2 Applicability, Diagnostic, DiagnosticBuilder, EmissionGuarantee, ErrorGuaranteed,
5 use rustc_hir::intravisit::Visitor;
7 use rustc_middle::hir::map::Map;
8 use rustc_middle::mir::{Mutability, Place, PlaceRef, ProjectionElem};
9 use rustc_middle::ty::{self, Ty, TyCtxt};
11 hir::place::PlaceBase,
12 mir::{self, BindingForm, ClearCrossCrate, Local, LocalDecl, LocalInfo, LocalKind, Location},
14 use rustc_span::source_map::DesugaringKind;
15 use rustc_span::symbol::{kw, Symbol};
16 use rustc_span::{sym, BytePos, Span};
18 use crate::diagnostics::BorrowedContentSource;
19 use crate::MirBorrowckCtxt;
20 use rustc_const_eval::util::collect_writes::FindAssignments;
22 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
23 pub(crate) enum AccessKind {
28 impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
29 pub(crate) fn report_mutability_error(
31 access_place: Place<'tcx>,
33 the_place_err: PlaceRef<'tcx>,
34 error_access: AccessKind,
38 "report_mutability_error(\
39 access_place={:?}, span={:?}, the_place_err={:?}, error_access={:?}, location={:?},\
41 access_place, span, the_place_err, error_access, location,
47 let mut opt_source = None;
48 let access_place_desc = self.describe_any_place(access_place.as_ref());
49 debug!("report_mutability_error: access_place_desc={:?}", access_place_desc);
52 PlaceRef { local, projection: [] } => {
53 item_msg = access_place_desc;
54 if access_place.as_local().is_some() {
55 reason = ", as it is not declared as mutable".to_string();
57 let name = self.local_names[local].expect("immutable unnamed local");
58 reason = format!(", as `{name}` is not declared as mutable");
64 projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)],
66 debug_assert!(is_closure_or_generator(
67 Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty
70 let imm_borrow_derefed = self.upvars[upvar_index.index()]
74 .any(|ty| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not)));
76 // If the place is immutable then:
78 // - Either we deref an immutable ref to get to our final place.
79 // - We don't capture derefs of raw ptrs
80 // - Or the final place is immut because the root variable of the capture
81 // isn't marked mut and we should suggest that to the user.
82 if imm_borrow_derefed {
83 // If we deref an immutable ref then the suggestion here doesn't help.
86 item_msg = access_place_desc;
87 if self.is_upvar_field_projection(access_place.as_ref()).is_some() {
88 reason = ", as it is not declared as mutable".to_string();
90 let name = self.upvars[upvar_index.index()].place.to_string(self.infcx.tcx);
91 reason = format!(", as `{name}` is not declared as mutable");
96 PlaceRef { local, projection: [ProjectionElem::Deref] }
97 if self.body.local_decls[local].is_ref_for_guard() =>
99 item_msg = access_place_desc;
100 reason = ", as it is immutable for the pattern guard".to_string();
102 PlaceRef { local, projection: [ProjectionElem::Deref] }
103 if self.body.local_decls[local].is_ref_to_static() =>
105 if access_place.projection.len() == 1 {
106 item_msg = format!("immutable static item {access_place_desc}");
107 reason = String::new();
109 item_msg = access_place_desc;
110 let local_info = &self.body.local_decls[local].local_info;
111 if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
112 let static_name = &self.infcx.tcx.item_name(def_id);
113 reason = format!(", as `{static_name}` is an immutable static item");
115 bug!("is_ref_to_static return true, but not ref to static?");
119 PlaceRef { local: _, projection: [proj_base @ .., ProjectionElem::Deref] } => {
120 if the_place_err.local == ty::CAPTURE_STRUCT_LOCAL
121 && proj_base.is_empty()
122 && !self.upvars.is_empty()
124 item_msg = access_place_desc;
126 self.body.local_decls[ty::CAPTURE_STRUCT_LOCAL].ty.is_region_ptr()
128 debug_assert!(is_closure_or_generator(
131 the_place_err.projection,
138 reason = if self.is_upvar_field_projection(access_place.as_ref()).is_some() {
139 ", as it is a captured variable in a `Fn` closure".to_string()
141 ", as `Fn` closures cannot mutate their captured variables".to_string()
144 let source = self.borrowed_content_source(PlaceRef {
145 local: the_place_err.local,
146 projection: proj_base,
148 let pointer_type = source.describe_for_immutable_place(self.infcx.tcx);
149 opt_source = Some(source);
150 if let Some(desc) = self.describe_place(access_place.as_ref()) {
151 item_msg = format!("`{desc}`");
152 reason = match error_access {
153 AccessKind::Mutate => format!(", which is behind {pointer_type}"),
154 AccessKind::MutableBorrow => {
155 format!(", as it is behind {pointer_type}")
159 item_msg = format!("data in {pointer_type}");
160 reason = String::new();
170 ProjectionElem::Index(_)
171 | ProjectionElem::ConstantIndex { .. }
172 | ProjectionElem::Subslice { .. }
173 | ProjectionElem::Downcast(..),
175 } => bug!("Unexpected immutable place."),
178 debug!("report_mutability_error: item_msg={:?}, reason={:?}", item_msg, reason);
180 // `act` and `acted_on` are strings that let us abstract over
181 // the verbs used in some diagnostic messages.
