subtyping_projections

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2828,6 +2828,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         }
                         ProjectionElem::ConstantIndex { .. }
                         | ProjectionElem::Subslice { .. }
+                        | ProjectionElem::Subtype(_)
                         | ProjectionElem::Index(_) => kind,
                     },
                     place_ty.projection_ty(tcx, elem),

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -242,6 +242,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 ProjectionElem::Downcast(..) if opt.including_downcast => return None,
                 ProjectionElem::Downcast(..) => (),
                 ProjectionElem::OpaqueCast(..) => (),
+                ProjectionElem::Subtype(..) => (),
                 ProjectionElem::Field(field, _ty) => {
                     // FIXME(project-rfc_2229#36): print capture precisely here.
                     if let Some(field) = self.is_upvar_field_projection(PlaceRef {
@@ -317,6 +318,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
                 ProjectionElem::Deref
                 | ProjectionElem::Index(..)
+                | ProjectionElem::Subtype(..)
                 | ProjectionElem::ConstantIndex { .. }
                 | ProjectionElem::Subslice { .. } => {
                     PlaceRef { local, projection: proj_base }.ty(self.body, self.infcx.tcx)

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -159,6 +159,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     [
                         ..,
                         ProjectionElem::Index(_)
+                        | ProjectionElem::Subtype(_)
                         | ProjectionElem::ConstantIndex { .. }
                         | ProjectionElem::OpaqueCast { .. }
                         | ProjectionElem::Subslice { .. }

compiler/rustc_borrowck/src/lib.rs

@@ -1803,6 +1803,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         for (place_base, elem) in place.iter_projections().rev() {
             match elem {
                 ProjectionElem::Index(_/*operand*/) |
+                ProjectionElem::Subtype(_) |
                 ProjectionElem::OpaqueCast(_) |
                 ProjectionElem::ConstantIndex { .. } |
                 // assigning to P[i] requires P to be valid.
@@ -2191,6 +2192,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     | ProjectionElem::Index(..)
                     | ProjectionElem::ConstantIndex { .. }
                     | ProjectionElem::Subslice { .. }
+                    | ProjectionElem::Subtype(..)
                     | ProjectionElem::OpaqueCast { .. }
                     | ProjectionElem::Downcast(..) => {
                         let upvar_field_projection = self.is_upvar_field_projection(place);

compiler/rustc_borrowck/src/places_conflict.rs

@@ -243,6 +243,7 @@ fn place_components_conflict<'tcx>(
                 }
 
                 (ProjectionElem::Deref, _, Deep)
+                | (ProjectionElem::Subtype(_), _, _)
                 | (ProjectionElem::Deref, _, AccessDepth::Drop)
                 | (ProjectionElem::Field { .. }, _, _)
                 | (ProjectionElem::Index { .. }, _, _)
@@ -359,6 +360,7 @@ fn place_projection_conflict<'tcx>(
         (
             ProjectionElem::Index(..),
             ProjectionElem::Index(..)
+            | ProjectionElem::Subtype(..)
             | ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Subslice { .. },
         )
@@ -503,6 +505,7 @@ fn place_projection_conflict<'tcx>(
             debug!("place_element_conflict: DISJOINT-OR-EQ-SLICE-SUBSLICES");
             Overlap::EqualOrDisjoint
         }
+        (ProjectionElem::Subtype(_), _) => Overlap::EqualOrDisjoint,
         (
             ProjectionElem::Deref
             | ProjectionElem::Field(..)

compiler/rustc_borrowck/src/prefixes.rs

@@ -89,6 +89,7 @@ impl<'cx, 'tcx> Iterator for Prefixes<'cx, 'tcx> {
                             cursor = cursor_base;
                             continue 'cursor;
                         }
+                        ProjectionElem::Subtype(..) => continue 'cursor,
                         ProjectionElem::Deref => {
                             // (handled below)
                         }

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -621,6 +621,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                     span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
                 }))
             }
+            ProjectionElem::Subtype(ty) => PlaceTy::from_ty(ty),
             ProjectionElem::Index(i) => {
                 let index_ty = Place::from(i).ty(self.body(), tcx).ty;
                 if index_ty != tcx.types.usize {
@@ -2556,6 +2557,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     }
                 }
                 ProjectionElem::Field(..)
+                | ProjectionElem::Subtype(..)
                 | ProjectionElem::Downcast(..)
                 | ProjectionElem::OpaqueCast(..)
                 | ProjectionElem::Index(..)

compiler/rustc_codegen_cranelift/src/base.rs

@@ -872,6 +872,9 @@ pub(crate) fn codegen_place<'tcx>(
 
     for elem in place.projection {
         match elem {
+            PlaceElem::Subtype(_) => {
+                continue;
+            }
             PlaceElem::Deref => {
                 cplace = cplace.place_deref(fx);
             }

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -499,6 +499,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     subslice
                 }
                 mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),
+                mir::ProjectionElem::Subtype(_) => continue,
             };
         }
         debug!("codegen_place(place={:?}) => {:?}", place_ref, cg_base);

