1 use crate::check::method::MethodCallee;
2 use crate::check::{has_expected_num_generic_args, FnCtxt, PlaceOp};
4 use rustc_errors::Applicability;
6 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
7 use rustc_infer::infer::InferOk;
8 use rustc_middle::ty::adjustment::{Adjust, Adjustment, OverloadedDeref, PointerCast};
9 use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
10 use rustc_middle::ty::{self, Ty};
11 use rustc_span::symbol::{sym, Ident};
13 use rustc_trait_selection::autoderef::Autoderef;
16 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
17 /// Type-check `*oprnd_expr` with `oprnd_expr` type-checked already.
18 pub(super) fn lookup_derefing(
21 oprnd_expr: &'tcx hir::Expr<'tcx>,
23 ) -> Option<Ty<'tcx>> {
24 if let Some(mt) = oprnd_ty.builtin_deref(true) {
28 let ok = self.try_overloaded_deref(expr.span, oprnd_ty)?;
29 let method = self.register_infer_ok_obligations(ok);
30 if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind() {
31 self.apply_adjustments(
34 kind: Adjust::Borrow(AutoBorrow::Ref(*region, AutoBorrowMutability::Not)),
35 target: method.sig.inputs()[0],
39 span_bug!(expr.span, "input to deref is not a ref?");
41 let ty = self.make_overloaded_place_return_type(method).ty;
42 self.write_method_call(expr.hir_id, method);
46 /// Type-check `*base_expr[index_expr]` with `base_expr` and `index_expr` type-checked already.
47 pub(super) fn lookup_indexing(
50 base_expr: &'tcx hir::Expr<'tcx>,
52 index_expr: &'tcx hir::Expr<'tcx>,
54 ) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
55 // FIXME(#18741) -- this is almost but not quite the same as the
56 // autoderef that normal method probing does. They could likely be
59 let mut autoderef = self.autoderef(base_expr.span, base_ty);
60 let mut result = None;
61 while result.is_none() && autoderef.next().is_some() {
62 result = self.try_index_step(expr, base_expr, &autoderef, idx_ty, index_expr);
64 self.register_predicates(autoderef.into_obligations());
72 base_expr: &hir::Expr<'_>,
73 ) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
74 let ty = self.resolve_vars_if_possible(ty);
75 let mut err = self.tcx.sess.struct_span_err(
77 &format!("negative integers cannot be used to index on a `{ty}`"),
79 err.span_label(span, &format!("cannot use a negative integer for indexing on `{ty}`"));
80 if let (hir::ExprKind::Path(..), Ok(snippet)) =
81 (&base_expr.kind, self.tcx.sess.source_map().span_to_snippet(base_expr.span))
83 // `foo[-1]` to `foo[foo.len() - 1]`
84 err.span_suggestion_verbose(
87 "to access an element starting from the end of the `{ty}`, compute the index",
89 format!("{snippet}.len() "),
90 Applicability::MachineApplicable,
94 Some((self.tcx.ty_error(), self.tcx.ty_error()))
97 /// To type-check `base_expr[index_expr]`, we progressively autoderef
98 /// (and otherwise adjust) `base_expr`, looking for a type which either
99 /// supports builtin indexing or overloaded indexing.
100 /// This loop implements one step in that search; the autoderef loop
101 /// is implemented by `lookup_indexing`.
104 expr: &hir::Expr<'_>,
105 base_expr: &hir::Expr<'_>,
106 autoderef: &Autoderef<'a, 'tcx>,
108 index_expr: &hir::Expr<'_>,
109 ) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
111 self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
113 "try_index_step(expr={:?}, base_expr={:?}, adjusted_ty={:?}, \
115 expr, base_expr, adjusted_ty, index_ty
118 if let hir::ExprKind::Unary(
121 kind: hir::ExprKind::Lit(hir::Lit { node: ast::LitKind::Int(..), .. }),
126 match adjusted_ty.kind() {
127 ty::Adt(def, _) if self.tcx.is_diagnostic_item(sym::Vec, def.did()) => {
128 return self.negative_index(adjusted_ty, index_expr.span, base_expr);
130 ty::Slice(_) | ty::Array(_, _) => {
131 return self.negative_index(adjusted_ty, index_expr.span, base_expr);
137 for unsize in [false, true] {
138 let mut self_ty = adjusted_ty;
140 // We only unsize arrays here.
141 if let ty::Array(element_ty, _) = adjusted_ty.kind() {
142 self_ty = self.tcx.mk_slice(*element_ty);
148 // If some lookup succeeds, write callee into table and extract index/element
149 // type from the method signature.