185 let span = match error_access {
186 AccessKind::Mutate => {
187 err = self.cannot_assign(span, &(item_msg + &reason));
189 acted_on = "written";
192 AccessKind::MutableBorrow => {
193 act = "borrow as mutable";
194 acted_on = "borrowed as mutable";
196 let borrow_spans = self.borrow_spans(span, location);
197 let borrow_span = borrow_spans.args_or_use();
198 err = self.cannot_borrow_path_as_mutable_because(borrow_span, &item_msg, &reason);
199 borrow_spans.var_span_label(
202 "mutable borrow occurs due to use of {} in closure",
203 self.describe_any_place(access_place.as_ref()),
211 debug!("report_mutability_error: act={:?}, acted_on={:?}", act, acted_on);
213 match the_place_err {
214 // Suggest making an existing shared borrow in a struct definition a mutable borrow.
216 // This is applicable when we have a deref of a field access to a deref of a local -
217 // something like `*((*_1).0`. The local that we get will be a reference to the
218 // struct we've got a field access of (it must be a reference since there's a deref
219 // after the field access).
225 ProjectionElem::Deref,
226 ProjectionElem::Field(field, _),
227 ProjectionElem::Deref,
230 err.span_label(span, format!("cannot {ACT}", ACT = act));
232 if let Some(span) = get_mut_span_in_struct_field(
234 Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty,
237 err.span_suggestion_verbose(
239 "consider changing this to be mutable",
241 Applicability::MaybeIncorrect,
246 // Suggest removing a `&mut` from the use of a mutable reference.
247 PlaceRef { local, projection: [] }
252 .map(|l| mut_borrow_of_mutable_ref(l, self.local_names[local]))
255 let decl = &self.body.local_decls[local];
256 err.span_label(span, format!("cannot {ACT}", ACT = act));
257 if let Some(mir::Statement {
260 mir::StatementKind::Assign(box (
264 mir::BorrowKind::Mut { allow_two_phase_borrow: false },
269 }) = &self.body[location.block].statements.get(location.statement_index)
271 match decl.local_info {
272 Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
273 mir::VarBindingForm {
274 binding_mode: ty::BindingMode::BindByValue(Mutability::Not),
275 opt_ty_info: Some(sp),
280 err.span_note(sp, "the binding is already a mutable borrow");
284 decl.source_info.span,
285 "the binding is already a mutable borrow",
290 self.infcx.tcx.sess.source_map().span_to_snippet(source_info.span)
292 if snippet.starts_with("&mut ") {
293 // We don't have access to the HIR to get accurate spans, but we can
294 // give a best effort structured suggestion.
295 err.span_suggestion_verbose(
296 source_info.span.with_hi(source_info.span.lo() + BytePos(5)),
297 "try removing `&mut` here",
299 Applicability::MachineApplicable,
302 // This can occur with things like `(&mut self).foo()`.
303 err.span_help(source_info.span, "try removing `&mut` here");
306 err.span_help(source_info.span, "try removing `&mut` here");
308 } else if decl.mutability == Mutability::Not
311 Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(
312 hir::ImplicitSelfKind::MutRef
316 err.span_suggestion_verbose(
317 decl.source_info.span.shrink_to_lo(),
318 "consider making the binding mutable",
320 Applicability::MachineApplicable,
325 // We want to suggest users use `let mut` for local (user
326 // variable) mutations...
