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,
13 self, BindingForm, ClearCrossCrate, ImplicitSelfKind, Local, LocalDecl, LocalInfo,
17 use rustc_span::source_map::DesugaringKind;
18 use rustc_span::symbol::{kw, Symbol};
19 use rustc_span::{sym, BytePos, Span};
21 use crate::diagnostics::BorrowedContentSource;
22 use crate::MirBorrowckCtxt;
23 use rustc_const_eval::util::collect_writes::FindAssignments;
25 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
26 pub(crate) enum AccessKind {
31 impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
32 pub(crate) fn report_mutability_error(
34 access_place: Place<'tcx>,
36 the_place_err: PlaceRef<'tcx>,
37 error_access: AccessKind,
41 "report_mutability_error(\
42 access_place={:?}, span={:?}, the_place_err={:?}, error_access={:?}, location={:?},\
44 access_place, span, the_place_err, error_access, location,
50 let mut opt_source = None;
51 let access_place_desc = self.describe_any_place(access_place.as_ref());
52 debug!("report_mutability_error: access_place_desc={:?}", access_place_desc);
55 PlaceRef { local, projection: [] } => {
56 item_msg = access_place_desc;
57 if access_place.as_local().is_some() {
58 reason = ", as it is not declared as mutable".to_string();
60 let name = self.local_names[local].expect("immutable unnamed local");
61 reason = format!(", as `{name}` is not declared as mutable");
67 projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)],
69 debug_assert!(is_closure_or_generator(
70 Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty
73 let imm_borrow_derefed = self.upvars[upvar_index.index()]
77 .any(|ty| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not)));
79 // If the place is immutable then:
81 // - Either we deref an immutable ref to get to our final place.
82 // - We don't capture derefs of raw ptrs
83 // - Or the final place is immut because the root variable of the capture
84 // isn't marked mut and we should suggest that to the user.
85 if imm_borrow_derefed {
86 // If we deref an immutable ref then the suggestion here doesn't help.
89 item_msg = access_place_desc;
90 if self.is_upvar_field_projection(access_place.as_ref()).is_some() {
91 reason = ", as it is not declared as mutable".to_string();
93 let name = self.upvars[upvar_index.index()].place.to_string(self.infcx.tcx);
94 reason = format!(", as `{name}` is not declared as mutable");
99 PlaceRef { local, projection: [ProjectionElem::Deref] }
100 if self.body.local_decls[local].is_ref_for_guard() =>
102 item_msg = access_place_desc;
103 reason = ", as it is immutable for the pattern guard".to_string();
105 PlaceRef { local, projection: [ProjectionElem::Deref] }
106 if self.body.local_decls[local].is_ref_to_static() =>
108 if access_place.projection.len() == 1 {
109 item_msg = format!("immutable static item {access_place_desc}");
110 reason = String::new();
112 item_msg = access_place_desc;
113 let local_info = &self.body.local_decls[local].local_info;
114 if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
115 let static_name = &self.infcx.tcx.item_name(def_id);
116 reason = format!(", as `{static_name}` is an immutable static item");
118 bug!("is_ref_to_static return true, but not ref to static?");
122 PlaceRef { local: _, projection: [proj_base @ .., ProjectionElem::Deref] } => {
123 if the_place_err.local == ty::CAPTURE_STRUCT_LOCAL
124 && proj_base.is_empty()
125 && !self.upvars.is_empty()
127 item_msg = access_place_desc;
129 self.body.local_decls[ty::CAPTURE_STRUCT_LOCAL].ty.is_region_ptr()
131 debug_assert!(is_closure_or_generator(
134 the_place_err.projection,
141 reason = if self.is_upvar_field_projection(access_place.as_ref()).is_some() {
142 ", as it is a captured variable in a `Fn` closure".to_string()
144 ", as `Fn` closures cannot mutate their captured variables".to_string()
147 let source = self.borrowed_content_source(PlaceRef {
148 local: the_place_err.local,
149 projection: proj_base,
151 let pointer_type = source.describe_for_immutable_place(self.infcx.tcx);
152 opt_source = Some(source);
153 if let Some(desc) = self.describe_place(access_place.as_ref()) {
154 item_msg = format!("`{desc}`");
155 reason = match error_access {
156 AccessKind::Mutate => format!(", which is behind {pointer_type}"),
157 AccessKind::MutableBorrow => {
158 format!(", as it is behind {pointer_type}")
162 item_msg = format!("data in {pointer_type}");
163 reason = String::new();
173 ProjectionElem::Index(_)
174 | ProjectionElem::ConstantIndex { .. }
175 | ProjectionElem::Subslice { .. }
176 | ProjectionElem::Downcast(..),
178 } => bug!("Unexpected immutable place."),
181 debug!("report_mutability_error: item_msg={:?}, reason={:?}", item_msg, reason);
183 // `act` and `acted_on` are strings that let us abstract over
184 // the verbs used in some diagnostic messages.
