src/librustc_mir/borrow_check/conflict_errors.rs

   1 use rustc::hir;
   2 use rustc::hir::def_id::DefId;
   3 use rustc::mir::{
   4     self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, ConstraintCategory, Local,
   5     LocalDecl, LocalKind, Location, Operand, Place, PlaceBase, Projection,
   6     ProjectionElem, Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
   7 };
   8 use rustc::ty::{self, Ty};
   9 use rustc_data_structures::fx::FxHashSet;
  10 use rustc_data_structures::indexed_vec::Idx;
  11 use rustc_errors::{Applicability, DiagnosticBuilder};
  12 use syntax_pos::Span;
  13 use syntax::source_map::CompilerDesugaringKind;
  14
  15 use super::nll::explain_borrow::BorrowExplanation;
  16 use super::nll::region_infer::{RegionName, RegionNameSource};
  17 use super::prefixes::IsPrefixOf;
  18 use super::WriteKind;
  19 use super::borrow_set::BorrowData;
  20 use super::MirBorrowckCtxt;
  21 use super::{InitializationRequiringAction, PrefixSet};
  22 use super::error_reporting::{IncludingDowncast, UseSpans};
  23 use crate::dataflow::drop_flag_effects;
  24 use crate::dataflow::indexes::{MovePathIndex, MoveOutIndex};
  25 use crate::util::borrowck_errors::{BorrowckErrors, Origin};
  26
  27 #[derive(Debug)]
  28 struct MoveSite {
  29     /// Index of the "move out" that we found. The `MoveData` can
  30     /// then tell us where the move occurred.
  31     moi: MoveOutIndex,
  32
  33     /// `true` if we traversed a back edge while walking from the point
  34     /// of error to the move site.
  35     traversed_back_edge: bool
  36 }
  37
  38 /// Which case a StorageDeadOrDrop is for.
  39 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
  40 enum StorageDeadOrDrop<'tcx> {
  41     LocalStorageDead,
  42     BoxedStorageDead,
  43     Destructor(Ty<'tcx>),
  44 }
  45
  46 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
  47     pub(super) fn report_use_of_moved_or_uninitialized(
  48         &mut self,
  49         location: Location,
  50         desired_action: InitializationRequiringAction,
  51         (moved_place, used_place, span): (&Place<'tcx>, &Place<'tcx>, Span),
  52         mpi: MovePathIndex,
  53     ) {
  54         debug!(
  55             "report_use_of_moved_or_uninitialized: location={:?} desired_action={:?} \
  56              moved_place={:?} used_place={:?} span={:?} mpi={:?}",
  57             location, desired_action, moved_place, used_place, span, mpi
  58         );
  59
  60         let use_spans = self.move_spans(moved_place, location)
  61             .or_else(|| self.borrow_spans(span, location));
  62         let span = use_spans.args_or_use();
  63
  64         let move_site_vec = self.get_moved_indexes(location, mpi);
  65         debug!(
  66             "report_use_of_moved_or_uninitialized: move_site_vec={:?}",
  67             move_site_vec
  68         );
  69         let move_out_indices: Vec<_> = move_site_vec
  70             .iter()
  71             .map(|move_site| move_site.moi)
  72             .collect();
  73
  74         if move_out_indices.is_empty() {
  75             let root_place = self.prefixes(&used_place, PrefixSet::All).last().unwrap();
  76
  77             if self.uninitialized_error_reported.contains(root_place) {
  78                 debug!(
  79                     "report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
  80                     root_place
  81                 );
  82                 return;
  83             }
  84
  85             self.uninitialized_error_reported.insert(root_place.clone());
  86
  87             let item_msg = match self.describe_place_with_options(used_place,
  88                                                                   IncludingDowncast(true)) {
  89                 Some(name) => format!("`{}`", name),
  90                 None => "value".to_owned(),
  91             };
  92             let mut err = self.infcx.tcx.cannot_act_on_uninitialized_variable(
  93                 span,
  94                 desired_action.as_noun(),
  95                 &self.describe_place_with_options(moved_place, IncludingDowncast(true))
  96                     .unwrap_or_else(|| "_".to_owned()),
  97                 Origin::Mir,
  98             );
  99             err.span_label(span, format!("use of possibly uninitialized {}", item_msg));
 100
 101             use_spans.var_span_label(
 102                 &mut err,
 103                 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
 104             );
 105
 106             err.buffer(&mut self.errors_buffer);
 107         } else {
 108             if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
 109                 if self.prefixes(&reported_place, PrefixSet::All)
 110                     .any(|p| p == used_place)
 111                 {
 112                     debug!(
 113                         "report_use_of_moved_or_uninitialized place: error suppressed \
 114                          mois={:?}",
 115                         move_out_indices
 116                     );
 117                     return;
 118                 }
 119             }
 120
 121             let msg = ""; //FIXME: add "partially " or "collaterally "
 122
 123             let mut err = self.infcx.tcx.cannot_act_on_moved_value(
 124                 span,
 125                 desired_action.as_noun(),
 126                 msg,
 127                 self.describe_place_with_options(&moved_place, IncludingDowncast(true)),
 128                 Origin::Mir,
 129             );
 130
 131             self.add_moved_or_invoked_closure_note(
 132                 location,
 133                 used_place,
 134                 &mut err,
 135             );
 136
 137             let mut is_loop_move = false;
 138             let is_partial_move = move_site_vec.iter().any(|move_site| {
 139                 let move_out = self.move_data.moves[(*move_site).moi];
 140                 let moved_place = &self.move_data.move_paths[move_out.path].place;
 141                 used_place != moved_place && used_place.is_prefix_of(moved_place)
 142             });
 143             for move_site in &move_site_vec {
 144                 let move_out = self.move_data.moves[(*move_site).moi];
 145                 let moved_place = &self.move_data.move_paths[move_out.path].place;
 146
 147                 let move_spans = self.move_spans(moved_place, move_out.source);
 148                 let move_span = move_spans.args_or_use();
 149
 150                 let move_msg = if move_spans.for_closure() {
 151                     " into closure"
 152                 } else {
 153                     ""
 154                 };
 155
 156                 if span == move_span {
 157                     err.span_label(
 158                         span,
 159                         format!("value moved{} here, in previous iteration of loop", move_msg),
 160                     );
 161                     is_loop_move = true;
 162                 } else if move_site.traversed_back_edge {
 163                     err.span_label(
 164                         move_span,
 165                         format!(
 166                             "value moved{} here, in previous iteration of loop",
 167                             move_msg
 168                         ),
 169                     );
 170                 } else {
 171                     err.span_label(move_span, format!("value moved{} here", move_msg));
 172                     move_spans.var_span_label(
 173                         &mut err,
 174                         format!("variable moved due to use{}", move_spans.describe()),
 175                     );
 176                 }
 177                 if Some(CompilerDesugaringKind::ForLoop) == move_span.compiler_desugaring_kind() {
 178                     if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) {
 179                         err.span_suggestion(
 180                             move_span,
 181                             "consider borrowing to avoid moving into the for loop",
 182                             format!("&{}", snippet),
 183                             Applicability::MaybeIncorrect,
 184                         );
 185                     }
 186                 }
 187             }
 188
 189             use_spans.var_span_label(
 190                 &mut err,
 191                 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
 192             );
 193
 194             if !is_loop_move {
 195                 err.span_label(
 196                     span,
 197                     format!(
 198                         "value {} here {}",
 199                         desired_action.as_verb_in_past_tense(),
 200                         if is_partial_move { "after partial move" } else { "after move" },
 201                     ),
 202                 );
 203             }
 204
 205             let ty = used_place.ty(self.body, self.infcx.tcx).ty;
 206             let needs_note = match ty.sty {
 207                 ty::Closure(id, _) => {
 208                     let tables = self.infcx.tcx.typeck_tables_of(id);
 209                     let hir_id = self.infcx.tcx.hir().as_local_hir_id(id).unwrap();
 210
 211                     tables.closure_kind_origins().get(hir_id).is_none()
 212                 }
 213                 _ => true,
 214             };
 215
 216             if needs_note {
 217                 let mpi = self.move_data.moves[move_out_indices[0]].path;
 218                 let place = &self.move_data.move_paths[mpi].place;
 219
 220                 let ty = place.ty(self.body, self.infcx.tcx).ty;
 221                 let opt_name = self.describe_place_with_options(place, IncludingDowncast(true));
 222                 let note_msg = match opt_name {
 223                     Some(ref name) => format!("`{}`", name),
 224                     None => "value".to_owned(),
 225                 };
 226                 if let ty::Param(param_ty) = ty.sty {
 227                     let tcx = self.infcx.tcx;
 228                     let generics = tcx.generics_of(self.mir_def_id);
 229                     let def_id = generics.type_param(&param_ty, tcx).def_id;
 230                     if let Some(sp) = tcx.hir().span_if_local(def_id) {
 231                         err.span_label(
 232                             sp,
 233                             "consider adding a `Copy` constraint to this type argument",
 234                         );
 235                     }
 236                 }
 237                 let span = if let Place::Base(PlaceBase::Local(local)) = place {
 238                     let decl = &self.body.local_decls[*local];
 239                     Some(decl.source_info.span)
 240                 } else {
 241                     None
 242                 };
 243                 self.note_type_does_not_implement_copy(
 244                     &mut err,
 245                     &note_msg,
 246                     ty,
 247                     span,
 248                 );
 249             }
 250
 251             if let Some((_, mut old_err)) = self.move_error_reported
 252                 .insert(move_out_indices, (used_place.clone(), err))
 253             {
 254                 // Cancel the old error so it doesn't ICE.
