3 use rustc_middle::hir::map::Map;
4 use rustc_middle::mir::{Mutability, Place, PlaceRef, ProjectionElem};
5 use rustc_middle::ty::{self, Ty, TyCtxt};
9 self, BindingForm, ClearCrossCrate, ImplicitSelfKind, Local, LocalDecl, LocalInfo,
13 use rustc_span::source_map::DesugaringKind;
14 use rustc_span::symbol::{kw, Symbol};
15 use rustc_span::{BytePos, Span};
17 use crate::diagnostics::BorrowedContentSource;
18 use crate::MirBorrowckCtxt;
19 use rustc_const_eval::util::collect_writes::FindAssignments;
20 use rustc_errors::{Applicability, Diagnostic};
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 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, 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::Unannotated,
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, 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}`",
623 err.span_label(span, format!("cannot {ACT}", ACT = act));
627 self.buffer_error(err);
630 /// User cannot make signature of a trait mutable without changing the
631 /// trait. So we find if this error belongs to a trait and if so we move
632 /// suggestion to the trait or disable it if it is out of scope of this crate
633 fn is_error_in_trait(&self, local: Local) -> (bool, Option<Span>) {
634 if self.body.local_kind(local) != LocalKind::Arg {
635 return (false, None);
637 let hir_map = self.infcx.tcx.hir();
638 let my_def = self.body.source.def_id();
639 let my_hir = hir_map.local_def_id_to_hir_id(my_def.as_local().unwrap());
641 self.infcx.tcx.impl_of_method(my_def).and_then(|x| self.infcx.tcx.trait_id_of_impl(x))
643 return (false, None);
647 td.as_local().and_then(|tld| match hir_map.find_by_def_id(tld) {
648 Some(Node::Item(hir::Item {
649 kind: hir::ItemKind::Trait(_, _, _, _, items),
652 let mut f_in_trait_opt = None;
653 for hir::TraitItemRef { id: fi, kind: k, .. } in *items {
654 let hi = fi.hir_id();
655 if !matches!(k, hir::AssocItemKind::Fn { .. }) {
658 if hir_map.name(hi) != hir_map.name(my_hir) {
661 f_in_trait_opt = Some(hi);
664 f_in_trait_opt.and_then(|f_in_trait| match hir_map.find(f_in_trait) {
665 Some(Node::TraitItem(hir::TraitItem {
667 hir::TraitItemKind::Fn(
668 hir::FnSig { decl: hir::FnDecl { inputs, .. }, .. },
673 let hir::Ty { span, .. } = inputs[local.index() - 1];
684 // point to span of upvar making closure call require mutable borrow
685 fn show_mutating_upvar(
688 id: hir::def_id::DefId,
689 the_place_err: PlaceRef<'tcx>,
690 err: &mut Diagnostic,
692 let closure_local_def_id = id.expect_local();
693 let tables = tcx.typeck(closure_local_def_id);
694 let closure_hir_id = tcx.hir().local_def_id_to_hir_id(closure_local_def_id);
695 if let Some((span, closure_kind_origin)) =
696 &tables.closure_kind_origins().get(closure_hir_id)
698 let reason = if let PlaceBase::Upvar(upvar_id) = closure_kind_origin.base {
699 let upvar = ty::place_to_string_for_capture(tcx, closure_kind_origin);
700 let root_hir_id = upvar_id.var_path.hir_id;
701 // we have an origin for this closure kind starting at this root variable so it's safe to unwrap here
702 let captured_places = tables.closure_min_captures[&id].get(&root_hir_id).unwrap();
704 let origin_projection = closure_kind_origin
707 .map(|proj| proj.kind)
708 .collect::<Vec<_>>();
709 let mut capture_reason = String::new();
710 for captured_place in captured_places {
711 let captured_place_kinds = captured_place
715 .map(|proj| proj.kind)
716 .collect::<Vec<_>>();
717 if rustc_middle::ty::is_ancestor_or_same_capture(
718 &captured_place_kinds,
721 match captured_place.info.capture_kind {
722 ty::UpvarCapture::ByRef(
723 ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
725 capture_reason = format!("mutable borrow of `{upvar}`");
727 ty::UpvarCapture::ByValue => {
728 capture_reason = format!("possible mutation of `{upvar}`");
730 _ => bug!("upvar `{upvar}` borrowed, but not mutably"),
735 if capture_reason.is_empty() {
736 bug!("upvar `{upvar}` borrowed, but cannot find reason");
745 "calling `{}` requires mutable binding due to {}",
746 self.describe_place(the_place_err).unwrap(),
753 // Attempt to search similar mutable associated items for suggestion.