327 PlaceRef { local, projection: [] }
328 if self.body.local_decls[local].can_be_made_mutable() =>
330 // ... but it doesn't make sense to suggest it on
331 // variables that are `ref x`, `ref mut x`, `&self`,
332 // or `&mut self` (such variables are simply not
334 let local_decl = &self.body.local_decls[local];
335 assert_eq!(local_decl.mutability, Mutability::Not);
337 err.span_label(span, format!("cannot {ACT}", ACT = act));
339 local_decl.source_info.span,
340 "consider changing this to be mutable",
341 format!("mut {}", self.local_names[local].unwrap()),
342 Applicability::MachineApplicable,
344 let tcx = self.infcx.tcx;
345 if let ty::Closure(id, _) = *the_place_err.ty(self.body, tcx).ty.kind() {
346 self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, &mut err);
350 // Also suggest adding mut for upvars
353 projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)],
355 debug_assert!(is_closure_or_generator(
356 Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty
359 let captured_place = &self.upvars[upvar_index.index()].place;
361 err.span_label(span, format!("cannot {ACT}", ACT = act));
363 let upvar_hir_id = captured_place.get_root_variable();
365 if let Some(Node::Pat(pat)) = self.infcx.tcx.hir().find(upvar_hir_id)
366 && let hir::PatKind::Binding(
367 hir::BindingAnnotation::NONE,
375 "consider changing this to be mutable",
376 format!("mut {}", upvar_ident.name),
377 Applicability::MachineApplicable,
381 let tcx = self.infcx.tcx;
382 if let ty::Ref(_, ty, Mutability::Mut) = the_place_err.ty(self.body, tcx).ty.kind()
383 && let ty::Closure(id, _) = *ty.kind()
385 self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, &mut err);
389 // complete hack to approximate old AST-borrowck
390 // diagnostic: if the span starts with a mutable borrow of
391 // a local variable, then just suggest the user remove it.
392 PlaceRef { local: _, projection: [] }
394 if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) {
395 snippet.starts_with("&mut ")
401 err.span_label(span, format!("cannot {ACT}", ACT = act));
404 "try removing `&mut` here",
406 Applicability::MaybeIncorrect,
410 PlaceRef { local, projection: [ProjectionElem::Deref] }
411 if self.body.local_decls[local].is_ref_for_guard() =>
413 err.span_label(span, format!("cannot {ACT}", ACT = act));
415 "variables bound in patterns are immutable until the end of the pattern guard",
419 // We want to point out when a `&` can be readily replaced
422 // FIXME: can this case be generalized to work for an
423 // arbitrary base for the projection?
424 PlaceRef { local, projection: [ProjectionElem::Deref] }
425 if self.body.local_decls[local].is_user_variable() =>
427 let local_decl = &self.body.local_decls[local];
429 let (pointer_sigil, pointer_desc) = if local_decl.ty.is_region_ptr() {
432 ("*const", "pointer")
435 match self.local_names[local] {
436 Some(name) if !local_decl.from_compiler_desugaring() => {
437 let label = match local_decl.local_info.as_deref().unwrap() {
438 LocalInfo::User(ClearCrossCrate::Set(
439 mir::BindingForm::ImplicitSelf(_),
441 let (span, suggestion) =
442 suggest_ampmut_self(self.infcx.tcx, local_decl);
443 Some((true, span, suggestion))
446 LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var(
447 mir::VarBindingForm {
448 binding_mode: ty::BindingMode::BindByValue(_),
453 // check if the RHS is from desugaring
454 let opt_assignment_rhs_span =
455 self.body.find_assignments(local).first().map(|&location| {
456 if let Some(mir::Statement {
459 mir::StatementKind::Assign(box (
461 mir::Rvalue::Use(mir::Operand::Copy(place)),
463 }) = self.body[location.block]
465 .get(location.statement_index)
