src/librustc_mir/borrow_check/error_reporting.rs

   1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use borrow_check::nll::explain_borrow::BorrowExplanation;
  12 use borrow_check::prefixes::IsPrefixOf;
  13 use borrow_check::WriteKind;
  14 use rustc::hir;
  15 use rustc::hir::def_id::DefId;
  16 use rustc::middle::region::ScopeTree;
  17 use rustc::mir::{
  18     self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, Field, Local,
  19     LocalDecl, LocalKind, Location, Operand, Place, PlaceProjection, ProjectionElem,
  20     Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
  21 };
  22 use rustc::ty;
  23 use rustc::util::ppaux::with_highlight_region_for_bound_region;
  24 use rustc_data_structures::fx::FxHashSet;
  25 use rustc_data_structures::sync::Lrc;
  26 use rustc_errors::{Applicability, DiagnosticBuilder};
  27 use syntax_pos::Span;
  28
  29 use super::borrow_set::BorrowData;
  30 use super::{Context, MirBorrowckCtxt};
  31 use super::{InitializationRequiringAction, PrefixSet};
  32
  33 use dataflow::drop_flag_effects;
  34 use dataflow::move_paths::indexes::MoveOutIndex;
  35 use dataflow::move_paths::MovePathIndex;
  36 use util::borrowck_errors::{BorrowckErrors, Origin};
  37
  38 #[derive(Debug)]
  39 struct MoveSite {
  40     /// Index of the "move out" that we found. The `MoveData` can
  41     /// then tell us where the move occurred.
  42     moi: MoveOutIndex,
  43
  44     /// True if we traversed a back edge while walking from the point
  45     /// of error to the move site.
  46     traversed_back_edge: bool
  47 }
  48
  49 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
  50     pub(super) fn report_use_of_moved_or_uninitialized(
  51         &mut self,
  52         context: Context,
  53         desired_action: InitializationRequiringAction,
  54         (place, span): (&Place<'tcx>, Span),
  55         mpi: MovePathIndex,
  56     ) {
  57         debug!(
  58             "report_use_of_moved_or_uninitialized: context={:?} desired_action={:?} place={:?} \
  59              span={:?} mpi={:?}",
  60             context, desired_action, place, span, mpi
  61         );
  62
  63         let use_spans = self.move_spans(place, context.loc)
  64             .or_else(|| self.borrow_spans(span, context.loc));
  65         let span = use_spans.args_or_use();
  66
  67         let move_site_vec = self.get_moved_indexes(context, mpi);
  68         debug!(
  69             "report_use_of_moved_or_uninitialized: move_site_vec={:?}",
  70             move_site_vec
  71         );
  72         let move_out_indices: Vec<_> = move_site_vec
  73             .iter()
  74             .map(|move_site| move_site.moi)
  75             .collect();
  76
  77         if move_out_indices.is_empty() {
  78             let root_place = self.prefixes(&place, PrefixSet::All).last().unwrap();
  79
  80             if self.uninitialized_error_reported
  81                 .contains(&root_place.clone())
  82             {
  83                 debug!(
  84                     "report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
  85                     root_place
  86                 );
  87                 return;
  88             }
  89
  90             self.uninitialized_error_reported.insert(root_place.clone());
  91
  92             let item_msg = match self.describe_place_with_options(place, IncludingDowncast(true)) {
  93                 Some(name) => format!("`{}`", name),
  94                 None => "value".to_owned(),
  95             };
  96             let mut err = self.infcx.tcx.cannot_act_on_uninitialized_variable(
  97                 span,
  98                 desired_action.as_noun(),
  99                 &self.describe_place_with_options(place, IncludingDowncast(true))
 100                     .unwrap_or("_".to_owned()),
 101                 Origin::Mir,
 102             );
 103             err.span_label(span, format!("use of possibly uninitialized {}", item_msg));
 104
 105             use_spans.var_span_label(
 106                 &mut err,
 107                 format!("{} occurs due to use in closure", desired_action.as_noun()),
 108             );
 109
 110             err.buffer(&mut self.errors_buffer);
 111         } else {
 112             if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
 113                 if self.prefixes(&reported_place, PrefixSet::All)
 114                     .any(|p| p == place)
 115                 {
 116                     debug!(
 117                         "report_use_of_moved_or_uninitialized place: error suppressed \
 118                          mois={:?}",
 119                         move_out_indices
 120                     );
 121                     return;
 122                 }
 123             }
 124
 125             let msg = ""; //FIXME: add "partially " or "collaterally "
 126
 127             let mut err = self.infcx.tcx.cannot_act_on_moved_value(
 128                 span,
 129                 desired_action.as_noun(),
 130                 msg,
 131                 self.describe_place_with_options(&place, IncludingDowncast(true)),
 132                 Origin::Mir,
 133             );
 134
 135             let mut is_loop_move = false;
 136             for move_site in &move_site_vec {
 137                 let move_out = self.move_data.moves[(*move_site).moi];
 138                 let moved_place = &self.move_data.move_paths[move_out.path].place;
 139
 140                 let move_spans = self.move_spans(moved_place, move_out.source);
 141                 let move_span = move_spans.args_or_use();
 142
 143                 let move_msg = if move_spans.for_closure() {
 144                     " into closure"
 145                 } else {
 146                     ""
 147                 };
 148
 149                 if span == move_span {
 150                     err.span_label(
 151                         span,
 152                         format!("value moved{} here, in previous iteration of loop", move_msg),
 153                     );
 154                     is_loop_move = true;
 155                 } else if move_site.traversed_back_edge {
 156                     err.span_label(
 157                         move_span,
 158                         format!(
 159                             "value moved{} here, in previous iteration of loop",
 160                             move_msg
 161                         ),
 162                     );
 163                 } else {
 164                     err.span_label(move_span, format!("value moved{} here", move_msg));
 165                     move_spans.var_span_label(&mut err, "variable moved due to use in closure");
 166                 };
 167             }
 168
 169             use_spans.var_span_label(
 170                 &mut err,
 171                 format!("{} occurs due to use in closure", desired_action.as_noun()),
 172             );
 173
 174             if !is_loop_move {
 175                 err.span_label(
 176                     span,
 177                     format!(
 178                         "value {} here after move",
 179                         desired_action.as_verb_in_past_tense()
 180                     ),
 181                 );
 182             }
 183
 184             if let Some(ty) = self.retrieve_type_for_place(place) {
 185                 let needs_note = match ty.sty {
 186                     ty::Closure(id, _) => {
 187                         let tables = self.infcx.tcx.typeck_tables_of(id);
 188                         let node_id = self.infcx.tcx.hir.as_local_node_id(id).unwrap();
 189                         let hir_id = self.infcx.tcx.hir.node_to_hir_id(node_id);
 190                         if tables.closure_kind_origins().get(hir_id).is_some() {
 191                             false
 192                         } else {
 193                             true
 194                         }
 195                     }
 196                     _ => true,
 197                 };
 198
 199                 if needs_note {
 200                     let mpi = self.move_data.moves[move_out_indices[0]].path;
 201                     let place = &self.move_data.move_paths[mpi].place;
 202
 203                     if let Some(ty) = self.retrieve_type_for_place(place) {
 204                         let note_msg = match self.describe_place_with_options(
 205                             place,
 206                             IncludingDowncast(true),
 207                         ) {
 208                             Some(name) => format!("`{}`", name),
 209                             None => "value".to_owned(),
 210                         };
 211
 212                         err.note(&format!(
 213                             "move occurs because {} has type `{}`, \
 214                              which does not implement the `Copy` trait",
 215                             note_msg, ty
 216                         ));
 217                     }
 218                 }
 219             }
 220
 221             if let Some((_, mut old_err)) = self.move_error_reported
 222                 .insert(move_out_indices, (place.clone(), err))
 223             {
 224                 // Cancel the old error so it doesn't ICE.
