1 //! Borrow checker diagnostics.
3 use rustc_errors::DiagnosticBuilder;
5 use rustc_hir::def::Namespace;
6 use rustc_hir::def_id::DefId;
7 use rustc_hir::GeneratorKind;
8 use rustc_middle::mir::{
9 AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
10 PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
12 use rustc_middle::ty::print::Print;
13 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt};
14 use rustc_span::{symbol::sym, Span};
15 use rustc_target::abi::VariantIdx;
17 use super::borrow_set::BorrowData;
18 use super::MirBorrowckCtxt;
19 use crate::dataflow::move_paths::{InitLocation, LookupResult};
22 mod outlives_suggestion;
29 mod mutability_errors;
32 crate use mutability_errors::AccessKind;
33 crate use outlives_suggestion::OutlivesSuggestionBuilder;
34 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
35 crate use region_name::{RegionName, RegionNameSource};
37 pub(super) struct IncludingDowncast(pub(super) bool);
39 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
40 /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
41 /// is moved after being invoked.
44 /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
46 /// --> $DIR/issue-42065.rs:16:29
48 /// LL | for (key, value) in dict {
51 pub(super) fn add_moved_or_invoked_closure_note(
54 place: PlaceRef<'tcx>,
55 diag: &mut DiagnosticBuilder<'_>,
57 debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
58 let mut target = place.local_or_deref_local();
59 for stmt in &self.body[location.block].statements[location.statement_index..] {
60 debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
61 if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
62 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
64 Operand::Copy(ref place) | Operand::Move(ref place)
65 if target == place.local_or_deref_local() =>
67 target = into.local_or_deref_local()
74 // Check if we are attempting to call a closure after it has been invoked.
75 let terminator = self.body[location.block].terminator();
76 debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
77 if let TerminatorKind::Call {
79 Operand::Constant(box Constant {
80 literal: ty::Const { ty: &ty::TyS { kind: ty::FnDef(id, _), .. }, .. },
87 debug!("add_moved_or_invoked_closure_note: id={:?}", id);
88 if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
89 let closure = match args.first() {
90 Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
91 if target == place.local_or_deref_local() =>
93 place.local_or_deref_local().unwrap()
98 debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
99 if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind {
100 let hir_id = self.infcx.tcx.hir().as_local_hir_id(did).unwrap();
102 if let Some((span, name)) =
103 self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
108 "closure cannot be invoked more than once because it moves the \
109 variable `{}` out of its environment",
119 // Check if we are just moving a closure after it has been invoked.
120 if let Some(target) = target {
121 if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind {
122 let hir_id = self.infcx.tcx.hir().as_local_hir_id(did).unwrap();
124 if let Some((span, name)) =
125 self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
130 "closure cannot be moved more than once as it is not `Copy` due to \
131 moving the variable `{}` out of its environment",
140 /// End-user visible description of `place` if one can be found.
141 /// If the place is a temporary for instance, `"value"` will be returned.
142 pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
143 match self.describe_place(place_ref) {
145 // Surround descr with `backticks`.
147 descr.insert_str(0, "`");
151 None => "value".to_string(),
155 /// End-user visible description of `place` if one can be found.
156 /// If the place is a temporary for instance, None will be returned.
157 pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
158 self.describe_place_with_options(place_ref, IncludingDowncast(false))
161 /// End-user visible description of `place` if one can be found. If the
162 /// place is a temporary for instance, None will be returned.
163 /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
164 /// `Downcast` and `IncludingDowncast` is true
165 pub(super) fn describe_place_with_options(
167 place: PlaceRef<'tcx>,
168 including_downcast: IncludingDowncast,
169 ) -> Option<String> {
170 let mut buf = String::new();
171 match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
177 /// Appends end-user visible description of `place` to `buf`.