467 self.body.local_decls[place.local].source_info.span
469 self.body.source_info(location).span
472 match opt_assignment_rhs_span.and_then(|s| s.desugaring_kind()) {
473 // on for loops, RHS points to the iterator part
474 Some(DesugaringKind::ForLoop) => {
475 self.suggest_similar_mut_method_for_for_loop(&mut err);
476 err.span_label(opt_assignment_rhs_span.unwrap(), format!(
477 "this iterator yields `{pointer_sigil}` {pointer_desc}s",
481 // don't create labels for compiler-generated spans
484 let label = if name != kw::SelfLower {
488 opt_assignment_rhs_span,
492 match local_decl.local_info.as_deref() {
493 Some(LocalInfo::User(ClearCrossCrate::Set(
494 mir::BindingForm::Var(mir::VarBindingForm {
499 let (span, sugg) = suggest_ampmut_self(
505 // explicit self (eg `self: &'a Self`)
509 opt_assignment_rhs_span,
519 LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var(
520 mir::VarBindingForm {
521 binding_mode: ty::BindingMode::BindByReference(_),
525 let pattern_span = local_decl.source_info.span;
526 suggest_ref_mut(self.infcx.tcx, pattern_span)
527 .map(|replacement| (true, pattern_span, replacement))
530 LocalInfo::User(ClearCrossCrate::Clear) => {
531 bug!("saw cleared local state")
538 Some((true, err_help_span, suggested_code)) => {
539 let (is_trait_sig, local_trait) = self.is_error_in_trait(local);
544 "consider changing this to be a mutable {pointer_desc}"
547 Applicability::MachineApplicable,
549 } else if let Some(x) = local_trait {
553 "consider changing that to be a mutable {pointer_desc}"
556 Applicability::MachineApplicable,
560 Some((false, err_label_span, message)) => {
564 "consider changing this binding's type to be: `{message}`"
573 "`{NAME}` is a `{SIGIL}` {DESC}, \
574 so the data it refers to cannot be {ACTED_ON}",
576 SIGIL = pointer_sigil,
586 "cannot {ACT} through `{SIGIL}` {DESC}",
588 SIGIL = pointer_sigil,
596 PlaceRef { local, projection: [ProjectionElem::Deref] }
597 if local == ty::CAPTURE_STRUCT_LOCAL && !self.upvars.is_empty() =>
599 self.expected_fn_found_fn_mut_call(&mut err, span, act);
602 PlaceRef { local: _, projection: [.., ProjectionElem::Deref] } => {
603 err.span_label(span, format!("cannot {ACT}", ACT = act));
606 Some(BorrowedContentSource::OverloadedDeref(ty)) => {
608 "trait `DerefMut` is required to modify through a dereference, \
609 but it is not implemented for `{ty}`",
612 Some(BorrowedContentSource::OverloadedIndex(ty)) => {
614 "trait `IndexMut` is required to modify indexed content, \
615 but it is not implemented for `{ty}`",
617 self.suggest_map_index_mut_alternatives(ty, &mut err, span);
624 err.span_label(span, format!("cannot {ACT}", ACT = act));
628 self.buffer_error(err);
631 fn suggest_map_index_mut_alternatives(
634 err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
637 let Some(adt) = ty.ty_adt_def() else { return };
639 if self.infcx.tcx.is_diagnostic_item(sym::HashMap, did)
640 || self.infcx.tcx.is_diagnostic_item(sym::BTreeMap, did)
642 struct V<'a, 'b, 'tcx, G: EmissionGuarantee> {
644 err: &'a mut DiagnosticBuilder<'b, G>,
648 impl<'a, 'b: 'a, 'hir, 'tcx, G: EmissionGuarantee> Visitor<'hir> for V<'a, 'b, 'tcx, G> {
649 fn visit_stmt(&mut self, stmt: &'hir hir::Stmt<'hir>) {
650 hir::intravisit::walk_stmt(self, stmt);
651 let expr = match stmt.kind {
652 hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr) => expr,
653 hir::StmtKind::Local(hir::Local { init: Some(expr), .. }) => expr,
658 if let hir::ExprKind::Assign(place, rv, _sp) = expr.kind
659 && let hir::ExprKind::Index(val, index) = place.kind
660 && (expr.span == self.assign_span || place.span == self.assign_span)
664 self.err.multipart_suggestions(
