1 //! Borrow checker diagnostics.
4 AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
5 PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
7 use rustc::ty::layout::VariantIdx;
8 use rustc::ty::print::Print;
9 use rustc::ty::{self, DefIdTree, Ty, TyCtxt};
10 use rustc_errors::DiagnosticBuilder;
12 use rustc_hir::def::Namespace;
13 use rustc_hir::def_id::DefId;
14 use rustc_hir::GeneratorKind;
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<'cx, '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. If the
141 /// place is a temporary for instance, None will be returned.
142 pub(super) fn describe_place(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<String> {
143 self.describe_place_with_options(place_ref, IncludingDowncast(false))
146 /// End-user visible description of `place` if one can be found. If the
147 /// place is a temporary for instance, None will be returned.
148 /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
149 /// `Downcast` and `IncludingDowncast` is true
150 pub(super) fn describe_place_with_options(
152 place: PlaceRef<'cx, 'tcx>,
153 including_downcast: IncludingDowncast,
154 ) -> Option<String> {
155 let mut buf = String::new();
156 match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
162 /// Appends end-user visible description of `place` to `buf`.
163 fn append_place_to_string(
165 place: PlaceRef<'cx, 'tcx>,
168 including_downcast: &IncludingDowncast,
169 ) -> Result<(), ()> {
171 PlaceRef { local, projection: [] } => {
172 self.append_local_to_string(local, buf)?;
174 PlaceRef { local, projection: [ProjectionElem::Deref] }
175 if self.body.local_decls[local].is_ref_for_guard() =>
177 self.append_place_to_string(
178 PlaceRef { local: local, projection: &[] },
184 PlaceRef { local, projection: [ProjectionElem::Deref] }
185 if self.body.local_decls[local].is_ref_to_static() =>
187 let local_info = &self.body.local_decls[local].local_info;
188 if let LocalInfo::StaticRef { def_id, .. } = *local_info {
189 buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
194 PlaceRef { local, projection: [proj_base @ .., elem] } => {
196 ProjectionElem::Deref => {
197 let upvar_field_projection = self.is_upvar_field_projection(place);
198 if let Some(field) = upvar_field_projection {
199 let var_index = field.index();
200 let name = self.upvars[var_index].name.to_string();
201 if self.upvars[var_index].by_ref {
204 buf.push_str(&format!("*{}", &name));
208 // FIXME turn this recursion into iteration
209 self.append_place_to_string(
210 PlaceRef { local, projection: proj_base },
217 self.append_place_to_string(
218 PlaceRef { local, projection: proj_base },
226 ProjectionElem::Downcast(..) => {
227 self.append_place_to_string(
228 PlaceRef { local, projection: proj_base },
233 if including_downcast.0 {
237 ProjectionElem::Field(field, _ty) => {
240 let upvar_field_projection = self.is_upvar_field_projection(place);
241 if let Some(field) = upvar_field_projection {
242 let var_index = field.index();
243 let name = self.upvars[var_index].name.to_string();
246 let field_name = self
247 .describe_field(PlaceRef { local, projection: proj_base }, *field);
248 self.append_place_to_string(
249 PlaceRef { local, projection: proj_base },
254 buf.push_str(&format!(".{}", field_name));
257 ProjectionElem::Index(index) => {
260 self.append_place_to_string(
261 PlaceRef { local, projection: proj_base },
267 if self.append_local_to_string(*index, buf).is_err() {
272 ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
274 // Since it isn't possible to borrow an element on a particular index and
275 // then use another while the borrow is held, don't output indices details
276 // to avoid confusing the end-user
277 self.append_place_to_string(
278 PlaceRef { local, projection: proj_base },
283 buf.push_str(&"[..]");
292 /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
293 /// a name, or its name was generated by the compiler, then `Err` is returned
294 fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
295 let decl = &self.body.local_decls[local];
296 match self.local_names[local] {
297 Some(name) if !decl.from_compiler_desugaring() => {
298 buf.push_str(&name.as_str());
305 /// End-user visible description of the `field`nth field of `base`
306 fn describe_field(&self, place: PlaceRef<'cx, 'tcx>, field: Field) -> String {
307 // FIXME Place2 Make this work iteratively
309 PlaceRef { local, projection: [] } => {
310 let local = &self.body.local_decls[local];
311 self.describe_field_from_ty(&local.ty, field, None)
313 PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
314 ProjectionElem::Deref => {
315 self.describe_field(PlaceRef { local, projection: proj_base }, field)
317 ProjectionElem::Downcast(_, variant_index) => {
319 Place::ty_from(place.local, place.projection, *self.body, self.infcx.tcx)
321 self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
323 ProjectionElem::Field(_, field_type) => {
324 self.describe_field_from_ty(&field_type, field, None)