178 fn append_place_to_string(
180 place: PlaceRef<'tcx>,
183 including_downcast: &IncludingDowncast,
184 ) -> Result<(), ()> {
186 PlaceRef { local, projection: [] } => {
187 self.append_local_to_string(local, buf)?;
189 PlaceRef { local, projection: [ProjectionElem::Deref] }
190 if self.body.local_decls[local].is_ref_for_guard() =>
192 self.append_place_to_string(
193 PlaceRef { local, projection: &[] },
199 PlaceRef { local, projection: [ProjectionElem::Deref] }
200 if self.body.local_decls[local].is_ref_to_static() =>
202 let local_info = &self.body.local_decls[local].local_info;
203 if let LocalInfo::StaticRef { def_id, .. } = *local_info {
204 buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
209 PlaceRef { local, projection: [proj_base @ .., elem] } => {
211 ProjectionElem::Deref => {
212 let upvar_field_projection = self.is_upvar_field_projection(place);
213 if let Some(field) = upvar_field_projection {
214 let var_index = field.index();
215 let name = self.upvars[var_index].name.to_string();
216 if self.upvars[var_index].by_ref {
219 buf.push_str(&format!("*{}", &name));
223 // FIXME turn this recursion into iteration
224 self.append_place_to_string(
225 PlaceRef { local, projection: proj_base },
232 self.append_place_to_string(
233 PlaceRef { local, projection: proj_base },
241 ProjectionElem::Downcast(..) => {
242 self.append_place_to_string(
243 PlaceRef { local, projection: proj_base },
248 if including_downcast.0 {
252 ProjectionElem::Field(field, _ty) => {
255 let upvar_field_projection = self.is_upvar_field_projection(place);
256 if let Some(field) = upvar_field_projection {
257 let var_index = field.index();
258 let name = self.upvars[var_index].name.to_string();
261 let field_name = self
262 .describe_field(PlaceRef { local, projection: proj_base }, *field);
263 self.append_place_to_string(
264 PlaceRef { local, projection: proj_base },
269 buf.push_str(&format!(".{}", field_name));
272 ProjectionElem::Index(index) => {
275 self.append_place_to_string(
276 PlaceRef { local, projection: proj_base },
282 if self.append_local_to_string(*index, buf).is_err() {
287 ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
289 // Since it isn't possible to borrow an element on a particular index and
290 // then use another while the borrow is held, don't output indices details
291 // to avoid confusing the end-user
292 self.append_place_to_string(
293 PlaceRef { local, projection: proj_base },
298 buf.push_str(&"[..]");
307 /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
308 /// a name, or its name was generated by the compiler, then `Err` is returned
309 fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
310 let decl = &self.body.local_decls[local];
311 match self.local_names[local] {
312 Some(name) if !decl.from_compiler_desugaring() => {
313 buf.push_str(&name.as_str());
320 /// End-user visible description of the `field`nth field of `base`
321 fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
322 // FIXME Place2 Make this work iteratively
324 PlaceRef { local, projection: [] } => {
325 let local = &self.body.local_decls[local];
326 self.describe_field_from_ty(&local.ty, field, None)
328 PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
329 ProjectionElem::Deref => {
330 self.describe_field(PlaceRef { local, projection: proj_base }, field)
332 ProjectionElem::Downcast(_, variant_index) => {
334 Place::ty_from(place.local, place.projection, *self.body, self.infcx.tcx)
336 self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
338 ProjectionElem::Field(_, field_type) => {
339 self.describe_field_from_ty(&field_type, field, None)
341 ProjectionElem::Index(..)
342 | ProjectionElem::ConstantIndex { .. }
343 | ProjectionElem::Subslice { .. } => {
344 self.describe_field(PlaceRef { local, projection: proj_base }, field)
350 /// End-user visible description of the `field_index`nth field of `ty`
351 fn describe_field_from_ty(
355 variant_index: Option<VariantIdx>,
358 // If the type is a box, the field is described from the boxed type
359 self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
363 let variant = if let Some(idx) = variant_index {
364 assert!(def.is_enum());
367 def.non_enum_variant()
369 variant.fields[field.index()].ident.to_string()
371 ty::Tuple(_) => field.index().to_string(),
372 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
373 self.describe_field_from_ty(&ty, field, variant_index)
375 ty::Array(ty, _) | ty::Slice(ty) => {
376 self.describe_field_from_ty(&ty, field, variant_index)
378 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
379 // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
380 // the closure comes from another crate. But in that case we wouldn't
381 // be borrowck'ing it, so we can just unwrap:
383 self.infcx.tcx.upvars(def_id).unwrap().get_index(field.index()).unwrap();
385 self.infcx.tcx.hir().name(var_id).to_string()
388 // Might need a revision when the fields in trait RFC is implemented
389 // (https://github.com/rust-lang/rfcs/pull/1546)
390 bug!("End-user description not implemented for field access on `{:?}`", ty);
396 /// Add a note that a type does not implement `Copy`
397 pub(super) fn note_type_does_not_implement_copy(
399 err: &mut DiagnosticBuilder<'a>,
404 let message = format!(
405 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
408 if let Some(span) = span {
409 err.span_label(span, message);
415 pub(super) fn borrowed_content_source(
417 deref_base: PlaceRef<'tcx>,
418 ) -> BorrowedContentSource<'tcx> {
419 let tcx = self.infcx.tcx;
421 // Look up the provided place and work out the move path index for it,
422 // we'll use this to check whether it was originally from an overloaded
424 match self.move_data.rev_lookup.find(deref_base) {
425 LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
426 debug!("borrowed_content_source: mpi={:?}", mpi);
428 for i in &self.move_data.init_path_map[mpi] {
429 let init = &self.move_data.inits[*i];
430 debug!("borrowed_content_source: init={:?}", init);
431 // We're only interested in statements that initialized a value, not the
432 // initializations from arguments.