666 "to modify a `{}`, use `.get_mut()`, `.insert()` or the entry API",
670 vec![ // val.insert(index, rv);
672 val.span.shrink_to_hi().with_hi(index.span.lo()),
673 ".insert(".to_string(),
676 index.span.shrink_to_hi().with_hi(rv.span.lo()),
679 (rv.span.shrink_to_hi(), ")".to_string()),
681 vec![ // val.get_mut(index).map(|v| { *v = rv; });
683 val.span.shrink_to_hi().with_hi(index.span.lo()),
684 ".get_mut(".to_string(),
687 index.span.shrink_to_hi().with_hi(place.span.hi()),
688 ").map(|val| { *val".to_string(),
691 rv.span.shrink_to_hi(),
695 vec![ // let x = val.entry(index).or_insert(rv);
696 (val.span.shrink_to_lo(), "let val = ".to_string()),
698 val.span.shrink_to_hi().with_hi(index.span.lo()),
699 ".entry(".to_string(),
702 index.span.shrink_to_hi().with_hi(rv.span.lo()),
703 ").or_insert(".to_string(),
705 (rv.span.shrink_to_hi(), ")".to_string()),
708 Applicability::MachineApplicable,
710 self.suggested = true;
711 } else if let hir::ExprKind::MethodCall(_path, receiver, _, sp) = expr.kind
712 && let hir::ExprKind::Index(val, index) = receiver.kind
713 && expr.span == self.assign_span
715 // val[index].path(args..);
716 self.err.multipart_suggestion(
717 &format!("to modify a `{}` use `.get_mut()`", self.ty),
720 val.span.shrink_to_hi().with_hi(index.span.lo()),
721 ".get_mut(".to_string(),
724 index.span.shrink_to_hi().with_hi(receiver.span.hi()),
725 ").map(|val| val".to_string(),
727 (sp.shrink_to_hi(), ")".to_string()),
729 Applicability::MachineApplicable,
731 self.suggested = true;
735 let hir_map = self.infcx.tcx.hir();
736 let def_id = self.body.source.def_id();
737 let hir_id = hir_map.local_def_id_to_hir_id(def_id.as_local().unwrap());
738 let node = hir_map.find(hir_id);
739 let Some(hir::Node::Item(item)) = node else { return; };
740 let hir::ItemKind::Fn(.., body_id) = item.kind else { return; };
741 let body = self.infcx.tcx.hir().body(body_id);
742 let mut v = V { assign_span: span, err, ty, suggested: false };
746 "to modify a `{ty}`, use `.get_mut()`, `.insert()` or the entry API",
752 /// User cannot make signature of a trait mutable without changing the
753 /// trait. So we find if this error belongs to a trait and if so we move
754 /// suggestion to the trait or disable it if it is out of scope of this crate
755 fn is_error_in_trait(&self, local: Local) -> (bool, Option<Span>) {
756 if self.body.local_kind(local) != LocalKind::Arg {
757 return (false, None);
759 let hir_map = self.infcx.tcx.hir();
760 let my_def = self.body.source.def_id();
761 let my_hir = hir_map.local_def_id_to_hir_id(my_def.as_local().unwrap());
763 self.infcx.tcx.impl_of_method(my_def).and_then(|x| self.infcx.tcx.trait_id_of_impl(x))
765 return (false, None);
769 td.as_local().and_then(|tld| match hir_map.find_by_def_id(tld) {
770 Some(Node::Item(hir::Item {
771 kind: hir::ItemKind::Trait(_, _, _, _, items),
774 let mut f_in_trait_opt = None;
775 for hir::TraitItemRef { id: fi, kind: k, .. } in *items {
776 let hi = fi.hir_id();
777 if !matches!(k, hir::AssocItemKind::Fn { .. }) {
780 if hir_map.name(hi) != hir_map.name(my_hir) {
783 f_in_trait_opt = Some(hi);
786 f_in_trait_opt.and_then(|f_in_trait| match hir_map.find(f_in_trait) {
787 Some(Node::TraitItem(hir::TraitItem {
789 hir::TraitItemKind::Fn(
790 hir::FnSig { decl: hir::FnDecl { inputs, .. }, .. },
795 let hir::Ty { span, .. } = inputs[local.index() - 1];
806 // point to span of upvar making closure call require mutable borrow
807 fn show_mutating_upvar(
810 closure_local_def_id: hir::def_id::LocalDefId,
811 the_place_err: PlaceRef<'tcx>,
812 err: &mut Diagnostic,
814 let tables = tcx.typeck(closure_local_def_id);
815 let closure_hir_id = tcx.hir().local_def_id_to_hir_id(closure_local_def_id);