 225                 old_err.cancel();
 226             }
 227         }
 228     }
 229
 230     pub(super) fn report_move_out_while_borrowed(
 231         &mut self,
 232         context: Context,
 233         (place, _span): (&Place<'tcx>, Span),
 234         borrow: &BorrowData<'tcx>,
 235     ) {
 236         let tcx = self.infcx.tcx;
 237         let value_msg = match self.describe_place(place) {
 238             Some(name) => format!("`{}`", name),
 239             None => "value".to_owned(),
 240         };
 241         let borrow_msg = match self.describe_place(&borrow.borrowed_place) {
 242             Some(name) => format!("`{}`", name),
 243             None => "value".to_owned(),
 244         };
 245
 246         let borrow_spans = self.retrieve_borrow_spans(borrow);
 247         let borrow_span = borrow_spans.args_or_use();
 248
 249         let move_spans = self.move_spans(place, context.loc);
 250         let span = move_spans.args_or_use();
 251
 252         let mut err = tcx.cannot_move_when_borrowed(
 253             span,
 254             &self.describe_place(place).unwrap_or("_".to_owned()),
 255             Origin::Mir,
 256         );
 257         err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
 258         err.span_label(span, format!("move out of {} occurs here", value_msg));
 259
 260         borrow_spans.var_span_label(&mut err, "borrow occurs due to use in closure");
 261
 262         move_spans.var_span_label(&mut err, "move occurs due to use in closure");
 263
 264         self.explain_why_borrow_contains_point(context, borrow, None)
 265             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 266         err.buffer(&mut self.errors_buffer);
 267     }
 268
 269     pub(super) fn report_use_while_mutably_borrowed(
 270         &mut self,
 271         context: Context,
 272         (place, _span): (&Place<'tcx>, Span),
 273         borrow: &BorrowData<'tcx>,
 274     ) {
 275         let tcx = self.infcx.tcx;
 276
 277         let borrow_spans = self.retrieve_borrow_spans(borrow);
 278         let borrow_span = borrow_spans.args_or_use();
 279
 280         // Conflicting borrows are reported separately, so only check for move
 281         // captures.
 282         let use_spans = self.move_spans(place, context.loc);
 283         let span = use_spans.var_or_use();
 284
 285         let mut err = tcx.cannot_use_when_mutably_borrowed(
 286             span,
 287             &self.describe_place(place).unwrap_or("_".to_owned()),
 288             borrow_span,
 289             &self.describe_place(&borrow.borrowed_place)
 290                 .unwrap_or("_".to_owned()),
 291             Origin::Mir,
 292         );
 293
 294         borrow_spans.var_span_label(&mut err, {
 295             let place = &borrow.borrowed_place;
 296             let desc_place = self.describe_place(place).unwrap_or("_".to_owned());
 297
 298             format!("borrow occurs due to use of `{}` in closure", desc_place)
 299         });
 300
 301         self.explain_why_borrow_contains_point(context, borrow, None)
 302             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 303         err.buffer(&mut self.errors_buffer);
 304     }
 305
 306     pub(super) fn report_conflicting_borrow(
 307         &mut self,
 308         context: Context,
 309         (place, span): (&Place<'tcx>, Span),
 310         gen_borrow_kind: BorrowKind,
 311         issued_borrow: &BorrowData<'tcx>,
 312     ) {
 313         let issued_spans = self.retrieve_borrow_spans(issued_borrow);
 314         let issued_span = issued_spans.args_or_use();
 315
 316         let borrow_spans = self.borrow_spans(span, context.loc);
 317         let span = borrow_spans.args_or_use();
 318
 319         let desc_place = self.describe_place(place).unwrap_or("_".to_owned());
 320         let tcx = self.infcx.tcx;
 321
 322         let first_borrow_desc;
 323
 324         // FIXME: supply non-"" `opt_via` when appropriate
 325         let mut err = match (
 326             gen_borrow_kind,
 327             "immutable",
 328             "mutable",
 329             issued_borrow.kind,
 330             "immutable",
 331             "mutable",
 332         ) {
 333             (BorrowKind::Shared, lft, _, BorrowKind::Mut { .. }, _, rgt) => {
 334                 first_borrow_desc = "mutable ";
 335                 tcx.cannot_reborrow_already_borrowed(
 336                     span,
 337                     &desc_place,
 338                     "",
 339                     lft,
 340                     issued_span,
 341                     "it",
 342                     rgt,
 343                     "",
 344                     None,
 345                     Origin::Mir,
 346                 )
 347             }
 348             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Shared, rgt, _) => {
 349                 first_borrow_desc = "immutable ";
 350                 tcx.cannot_reborrow_already_borrowed(
 351                     span,
 352                     &desc_place,
 353                     "",
 354                     lft,
 355                     issued_span,
 356                     "it",
 357                     rgt,
 358                     "",
 359                     None,
 360                     Origin::Mir,
 361                 )
 362             }
 363
 364             (BorrowKind::Mut { .. }, _, _, BorrowKind::Mut { .. }, _, _) => {
 365                 first_borrow_desc = "first ";
 366                 tcx.cannot_mutably_borrow_multiply(
 367                     span,
 368                     &desc_place,
 369                     "",
 370                     issued_span,
 371                     "",
 372                     None,
 373                     Origin::Mir,
 374                 )
 375             }
 376
 377             (BorrowKind::Unique, _, _, BorrowKind::Unique, _, _) => {
 378                 first_borrow_desc = "first ";
 379                 tcx.cannot_uniquely_borrow_by_two_closures(
 380                     span,
 381                     &desc_place,
 382                     issued_span,
 383                     None,
 384                     Origin::Mir,
 385                 )
 386             }
 387
 388             (BorrowKind::Mut { .. }, _, _, BorrowKind::Shallow, _, _)
 389             | (BorrowKind::Unique, _, _, BorrowKind::Shallow, _, _) => {
 390                 let mut err = tcx.cannot_mutate_in_match_guard(
 391                     span,
 392                     issued_span,
 393                     &desc_place,
 394                     "mutably borrow",
 395                     Origin::Mir,
 396                 );
 397                 borrow_spans.var_span_label(
 398                     &mut err,
 399                     format!("borrow occurs due to use of `{}` in closure", desc_place),
 400                 );
 401                 err.buffer(&mut self.errors_buffer);
 402
 403                 return;
 404             }
 405
 406             (BorrowKind::Unique, _, _, _, _, _) => {
 407                 first_borrow_desc = "first ";
 408                 tcx.cannot_uniquely_borrow_by_one_closure(
 409                     span,
 410                     &desc_place,
 411                     "",
 412                     issued_span,
 413                     "it",
 414                     "",
 415                     None,
 416                     Origin::Mir,
 417                 )
 418             },
 419
 420             (BorrowKind::Shared, lft, _, BorrowKind::Unique, _, _) => {
 421                 first_borrow_desc = "first ";
 422                 tcx.cannot_reborrow_already_uniquely_borrowed(
 423                     span,
 424                     &desc_place,
 425                     "",
 426                     lft,
 427                     issued_span,
 428                     "",
 429                     None,
 430                     Origin::Mir,
 431                 )
 432             }
 433
 434             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Unique, _, _) => {
 435                 first_borrow_desc = "first ";
 436                 tcx.cannot_reborrow_already_uniquely_borrowed(
 437                     span,
 438                     &desc_place,
 439                     "",
 440                     lft,
 441                     issued_span,
 442                     "",
 443                     None,
 444                     Origin::Mir,
 445                 )
 446             }
 447
 448             (BorrowKind::Shallow, _, _, BorrowKind::Unique, _, _)
 449             | (BorrowKind::Shallow, _, _, BorrowKind::Mut { .. }, _, _) => {
 450                 // Shallow borrows are uses from the user's point of view.