326 ProjectionElem::Index(..)
327 | ProjectionElem::ConstantIndex { .. }
328 | ProjectionElem::Subslice { .. } => {
329 self.describe_field(PlaceRef { local, projection: proj_base }, field)
335 /// End-user visible description of the `field_index`nth field of `ty`
336 fn describe_field_from_ty(
340 variant_index: Option<VariantIdx>,
343 // If the type is a box, the field is described from the boxed type
344 self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
348 let variant = if let Some(idx) = variant_index {
349 assert!(def.is_enum());
352 def.non_enum_variant()
354 variant.fields[field.index()].ident.to_string()
356 ty::Tuple(_) => field.index().to_string(),
357 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
358 self.describe_field_from_ty(&ty, field, variant_index)
360 ty::Array(ty, _) | ty::Slice(ty) => {
361 self.describe_field_from_ty(&ty, field, variant_index)
363 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
364 // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
365 // the closure comes from another crate. But in that case we wouldn't
366 // be borrowck'ing it, so we can just unwrap:
368 self.infcx.tcx.upvars(def_id).unwrap().get_index(field.index()).unwrap();
370 self.infcx.tcx.hir().name(var_id).to_string()
373 // Might need a revision when the fields in trait RFC is implemented
374 // (https://github.com/rust-lang/rfcs/pull/1546)
375 bug!("End-user description not implemented for field access on `{:?}`", ty);
381 /// Add a note that a type does not implement `Copy`
382 pub(super) fn note_type_does_not_implement_copy(
384 err: &mut DiagnosticBuilder<'a>,
389 let message = format!(
390 "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
393 if let Some(span) = span {
394 err.span_label(span, message);
400 pub(super) fn borrowed_content_source(
402 deref_base: PlaceRef<'cx, 'tcx>,
403 ) -> BorrowedContentSource<'tcx> {
404 let tcx = self.infcx.tcx;
406 // Look up the provided place and work out the move path index for it,
407 // we'll use this to check whether it was originally from an overloaded
409 match self.move_data.rev_lookup.find(deref_base) {
410 LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
411 debug!("borrowed_content_source: mpi={:?}", mpi);
413 for i in &self.move_data.init_path_map[mpi] {
414 let init = &self.move_data.inits[*i];
415 debug!("borrowed_content_source: init={:?}", init);
416 // We're only interested in statements that initialized a value, not the
417 // initializations from arguments.
418 let loc = match init.location {
419 InitLocation::Statement(stmt) => stmt,
423 let bbd = &self.body[loc.block];
424 let is_terminator = bbd.statements.len() == loc.statement_index;
426 "borrowed_content_source: loc={:?} is_terminator={:?}",
431 } else if let Some(Terminator {
432 kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
436 if let Some(source) =
437 BorrowedContentSource::from_call(func.ty(*self.body, tcx), tcx)
444 // Base is a `static` so won't be from an overloaded operator
448 // If we didn't find an overloaded deref or index, then assume it's a
449 // built in deref and check the type of the base.