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -665,6 +665,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let mut op = self.local_to_op(self.frame(), mir_place.local, layout)?;
         // Using `try_fold` turned out to be bad for performance, hence the loop.
         for elem in mir_place.projection.iter() {
+            if elem.is_subtype() {
+                continue;
+            }
             op = self.project(&op, elem)?
         }
 

compiler/rustc_const_eval/src/interpret/projection.rs

@@ -332,6 +332,7 @@ where
                 self.project_constant_index(base, offset, min_length, from_end)?
             }
             Subslice { from, to, from_end } => self.project_subslice(base, from, to, from_end)?,
+            Subtype(ty) => base.transmute(self.layout_of(ty)?, self)?,
         })
     }
 }

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -664,6 +664,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
             | ProjectionElem::Downcast(..)
             | ProjectionElem::OpaqueCast(..)
             | ProjectionElem::Subslice { .. }
+            | ProjectionElem::Subtype(..)
             | ProjectionElem::Field(..)
             | ProjectionElem::Index(_) => {}
         }

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -306,6 +306,7 @@ where
             ProjectionElem::Index(index) if in_local(index) => return true,
 
             ProjectionElem::Deref
+            | ProjectionElem::Subtype(_)
             | ProjectionElem::Field(_, _)
             | ProjectionElem::OpaqueCast(_)
             | ProjectionElem::ConstantIndex { .. }

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -357,7 +357,9 @@ impl<'tcx> Validator<'_, 'tcx> {
                         return Err(Unpromotable);
                     }
 
-                    ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {}
+                    ProjectionElem::ConstantIndex { .. }
+                    | ProjectionElem::Subtype(_)
+                    | ProjectionElem::Subslice { .. } => {}
 
                     ProjectionElem::Index(local) => {
                         let mut promotable = false;

compiler/rustc_const_eval/src/transform/validate.rs

@@ -608,6 +608,29 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 
 impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
     fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
+        match operand {
+            Operand::Copy(place) | Operand::Move(place) => {
+                if let Some(stmt) = self.body.stmt_at(location).left() {
+                    match &stmt.kind {
+                        StatementKind::Assign(box (lval, rvalue)) => {
+                            let place_ty = place.ty(&self.body.local_decls, self.tcx).ty;
+                            let lval_ty = lval.ty(&self.body.local_decls, self.tcx).ty;
+
+                            if !place.is_subtype()
+                                && place_ty != lval_ty
+                                && rvalue.ty(&self.body.local_decls, self.tcx) != lval_ty
+                                && (rvalue.ty(&self.body.local_decls, self.tcx).is_closure()
+                                    != lval_ty.is_closure())
+                            {
+                                self.fail(location, format!("Subtyping is not allowed between types {place_ty:#?} and {lval_ty:#?}"))
+                            }
+                        }
+                        _ => (),
+                    }
+                }
+            }
+            _ => (),
+        }
         // This check is somewhat expensive, so only run it when -Zvalidate-mir is passed.
         if self.tcx.sess.opts.unstable_opts.validate_mir
             && self.mir_phase < MirPhase::Runtime(RuntimePhase::Initial)
@@ -1088,6 +1111,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 // LHS and RHS of the assignment must have the same type.
                 let left_ty = dest.ty(&self.body.local_decls, self.tcx).ty;
                 let right_ty = rvalue.ty(&self.body.local_decls, self.tcx);
+
                 if !self.mir_assign_valid_types(right_ty, left_ty) {
                     self.fail(
                         location,

compiler/rustc_middle/src/mir/syntax.rs

@@ -1075,6 +1075,8 @@ pub enum ProjectionElem<V, T> {
     /// Like an explicit cast from an opaque type to a concrete type, but without
     /// requiring an intermediate variable.
     OpaqueCast(T),
+
+    Subtype(T),
 }
 
 /// Alias for projections as they appear in places, where the base is a place

compiler/rustc_middle/src/mir/tcx.rs

@@ -111,6 +111,7 @@ impl<'tcx> PlaceTy<'tcx> {
             }
             ProjectionElem::Field(f, fty) => PlaceTy::from_ty(handle_field(&self, f, fty)),
             ProjectionElem::OpaqueCast(ty) => PlaceTy::from_ty(handle_opaque_cast(&self, ty)),
+            ProjectionElem::Subtype(_) => PlaceTy::from_ty(self.ty),
         };
         debug!("projection_ty self: {:?} elem: {:?} yields: {:?}", self, elem, answer);
         answer

compiler/rustc_middle/src/mir/visit.rs

@@ -1110,6 +1110,7 @@ macro_rules! visit_place_fns {
                     if ty != new_ty { Some(PlaceElem::OpaqueCast(new_ty)) } else { None }
                 }
                 PlaceElem::Deref
+                | PlaceElem::Subtype { .. }
                 | PlaceElem::ConstantIndex { .. }
                 | PlaceElem::Subslice { .. }
                 | PlaceElem::Downcast(..) => None,
@@ -1175,7 +1176,9 @@ macro_rules! visit_place_fns {
             location: Location,
         ) {
             match elem {
-                ProjectionElem::OpaqueCast(ty) | ProjectionElem::Field(_, ty) => {
+                ProjectionElem::OpaqueCast(ty)
+                | ProjectionElem::Subtype(ty)
+                | ProjectionElem::Field(_, ty) => {
                     self.visit_ty(ty, TyContext::Location(location));
                 }
                 ProjectionElem::Index(local) => {