816 if let Some((span, closure_kind_origin)) =
817 &tables.closure_kind_origins().get(closure_hir_id)
819 let reason = if let PlaceBase::Upvar(upvar_id) = closure_kind_origin.base {
820 let upvar = ty::place_to_string_for_capture(tcx, closure_kind_origin);
821 let root_hir_id = upvar_id.var_path.hir_id;
822 // we have an origin for this closure kind starting at this root variable so it's safe to unwrap here
823 let captured_places =
824 tables.closure_min_captures[&closure_local_def_id].get(&root_hir_id).unwrap();
826 let origin_projection = closure_kind_origin
829 .map(|proj| proj.kind)
830 .collect::<Vec<_>>();
831 let mut capture_reason = String::new();
832 for captured_place in captured_places {
833 let captured_place_kinds = captured_place
837 .map(|proj| proj.kind)
838 .collect::<Vec<_>>();
839 if rustc_middle::ty::is_ancestor_or_same_capture(
840 &captured_place_kinds,
843 match captured_place.info.capture_kind {
844 ty::UpvarCapture::ByRef(
845 ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
847 capture_reason = format!("mutable borrow of `{upvar}`");
849 ty::UpvarCapture::ByValue => {
850 capture_reason = format!("possible mutation of `{upvar}`");
852 _ => bug!("upvar `{upvar}` borrowed, but not mutably"),
857 if capture_reason.is_empty() {
858 bug!("upvar `{upvar}` borrowed, but cannot find reason");
867 "calling `{}` requires mutable binding due to {}",
868 self.describe_place(the_place_err).unwrap(),
875 // Attempt to search similar mutable associated items for suggestion.
876 // In the future, attempt in all path but initially for RHS of for_loop
877 fn suggest_similar_mut_method_for_for_loop(&self, err: &mut Diagnostic) {
880 ExprKind::{Block, Call, DropTemps, Match, MethodCall},
881 HirId, ImplItem, ImplItemKind, Item, ItemKind,
884 fn maybe_body_id_of_fn(hir_map: Map<'_>, id: HirId) -> Option<BodyId> {
885 match hir_map.find(id) {
886 Some(Node::Item(Item { kind: ItemKind::Fn(_, _, body_id), .. }))
887 | Some(Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(_, body_id), .. })) => {
893 let hir_map = self.infcx.tcx.hir();
894 let mir_body_hir_id = self.mir_hir_id();
895 if let Some(fn_body_id) = maybe_body_id_of_fn(hir_map, mir_body_hir_id) {
911 MethodCall(path_segment, _, _, span),
929 ) = hir_map.body(fn_body_id).value.kind
931 let opt_suggestions = self
934 .typeck(path_segment.hir_id.owner)
935 .type_dependent_def_id(*hir_id)
936 .and_then(|def_id| self.infcx.tcx.impl_of_method(def_id))
937 .map(|def_id| self.infcx.tcx.associated_items(def_id))
940 .in_definition_order()
941 .map(|assoc_item_def| assoc_item_def.ident(self.infcx.tcx))
943 let original_method_ident = path_segment.ident;
944 original_method_ident != ident
947 .starts_with(&original_method_ident.name.to_string())
949 .map(|ident| format!("{ident}()"))
953 if let Some(mut suggestions) = opt_suggestions
954 && suggestions.peek().is_some()
956 err.span_suggestions(
958 "use mutable method",
960 Applicability::MaybeIncorrect,
967 /// Targeted error when encountering an `FnMut` closure where an `Fn` closure was expected.
968 fn expected_fn_found_fn_mut_call(&self, err: &mut Diagnostic, sp: Span, act: &str) {
969 err.span_label(sp, format!("cannot {act}"));
971 let hir = self.infcx.tcx.hir();
972 let closure_id = self.mir_hir_id();
973 let closure_span = self.infcx.tcx.def_span(self.mir_def_id());
974 let fn_call_id = hir.get_parent_node(closure_id);
975 let node = hir.get(fn_call_id);
976 let def_id = hir.enclosing_body_owner(fn_call_id);
977 let mut look_at_return = true;
978 // If we can detect the expression to be an `fn` call where the closure was an argument,
979 // we point at the `fn` definition argument...