450 let base_ty = Place::ty_from(deref_base.local, deref_base.projection, *self.body, tcx).ty;
451 if base_ty.is_unsafe_ptr() {
452 BorrowedContentSource::DerefRawPointer
453 } else if base_ty.is_mutable_ptr() {
454 BorrowedContentSource::DerefMutableRef
456 BorrowedContentSource::DerefSharedRef
461 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
462 /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
463 /// name where required.
464 pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
465 let mut s = String::new();
466 let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
468 // We need to add synthesized lifetimes where appropriate. We do
469 // this by hooking into the pretty printer and telling it to label the
470 // lifetimes without names with the value `'0`.
472 ty::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
474 ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
477 ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
481 let _ = ty.print(printer);
485 /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
486 /// synthesized lifetime name where required.
487 pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
488 let mut s = String::new();
489 let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
491 let region = match ty.kind {
492 ty::Ref(region, _, _) => {
494 ty::RegionKind::ReLateBound(_, br)
495 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
496 printer.region_highlight_mode.highlighting_bound_region(*br, counter)
503 _ => bug!("ty for annotation of borrow region is not a reference"),
506 let _ = region.print(printer);
511 // The span(s) associated to a use of a place.
512 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
513 pub(super) enum UseSpans {
514 // The access is caused by capturing a variable for a closure.
516 // This is true if the captured variable was from a generator.
517 generator_kind: Option<GeneratorKind>,
518 // The span of the args of the closure, including the `move` keyword if
521 // The span of the first use of the captured variable inside the closure.
524 // This access has a single span associated to it: common case.
529 pub(super) fn args_or_use(self) -> Span {
531 UseSpans::ClosureUse { args_span: span, .. } | UseSpans::OtherUse(span) => span,
535 pub(super) fn var_or_use(self) -> Span {
537 UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
541 pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
543 UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
548 // Add a span label to the arguments of the closure, if it exists.
549 pub(super) fn args_span_label(
551 err: &mut DiagnosticBuilder<'_>,
552 message: impl Into<String>,
554 if let UseSpans::ClosureUse { args_span, .. } = self {
555 err.span_label(args_span, message);
559 // Add a span label to the use of the captured variable, if it exists.
560 pub(super) fn var_span_label(
562 err: &mut DiagnosticBuilder<'_>,
563 message: impl Into<String>,
565 if let UseSpans::ClosureUse { var_span, .. } = self {
566 err.span_label(var_span, message);
570 /// Returns `false` if this place is not used in a closure.
571 pub(super) fn for_closure(&self) -> bool {
573 UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
578 /// Returns `false` if this place is not used in a generator.
579 pub(super) fn for_generator(&self) -> bool {
581 UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
586 /// Describe the span associated with a use of a place.
587 pub(super) fn describe(&self) -> String {
589 UseSpans::ClosureUse { generator_kind, .. } => {
590 if generator_kind.is_some() {
591 " in generator".to_string()
593 " in closure".to_string()
600 pub(super) fn or_else<F>(self, if_other: F) -> Self
605 closure @ UseSpans::ClosureUse { .. } => closure,
606 UseSpans::OtherUse(_) => if_other(),
611 pub(super) enum BorrowedContentSource<'tcx> {
615 OverloadedDeref(Ty<'tcx>),
616 OverloadedIndex(Ty<'tcx>),
619 impl BorrowedContentSource<'tcx> {
620 pub(super) fn describe_for_unnamed_place(&self) -> String {
622 BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
623 BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
624 BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
625 BorrowedContentSource::OverloadedDeref(ty) => {
627 "an `Rc`".to_string()
628 } else if ty.is_arc() {
629 "an `Arc`".to_string()
631 format!("dereference of `{}`", ty)
634 BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
638 pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
640 BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
641 BorrowedContentSource::DerefSharedRef => Some("shared reference"),
642 BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
643 // Overloaded deref and index operators should be evaluated into a
644 // temporary. So we don't need a description here.