compiler/rustc_mir_build/src/build/expr/as_place.rs

@@ -102,7 +102,7 @@ fn convert_to_hir_projections_and_truncate_for_capture(
                 continue;
             }
             // These do not affect anything, they just make sure we know the right type.
-            ProjectionElem::OpaqueCast(_) => continue,
+            ProjectionElem::OpaqueCast(_) | ProjectionElem::Subtype(..) => continue,
             ProjectionElem::Index(..)
             | ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Subslice { .. } => {
@@ -709,6 +709,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     ProjectionElem::Field(..)
                     | ProjectionElem::Downcast(..)
                     | ProjectionElem::OpaqueCast(..)
+                    | ProjectionElem::Subtype(..)
                     | ProjectionElem::ConstantIndex { .. }
                     | ProjectionElem::Subslice { .. } => (),
                 }

compiler/rustc_mir_dataflow/src/move_paths/abs_domain.rs

@@ -57,6 +57,7 @@ impl<'tcx> Lift for PlaceElem<'tcx> {
                 ProjectionElem::ConstantIndex { offset, min_length, from_end }
             }
             ProjectionElem::Downcast(a, u) => ProjectionElem::Downcast(a, u),
+            ProjectionElem::Subtype(ty) => ProjectionElem::Subtype(ty.lift()),
         }
     }
 }

compiler/rustc_mir_dataflow/src/move_paths/builder.rs

@@ -112,6 +112,9 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
         let mut union_path = None;
 
         for (place_ref, elem) in data.rev_lookup.un_derefer.iter_projections(place.as_ref()) {
+            if elem.is_subtype() {
+                continue;
+            }
             let body = self.builder.body;
             let tcx = self.builder.tcx;
             let place_ty = place_ref.ty(body, tcx).ty;

compiler/rustc_mir_transform/src/add_subtyping_projections.rs

@@ -0,0 +1,57 @@
+use crate::MirPass;
+use rustc_index::IndexVec;
+use rustc_middle::mir::patch::MirPatch;
+use rustc_middle::mir::visit::MutVisitor;
+use rustc_middle::mir::*;
+use rustc_middle::ty::TyCtxt;
+
+pub struct Subtyper;
+
+pub struct SubTypeCheker<'a, 'tcx> {
+    tcx: TyCtxt<'tcx>,
+    patcher: MirPatch<'tcx>,
+    local_decls: &'a IndexVec<Local, LocalDecl<'tcx>>,
+}
+
+impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeCheker<'a, 'tcx> {
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn visit_assign(
+        &mut self,
+        place: &mut Place<'tcx>,
+        rvalue: &mut Rvalue<'tcx>,
+        location: Location,
+    ) {
+        let place_ty = place.ty(self.local_decls, self.tcx);
+        let rval_ty = rvalue.ty(self.local_decls, self.tcx);
+        if place_ty.ty != rval_ty {
+            let temp = self
+                .patcher
+                .new_temp(rval_ty, self.local_decls[place.as_ref().local].source_info.span);
+            let new_place =
+                Place::from(temp).project_deeper(&[ProjectionElem::Subtype(place_ty.ty)], self.tcx);
+            self.patcher.add_assign(location, new_place, rvalue.clone());
+            let new_rval = Rvalue::Use(Operand::Move(new_place));
+            *rvalue = new_rval;
+        }
+    }
+}
+
+pub fn subtype_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+    let patch = MirPatch::new(body);
+    let mut checker = SubTypeCheker { tcx, patcher: patch, local_decls: &body.local_decls };
+
+    for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
+        checker.visit_basic_block_data(bb, data);
+    }
+
+    checker.patcher.apply(body);
+}
+
+impl<'tcx> MirPass<'tcx> for Subtyper {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        subtype_finder(tcx, body);
+    }
+}

compiler/rustc_mir_transform/src/lib.rs

@@ -54,6 +54,7 @@ mod check_packed_ref;
 pub mod check_unsafety;
 mod remove_place_mention;
 // This pass is public to allow external drivers to perform MIR cleanup
+mod add_subtyping_projections;
 pub mod cleanup_post_borrowck;
 mod const_debuginfo;
 mod const_goto;
@@ -466,6 +467,7 @@ pub fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'
 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let passes: &[&dyn MirPass<'tcx>] = &[
+        &add_subtyping_projections::Subtyper,
         &cleanup_post_borrowck::CleanupPostBorrowck,
         &remove_noop_landing_pads::RemoveNoopLandingPads,
         &simplify::SimplifyCfg::EarlyOpt,

src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs

@@ -272,6 +272,7 @@ fn check_place<'tcx>(tcx: TyCtxt<'tcx>, place: Place<'tcx>, span: Span, body: &B
             | ProjectionElem::Downcast(..)
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Deref
+            | ProjectionElem::Subtype(_)
             | ProjectionElem::Index(_) => {},
         }
     }