 255                 old_err.cancel();
 256             }
 257         }
 258     }
 259
 260     pub(super) fn report_move_out_while_borrowed(
 261         &mut self,
 262         location: Location,
 263         (place, span): (&Place<'tcx>, Span),
 264         borrow: &BorrowData<'tcx>,
 265     ) {
 266         debug!(
 267             "report_move_out_while_borrowed: location={:?} place={:?} span={:?} borrow={:?}",
 268             location, place, span, borrow
 269         );
 270         let tcx = self.infcx.tcx;
 271         let value_msg = match self.describe_place(place) {
 272             Some(name) => format!("`{}`", name),
 273             None => "value".to_owned(),
 274         };
 275         let borrow_msg = match self.describe_place(&borrow.borrowed_place) {
 276             Some(name) => format!("`{}`", name),
 277             None => "value".to_owned(),
 278         };
 279
 280         let borrow_spans = self.retrieve_borrow_spans(borrow);
 281         let borrow_span = borrow_spans.args_or_use();
 282
 283         let move_spans = self.move_spans(place, location);
 284         let span = move_spans.args_or_use();
 285
 286         let mut err = tcx.cannot_move_when_borrowed(
 287             span,
 288             &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
 289             Origin::Mir,
 290         );
 291         err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
 292         err.span_label(span, format!("move out of {} occurs here", value_msg));
 293
 294         borrow_spans.var_span_label(
 295             &mut err,
 296             format!("borrow occurs due to use{}", borrow_spans.describe())
 297         );
 298
 299         move_spans.var_span_label(
 300             &mut err,
 301             format!("move occurs due to use{}", move_spans.describe())
 302         );
 303
 304         self.explain_why_borrow_contains_point(
 305             location,
 306             borrow,
 307             None,
 308         ).add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", Some(borrow_span));
 309         err.buffer(&mut self.errors_buffer);
 310     }
 311
 312     pub(super) fn report_use_while_mutably_borrowed(
 313         &mut self,
 314         location: Location,
 315         (place, _span): (&Place<'tcx>, Span),
 316         borrow: &BorrowData<'tcx>,
 317     ) -> DiagnosticBuilder<'cx> {
 318         let tcx = self.infcx.tcx;
 319
 320         let borrow_spans = self.retrieve_borrow_spans(borrow);
 321         let borrow_span = borrow_spans.args_or_use();
 322
 323         // Conflicting borrows are reported separately, so only check for move
 324         // captures.
 325         let use_spans = self.move_spans(place, location);
 326         let span = use_spans.var_or_use();
 327
 328         let mut err = tcx.cannot_use_when_mutably_borrowed(
 329             span,
 330             &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
 331             borrow_span,
 332             &self.describe_place(&borrow.borrowed_place)
 333                 .unwrap_or_else(|| "_".to_owned()),
 334             Origin::Mir,
 335         );
 336
 337         borrow_spans.var_span_label(&mut err, {
 338             let place = &borrow.borrowed_place;
 339             let desc_place = self.describe_place(place).unwrap_or_else(|| "_".to_owned());
 340
 341             format!("borrow occurs due to use of `{}`{}", desc_place, borrow_spans.describe())
 342         });
 343
 344         self.explain_why_borrow_contains_point(location, borrow, None)
 345             .add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
 346         err
 347     }
 348
 349     pub(super) fn report_conflicting_borrow(
 350         &mut self,
 351         location: Location,
 352         (place, span): (&Place<'tcx>, Span),
 353         gen_borrow_kind: BorrowKind,
 354         issued_borrow: &BorrowData<'tcx>,
 355     ) -> DiagnosticBuilder<'cx> {
 356         let issued_spans = self.retrieve_borrow_spans(issued_borrow);
 357         let issued_span = issued_spans.args_or_use();
 358
 359         let borrow_spans = self.borrow_spans(span, location);
 360         let span = borrow_spans.args_or_use();
 361
 362         let container_name = if issued_spans.for_generator() || borrow_spans.for_generator() {
 363             "generator"
 364         } else {
 365             "closure"
 366         };
 367
 368         let (desc_place, msg_place, msg_borrow, union_type_name) =
 369             self.describe_place_for_conflicting_borrow(place, &issued_borrow.borrowed_place);
 370
 371         let explanation = self.explain_why_borrow_contains_point(location, issued_borrow, None);
 372         let second_borrow_desc = if explanation.is_explained() {
 373             "second "
 374         } else {
 375             ""
 376         };
 377
 378         // FIXME: supply non-"" `opt_via` when appropriate
 379         let tcx = self.infcx.tcx;
 380         let first_borrow_desc;
 381         let mut err = match (
 382             gen_borrow_kind,
 383             "immutable",
 384             "mutable",
 385             issued_borrow.kind,
 386             "immutable",
 387             "mutable",
 388         ) {
 389             (BorrowKind::Shared, lft, _, BorrowKind::Mut { .. }, _, rgt) => {
 390                 first_borrow_desc = "mutable ";
 391                 tcx.cannot_reborrow_already_borrowed(
 392                     span,
 393                     &desc_place,
 394                     &msg_place,
 395                     lft,
 396                     issued_span,
 397                     "it",
 398                     rgt,
 399                     &msg_borrow,
 400                     None,
 401                     Origin::Mir,
 402                 )
 403             }
 404             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Shared, rgt, _) => {
 405                 first_borrow_desc = "immutable ";
 406                 tcx.cannot_reborrow_already_borrowed(
 407                     span,
 408                     &desc_place,
 409                     &msg_place,
 410                     lft,
 411                     issued_span,
 412                     "it",
 413                     rgt,
 414                     &msg_borrow,
 415                     None,
 416                     Origin::Mir,
 417                 )
 418             }
 419
 420             (BorrowKind::Mut { .. }, _, _, BorrowKind::Mut { .. }, _, _) => {
 421                 first_borrow_desc = "first ";
 422                 tcx.cannot_mutably_borrow_multiply(
 423                     span,
 424                     &desc_place,
 425                     &msg_place,
 426                     issued_span,
 427                     &msg_borrow,
 428                     None,
 429                     Origin::Mir,
 430                 )
 431             }
 432
 433             (BorrowKind::Unique, _, _, BorrowKind::Unique, _, _) => {
 434                 first_borrow_desc = "first ";
 435                 tcx.cannot_uniquely_borrow_by_two_closures(
 436                     span,
 437                     &desc_place,
 438                     issued_span,
 439                     None,
 440                     Origin::Mir,
 441                 )
 442             }
 443
 444             (BorrowKind::Mut { .. }, _, _, BorrowKind::Shallow, _, _)
 445             | (BorrowKind::Unique, _, _, BorrowKind::Shallow, _, _) => {
 446                 let mut err = tcx.cannot_mutate_in_match_guard(
 447                     span,
 448                     issued_span,
 449                     &desc_place,
 450                     "mutably borrow",
 451                     Origin::Mir,
 452                 );
 453                 borrow_spans.var_span_label(
 454                     &mut err,
 455                     format!(
 456                         "borrow occurs due to use of `{}`{}", desc_place, borrow_spans.describe()
 457                     ),
 458                 );
 459
 460                 return err;
 461             }
 462
 463             (BorrowKind::Unique, _, _, _, _, _) => {
 464                 first_borrow_desc = "first ";
 465                 tcx.cannot_uniquely_borrow_by_one_closure(
 466                     span,
 467                     container_name,
 468                     &desc_place,
 469                     "",
 470                     issued_span,
 471                     "it",
 472                     "",
 473                     None,
 474                     Origin::Mir,
 475                 )
 476             },
 477
 478             (BorrowKind::Shared, lft, _, BorrowKind::Unique, _, _) => {
 479                 first_borrow_desc = "first ";
 480                 tcx.cannot_reborrow_already_uniquely_borrowed(
 481                     span,
 482                     container_name,
 483                     &desc_place,
 484                     "",
 485                     lft,
 486                     issued_span,
 487                     "",
 488                     None,
 489                     second_borrow_desc,
 490                     Origin::Mir,
 491                 )
 492             }
 493
 494             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Unique, _, _) => {
 495                 first_borrow_desc = "first ";
 496                 tcx.cannot_reborrow_already_uniquely_borrowed(
 497                     span,
 498                     container_name,
 499                     &desc_place,
 500                     "",
 501                     lft,
 502                     issued_span,
 503                     "",
 504                     None,
 505                     second_borrow_desc,