188 let span = match error_access {
189 AccessKind::Mutate => {
190 err = self.cannot_assign(span, &(item_msg + &reason));
192 acted_on = "written";
195 AccessKind::MutableBorrow => {
196 act = "borrow as mutable";
197 acted_on = "borrowed as mutable";
199 let borrow_spans = self.borrow_spans(span, location);
200 let borrow_span = borrow_spans.args_or_use();
201 err = self.cannot_borrow_path_as_mutable_because(borrow_span, &item_msg, &reason);
202 borrow_spans.var_span_label(
205 "mutable borrow occurs due to use of {} in closure",
206 self.describe_any_place(access_place.as_ref()),
214 debug!("report_mutability_error: act={:?}, acted_on={:?}", act, acted_on);
216 match the_place_err {
217 // Suggest making an existing shared borrow in a struct definition a mutable borrow.
219 // This is applicable when we have a deref of a field access to a deref of a local -
220 // something like `*((*_1).0`. The local that we get will be a reference to the
221 // struct we've got a field access of (it must be a reference since there's a deref
222 // after the field access).
228 ProjectionElem::Deref,
229 ProjectionElem::Field(field, _),
230 ProjectionElem::Deref,
233 err.span_label(span, format!("cannot {ACT}", ACT = act));
235 if let Some(span) = get_mut_span_in_struct_field(
237 Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty,
240 err.span_suggestion_verbose(
242 "consider changing this to be mutable",
244 Applicability::MaybeIncorrect,
249 // Suggest removing a `&mut` from the use of a mutable reference.
250 PlaceRef { local, projection: [] }
255 .map(|l| mut_borrow_of_mutable_ref(l, self.local_names[local]))
258 let decl = &self.body.local_decls[local];
259 err.span_label(span, format!("cannot {ACT}", ACT = act));
260 if let Some(mir::Statement {
263 mir::StatementKind::Assign(box (
267 mir::BorrowKind::Mut { allow_two_phase_borrow: false },
272 }) = &self.body[location.block].statements.get(location.statement_index)
274 match decl.local_info {
275 Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
276 mir::VarBindingForm {
277 binding_mode: ty::BindingMode::BindByValue(Mutability::Not),
278 opt_ty_info: Some(sp),
283 err.span_note(sp, "the binding is already a mutable borrow");
287 decl.source_info.span,
288 "the binding is already a mutable borrow",
293 self.infcx.tcx.sess.source_map().span_to_snippet(source_info.span)
295 if snippet.starts_with("&mut ") {
296 // We don't have access to the HIR to get accurate spans, but we can
297 // give a best effort structured suggestion.
298 err.span_suggestion_verbose(
299 source_info.span.with_hi(source_info.span.lo() + BytePos(5)),
300 "try removing `&mut` here",
302 Applicability::MachineApplicable,
305 // This can occur with things like `(&mut self).foo()`.
306 err.span_help(source_info.span, "try removing `&mut` here");
309 err.span_help(source_info.span, "try removing `&mut` here");
311 } else if decl.mutability == Mutability::Not
314 Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(
315 ImplicitSelfKind::MutRef
319 err.span_suggestion_verbose(
320 decl.source_info.span.shrink_to_lo(),
321 "consider making the binding mutable",
323 Applicability::MachineApplicable,
328 // We want to suggest users use `let mut` for local (user
329 // variable) mutations...