150 // If some lookup succeeded, install method in table
151 let input_ty = self.next_ty_var(TypeVariableOrigin {
152 kind: TypeVariableOriginKind::AutoDeref,
153 span: base_expr.span,
156 self.try_overloaded_place_op(expr.span, self_ty, &[input_ty], PlaceOp::Index);
158 if let Some(result) = method {
159 debug!("try_index_step: success, using overloaded indexing");
160 let method = self.register_infer_ok_obligations(result);
162 let mut adjustments = self.adjust_steps(autoderef);
163 if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind() {
164 adjustments.push(Adjustment {
165 kind: Adjust::Borrow(AutoBorrow::Ref(*region, AutoBorrowMutability::Not)),
166 target: self.tcx.mk_ref(
168 ty::TypeAndMut { mutbl: hir::Mutability::Not, ty: adjusted_ty },
172 span_bug!(expr.span, "input to index is not a ref?");
175 adjustments.push(Adjustment {
176 kind: Adjust::Pointer(PointerCast::Unsize),
177 target: method.sig.inputs()[0],
180 self.apply_adjustments(base_expr, adjustments);
182 self.write_method_call(expr.hir_id, method);
184 return Some((input_ty, self.make_overloaded_place_return_type(method).ty));
191 /// Try to resolve an overloaded place op. We only deal with the immutable
192 /// variant here (Deref/Index). In some contexts we would need the mutable
193 /// variant (DerefMut/IndexMut); those would be later converted by
194 /// `convert_place_derefs_to_mutable`.
195 pub(super) fn try_overloaded_place_op(
199 arg_tys: &[Ty<'tcx>],
201 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
202 debug!("try_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
204 let (imm_tr, imm_op) = match op {
205 PlaceOp::Deref => (self.tcx.lang_items().deref_trait(), sym::deref),
206 PlaceOp::Index => (self.tcx.lang_items().index_trait(), sym::index),
209 // If the lang item was declared incorrectly, stop here so that we don't
210 // run into an ICE (#83893). The error is reported where the lang item is
212 if !has_expected_num_generic_args(
223 imm_tr.and_then(|trait_did| {
224 self.lookup_method_in_trait(
226 Ident::with_dummy_span(imm_op),
234 fn try_mutable_overloaded_place_op(
238 arg_tys: &[Ty<'tcx>],
240 ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
241 debug!("try_mutable_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
243 let (mut_tr, mut_op) = match op {
244 PlaceOp::Deref => (self.tcx.lang_items().deref_mut_trait(), sym::deref_mut),
245 PlaceOp::Index => (self.tcx.lang_items().index_mut_trait(), sym::index_mut),
248 // If the lang item was declared incorrectly, stop here so that we don't
249 // run into an ICE (#83893). The error is reported where the lang item is
251 if !has_expected_num_generic_args(
262 mut_tr.and_then(|trait_did| {
263 self.lookup_method_in_trait(
265 Ident::with_dummy_span(mut_op),
273 /// Convert auto-derefs, indices, etc of an expression from `Deref` and `Index`
274 /// into `DerefMut` and `IndexMut` respectively.
276 /// This is a second pass of typechecking derefs/indices. We need this because we do not
277 /// always know whether a place needs to be mutable or not in the first pass.
278 /// This happens whether there is an implicit mutable reborrow, e.g. when the type
279 /// is used as the receiver of a method call.
280 pub fn convert_place_derefs_to_mutable(&self, expr: &hir::Expr<'_>) {
281 // Gather up expressions we want to munge.
282 let mut exprs = vec![expr];
284 while let hir::ExprKind::Field(ref expr, _)
285 | hir::ExprKind::Index(ref expr, _)
286 | hir::ExprKind::Unary(hir::UnOp::Deref, ref expr) = exprs.last().unwrap().kind
291 debug!("convert_place_derefs_to_mutable: exprs={:?}", exprs);
293 // Fix up autoderefs and derefs.
294 let mut inside_union = false;
295 for (i, &expr) in exprs.iter().rev().enumerate() {
296 debug!("convert_place_derefs_to_mutable: i={} expr={:?}", i, expr);
298 let mut source = self.node_ty(expr.hir_id);
299 if matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Deref, _)) {
300 // Clear previous flag; after a pointer indirection it does not apply any more.
301 inside_union = false;
303 if source.is_union() {
306 // Fix up the autoderefs. Autorefs can only occur immediately preceding
307 // overloaded place ops, and will be fixed by them in order to get
308 // the correct region.
309 // Do not mutate adjustments in place, but rather take them,
310 // and replace them after mutating them, to avoid having the
311 // typeck results borrowed during (`deref_mut`) method resolution.