 506                     Origin::Mir,
 507                 )
 508             }
 509
 510             (BorrowKind::Shared, _, _, BorrowKind::Shared, _, _)
 511             | (BorrowKind::Shared, _, _, BorrowKind::Shallow, _, _)
 512             | (BorrowKind::Shallow, _, _, BorrowKind::Mut { .. }, _, _)
 513             | (BorrowKind::Shallow, _, _, BorrowKind::Unique, _, _)
 514             | (BorrowKind::Shallow, _, _, BorrowKind::Shared, _, _)
 515             | (BorrowKind::Shallow, _, _, BorrowKind::Shallow, _, _) => unreachable!(),
 516         };
 517
 518         if issued_spans == borrow_spans {
 519             borrow_spans.var_span_label(
 520                 &mut err,
 521                 format!("borrows occur due to use of `{}`{}", desc_place, borrow_spans.describe()),
 522             );
 523         } else {
 524             let borrow_place = &issued_borrow.borrowed_place;
 525             let borrow_place_desc = self.describe_place(borrow_place)
 526                                         .unwrap_or_else(|| "_".to_owned());
 527             issued_spans.var_span_label(
 528                 &mut err,
 529                 format!(
 530                     "first borrow occurs due to use of `{}`{}",
 531                     borrow_place_desc,
 532                     issued_spans.describe(),
 533                 ),
 534             );
 535
 536             borrow_spans.var_span_label(
 537                 &mut err,
 538                 format!(
 539                     "second borrow occurs due to use of `{}`{}",
 540                     desc_place,
 541                     borrow_spans.describe(),
 542                 ),
 543             );
 544         }
 545
 546         if union_type_name != "" {
 547             err.note(&format!(
 548                 "`{}` is a field of the union `{}`, so it overlaps the field `{}`",
 549                 msg_place, union_type_name, msg_borrow,
 550             ));
 551         }
 552
 553         explanation.add_explanation_to_diagnostic(
 554             self.infcx.tcx,
 555             self.body,
 556             &mut err,
 557             first_borrow_desc,
 558             None,
 559         );
 560
 561         err
 562     }
 563
 564     /// Returns the description of the root place for a conflicting borrow and the full
 565     /// descriptions of the places that caused the conflict.
 566     ///
 567     /// In the simplest case, where there are no unions involved, if a mutable borrow of `x` is
 568     /// attempted while a shared borrow is live, then this function will return:
 569     ///
 570     ///     ("x", "", "")
 571     ///
 572     /// In the simple union case, if a mutable borrow of a union field `x.z` is attempted while
 573     /// a shared borrow of another field `x.y`, then this function will return:
 574     ///
 575     ///     ("x", "x.z", "x.y")
 576     ///
 577     /// In the more complex union case, where the union is a field of a struct, then if a mutable
 578     /// borrow of a union field in a struct `x.u.z` is attempted while a shared borrow of
 579     /// another field `x.u.y`, then this function will return:
 580     ///
 581     ///     ("x.u", "x.u.z", "x.u.y")
 582     ///
 583     /// This is used when creating error messages like below:
 584     ///
 585     /// >  cannot borrow `a.u` (via `a.u.z.c`) as immutable because it is also borrowed as
 586     /// >  mutable (via `a.u.s.b`) [E0502]
 587     pub(super) fn describe_place_for_conflicting_borrow(
 588         &self,
 589         first_borrowed_place: &Place<'tcx>,
 590         second_borrowed_place: &Place<'tcx>,
 591     ) -> (String, String, String, String) {
 592         // Define a small closure that we can use to check if the type of a place
 593         // is a union.
 594         let union_ty = |place: &Place<'tcx>| -> Option<Ty<'tcx>> {
 595             let ty = place.ty(self.body, self.infcx.tcx).ty;
 596             ty.ty_adt_def().filter(|adt| adt.is_union()).map(|_| ty)
 597         };
 598         let describe_place = |place| self.describe_place(place).unwrap_or_else(|| "_".to_owned());
 599
 600         // Start with an empty tuple, so we can use the functions on `Option` to reduce some
 601         // code duplication (particularly around returning an empty description in the failure
 602         // case).
 603         Some(())
 604             .filter(|_| {
 605                 // If we have a conflicting borrow of the same place, then we don't want to add
 606                 // an extraneous "via x.y" to our diagnostics, so filter out this case.
 607                 first_borrowed_place != second_borrowed_place
 608             })
 609             .and_then(|_| {
 610                 // We're going to want to traverse the first borrowed place to see if we can find
 611                 // field access to a union. If we find that, then we will keep the place of the
 612                 // union being accessed and the field that was being accessed so we can check the
 613                 // second borrowed place for the same union and a access to a different field.
 614                 let mut current = first_borrowed_place;
 615                 while let Place::Projection(box Projection { base, elem }) = current {
 616                     match elem {
 617                         ProjectionElem::Field(field, _) if union_ty(base).is_some() => {
 618                             return Some((base, field));
 619                         },
 620                         _ => current = base,
 621                     }
 622                 }
 623                 None
 624             })
 625             .and_then(|(target_base, target_field)| {
 626                 // With the place of a union and a field access into it, we traverse the second
 627                 // borrowed place and look for a access to a different field of the same union.
 628                 let mut current = second_borrowed_place;
 629                 while let Place::Projection(box Projection { base, elem }) = current {
 630                     if let ProjectionElem::Field(field, _) = elem {
 631                         if let Some(union_ty) = union_ty(base) {
 632                             if field != target_field && base == target_base {
 633                                 return Some((
 634                                     describe_place(base),
 635                                     describe_place(first_borrowed_place),
 636                                     describe_place(second_borrowed_place),
 637                                     union_ty.to_string(),
 638                                 ));
 639                             }
 640                         }
 641                     }
 642
 643                     current = base;
 644                 }
 645                 None
 646             })
 647             .unwrap_or_else(|| {
 648                 // If we didn't find a field access into a union, or both places match, then
 649                 // only return the description of the first place.
 650                 (
 651                     describe_place(first_borrowed_place),
 652                     "".to_string(),
 653                     "".to_string(),
 654                     "".to_string(),
 655                 )
 656             })
 657     }
 658
 659     /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
 660     ///
 661     /// This means that some data referenced by `borrow` needs to live
 662     /// past the point where the StorageDeadOrDrop of `place` occurs.
 663     /// This is usually interpreted as meaning that `place` has too
 664     /// short a lifetime. (But sometimes it is more useful to report
 665     /// it as a more direct conflict between the execution of a
 666     /// `Drop::drop` with an aliasing borrow.)
 667     pub(super) fn report_borrowed_value_does_not_live_long_enough(
 668         &mut self,
 669         location: Location,
 670         borrow: &BorrowData<'tcx>,
 671         place_span: (&Place<'tcx>, Span),
 672         kind: Option<WriteKind>,
 673     ) {
 674         debug!(
 675             "report_borrowed_value_does_not_live_long_enough(\
 676              {:?}, {:?}, {:?}, {:?}\
 677              )",
 678             location, borrow, place_span, kind
 679         );
 680
 681         let drop_span = place_span.1;
 682         let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
 683             .last()
 684             .unwrap();
 685
 686         let borrow_spans = self.retrieve_borrow_spans(borrow);
 687         let borrow_span = borrow_spans.var_or_use();
 688
 689         let proper_span = match *root_place {
 690             Place::Base(PlaceBase::Local(local)) => self.body.local_decls[local].source_info.span,
 691             _ => drop_span,
 692         };
 693
 694         if self.access_place_error_reported
 695             .contains(&(root_place.clone(), borrow_span))
 696         {
 697             debug!(
 698                 "suppressing access_place error when borrow doesn't live long enough for {:?}",
 699                 borrow_span
 700             );
 701             return;
 702         }
 703
 704         self.access_place_error_reported
 705             .insert((root_place.clone(), borrow_span));
 706
 707         if let StorageDeadOrDrop::Destructor(dropped_ty) =
 708             self.classify_drop_access_kind(&borrow.borrowed_place)
 709         {
 710             // If a borrow of path `B` conflicts with drop of `D` (and
 711             // we're not in the uninteresting case where `B` is a
 712             // prefix of `D`), then report this as a more interesting
 713             // destructor conflict.