 451                 self.report_use_while_mutably_borrowed(context, (place, span), issued_borrow);
 452                 return;
 453             }
 454             (BorrowKind::Shared, _, _, BorrowKind::Shared, _, _)
 455             | (BorrowKind::Shared, _, _, BorrowKind::Shallow, _, _)
 456             | (BorrowKind::Shallow, _, _, BorrowKind::Shared, _, _)
 457             | (BorrowKind::Shallow, _, _, BorrowKind::Shallow, _, _) => unreachable!(),
 458         };
 459
 460         if issued_spans == borrow_spans {
 461             borrow_spans.var_span_label(
 462                 &mut err,
 463                 format!("borrows occur due to use of `{}` in closure", desc_place),
 464             );
 465         } else {
 466             let borrow_place = &issued_borrow.borrowed_place;
 467             let borrow_place_desc = self.describe_place(borrow_place).unwrap_or("_".to_owned());
 468             issued_spans.var_span_label(
 469                 &mut err,
 470                 format!(
 471                     "first borrow occurs due to use of `{}` in closure",
 472                     borrow_place_desc
 473                 ),
 474             );
 475
 476             borrow_spans.var_span_label(
 477                 &mut err,
 478                 format!(
 479                     "second borrow occurs due to use of `{}` in closure",
 480                     desc_place
 481                 ),
 482             );
 483         }
 484
 485         self.explain_why_borrow_contains_point(context, issued_borrow, None)
 486             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, first_borrow_desc);
 487
 488         err.buffer(&mut self.errors_buffer);
 489     }
 490
 491     /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
 492     ///
 493     /// This means that some data referenced by `borrow` needs to live
 494     /// past the point where the StorageDeadOrDrop of `place` occurs.
 495     /// This is usually interpreted as meaning that `place` has too
 496     /// short a lifetime. (But sometimes it is more useful to report
 497     /// it as a more direct conflict between the execution of a
 498     /// `Drop::drop` with an aliasing borrow.)
 499     pub(super) fn report_borrowed_value_does_not_live_long_enough(
 500         &mut self,
 501         context: Context,
 502         borrow: &BorrowData<'tcx>,
 503         place_span: (&Place<'tcx>, Span),
 504         kind: Option<WriteKind>,
 505     ) {
 506         debug!(
 507             "report_borrowed_value_does_not_live_long_enough(\
 508              {:?}, {:?}, {:?}, {:?}\
 509              )",
 510             context, borrow, place_span, kind
 511         );
 512
 513         let drop_span = place_span.1;
 514         let scope_tree = self.infcx.tcx.region_scope_tree(self.mir_def_id);
 515         let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
 516             .last()
 517             .unwrap();
 518
 519         let borrow_spans = self.retrieve_borrow_spans(borrow);
 520         let borrow_span = borrow_spans.var_or_use();
 521
 522         let proper_span = match *root_place {
 523             Place::Local(local) => self.mir.local_decls[local].source_info.span,
 524             _ => drop_span,
 525         };
 526
 527         if self.access_place_error_reported
 528             .contains(&(root_place.clone(), borrow_span))
 529         {
 530             debug!(
 531                 "suppressing access_place error when borrow doesn't live long enough for {:?}",
 532                 borrow_span
 533             );
 534             return;
 535         }
 536
 537         self.access_place_error_reported
 538             .insert((root_place.clone(), borrow_span));
 539
 540         if let StorageDeadOrDrop::Destructor(dropped_ty) =
 541             self.classify_drop_access_kind(&borrow.borrowed_place)
 542         {
 543             // If a borrow of path `B` conflicts with drop of `D` (and
 544             // we're not in the uninteresting case where `B` is a
 545             // prefix of `D`), then report this as a more interesting
 546             // destructor conflict.
