--- /dev/null
+use either::Either;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::{Applicability, DiagnosticBuilder};
+use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
+use rustc_hir::{AsyncGeneratorKind, GeneratorKind};
+use rustc_middle::mir::{
+ self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, ConstraintCategory,
+ FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, Operand, Place, PlaceRef,
+ ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind, VarBindingForm,
+};
+use rustc_middle::ty::{self, suggest_constraining_type_param, Ty};
+use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
+use rustc_span::source_map::DesugaringKind;
+use rustc_span::symbol::sym;
+use rustc_span::{BytePos, MultiSpan, Span, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtExt;
+
+use crate::borrowck_errors;
+
+use crate::{
+ borrow_set::BorrowData, diagnostics::Instance, prefixes::IsPrefixOf,
+ InitializationRequiringAction, MirBorrowckCtxt, PrefixSet, WriteKind,
+};
+
+use super::{
+ explain_borrow::BorrowExplanation, FnSelfUseKind, IncludingDowncast, RegionName,
+ RegionNameSource, UseSpans,
+};
+
+#[derive(Debug)]
+struct MoveSite {
+ /// Index of the "move out" that we found. The `MoveData` can
+ /// then tell us where the move occurred.
+ moi: MoveOutIndex,
+
+ /// `true` if we traversed a back edge while walking from the point
+ /// of error to the move site.
+ traversed_back_edge: bool,
+}
+
+/// Which case a StorageDeadOrDrop is for.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+enum StorageDeadOrDrop<'tcx> {
+ LocalStorageDead,
+ BoxedStorageDead,
+ Destructor(Ty<'tcx>),
+}
+
+impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
+ pub(crate) fn report_use_of_moved_or_uninitialized(
+ &mut self,
+ location: Location,
+ desired_action: InitializationRequiringAction,
+ (moved_place, used_place, span): (PlaceRef<'tcx>, PlaceRef<'tcx>, Span),
+ mpi: MovePathIndex,
+ ) {
+ debug!(
+ "report_use_of_moved_or_uninitialized: location={:?} desired_action={:?} \
+ moved_place={:?} used_place={:?} span={:?} mpi={:?}",
+ location, desired_action, moved_place, used_place, span, mpi
+ );
+
+ let use_spans =
+ self.move_spans(moved_place, location).or_else(|| self.borrow_spans(span, location));
+ let span = use_spans.args_or_use();
+
+ let (move_site_vec, maybe_reinitialized_locations) = self.get_moved_indexes(location, mpi);
+ debug!(
+ "report_use_of_moved_or_uninitialized: move_site_vec={:?} use_spans={:?}",
+ move_site_vec, use_spans
+ );
+ let move_out_indices: Vec<_> =
+ move_site_vec.iter().map(|move_site| move_site.moi).collect();
+
+ if move_out_indices.is_empty() {
+ let root_place = PlaceRef { projection: &[], ..used_place };
+
+ if !self.uninitialized_error_reported.insert(root_place) {
+ debug!(
+ "report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
+ root_place
+ );
+ return;
+ }
+
+ let item_msg =
+ match self.describe_place_with_options(used_place, IncludingDowncast(true)) {
+ Some(name) => format!("`{}`", name),
+ None => "value".to_owned(),
+ };
+ let mut err = self.cannot_act_on_uninitialized_variable(
+ span,
+ desired_action.as_noun(),
+ &self
+ .describe_place_with_options(moved_place, IncludingDowncast(true))
+ .unwrap_or_else(|| "_".to_owned()),
+ );
+ err.span_label(span, format!("use of possibly-uninitialized {}", item_msg));
+
+ use_spans.var_span_label_path_only(
+ &mut err,
+ format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
+ );
+
+ err.buffer(&mut self.errors_buffer);
+ } else {
+ if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
+ if self.prefixes(*reported_place, PrefixSet::All).any(|p| p == used_place) {
+ debug!(
+ "report_use_of_moved_or_uninitialized place: error suppressed \
+ mois={:?}",
+ move_out_indices
+ );
+ return;
+ }
+ }
+
+ let is_partial_move = move_site_vec.iter().any(|move_site| {
+ let move_out = self.move_data.moves[(*move_site).moi];
+ let moved_place = &self.move_data.move_paths[move_out.path].place;
+ // `*(_1)` where `_1` is a `Box` is actually a move out.
+ let is_box_move = moved_place.as_ref().projection == [ProjectionElem::Deref]
+ && self.body.local_decls[moved_place.local].ty.is_box();
+
+ !is_box_move
+ && used_place != moved_place.as_ref()
+ && used_place.is_prefix_of(moved_place.as_ref())
+ });
+
+ let partial_str = if is_partial_move { "partial " } else { "" };
+ let partially_str = if is_partial_move { "partially " } else { "" };
+
+ let mut err = self.cannot_act_on_moved_value(
+ span,
+ desired_action.as_noun(),
+ partially_str,
+ self.describe_place_with_options(moved_place, IncludingDowncast(true)),
+ );
+
+ let reinit_spans = maybe_reinitialized_locations
+ .iter()
+ .take(3)
+ .map(|loc| {
+ self.move_spans(self.move_data.move_paths[mpi].place.as_ref(), *loc)
+ .args_or_use()
+ })
+ .collect::<Vec<Span>>();
+ let reinits = maybe_reinitialized_locations.len();
+ if reinits == 1 {
+ err.span_label(reinit_spans[0], "this reinitialization might get skipped");
+ } else if reinits > 1 {
+ err.span_note(
+ MultiSpan::from_spans(reinit_spans),
+ &if reinits <= 3 {
+ format!("these {} reinitializations might get skipped", reinits)
+ } else {
+ format!(
+ "these 3 reinitializations and {} other{} might get skipped",
+ reinits - 3,
+ if reinits == 4 { "" } else { "s" }
+ )
+ },
+ );
+ }
+
+ self.add_moved_or_invoked_closure_note(location, used_place, &mut err);
+
+ let mut is_loop_move = false;
+ let mut in_pattern = false;
+
+ for move_site in &move_site_vec {
+ let move_out = self.move_data.moves[(*move_site).moi];
+ let moved_place = &self.move_data.move_paths[move_out.path].place;
+
+ let move_spans = self.move_spans(moved_place.as_ref(), move_out.source);
+ let move_span = move_spans.args_or_use();
+
+ let move_msg = if move_spans.for_closure() { " into closure" } else { "" };
+
+ let loop_message = if location == move_out.source || move_site.traversed_back_edge {
+ ", in previous iteration of loop"
+ } else {
+ ""
+ };
+
+ if location == move_out.source {
+ is_loop_move = true;
+ }
+
+ if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
+ let place_name = self
+ .describe_place(moved_place.as_ref())
+ .map(|n| format!("`{}`", n))
+ .unwrap_or_else(|| "value".to_owned());
+ match kind {
+ FnSelfUseKind::FnOnceCall => {
+ err.span_label(
+ fn_call_span,
+ &format!(
+ "{} {}moved due to this call{}",
+ place_name, partially_str, loop_message
+ ),
+ );
+ err.span_note(
+ var_span,
+ "this value implements `FnOnce`, which causes it to be moved when called",
+ );
+ }
+ FnSelfUseKind::Operator { self_arg } => {
+ err.span_label(
+ fn_call_span,
+ &format!(
+ "{} {}moved due to usage in operator{}",
+ place_name, partially_str, loop_message
+ ),
+ );
+ if self.fn_self_span_reported.insert(fn_span) {
+ err.span_note(
+ // Check whether the source is accessible
+ if self
+ .infcx
+ .tcx
+ .sess
+ .source_map()
+ .span_to_snippet(self_arg.span)
+ .is_ok()
+ {
+ self_arg.span
+ } else {
+ fn_call_span
+ },
+ "calling this operator moves the left-hand side",
+ );
+ }
+ }
+ FnSelfUseKind::Normal {
+ self_arg,
+ implicit_into_iter,
+ is_option_or_result,
+ } => {
+ if implicit_into_iter {
+ err.span_label(
+ fn_call_span,
+ &format!(
+ "{} {}moved due to this implicit call to `.into_iter()`{}",
+ place_name, partially_str, loop_message
+ ),
+ );
+ } else {
+ err.span_label(
+ fn_call_span,
+ &format!(
+ "{} {}moved due to this method call{}",
+ place_name, partially_str, loop_message
+ ),
+ );
+ }
+ if is_option_or_result && maybe_reinitialized_locations.is_empty() {
+ err.span_suggestion_verbose(
+ fn_call_span.shrink_to_lo(),
+ "consider calling `.as_ref()` to borrow the type's contents",
+ "as_ref().".to_string(),
+ Applicability::MachineApplicable,
+ );
+ }
+ // Avoid pointing to the same function in multiple different
+ // error messages.
+ if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span)
+ {
+ err.span_note(
+ self_arg.span,
+ &format!("this function takes ownership of the receiver `self`, which moves {}", place_name)
+ );
+ }
+ }
+ // Deref::deref takes &self, which cannot cause a move
+ FnSelfUseKind::DerefCoercion { .. } => unreachable!(),
+ }
+ } else {
+ err.span_label(
+ move_span,
+ format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
+ );
+ // If the move error occurs due to a loop, don't show
+ // another message for the same span
+ if loop_message.is_empty() {
+ move_spans.var_span_label(
+ &mut err,
+ format!(
+ "variable {}moved due to use{}",
+ partially_str,
+ move_spans.describe()
+ ),
+ "moved",
+ );
+ }
+ }
+
+ if let (UseSpans::PatUse(span), []) =
+ (move_spans, &maybe_reinitialized_locations[..])