 714             if !borrow.borrowed_place.is_prefix_of(place_span.0) {
 715                 self.report_borrow_conflicts_with_destructor(
 716                     location, borrow, place_span, kind, dropped_ty,
 717                 );
 718                 return;
 719             }
 720         }
 721
 722         let place_desc = self.describe_place(&borrow.borrowed_place);
 723
 724         let kind_place = kind.filter(|_| place_desc.is_some()).map(|k| (k, place_span.0));
 725         let explanation = self.explain_why_borrow_contains_point(location, &borrow, kind_place);
 726
 727         let err = match (place_desc, explanation) {
 728             (Some(_), _) if self.is_place_thread_local(root_place) => {
 729                 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span)
 730             }
 731             // If the outlives constraint comes from inside the closure,
 732             // for example:
 733             //
 734             // let x = 0;
 735             // let y = &x;
 736             // Box::new(|| y) as Box<Fn() -> &'static i32>
 737             //
 738             // then just use the normal error. The closure isn't escaping
 739             // and `move` will not help here.
 740             (
 741                 Some(ref name),
 742                 BorrowExplanation::MustBeValidFor {
 743                     category: category @ ConstraintCategory::Return,
 744                     from_closure: false,
 745                     ref region_name,
 746                     span,
 747                     ..
 748                 },
 749             )
 750             | (
 751                 Some(ref name),
 752                 BorrowExplanation::MustBeValidFor {
 753                     category: category @ ConstraintCategory::CallArgument,
 754                     from_closure: false,
 755                     ref region_name,
 756                     span,
 757                     ..
 758                 },
 759             ) if borrow_spans.for_closure() => self.report_escaping_closure_capture(
 760                 borrow_spans.args_or_use(),
 761                 borrow_span,
 762                 region_name,
 763                 category,
 764                 span,
 765                 &format!("`{}`", name),
 766             ),
 767             (
 768                 ref name,
 769                 BorrowExplanation::MustBeValidFor {
 770                     category: ConstraintCategory::Assignment,
 771                     from_closure: false,
 772                     region_name: RegionName {
 773                         source: RegionNameSource::AnonRegionFromUpvar(upvar_span, ref upvar_name),
 774                         ..
 775                     },
 776                     span,
 777                     ..
 778                 },
 779             ) => self.report_escaping_data(borrow_span, name, upvar_span, upvar_name, span),
 780             (Some(name), explanation) => self.report_local_value_does_not_live_long_enough(
 781                 location,
 782                 &name,
 783                 &borrow,
 784                 drop_span,
 785                 borrow_spans,
 786                 explanation,
 787             ),
 788             (None, explanation) => self.report_temporary_value_does_not_live_long_enough(
 789                 location,
 790                 &borrow,
 791                 drop_span,
 792                 borrow_spans,
 793                 proper_span,
 794                 explanation,
 795             ),
 796         };
 797
 798         err.buffer(&mut self.errors_buffer);
 799     }
 800
 801     fn report_local_value_does_not_live_long_enough(
 802         &mut self,
 803         location: Location,
 804         name: &str,
 805         borrow: &BorrowData<'tcx>,
 806         drop_span: Span,
 807         borrow_spans: UseSpans,
 808         explanation: BorrowExplanation,
 809     ) -> DiagnosticBuilder<'cx> {
 810         debug!(
 811             "report_local_value_does_not_live_long_enough(\
 812              {:?}, {:?}, {:?}, {:?}, {:?}\
 813              )",
 814             location, name, borrow, drop_span, borrow_spans
 815         );
 816
 817         let borrow_span = borrow_spans.var_or_use();
 818         if let BorrowExplanation::MustBeValidFor {
 819             category,
 820             span,
 821             ref opt_place_desc,
 822             from_closure: false,
 823             ..
 824         } = explanation {
 825             if let Some(diag) = self.try_report_cannot_return_reference_to_local(
 826                 borrow,
 827                 borrow_span,
 828                 span,
 829                 category,
 830                 opt_place_desc.as_ref(),
 831             ) {
 832                 return diag;
 833             }
 834         }
 835
 836         let mut err = self.infcx.tcx.path_does_not_live_long_enough(
 837             borrow_span,
 838             &format!("`{}`", name),
 839             Origin::Mir,
 840         );
 841
 842         if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
 843             let region_name = annotation.emit(self, &mut err);
 844
 845             err.span_label(
 846                 borrow_span,
 847                 format!("`{}` would have to be valid for `{}`...", name, region_name),
 848             );
 849
 850             if let Some(fn_hir_id) = self.infcx.tcx.hir().as_local_hir_id(self.mir_def_id) {
 851                 err.span_label(
 852                     drop_span,
 853                     format!(
 854                         "...but `{}` will be dropped here, when the function `{}` returns",
 855                         name,
 856                         self.infcx.tcx.hir().name_by_hir_id(fn_hir_id),
 857                     ),
 858                 );
 859
 860                 err.note(
 861                     "functions cannot return a borrow to data owned within the function's scope, \
 862                      functions can only return borrows to data passed as arguments",
 863                 );
 864                 err.note(
 865                     "to learn more, visit <https://doc.rust-lang.org/book/ch04-02-\
 866                      references-and-borrowing.html#dangling-references>",
 867                 );
 868             } else {
 869                 err.span_label(
 870                     drop_span,
 871                     format!("...but `{}` dropped here while still borrowed", name),
 872                 );
 873             }
 874
 875             if let BorrowExplanation::MustBeValidFor { .. } = explanation {
 876             } else {
 877                 explanation.add_explanation_to_diagnostic(
 878                     self.infcx.tcx,
 879                     self.body,
 880                     &mut err,
 881                     "",
 882                     None,
 883                 );
 884             }
 885         } else {
 886             err.span_label(borrow_span, "borrowed value does not live long enough");
 887             err.span_label(
 888                 drop_span,
 889                 format!("`{}` dropped here while still borrowed", name),
 890             );
 891
 892             let within = if borrow_spans.for_generator() {
 893                 " by generator"
 894             } else {
 895                 ""
 896             };
 897
 898             borrow_spans.args_span_label(
 899                 &mut err,
 900                 format!("value captured here{}", within),
 901             );
 902
 903             explanation.add_explanation_to_diagnostic(
 904                 self.infcx.tcx, self.body, &mut err, "", None);
 905         }
 906
 907         err
 908     }
 909
 910     fn report_borrow_conflicts_with_destructor(
 911         &mut self,
 912         location: Location,
 913         borrow: &BorrowData<'tcx>,
 914         (place, drop_span): (&Place<'tcx>, Span),
 915         kind: Option<WriteKind>,
 916         dropped_ty: Ty<'tcx>,
 917     ) {
 918         debug!(
 919             "report_borrow_conflicts_with_destructor(\
 920              {:?}, {:?}, ({:?}, {:?}), {:?}\
 921              )",
 922             location, borrow, place, drop_span, kind,
 923         );
 924
 925         let borrow_spans = self.retrieve_borrow_spans(borrow);
 926         let borrow_span = borrow_spans.var_or_use();
 927
 928         let mut err = self.infcx
 929             .tcx
 930             .cannot_borrow_across_destructor(borrow_span, Origin::Mir);
 931
 932         let what_was_dropped = match self.describe_place(place) {
 933             Some(name) => format!("`{}`", name.as_str()),
 934             None => String::from("temporary value"),
 935         };
 936
 937         let label = match self.describe_place(&borrow.borrowed_place) {
 938             Some(borrowed) => format!(
 939                 "here, drop of {D} needs exclusive access to `{B}`, \
 940                  because the type `{T}` implements the `Drop` trait",
 941                 D = what_was_dropped,
 942                 T = dropped_ty,
 943                 B = borrowed
 944             ),
 945             None => format!(
 946                 "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
 947                 D = what_was_dropped,
 948                 T = dropped_ty
 949             ),
 950         };
 951         err.span_label(drop_span, label);
 952
 953         // Only give this note and suggestion if they could be relevant.