 547             if !borrow.borrowed_place.is_prefix_of(place_span.0) {
 548                 self.report_borrow_conflicts_with_destructor(
 549                     context, borrow, place_span, kind, dropped_ty,
 550                 );
 551                 return;
 552             }
 553         }
 554
 555         let err = match &self.describe_place(&borrow.borrowed_place) {
 556             Some(_) if self.is_place_thread_local(root_place) => {
 557                 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span)
 558             }
 559             Some(name) => self.report_local_value_does_not_live_long_enough(
 560                 context,
 561                 name,
 562                 &scope_tree,
 563                 &borrow,
 564                 drop_span,
 565                 borrow_spans,
 566                 kind.map(|k| (k, place_span.0)),
 567             ),
 568             None => self.report_temporary_value_does_not_live_long_enough(
 569                 context,
 570                 &scope_tree,
 571                 &borrow,
 572                 drop_span,
 573                 borrow_spans,
 574                 proper_span,
 575             ),
 576         };
 577
 578         err.buffer(&mut self.errors_buffer);
 579     }
 580
 581     fn report_local_value_does_not_live_long_enough(
 582         &mut self,
 583         context: Context,
 584         name: &String,
 585         scope_tree: &Lrc<ScopeTree>,
 586         borrow: &BorrowData<'tcx>,
 587         drop_span: Span,
 588         borrow_spans: UseSpans,
 589         kind_place: Option<(WriteKind, &Place<'tcx>)>,
 590     ) -> DiagnosticBuilder<'cx> {
 591         debug!(
 592             "report_local_value_does_not_live_long_enough(\
 593              {:?}, {:?}, {:?}, {:?}, {:?}, {:?}\
 594              )",
 595             context, name, scope_tree, borrow, drop_span, borrow_spans
 596         );
 597
 598         let borrow_span = borrow_spans.var_or_use();
 599         let mut err = self.infcx.tcx.path_does_not_live_long_enough(
 600             borrow_span,
 601             &format!("`{}`", name),
 602             Origin::Mir,
 603         );
 604
 605         let explanation = self.explain_why_borrow_contains_point(context, borrow, kind_place);
 606         if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
 607             let region_name = annotation.emit(&mut err);
 608
 609             err.span_label(
 610                 borrow_span,
 611                 format!("`{}` would have to be valid for `{}`...", name, region_name),
 612             );
 613
 614             if let Some(fn_node_id) = self.infcx.tcx.hir.as_local_node_id(self.mir_def_id) {
 615                 err.span_label(
 616                     drop_span,
 617                     format!(
 618                         "...but `{}` will be dropped here, when the function `{}` returns",
 619                         name,
 620                         self.infcx.tcx.hir.name(fn_node_id),
 621                     ),
 622                 );
 623
 624                 err.note(
 625                     "functions cannot return a borrow to data owned within the function's scope, \
 626                      functions can only return borrows to data passed as arguments",
 627                 );
 628                 err.note(
 629                     "to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch04-02-\
 630                      references-and-borrowing.html#dangling-references>",
 631                 );
 632             } else {
 633                 err.span_label(
 634                     drop_span,
 635                     format!("...but `{}` dropped here while still borrowed", name),
 636                 );
 637             }
 638
 639             if let BorrowExplanation::MustBeValidFor(..) = explanation {
 640             } else {
 641                 explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 642             }
 643         } else {
 644             err.span_label(borrow_span, "borrowed value does not live long enough");
 645             err.span_label(
 646                 drop_span,
 647                 format!("`{}` dropped here while still borrowed", name),
 648             );
 649
 650             borrow_spans.args_span_label(&mut err, "value captured here");
 651
 652             explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 653         }
 654
 655         err
 656     }
 657
 658     pub(super) fn report_borrow_conflicts_with_destructor(
 659         &mut self,
 660         context: Context,
 661         borrow: &BorrowData<'tcx>,
 662         (place, drop_span): (&Place<'tcx>, Span),
 663         kind: Option<WriteKind>,
 664         dropped_ty: ty::Ty<'tcx>,
 665     ) {
 666         debug!(
 667             "report_borrow_conflicts_with_destructor(\
 668              {:?}, {:?}, ({:?}, {:?}), {:?}\
 669              )",
 670             context, borrow, place, drop_span, kind,
 671         );
 672
 673         let borrow_spans = self.retrieve_borrow_spans(borrow);
 674         let borrow_span = borrow_spans.var_or_use();
 675
 676         let mut err = self.infcx
 677             .tcx
 678             .cannot_borrow_across_destructor(borrow_span, Origin::Mir);
 679
 680         let what_was_dropped = match self.describe_place(place) {
 681             Some(name) => format!("`{}`", name.as_str()),
 682             None => format!("temporary value"),
 683         };
 684
 685         let label = match self.describe_place(&borrow.borrowed_place) {
 686             Some(borrowed) => format!(
 687                 "here, drop of {D} needs exclusive access to `{B}`, \
 688                  because the type `{T}` implements the `Drop` trait",
 689                 D = what_was_dropped,
 690                 T = dropped_ty,
 691                 B = borrowed
 692             ),
 693             None => format!(
 694                 "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
 695                 D = what_was_dropped,
 696                 T = dropped_ty
 697             ),
 698         };
 699         err.span_label(drop_span, label);
 700
 701         // Only give this note and suggestion if they could be relevant.
 702         let explanation =
 703             self.explain_why_borrow_contains_point(context, borrow, kind.map(|k| (k, place)));
 704         match explanation {
 705             BorrowExplanation::UsedLater { .. }
 706             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
 707                 err.note("consider using a `let` binding to create a longer lived value");
 708             }
 709             _ => {}
 710         }
 711
 712         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 713
 714         err.buffer(&mut self.errors_buffer);
 715     }
 716
 717     fn report_thread_local_value_does_not_live_long_enough(
 718         &mut self,
 719         drop_span: Span,
 720         borrow_span: Span,
 721     ) -> DiagnosticBuilder<'cx> {
 722         debug!(
 723             "report_thread_local_value_does_not_live_long_enough(\
 724              {:?}, {:?}\
 725              )",
 726             drop_span, borrow_span
 727         );
 728
 729         let mut err = self.infcx
 730             .tcx
 731             .thread_local_value_does_not_live_long_enough(borrow_span, Origin::Mir);
 732
 733         err.span_label(
 734             borrow_span,
 735             "thread-local variables cannot be borrowed beyond the end of the function",
 736         );
 737         err.span_label(drop_span, "end of enclosing function is here");
 738
 739         err
 740     }
 741
 742     fn report_temporary_value_does_not_live_long_enough(
 743         &mut self,
 744         context: Context,
 745         scope_tree: &Lrc<ScopeTree>,
 746         borrow: &BorrowData<'tcx>,
 747         drop_span: Span,
 748         borrow_spans: UseSpans,
 749         proper_span: Span,
 750     ) -> DiagnosticBuilder<'cx> {
 751         debug!(
 752             "report_temporary_value_does_not_live_long_enough(\
 753              {:?}, {:?}, {:?}, {:?}, {:?}\
 754              )",
 755             context, scope_tree, borrow, drop_span, proper_span
 756         );
 757
 758         let tcx = self.infcx.tcx;
 759         let mut err = tcx.temporary_value_borrowed_for_too_long(proper_span, Origin::Mir);
 760         err.span_label(
 761             proper_span,
 762             "creates a temporary which is freed while still in use",
 763         );
 764         err.span_label(
 765             drop_span,
 766             "temporary value is freed at the end of this statement",
 767         );
 768
 769         let explanation = self.explain_why_borrow_contains_point(context, borrow, None);
 770         match explanation {
 771             BorrowExplanation::UsedLater(..)
 772             | BorrowExplanation::UsedLaterInLoop(..)
 773             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
 774                 // Only give this note and suggestion if it could be relevant.
 775                 err.note("consider using a `let` binding to create a longer lived value");
 776             }
 777             _ => {}
 778         }
 779         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 780
 781         borrow_spans.args_span_label(&mut err, "value captured here");
 782
 783         err
 784     }
 785
 786     fn get_moved_indexes(&mut self, context: Context, mpi: MovePathIndex) -> Vec<MoveSite> {
 787         let mir = self.mir;
 788
 789         let mut stack = Vec::new();
 790         stack.extend(mir.predecessor_locations(context.loc).map(|predecessor| {
 791             let is_back_edge = context.loc.dominates(predecessor, &self.dominators);
 792             (predecessor, is_back_edge)
 793         }));
 794
 795         let mut visited = FxHashSet();
 796         let mut result = vec![];
 797
 798         'dfs: while let Some((location, is_back_edge)) = stack.pop() {
 799             debug!(
 800                 "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
 801                 location, is_back_edge
 802             );
 803
 804             if !visited.insert(location) {
 805                 continue;
 806             }
 807
 808             // check for moves
 809             let stmt_kind = mir[location.block]
 810                 .statements
 811                 .get(location.statement_index)
 812                 .map(|s| &s.kind);
 813             if let Some(StatementKind::StorageDead(..)) = stmt_kind {
 814                 // this analysis only tries to find moves explicitly
 815                 // written by the user, so we ignore the move-outs
 816                 // created by `StorageDead` and at the beginning
 817                 // of a function.