330 PlaceRef { local, projection: [] }
331 if self.body.local_decls[local].can_be_made_mutable() =>
333 // ... but it doesn't make sense to suggest it on
334 // variables that are `ref x`, `ref mut x`, `&self`,
335 // or `&mut self` (such variables are simply not
337 let local_decl = &self.body.local_decls[local];
338 assert_eq!(local_decl.mutability, Mutability::Not);
340 err.span_label(span, format!("cannot {ACT}", ACT = act));
342 local_decl.source_info.span,
343 "consider changing this to be mutable",
344 format!("mut {}", self.local_names[local].unwrap()),
345 Applicability::MachineApplicable,
347 let tcx = self.infcx.tcx;
348 if let ty::Closure(id, _) = *the_place_err.ty(self.body, tcx).ty.kind() {
349 self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, &mut err);
353 // Also suggest adding mut for upvars
356 projection: [proj_base @ .., ProjectionElem::Field(upvar_index, _)],
358 debug_assert!(is_closure_or_generator(
359 Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty
362 let captured_place = &self.upvars[upvar_index.index()].place;
364 err.span_label(span, format!("cannot {ACT}", ACT = act));
366 let upvar_hir_id = captured_place.get_root_variable();
368 if let Some(Node::Pat(pat)) = self.infcx.tcx.hir().find(upvar_hir_id)
369 && let hir::PatKind::Binding(
370 hir::BindingAnnotation::NONE,
378 "consider changing this to be mutable",
379 format!("mut {}", upvar_ident.name),
380 Applicability::MachineApplicable,
384 let tcx = self.infcx.tcx;
385 if let ty::Ref(_, ty, Mutability::Mut) = the_place_err.ty(self.body, tcx).ty.kind()
386 && let ty::Closure(id, _) = *ty.kind()
388 self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, &mut err);
392 // complete hack to approximate old AST-borrowck
393 // diagnostic: if the span starts with a mutable borrow of
394 // a local variable, then just suggest the user remove it.
395 PlaceRef { local: _, projection: [] }
397 if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) {
398 snippet.starts_with("&mut ")
404 err.span_label(span, format!("cannot {ACT}", ACT = act));
407 "try removing `&mut` here",
409 Applicability::MaybeIncorrect,
413 PlaceRef { local, projection: [ProjectionElem::Deref] }
414 if self.body.local_decls[local].is_ref_for_guard() =>
416 err.span_label(span, format!("cannot {ACT}", ACT = act));
418 "variables bound in patterns are immutable until the end of the pattern guard",
422 // We want to point out when a `&` can be readily replaced
425 // FIXME: can this case be generalized to work for an
426 // arbitrary base for the projection?
427 PlaceRef { local, projection: [ProjectionElem::Deref] }
428 if self.body.local_decls[local].is_user_variable() =>
430 let local_decl = &self.body.local_decls[local];
432 let (pointer_sigil, pointer_desc) = if local_decl.ty.is_region_ptr() {
435 ("*const", "pointer")
438 match self.local_names[local] {
439 Some(name) if !local_decl.from_compiler_desugaring() => {
440 let label = match local_decl.local_info.as_deref().unwrap() {
441 LocalInfo::User(ClearCrossCrate::Set(
442 mir::BindingForm::ImplicitSelf(_),
444 let (span, suggestion) =
445 suggest_ampmut_self(self.infcx.tcx, local_decl);
446 Some((true, span, suggestion))
449 LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var(
450 mir::VarBindingForm {
451 binding_mode: ty::BindingMode::BindByValue(_),
456 // check if the RHS is from desugaring
457 let opt_assignment_rhs_span =
458 self.body.find_assignments(local).first().map(|&location| {
459 if let Some(mir::Statement {
462 mir::StatementKind::Assign(box (
464 mir::Rvalue::Use(mir::Operand::Copy(place)),
466 }) = self.body[location.block]
468 .get(location.statement_index)