+ {
+ if maybe_reinitialized_locations.is_empty() {
+ err.span_suggestion_verbose(
+ span.shrink_to_lo(),
+ &format!(
+ "borrow this field in the pattern to avoid moving {}",
+ self.describe_place(moved_place.as_ref())
+ .map(|n| format!("`{}`", n))
+ .unwrap_or_else(|| "the value".to_string())
+ ),
+ "ref ".to_string(),
+ Applicability::MachineApplicable,
+ );
+ in_pattern = true;
+ }
+ }
+
+ if let Some(DesugaringKind::ForLoop(_)) = move_span.desugaring_kind() {
+ let sess = self.infcx.tcx.sess;
+ let ty = used_place.ty(self.body, self.infcx.tcx).ty;
+ // If we have a `&mut` ref, we need to reborrow.
+ if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind() {
+ // If we are in a loop this will be suggested later.
+ if !is_loop_move {
+ err.span_suggestion_verbose(
+ move_span.shrink_to_lo(),
+ &format!(
+ "consider creating a fresh reborrow of {} here",
+ self.describe_place(moved_place.as_ref())
+ .map(|n| format!("`{}`", n))
+ .unwrap_or_else(|| "the mutable reference".to_string()),
+ ),
+ "&mut *".to_string(),
+ Applicability::MachineApplicable,
+ );
+ }
+ } else if let Ok(snippet) = sess.source_map().span_to_snippet(move_span) {
+ err.span_suggestion(
+ move_span,
+ "consider borrowing to avoid moving into the for loop",
+ format!("&{}", snippet),
+ Applicability::MaybeIncorrect,
+ );
+ }
+ }
+ }
+
+ use_spans.var_span_label_path_only(
+ &mut err,
+ format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
+ );
+
+ if !is_loop_move {
+ err.span_label(
+ span,
+ format!(
+ "value {} here after {}move",
+ desired_action.as_verb_in_past_tense(),
+ partial_str
+ ),
+ );
+ }
+
+ let ty = used_place.ty(self.body, self.infcx.tcx).ty;
+ let needs_note = match ty.kind() {
+ ty::Closure(id, _) => {
+ let tables = self.infcx.tcx.typeck(id.expect_local());
+ let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(id.expect_local());
+
+ tables.closure_kind_origins().get(hir_id).is_none()
+ }
+ _ => true,
+ };
+
+ let mpi = self.move_data.moves[move_out_indices[0]].path;
+ let place = &self.move_data.move_paths[mpi].place;
+ let ty = place.ty(self.body, self.infcx.tcx).ty;
+
+ // If we're in pattern, we do nothing in favor of the previous suggestion (#80913).
+ if is_loop_move & !in_pattern {
+ if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind() {
+ // We have a `&mut` ref, we need to reborrow on each iteration (#62112).
+ err.span_suggestion_verbose(
+ span.shrink_to_lo(),
+ &format!(
+ "consider creating a fresh reborrow of {} here",
+ self.describe_place(moved_place)
+ .map(|n| format!("`{}`", n))
+ .unwrap_or_else(|| "the mutable reference".to_string()),
+ ),
+ "&mut *".to_string(),
+ Applicability::MachineApplicable,
+ );
+ }
+ }
+
+ if needs_note {
+ let opt_name =
+ self.describe_place_with_options(place.as_ref(), IncludingDowncast(true));
+ let note_msg = match opt_name {
+ Some(ref name) => format!("`{}`", name),
+ None => "value".to_owned(),
+ };
+ if let ty::Param(param_ty) = ty.kind() {
+ let tcx = self.infcx.tcx;
+ let generics = tcx.generics_of(self.mir_def_id());
+ let param = generics.type_param(¶m_ty, tcx);
+ if let Some(generics) = tcx
+ .hir()
+ .get_generics(tcx.closure_base_def_id(self.mir_def_id().to_def_id()))
+ {
+ suggest_constraining_type_param(
+ tcx,
+ generics,
+ &mut err,
+ ¶m.name.as_str(),
+ "Copy",
+ None,
+ );
+ }
+ }
+ let span = if let Some(local) = place.as_local() {
+ let decl = &self.body.local_decls[local];
+ Some(decl.source_info.span)
+ } else {
+ None
+ };
+ self.note_type_does_not_implement_copy(&mut err, ¬e_msg, ty, span, partial_str);
+ }
+
+ if let UseSpans::FnSelfUse {
+ kind: FnSelfUseKind::DerefCoercion { deref_target, deref_target_ty },
+ ..
+ } = use_spans
+ {
+ err.note(&format!(
+ "{} occurs due to deref coercion to `{}`",
+ desired_action.as_noun(),
+ deref_target_ty
+ ));
+
+ // Check first whether the source is accessible (issue #87060)
+ if self.infcx.tcx.sess.source_map().span_to_snippet(deref_target).is_ok() {
+ err.span_note(deref_target, "deref defined here");
+ }
+ }
+
+ if let Some((_, mut old_err)) =
+ self.move_error_reported.insert(move_out_indices, (used_place, err))
+ {
+ // Cancel the old error so it doesn't ICE.
+ old_err.cancel();
+ }
+ }
+ }
+
+ pub(crate) fn report_move_out_while_borrowed(
+ &mut self,
+ location: Location,
+ (place, span): (Place<'tcx>, Span),
+ borrow: &BorrowData<'tcx>,
+ ) {
+ debug!(
+ "report_move_out_while_borrowed: location={:?} place={:?} span={:?} borrow={:?}",
+ location, place, span, borrow
+ );
+ let value_msg = self.describe_any_place(place.as_ref());
+ let borrow_msg = self.describe_any_place(borrow.borrowed_place.as_ref());
+
+ let borrow_spans = self.retrieve_borrow_spans(borrow);
+ let borrow_span = borrow_spans.args_or_use();
+
+ let move_spans = self.move_spans(place.as_ref(), location);
+ let span = move_spans.args_or_use();
+
+ let mut err =
+ self.cannot_move_when_borrowed(span, &self.describe_any_place(place.as_ref()));
+ err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
+ err.span_label(span, format!("move out of {} occurs here", value_msg));
+
+ borrow_spans.var_span_label_path_only(
+ &mut err,
+ format!("borrow occurs due to use{}", borrow_spans.describe()),
+ );
+
+ move_spans.var_span_label(
+ &mut err,
+ format!("move occurs due to use{}", move_spans.describe()),
+ "moved",
+ );
+
+ self.explain_why_borrow_contains_point(location, borrow, None)
+ .add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ "",
+ Some(borrow_span),
+ None,
+ );
+ err.buffer(&mut self.errors_buffer);
+ }
+
+ pub(crate) fn report_use_while_mutably_borrowed(
+ &mut self,
+ location: Location,
+ (place, _span): (Place<'tcx>, Span),
+ borrow: &BorrowData<'tcx>,
+ ) -> DiagnosticBuilder<'cx> {
+ let borrow_spans = self.retrieve_borrow_spans(borrow);
+ let borrow_span = borrow_spans.args_or_use();
+
+ // Conflicting borrows are reported separately, so only check for move
+ // captures.
