src/librustc_typeck/check/place_op.rs

   1 use crate::check::method::MethodCallee;
   2 use crate::check::{FnCtxt, PlaceOp};
   3 use rustc_hir as hir;
   4 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
   5 use rustc_infer::infer::InferOk;
   6 use rustc_middle::ty::adjustment::{Adjust, Adjustment, OverloadedDeref, PointerCast};
   7 use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
   8 use rustc_middle::ty::{self, Ty};
   9 use rustc_span::symbol::{sym, Ident};
  10 use rustc_span::Span;
  11 use rustc_trait_selection::autoderef::Autoderef;
  12
  13 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  14     /// Type-check `*oprnd_expr` with `oprnd_expr` type-checked already.
  15     pub(super) fn lookup_derefing(
  16         &self,
  17         expr: &hir::Expr<'_>,
  18         oprnd_expr: &'tcx hir::Expr<'tcx>,
  19         oprnd_ty: Ty<'tcx>,
  20     ) -> Option<Ty<'tcx>> {
  21         if let Some(mt) = oprnd_ty.builtin_deref(true) {
  22             return Some(mt.ty);
  23         }
  24
  25         let ok = self.try_overloaded_deref(expr.span, oprnd_ty)?;
  26         let method = self.register_infer_ok_obligations(ok);
  27         if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind {
  28             self.apply_adjustments(
  29                 oprnd_expr,
  30                 vec![Adjustment {
  31                     kind: Adjust::Borrow(AutoBorrow::Ref(region, AutoBorrowMutability::Not)),
  32                     target: method.sig.inputs()[0],
  33                 }],
  34             );
  35         } else {
  36             span_bug!(expr.span, "input to deref is not a ref?");
  37         }
  38         let ty = self.make_overloaded_place_return_type(method).ty;
  39         self.write_method_call(expr.hir_id, method);
  40         Some(ty)
  41     }
  42
  43     /// Type-check `*base_expr[index_expr]` with `base_expr` and `index_expr` type-checked already.
  44     pub(super) fn lookup_indexing(
  45         &self,
  46         expr: &hir::Expr<'_>,
  47         base_expr: &'tcx hir::Expr<'tcx>,
  48         base_ty: Ty<'tcx>,
  49         idx_ty: Ty<'tcx>,
  50     ) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
  51         // FIXME(#18741) -- this is almost but not quite the same as the
  52         // autoderef that normal method probing does. They could likely be
  53         // consolidated.
  54
  55         let mut autoderef = self.autoderef(base_expr.span, base_ty);
  56         let mut result = None;
  57         while result.is_none() && autoderef.next().is_some() {
  58             result = self.try_index_step(expr, base_expr, &autoderef, idx_ty);
  59         }
  60         self.register_predicates(autoderef.into_obligations());
  61         result
  62     }
  63
  64     /// To type-check `base_expr[index_expr]`, we progressively autoderef
  65     /// (and otherwise adjust) `base_expr`, looking for a type which either
  66     /// supports builtin indexing or overloaded indexing.
  67     /// This loop implements one step in that search; the autoderef loop
  68     /// is implemented by `lookup_indexing`.
  69     fn try_index_step(
  70         &self,
  71         expr: &hir::Expr<'_>,
  72         base_expr: &hir::Expr<'_>,
  73         autoderef: &Autoderef<'a, 'tcx>,
  74         index_ty: Ty<'tcx>,
  75     ) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
  76         let adjusted_ty =
  77             self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
  78         debug!(
  79             "try_index_step(expr={:?}, base_expr={:?}, adjusted_ty={:?}, \
  80              index_ty={:?})",
  81             expr, base_expr, adjusted_ty, index_ty
  82         );
  83
  84         for &unsize in &[false, true] {
  85             let mut self_ty = adjusted_ty;
  86             if unsize {
  87                 // We only unsize arrays here.
  88                 if let ty::Array(element_ty, _) = adjusted_ty.kind {
  89                     self_ty = self.tcx.mk_slice(element_ty);
  90                 } else {
  91                     continue;
  92                 }
  93             }
  94
  95             // If some lookup succeeds, write callee into table and extract index/element
  96             // type from the method signature.