 954         let explanation =
 955             self.explain_why_borrow_contains_point(location, borrow, kind.map(|k| (k, place)));
 956         match explanation {
 957             BorrowExplanation::UsedLater { .. }
 958             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
 959                 err.note("consider using a `let` binding to create a longer lived value");
 960             }
 961             _ => {}
 962         }
 963
 964         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
 965
 966         err.buffer(&mut self.errors_buffer);
 967     }
 968
 969     fn report_thread_local_value_does_not_live_long_enough(
 970         &mut self,
 971         drop_span: Span,
 972         borrow_span: Span,
 973     ) -> DiagnosticBuilder<'cx> {
 974         debug!(
 975             "report_thread_local_value_does_not_live_long_enough(\
 976              {:?}, {:?}\
 977              )",
 978             drop_span, borrow_span
 979         );
 980
 981         let mut err = self.infcx
 982             .tcx
 983             .thread_local_value_does_not_live_long_enough(borrow_span, Origin::Mir);
 984
 985         err.span_label(
 986             borrow_span,
 987             "thread-local variables cannot be borrowed beyond the end of the function",
 988         );
 989         err.span_label(drop_span, "end of enclosing function is here");
 990
 991         err
 992     }
 993
 994     fn report_temporary_value_does_not_live_long_enough(
 995         &mut self,
 996         location: Location,
 997         borrow: &BorrowData<'tcx>,
 998         drop_span: Span,
 999         borrow_spans: UseSpans,
1000         proper_span: Span,
1001         explanation: BorrowExplanation,
1002     ) -> DiagnosticBuilder<'cx> {
1003         debug!(
1004             "report_temporary_value_does_not_live_long_enough(\
1005              {:?}, {:?}, {:?}, {:?}\
1006              )",
1007             location, borrow, drop_span, proper_span
1008         );
1009
1010         if let BorrowExplanation::MustBeValidFor {
1011             category,
1012             span,
1013             from_closure: false,
1014             ..
1015         } = explanation {
1016             if let Some(diag) = self.try_report_cannot_return_reference_to_local(
1017                 borrow,
1018                 proper_span,
1019                 span,
1020                 category,
1021                 None,
1022             ) {
1023                 return diag;
1024             }
1025         }
1026
1027         let tcx = self.infcx.tcx;
1028         let mut err = tcx.temporary_value_borrowed_for_too_long(proper_span, Origin::Mir);
1029         err.span_label(
1030             proper_span,
1031             "creates a temporary which is freed while still in use",
1032         );
1033         err.span_label(
1034             drop_span,
1035             "temporary value is freed at the end of this statement",
1036         );
1037
1038         match explanation {
1039             BorrowExplanation::UsedLater(..)
1040             | BorrowExplanation::UsedLaterInLoop(..)
1041             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
1042                 // Only give this note and suggestion if it could be relevant.
1043                 err.note("consider using a `let` binding to create a longer lived value");
1044             }
1045             _ => {}
1046         }
1047         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
1048
1049         let within = if borrow_spans.for_generator() {
1050             " by generator"
1051         } else {
1052             ""
1053         };
1054
1055         borrow_spans.args_span_label(
1056             &mut err,
1057             format!("value captured here{}", within),
1058         );
1059
1060         err
1061     }
1062
1063     fn try_report_cannot_return_reference_to_local(
1064         &self,
1065         borrow: &BorrowData<'tcx>,
1066         borrow_span: Span,
1067         return_span: Span,
1068         category: ConstraintCategory,
1069         opt_place_desc: Option<&String>,
1070     ) -> Option<DiagnosticBuilder<'cx>> {
1071         let tcx = self.infcx.tcx;
1072
1073         let return_kind = match category {
1074             ConstraintCategory::Return => "return",
1075             ConstraintCategory::Yield => "yield",
1076             _ => return None,
1077         };
1078
1079         // FIXME use a better heuristic than Spans
1080         let reference_desc = if return_span == self.body.source_info(borrow.reserve_location).span {
1081             "reference to"
1082         } else {
1083             "value referencing"
1084         };
1085
1086         let (place_desc, note) = if let Some(place_desc) = opt_place_desc {
1087             let local_kind = match borrow.borrowed_place {
1088                 Place::Base(PlaceBase::Local(local)) => {
1089                     match self.body.local_kind(local) {
1090                         LocalKind::ReturnPointer
1091                         | LocalKind::Temp => bug!("temporary or return pointer with a name"),
1092                         LocalKind::Var => "local variable ",
1093                         LocalKind::Arg
1094                         if !self.upvars.is_empty()
1095                             && local == Local::new(1) => {
1096                             "variable captured by `move` "
1097                         }
1098                         LocalKind::Arg => {
1099                             "function parameter "
1100                         }
1101                     }
1102                 }
1103                 _ => "local data ",
1104             };
1105             (
1106                 format!("{}`{}`", local_kind, place_desc),
1107                 format!("`{}` is borrowed here", place_desc),
1108             )
1109         } else {
1110             let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
1111                 .last()
1112                 .unwrap();
1113             let local = if let Place::Base(PlaceBase::Local(local)) = *root_place {
1114                 local
1115             } else {
1116                 bug!("try_report_cannot_return_reference_to_local: not a local")
1117             };
1118             match self.body.local_kind(local) {
1119                 LocalKind::ReturnPointer | LocalKind::Temp => {
1120                     (
1121                         "temporary value".to_string(),
1122                         "temporary value created here".to_string(),
1123                     )
1124                 }
1125                 LocalKind::Arg => {
1126                     (
1127                         "function parameter".to_string(),
1128                         "function parameter borrowed here".to_string(),
1129                     )
1130                 },
1131                 LocalKind::Var => bug!("local variable without a name"),
1132             }
1133         };
1134
1135         let mut err = tcx.cannot_return_reference_to_local(
1136             return_span,
1137             return_kind,
1138             reference_desc,
1139             &place_desc,
1140             Origin::Mir,
1141         );
1142
1143         if return_span != borrow_span {
1144             err.span_label(borrow_span, note);
1145         }
1146
1147         Some(err)
1148     }
1149
1150     fn report_escaping_closure_capture(
1151         &mut self,
1152         args_span: Span,
1153         var_span: Span,
1154         fr_name: &RegionName,
1155         category: ConstraintCategory,
1156         constraint_span: Span,
1157         captured_var: &str,
1158     ) -> DiagnosticBuilder<'cx> {
1159         let tcx = self.infcx.tcx;
1160
1161         let mut err = tcx.cannot_capture_in_long_lived_closure(
1162             args_span,
1163             captured_var,
1164             var_span,
1165           Origin::Mir,
1166         );
1167
1168         let suggestion = match tcx.sess.source_map().span_to_snippet(args_span) {
1169             Ok(string) => format!("move {}", string),
1170             Err(_) => "move |<args>| <body>".to_string()
1171         };
1172
1173         err.span_suggestion(
1174             args_span,
1175             &format!("to force the closure to take ownership of {} (and any \
1176                       other referenced variables), use the `move` keyword",
1177                       captured_var),
1178             suggestion,
1179             Applicability::MachineApplicable,
1180         );
1181
1182         match category {
1183             ConstraintCategory::Return => {
1184                 err.span_note(constraint_span, "closure is returned here");
1185             }
1186             ConstraintCategory::CallArgument => {
1187                 fr_name.highlight_region_name(&mut err);
1188                 err.span_note(
1189                     constraint_span,
1190                     &format!("function requires argument type to outlive `{}`", fr_name),
1191                 );
1192             }
1193             _ => bug!("report_escaping_closure_capture called with unexpected constraint \
1194                        category: `{:?}`", category),
1195         }
1196         err
1197     }
1198
1199     fn report_escaping_data(
1200         &mut self,
1201         borrow_span: Span,
1202         name: &Option<String>,
1203         upvar_span: Span,
1204         upvar_name: &str,
1205         escape_span: Span,
1206     ) -> DiagnosticBuilder<'cx> {
1207         let tcx = self.infcx.tcx;
1208
1209         let escapes_from = if tcx.is_closure(self.mir_def_id) {
1210             let tables = tcx.typeck_tables_of(self.mir_def_id);
1211             let mir_hir_id = tcx.hir().def_index_to_hir_id(self.mir_def_id.index);
1212             match tables.node_type(mir_hir_id).sty {
1213                 ty::Closure(..) => "closure",
1214                 ty::Generator(..) => "generator",
1215                 _ => bug!("Closure body doesn't have a closure or generator type"),
1216             }
1217         } else {
1218             "function"
1219         };
1220
1221         let mut err = tcx.borrowed_data_escapes_closure(escape_span, escapes_from, Origin::Mir);
1222
1223         err.span_label(
1224             upvar_span,
1225             format!(
1226                 "`{}` is declared here, outside of the {} body",
1227                 upvar_name, escapes_from
1228             ),
1229         );
1230
1231         err.span_label(
1232             borrow_span,
1233             format!(
1234                 "borrow is only valid in the {} body",
1235                 escapes_from
1236             ),
1237         );
1238
1239         if let Some(name) = name {
1240             err.span_label(
1241                 escape_span,
1242                 format!("reference to `{}` escapes the {} body here", name, escapes_from),
1243             );
1244         } else {
1245             err.span_label(
1246                 escape_span,
1247                 format!("reference escapes the {} body here", escapes_from),
1248             );
1249         }
1250
1251         err
1252     }
1253
1254     fn get_moved_indexes(&mut self, location: Location, mpi: MovePathIndex) -> Vec<MoveSite> {
1255         let body = self.body;
1256
1257         let mut stack = Vec::new();
1258         stack.extend(body.predecessor_locations(location).map(|predecessor| {
1259             let is_back_edge = location.dominates(predecessor, &self.dominators);
1260             (predecessor, is_back_edge)
1261         }));
1262
1263         let mut visited = FxHashSet::default();
1264         let mut result = vec![];
1265
1266         'dfs: while let Some((location, is_back_edge)) = stack.pop() {
1267             debug!(
1268                 "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
1269                 location, is_back_edge
1270             );
1271
1272             if !visited.insert(location) {
1273                 continue;
1274             }
1275
1276             // check for moves
1277             let stmt_kind = body[location.block]
1278                 .statements
1279                 .get(location.statement_index)
1280                 .map(|s| &s.kind);
1281             if let Some(StatementKind::StorageDead(..)) = stmt_kind {
1282                 // this analysis only tries to find moves explicitly
1283                 // written by the user, so we ignore the move-outs
1284                 // created by `StorageDead` and at the beginning
1285                 // of a function.