433 let loc = match init.location {
434 InitLocation::Statement(stmt) => stmt,
438 let bbd = &self.body[loc.block];
439 let is_terminator = bbd.statements.len() == loc.statement_index;
441 "borrowed_content_source: loc={:?} is_terminator={:?}",
446 } else if let Some(Terminator {
447 kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
451 if let Some(source) =
452 BorrowedContentSource::from_call(func.ty(*self.body, tcx), tcx)
459 // Base is a `static` so won't be from an overloaded operator
463 // If we didn't find an overloaded deref or index, then assume it's a
464 // built in deref and check the type of the base.
465 let base_ty = Place::ty_from(deref_base.local, deref_base.projection, *self.body, tcx).ty;
466 if base_ty.is_unsafe_ptr() {
467 BorrowedContentSource::DerefRawPointer
468 } else if base_ty.is_mutable_ptr() {
469 BorrowedContentSource::DerefMutableRef
471 BorrowedContentSource::DerefSharedRef
476 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
477 /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
478 /// name where required.
479 pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
480 let mut s = String::new();
481 let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
483 // We need to add synthesized lifetimes where appropriate. We do
484 // this by hooking into the pretty printer and telling it to label the
485 // lifetimes without names with the value `'0`.
488 ty::RegionKind::ReLateBound(_, br)
489 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
492 ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
496 let _ = ty.print(printer);
500 /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
501 /// synthesized lifetime name where required.
502 pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
503 let mut s = String::new();
504 let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
506 let region = match ty.kind {
507 ty::Ref(region, _, _) => {
509 ty::RegionKind::ReLateBound(_, br)
510 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
511 printer.region_highlight_mode.highlighting_bound_region(*br, counter)
518 _ => bug!("ty for annotation of borrow region is not a reference"),
521 let _ = region.print(printer);
526 // The span(s) associated to a use of a place.
527 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
528 pub(super) enum UseSpans {
529 // The access is caused by capturing a variable for a closure.
531 // This is true if the captured variable was from a generator.
532 generator_kind: Option<GeneratorKind>,
533 // The span of the args of the closure, including the `move` keyword if
536 // The span of the first use of the captured variable inside the closure.
539 // This access has a single span associated to it: common case.
544 pub(super) fn args_or_use(self) -> Span {
546 UseSpans::ClosureUse { args_span: span, .. } | UseSpans::OtherUse(span) => span,
550 pub(super) fn var_or_use(self) -> Span {
552 UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
556 pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
558 UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
563 // Add a span label to the arguments of the closure, if it exists.
564 pub(super) fn args_span_label(
566 err: &mut DiagnosticBuilder<'_>,
567 message: impl Into<String>,
569 if let UseSpans::ClosureUse { args_span, .. } = self {
570 err.span_label(args_span, message);
574 // Add a span label to the use of the captured variable, if it exists.
575 pub(super) fn var_span_label(
577 err: &mut DiagnosticBuilder<'_>,
578 message: impl Into<String>,
580 if let UseSpans::ClosureUse { var_span, .. } = self {
581 err.span_label(var_span, message);
585 /// Returns `false` if this place is not used in a closure.
586 pub(super) fn for_closure(&self) -> bool {
588 UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
593 /// Returns `false` if this place is not used in a generator.
594 pub(super) fn for_generator(&self) -> bool {
596 UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
601 /// Describe the span associated with a use of a place.