980 if let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Call(func, args), .. }) = node {
984 .filter(|(_, arg)| arg.hir_id == closure_id)
987 let tables = self.infcx.tcx.typeck(def_id);
988 if let Some(ty::FnDef(def_id, _)) =
989 tables.node_type_opt(func.hir_id).as_ref().map(|ty| ty.kind())
991 let arg = match hir.get_if_local(*def_id) {
993 hir::Node::Item(hir::Item {
994 ident, kind: hir::ItemKind::Fn(sig, ..), ..
996 | hir::Node::TraitItem(hir::TraitItem {
998 kind: hir::TraitItemKind::Fn(sig, _),
1001 | hir::Node::ImplItem(hir::ImplItem {
1003 kind: hir::ImplItemKind::Fn(sig, _),
1009 sig.decl.inputs.get(
1010 pos + if sig.decl.implicit_self.has_implicit_self() {
1017 .map(|arg| arg.span)
1018 .unwrap_or(ident.span),
1022 if let Some(span) = arg {
1023 err.span_label(span, "change this to accept `FnMut` instead of `Fn`");
1024 err.span_label(func.span, "expects `Fn` instead of `FnMut`");
1025 err.span_label(closure_span, "in this closure");
1026 look_at_return = false;
1031 if look_at_return && hir.get_return_block(closure_id).is_some() {
1032 // ...otherwise we are probably in the tail expression of the function, point at the
1034 match hir.get_by_def_id(hir.get_parent_item(fn_call_id)) {
1035 hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(sig, ..), .. })
1036 | hir::Node::TraitItem(hir::TraitItem {
1038 kind: hir::TraitItemKind::Fn(sig, _),
1041 | hir::Node::ImplItem(hir::ImplItem {
1043 kind: hir::ImplItemKind::Fn(sig, _),
1046 err.span_label(ident.span, "");
1048 sig.decl.output.span(),
1049 "change this to return `FnMut` instead of `Fn`",
1051 err.span_label(closure_span, "in this closure");
1059 fn mut_borrow_of_mutable_ref(local_decl: &LocalDecl<'_>, local_name: Option<Symbol>) -> bool {
1060 debug!("local_info: {:?}, ty.kind(): {:?}", local_decl.local_info, local_decl.ty.kind());
1062 match local_decl.local_info.as_deref() {
1063 // Check if mutably borrowing a mutable reference.
1064 Some(LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var(
1065 mir::VarBindingForm {
1066 binding_mode: ty::BindingMode::BindByValue(Mutability::Not), ..
1068 )))) => matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut)),
1069 Some(LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::ImplicitSelf(kind)))) => {
1070 // Check if the user variable is a `&mut self` and we can therefore
1071 // suggest removing the `&mut`.
1073 // Deliberately fall into this case for all implicit self types,
1074 // so that we don't fall in to the next case with them.
1075 *kind == hir::ImplicitSelfKind::MutRef
1077 _ if Some(kw::SelfLower) == local_name => {
1078 // Otherwise, check if the name is the `self` keyword - in which case
1079 // we have an explicit self. Do the same thing in this case and check
1080 // for a `self: &mut Self` to suggest removing the `&mut`.
1081 matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut))
1087 fn suggest_ampmut_self<'tcx>(
1089 local_decl: &mir::LocalDecl<'tcx>,
1090 ) -> (Span, String) {
1091 let sp = local_decl.source_info.span;
1094 match tcx.sess.source_map().span_to_snippet(sp) {
1096 let lt_pos = snippet.find('\'');
1097 if let Some(lt_pos) = lt_pos {
1098 format!("&{}mut self", &snippet[lt_pos..snippet.len() - 4])
1100 "&mut self".to_string()
1103 _ => "&mut self".to_string(),
1108 // When we want to suggest a user change a local variable to be a `&mut`, there
1109 // are three potential "obvious" things to highlight:
1111 // let ident [: Type] [= RightHandSideExpression];
1112 // ^^^^^ ^^^^ ^^^^^^^^^^^^^^^^^^^^^^^
1115 // We can always fallback on highlighting the first. But chances are good that
1116 // the user experience will be better if we highlight one of the others if possible;
1117 // for example, if the RHS is present and the Type is not, then the type is going to
1118 // be inferred *from* the RHS, which means we should highlight that (and suggest
1119 // that they borrow the RHS mutably).