312 let previous_adjustments =
313 self.typeck_results.borrow_mut().adjustments_mut().remove(expr.hir_id);
314 if let Some(mut adjustments) = previous_adjustments {
315 for adjustment in &mut adjustments {
316 if let Adjust::Deref(Some(ref mut deref)) = adjustment.kind
317 && let Some(ok) = self.try_mutable_overloaded_place_op(
324 let method = self.register_infer_ok_obligations(ok);
325 if let ty::Ref(region, _, mutbl) = *method.sig.output().kind() {
326 *deref = OverloadedDeref { region, mutbl, span: deref.span };
328 // If this is a union field, also throw an error for `DerefMut` of `ManuallyDrop` (see RFC 2514).
329 // This helps avoid accidental drops.
331 && source.ty_adt_def().map_or(false, |adt| adt.is_manually_drop())
333 let mut err = self.tcx.sess.struct_span_err(
335 "not automatically applying `DerefMut` on `ManuallyDrop` union field",
338 "writing to this reference calls the destructor for the old value",
340 err.help("add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor");
344 source = adjustment.target;
346 self.typeck_results.borrow_mut().adjustments_mut().insert(expr.hir_id, adjustments);
350 hir::ExprKind::Index(base_expr, ..) => {
351 self.convert_place_op_to_mutable(PlaceOp::Index, expr, base_expr);
353 hir::ExprKind::Unary(hir::UnOp::Deref, base_expr) => {
354 self.convert_place_op_to_mutable(PlaceOp::Deref, expr, base_expr);
361 fn convert_place_op_to_mutable(
364 expr: &hir::Expr<'_>,
365 base_expr: &hir::Expr<'_>,
367 debug!("convert_place_op_to_mutable({:?}, {:?}, {:?})", op, expr, base_expr);
368 if !self.typeck_results.borrow().is_method_call(expr) {
369 debug!("convert_place_op_to_mutable - builtin, nothing to do");
373 // Need to deref because overloaded place ops take self by-reference.
377 .expr_ty_adjusted(base_expr)
378 .builtin_deref(false)
379 .expect("place op takes something that is not a ref")
382 let arg_ty = match op {
383 PlaceOp::Deref => None,
385 // We would need to recover the `T` used when we resolve `<_ as Index<T>>::index`
386 // in try_index_step. This is the subst at index 1.
388 // Note: we should *not* use `expr_ty` of index_expr here because autoderef
389 // during coercions can cause type of index_expr to differ from `T` (#72002).
390 // We also could not use `expr_ty_adjusted` of index_expr because reborrowing
391 // during coercions can also cause type of index_expr to differ from `T`,
392 // which can potentially cause regionck failure (#74933).
393 Some(self.typeck_results.borrow().node_substs(expr.hir_id).type_at(1))
396 let arg_tys = match arg_ty {
398 Some(ref ty) => slice::from_ref(ty),
401 let method = self.try_mutable_overloaded_place_op(expr.span, base_ty, arg_tys, op);
402 let method = match method {
403 Some(ok) => self.register_infer_ok_obligations(ok),
404 // Couldn't find the mutable variant of the place op, keep the
405 // current, immutable version.
408 debug!("convert_place_op_to_mutable: method={:?}", method);
409 self.write_method_call(expr.hir_id, method);
411 let ty::Ref(region, _, hir::Mutability::Mut) = method.sig.inputs()[0].kind() else {
412 span_bug!(expr.span, "input to mutable place op is not a mut ref?");
415 // Convert the autoref in the base expr to mutable with the correct
416 // region and mutability.
417 let base_expr_ty = self.node_ty(base_expr.hir_id);
418 if let Some(adjustments) =
419 self.typeck_results.borrow_mut().adjustments_mut().get_mut(base_expr.hir_id)
421 let mut source = base_expr_ty;
422 for adjustment in &mut adjustments[..] {
423 if let Adjust::Borrow(AutoBorrow::Ref(..)) = adjustment.kind {
424 debug!("convert_place_op_to_mutable: converting autoref {:?}", adjustment);
425 let mutbl = AutoBorrowMutability::Mut {
426 // Deref/indexing can be desugared to a method call,
427 // so maybe we could use two-phase here.
428 // See the documentation of AllowTwoPhase for why that's
429 // not the case today.
430 allow_two_phase_borrow: AllowTwoPhase::No,
432 adjustment.kind = Adjust::Borrow(AutoBorrow::Ref(*region, mutbl));
433 adjustment.target = self
435 .mk_ref(*region, ty::TypeAndMut { ty: source, mutbl: mutbl.into() });
437 source = adjustment.target;
440 // If we have an autoref followed by unsizing at the end, fix the unsize target.
443 Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. },
444 Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), ref mut target },
447 *target = method.sig.inputs()[0];