645 BorrowedContentSource::OverloadedDeref(_)
646 | BorrowedContentSource::OverloadedIndex(_) => None,
650 pub(super) fn describe_for_immutable_place(&self) -> String {
652 BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
653 BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
654 BorrowedContentSource::DerefMutableRef => {
655 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
657 BorrowedContentSource::OverloadedDeref(ty) => {
659 "an `Rc`".to_string()
660 } else if ty.is_arc() {
661 "an `Arc`".to_string()
663 format!("a dereference of `{}`", ty)
666 BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
670 fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
672 ty::FnDef(def_id, substs) => {
673 let trait_id = tcx.trait_of_item(def_id)?;
675 let lang_items = tcx.lang_items();
676 if Some(trait_id) == lang_items.deref_trait()
677 || Some(trait_id) == lang_items.deref_mut_trait()
679 Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
680 } else if Some(trait_id) == lang_items.index_trait()
681 || Some(trait_id) == lang_items.index_mut_trait()
683 Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
693 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
694 /// Finds the spans associated to a move or copy of move_place at location.
695 pub(super) fn move_spans(
697 moved_place: PlaceRef<'cx, 'tcx>, // Could also be an upvar.
700 use self::UseSpans::*;
702 let stmt = match self.body[location.block].statements.get(location.statement_index) {
704 None => return OtherUse(self.body.source_info(location).span),
707 debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
708 if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
709 let def_id = match kind {
710 box AggregateKind::Closure(def_id, _)
711 | box AggregateKind::Generator(def_id, _, _) => def_id,
712 _ => return OtherUse(stmt.source_info.span),
715 debug!("move_spans: def_id={:?} places={:?}", def_id, places);
716 if let Some((args_span, generator_kind, var_span)) =
717 self.closure_span(*def_id, moved_place, places)
719 return ClosureUse { generator_kind, args_span, var_span };
723 OtherUse(stmt.source_info.span)
726 /// Finds the span of arguments of a closure (within `maybe_closure_span`)
727 /// and its usage of the local assigned at `location`.
728 /// This is done by searching in statements succeeding `location`
729 /// and originating from `maybe_closure_span`.
730 pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
731 use self::UseSpans::*;
732 debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
734 let target = match self.body[location.block].statements.get(location.statement_index) {
735 Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
736 if let Some(local) = place.as_local() {
739 return OtherUse(use_span);
742 _ => return OtherUse(use_span),
745 if self.body.local_kind(target) != LocalKind::Temp {
746 // operands are always temporaries.
747 return OtherUse(use_span);
750 for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
751 if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
754 let (def_id, is_generator) = match kind {
755 box AggregateKind::Closure(def_id, _) => (def_id, false),
756 box AggregateKind::Generator(def_id, _, _) => (def_id, true),
761 "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
762 def_id, is_generator, places
764 if let Some((args_span, generator_kind, var_span)) =
765 self.closure_span(*def_id, Place::from(target).as_ref(), places)
767 return ClosureUse { generator_kind, args_span, var_span };
769 return OtherUse(use_span);
773 if use_span != stmt.source_info.span {
781 /// Finds the span of a captured variable within a closure or generator.
785 target_place: PlaceRef<'cx, 'tcx>,
786 places: &Vec<Operand<'tcx>>,
787 ) -> Option<(Span, Option<GeneratorKind>, Span)> {
789 "closure_span: def_id={:?} target_place={:?} places={:?}",
790 def_id, target_place, places
792 let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
793 let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
794 debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
795 if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
796 for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
798 Operand::Copy(place) | Operand::Move(place)
799 if target_place == place.as_ref() =>
801 debug!("closure_span: found captured local {:?}", place);
802 let body = self.infcx.tcx.hir().body(*body_id);
803 let generator_kind = body.generator_kind();
804 return Some((*args_span, generator_kind, upvar.span));
813 /// Helper to retrieve span(s) of given borrow from the current MIR
815 pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
816 let span = self.body.source_info(borrow.reserve_location).span;
817 self.borrow_spans(span, borrow.reserve_location)