470 self.body.local_decls[place.local].source_info.span
472 self.body.source_info(location).span
475 match opt_assignment_rhs_span.and_then(|s| s.desugaring_kind()) {
476 // on for loops, RHS points to the iterator part
477 Some(DesugaringKind::ForLoop) => {
478 self.suggest_similar_mut_method_for_for_loop(&mut err);
479 err.span_label(opt_assignment_rhs_span.unwrap(), format!(
480 "this iterator yields `{pointer_sigil}` {pointer_desc}s",
484 // don't create labels for compiler-generated spans
487 let label = if name != kw::SelfLower {
491 opt_assignment_rhs_span,
495 match local_decl.local_info.as_deref() {
496 Some(LocalInfo::User(ClearCrossCrate::Set(
497 mir::BindingForm::Var(mir::VarBindingForm {
502 let (span, sugg) = suggest_ampmut_self(
508 // explicit self (eg `self: &'a Self`)
512 opt_assignment_rhs_span,
522 LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var(
523 mir::VarBindingForm {
524 binding_mode: ty::BindingMode::BindByReference(_),
528 let pattern_span = local_decl.source_info.span;
529 suggest_ref_mut(self.infcx.tcx, pattern_span)
530 .map(|replacement| (true, pattern_span, replacement))
533 LocalInfo::User(ClearCrossCrate::Clear) => {
534 bug!("saw cleared local state")
541 Some((true, err_help_span, suggested_code)) => {
542 let (is_trait_sig, local_trait) = self.is_error_in_trait(local);
547 "consider changing this to be a mutable {pointer_desc}"
550 Applicability::MachineApplicable,
552 } else if let Some(x) = local_trait {
556 "consider changing that to be a mutable {pointer_desc}"
559 Applicability::MachineApplicable,
563 Some((false, err_label_span, message)) => {
567 "consider changing this binding's type to be: `{message}`"
576 "`{NAME}` is a `{SIGIL}` {DESC}, \
577 so the data it refers to cannot be {ACTED_ON}",
579 SIGIL = pointer_sigil,
589 "cannot {ACT} through `{SIGIL}` {DESC}",
591 SIGIL = pointer_sigil,
599 PlaceRef { local, projection: [ProjectionElem::Deref] }
600 if local == ty::CAPTURE_STRUCT_LOCAL && !self.upvars.is_empty() =>
602 self.expected_fn_found_fn_mut_call(&mut err, span, act);
605 PlaceRef { local: _, projection: [.., ProjectionElem::Deref] } => {
606 err.span_label(span, format!("cannot {ACT}", ACT = act));
609 Some(BorrowedContentSource::OverloadedDeref(ty)) => {
611 "trait `DerefMut` is required to modify through a dereference, \
612 but it is not implemented for `{ty}`",
615 Some(BorrowedContentSource::OverloadedIndex(ty)) => {
617 "trait `IndexMut` is required to modify indexed content, \
618 but it is not implemented for `{ty}`",
620 self.suggest_map_index_mut_alternatives(ty, &mut err, span);
627 err.span_label(span, format!("cannot {ACT}", ACT = act));
631 self.buffer_error(err);
634 fn suggest_map_index_mut_alternatives(
637 err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
640 let Some(adt) = ty.ty_adt_def() else { return };
642 if self.infcx.tcx.is_diagnostic_item(sym::HashMap, did)
643 || self.infcx.tcx.is_diagnostic_item(sym::BTreeMap, did)
645 struct V<'a, 'b, 'tcx, G: EmissionGuarantee> {
647 err: &'a mut DiagnosticBuilder<'b, G>,
651 impl<'a, 'b: 'a, 'hir, 'tcx, G: EmissionGuarantee> Visitor<'hir> for V<'a, 'b, 'tcx, G> {
652 fn visit_stmt(&mut self, stmt: &'hir hir::Stmt<'hir>) {
653 hir::intravisit::walk_stmt(self, stmt);
654 let expr = match stmt.kind {
655 hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr) => expr,
656 hir::StmtKind::Local(hir::Local { init: Some(expr), .. }) => expr,
661 if let hir::ExprKind::Assign(place, rv, _sp) = expr.kind
662 && let hir::ExprKind::Index(val, index) = place.kind
663 && (expr.span == self.assign_span || place.span == self.assign_span)
667 self.err.multipart_suggestions(
