1 use crate::check::method::MethodCallee;
2 use crate::check::{FnCtxt, PlaceOp};
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};
11 use rustc_trait_selection::autoderef::Autoderef;
14 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
15 /// Type-check `*oprnd_expr` with `oprnd_expr` type-checked already.
16 pub(super) fn lookup_derefing(
19 oprnd_expr: &'tcx hir::Expr<'tcx>,
21 ) -> Option<Ty<'tcx>> {
22 if let Some(mt) = oprnd_ty.builtin_deref(true) {
26 let ok = self.try_overloaded_deref(expr.span, oprnd_ty)?;
27 let method = self.register_infer_ok_obligations(ok);
28 if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind() {
29 self.apply_adjustments(
32 kind: Adjust::Borrow(AutoBorrow::Ref(region, AutoBorrowMutability::Not)),
33 target: method.sig.inputs()[0],
37 span_bug!(expr.span, "input to deref is not a ref?");
39 let ty = self.make_overloaded_place_return_type(method).ty;
40 self.write_method_call(expr.hir_id, method);
44 /// Type-check `*base_expr[index_expr]` with `base_expr` and `index_expr` type-checked already.
45 pub(super) fn lookup_indexing(
48 base_expr: &'tcx hir::Expr<'tcx>,
51 ) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
52 // FIXME(#18741) -- this is almost but not quite the same as the
53 // autoderef that normal method probing does. They could likely be
56 let mut autoderef = self.autoderef(base_expr.span, base_ty);
57 let mut result = None;
58 while result.is_none() && autoderef.next().is_some() {
59 result = self.try_index_step(expr, base_expr, &autoderef, idx_ty);
61 self.register_predicates(autoderef.into_obligations());
65 /// To type-check `base_expr[index_expr]`, we progressively autoderef
66 /// (and otherwise adjust) `base_expr`, looking for a type which either
67 /// supports builtin indexing or overloaded indexing.
68 /// This loop implements one step in that search; the autoderef loop
69 /// is implemented by `lookup_indexing`.
73 base_expr: &hir::Expr<'_>,
74 autoderef: &Autoderef<'a, 'tcx>,
76 ) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
78 self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
80 "try_index_step(expr={:?}, base_expr={:?}, adjusted_ty={:?}, \
82 expr, base_expr, adjusted_ty, index_ty
85 for &unsize in &[false, true] {
86 let mut self_ty = adjusted_ty;
88 // We only unsize arrays here.
89 if let ty::Array(element_ty, _) = adjusted_ty.kind() {
90 self_ty = self.tcx.mk_slice(element_ty);
96 // If some lookup succeeds, write callee into table and extract index/element
97 // type from the method signature.
98 // If some lookup succeeded, install method in table
99 let input_ty = self.next_ty_var(TypeVariableOrigin {
100 kind: TypeVariableOriginKind::AutoDeref,
101 span: base_expr.span,
104 self.try_overloaded_place_op(expr.span, self_ty, &[input_ty], PlaceOp::Index);
106 let result = method.map(|ok| {
107 debug!("try_index_step: success, using overloaded indexing");
108 let method = self.register_infer_ok_obligations(ok);
110 let mut adjustments = self.adjust_steps(autoderef);
111 if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind() {
112 adjustments.push(Adjustment {
113 kind: Adjust::Borrow(AutoBorrow::Ref(region, AutoBorrowMutability::Not)),
114 target: self.tcx.mk_ref(
116 ty::TypeAndMut { mutbl: hir::Mutability::Not, ty: adjusted_ty },
120 span_bug!(expr.span, "input to index is not a ref?");
123 adjustments.push(Adjustment {
124 kind: Adjust::Pointer(PointerCast::Unsize),
125 target: method.sig.inputs()[0],
128 self.apply_adjustments(base_expr, adjustments);
130 self.write_method_call(expr.hir_id, method);
131 (input_ty, self.make_overloaded_place_return_type(method).ty)
133 if result.is_some() {
141 /// Try to resolve an overloaded place op. We only deal with the immutable
142 /// variant here (Deref/Index). In some contexts we would need the mutable
143 /// variant (DerefMut/IndexMut); those would be later converted by
144 /// `convert_place_derefs_to_mutable`.