+ let use_spans = self.move_spans(place.as_ref(), location);
+ let span = use_spans.var_or_use();
+
+ // If the attempted use is in a closure then we do not care about the path span of the place we are currently trying to use
+ // we call `var_span_label` on `borrow_spans` to annotate if the existing borrow was in a closure
+ let mut err = self.cannot_use_when_mutably_borrowed(
+ span,
+ &self.describe_any_place(place.as_ref()),
+ borrow_span,
+ &self.describe_any_place(borrow.borrowed_place.as_ref()),
+ );
+
+ borrow_spans.var_span_label(
+ &mut err,
+ {
+ let place = &borrow.borrowed_place;
+ let desc_place = self.describe_any_place(place.as_ref());
+ format!("borrow occurs due to use of {}{}", desc_place, borrow_spans.describe())
+ },
+ "mutable",
+ );
+
+ self.explain_why_borrow_contains_point(location, borrow, None)
+ .add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ "",
+ None,
+ None,
+ );
+ err
+ }
+
+ pub(crate) fn report_conflicting_borrow(
+ &mut self,
+ location: Location,
+ (place, span): (Place<'tcx>, Span),
+ gen_borrow_kind: BorrowKind,
+ issued_borrow: &BorrowData<'tcx>,
+ ) -> DiagnosticBuilder<'cx> {
+ let issued_spans = self.retrieve_borrow_spans(issued_borrow);
+ let issued_span = issued_spans.args_or_use();
+
+ let borrow_spans = self.borrow_spans(span, location);
+ let span = borrow_spans.args_or_use();
+
+ let container_name = if issued_spans.for_generator() || borrow_spans.for_generator() {
+ "generator"
+ } else {
+ "closure"
+ };
+
+ let (desc_place, msg_place, msg_borrow, union_type_name) =
+ self.describe_place_for_conflicting_borrow(place, issued_borrow.borrowed_place);
+
+ let explanation = self.explain_why_borrow_contains_point(location, issued_borrow, None);
+ let second_borrow_desc = if explanation.is_explained() { "second " } else { "" };
+
+ // FIXME: supply non-"" `opt_via` when appropriate
+ let first_borrow_desc;
+ let mut err = match (gen_borrow_kind, issued_borrow.kind) {
+ (BorrowKind::Shared, BorrowKind::Mut { .. }) => {
+ first_borrow_desc = "mutable ";
+ self.cannot_reborrow_already_borrowed(
+ span,
+ &desc_place,
+ &msg_place,
+ "immutable",
+ issued_span,
+ "it",
+ "mutable",
+ &msg_borrow,
+ None,
+ )
+ }
+ (BorrowKind::Mut { .. }, BorrowKind::Shared) => {
+ first_borrow_desc = "immutable ";
+ self.cannot_reborrow_already_borrowed(
+ span,
+ &desc_place,
+ &msg_place,
+ "mutable",
+ issued_span,
+ "it",
+ "immutable",
+ &msg_borrow,
+ None,
+ )
+ }
+
+ (BorrowKind::Mut { .. }, BorrowKind::Mut { .. }) => {
+ first_borrow_desc = "first ";
+ let mut err = self.cannot_mutably_borrow_multiply(
+ span,
+ &desc_place,
+ &msg_place,
+ issued_span,
+ &msg_borrow,
+ None,
+ );
+ self.suggest_split_at_mut_if_applicable(
+ &mut err,
+ place,
+ issued_borrow.borrowed_place,
+ );
+ err
+ }
+
+ (BorrowKind::Unique, BorrowKind::Unique) => {
+ first_borrow_desc = "first ";
+ self.cannot_uniquely_borrow_by_two_closures(span, &desc_place, issued_span, None)
+ }
+
+ (BorrowKind::Mut { .. } | BorrowKind::Unique, BorrowKind::Shallow) => {
+ if let Some(immutable_section_description) =
+ self.classify_immutable_section(issued_borrow.assigned_place)
+ {
+ let mut err = self.cannot_mutate_in_immutable_section(
+ span,
+ issued_span,
+ &desc_place,
+ immutable_section_description,
+ "mutably borrow",
+ );
+ borrow_spans.var_span_label(
+ &mut err,
+ format!(
+ "borrow occurs due to use of {}{}",
+ desc_place,
+ borrow_spans.describe(),
+ ),
+ "immutable",
+ );
+
+ return err;
+ } else {
+ first_borrow_desc = "immutable ";
+ self.cannot_reborrow_already_borrowed(
+ span,
+ &desc_place,
+ &msg_place,
+ "mutable",
+ issued_span,
+ "it",
+ "immutable",
+ &msg_borrow,
+ None,
+ )
+ }
+ }
+
+ (BorrowKind::Unique, _) => {
+ first_borrow_desc = "first ";
+ self.cannot_uniquely_borrow_by_one_closure(
+ span,
+ container_name,
+ &desc_place,
+ "",
+ issued_span,
+ "it",
+ "",
+ None,
+ )
+ }
+
+ (BorrowKind::Shared, BorrowKind::Unique) => {
+ first_borrow_desc = "first ";
+ self.cannot_reborrow_already_uniquely_borrowed(
+ span,
+ container_name,
+ &desc_place,
+ "",
+ "immutable",
+ issued_span,
+ "",
+ None,
+ second_borrow_desc,
+ )
+ }
+
+ (BorrowKind::Mut { .. }, BorrowKind::Unique) => {
+ first_borrow_desc = "first ";
+ self.cannot_reborrow_already_uniquely_borrowed(
+ span,
+ container_name,
+ &desc_place,
+ "",
+ "mutable",
+ issued_span,
+ "",
+ None,
+ second_borrow_desc,
+ )
+ }
+
+ (BorrowKind::Shared, BorrowKind::Shared | BorrowKind::Shallow)
+ | (
+ BorrowKind::Shallow,
+ BorrowKind::Mut { .. }
+ | BorrowKind::Unique
+ | BorrowKind::Shared
+ | BorrowKind::Shallow,
+ ) => unreachable!(),
+ };
+
+ if issued_spans == borrow_spans {
+ borrow_spans.var_span_label(
+ &mut err,
+ format!("borrows occur due to use of {}{}", desc_place, borrow_spans.describe(),),
+ gen_borrow_kind.describe_mutability(),
+ );
+ } else {
+ let borrow_place = &issued_borrow.borrowed_place;
+ let borrow_place_desc = self.describe_any_place(borrow_place.as_ref());
+ issued_spans.var_span_label(
+ &mut err,
+ format!(
+ "first borrow occurs due to use of {}{}",
+ borrow_place_desc,
+ issued_spans.describe(),
+ ),
+ issued_borrow.kind.describe_mutability(),
+ );
+
+ borrow_spans.var_span_label(
+ &mut err,
+ format!(
+ "second borrow occurs due to use of {}{}",
+ desc_place,
+ borrow_spans.describe(),
+ ),
+ gen_borrow_kind.describe_mutability(),
+ );
+ }
+
+ if union_type_name != "" {
+ err.note(&format!(
+ "{} is a field of the union `{}`, so it overlaps the field {}",
+ msg_place, union_type_name, msg_borrow,
+ ));
+ }
+
+ explanation.add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ first_borrow_desc,
+ None,
+ Some((issued_span, span)),
+ );
+
+ err
+ }
+
+ fn suggest_split_at_mut_if_applicable(
+ &self,
+ err: &mut DiagnosticBuilder<'_>,
+ place: Place<'tcx>,
+ borrowed_place: Place<'tcx>,
+ ) {
+ if let ([ProjectionElem::Index(_)], [ProjectionElem::Index(_)]) =
+ (&place.projection[..], &borrowed_place.projection[..])
+ {
+ err.help(
+ "consider using `.split_at_mut(position)` or similar method to obtain \
+ two mutable non-overlapping sub-slices",
+ );
+ }
+ }
+
+ /// Returns the description of the root place for a conflicting borrow and the full
+ /// descriptions of the places that caused the conflict.
+ ///
+ /// In the simplest case, where there are no unions involved, if a mutable borrow of `x` is
+ /// attempted while a shared borrow is live, then this function will return:
+ ///
+ /// ("x", "", "")
+ ///
+ /// In the simple union case, if a mutable borrow of a union field `x.z` is attempted while
+ /// a shared borrow of another field `x.y`, then this function will return:
+ ///
+ /// ("x", "x.z", "x.y")
+ ///
+ /// In the more complex union case, where the union is a field of a struct, then if a mutable
+ /// borrow of a union field in a struct `x.u.z` is attempted while a shared borrow of
+ /// another field `x.u.y`, then this function will return:
+ ///
+ /// ("x.u", "x.u.z", "x.u.y")
+ ///
+ /// This is used when creating error messages like below:
+ ///
+ /// ```text
+ /// cannot borrow `a.u` (via `a.u.z.c`) as immutable because it is also borrowed as
+ /// mutable (via `a.u.s.b`) [E0502]
+ /// ```
+ pub(crate) fn describe_place_for_conflicting_borrow(
+ &self,
+ first_borrowed_place: Place<'tcx>,
+ second_borrowed_place: Place<'tcx>,
+ ) -> (String, String, String, String) {
+ // Define a small closure that we can use to check if the type of a place
+ // is a union.
+ let union_ty = |place_base| {
+ // Need to use fn call syntax `PlaceRef::ty` to determine the type of `place_base`;
+ // using a type annotation in the closure argument instead leads to a lifetime error.
+ let ty = PlaceRef::ty(&place_base, self.body, self.infcx.tcx).ty;
+ ty.ty_adt_def().filter(|adt| adt.is_union()).map(|_| ty)
+ };
+
+ // Start with an empty tuple, so we can use the functions on `Option` to reduce some
+ // code duplication (particularly around returning an empty description in the failure
+ // case).
+ Some(())
+ .filter(|_| {
+ // If we have a conflicting borrow of the same place, then we don't want to add
+ // an extraneous "via x.y" to our diagnostics, so filter out this case.
+ first_borrowed_place != second_borrowed_place
+ })
+ .and_then(|_| {
+ // We're going to want to traverse the first borrowed place to see if we can find
+ // field access to a union. If we find that, then we will keep the place of the
+ // union being accessed and the field that was being accessed so we can check the
+ // second borrowed place for the same union and an access to a different field.
+ for (place_base, elem) in first_borrowed_place.iter_projections().rev() {
+ match elem {
+ ProjectionElem::Field(field, _) if union_ty(place_base).is_some() => {
+ return Some((place_base, field));
+ }
+ _ => {}
+ }
+ }
+ None
+ })
+ .and_then(|(target_base, target_field)| {
+ // With the place of a union and a field access into it, we traverse the second
+ // borrowed place and look for an access to a different field of the same union.
+ for (place_base, elem) in second_borrowed_place.iter_projections().rev() {
+ if let ProjectionElem::Field(field, _) = elem {
+ if let Some(union_ty) = union_ty(place_base) {
+ if field != target_field && place_base == target_base {
+ return Some((
+ self.describe_any_place(place_base),
+ self.describe_any_place(first_borrowed_place.as_ref()),
+ self.describe_any_place(second_borrowed_place.as_ref()),
+ union_ty.to_string(),
+ ));
+ }
+ }
+ }
+ }
+ None
+ })
+ .unwrap_or_else(|| {
+ // If we didn't find a field access into a union, or both places match, then
+ // only return the description of the first place.
+ (
+ self.describe_any_place(first_borrowed_place.as_ref()),
+ "".to_string(),
+ "".to_string(),
+ "".to_string(),
+ )
+ })
+ }
+
+ /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
+ ///
+ /// This means that some data referenced by `borrow` needs to live
+ /// past the point where the StorageDeadOrDrop of `place` occurs.