669 "to modify a `{}`, use `.get_mut()`, `.insert()` or the entry API",
673 vec![ // val.insert(index, rv);
675 val.span.shrink_to_hi().with_hi(index.span.lo()),
676 ".insert(".to_string(),
679 index.span.shrink_to_hi().with_hi(rv.span.lo()),
682 (rv.span.shrink_to_hi(), ")".to_string()),
684 vec![ // val.get_mut(index).map(|v| { *v = rv; });
686 val.span.shrink_to_hi().with_hi(index.span.lo()),
687 ".get_mut(".to_string(),
690 index.span.shrink_to_hi().with_hi(place.span.hi()),
691 ").map(|val| { *val".to_string(),
694 rv.span.shrink_to_hi(),
698 vec![ // let x = val.entry(index).or_insert(rv);
699 (val.span.shrink_to_lo(), "let val = ".to_string()),
701 val.span.shrink_to_hi().with_hi(index.span.lo()),
702 ".entry(".to_string(),
705 index.span.shrink_to_hi().with_hi(rv.span.lo()),
706 ").or_insert(".to_string(),
708 (rv.span.shrink_to_hi(), ")".to_string()),
711 Applicability::MachineApplicable,
713 self.suggested = true;
714 } else if let hir::ExprKind::MethodCall(_path, receiver, _, sp) = expr.kind
715 && let hir::ExprKind::Index(val, index) = receiver.kind
716 && expr.span == self.assign_span
718 // val[index].path(args..);
719 self.err.multipart_suggestion(
720 &format!("to modify a `{}` use `.get_mut()`", self.ty),
723 val.span.shrink_to_hi().with_hi(index.span.lo()),
724 ".get_mut(".to_string(),
727 index.span.shrink_to_hi().with_hi(receiver.span.hi()),
728 ").map(|val| val".to_string(),
730 (sp.shrink_to_hi(), ")".to_string()),
732 Applicability::MachineApplicable,
734 self.suggested = true;
738 let hir_map = self.infcx.tcx.hir();
739 let def_id = self.body.source.def_id();
740 let hir_id = hir_map.local_def_id_to_hir_id(def_id.as_local().unwrap());
741 let node = hir_map.find(hir_id);
742 let Some(hir::Node::Item(item)) = node else { return; };
743 let hir::ItemKind::Fn(.., body_id) = item.kind else { return; };
744 let body = self.infcx.tcx.hir().body(body_id);
745 let mut v = V { assign_span: span, err, ty, suggested: false };
749 "to modify a `{ty}`, use `.get_mut()`, `.insert()` or the entry API",
755 /// User cannot make signature of a trait mutable without changing the
756 /// trait. So we find if this error belongs to a trait and if so we move
757 /// suggestion to the trait or disable it if it is out of scope of this crate
758 fn is_error_in_trait(&self, local: Local) -> (bool, Option<Span>) {
759 if self.body.local_kind(local) != LocalKind::Arg {
760 return (false, None);
762 let hir_map = self.infcx.tcx.hir();
763 let my_def = self.body.source.def_id();
764 let my_hir = hir_map.local_def_id_to_hir_id(my_def.as_local().unwrap());
766 self.infcx.tcx.impl_of_method(my_def).and_then(|x| self.infcx.tcx.trait_id_of_impl(x))
768 return (false, None);
772 td.as_local().and_then(|tld| match hir_map.find_by_def_id(tld) {
773 Some(Node::Item(hir::Item {
774 kind: hir::ItemKind::Trait(_, _, _, _, items),
777 let mut f_in_trait_opt = None;
778 for hir::TraitItemRef { id: fi, kind: k, .. } in *items {
779 let hi = fi.hir_id();
780 if !matches!(k, hir::AssocItemKind::Fn { .. }) {
783 if hir_map.name(hi) != hir_map.name(my_hir) {
786 f_in_trait_opt = Some(hi);
789 f_in_trait_opt.and_then(|f_in_trait| match hir_map.find(f_in_trait) {
790 Some(Node::TraitItem(hir::TraitItem {
792 hir::TraitItemKind::Fn(
793 hir::FnSig { decl: hir::FnDecl { inputs, .. }, .. },
798 let hir::Ty { span, .. } = inputs[local.index() - 1];
809 // point to span of upvar making closure call require mutable borrow
810 fn show_mutating_upvar(
813 closure_local_def_id: hir::def_id::LocalDefId,
814 the_place_err: PlaceRef<'tcx>,
815 err: &mut Diagnostic,
817 let tables = tcx.typeck(closure_local_def_id);