145 pub(super) fn try_overloaded_place_op(
149 arg_tys: &[Ty<'tcx>],
151 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
152 debug!("try_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
154 let (imm_tr, imm_op) = match op {
155 PlaceOp::Deref => (self.tcx.lang_items().deref_trait(), sym::deref),
156 PlaceOp::Index => (self.tcx.lang_items().index_trait(), sym::index),
158 imm_tr.and_then(|trait_did| {
159 self.lookup_method_in_trait(
161 Ident::with_dummy_span(imm_op),
169 fn try_mutable_overloaded_place_op(
173 arg_tys: &[Ty<'tcx>],
175 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
176 debug!("try_mutable_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
178 let (mut_tr, mut_op) = match op {
179 PlaceOp::Deref => (self.tcx.lang_items().deref_mut_trait(), sym::deref_mut),
180 PlaceOp::Index => (self.tcx.lang_items().index_mut_trait(), sym::index_mut),
182 mut_tr.and_then(|trait_did| {
183 self.lookup_method_in_trait(
185 Ident::with_dummy_span(mut_op),
193 /// Convert auto-derefs, indices, etc of an expression from `Deref` and `Index`
194 /// into `DerefMut` and `IndexMut` respectively.
196 /// This is a second pass of typechecking derefs/indices. We need this because we do not
197 /// always know whether a place needs to be mutable or not in the first pass.
198 /// This happens whether there is an implicit mutable reborrow, e.g. when the type
199 /// is used as the receiver of a method call.
200 pub fn convert_place_derefs_to_mutable(&self, expr: &hir::Expr<'_>) {
201 // Gather up expressions we want to munge.
202 let mut exprs = vec![expr];
204 while let hir::ExprKind::Field(ref expr, _)
205 | hir::ExprKind::Index(ref expr, _)
206 | hir::ExprKind::Unary(hir::UnOp::UnDeref, ref expr) = exprs.last().unwrap().kind
211 debug!("convert_place_derefs_to_mutable: exprs={:?}", exprs);
213 // Fix up autoderefs and derefs.
214 let mut inside_union = false;
215 for (i, &expr) in exprs.iter().rev().enumerate() {
216 debug!("convert_place_derefs_to_mutable: i={} expr={:?}", i, expr);
218 let mut source = self.node_ty(expr.hir_id);
219 if matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::UnDeref, _)) {
220 // Clear previous flag; after a pointer indirection it does not apply any more.
221 inside_union = false;
223 if source.ty_adt_def().map_or(false, |adt| adt.is_union()) {
226 // Fix up the autoderefs. Autorefs can only occur immediately preceding
227 // overloaded place ops, and will be fixed by them in order to get
228 // the correct region.
229 // Do not mutate adjustments in place, but rather take them,
230 // and replace them after mutating them, to avoid having the
231 // typeck results borrowed during (`deref_mut`) method resolution.
232 let previous_adjustments =
233 self.typeck_results.borrow_mut().adjustments_mut().remove(expr.hir_id);
234 if let Some(mut adjustments) = previous_adjustments {
235 for adjustment in &mut adjustments {
236 if let Adjust::Deref(Some(ref mut deref)) = adjustment.kind {
237 if let Some(ok) = self.try_mutable_overloaded_place_op(
243 let method = self.register_infer_ok_obligations(ok);
244 if let ty::Ref(region, _, mutbl) = *method.sig.output().kind() {
245 *deref = OverloadedDeref { region, mutbl };
247 // If this is a union field, also throw an error for `DerefMut` of `ManuallyDrop` (see RFC 2514).
248 // This helps avoid accidental drops.