+ /// This is usually interpreted as meaning that `place` has too
+ /// short a lifetime. (But sometimes it is more useful to report
+ /// it as a more direct conflict between the execution of a
+ /// `Drop::drop` with an aliasing borrow.)
+ pub(crate) fn report_borrowed_value_does_not_live_long_enough(
+ &mut self,
+ location: Location,
+ borrow: &BorrowData<'tcx>,
+ place_span: (Place<'tcx>, Span),
+ kind: Option<WriteKind>,
+ ) {
+ debug!(
+ "report_borrowed_value_does_not_live_long_enough(\
+ {:?}, {:?}, {:?}, {:?}\
+ )",
+ location, borrow, place_span, kind
+ );
+
+ let drop_span = place_span.1;
+ let root_place =
+ self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
+
+ let borrow_spans = self.retrieve_borrow_spans(borrow);
+ let borrow_span = borrow_spans.var_or_use_path_span();
+
+ assert!(root_place.projection.is_empty());
+ let proper_span = self.body.local_decls[root_place.local].source_info.span;
+
+ let root_place_projection = self.infcx.tcx.intern_place_elems(root_place.projection);
+
+ if self.access_place_error_reported.contains(&(
+ Place { local: root_place.local, projection: root_place_projection },
+ borrow_span,
+ )) {
+ debug!(
+ "suppressing access_place error when borrow doesn't live long enough for {:?}",
+ borrow_span
+ );
+ return;
+ }
+
+ self.access_place_error_reported.insert((
+ Place { local: root_place.local, projection: root_place_projection },
+ borrow_span,
+ ));
+
+ let borrowed_local = borrow.borrowed_place.local;
+ if self.body.local_decls[borrowed_local].is_ref_to_thread_local() {
+ let err =
+ self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span);
+ err.buffer(&mut self.errors_buffer);
+ return;
+ }
+
+ if let StorageDeadOrDrop::Destructor(dropped_ty) =
+ self.classify_drop_access_kind(borrow.borrowed_place.as_ref())
+ {
+ // If a borrow of path `B` conflicts with drop of `D` (and
+ // we're not in the uninteresting case where `B` is a
+ // prefix of `D`), then report this as a more interesting
+ // destructor conflict.
+ if !borrow.borrowed_place.as_ref().is_prefix_of(place_span.0.as_ref()) {
+ self.report_borrow_conflicts_with_destructor(
+ location, borrow, place_span, kind, dropped_ty,
+ );
+ return;
+ }
+ }
+
+ let place_desc = self.describe_place(borrow.borrowed_place.as_ref());
+
+ let kind_place = kind.filter(|_| place_desc.is_some()).map(|k| (k, place_span.0));
+ let explanation = self.explain_why_borrow_contains_point(location, &borrow, kind_place);
+
+ debug!(
+ "report_borrowed_value_does_not_live_long_enough(place_desc: {:?}, explanation: {:?})",
+ place_desc, explanation
+ );
+ let err = match (place_desc, explanation) {
+ // If the outlives constraint comes from inside the closure,
+ // for example:
+ //
+ // let x = 0;
+ // let y = &x;
+ // Box::new(|| y) as Box<Fn() -> &'static i32>
+ //
+ // then just use the normal error. The closure isn't escaping
+ // and `move` will not help here.
+ (
+ Some(ref name),
+ BorrowExplanation::MustBeValidFor {
+ category:
+ category
+ @
+ (ConstraintCategory::Return(_)
+ | ConstraintCategory::CallArgument
+ | ConstraintCategory::OpaqueType),
+ from_closure: false,
+ ref region_name,
+ span,
+ ..
+ },
+ ) if borrow_spans.for_generator() | borrow_spans.for_closure() => self
+ .report_escaping_closure_capture(
+ borrow_spans,
+ borrow_span,
+ region_name,
+ category,
+ span,
+ &format!("`{}`", name),
+ ),
+ (
+ ref name,
+ BorrowExplanation::MustBeValidFor {
+ category: ConstraintCategory::Assignment,
+ from_closure: false,
+ region_name:
+ RegionName {
+ source:
+ RegionNameSource::AnonRegionFromUpvar(upvar_span, ref upvar_name),
+ ..
+ },
+ span,
+ ..
+ },
+ ) => self.report_escaping_data(borrow_span, name, upvar_span, upvar_name, span),
+ (Some(name), explanation) => self.report_local_value_does_not_live_long_enough(
+ location,
+ &name,
+ &borrow,
+ drop_span,
+ borrow_spans,
+ explanation,
+ ),
+ (None, explanation) => self.report_temporary_value_does_not_live_long_enough(
+ location,
+ &borrow,
+ drop_span,
+ borrow_spans,
+ proper_span,
+ explanation,
+ ),
+ };
+
+ err.buffer(&mut self.errors_buffer);
+ }
+
+ fn report_local_value_does_not_live_long_enough(
+ &mut self,
+ location: Location,
+ name: &str,
+ borrow: &BorrowData<'tcx>,
+ drop_span: Span,
+ borrow_spans: UseSpans<'tcx>,
+ explanation: BorrowExplanation,
+ ) -> DiagnosticBuilder<'cx> {
+ debug!(
+ "report_local_value_does_not_live_long_enough(\
+ {:?}, {:?}, {:?}, {:?}, {:?}\
+ )",
+ location, name, borrow, drop_span, borrow_spans
+ );
+
+ let borrow_span = borrow_spans.var_or_use_path_span();
+ if let BorrowExplanation::MustBeValidFor {
+ category,
+ span,
+ ref opt_place_desc,
+ from_closure: false,
+ ..
+ } = explanation
+ {
+ if let Some(diag) = self.try_report_cannot_return_reference_to_local(
+ borrow,
+ borrow_span,
+ span,
+ category,
+ opt_place_desc.as_ref(),
+ ) {
+ return diag;
+ }
+ }
+
+ let mut err = self.path_does_not_live_long_enough(borrow_span, &format!("`{}`", name));
+
+ if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
+ let region_name = annotation.emit(self, &mut err);
+
+ err.span_label(
+ borrow_span,
+ format!("`{}` would have to be valid for `{}`...", name, region_name),
+ );
+
+ let fn_hir_id = self.mir_hir_id();
+ err.span_label(
+ drop_span,
+ format!(
+ "...but `{}` will be dropped here, when the {} returns",
+ name,
+ self.infcx
+ .tcx
+ .hir()
+ .opt_name(fn_hir_id)
+ .map(|name| format!("function `{}`", name))
+ .unwrap_or_else(|| {
+ match &self
+ .infcx
+ .tcx
+ .typeck(self.mir_def_id())
+ .node_type(fn_hir_id)
+ .kind()
+ {
+ ty::Closure(..) => "enclosing closure",
+ ty::Generator(..) => "enclosing generator",
+ kind => bug!("expected closure or generator, found {:?}", kind),
+ }
+ .to_string()
+ })
+ ),
+ );
+
+ err.note(
+ "functions cannot return a borrow to data owned within the function's scope, \
+ functions can only return borrows to data passed as arguments",
+ );
+ err.note(
+ "to learn more, visit <https://doc.rust-lang.org/book/ch04-02-\
+ references-and-borrowing.html#dangling-references>",
+ );
+
+ if let BorrowExplanation::MustBeValidFor { .. } = explanation {
+ } else {
+ explanation.add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ "",
+ None,
+ None,
+ );
+ }
+ } else {
+ err.span_label(borrow_span, "borrowed value does not live long enough");
+ err.span_label(drop_span, format!("`{}` dropped here while still borrowed", name));
+
+ let within = if borrow_spans.for_generator() { " by generator" } else { "" };
+
+ borrow_spans.args_span_label(&mut err, format!("value captured here{}", within));
+
+ explanation.add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ "",
+ None,
+ None,
+ );
+ }
+
+ err
+ }
+
+ fn report_borrow_conflicts_with_destructor(
+ &mut self,
+ location: Location,
+ borrow: &BorrowData<'tcx>,
+ (place, drop_span): (Place<'tcx>, Span),
+ kind: Option<WriteKind>,
+ dropped_ty: Ty<'tcx>,
+ ) {
+ debug!(
+ "report_borrow_conflicts_with_destructor(\
+ {:?}, {:?}, ({:?}, {:?}), {:?}\
+ )",
+ location, borrow, place, drop_span, kind,
+ );
+
+ let borrow_spans = self.retrieve_borrow_spans(borrow);
+ let borrow_span = borrow_spans.var_or_use();
+
+ let mut err = self.cannot_borrow_across_destructor(borrow_span);
+
+ let what_was_dropped = match self.describe_place(place.as_ref()) {
+ Some(name) => format!("`{}`", name),
+ None => String::from("temporary value"),
+ };
+
+ let label = match self.describe_place(borrow.borrowed_place.as_ref()) {
+ Some(borrowed) => format!(
+ "here, drop of {D} needs exclusive access to `{B}`, \
+ because the type `{T}` implements the `Drop` trait",
+ D = what_was_dropped,
+ T = dropped_ty,
+ B = borrowed
+ ),
+ None => format!(
+ "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
+ D = what_was_dropped,
+ T = dropped_ty
+ ),
+ };
+ err.span_label(drop_span, label);
+
+ // Only give this note and suggestion if they could be relevant.