818 let closure_hir_id = tcx.hir().local_def_id_to_hir_id(closure_local_def_id);
819 if let Some((span, closure_kind_origin)) =
820 &tables.closure_kind_origins().get(closure_hir_id)
822 let reason = if let PlaceBase::Upvar(upvar_id) = closure_kind_origin.base {
823 let upvar = ty::place_to_string_for_capture(tcx, closure_kind_origin);
824 let root_hir_id = upvar_id.var_path.hir_id;
825 // we have an origin for this closure kind starting at this root variable so it's safe to unwrap here
826 let captured_places =
827 tables.closure_min_captures[&closure_local_def_id].get(&root_hir_id).unwrap();
829 let origin_projection = closure_kind_origin
832 .map(|proj| proj.kind)
833 .collect::<Vec<_>>();
834 let mut capture_reason = String::new();
835 for captured_place in captured_places {
836 let captured_place_kinds = captured_place
840 .map(|proj| proj.kind)
841 .collect::<Vec<_>>();
842 if rustc_middle::ty::is_ancestor_or_same_capture(
843 &captured_place_kinds,
846 match captured_place.info.capture_kind {
847 ty::UpvarCapture::ByRef(
848 ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
850 capture_reason = format!("mutable borrow of `{upvar}`");
852 ty::UpvarCapture::ByValue => {
853 capture_reason = format!("possible mutation of `{upvar}`");
855 _ => bug!("upvar `{upvar}` borrowed, but not mutably"),
860 if capture_reason.is_empty() {
861 bug!("upvar `{upvar}` borrowed, but cannot find reason");
870 "calling `{}` requires mutable binding due to {}",
871 self.describe_place(the_place_err).unwrap(),
878 // Attempt to search similar mutable associated items for suggestion.
879 // In the future, attempt in all path but initially for RHS of for_loop
880 fn suggest_similar_mut_method_for_for_loop(&self, err: &mut Diagnostic) {
883 ExprKind::{Block, Call, DropTemps, Match, MethodCall},
884 HirId, ImplItem, ImplItemKind, Item, ItemKind,
887 fn maybe_body_id_of_fn(hir_map: Map<'_>, id: HirId) -> Option<BodyId> {
888 match hir_map.find(id) {
889 Some(Node::Item(Item { kind: ItemKind::Fn(_, _, body_id), .. }))
890 | Some(Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(_, body_id), .. })) => {
896 let hir_map = self.infcx.tcx.hir();
897 let mir_body_hir_id = self.mir_hir_id();
898 if let Some(fn_body_id) = maybe_body_id_of_fn(hir_map, mir_body_hir_id) {
914 MethodCall(path_segment, _, _, span),
932 ) = hir_map.body(fn_body_id).value.kind
934 let opt_suggestions = self
937 .typeck(path_segment.hir_id.owner)
938 .type_dependent_def_id(*hir_id)
939 .and_then(|def_id| self.infcx.tcx.impl_of_method(def_id))
940 .map(|def_id| self.infcx.tcx.associated_items(def_id))
943 .in_definition_order()
944 .map(|assoc_item_def| assoc_item_def.ident(self.infcx.tcx))
946 let original_method_ident = path_segment.ident;
947 original_method_ident != ident
950 .starts_with(&original_method_ident.name.to_string())
952 .map(|ident| format!("{ident}()"))
956 if let Some(mut suggestions) = opt_suggestions
957 && suggestions.peek().is_some()
959 err.span_suggestions(
961 "use mutable method",
963 Applicability::MaybeIncorrect,
970 /// Targeted error when encountering an `FnMut` closure where an `Fn` closure was expected.
971 fn expected_fn_found_fn_mut_call(&self, err: &mut Diagnostic, sp: Span, act: &str) {
972 err.span_label(sp, format!("cannot {act}"));
974 let hir = self.infcx.tcx.hir();
975 let closure_id = self.mir_hir_id();
976 let fn_call_id = hir.get_parent_node(closure_id);
977 let node = hir.get(fn_call_id);
978 let def_id = hir.enclosing_body_owner(fn_call_id);
979 let mut look_at_return = true;
980 // If we can detect the expression to be an `fn` call where the closure was an argument,
981 // we point at the `fn` definition argument...