754 // In the future, attempt in all path but initially for RHS of for_loop
755 fn suggest_similar_mut_method_for_for_loop(&self, err: &mut Diagnostic) {
758 ExprKind::{Block, Call, DropTemps, Match, MethodCall},
759 HirId, ImplItem, ImplItemKind, Item, ItemKind,
762 fn maybe_body_id_of_fn(hir_map: Map<'_>, id: HirId) -> Option<BodyId> {
763 match hir_map.find(id) {
764 Some(Node::Item(Item { kind: ItemKind::Fn(_, _, body_id), .. }))
765 | Some(Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(_, body_id), .. })) => {
771 let hir_map = self.infcx.tcx.hir();
772 let mir_body_hir_id = self.mir_hir_id();
773 if let Some(fn_body_id) = maybe_body_id_of_fn(hir_map, mir_body_hir_id) {
811 ) = hir_map.body(fn_body_id).value.kind
813 let opt_suggestions = path_segment
815 .map(|path_hir_id| self.infcx.tcx.typeck(path_hir_id.owner))
816 .and_then(|typeck| typeck.type_dependent_def_id(*hir_id))
817 .and_then(|def_id| self.infcx.tcx.impl_of_method(def_id))
818 .map(|def_id| self.infcx.tcx.associated_items(def_id))
821 .in_definition_order()
822 .map(|assoc_item_def| assoc_item_def.ident(self.infcx.tcx))
824 let original_method_ident = path_segment.ident;
825 original_method_ident != ident
828 .starts_with(&original_method_ident.name.to_string())
830 .map(|ident| format!("{ident}()"))
834 if let Some(mut suggestions) = opt_suggestions
835 && suggestions.peek().is_some()
837 err.span_suggestions(
839 "use mutable method",
841 Applicability::MaybeIncorrect,
848 /// Targeted error when encountering an `FnMut` closure where an `Fn` closure was expected.
849 fn expected_fn_found_fn_mut_call(&self, err: &mut Diagnostic, sp: Span, act: &str) {
850 err.span_label(sp, format!("cannot {act}"));
852 let hir = self.infcx.tcx.hir();
853 let closure_id = self.mir_hir_id();
854 let fn_call_id = hir.get_parent_node(closure_id);
855 let node = hir.get(fn_call_id);
856 let item_id = hir.enclosing_body_owner(fn_call_id);
857 let mut look_at_return = true;
858 // If we can detect the expression to be an `fn` call where the closure was an argument,
859 // we point at the `fn` definition argument...
860 if let hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Call(func, args), .. }) = node {
864 .filter(|(_, arg)| arg.hir_id == closure_id)
867 let def_id = hir.local_def_id(item_id);
868 let tables = self.infcx.tcx.typeck(def_id);
869 if let Some(ty::FnDef(def_id, _)) =
870 tables.node_type_opt(func.hir_id).as_ref().map(|ty| ty.kind())
872 let arg = match hir.get_if_local(*def_id) {
874 hir::Node::Item(hir::Item {
875 ident, kind: hir::ItemKind::Fn(sig, ..), ..