 818             } else {
 819                 // If we are found a use of a.b.c which was in error, then we want to look for
 820                 // moves not only of a.b.c but also a.b and a.
 821                 //
 822                 // Note that the moves data already includes "parent" paths, so we don't have to
 823                 // worry about the other case: that is, if there is a move of a.b.c, it is already
 824                 // marked as a move of a.b and a as well, so we will generate the correct errors
 825                 // there.
 826                 let mut mpis = vec![mpi];
 827                 let move_paths = &self.move_data.move_paths;
 828                 mpis.extend(move_paths[mpi].parents(move_paths));
 829
 830                 for moi in &self.move_data.loc_map[location] {
 831                     debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
 832                     if mpis.contains(&self.move_data.moves[*moi].path) {
 833                         debug!("report_use_of_moved_or_uninitialized: found");
 834                         result.push(MoveSite {
 835                             moi: *moi,
 836                             traversed_back_edge: is_back_edge,
 837                         });
 838
 839                         // Strictly speaking, we could continue our DFS here. There may be
 840                         // other moves that can reach the point of error. But it is kind of
 841                         // confusing to highlight them.
 842                         //
 843                         // Example:
 844                         //
 845                         // ```
 846                         // let a = vec![];
 847                         // let b = a;
 848                         // let c = a;
 849                         // drop(a); // <-- current point of error
 850                         // ```
 851                         //
 852                         // Because we stop the DFS here, we only highlight `let c = a`,
 853                         // and not `let b = a`. We will of course also report an error at
 854                         // `let c = a` which highlights `let b = a` as the move.
 855                         continue 'dfs;
 856                     }
 857                 }
 858             }
 859
 860             // check for inits
 861             let mut any_match = false;
 862             drop_flag_effects::for_location_inits(
 863                 self.infcx.tcx,
 864                 self.mir,
 865                 self.move_data,
 866                 location,
 867                 |m| {
 868                     if m == mpi {
 869                         any_match = true;
 870                     }
 871                 },
 872             );
 873             if any_match {
 874                 continue 'dfs;
 875             }
 876
 877             stack.extend(mir.predecessor_locations(location).map(|predecessor| {
 878                 let back_edge = location.dominates(predecessor, &self.dominators);
 879                 (predecessor, is_back_edge || back_edge)
 880             }));
 881         }
 882
 883         result
 884     }
 885
 886     pub(super) fn report_illegal_mutation_of_borrowed(
 887         &mut self,
 888         context: Context,
 889         (place, span): (&Place<'tcx>, Span),
 890         loan: &BorrowData<'tcx>,
 891     ) {
 892         let loan_spans = self.retrieve_borrow_spans(loan);
 893         let loan_span = loan_spans.args_or_use();
 894
 895         let tcx = self.infcx.tcx;
 896         let mut err = if loan.kind == BorrowKind::Shallow {
 897             tcx.cannot_mutate_in_match_guard(
 898                 span,
 899                 loan_span,
 900                 &self.describe_place(place).unwrap_or("_".to_owned()),
 901                 "assign",
 902                 Origin::Mir,
 903             )
 904         } else {
 905             tcx.cannot_assign_to_borrowed(
 906                 span,
 907                 loan_span,
 908                 &self.describe_place(place).unwrap_or("_".to_owned()),
 909                 Origin::Mir,
 910             )
 911         };
 912
 913         loan_spans.var_span_label(&mut err, "borrow occurs due to use in closure");
 914
 915         self.explain_why_borrow_contains_point(context, loan, None)
 916             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 917
 918         err.buffer(&mut self.errors_buffer);
 919     }
 920
 921     /// Reports an illegal reassignment; for example, an assignment to
 922     /// (part of) a non-`mut` local that occurs potentially after that
 923     /// local has already been initialized. `place` is the path being
 924     /// assigned; `err_place` is a place providing a reason why
 925     /// `place` is not mutable (e.g. the non-`mut` local `x` in an
 926     /// assignment to `x.f`).
 927     pub(super) fn report_illegal_reassignment(
 928         &mut self,
 929         _context: Context,
 930         (place, span): (&Place<'tcx>, Span),
 931         assigned_span: Span,
 932         err_place: &Place<'tcx>,
 933     ) {
 934         let (from_arg, local_decl) = if let Place::Local(local) = *err_place {
 935             if let LocalKind::Arg = self.mir.local_kind(local) {
 936                 (true, Some(&self.mir.local_decls[local]))
 937             } else {
 938                 (false, Some(&self.mir.local_decls[local]))
 939             }
 940         } else {
 941             (false, None)
 942         };
 943
 944         // If root local is initialized immediately (everything apart from let
 945         // PATTERN;) then make the error refer to that local, rather than the
 946         // place being assigned later.
 947         let (place_description, assigned_span) = match local_decl {
 948             Some(LocalDecl {
 949                 is_user_variable: Some(ClearCrossCrate::Clear),
 950                 ..
 951             })
 952             | Some(LocalDecl {
 953                 is_user_variable:
 954                     Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
 955                         opt_match_place: None,
 956                         ..
 957                     }))),
 958                 ..
 959             })
 960             | Some(LocalDecl {
 961                 is_user_variable: None,
 962                 ..
 963             })
 964             | None => (self.describe_place(place), assigned_span),
 965             Some(decl) => (self.describe_place(err_place), decl.source_info.span),
 966         };
 967
 968         let mut err = self.infcx.tcx.cannot_reassign_immutable(
 969             span,
 970             place_description.as_ref().map(AsRef::as_ref).unwrap_or("_"),
 971             from_arg,
 972             Origin::Mir,
 973         );
 974         let msg = if from_arg {
 975             "cannot assign to immutable argument"
 976         } else {
 977             "cannot assign twice to immutable variable"
 978         };
 979         if span != assigned_span {
 980             if !from_arg {
 981                 let value_msg = match place_description {
 982                     Some(name) => format!("`{}`", name),
 983                     None => "value".to_owned(),
 984                 };
 985                 err.span_label(assigned_span, format!("first assignment to {}", value_msg));
 986             }
 987         }
 988         if let Some(decl) = local_decl {
 989             if let Some(name) = decl.name {
 990                 if decl.can_be_made_mutable() {
 991                     err.span_suggestion_with_applicability(
 992                         decl.source_info.span,
 993                         "make this binding mutable",
 994                         format!("mut {}", name),
 995                         Applicability::MachineApplicable,
 996                     );
 997                 }
 998             }
 999         }
1000         err.span_label(span, msg);
1001         err.buffer(&mut self.errors_buffer);
1002     }
1003 }
1004
1005 pub(super) struct IncludingDowncast(bool);
1006
1007 /// Which case a StorageDeadOrDrop is for.