  97             // If some lookup succeeded, install method in table
  98             let input_ty = self.next_ty_var(TypeVariableOrigin {
  99                 kind: TypeVariableOriginKind::AutoDeref,
 100                 span: base_expr.span,
 101             });
 102             let method =
 103                 self.try_overloaded_place_op(expr.span, self_ty, &[input_ty], PlaceOp::Index);
 104
 105             let result = method.map(|ok| {
 106                 debug!("try_index_step: success, using overloaded indexing");
 107                 let method = self.register_infer_ok_obligations(ok);
 108
 109                 let mut adjustments = self.adjust_steps(autoderef);
 110                 if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind {
 111                     adjustments.push(Adjustment {
 112                         kind: Adjust::Borrow(AutoBorrow::Ref(region, AutoBorrowMutability::Not)),
 113                         target: self.tcx.mk_ref(
 114                             region,
 115                             ty::TypeAndMut { mutbl: hir::Mutability::Not, ty: adjusted_ty },
 116                         ),
 117                     });
 118                 } else {
 119                     span_bug!(expr.span, "input to index is not a ref?");
 120                 }
 121                 if unsize {
 122                     adjustments.push(Adjustment {
 123                         kind: Adjust::Pointer(PointerCast::Unsize),
 124                         target: method.sig.inputs()[0],
 125                     });
 126                 }
 127                 self.apply_adjustments(base_expr, adjustments);
 128
 129                 self.write_method_call(expr.hir_id, method);
 130                 (input_ty, self.make_overloaded_place_return_type(method).ty)
 131             });
 132             if result.is_some() {
 133                 return result;
 134             }
 135         }
 136
 137         None
 138     }
 139
 140     /// Try to resolve an overloaded place op. We only deal with the immutable
 141     /// variant here (Deref/Index). In some contexts we would need the mutable
 142     /// variant (DerefMut/IndexMut); those would be later converted by
 143     /// `convert_place_derefs_to_mutable`.
 144     pub(super) fn try_overloaded_place_op(
 145         &self,
 146         span: Span,
 147         base_ty: Ty<'tcx>,
 148         arg_tys: &[Ty<'tcx>],
 149         op: PlaceOp,
 150     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 151         debug!("try_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
 152
 153         let (imm_tr, imm_op) = match op {
 154             PlaceOp::Deref => (self.tcx.lang_items().deref_trait(), sym::deref),
 155             PlaceOp::Index => (self.tcx.lang_items().index_trait(), sym::index),
 156         };
 157         imm_tr.and_then(|trait_did| {
 158             self.lookup_method_in_trait(
 159                 span,
 160                 Ident::with_dummy_span(imm_op),
 161                 trait_did,
 162                 base_ty,
 163                 Some(arg_tys),
 164             )
 165         })
 166     }
 167
 168     fn try_mutable_overloaded_place_op(
 169         &self,
 170         span: Span,
 171         base_ty: Ty<'tcx>,
 172         arg_tys: &[Ty<'tcx>],
 173         op: PlaceOp,
 174     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 175         debug!("try_mutable_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
 176
 177         let (mut_tr, mut_op) = match op {
 178             PlaceOp::Deref => (self.tcx.lang_items().deref_mut_trait(), sym::deref_mut),
 179             PlaceOp::Index => (self.tcx.lang_items().index_mut_trait(), sym::index_mut),
 180         };
 181         mut_tr.and_then(|trait_did| {
 182             self.lookup_method_in_trait(
 183                 span,
 184                 Ident::with_dummy_span(mut_op),
 185                 trait_did,
 186                 base_ty,
 187                 Some(arg_tys),
 188             )
 189         })
 190     }
 191
 192     /// Convert auto-derefs, indices, etc of an expression from `Deref` and `Index`
 193     /// into `DerefMut` and `IndexMut` respectively.
 194     ///
 195     /// This is a second pass of typechecking derefs/indices. We need this we do not
 196     /// always know whether a place needs to be mutable or not in the first pass.
 197     /// This happens whether there is an implicit mutable reborrow, e.g. when the type
 198     /// is used as the receiver of a method call.
 199     pub fn convert_place_derefs_to_mutable(&self, expr: &hir::Expr<'_>) {
 200         // Gather up expressions we want to munge.
 201         let mut exprs = vec![expr];
 202
 203         while let hir::ExprKind::Field(ref expr, _)
 204         | hir::ExprKind::Index(ref expr, _)
 205         | hir::ExprKind::Unary(hir::UnOp::UnDeref, ref expr) = exprs.last().unwrap().kind
 206         {
 207             exprs.push(&expr);
 208         }
 209
 210         debug!("convert_place_derefs_to_mutable: exprs={:?}", exprs);
 211
 212         // Fix up autoderefs and derefs.
 213         for (i, &expr) in exprs.iter().rev().enumerate() {
 214             debug!("convert_place_derefs_to_mutable: i={} expr={:?}", i, expr);
 215
 216             // Fix up the autoderefs. Autorefs can only occur immediately preceding
 217             // overloaded place ops, and will be fixed by them in order to get
 218             // the correct region.
 219             let mut source = self.node_ty(expr.hir_id);
 220             // Do not mutate adjustments in place, but rather take them,
 221             // and replace them after mutating them, to avoid having the
 222             // typeck results borrowed during (`deref_mut`) method resolution.