877 | hir::Node::TraitItem(hir::TraitItem {
879 kind: hir::TraitItemKind::Fn(sig, _),
882 | hir::Node::ImplItem(hir::ImplItem {
884 kind: hir::ImplItemKind::Fn(sig, _),
891 pos + if sig.decl.implicit_self.has_implicit_self() {
899 .unwrap_or(ident.span),
903 if let Some(span) = arg {
904 err.span_label(span, "change this to accept `FnMut` instead of `Fn`");
905 err.span_label(func.span, "expects `Fn` instead of `FnMut`");
906 err.span_label(self.body.span, "in this closure");
907 look_at_return = false;
912 if look_at_return && hir.get_return_block(closure_id).is_some() {
913 // ...otherwise we are probably in the tail expression of the function, point at the
915 match hir.get_by_def_id(hir.get_parent_item(fn_call_id)) {
916 hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(sig, ..), .. })
917 | hir::Node::TraitItem(hir::TraitItem {
919 kind: hir::TraitItemKind::Fn(sig, _),
922 | hir::Node::ImplItem(hir::ImplItem {
924 kind: hir::ImplItemKind::Fn(sig, _),
927 err.span_label(ident.span, "");
929 sig.decl.output.span(),
930 "change this to return `FnMut` instead of `Fn`",
932 err.span_label(self.body.span, "in this closure");
940 fn mut_borrow_of_mutable_ref(local_decl: &LocalDecl<'_>, local_name: Option<Symbol>) -> bool {
941 debug!("local_info: {:?}, ty.kind(): {:?}", local_decl.local_info, local_decl.ty.kind());
943 match local_decl.local_info.as_deref() {
944 // Check if mutably borrowing a mutable reference.
945 Some(LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::Var(
946 mir::VarBindingForm {
947 binding_mode: ty::BindingMode::BindByValue(Mutability::Not), ..
949 )))) => matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut)),
950 Some(LocalInfo::User(ClearCrossCrate::Set(mir::BindingForm::ImplicitSelf(kind)))) => {
951 // Check if the user variable is a `&mut self` and we can therefore
952 // suggest removing the `&mut`.
954 // Deliberately fall into this case for all implicit self types,
955 // so that we don't fall in to the next case with them.
956 *kind == mir::ImplicitSelfKind::MutRef
958 _ if Some(kw::SelfLower) == local_name => {
959 // Otherwise, check if the name is the `self` keyword - in which case
960 // we have an explicit self. Do the same thing in this case and check
961 // for a `self: &mut Self` to suggest removing the `&mut`.
962 matches!(local_decl.ty.kind(), ty::Ref(_, _, hir::Mutability::Mut))
968 fn suggest_ampmut_self<'tcx>(
970 local_decl: &mir::LocalDecl<'tcx>,
971 ) -> (Span, String) {
972 let sp = local_decl.source_info.span;
975 match tcx.sess.source_map().span_to_snippet(sp) {
977 let lt_pos = snippet.find('\'');
978 if let Some(lt_pos) = lt_pos {
979 format!("&{}mut self", &snippet[lt_pos..snippet.len() - 4])
981 "&mut self".to_string()
984 _ => "&mut self".to_string(),
989 // When we want to suggest a user change a local variable to be a `&mut`, there
990 // are three potential "obvious" things to highlight:
992 // let ident [: Type] [= RightHandSideExpression];
993 // ^^^^^ ^^^^ ^^^^^^^^^^^^^^^^^^^^^^^
996 // We can always fallback on highlighting the first. But chances are good that
997 // the user experience will be better if we highlight one of the others if possible;
998 // for example, if the RHS is present and the Type is not, then the type is going to
999 // be inferred *from* the RHS, which means we should highlight that (and suggest
1000 // that they borrow the RHS mutably).
1002 // This implementation attempts to emulate AST-borrowck prioritization
1003 // by trying (3.), then (2.) and finally falling back on (1.).