1008 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
1009 enum StorageDeadOrDrop<'tcx> {
1010     LocalStorageDead,
1011     BoxedStorageDead,
1012     Destructor(ty::Ty<'tcx>),
1013 }
1014
1015 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1016     // End-user visible description of `place` if one can be found. If the
1017     // place is a temporary for instance, None will be returned.
1018     pub(super) fn describe_place(&self, place: &Place<'tcx>) -> Option<String> {
1019         self.describe_place_with_options(place, IncludingDowncast(false))
1020     }
1021
1022     // End-user visible description of `place` if one can be found. If the
1023     // place is a temporary for instance, None will be returned.
1024     // `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
1025     // `Downcast` and `IncludingDowncast` is true
1026     pub(super) fn describe_place_with_options(
1027         &self,
1028         place: &Place<'tcx>,
1029         including_downcast: IncludingDowncast,
1030     ) -> Option<String> {
1031         let mut buf = String::new();
1032         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
1033             Ok(()) => Some(buf),
1034             Err(()) => None,
1035         }
1036     }
1037
1038     // Appends end-user visible description of `place` to `buf`.
1039     fn append_place_to_string(
1040         &self,
1041         place: &Place<'tcx>,
1042         buf: &mut String,
1043         mut autoderef: bool,
1044         including_downcast: &IncludingDowncast,
1045     ) -> Result<(), ()> {
1046         match *place {
1047             Place::Promoted(_) => {
1048                 buf.push_str("promoted");
1049             }
1050             Place::Local(local) => {
1051                 self.append_local_to_string(local, buf)?;
1052             }
1053             Place::Static(ref static_) => {
1054                 buf.push_str(&self.infcx.tcx.item_name(static_.def_id).to_string());
1055             }
1056             Place::Projection(ref proj) => {
1057                 match proj.elem {
1058                     ProjectionElem::Deref => {
1059                         let upvar_field_projection =
1060                             place.is_upvar_field_projection(self.mir, &self.infcx.tcx);
1061                         if let Some(field) = upvar_field_projection {
1062                             let var_index = field.index();
1063                             let name = self.mir.upvar_decls[var_index].debug_name.to_string();
1064                             if self.mir.upvar_decls[var_index].by_ref {
1065                                 buf.push_str(&name);
1066                             } else {
1067                                 buf.push_str(&format!("*{}", &name));
1068                             }
1069                         } else {
1070                             if autoderef {
1071                                 self.append_place_to_string(
1072                                     &proj.base,
1073                                     buf,
1074                                     autoderef,
1075                                     &including_downcast,
1076                                 )?;
1077                             } else if let Place::Local(local) = proj.base {
1078                                 if let Some(ClearCrossCrate::Set(BindingForm::RefForGuard)) =
1079                                     self.mir.local_decls[local].is_user_variable
1080                                 {
1081                                     self.append_place_to_string(
1082                                         &proj.base,
1083                                         buf,
1084                                         autoderef,
1085                                         &including_downcast,
1086                                     )?;
1087                                 } else {
1088                                     buf.push_str(&"*");
1089                                     self.append_place_to_string(
1090                                         &proj.base,
1091                                         buf,
1092                                         autoderef,
1093                                         &including_downcast,
1094                                     )?;
1095                                 }
1096                             } else {
1097                                 buf.push_str(&"*");
1098                                 self.append_place_to_string(
1099                                     &proj.base,
1100                                     buf,
1101                                     autoderef,
1102                                     &including_downcast,
1103                                 )?;
1104                             }
1105                         }
1106                     }
1107                     ProjectionElem::Downcast(..) => {
1108                         self.append_place_to_string(
1109                             &proj.base,
1110                             buf,
1111                             autoderef,
1112                             &including_downcast,
1113                         )?;
1114                         if including_downcast.0 {
1115                             return Err(());
1116                         }
1117                     }
1118                     ProjectionElem::Field(field, _ty) => {
1119                         autoderef = true;
1120
1121                         let upvar_field_projection =
1122                             place.is_upvar_field_projection(self.mir, &self.infcx.tcx);
1123                         if let Some(field) = upvar_field_projection {
1124                             let var_index = field.index();
1125                             let name = self.mir.upvar_decls[var_index].debug_name.to_string();
1126                             buf.push_str(&name);
1127                         } else {
1128                             let field_name = self.describe_field(&proj.base, field);
1129                             self.append_place_to_string(
1130                                 &proj.base,
1131                                 buf,
1132                                 autoderef,
1133                                 &including_downcast,
1134                             )?;
1135                             buf.push_str(&format!(".{}", field_name));
1136                         }
1137                     }
1138                     ProjectionElem::Index(index) => {
1139                         autoderef = true;
1140
1141                         self.append_place_to_string(
1142                             &proj.base,
1143                             buf,
1144                             autoderef,
1145                             &including_downcast,
1146                         )?;
1147                         buf.push_str("[");
1148                         if self.append_local_to_string(index, buf).is_err() {
1149                             buf.push_str("..");
1150                         }
1151                         buf.push_str("]");
1152                     }
1153                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
1154                         autoderef = true;
1155                         // Since it isn't possible to borrow an element on a particular index and
1156                         // then use another while the borrow is held, don't output indices details
1157                         // to avoid confusing the end-user
1158                         self.append_place_to_string(
1159                             &proj.base,
1160                             buf,
1161                             autoderef,
1162                             &including_downcast,
1163                         )?;
1164                         buf.push_str(&"[..]");
1165                     }
1166                 };
1167             }
1168         }
1169
1170         Ok(())
1171     }
1172
1173     // Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
1174     // a name, then `Err` is returned
1175     fn append_local_to_string(&self, local_index: Local, buf: &mut String) -> Result<(), ()> {
1176         let local = &self.mir.local_decls[local_index];
1177         match local.name {
1178             Some(name) => {
1179                 buf.push_str(&name.to_string());
1180                 Ok(())
1181             }
1182             None => Err(()),
1183         }
1184     }
1185
1186     // End-user visible description of the `field`nth field of `base`
1187     fn describe_field(&self, base: &Place, field: Field) -> String {
1188         match *base {
1189             Place::Local(local) => {
1190                 let local = &self.mir.local_decls[local];
1191                 self.describe_field_from_ty(&local.ty, field)
1192             }
1193             Place::Promoted(ref prom) => self.describe_field_from_ty(&prom.1, field),
1194             Place::Static(ref static_) => self.describe_field_from_ty(&static_.ty, field),
1195             Place::Projection(ref proj) => match proj.elem {
1196                 ProjectionElem::Deref => self.describe_field(&proj.base, field),
1197                 ProjectionElem::Downcast(def, variant_index) => format!(
1198                     "{}",
1199                     def.variants[variant_index].fields[field.index()].ident
1200                 ),
1201                 ProjectionElem::Field(_, field_type) => {
1202                     self.describe_field_from_ty(&field_type, field)