1286             } else {
1287                 // If we are found a use of a.b.c which was in error, then we want to look for
1288                 // moves not only of a.b.c but also a.b and a.
1289                 //
1290                 // Note that the moves data already includes "parent" paths, so we don't have to
1291                 // worry about the other case: that is, if there is a move of a.b.c, it is already
1292                 // marked as a move of a.b and a as well, so we will generate the correct errors
1293                 // there.
1294                 let mut mpis = vec![mpi];
1295                 let move_paths = &self.move_data.move_paths;
1296                 mpis.extend(move_paths[mpi].parents(move_paths));
1297
1298                 for moi in &self.move_data.loc_map[location] {
1299                     debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
1300                     if mpis.contains(&self.move_data.moves[*moi].path) {
1301                         debug!("report_use_of_moved_or_uninitialized: found");
1302                         result.push(MoveSite {
1303                             moi: *moi,
1304                             traversed_back_edge: is_back_edge,
1305                         });
1306
1307                         // Strictly speaking, we could continue our DFS here. There may be
1308                         // other moves that can reach the point of error. But it is kind of
1309                         // confusing to highlight them.
1310                         //
1311                         // Example:
1312                         //
1313                         // ```
1314                         // let a = vec![];
1315                         // let b = a;
1316                         // let c = a;
1317                         // drop(a); // <-- current point of error
1318                         // ```
1319                         //
1320                         // Because we stop the DFS here, we only highlight `let c = a`,
1321                         // and not `let b = a`. We will of course also report an error at
1322                         // `let c = a` which highlights `let b = a` as the move.
1323                         continue 'dfs;
1324                     }
1325                 }
1326             }
1327
1328             // check for inits
1329             let mut any_match = false;
1330             drop_flag_effects::for_location_inits(
1331                 self.infcx.tcx,
1332                 self.body,
1333                 self.move_data,
1334                 location,
1335                 |m| {
1336                     if m == mpi {
1337                         any_match = true;
1338                     }
1339                 },
1340             );
1341             if any_match {
1342                 continue 'dfs;
1343             }
1344
1345             stack.extend(body.predecessor_locations(location).map(|predecessor| {
1346                 let back_edge = location.dominates(predecessor, &self.dominators);
1347                 (predecessor, is_back_edge || back_edge)
1348             }));
1349         }
1350
1351         result
1352     }
1353
1354     pub(super) fn report_illegal_mutation_of_borrowed(
1355         &mut self,
1356         location: Location,
1357         (place, span): (&Place<'tcx>, Span),
1358         loan: &BorrowData<'tcx>,
1359     ) {
1360         let loan_spans = self.retrieve_borrow_spans(loan);
1361         let loan_span = loan_spans.args_or_use();
1362
1363         let tcx = self.infcx.tcx;
1364         if loan.kind == BorrowKind::Shallow {
1365             let mut err = tcx.cannot_mutate_in_match_guard(
1366                 span,
1367                 loan_span,
1368                 &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
1369                 "assign",
1370                 Origin::Mir,
1371             );
1372             loan_spans.var_span_label(
1373                 &mut err,
1374                 format!("borrow occurs due to use{}", loan_spans.describe()),
1375             );
1376
1377             err.buffer(&mut self.errors_buffer);
1378
1379             return;
1380         }
1381
1382         let mut err = tcx.cannot_assign_to_borrowed(
1383             span,
1384             loan_span,
1385             &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
1386             Origin::Mir,
1387         );
1388
1389         loan_spans.var_span_label(
1390             &mut err,
1391             format!("borrow occurs due to use{}", loan_spans.describe()),
1392         );
1393
1394         self.explain_why_borrow_contains_point(location, loan, None)
1395             .add_explanation_to_diagnostic(self.infcx.tcx, self.body, &mut err, "", None);
1396
1397         err.buffer(&mut self.errors_buffer);
1398     }
1399
1400     /// Reports an illegal reassignment; for example, an assignment to
1401     /// (part of) a non-`mut` local that occurs potentially after that
1402     /// local has already been initialized. `place` is the path being
1403     /// assigned; `err_place` is a place providing a reason why
1404     /// `place` is not mutable (e.g., the non-`mut` local `x` in an
1405     /// assignment to `x.f`).
1406     pub(super) fn report_illegal_reassignment(
1407         &mut self,
1408         _location: Location,
1409         (place, span): (&Place<'tcx>, Span),
1410         assigned_span: Span,
1411         err_place: &Place<'tcx>,
1412     ) {
1413         let (from_arg, local_decl) = if let Place::Base(PlaceBase::Local(local)) = *err_place {
1414             if let LocalKind::Arg = self.body.local_kind(local) {
1415                 (true, Some(&self.body.local_decls[local]))
1416             } else {
1417                 (false, Some(&self.body.local_decls[local]))
1418             }
1419         } else {
1420             (false, None)
1421         };
1422
1423         // If root local is initialized immediately (everything apart from let
1424         // PATTERN;) then make the error refer to that local, rather than the
1425         // place being assigned later.
1426         let (place_description, assigned_span) = match local_decl {
1427             Some(LocalDecl {
1428                 is_user_variable: Some(ClearCrossCrate::Clear),
1429                 ..
1430             })
1431             | Some(LocalDecl {
1432                 is_user_variable:
1433                     Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
1434                         opt_match_place: None,
1435                         ..
1436                     }))),
1437                 ..
1438             })
1439             | Some(LocalDecl {
1440                 is_user_variable: None,
1441                 ..
1442             })
1443             | None => (self.describe_place(place), assigned_span),
1444             Some(decl) => (self.describe_place(err_place), decl.source_info.span),
1445         };
1446
1447         let mut err = self.infcx.tcx.cannot_reassign_immutable(
1448             span,
1449             place_description.as_ref().map(AsRef::as_ref).unwrap_or("_"),
1450             from_arg,
1451             Origin::Mir,
1452         );
1453         let msg = if from_arg {
1454             "cannot assign to immutable argument"
1455         } else {
1456             "cannot assign twice to immutable variable"
1457         };
1458         if span != assigned_span {
1459             if !from_arg {
1460                 let value_msg = match place_description {
1461                     Some(name) => format!("`{}`", name),
1462                     None => "value".to_owned(),
1463                 };
1464                 err.span_label(assigned_span, format!("first assignment to {}", value_msg));
1465             }
1466         }
1467         if let Some(decl) = local_decl {
1468             if let Some(name) = decl.name {
1469                 if decl.can_be_made_mutable() {
1470                     err.span_suggestion(
1471                         decl.source_info.span,
1472                         "make this binding mutable",
1473                         format!("mut {}", name),
1474                         Applicability::MachineApplicable,
1475                     );
1476                 }
1477             }
1478         }
1479         err.span_label(span, msg);
1480         err.buffer(&mut self.errors_buffer);
1481     }
1482
1483     fn classify_drop_access_kind(&self, place: &Place<'tcx>) -> StorageDeadOrDrop<'tcx> {
1484         let tcx = self.infcx.tcx;
1485         match place {
1486             Place::Base(PlaceBase::Local(_)) |
1487             Place::Base(PlaceBase::Static(_)) => {
1488                 StorageDeadOrDrop::LocalStorageDead
1489             }
1490             Place::Projection(box Projection { base, elem }) => {
1491                 let base_access = self.classify_drop_access_kind(base);
1492                 match elem {
1493                     ProjectionElem::Deref => match base_access {
1494                         StorageDeadOrDrop::LocalStorageDead
1495                         | StorageDeadOrDrop::BoxedStorageDead => {
1496                             assert!(
1497                                 base.ty(self.body, tcx).ty.is_box(),
1498                                 "Drop of value behind a reference or raw pointer"
1499                             );
1500                             StorageDeadOrDrop::BoxedStorageDead
1501                         }
1502                         StorageDeadOrDrop::Destructor(_) => base_access,
1503                     },
1504                     ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
1505                         let base_ty = base.ty(self.body, tcx).ty;
1506                         match base_ty.sty {
1507                             ty::Adt(def, _) if def.has_dtor(tcx) => {
1508                                 // Report the outermost adt with a destructor
1509                                 match base_access {
1510                                     StorageDeadOrDrop::Destructor(_) => base_access,
1511                                     StorageDeadOrDrop::LocalStorageDead
1512                                     | StorageDeadOrDrop::BoxedStorageDead => {
1513                                         StorageDeadOrDrop::Destructor(base_ty)
1514                                     }
1515                                 }
1516                             }
1517                             _ => base_access,
1518                         }
1519                     }
1520
1521                     ProjectionElem::ConstantIndex { .. }
1522                     | ProjectionElem::Subslice { .. }
1523                     | ProjectionElem::Index(_) => base_access,
1524                 }
1525             }
1526         }
1527     }
1528
1529     /// Annotate argument and return type of function and closure with (synthesized) lifetime for
1530     /// borrow of local value that does not live long enough.