+ let explanation =
+ self.explain_why_borrow_contains_point(location, borrow, kind.map(|k| (k, place)));
+ match explanation {
+ BorrowExplanation::UsedLater { .. }
+ | BorrowExplanation::UsedLaterWhenDropped { .. } => {
+ err.note("consider using a `let` binding to create a longer lived value");
+ }
+ _ => {}
+ }
+
+ explanation.add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ "",
+ None,
+ None,
+ );
+
+ err.buffer(&mut self.errors_buffer);
+ }
+
+ fn report_thread_local_value_does_not_live_long_enough(
+ &mut self,
+ drop_span: Span,
+ borrow_span: Span,
+ ) -> DiagnosticBuilder<'cx> {
+ debug!(
+ "report_thread_local_value_does_not_live_long_enough(\
+ {:?}, {:?}\
+ )",
+ drop_span, borrow_span
+ );
+
+ let mut err = self.thread_local_value_does_not_live_long_enough(borrow_span);
+
+ err.span_label(
+ borrow_span,
+ "thread-local variables cannot be borrowed beyond the end of the function",
+ );
+ err.span_label(drop_span, "end of enclosing function is here");
+
+ err
+ }
+
+ fn report_temporary_value_does_not_live_long_enough(
+ &mut self,
+ location: Location,
+ borrow: &BorrowData<'tcx>,
+ drop_span: Span,
+ borrow_spans: UseSpans<'tcx>,
+ proper_span: Span,
+ explanation: BorrowExplanation,
+ ) -> DiagnosticBuilder<'cx> {
+ debug!(
+ "report_temporary_value_does_not_live_long_enough(\
+ {:?}, {:?}, {:?}, {:?}\
+ )",
+ location, borrow, drop_span, proper_span
+ );
+
+ if let BorrowExplanation::MustBeValidFor { category, span, from_closure: false, .. } =
+ explanation
+ {
+ if let Some(diag) = self.try_report_cannot_return_reference_to_local(
+ borrow,
+ proper_span,
+ span,
+ category,
+ None,
+ ) {
+ return diag;
+ }
+ }
+
+ let mut err = self.temporary_value_borrowed_for_too_long(proper_span);
+ err.span_label(proper_span, "creates a temporary which is freed while still in use");
+ err.span_label(drop_span, "temporary value is freed at the end of this statement");
+
+ match explanation {
+ BorrowExplanation::UsedLater(..)
+ | BorrowExplanation::UsedLaterInLoop(..)
+ | BorrowExplanation::UsedLaterWhenDropped { .. } => {
+ // Only give this note and suggestion if it could be relevant.
+ err.note("consider using a `let` binding to create a longer lived value");
+ }
+ _ => {}
+ }
+ explanation.add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ "",
+ None,
+ None,
+ );
+
+ let within = if borrow_spans.for_generator() { " by generator" } else { "" };
+
+ borrow_spans.args_span_label(&mut err, format!("value captured here{}", within));
+
+ err
+ }
+
+ fn try_report_cannot_return_reference_to_local(
+ &self,
+ borrow: &BorrowData<'tcx>,
+ borrow_span: Span,
+ return_span: Span,
+ category: ConstraintCategory,
+ opt_place_desc: Option<&String>,
+ ) -> Option<DiagnosticBuilder<'cx>> {
+ let return_kind = match category {
+ ConstraintCategory::Return(_) => "return",
+ ConstraintCategory::Yield => "yield",
+ _ => return None,
+ };
+
+ // FIXME use a better heuristic than Spans
+ let reference_desc = if return_span == self.body.source_info(borrow.reserve_location).span {
+ "reference to"
+ } else {
+ "value referencing"
+ };
+
+ let (place_desc, note) = if let Some(place_desc) = opt_place_desc {
+ let local_kind = if let Some(local) = borrow.borrowed_place.as_local() {
+ match self.body.local_kind(local) {
+ LocalKind::ReturnPointer | LocalKind::Temp => {
+ bug!("temporary or return pointer with a name")
+ }
+ LocalKind::Var => "local variable ",
+ LocalKind::Arg
+ if !self.upvars.is_empty() && local == ty::CAPTURE_STRUCT_LOCAL =>
+ {
+ "variable captured by `move` "
+ }
+ LocalKind::Arg => "function parameter ",
+ }
+ } else {
+ "local data "
+ };
+ (
+ format!("{}`{}`", local_kind, place_desc),
+ format!("`{}` is borrowed here", place_desc),
+ )
+ } else {
+ let root_place =
+ self.prefixes(borrow.borrowed_place.as_ref(), PrefixSet::All).last().unwrap();
+ let local = root_place.local;
+ match self.body.local_kind(local) {
+ LocalKind::ReturnPointer | LocalKind::Temp => {
+ ("temporary value".to_string(), "temporary value created here".to_string())
+ }
+ LocalKind::Arg => (
+ "function parameter".to_string(),
+ "function parameter borrowed here".to_string(),
+ ),
+ LocalKind::Var => {
+ ("local binding".to_string(), "local binding introduced here".to_string())
+ }
+ }
+ };
+
+ let mut err = self.cannot_return_reference_to_local(
+ return_span,
+ return_kind,
+ reference_desc,
+ &place_desc,
+ );
+
+ if return_span != borrow_span {
+ err.span_label(borrow_span, note);
+
+ let tcx = self.infcx.tcx;
+ let ty_params = ty::List::empty();
+
+ let return_ty = self.regioncx.universal_regions().unnormalized_output_ty;
+ let return_ty = tcx.erase_regions(return_ty);
+
+ // to avoid panics
+ if let Some(iter_trait) = tcx.get_diagnostic_item(sym::Iterator) {
+ if self
+ .infcx
+ .type_implements_trait(iter_trait, return_ty, ty_params, self.param_env)
+ .must_apply_modulo_regions()
+ {
+ if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(return_span) {
+ err.span_suggestion_hidden(
+ return_span,
+ "use `.collect()` to allocate the iterator",
+ format!("{}{}", snippet, ".collect::<Vec<_>>()"),
+ Applicability::MaybeIncorrect,
+ );
+ }
+ }
+ }
+ }
+
+ Some(err)
+ }
+
+ fn report_escaping_closure_capture(
+ &mut self,
+ use_span: UseSpans<'tcx>,
+ var_span: Span,
+ fr_name: &RegionName,
+ category: ConstraintCategory,
+ constraint_span: Span,
+ captured_var: &str,
+ ) -> DiagnosticBuilder<'cx> {
+ let tcx = self.infcx.tcx;
+ let args_span = use_span.args_or_use();
+
+ let (sugg_span, suggestion) = match tcx.sess.source_map().span_to_snippet(args_span) {
+ Ok(string) => {
+ if string.starts_with("async ") {
+ let pos = args_span.lo() + BytePos(6);
+ (args_span.with_lo(pos).with_hi(pos), "move ".to_string())
+ } else if string.starts_with("async|") {
+ let pos = args_span.lo() + BytePos(5);
+ (args_span.with_lo(pos).with_hi(pos), " move".to_string())
+ } else {
+ (args_span.shrink_to_lo(), "move ".to_string())
+ }
+ }
+ Err(_) => (args_span, "move |<args>| <body>".to_string()),
+ };
+ let kind = match use_span.generator_kind() {
+ Some(generator_kind) => match generator_kind {
+ GeneratorKind::Async(async_kind) => match async_kind {
+ AsyncGeneratorKind::Block => "async block",
+ AsyncGeneratorKind::Closure => "async closure",
+ _ => bug!("async block/closure expected, but async function found."),
+ },
+ GeneratorKind::Gen => "generator",
+ },
+ None => "closure",
+ };
+
+ let mut err =
+ self.cannot_capture_in_long_lived_closure(args_span, kind, captured_var, var_span);
+ err.span_suggestion_verbose(
+ sugg_span,
+ &format!(
+ "to force the {} to take ownership of {} (and any \
+ other referenced variables), use the `move` keyword",
+ kind, captured_var
+ ),
+ suggestion,
+ Applicability::MachineApplicable,
+ );
+
+ match category {
+ ConstraintCategory::Return(_) | ConstraintCategory::OpaqueType => {
+ let msg = format!("{} is returned here", kind);
+ err.span_note(constraint_span, &msg);
+ }
+ ConstraintCategory::CallArgument => {
+ fr_name.highlight_region_name(&mut err);
+ if matches!(use_span.generator_kind(), Some(GeneratorKind::Async(_))) {
+ err.note(
+ "async blocks are not executed immediately and must either take a \
+ reference or ownership of outside variables they use",
+ );
+ } else {
+ let msg = format!("function requires argument type to outlive `{}`", fr_name);
+ err.span_note(constraint_span, &msg);
+ }
+ }
+ _ => bug!(
+ "report_escaping_closure_capture called with unexpected constraint \
+ category: `{:?}`",
+ category
+ ),
+ }
+
+ err
+ }
+
+ fn report_escaping_data(
+ &mut self,
+ borrow_span: Span,
+ name: &Option<String>,
+ upvar_span: Span,
+ upvar_name: &str,
+ escape_span: Span,
+ ) -> DiagnosticBuilder<'cx> {
+ let tcx = self.infcx.tcx;
+
+ let (_, escapes_from) = tcx.article_and_description(self.mir_def_id().to_def_id());
+
+ let mut err =
+ borrowck_errors::borrowed_data_escapes_closure(tcx, escape_span, escapes_from);
+
+ err.span_label(
+ upvar_span,
+ format!("`{}` declared here, outside of the {} body", upvar_name, escapes_from),
+ );
+
+ err.span_label(borrow_span, format!("borrow is only valid in the {} body", escapes_from));
+
+ if let Some(name) = name {
+ err.span_label(
+ escape_span,