250 && source.ty_adt_def().map_or(false, |adt| adt.is_manually_drop())
252 let mut err = self.tcx.sess.struct_span_err(
254 "not automatically applying `DerefMut` on `ManuallyDrop` union field",
257 "writing to this reference calls the destructor for the old value",
259 err.help("add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor");
264 source = adjustment.target;
266 self.typeck_results.borrow_mut().adjustments_mut().insert(expr.hir_id, adjustments);
270 hir::ExprKind::Index(ref base_expr, ..) => {
271 self.convert_place_op_to_mutable(PlaceOp::Index, expr, base_expr);
273 hir::ExprKind::Unary(hir::UnOp::UnDeref, ref base_expr) => {
274 self.convert_place_op_to_mutable(PlaceOp::Deref, expr, base_expr);
281 fn convert_place_op_to_mutable(
284 expr: &hir::Expr<'_>,
285 base_expr: &hir::Expr<'_>,
287 debug!("convert_place_op_to_mutable({:?}, {:?}, {:?})", op, expr, base_expr);
288 if !self.typeck_results.borrow().is_method_call(expr) {
289 debug!("convert_place_op_to_mutable - builtin, nothing to do");
293 // Need to deref because overloaded place ops take self by-reference.
297 .expr_ty_adjusted(base_expr)
298 .builtin_deref(false)
299 .expect("place op takes something that is not a ref")
302 let arg_ty = match op {
303 PlaceOp::Deref => None,
305 // We would need to recover the `T` used when we resolve `<_ as Index<T>>::index`
306 // in try_index_step. This is the subst at index 1.
308 // Note: we should *not* use `expr_ty` of index_expr here because autoderef
309 // during coercions can cause type of index_expr to differ from `T` (#72002).
310 // We also could not use `expr_ty_adjusted` of index_expr because reborrowing
311 // during coercions can also cause type of index_expr to differ from `T`,
312 // which can potentially cause regionck failure (#74933).
313 Some(self.typeck_results.borrow().node_substs(expr.hir_id).type_at(1))
316 let arg_tys = match arg_ty {
318 Some(ref ty) => slice::from_ref(ty),
321 let method = self.try_mutable_overloaded_place_op(expr.span, base_ty, arg_tys, op);
322 let method = match method {
323 Some(ok) => self.register_infer_ok_obligations(ok),
324 // Couldn't find the mutable variant of the place op, keep the
325 // current, immutable version.
328 debug!("convert_place_op_to_mutable: method={:?}", method);
329 self.write_method_call(expr.hir_id, method);
331 let region = if let ty::Ref(r, _, hir::Mutability::Mut) = method.sig.inputs()[0].kind() {
334 span_bug!(expr.span, "input to mutable place op is not a mut ref?");
337 // Convert the autoref in the base expr to mutable with the correct
338 // region and mutability.
339 let base_expr_ty = self.node_ty(base_expr.hir_id);
340 if let Some(adjustments) =
341 self.typeck_results.borrow_mut().adjustments_mut().get_mut(base_expr.hir_id)
343 let mut source = base_expr_ty;
344 for adjustment in &mut adjustments[..] {
345 if let Adjust::Borrow(AutoBorrow::Ref(..)) = adjustment.kind {
346 debug!("convert_place_op_to_mutable: converting autoref {:?}", adjustment);
347 let mutbl = AutoBorrowMutability::Mut {
348 // Deref/indexing can be desugared to a method call,
349 // so maybe we could use two-phase here.
350 // See the documentation of AllowTwoPhase for why that's
351 // not the case today.
352 allow_two_phase_borrow: AllowTwoPhase::No,
354 adjustment.kind = Adjust::Borrow(AutoBorrow::Ref(region, mutbl));
356 self.tcx.mk_ref(region, ty::TypeAndMut { ty: source, mutbl: mutbl.into() });
358 source = adjustment.target;
361 // If we have an autoref followed by unsizing at the end, fix the unsize target.
362 if let [.., Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. }, Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), ref mut target }] =
365 *target = method.sig.inputs()[0];