1531     fn annotate_argument_and_return_for_borrow(
1532         &self,
1533         borrow: &BorrowData<'tcx>,
1534     ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
1535         // Define a fallback for when we can't match a closure.
1536         let fallback = || {
1537             let is_closure = self.infcx.tcx.is_closure(self.mir_def_id);
1538             if is_closure {
1539                 None
1540             } else {
1541                 let ty = self.infcx.tcx.type_of(self.mir_def_id);
1542                 match ty.sty {
1543                     ty::FnDef(_, _) | ty::FnPtr(_) => self.annotate_fn_sig(
1544                         self.mir_def_id,
1545                         self.infcx.tcx.fn_sig(self.mir_def_id),
1546                     ),
1547                     _ => None,
1548                 }
1549             }
1550         };
1551
1552         // In order to determine whether we need to annotate, we need to check whether the reserve
1553         // place was an assignment into a temporary.
1554         //
1555         // If it was, we check whether or not that temporary is eventually assigned into the return
1556         // place. If it was, we can add annotations about the function's return type and arguments
1557         // and it'll make sense.
1558         let location = borrow.reserve_location;
1559         debug!(
1560             "annotate_argument_and_return_for_borrow: location={:?}",
1561             location
1562         );
1563         if let Some(&Statement { kind: StatementKind::Assign(ref reservation, _), ..})
1564              = &self.body[location.block].statements.get(location.statement_index)
1565         {
1566             debug!(
1567                 "annotate_argument_and_return_for_borrow: reservation={:?}",
1568                 reservation
1569             );
1570             // Check that the initial assignment of the reserve location is into a temporary.
1571             let mut target = *match reservation {
1572                 Place::Base(PlaceBase::Local(local))
1573                     if self.body.local_kind(*local) == LocalKind::Temp => local,
1574                 _ => return None,
1575             };
1576
1577             // Next, look through the rest of the block, checking if we are assigning the
1578             // `target` (that is, the place that contains our borrow) to anything.
1579             let mut annotated_closure = None;
1580             for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
1581                 debug!(
1582                     "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
1583                     target, stmt
1584                 );
1585                 if let StatementKind::Assign(
1586                     Place::Base(PlaceBase::Local(assigned_to)),
1587                     box rvalue
1588                 ) = &stmt.kind {
1589                     debug!(
1590                         "annotate_argument_and_return_for_borrow: assigned_to={:?} \
1591                          rvalue={:?}",
1592                         assigned_to, rvalue
1593                     );
1594                     // Check if our `target` was captured by a closure.
1595                     if let Rvalue::Aggregate(
1596                         box AggregateKind::Closure(def_id, substs),
1597                         operands,
1598                     ) = rvalue
1599                     {
1600                         for operand in operands {
1601                             let assigned_from = match operand {
1602                                 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1603                                     assigned_from
1604                                 }
1605                                 _ => continue,
1606                             };
1607                             debug!(
1608                                 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1609                                 assigned_from
1610                             );
1611
1612                             // Find the local from the operand.
1613                             let assigned_from_local = match assigned_from.local_or_deref_local() {
1614                                 Some(local) => local,
1615                                 None => continue,
1616                             };
1617
1618                             if assigned_from_local != target {
1619                                 continue;
1620                             }
1621
1622                             // If a closure captured our `target` and then assigned
1623                             // into a place then we should annotate the closure in
1624                             // case it ends up being assigned into the return place.
1625                             annotated_closure = self.annotate_fn_sig(
1626                                 *def_id,
1627                                 self.infcx.closure_sig(*def_id, *substs),
1628                             );
1629                             debug!(
1630                                 "annotate_argument_and_return_for_borrow: \
1631                                  annotated_closure={:?} assigned_from_local={:?} \
1632                                  assigned_to={:?}",
1633                                 annotated_closure, assigned_from_local, assigned_to
1634                             );
1635
1636                             if *assigned_to == mir::RETURN_PLACE {
1637                                 // If it was assigned directly into the return place, then
1638                                 // return now.
1639                                 return annotated_closure;
1640                             } else {
1641                                 // Otherwise, update the target.
1642                                 target = *assigned_to;
1643                             }
1644                         }
1645
1646                         // If none of our closure's operands matched, then skip to the next
1647                         // statement.
1648                         continue;
1649                     }
1650
1651                     // Otherwise, look at other types of assignment.
1652                     let assigned_from = match rvalue {
1653                         Rvalue::Ref(_, _, assigned_from) => assigned_from,
1654                         Rvalue::Use(operand) => match operand {
1655                             Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1656                                 assigned_from
1657                             }
1658                             _ => continue,
1659                         },
1660                         _ => continue,
1661                     };
1662                     debug!(
1663                         "annotate_argument_and_return_for_borrow: \
1664                          assigned_from={:?}",
1665                         assigned_from,
1666                     );
1667
1668                     // Find the local from the rvalue.
1669                     let assigned_from_local = match assigned_from.local_or_deref_local() {
1670                         Some(local) => local,
1671                         None => continue,
1672                     };
1673                     debug!(
1674                         "annotate_argument_and_return_for_borrow: \
1675                          assigned_from_local={:?}",
1676                         assigned_from_local,
1677                     );
1678
1679                     // Check if our local matches the target - if so, we've assigned our
1680                     // borrow to a new place.
1681                     if assigned_from_local != target {
1682                         continue;
1683                     }
1684
1685                     // If we assigned our `target` into a new place, then we should
1686                     // check if it was the return place.
1687                     debug!(
1688                         "annotate_argument_and_return_for_borrow: \
1689                          assigned_from_local={:?} assigned_to={:?}",
1690                         assigned_from_local, assigned_to
1691                     );
1692                     if *assigned_to == mir::RETURN_PLACE {
1693                         // If it was then return the annotated closure if there was one,
1694                         // else, annotate this function.
1695                         return annotated_closure.or_else(fallback);
1696                     }
1697
1698                     // If we didn't assign into the return place, then we just update
1699                     // the target.
1700                     target = *assigned_to;
1701                 }
1702             }
1703
1704             // Check the terminator if we didn't find anything in the statements.
1705             let terminator = &self.body[location.block].terminator();
1706             debug!(
1707                 "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
1708                 target, terminator
1709             );
1710             if let TerminatorKind::Call {
1711                 destination: Some((Place::Base(PlaceBase::Local(assigned_to)), _)),
1712                 args,
1713                 ..
1714             } = &terminator.kind
1715             {
1716                 debug!(
1717                     "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
1718                     assigned_to, args
1719                 );
1720                 for operand in args {
1721                     let assigned_from = match operand {
1722                         Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1723                             assigned_from
1724                         }
1725                         _ => continue,
1726                     };
1727                     debug!(
1728                         "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1729                         assigned_from,
1730                     );
1731
1732                     if let Some(assigned_from_local) = assigned_from.local_or_deref_local() {
1733                         debug!(
1734                             "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
1735                             assigned_from_local,
1736                         );
1737
1738                         if *assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
1739                             return annotated_closure.or_else(fallback);
1740                         }
1741                     }
1742                 }
1743             }
1744         }
1745
1746         // If we haven't found an assignment into the return place, then we need not add
1747         // any annotations.