1004 fn suggest_ampmut<'tcx>(
1006 local_decl: &mir::LocalDecl<'tcx>,
1007 opt_assignment_rhs_span: Option<Span>,
1008 opt_ty_info: Option<Span>,
1009 ) -> (bool, Span, String) {
1010 if let Some(assignment_rhs_span) = opt_assignment_rhs_span
1011 && let Ok(src) = tcx.sess.source_map().span_to_snippet(assignment_rhs_span)
1013 let is_mutbl = |ty: &str| -> bool {
1014 if let Some(rest) = ty.strip_prefix("mut") {
1015 match rest.chars().next() {
1017 Some(c) if c.is_whitespace() => true,
1022 // e.g. `&mutablevar`
1029 if let (true, Some(ws_pos)) = (src.starts_with("&'"), src.find(char::is_whitespace)) {
1030 let lt_name = &src[1..ws_pos];
1031 let ty = src[ws_pos..].trim_start();
1033 return (true, assignment_rhs_span, format!("&{lt_name} mut {ty}"));
1035 } else if let Some(stripped) = src.strip_prefix('&') {
1036 let stripped = stripped.trim_start();
1037 if !is_mutbl(stripped) {
1038 return (true, assignment_rhs_span, format!("&mut {stripped}"));
1043 let (suggestability, highlight_span) = match opt_ty_info {
1044 // if this is a variable binding with an explicit type,
1045 // try to highlight that for the suggestion.
1046 Some(ty_span) => (true, ty_span),
1048 // otherwise, just highlight the span associated with
1049 // the (MIR) LocalDecl.
1050 None => (false, local_decl.source_info.span),
1053 if let Ok(src) = tcx.sess.source_map().span_to_snippet(highlight_span)
1054 && let (true, Some(ws_pos)) = (src.starts_with("&'"), src.find(char::is_whitespace))
1056 let lt_name = &src[1..ws_pos];
1057 let ty = &src[ws_pos..];
1058 return (true, highlight_span, format!("&{} mut{}", lt_name, ty));
1061 let ty_mut = local_decl.ty.builtin_deref(true).unwrap();
1062 assert_eq!(ty_mut.mutbl, hir::Mutability::Not);
1066 if local_decl.ty.is_region_ptr() {
1067 format!("&mut {}", ty_mut.ty)
1069 format!("*mut {}", ty_mut.ty)
1074 fn is_closure_or_generator(ty: Ty<'_>) -> bool {
1075 ty.is_closure() || ty.is_generator()
1078 /// Given a field that needs to be mutable, returns a span where the " mut " could go.
1079 /// This function expects the local to be a reference to a struct in order to produce a span.
1082 /// LL | s: &'a String
1083 /// | ^^^ returns a span taking up the space here
1085 fn get_mut_span_in_struct_field<'tcx>(
1090 // Expect our local to be a reference to a struct of some kind.
1091 if let ty::Ref(_, ty, _) = ty.kind()
1092 && let ty::Adt(def, _) = ty.kind()
1093 && let field = def.all_fields().nth(field.index())?
1094 // Use the HIR types to construct the diagnostic message.
1095 && let node = tcx.hir().find_by_def_id(field.did.as_local()?)?
1096 // Now we're dealing with the actual struct that we're going to suggest a change to,
1097 // we can expect a field that is an immutable reference to a type.
1098 && let hir::Node::Field(field) = node
1099 && let hir::TyKind::Rptr(lt, hir::MutTy { mutbl: hir::Mutability::Not, ty }) = field.ty.kind
1101 return Some(lt.span.between(ty.span));
1107 /// If possible, suggest replacing `ref` with `ref mut`.
1108 fn suggest_ref_mut(tcx: TyCtxt<'_>, binding_span: Span) -> Option<String> {
1109 let hi_src = tcx.sess.source_map().span_to_snippet(binding_span).ok()?;
1110 if hi_src.starts_with("ref") && hi_src["ref".len()..].starts_with(rustc_lexer::is_whitespace) {
1111 let replacement = format!("ref mut{}", &hi_src["ref".len()..]);