do not emit OpaqueCast projections with -Znext-solver

Author: lcnr

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -1502,16 +1502,21 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         let mut projections = base_place.place.projections;
 
         let node_ty = self.cx.typeck_results().node_type(node);
-        // Opaque types can't have field projections, but we can instead convert
-        // the current place in-place (heh) to the hidden type, and then apply all
-        // follow up projections on that.
-        if node_ty != place_ty
-            && self
-                .cx
-                .try_structurally_resolve_type(self.cx.tcx().hir_span(base_place.hir_id), place_ty)
-                .is_impl_trait()
-        {
-            projections.push(Projection { kind: ProjectionKind::OpaqueCast, ty: node_ty });
+        if !self.cx.tcx().next_trait_solver_globally() {
+            // Opaque types can't have field projections, but we can instead convert
+            // the current place in-place (heh) to the hidden type, and then apply all
+            // follow up projections on that.
+            if node_ty != place_ty
+                && self
+                    .cx
+                    .try_structurally_resolve_type(
+                        self.cx.tcx().hir_span(base_place.hir_id),
+                        place_ty,
+                    )
+                    .is_impl_trait()
+            {
+                projections.push(Projection { kind: ProjectionKind::OpaqueCast, ty: node_ty });
+            }
         }
         projections.push(Projection { kind, ty });
         PlaceWithHirId::new(node, base_place.place.base_ty, base_place.place.base, projections)

compiler/rustc_middle/src/hir/place.rs

@@ -40,6 +40,8 @@ pub enum ProjectionKind {
 
     /// A conversion from an opaque type to its hidden type so we can
     /// do further projections on it.
+    ///
+    /// This is unused if `-Znext-solver` is enabled.
     OpaqueCast,
 }
 

compiler/rustc_middle/src/mir/syntax.rs

@@ -1242,6 +1242,8 @@ pub enum ProjectionElem<V, T> {
 
     /// Like an explicit cast from an opaque type to a concrete type, but without
     /// requiring an intermediate variable.
+    ///
+    /// This is unused with `-Znext-solver`.
     OpaqueCast(T),
 
     /// A transmute from an unsafe binder to the type that it wraps. This is a projection

compiler/rustc_mir_build/src/builder/matches/match_pair.rs

@@ -101,18 +101,21 @@ impl<'tcx> MatchPairTree<'tcx> {
             place_builder = resolved;
         }
 
-        // Only add the OpaqueCast projection if the given place is an opaque type and the
-        // expected type from the pattern is not.
-        let may_need_cast = match place_builder.base() {
-            PlaceBase::Local(local) => {
-                let ty =
-                    Place::ty_from(local, place_builder.projection(), &cx.local_decls, cx.tcx).ty;
-                ty != pattern.ty && ty.has_opaque_types()
+        if !cx.tcx.next_trait_solver_globally() {
+            // Only add the OpaqueCast projection if the given place is an opaque type and the
+            // expected type from the pattern is not.
+            let may_need_cast = match place_builder.base() {
+                PlaceBase::Local(local) => {
+                    let ty =
+                        Place::ty_from(local, place_builder.projection(), &cx.local_decls, cx.tcx)
+                            .ty;
+                    ty != pattern.ty && ty.has_opaque_types()
+                }
+                _ => true,
+            };
+            if may_need_cast {
+                place_builder = place_builder.project(ProjectionElem::OpaqueCast(pattern.ty));
             }
-            _ => true,
-        };
-        if may_need_cast {
-            place_builder = place_builder.project(ProjectionElem::OpaqueCast(pattern.ty));
         }
 
         let place = place_builder.try_to_place(cx);

compiler/rustc_mir_transform/src/post_analysis_normalize.rs

@@ -39,20 +39,22 @@ impl<'tcx> MutVisitor<'tcx> for PostAnalysisNormalizeVisitor<'tcx> {
         _context: PlaceContext,
         _location: Location,
     ) {
-        // Performance optimization: don't reintern if there is no `OpaqueCast` to remove.
-        if place.projection.iter().all(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_))) {
-            return;
+        if !self.tcx.next_trait_solver_globally() {
+            // `OpaqueCast` projections are only needed if there are opaque types on which projections
+            // are performed. After the `PostAnalysisNormalize` pass, all opaque types are replaced with their
+            // hidden types, so we don't need these projections anymore.
+            //
+            // Performance optimization: don't reintern if there is no `OpaqueCast` to remove.
+            if place.projection.iter().any(|elem| matches!(elem, ProjectionElem::OpaqueCast(_))) {
+                place.projection = self.tcx.mk_place_elems(
+                    &place
+                        .projection
+                        .into_iter()
+                        .filter(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_)))
+                        .collect::<Vec<_>>(),
+                );
+            };
         }
-        // `OpaqueCast` projections are only needed if there are opaque types on which projections
-        // are performed. After the `PostAnalysisNormalize` pass, all opaque types are replaced with their
-        // hidden types, so we don't need these projections anymore.
-        place.projection = self.tcx.mk_place_elems(
-            &place
-                .projection
-                .into_iter()
-                .filter(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_)))
-                .collect::<Vec<_>>(),
-        );
         self.super_place(place, _context, _location);
     }