1748         debug!("annotate_argument_and_return_for_borrow: none found");
1749         None
1750     }
1751
1752     /// Annotate the first argument and return type of a function signature if they are
1753     /// references.
1754     fn annotate_fn_sig(
1755         &self,
1756         did: DefId,
1757         sig: ty::PolyFnSig<'tcx>,
1758     ) -> Option<AnnotatedBorrowFnSignature<'tcx>> {
1759         debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
1760         let is_closure = self.infcx.tcx.is_closure(did);
1761         let fn_hir_id = self.infcx.tcx.hir().as_local_hir_id(did)?;
1762         let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(fn_hir_id)?;
1763
1764         // We need to work out which arguments to highlight. We do this by looking
1765         // at the return type, where there are three cases:
1766         //
1767         // 1. If there are named arguments, then we should highlight the return type and
1768         //    highlight any of the arguments that are also references with that lifetime.
1769         //    If there are no arguments that have the same lifetime as the return type,
1770         //    then don't highlight anything.
1771         // 2. The return type is a reference with an anonymous lifetime. If this is
1772         //    the case, then we can take advantage of (and teach) the lifetime elision
1773         //    rules.
1774         //
1775         //    We know that an error is being reported. So the arguments and return type
1776         //    must satisfy the elision rules. Therefore, if there is a single argument
1777         //    then that means the return type and first (and only) argument have the same
1778         //    lifetime and the borrow isn't meeting that, we can highlight the argument
1779         //    and return type.
1780         //
1781         //    If there are multiple arguments then the first argument must be self (else
1782         //    it would not satisfy the elision rules), so we can highlight self and the
1783         //    return type.
1784         // 3. The return type is not a reference. In this case, we don't highlight
1785         //    anything.
1786         let return_ty = sig.output();
1787         match return_ty.skip_binder().sty {
1788             ty::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
1789                 // This is case 1 from above, return type is a named reference so we need to
1790                 // search for relevant arguments.
1791                 let mut arguments = Vec::new();
1792                 for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
1793                     if let ty::Ref(argument_region, _, _) = argument.sty {
1794                         if argument_region == return_region {
1795                             // Need to use the `rustc::ty` types to compare against the
1796                             // `return_region`. Then use the `rustc::hir` type to get only
1797                             // the lifetime span.
1798                             if let hir::TyKind::Rptr(lifetime, _) = &fn_decl.inputs[index].node {
1799                                 // With access to the lifetime, we can get
1800                                 // the span of it.
1801                                 arguments.push((*argument, lifetime.span));
1802                             } else {
1803                                 bug!("ty type is a ref but hir type is not");
1804                             }
1805                         }
1806                     }
1807                 }
1808
1809                 // We need to have arguments. This shouldn't happen, but it's worth checking.
1810                 if arguments.is_empty() {
1811                     return None;
1812                 }
1813
1814                 // We use a mix of the HIR and the Ty types to get information
1815                 // as the HIR doesn't have full types for closure arguments.
1816                 let return_ty = *sig.output().skip_binder();
1817                 let mut return_span = fn_decl.output.span();
1818                 if let hir::FunctionRetTy::Return(ty) = fn_decl.output {
1819                     if let hir::TyKind::Rptr(lifetime, _) = ty.into_inner().node {
1820                         return_span = lifetime.span;
1821                     }
1822                 }
1823
1824                 Some(AnnotatedBorrowFnSignature::NamedFunction {
1825                     arguments,
1826                     return_ty,
1827                     return_span,
1828                 })
1829             }
1830             ty::Ref(_, _, _) if is_closure => {
1831                 // This is case 2 from above but only for closures, return type is anonymous
1832                 // reference so we select
1833                 // the first argument.
1834                 let argument_span = fn_decl.inputs.first()?.span;
1835                 let argument_ty = sig.inputs().skip_binder().first()?;
1836
1837                 // Closure arguments are wrapped in a tuple, so we need to get the first
1838                 // from that.
1839                 if let ty::Tuple(elems) = argument_ty.sty {
1840                     let argument_ty = elems.first()?.expect_ty();
1841                     if let ty::Ref(_, _, _) = argument_ty.sty {
1842                         return Some(AnnotatedBorrowFnSignature::Closure {
1843                             argument_ty,
1844                             argument_span,
1845                         });
1846                     }
1847                 }
1848
1849                 None
1850             }
1851             ty::Ref(_, _, _) => {
1852                 // This is also case 2 from above but for functions, return type is still an
1853                 // anonymous reference so we select the first argument.
1854                 let argument_span = fn_decl.inputs.first()?.span;
1855                 let argument_ty = sig.inputs().skip_binder().first()?;
1856
1857                 let return_span = fn_decl.output.span();
1858                 let return_ty = *sig.output().skip_binder();
1859
1860                 // We expect the first argument to be a reference.
1861                 match argument_ty.sty {
1862                     ty::Ref(_, _, _) => {}
1863                     _ => return None,
1864                 }
1865
1866                 Some(AnnotatedBorrowFnSignature::AnonymousFunction {
1867                     argument_ty,
1868                     argument_span,
1869                     return_ty,
1870                     return_span,
1871                 })
1872             }
1873             _ => {
1874                 // This is case 3 from above, return type is not a reference so don't highlight
1875                 // anything.
1876                 None
1877             }
1878         }
1879     }
1880 }
1881
1882 #[derive(Debug)]
1883 enum AnnotatedBorrowFnSignature<'tcx> {
1884     NamedFunction {
1885         arguments: Vec<(Ty<'tcx>, Span)>,
1886         return_ty: Ty<'tcx>,
1887         return_span: Span,
1888     },
1889     AnonymousFunction {
1890         argument_ty: Ty<'tcx>,
1891         argument_span: Span,
1892         return_ty: Ty<'tcx>,
1893         return_span: Span,
1894     },
1895     Closure {
1896         argument_ty: Ty<'tcx>,
1897         argument_span: Span,
1898     },
1899 }
1900
1901 impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
1902     /// Annotate the provided diagnostic with information about borrow from the fn signature that
1903     /// helps explain.
1904     pub(super) fn emit(
1905         &self,
1906         cx: &mut MirBorrowckCtxt<'_, '_, 'tcx>,
1907         diag: &mut DiagnosticBuilder<'_>,
1908     ) -> String {
1909         match self {
1910             AnnotatedBorrowFnSignature::Closure {
1911                 argument_ty,
1912                 argument_span,
1913             } => {
1914                 diag.span_label(
1915                     *argument_span,
1916                     format!("has type `{}`", cx.get_name_for_ty(argument_ty, 0)),
1917                 );
1918
1919                 cx.get_region_name_for_ty(argument_ty, 0)
1920             }
1921             AnnotatedBorrowFnSignature::AnonymousFunction {
1922                 argument_ty,
1923                 argument_span,
1924                 return_ty,
1925                 return_span,
1926             } => {
1927                 let argument_ty_name = cx.get_name_for_ty(argument_ty, 0);
1928                 diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
1929
1930                 let return_ty_name = cx.get_name_for_ty(return_ty, 0);
1931                 let types_equal = return_ty_name == argument_ty_name;
1932                 diag.span_label(
1933                     *return_span,
1934                     format!(
1935                         "{}has type `{}`",
1936                         if types_equal { "also " } else { "" },
1937                         return_ty_name,
1938                     ),
1939                 );
1940
1941                 diag.note(
1942                     "argument and return type have the same lifetime due to lifetime elision rules",
1943                 );
1944                 diag.note(
1945                     "to learn more, visit <https://doc.rust-lang.org/book/ch10-03-\
1946                      lifetime-syntax.html#lifetime-elision>",
1947                 );
1948
1949                 cx.get_region_name_for_ty(return_ty, 0)
1950             }
1951             AnnotatedBorrowFnSignature::NamedFunction {
1952                 arguments,
1953                 return_ty,
1954                 return_span,
1955             } => {
1956                 // Region of return type and arguments checked to be the same earlier.
1957                 let region_name = cx.get_region_name_for_ty(return_ty, 0);
1958                 for (_, argument_span) in arguments {
1959                     diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
1960                 }
1961
1962                 diag.span_label(
1963                     *return_span,
1964                     format!("also has lifetime `{}`", region_name,),
1965                 );
1966
1967                 diag.help(&format!(
1968                     "use data from the highlighted arguments which match the `{}` lifetime of \
1969                      the return type",
1970                     region_name,
1971                 ));
1972
1973                 region_name
1974             }
1975         }
1976     }
1977 }