match goal.predicate.self_ty().kind() {
-            ty::Field(..) => ecx
-                .probe_builtin_trait_candidate(BuiltinImplSource::Misc)
-                .enter(|ecx| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)),
+            ty::Field(container, field_path)
+                if field_path
+                    .walk(ecx.cx(), container, |base, _, _, _| {
+                        if let ty::Adt(def, _) = base.kind()
+                            && def.is_packed()
+                        {
+                            ControlFlow::Break(())
+                        } else {
+                            ControlFlow::Continue(())
+                        }
+                    })
+                    .is_none() =>
+            {
+                ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                })
+            }
             _ => Err(NoSolution),
         }
     }

compiler/rustc_type_ir/src/inherent.rs

@@ -633,6 +633,8 @@ pub trait AdtDef<I: Interner>: Copy + Debug + Hash + Eq {
     fn is_fundamental(self) -> bool;
 
     fn destructor(self, interner: I) -> Option<AdtDestructorKind>;
+
+    fn is_packed(self) -> bool;
 }
 
 pub trait FieldPath<I: Interner>: Copy + Debug + Hash + Eq {