add next solver trait assembly

Author: BennoLossin

compiler/rustc_middle/src/ty/context.rs

@@ -807,6 +807,8 @@ bidirectional_lang_item_map! {
     CoroutineReturn,
     CoroutineYield,
     DynMetadata,
+    FieldBase,
+    FieldType,
     FutureOutput,
     Metadata,
 // tidy-alphabetical-end

compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs

@@ -351,6 +351,11 @@ where
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
     ) -> Vec<Candidate<I>>;
+
+    fn consider_builtin_field_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution>;
 }
 
 /// Allows callers of `assemble_and_evaluate_candidates` to choose whether to limit
@@ -606,6 +611,7 @@ where
                 Some(SolverTraitLangItem::BikeshedGuaranteedNoDrop) => {
                     G::consider_builtin_bikeshed_guaranteed_no_drop_candidate(self, goal)
                 }
+                Some(SolverTraitLangItem::Field) => G::consider_builtin_field_candidate(self, goal),
                 _ => Err(NoSolution),
             }
         };

compiler/rustc_next_trait_solver/src/solve/effect_goals.rs

@@ -385,6 +385,13 @@ where
     ) -> Vec<Candidate<I>> {
         unreachable!("Unsize is not const")
     }
+
+    fn consider_builtin_field_candidate(
+        _ecx: &mut EvalCtxt<'_, D>,
+        _goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        unreachable!("Field is not const")
+    }
 }
 
 impl<D, I> EvalCtxt<'_, D>

compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs

@@ -970,6 +970,26 @@ where
     ) -> Result<Candidate<I>, NoSolution> {
         unreachable!("`BikeshedGuaranteedNoDrop` does not have an associated type: {:?}", goal)
     }
+    fn consider_builtin_field_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<<D as SolverDelegate>::Interner, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        let cx = ecx.cx();
+        let ty::Field(container, field_path) = goal.predicate.self_ty().kind() else {
+            panic!("only `field_of!()` can implement `Field`")
+        };
+        let ty = if cx.is_lang_item(goal.predicate.def_id(), SolverLangItem::FieldBase) {
+            container
+        } else if cx.is_lang_item(goal.predicate.def_id(), SolverLangItem::FieldType) {
+            field_path.field_ty(cx, container)
+        } else {
+            panic!("unexpected associated type {:?} in `Field`", goal.predicate)
+        };
+        ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
+            ecx.instantiate_normalizes_to_term(goal, ty.into());
+            ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+        })
+    }
 }
 
 impl<D, I> EvalCtxt<'_, D>

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -846,6 +846,22 @@ where
             }
         })
     }
+
+    fn consider_builtin_field_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        if goal.predicate.polarity != ty::PredicatePolarity::Positive {
+            return Err(NoSolution);
+        }
+
+        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)),
+            _ => Err(NoSolution),
+        }
+    }
 }
 
 /// Small helper function to change the `def_id` of a trait predicate - this is not normally

compiler/rustc_type_ir/src/lang_items.rs

@@ -9,6 +9,8 @@ pub enum SolverLangItem {
     CoroutineReturn,
     CoroutineYield,
     DynMetadata,
+    FieldBase,
+    FieldType,
     FutureOutput,
     Metadata,
     // tidy-alphabetical-end

tests/ui/field_projections/deny-manual-impl.next.stderr

@@ -1,15 +1,9 @@
-error[E0322]: explicit impls for the `UnalignedField` trait are not permitted
-  --> $DIR/deny-manual-impl.rs:11:1
-   |
-LL | unsafe impl UnalignedField for MyStruct {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `UnalignedField` not allowed
-
 error[E0322]: explicit impls for the `Field` trait are not permitted
-  --> $DIR/deny-manual-impl.rs:18:1
+  --> $DIR/deny-manual-impl.rs:11:1
    |
-LL | unsafe impl Field for field_of!(MyStruct, 0) {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `Field` not allowed
+LL | unsafe impl Field for MyStruct {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `Field` not allowed
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0322`.

tests/ui/field_projections/deny-manual-impl.old.stderr

@@ -0,0 +1,9 @@
+error[E0322]: explicit impls for the `Field` trait are not permitted
+  --> $DIR/deny-manual-impl.rs:11:1
+   |
+LL | unsafe impl Field for MyStruct {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `Field` not allowed
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0322`.