1203                 }
1204                 ProjectionElem::Index(..)
1205                 | ProjectionElem::ConstantIndex { .. }
1206                 | ProjectionElem::Subslice { .. } => {
1207                     self.describe_field(&proj.base, field).to_string()
1208                 }
1209             },
1210         }
1211     }
1212
1213     // End-user visible description of the `field_index`nth field of `ty`
1214     fn describe_field_from_ty(&self, ty: &ty::Ty, field: Field) -> String {
1215         if ty.is_box() {
1216             // If the type is a box, the field is described from the boxed type
1217             self.describe_field_from_ty(&ty.boxed_ty(), field)
1218         } else {
1219             match ty.sty {
1220                 ty::Adt(def, _) => if def.is_enum() {
1221                     field.index().to_string()
1222                 } else {
1223                     def.non_enum_variant().fields[field.index()]
1224                         .ident
1225                         .to_string()
1226                 },
1227                 ty::Tuple(_) => field.index().to_string(),
1228                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
1229                     self.describe_field_from_ty(&ty, field)
1230                 }
1231                 ty::Array(ty, _) | ty::Slice(ty) => self.describe_field_from_ty(&ty, field),
1232                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
1233                     // Convert the def-id into a node-id. node-ids are only valid for
1234                     // the local code in the current crate, so this returns an `Option` in case
1235                     // the closure comes from another crate. But in that case we wouldn't
1236                     // be borrowck'ing it, so we can just unwrap:
1237                     let node_id = self.infcx.tcx.hir.as_local_node_id(def_id).unwrap();
1238                     let freevar = self.infcx
1239                         .tcx
1240                         .with_freevars(node_id, |fv| fv[field.index()]);
1241
1242                     self.infcx.tcx.hir.name(freevar.var_id()).to_string()
1243                 }
1244                 _ => {
1245                     // Might need a revision when the fields in trait RFC is implemented
1246                     // (https://github.com/rust-lang/rfcs/pull/1546)
1247                     bug!(
1248                         "End-user description not implemented for field access on `{:?}`",
1249                         ty.sty
1250                     );
1251                 }
1252             }
1253         }
1254     }
1255
1256     // Retrieve type of a place for the current MIR representation
1257     fn retrieve_type_for_place(&self, place: &Place<'tcx>) -> Option<ty::Ty> {
1258         match place {
1259             Place::Local(local) => {
1260                 let local = &self.mir.local_decls[*local];
1261                 Some(local.ty)
1262             }
1263             Place::Promoted(ref prom) => Some(prom.1),
1264             Place::Static(ref st) => Some(st.ty),
1265             Place::Projection(ref proj) => match proj.elem {
1266                 ProjectionElem::Field(_, ty) => Some(ty),
1267                 _ => None,
1268             },
1269         }
1270     }
1271
1272     /// Check if a place is a thread-local static.
1273     pub fn is_place_thread_local(&self, place: &Place<'tcx>) -> bool {
1274         if let Place::Static(statik) = place {
1275             let attrs = self.infcx.tcx.get_attrs(statik.def_id);
1276             let is_thread_local = attrs.iter().any(|attr| attr.check_name("thread_local"));
1277
1278             debug!(
1279                 "is_place_thread_local: attrs={:?} is_thread_local={:?}",
1280                 attrs, is_thread_local
1281             );
1282             is_thread_local
1283         } else {
1284             debug!("is_place_thread_local: no");
1285             false
1286         }
1287     }
1288
1289     fn classify_drop_access_kind(&self, place: &Place<'tcx>) -> StorageDeadOrDrop<'tcx> {
1290         let tcx = self.infcx.tcx;
1291         match place {
1292             Place::Local(_) | Place::Static(_) | Place::Promoted(_) => {
1293                 StorageDeadOrDrop::LocalStorageDead
1294             }
1295             Place::Projection(box PlaceProjection { base, elem }) => {
1296                 let base_access = self.classify_drop_access_kind(base);
1297                 match elem {
1298                     ProjectionElem::Deref => match base_access {
1299                         StorageDeadOrDrop::LocalStorageDead
1300                         | StorageDeadOrDrop::BoxedStorageDead => {
1301                             assert!(
1302                                 base.ty(self.mir, tcx).to_ty(tcx).is_box(),
1303                                 "Drop of value behind a reference or raw pointer"
1304                             );
1305                             StorageDeadOrDrop::BoxedStorageDead
1306                         }
1307                         StorageDeadOrDrop::Destructor(_) => base_access,
1308                     },
1309                     ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
1310                         let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
1311                         match base_ty.sty {
1312                             ty::Adt(def, _) if def.has_dtor(tcx) => {
1313                                 // Report the outermost adt with a destructor
1314                                 match base_access {
1315                                     StorageDeadOrDrop::Destructor(_) => base_access,
1316                                     StorageDeadOrDrop::LocalStorageDead
1317                                     | StorageDeadOrDrop::BoxedStorageDead => {
1318                                         StorageDeadOrDrop::Destructor(base_ty)
1319                                     }
1320                                 }
1321                             }
1322                             _ => base_access,
1323                         }
1324                     }
1325
1326                     ProjectionElem::ConstantIndex { .. }
1327                     | ProjectionElem::Subslice { .. }
1328                     | ProjectionElem::Index(_) => base_access,
1329                 }
1330             }
1331         }
1332     }
1333
1334     /// Annotate argument and return type of function and closure with (synthesized) lifetime for
1335     /// borrow of local value that does not live long enough.
1336     fn annotate_argument_and_return_for_borrow(
1337         &self,
1338         borrow: &BorrowData<'tcx>,
1339     ) -> Option<AnnotatedBorrowFnSignature> {
1340         // Define a fallback for when we can't match a closure.
1341         let fallback = || {
1342             let is_closure = self.infcx.tcx.is_closure(self.mir_def_id);
1343             if is_closure {
1344                 None
1345             } else {
1346                 let ty = self.infcx.tcx.type_of(self.mir_def_id);
1347                 match ty.sty {
1348                     ty::TyKind::FnDef(_, _) | ty::TyKind::FnPtr(_) => self.annotate_fn_sig(
1349                         self.mir_def_id,
1350                         self.infcx.tcx.fn_sig(self.mir_def_id),
1351                     ),
1352                     _ => None,
1353                 }
1354             }
1355         };
1356
1357         // In order to determine whether we need to annotate, we need to check whether the reserve
1358         // place was an assignment into a temporary.
1359         //
1360         // If it was, we check whether or not that temporary is eventually assigned into the return
1361         // place. If it was, we can add annotations about the function's return type and arguments
1362         // and it'll make sense.
1363         let location = borrow.reserve_location;
1364         debug!(
1365             "annotate_argument_and_return_for_borrow: location={:?}",
1366             location
1367         );
1368         match &self.mir[location.block]
1369             .statements
1370             .get(location.statement_index)
1371         {
1372             Some(&Statement {
1373                 kind: StatementKind::Assign(ref reservation, _),
1374                 ..