982 if let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Call(func, args), .. }) = node {
986 .filter(|(_, arg)| arg.hir_id == closure_id)
989 let tables = self.infcx.tcx.typeck(def_id);
990 if let Some(ty::FnDef(def_id, _)) =
991 tables.node_type_opt(func.hir_id).as_ref().map(|ty| ty.kind())
993 let arg = match hir.get_if_local(*def_id) {
995 hir::Node::Item(hir::Item {
996 ident, kind: hir::ItemKind::Fn(sig, ..), ..
998 | hir::Node::TraitItem(hir::TraitItem {
1000 kind: hir::TraitItemKind::Fn(sig, _),
1003 | hir::Node::ImplItem(hir::ImplItem {
1005 kind: hir::ImplItemKind::Fn(sig, _),
1011 sig.decl.inputs.get(
1012 pos + if sig.decl.implicit_self.has_implicit_self() {
1019 .map(|arg| arg.span)
1020 .unwrap_or(ident.span),
1024 if let Some(span) = arg {
1025 err.span_label(span, "change this to accept `FnMut` instead of `Fn`");
1026 err.span_label(func.span, "expects `Fn` instead of `FnMut`");
1027 err.span_label(self.body.span, "in this closure");
1028 look_at_return = false;
1033 if look_at_return && hir.get_return_block(closure_id).is_some() {
1034 // ...otherwise we are probably in the tail expression of the function, point at the
1036 match hir.get_by_def_id(hir.get_parent_item(fn_call_id)) {
1037 hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(sig, ..), .. })
1038 | hir::Node::TraitItem(hir::TraitItem {
1040 kind: hir::TraitItemKind::Fn(sig, _),
1043 | hir::Node::ImplItem(hir::ImplItem {
1045 kind: hir::ImplItemKind::Fn(sig, _),
1048 err.span_label(ident.span, "");
1050 sig.decl.output.span(),
1051 "change this to return `FnMut` instead of `Fn`",
1053 err.span_label(self.body.span, "in this closure");
1061 fn mut_borrow_of_mutable_ref(local_decl: &LocalDecl<'_>, local_name: Option<Symbol>) -> bool {
1062 debug!("local_info: {:?}, ty.kind(): {:?}", local_decl.local_info, local_decl.ty.kind());
1064 match local_decl.local_info.as_deref() {
1065 // Check if mutably borrowing a mutable reference.
1066 Some(LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var(
1067 mir::VarBindingForm {
1068 binding_mode: ty::BindingMode::BindByValue(Mutability::Not), ..
1070 )))) => matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut)),
1071 Some(LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::ImplicitSelf(kind)))) => {
1072 // Check if the user variable is a `&mut self` and we can therefore
1073 // suggest removing the `&mut`.
1075 // Deliberately fall into this case for all implicit self types,
1076 // so that we don't fall in to the next case with them.
1077 *kind == mir::ImplicitSelfKind::MutRef
1079 _ if Some(kw::SelfLower) == local_name => {
1080 // Otherwise, check if the name is the `self` keyword - in which case
1081 // we have an explicit self. Do the same thing in this case and check
1082 // for a `self: &mut Self` to suggest removing the `&mut`.
1083 matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut))
1089 fn suggest_ampmut_self<'tcx>(
1091 local_decl: &mir::LocalDecl<'tcx>,
1092 ) -> (Span, String) {
1093 let sp = local_decl.source_info.span;
1096 match tcx.sess.source_map().span_to_snippet(sp) {
1098 let lt_pos = snippet.find('\'');
1099 if let Some(lt_pos) = lt_pos {
1100 format!("&{}mut self", &snippet[lt_pos..snippet.len() - 4])
1102 "&mut self".to_string()
1105 _ => "&mut self".to_string(),
1110 // When we want to suggest a user change a local variable to be a `&mut`, there
1111 // are three potential "obvious" things to highlight:
1113 // let ident [: Type] [= RightHandSideExpression];
1114 // ^^^^^ ^^^^ ^^^^^^^^^^^^^^^^^^^^^^^
1117 // We can always fallback on highlighting the first. But chances are good that
1118 // the user experience will be better if we highlight one of the others if possible;
1119 // for example, if the RHS is present and the Type is not, then the type is going to
1120 // be inferred *from* the RHS, which means we should highlight that (and suggest
1121 // that they borrow the RHS mutably).