602 pub(super) fn describe(&self) -> String {
604 UseSpans::ClosureUse { generator_kind, .. } => {
605 if generator_kind.is_some() {
606 " in generator".to_string()
608 " in closure".to_string()
615 pub(super) fn or_else<F>(self, if_other: F) -> Self
620 closure @ UseSpans::ClosureUse { .. } => closure,
621 UseSpans::OtherUse(_) => if_other(),
626 pub(super) enum BorrowedContentSource<'tcx> {
630 OverloadedDeref(Ty<'tcx>),
631 OverloadedIndex(Ty<'tcx>),
634 impl BorrowedContentSource<'tcx> {
635 pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
637 BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
638 BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
639 BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
640 BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
641 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
642 "an `Rc`".to_string()
644 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
645 "an `Arc`".to_string()
647 _ => format!("dereference of `{}`", ty),
649 BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
653 pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
655 BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
656 BorrowedContentSource::DerefSharedRef => Some("shared reference"),
657 BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
658 // Overloaded deref and index operators should be evaluated into a
659 // temporary. So we don't need a description here.
660 BorrowedContentSource::OverloadedDeref(_)
661 | BorrowedContentSource::OverloadedIndex(_) => None,
665 pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
667 BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
668 BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
669 BorrowedContentSource::DerefMutableRef => {
670 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
672 BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
673 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
674 "an `Rc`".to_string()
676 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
677 "an `Arc`".to_string()
679 _ => format!("a dereference of `{}`", ty),
681 BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
685 fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
687 ty::FnDef(def_id, substs) => {
688 let trait_id = tcx.trait_of_item(def_id)?;
690 let lang_items = tcx.lang_items();
691 if Some(trait_id) == lang_items.deref_trait()
692 || Some(trait_id) == lang_items.deref_mut_trait()
694 Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
695 } else if Some(trait_id) == lang_items.index_trait()
696 || Some(trait_id) == lang_items.index_mut_trait()
698 Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
708 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
709 /// Finds the spans associated to a move or copy of move_place at location.
710 pub(super) fn move_spans(
712 moved_place: PlaceRef<'tcx>, // Could also be an upvar.
715 use self::UseSpans::*;
717 let stmt = match self.body[location.block].statements.get(location.statement_index) {
719 None => return OtherUse(self.body.source_info(location).span),
722 debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
723 if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
724 let def_id = match kind {
725 box AggregateKind::Closure(def_id, _)
726 | box AggregateKind::Generator(def_id, _, _) => def_id,
727 _ => return OtherUse(stmt.source_info.span),
730 debug!("move_spans: def_id={:?} places={:?}", def_id, places);
731 if let Some((args_span, generator_kind, var_span)) =
732 self.closure_span(*def_id, moved_place, places)
734 return ClosureUse { generator_kind, args_span, var_span };
738 OtherUse(stmt.source_info.span)
741 /// Finds the span of arguments of a closure (within `maybe_closure_span`)
742 /// and its usage of the local assigned at `location`.
743 /// This is done by searching in statements succeeding `location`
744 /// and originating from `maybe_closure_span`.
745 pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
746 use self::UseSpans::*;
747 debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
749 let target = match self.body[location.block].statements.get(location.statement_index) {
750 Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
751 if let Some(local) = place.as_local() {
754 return OtherUse(use_span);
757 _ => return OtherUse(use_span),
760 if self.body.local_kind(target) != LocalKind::Temp {
761 // operands are always temporaries.
762 return OtherUse(use_span);
765 for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
766 if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
769 let (def_id, is_generator) = match kind {
770 box AggregateKind::Closure(def_id, _) => (def_id, false),
771 box AggregateKind::Generator(def_id, _, _) => (def_id, true),
776 "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
777 def_id, is_generator, places
779 if let Some((args_span, generator_kind, var_span)) =
780 self.closure_span(*def_id, Place::from(target).as_ref(), places)
782 return ClosureUse { generator_kind, args_span, var_span };
784 return OtherUse(use_span);
788 if use_span != stmt.source_info.span {
796 /// Finds the span of a captured variable within a closure or generator.
800 target_place: PlaceRef<'tcx>,
801 places: &Vec<Operand<'tcx>>,
802 ) -> Option<(Span, Option<GeneratorKind>, Span)> {
804 "closure_span: def_id={:?} target_place={:?} places={:?}",
805 def_id, target_place, places
807 let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
808 let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
809 debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
810 if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
811 for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
813 Operand::Copy(place) | Operand::Move(place)
814 if target_place == place.as_ref() =>
816 debug!("closure_span: found captured local {:?}", place);
817 let body = self.infcx.tcx.hir().body(*body_id);
818 let generator_kind = body.generator_kind();
819 return Some((*args_span, generator_kind, upvar.span));
828 /// Helper to retrieve span(s) of given borrow from the current MIR
830 pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
831 let span = self.body.source_info(borrow.reserve_location).span;
832 self.borrow_spans(span, borrow.reserve_location)