1121 // This implementation attempts to emulate AST-borrowck prioritization
1122 // by trying (3.), then (2.) and finally falling back on (1.).
1123 fn suggest_ampmut<'tcx>(
1125 local_decl: &mir::LocalDecl<'tcx>,
1126 opt_assignment_rhs_span: Option<Span>,
1127 opt_ty_info: Option<Span>,
1128 ) -> (bool, Span, String) {
1129 if let Some(assignment_rhs_span) = opt_assignment_rhs_span
1130 && let Ok(src) = tcx.sess.source_map().span_to_snippet(assignment_rhs_span)
1132 let is_mutbl = |ty: &str| -> bool {
1133 if let Some(rest) = ty.strip_prefix("mut") {
1134 match rest.chars().next() {
1136 Some(c) if c.is_whitespace() => true,
1141 // e.g. `&mutablevar`
1148 if let (true, Some(ws_pos)) = (src.starts_with("&'"), src.find(char::is_whitespace)) {
1149 let lt_name = &src[1..ws_pos];
1150 let ty = src[ws_pos..].trim_start();
1152 return (true, assignment_rhs_span, format!("&{lt_name} mut {ty}"));
1154 } else if let Some(stripped) = src.strip_prefix('&') {
1155 let stripped = stripped.trim_start();
1156 if !is_mutbl(stripped) {
1157 return (true, assignment_rhs_span, format!("&mut {stripped}"));
1162 let (suggestability, highlight_span) = match opt_ty_info {
1163 // if this is a variable binding with an explicit type,
1164 // try to highlight that for the suggestion.
1165 Some(ty_span) => (true, ty_span),
1167 // otherwise, just highlight the span associated with
1168 // the (MIR) LocalDecl.
1169 None => (false, local_decl.source_info.span),
1172 if let Ok(src) = tcx.sess.source_map().span_to_snippet(highlight_span)
1173 && let (true, Some(ws_pos)) = (src.starts_with("&'"), src.find(char::is_whitespace))
1175 let lt_name = &src[1..ws_pos];
1176 let ty = &src[ws_pos..];
1177 return (true, highlight_span, format!("&{} mut{}", lt_name, ty));
1180 let ty_mut = local_decl.ty.builtin_deref(true).unwrap();
1181 assert_eq!(ty_mut.mutbl, hir::Mutability::Not);
1185 if local_decl.ty.is_region_ptr() {
1186 format!("&mut {}", ty_mut.ty)
1188 format!("*mut {}", ty_mut.ty)
1193 fn is_closure_or_generator(ty: Ty<'_>) -> bool {
1194 ty.is_closure() || ty.is_generator()
1197 /// Given a field that needs to be mutable, returns a span where the " mut " could go.
1198 /// This function expects the local to be a reference to a struct in order to produce a span.
1201 /// LL | s: &'a String
1202 /// | ^^^ returns a span taking up the space here
1204 fn get_mut_span_in_struct_field<'tcx>(
1209 // Expect our local to be a reference to a struct of some kind.
1210 if let ty::Ref(_, ty, _) = ty.kind()
1211 && let ty::Adt(def, _) = ty.kind()
1212 && let field = def.all_fields().nth(field.index())?
1213 // Use the HIR types to construct the diagnostic message.
1214 && let node = tcx.hir().find_by_def_id(field.did.as_local()?)?
1215 // Now we're dealing with the actual struct that we're going to suggest a change to,
1216 // we can expect a field that is an immutable reference to a type.
1217 && let hir::Node::Field(field) = node
1218 && let hir::TyKind::Rptr(lt, hir::MutTy { mutbl: hir::Mutability::Not, ty }) = field.ty.kind
1220 return Some(lt.span.between(ty.span));
1226 /// If possible, suggest replacing `ref` with `ref mut`.
1227 fn suggest_ref_mut(tcx: TyCtxt<'_>, binding_span: Span) -> Option<String> {
1228 let hi_src = tcx.sess.source_map().span_to_snippet(binding_span).ok()?;
1229 if hi_src.starts_with("ref") && hi_src["ref".len()..].starts_with(rustc_lexer::is_whitespace) {
1230 let replacement = format!("ref mut{}", &hi_src["ref".len()..]);