+ format!("reference to `{}` escapes the {} body here", name, escapes_from),
+ );
+ } else {
+ err.span_label(
+ escape_span,
+ format!("reference escapes the {} body here", escapes_from),
+ );
+ }
+
+ err
+ }
+
+ fn get_moved_indexes(
+ &mut self,
+ location: Location,
+ mpi: MovePathIndex,
+ ) -> (Vec<MoveSite>, Vec<Location>) {
+ fn predecessor_locations(
+ body: &'a mir::Body<'tcx>,
+ location: Location,
+ ) -> impl Iterator<Item = Location> + 'a {
+ if location.statement_index == 0 {
+ let predecessors = body.predecessors()[location.block].to_vec();
+ Either::Left(predecessors.into_iter().map(move |bb| body.terminator_loc(bb)))
+ } else {
+ Either::Right(std::iter::once(Location {
+ statement_index: location.statement_index - 1,
+ ..location
+ }))
+ }
+ }
+
+ let mut mpis = vec![mpi];
+ let move_paths = &self.move_data.move_paths;
+ mpis.extend(move_paths[mpi].parents(move_paths).map(|(mpi, _)| mpi));
+
+ let mut stack = Vec::new();
+ let mut back_edge_stack = Vec::new();
+
+ predecessor_locations(self.body, location).for_each(|predecessor| {
+ if location.dominates(predecessor, &self.dominators) {
+ back_edge_stack.push(predecessor)
+ } else {
+ stack.push(predecessor);
+ }
+ });
+
+ let mut reached_start = false;
+
+ /* Check if the mpi is initialized as an argument */
+ let mut is_argument = false;
+ for arg in self.body.args_iter() {
+ let path = self.move_data.rev_lookup.find_local(arg);
+ if mpis.contains(&path) {
+ is_argument = true;
+ }
+ }
+
+ let mut visited = FxHashSet::default();
+ let mut move_locations = FxHashSet::default();
+ let mut reinits = vec![];
+ let mut result = vec![];
+
+ let mut dfs_iter = |result: &mut Vec<MoveSite>, location: Location, is_back_edge: bool| {
+ debug!(
+ "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
+ location, is_back_edge
+ );
+
+ if !visited.insert(location) {
+ return true;
+ }
+
+ // check for moves
+ let stmt_kind =
+ self.body[location.block].statements.get(location.statement_index).map(|s| &s.kind);
+ if let Some(StatementKind::StorageDead(..)) = stmt_kind {
+ // this analysis only tries to find moves explicitly
+ // written by the user, so we ignore the move-outs
+ // created by `StorageDead` and at the beginning
+ // of a function.
+ } else {
+ // If we are found a use of a.b.c which was in error, then we want to look for
+ // moves not only of a.b.c but also a.b and a.
+ //
+ // Note that the moves data already includes "parent" paths, so we don't have to
+ // worry about the other case: that is, if there is a move of a.b.c, it is already
+ // marked as a move of a.b and a as well, so we will generate the correct errors
+ // there.
+ for moi in &self.move_data.loc_map[location] {
+ debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
+ let path = self.move_data.moves[*moi].path;
+ if mpis.contains(&path) {
+ debug!(
+ "report_use_of_moved_or_uninitialized: found {:?}",
+ move_paths[path].place
+ );
+ result.push(MoveSite { moi: *moi, traversed_back_edge: is_back_edge });
+ move_locations.insert(location);
+
+ // Strictly speaking, we could continue our DFS here. There may be
+ // other moves that can reach the point of error. But it is kind of
+ // confusing to highlight them.
+ //
+ // Example:
+ //
+ // ```
+ // let a = vec![];
+ // let b = a;
+ // let c = a;
+ // drop(a); // <-- current point of error
+ // ```
+ //
+ // Because we stop the DFS here, we only highlight `let c = a`,
+ // and not `let b = a`. We will of course also report an error at
+ // `let c = a` which highlights `let b = a` as the move.
+ return true;
+ }
+ }
+ }
+
+ // check for inits
+ let mut any_match = false;
+ for ii in &self.move_data.init_loc_map[location] {
+ let init = self.move_data.inits[*ii];
+ match init.kind {
+ InitKind::Deep | InitKind::NonPanicPathOnly => {
+ if mpis.contains(&init.path) {
+ any_match = true;
+ }
+ }
+ InitKind::Shallow => {
+ if mpi == init.path {
+ any_match = true;
+ }
+ }
+ }
+ }
+ if any_match {
+ reinits.push(location);
+ return true;
+ }
+ return false;
+ };
+
+ while let Some(location) = stack.pop() {
+ if dfs_iter(&mut result, location, false) {
+ continue;
+ }
+
+ let mut has_predecessor = false;
+ predecessor_locations(self.body, location).for_each(|predecessor| {
+ if location.dominates(predecessor, &self.dominators) {
+ back_edge_stack.push(predecessor)
+ } else {
+ stack.push(predecessor);
+ }
+ has_predecessor = true;
+ });
+
+ if !has_predecessor {
+ reached_start = true;
+ }
+ }
+ if (is_argument || !reached_start) && result.is_empty() {
+ /* Process back edges (moves in future loop iterations) only if
+ the move path is definitely initialized upon loop entry,
+ to avoid spurious "in previous iteration" errors.
+ During DFS, if there's a path from the error back to the start
+ of the function with no intervening init or move, then the
+ move path may be uninitialized at loop entry.
+ */
+ while let Some(location) = back_edge_stack.pop() {
+ if dfs_iter(&mut result, location, true) {
+ continue;
+ }
+
+ predecessor_locations(self.body, location)
+ .for_each(|predecessor| back_edge_stack.push(predecessor));
+ }
+ }
+
+ // Check if we can reach these reinits from a move location.
+ let reinits_reachable = reinits
+ .into_iter()
+ .filter(|reinit| {
+ let mut visited = FxHashSet::default();
+ let mut stack = vec![*reinit];
+ while let Some(location) = stack.pop() {
+ if !visited.insert(location) {
+ continue;
+ }
+ if move_locations.contains(&location) {
+ return true;
+ }
+ stack.extend(predecessor_locations(self.body, location));
+ }
+ false
+ })
+ .collect::<Vec<Location>>();
+ (result, reinits_reachable)
+ }
+
+ pub(crate) fn report_illegal_mutation_of_borrowed(
+ &mut self,
+ location: Location,
+ (place, span): (Place<'tcx>, Span),
+ loan: &BorrowData<'tcx>,
+ ) {
+ let loan_spans = self.retrieve_borrow_spans(loan);
+ let loan_span = loan_spans.args_or_use();
+
+ let descr_place = self.describe_any_place(place.as_ref());
+ if loan.kind == BorrowKind::Shallow {
+ if let Some(section) = self.classify_immutable_section(loan.assigned_place) {
+ let mut err = self.cannot_mutate_in_immutable_section(
+ span,
+ loan_span,
+ &descr_place,
+ section,
+ "assign",
+ );
+ loan_spans.var_span_label(
+ &mut err,
+ format!("borrow occurs due to use{}", loan_spans.describe()),
+ loan.kind.describe_mutability(),
+ );
+
+ err.buffer(&mut self.errors_buffer);
+
+ return;
+ }
+ }
+
+ let mut err = self.cannot_assign_to_borrowed(span, loan_span, &descr_place);
+
+ loan_spans.var_span_label(
+ &mut err,
+ format!("borrow occurs due to use{}", loan_spans.describe()),
+ loan.kind.describe_mutability(),
+ );
+
+ self.explain_why_borrow_contains_point(location, loan, None).add_explanation_to_diagnostic(
+ self.infcx.tcx,
+ &self.body,
+ &self.local_names,
+ &mut err,
+ "",
+ None,
+ None,
+ );
+
+ self.explain_deref_coercion(loan, &mut err);
+
+ err.buffer(&mut self.errors_buffer);
+ }
+
+ fn explain_deref_coercion(&mut self, loan: &BorrowData<'tcx>, err: &mut DiagnosticBuilder<'_>) {
+ let tcx = self.infcx.tcx;
+ if let (
+ Some(Terminator { kind: TerminatorKind::Call { from_hir_call: false, .. }, .. }),
+ Some((method_did, method_substs)),
+ ) = (
+ &self.body[loan.reserve_location.block].terminator,
+ rustc_const_eval::util::find_self_call(
+ tcx,
+ self.body,
+ loan.assigned_place.local,
+ loan.reserve_location.block,
+ ),
+ ) {
+ if tcx.is_diagnostic_item(sym::deref_method, method_did) {
+ let deref_target =
+ tcx.get_diagnostic_item(sym::deref_target).and_then(|deref_target| {
+ Instance::resolve(tcx, self.param_env, deref_target, method_substs)
+ .transpose()
+ });
+ if let Some(Ok(instance)) = deref_target {
+ let deref_target_ty = instance.ty(tcx, self.param_env);
+ err.note(&format!(
+ "borrow occurs due to deref coercion to `{}`",
+ deref_target_ty
+ ));
+ err.span_note(tcx.def_span(instance.def_id()), "deref defined here");
+ }
+ }
+ }
+ }
+
+ /// Reports an illegal reassignment; for example, an assignment to
+ /// (part of) a non-`mut` local that occurs potentially after that
+ /// local has already been initialized. `place` is the path being
+ /// assigned; `err_place` is a place providing a reason why
+ /// `place` is not mutable (e.g., the non-`mut` local `x` in an
+ /// assignment to `x.f`).