 223             let previous_adjustments =
 224                 self.typeck_results.borrow_mut().adjustments_mut().remove(expr.hir_id);
 225             if let Some(mut adjustments) = previous_adjustments {
 226                 for adjustment in &mut adjustments {
 227                     if let Adjust::Deref(Some(ref mut deref)) = adjustment.kind {
 228                         if let Some(ok) = self.try_mutable_overloaded_place_op(
 229                             expr.span,
 230                             source,
 231                             &[],
 232                             PlaceOp::Deref,
 233                         ) {
 234                             let method = self.register_infer_ok_obligations(ok);
 235                             if let ty::Ref(region, _, mutbl) = method.sig.output().kind {
 236                                 *deref = OverloadedDeref { region, mutbl };
 237                             }
 238                         }
 239                     }
 240                     source = adjustment.target;
 241                 }
 242                 self.typeck_results.borrow_mut().adjustments_mut().insert(expr.hir_id, adjustments);
 243             }
 244
 245             match expr.kind {
 246                 hir::ExprKind::Index(ref base_expr, ref index_expr) => {
 247                     // We need to get the final type in case dereferences were needed for the trait
 248                     // to apply (#72002).
 249                     let index_expr_ty = self.typeck_results.borrow().expr_ty_adjusted(index_expr);
 250                     self.convert_place_op_to_mutable(
 251                         PlaceOp::Index,
 252                         expr,
 253                         base_expr,
 254                         &[index_expr_ty],
 255                     );
 256                 }
 257                 hir::ExprKind::Unary(hir::UnOp::UnDeref, ref base_expr) => {
 258                     self.convert_place_op_to_mutable(PlaceOp::Deref, expr, base_expr, &[]);
 259                 }
 260                 _ => {}
 261             }
 262         }
 263     }
 264
 265     fn convert_place_op_to_mutable(
 266         &self,
 267         op: PlaceOp,
 268         expr: &hir::Expr<'_>,
 269         base_expr: &hir::Expr<'_>,
 270         arg_tys: &[Ty<'tcx>],
 271     ) {
 272         debug!("convert_place_op_to_mutable({:?}, {:?}, {:?}, {:?})", op, expr, base_expr, arg_tys);
 273         if !self.typeck_results.borrow().is_method_call(expr) {
 274             debug!("convert_place_op_to_mutable - builtin, nothing to do");
 275             return;
 276         }
 277
 278         // Need to deref because overloaded place ops take self by-reference.
 279         let base_ty = self
 280             .typeck_results
 281             .borrow()
 282             .expr_ty_adjusted(base_expr)
 283             .builtin_deref(false)
 284             .expect("place op takes something that is not a ref")
 285             .ty;
 286
 287         let method = self.try_mutable_overloaded_place_op(expr.span, base_ty, arg_tys, op);
 288         let method = match method {
 289             Some(ok) => self.register_infer_ok_obligations(ok),
 290             // Couldn't find the mutable variant of the place op, keep the
 291             // current, immutable version.
 292             None => return,
 293         };
 294         debug!("convert_place_op_to_mutable: method={:?}", method);
 295         self.write_method_call(expr.hir_id, method);
 296
 297         let region = if let ty::Ref(r, _, hir::Mutability::Mut) = method.sig.inputs()[0].kind {
 298             r
 299         } else {
 300             span_bug!(expr.span, "input to mutable place op is not a mut ref?");
 301         };
 302
 303         // Convert the autoref in the base expr to mutable with the correct
 304         // region and mutability.
 305         let base_expr_ty = self.node_ty(base_expr.hir_id);
 306         if let Some(adjustments) =
 307             self.typeck_results.borrow_mut().adjustments_mut().get_mut(base_expr.hir_id)
 308         {
 309             let mut source = base_expr_ty;
 310             for adjustment in &mut adjustments[..] {
 311                 if let Adjust::Borrow(AutoBorrow::Ref(..)) = adjustment.kind {
 312                     debug!("convert_place_op_to_mutable: converting autoref {:?}", adjustment);
 313                     let mutbl = AutoBorrowMutability::Mut {
 314                         // Deref/indexing can be desugared to a method call,
 315                         // so maybe we could use two-phase here.
 316                         // See the documentation of AllowTwoPhase for why that's
 317                         // not the case today.
 318                         allow_two_phase_borrow: AllowTwoPhase::No,
 319                     };
 320                     adjustment.kind = Adjust::Borrow(AutoBorrow::Ref(region, mutbl));
 321                     adjustment.target =
 322                         self.tcx.mk_ref(region, ty::TypeAndMut { ty: source, mutbl: mutbl.into() });
 323                 }
 324                 source = adjustment.target;
 325             }
 326
 327             // If we have an autoref followed by unsizing at the end, fix the unsize target.
 328             if let [.., Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. }, Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), ref mut target }] =
 329                 adjustments[..]
 330             {
 331                 *target = method.sig.inputs()[0];
 332             }
 333         }
 334     }
 335 }