1123 // This implementation attempts to emulate AST-borrowck prioritization
1124 // by trying (3.), then (2.) and finally falling back on (1.).
1125 fn suggest_ampmut<'tcx>(
1127 local_decl: &mir::LocalDecl<'tcx>,
1128 opt_assignment_rhs_span: Option<Span>,
1129 opt_ty_info: Option<Span>,
1130 ) -> (bool, Span, String) {
1131 if let Some(assignment_rhs_span) = opt_assignment_rhs_span
1132 && let Ok(src) = tcx.sess.source_map().span_to_snippet(assignment_rhs_span)
1134 let is_mutbl = |ty: &str| -> bool {
1135 if let Some(rest) = ty.strip_prefix("mut") {
1136 match rest.chars().next() {
1138 Some(c) if c.is_whitespace() => true,
1143 // e.g. `&mutablevar`
1150 if let (true, Some(ws_pos)) = (src.starts_with("&'"), src.find(char::is_whitespace)) {
1151 let lt_name = &src[1..ws_pos];
1152 let ty = src[ws_pos..].trim_start();
1154 return (true, assignment_rhs_span, format!("&{lt_name} mut {ty}"));
1156 } else if let Some(stripped) = src.strip_prefix('&') {
1157 let stripped = stripped.trim_start();
1158 if !is_mutbl(stripped) {
1159 return (true, assignment_rhs_span, format!("&mut {stripped}"));
1164 let (suggestability, highlight_span) = match opt_ty_info {
1165 // if this is a variable binding with an explicit type,
1166 // try to highlight that for the suggestion.
1167 Some(ty_span) => (true, ty_span),
1169 // otherwise, just highlight the span associated with
1170 // the (MIR) LocalDecl.
1171 None => (false, local_decl.source_info.span),
1174 if let Ok(src) = tcx.sess.source_map().span_to_snippet(highlight_span)
1175 && let (true, Some(ws_pos)) = (src.starts_with("&'"), src.find(char::is_whitespace))
1177 let lt_name = &src[1..ws_pos];
1178 let ty = &src[ws_pos..];
1179 return (true, highlight_span, format!("&{} mut{}", lt_name, ty));
1182 let ty_mut = local_decl.ty.builtin_deref(true).unwrap();
1183 assert_eq!(ty_mut.mutbl, hir::Mutability::Not);
1187 if local_decl.ty.is_region_ptr() {
1188 format!("&mut {}", ty_mut.ty)
1190 format!("*mut {}", ty_mut.ty)
1195 fn is_closure_or_generator(ty: Ty<'_>) -> bool {
1196 ty.is_closure() || ty.is_generator()
1199 /// Given a field that needs to be mutable, returns a span where the " mut " could go.
1200 /// This function expects the local to be a reference to a struct in order to produce a span.
1203 /// LL | s: &'a String
1204 /// | ^^^ returns a span taking up the space here
1206 fn get_mut_span_in_struct_field<'tcx>(
1211 // Expect our local to be a reference to a struct of some kind.
1212 if let ty::Ref(_, ty, _) = ty.kind()
1213 && let ty::Adt(def, _) = ty.kind()
1214 && let field = def.all_fields().nth(field.index())?
1215 // Use the HIR types to construct the diagnostic message.
1216 && let node = tcx.hir().find_by_def_id(field.did.as_local()?)?
1217 // Now we're dealing with the actual struct that we're going to suggest a change to,
1218 // we can expect a field that is an immutable reference to a type.
1219 && let hir::Node::Field(field) = node
1220 && let hir::TyKind::Rptr(lt, hir::MutTy { mutbl: hir::Mutability::Not, ty }) = field.ty.kind
1222 return Some(lt.span.between(ty.span));
1228 /// If possible, suggest replacing `ref` with `ref mut`.
1229 fn suggest_ref_mut(tcx: TyCtxt<'_>, binding_span: Span) -> Option<String> {
1230 let hi_src = tcx.sess.source_map().span_to_snippet(binding_span).ok()?;
1231 if hi_src.starts_with("ref") && hi_src["ref".len()..].starts_with(rustc_lexer::is_whitespace) {
1232 let replacement = format!("ref mut{}", &hi_src["ref".len()..]);