+ pub(crate) fn report_illegal_reassignment(
+ &mut self,
+ _location: Location,
+ (place, span): (Place<'tcx>, Span),
+ assigned_span: Span,
+ err_place: Place<'tcx>,
+ ) {
+ let (from_arg, local_decl, local_name) = match err_place.as_local() {
+ Some(local) => (
+ self.body.local_kind(local) == LocalKind::Arg,
+ Some(&self.body.local_decls[local]),
+ self.local_names[local],
+ ),
+ None => (false, None, None),
+ };
+
+ // If root local is initialized immediately (everything apart from let
+ // PATTERN;) then make the error refer to that local, rather than the
+ // place being assigned later.
+ let (place_description, assigned_span) = match local_decl {
+ Some(LocalDecl {
+ local_info:
+ Some(box LocalInfo::User(
+ ClearCrossCrate::Clear
+ | ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
+ opt_match_place: None,
+ ..
+ })),
+ ))
+ | Some(box LocalInfo::StaticRef { .. })
+ | None,
+ ..
+ })
+ | None => (self.describe_any_place(place.as_ref()), assigned_span),
+ Some(decl) => (self.describe_any_place(err_place.as_ref()), decl.source_info.span),
+ };
+
+ let mut err = self.cannot_reassign_immutable(span, &place_description, from_arg);
+ let msg = if from_arg {
+ "cannot assign to immutable argument"
+ } else {
+ "cannot assign twice to immutable variable"
+ };
+ if span != assigned_span {
+ if !from_arg {
+ err.span_label(assigned_span, format!("first assignment to {}", place_description));
+ }
+ }
+ if let Some(decl) = local_decl {
+ if let Some(name) = local_name {
+ if decl.can_be_made_mutable() {
+ err.span_suggestion(
+ decl.source_info.span,
+ "consider making this binding mutable",
+ format!("mut {}", name),
+ Applicability::MachineApplicable,
+ );
+ }
+ }
+ }
+ err.span_label(span, msg);
+ err.buffer(&mut self.errors_buffer);
+ }
+
+ fn classify_drop_access_kind(&self, place: PlaceRef<'tcx>) -> StorageDeadOrDrop<'tcx> {
+ let tcx = self.infcx.tcx;
+ match place.last_projection() {
+ None => StorageDeadOrDrop::LocalStorageDead,
+ Some((place_base, elem)) => {
+ // FIXME(spastorino) make this iterate
+ let base_access = self.classify_drop_access_kind(place_base);
+ match elem {
+ ProjectionElem::Deref => match base_access {
+ StorageDeadOrDrop::LocalStorageDead
+ | StorageDeadOrDrop::BoxedStorageDead => {
+ assert!(
+ place_base.ty(self.body, tcx).ty.is_box(),
+ "Drop of value behind a reference or raw pointer"
+ );
+ StorageDeadOrDrop::BoxedStorageDead
+ }
+ StorageDeadOrDrop::Destructor(_) => base_access,
+ },
+ ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
+ let base_ty = place_base.ty(self.body, tcx).ty;
+ match base_ty.kind() {
+ ty::Adt(def, _) if def.has_dtor(tcx) => {
+ // Report the outermost adt with a destructor
+ match base_access {
+ StorageDeadOrDrop::Destructor(_) => base_access,
+ StorageDeadOrDrop::LocalStorageDead
+ | StorageDeadOrDrop::BoxedStorageDead => {
+ StorageDeadOrDrop::Destructor(base_ty)
+ }
+ }
+ }
+ _ => base_access,
+ }
+ }
+ ProjectionElem::ConstantIndex { .. }
+ | ProjectionElem::Subslice { .. }
+ | ProjectionElem::Index(_) => base_access,
+ }
+ }
+ }
+ }
+
+ /// Describe the reason for the fake borrow that was assigned to `place`.
+ fn classify_immutable_section(&self, place: Place<'tcx>) -> Option<&'static str> {
+ use rustc_middle::mir::visit::Visitor;
+ struct FakeReadCauseFinder<'tcx> {
+ place: Place<'tcx>,
+ cause: Option<FakeReadCause>,
+ }
+ impl<'tcx> Visitor<'tcx> for FakeReadCauseFinder<'tcx> {
+ fn visit_statement(&mut self, statement: &Statement<'tcx>, _: Location) {
+ match statement {
+ Statement { kind: StatementKind::FakeRead(box (cause, place)), .. }
+ if *place == self.place =>
+ {
+ self.cause = Some(*cause);
+ }
+ _ => (),
+ }
+ }
+ }
+ let mut visitor = FakeReadCauseFinder { place, cause: None };
+ visitor.visit_body(&self.body);
+ match visitor.cause {
+ Some(FakeReadCause::ForMatchGuard) => Some("match guard"),
+ Some(FakeReadCause::ForIndex) => Some("indexing expression"),
+ _ => None,
+ }
+ }
+
+ /// Annotate argument and return type of function and closure with (synthesized) lifetime for
+ /// borrow of local value that does not live long enough.
+ fn annotate_argument_and_return_for_borrow(
+ &self,
+ borrow: &BorrowData<'tcx>,
+ ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
+ // Define a fallback for when we can't match a closure.
+ let fallback = || {
+ let is_closure = self.infcx.tcx.is_closure(self.mir_def_id().to_def_id());
+ if is_closure {
+ None
+ } else {
+ let ty = self.infcx.tcx.type_of(self.mir_def_id());
+ match ty.kind() {
+ ty::FnDef(_, _) | ty::FnPtr(_) => self.annotate_fn_sig(
+ self.mir_def_id().to_def_id(),
+ self.infcx.tcx.fn_sig(self.mir_def_id()),
+ ),
+ _ => None,
+ }
+ }
+ };
+
+ // In order to determine whether we need to annotate, we need to check whether the reserve
+ // place was an assignment into a temporary.
+ //
+ // If it was, we check whether or not that temporary is eventually assigned into the return
+ // place. If it was, we can add annotations about the function's return type and arguments
+ // and it'll make sense.
+ let location = borrow.reserve_location;
+ debug!("annotate_argument_and_return_for_borrow: location={:?}", location);
+ if let Some(&Statement { kind: StatementKind::Assign(box (ref reservation, _)), .. }) =
+ &self.body[location.block].statements.get(location.statement_index)
+ {
+ debug!("annotate_argument_and_return_for_borrow: reservation={:?}", reservation);
+ // Check that the initial assignment of the reserve location is into a temporary.
+ let mut target = match reservation.as_local() {
+ Some(local) if self.body.local_kind(local) == LocalKind::Temp => local,
+ _ => return None,
+ };
+
+ // Next, look through the rest of the block, checking if we are assigning the
+ // `target` (that is, the place that contains our borrow) to anything.
+ let mut annotated_closure = None;
+ for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
+ debug!(
+ "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
+ target, stmt
+ );
+ if let StatementKind::Assign(box (place, rvalue)) = &stmt.kind {
+ if let Some(assigned_to) = place.as_local() {
+ debug!(
+ "annotate_argument_and_return_for_borrow: assigned_to={:?} \
+ rvalue={:?}",
+ assigned_to, rvalue
+ );
+ // Check if our `target` was captured by a closure.
+ if let Rvalue::Aggregate(
+ box AggregateKind::Closure(def_id, substs),
+ operands,
+ ) = rvalue
+ {
+ for operand in operands {
+ let assigned_from = match operand {
+ Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
+ assigned_from
+ }
+ _ => continue,
+ };
+ debug!(
+ "annotate_argument_and_return_for_borrow: assigned_from={:?}",
+ assigned_from
+ );
+
+ // Find the local from the operand.
+ let assigned_from_local = match assigned_from.local_or_deref_local()
+ {
+ Some(local) => local,
+ None => continue,
+ };
+
+ if assigned_from_local != target {
+ continue;
+ }
+
+ // If a closure captured our `target` and then assigned
+ // into a place then we should annotate the closure in
+ // case it ends up being assigned into the return place.
+ annotated_closure =
+ self.annotate_fn_sig(*def_id, substs.as_closure().sig());
+ debug!(
+ "annotate_argument_and_return_for_borrow: \
+ annotated_closure={:?} assigned_from_local={:?} \
+ assigned_to={:?}",
+ annotated_closure, assigned_from_local, assigned_to
+ );
+
+ if assigned_to == mir::RETURN_PLACE {
+ // If it was assigned directly into the return place, then
+ // return now.
+ return annotated_closure;
+ } else {
+ // Otherwise, update the target.
+ target = assigned_to;
+ }
+ }
+
+ // If none of our closure's operands matched, then skip to the next
+ // statement.
+ continue;
+ }
+
+ // Otherwise, look at other types of assignment.
+ let assigned_from = match rvalue {
+ Rvalue::Ref(_, _, assigned_from) => assigned_from,
+ Rvalue::Use(operand) => match operand {
+ Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
+ assigned_from
+ }
+ _ => continue,
+ },
+ _ => continue,
+ };
+ debug!(
+ "annotate_argument_and_return_for_borrow: \
+ assigned_from={:?}",
+ assigned_from,
+ );
+
+ // Find the local from the rvalue.
+ let assigned_from_local = match assigned_from.local_or_deref_local() {
+ Some(local) => local,
+ None => continue,
+ };
+ debug!(
+ "annotate_argument_and_return_for_borrow: \
+ assigned_from_local={:?}",
+ assigned_from_local,
+ );
+
+ // Check if our local matches the target - if so, we've assigned our
+ // borrow to a new place.
+ if assigned_from_local != target {
+ continue;
+ }
+
+ // If we assigned our `target` into a new place, then we should
+ // check if it was the return place.
+ debug!(
+ "annotate_argument_and_return_for_borrow: \
+ assigned_from_local={:?} assigned_to={:?}",
+ assigned_from_local, assigned_to
+ );
+ if assigned_to == mir::RETURN_PLACE {
+ // If it was then return the annotated closure if there was one,
+ // else, annotate this function.
+ return annotated_closure.or_else(fallback);
+ }
+
+ // If we didn't assign into the return place, then we just update
+ // the target.
+ target = assigned_to;
+ }
+ }
+ }
+
+ // Check the terminator if we didn't find anything in the statements.
+ let terminator = &self.body[location.block].terminator();
+ debug!(
+ "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
+ target, terminator
+ );
+ if let TerminatorKind::Call { destination: Some((place, _)), args, .. } =
+ &terminator.kind
+ {
+ if let Some(assigned_to) = place.as_local() {
+ debug!(
+ "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
+ assigned_to, args
+ );
+ for operand in args {
+ let assigned_from = match operand {
+ Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
+ assigned_from
+ }
+ _ => continue,
+ };
+ debug!(
+ "annotate_argument_and_return_for_borrow: assigned_from={:?}",
+ assigned_from,
+ );
+
+ if let Some(assigned_from_local) = assigned_from.local_or_deref_local() {
+ debug!(
+ "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
+ assigned_from_local,
+ );
+
+ if assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
+ return annotated_closure.or_else(fallback);
+ }
+ }
+ }
+ }
+ }
+ }
+
+ // If we haven't found an assignment into the return place, then we need not add
+ // any annotations.
+ debug!("annotate_argument_and_return_for_borrow: none found");
+ None
+ }
+
+ /// Annotate the first argument and return type of a function signature if they are
+ /// references.
+ fn annotate_fn_sig(
+ &self,
+ did: DefId,
+ sig: ty::PolyFnSig<'tcx>,
+ ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
+ debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
+ let is_closure = self.infcx.tcx.is_closure(did);
+ let fn_hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did.as_local()?);
+ let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(fn_hir_id)?;
+
+ // We need to work out which arguments to highlight. We do this by looking
+ // at the return type, where there are three cases:
+ //
+ // 1. If there are named arguments, then we should highlight the return type and
+ // highlight any of the arguments that are also references with that lifetime.
+ // If there are no arguments that have the same lifetime as the return type,
+ // then don't highlight anything.
+ // 2. The return type is a reference with an anonymous lifetime. If this is
+ // the case, then we can take advantage of (and teach) the lifetime elision
+ // rules.
+ //
+ // We know that an error is being reported. So the arguments and return type
+ // must satisfy the elision rules. Therefore, if there is a single argument
+ // then that means the return type and first (and only) argument have the same
+ // lifetime and the borrow isn't meeting that, we can highlight the argument
+ // and return type.
+ //
+ // If there are multiple arguments then the first argument must be self (else
+ // it would not satisfy the elision rules), so we can highlight self and the
+ // return type.
+ // 3. The return type is not a reference. In this case, we don't highlight
+ // anything.
+ let return_ty = sig.output();
+ match return_ty.skip_binder().kind() {
+ ty::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
+ // This is case 1 from above, return type is a named reference so we need to
+ // search for relevant arguments.
+ let mut arguments = Vec::new();
+ for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
+ if let ty::Ref(argument_region, _, _) = argument.kind() {
+ if argument_region == return_region {
+ // Need to use the `rustc_middle::ty` types to compare against the
+ // `return_region`. Then use the `rustc_hir` type to get only
+ // the lifetime span.
+ if let hir::TyKind::Rptr(lifetime, _) = &fn_decl.inputs[index].kind {
+ // With access to the lifetime, we can get
+ // the span of it.
+ arguments.push((*argument, lifetime.span));
+ } else {
+ bug!("ty type is a ref but hir type is not");
+ }
+ }
+ }
+ }
+
+ // We need to have arguments. This shouldn't happen, but it's worth checking.
+ if arguments.is_empty() {
+ return None;
+ }
+
+ // We use a mix of the HIR and the Ty types to get information
+ // as the HIR doesn't have full types for closure arguments.
+ let return_ty = sig.output().skip_binder();
+ let mut return_span = fn_decl.output.span();
+ if let hir::FnRetTy::Return(ty) = &fn_decl.output {
+ if let hir::TyKind::Rptr(lifetime, _) = ty.kind {
+ return_span = lifetime.span;
+ }
+ }
+
+ Some(AnnotatedBorrowFnSignature::NamedFunction {
+ arguments,
+ return_ty,
+ return_span,
+ })
+ }
+ ty::Ref(_, _, _) if is_closure => {
+ // This is case 2 from above but only for closures, return type is anonymous
+ // reference so we select
+ // the first argument.
+ let argument_span = fn_decl.inputs.first()?.span;
+ let argument_ty = sig.inputs().skip_binder().first()?;
+
+ // Closure arguments are wrapped in a tuple, so we need to get the first
+ // from that.
+ if let ty::Tuple(elems) = argument_ty.kind() {
+ let argument_ty = elems.first()?.expect_ty();
+ if let ty::Ref(_, _, _) = argument_ty.kind() {
+ return Some(AnnotatedBorrowFnSignature::Closure {
+ argument_ty,
+ argument_span,
+ });
+ }
+ }
+
+ None
+ }
+ ty::Ref(_, _, _) => {
+ // This is also case 2 from above but for functions, return type is still an
+ // anonymous reference so we select the first argument.
+ let argument_span = fn_decl.inputs.first()?.span;
+ let argument_ty = sig.inputs().skip_binder().first()?;
+
+ let return_span = fn_decl.output.span();
+ let return_ty = sig.output().skip_binder();
+
+ // We expect the first argument to be a reference.
+ match argument_ty.kind() {
+ ty::Ref(_, _, _) => {}
+ _ => return None,
+ }
+
+ Some(AnnotatedBorrowFnSignature::AnonymousFunction {
+ argument_ty,
+ argument_span,
+ return_ty,
+ return_span,
+ })
+ }
+ _ => {
+ // This is case 3 from above, return type is not a reference so don't highlight
+ // anything.
+ None
+ }
+ }
+ }
+}
+
+#[derive(Debug)]
+enum AnnotatedBorrowFnSignature<'tcx> {
+ NamedFunction {
+ arguments: Vec<(Ty<'tcx>, Span)>,
+ return_ty: Ty<'tcx>,
+ return_span: Span,
+ },
+ AnonymousFunction {
+ argument_ty: Ty<'tcx>,
+ argument_span: Span,
+ return_ty: Ty<'tcx>,
+ return_span: Span,
+ },
+ Closure {
+ argument_ty: Ty<'tcx>,
+ argument_span: Span,
+ },
+}
+
+impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
+ /// Annotate the provided diagnostic with information about borrow from the fn signature that
+ /// helps explain.
+ pub(crate) fn emit(
+ &self,
+ cx: &mut MirBorrowckCtxt<'_, 'tcx>,
+ diag: &mut DiagnosticBuilder<'_>,
+ ) -> String {
+ match self {
+ AnnotatedBorrowFnSignature::Closure { argument_ty, argument_span } => {
+ diag.span_label(
+ *argument_span,
+ format!("has type `{}`", cx.get_name_for_ty(argument_ty, 0)),
+ );
+
+ cx.get_region_name_for_ty(argument_ty, 0)
+ }
+ AnnotatedBorrowFnSignature::AnonymousFunction {
+ argument_ty,
+ argument_span,
+ return_ty,
+ return_span,
+ } => {
+ let argument_ty_name = cx.get_name_for_ty(argument_ty, 0);
+ diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
+
+ let return_ty_name = cx.get_name_for_ty(return_ty, 0);
+ let types_equal = return_ty_name == argument_ty_name;
+ diag.span_label(
+ *return_span,
+ format!(
+ "{}has type `{}`",
+ if types_equal { "also " } else { "" },
+ return_ty_name,
+ ),
+ );
+
+ diag.note(
+ "argument and return type have the same lifetime due to lifetime elision rules",
+ );
+ diag.note(
+ "to learn more, visit <https://doc.rust-lang.org/book/ch10-03-\
+ lifetime-syntax.html#lifetime-elision>",
+ );
+
+ cx.get_region_name_for_ty(return_ty, 0)
+ }
+ AnnotatedBorrowFnSignature::NamedFunction { arguments, return_ty, return_span } => {
+ // Region of return type and arguments checked to be the same earlier.
+ let region_name = cx.get_region_name_for_ty(return_ty, 0);
+ for (_, argument_span) in arguments {
+ diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
+ }
+
+ diag.span_label(*return_span, format!("also has lifetime `{}`", region_name,));
+
+ diag.help(&format!(
+ "use data from the highlighted arguments which match the `{}` lifetime of \
+ the return type",
+ region_name,
+ ));
+
+ region_name
+ }
+ }
+ }
+}
projects / rustc.git / blobdiff