1375             }) => {
1376                 debug!(
1377                     "annotate_argument_and_return_for_borrow: reservation={:?}",
1378                     reservation
1379                 );
1380                 // Check that the initial assignment of the reserve location is into a temporary.
1381                 let mut target = *match reservation {
1382                     Place::Local(local) if self.mir.local_kind(*local) == LocalKind::Temp => local,
1383                     _ => return None,
1384                 };
1385
1386                 // Next, look through the rest of the block, checking if we are assigning the
1387                 // `target` (that is, the place that contains our borrow) to anything.
1388                 let mut annotated_closure = None;
1389                 for stmt in &self.mir[location.block].statements[location.statement_index + 1..] {
1390                     debug!(
1391                         "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
1392                         target, stmt
1393                     );
1394                     if let StatementKind::Assign(Place::Local(assigned_to), box rvalue) = &stmt.kind
1395                     {
1396                         debug!(
1397                             "annotate_argument_and_return_for_borrow: assigned_to={:?} \
1398                              rvalue={:?}",
1399                             assigned_to, rvalue
1400                         );
1401                         // Check if our `target` was captured by a closure.
1402                         if let Rvalue::Aggregate(
1403                             box AggregateKind::Closure(def_id, substs),
1404                             operands,
1405                         ) = rvalue
1406                         {
1407                             for operand in operands {
1408                                 let assigned_from = match operand {
1409                                     Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1410                                         assigned_from
1411                                     }
1412                                     _ => continue,
1413                                 };
1414                                 debug!(
1415                                     "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1416                                     assigned_from
1417                                 );
1418
1419                                 // Find the local from the operand.
1420                                 let assigned_from_local = match assigned_from.local() {
1421                                     Some(local) => local,
1422                                     None => continue,
1423                                 };
1424
1425                                 if assigned_from_local != target {
1426                                     continue;
1427                                 }
1428
1429                                 // If a closure captured our `target` and then assigned
1430                                 // into a place then we should annotate the closure in
1431                                 // case it ends up being assigned into the return place.
1432                                 annotated_closure = self.annotate_fn_sig(
1433                                     *def_id,
1434                                     self.infcx.closure_sig(*def_id, *substs),
1435                                 );
1436                                 debug!(
1437                                     "annotate_argument_and_return_for_borrow: \
1438                                      annotated_closure={:?} assigned_from_local={:?} \
1439                                      assigned_to={:?}",
1440                                     annotated_closure, assigned_from_local, assigned_to
1441                                 );
1442
1443                                 if *assigned_to == mir::RETURN_PLACE {
1444                                     // If it was assigned directly into the return place, then
1445                                     // return now.
1446                                     return annotated_closure;
1447                                 } else {
1448                                     // Otherwise, update the target.
1449                                     target = *assigned_to;
1450                                 }
1451                             }
1452
1453                             // If none of our closure's operands matched, then skip to the next
1454                             // statement.
1455                             continue;
1456                         }
1457
1458                         // Otherwise, look at other types of assignment.
1459                         let assigned_from = match rvalue {
1460                             Rvalue::Ref(_, _, assigned_from) => assigned_from,
1461                             Rvalue::Use(operand) => match operand {
1462                                 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1463                                     assigned_from
1464                                 }
1465                                 _ => continue,
1466                             },
1467                             _ => continue,
1468                         };
1469                         debug!(
1470                             "annotate_argument_and_return_for_borrow: \
1471                              assigned_from={:?}",
1472                             assigned_from,
1473                         );
1474
1475                         // Find the local from the rvalue.
1476                         let assigned_from_local = match assigned_from.local() {
1477                             Some(local) => local,
1478                             None => continue,
1479                         };
1480                         debug!(
1481                             "annotate_argument_and_return_for_borrow: \
1482                              assigned_from_local={:?}",
1483                             assigned_from_local,
1484                         );
1485
1486                         // Check if our local matches the target - if so, we've assigned our
1487                         // borrow to a new place.
1488                         if assigned_from_local != target {
1489                             continue;
1490                         }
1491
1492                         // If we assigned our `target` into a new place, then we should
1493                         // check if it was the return place.
1494                         debug!(
1495                             "annotate_argument_and_return_for_borrow: \
1496                              assigned_from_local={:?} assigned_to={:?}",
1497                             assigned_from_local, assigned_to
1498                         );
1499                         if *assigned_to == mir::RETURN_PLACE {
1500                             // If it was then return the annotated closure if there was one,
1501                             // else, annotate this function.
1502                             return annotated_closure.or_else(fallback);
1503                         }
1504
1505                         // If we didn't assign into the return place, then we just update
1506                         // the target.
1507                         target = *assigned_to;
1508                     }
1509                 }
1510
1511                 // Check the terminator if we didn't find anything in the statements.
1512                 let terminator = &self.mir[location.block].terminator();
1513                 debug!(
1514                     "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
1515                     target, terminator
1516                 );
1517                 if let TerminatorKind::Call {
1518                     destination: Some((Place::Local(assigned_to), _)),
1519                     args,
1520                     ..
1521                 } = &terminator.kind
1522                 {
1523                     debug!(
1524                         "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
1525                         assigned_to, args
1526                     );
1527                     for operand in args {
1528                         let assigned_from = match operand {
1529                             Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1530                                 assigned_from
1531                             }
1532                             _ => continue,
1533                         };
1534                         debug!(
1535                             "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1536                             assigned_from,
1537                         );
1538
1539                         if let Some(assigned_from_local) = assigned_from.local() {
1540                             debug!(
1541                                 "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
1542                                 assigned_from_local,
1543                             );
1544
1545                             if *assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
1546                                 return annotated_closure.or_else(fallback);
1547                             }
1548                         }
1549                     }
1550                 }
1551             }
1552             _ => {}
1553         }
1554
1555         // If we haven't found an assignment into the return place, then we need not add
1556         // any annotations.
1557         debug!("annotate_argument_and_return_for_borrow: none found");
1558         None
1559     }
1560
1561     /// Annotate the first argument and return type of a function signature if they are
1562     /// references.
1563     fn annotate_fn_sig(
1564         &self,
1565         did: DefId,
1566         sig: ty::PolyFnSig<'tcx>,
1567     ) -> Option<AnnotatedBorrowFnSignature> {
1568         debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
1569         let is_closure = self.infcx.tcx.is_closure(did);
1570         let fn_node_id = self.infcx.tcx.hir.as_local_node_id(did)?;
1571         let fn_decl = self.infcx.tcx.hir.fn_decl(fn_node_id)?;
1572
1573         // We need to work out which arguments to highlight. We do this by looking
1574         // at the return type, where there are three cases:
1575         //
1576         // 1. If there are named arguments, then we should highlight the return type and
1577         //    highlight any of the arguments that are also references with that lifetime.
1578         //    If there are no arguments that have the same lifetime as the return type,
1579         //    then don't highlight anything.
1580         // 2. The return type is a reference with an anonymous lifetime. If this is
1581         //    the case, then we can take advantage of (and teach) the lifetime elision
1582         //    rules.
1583         //
1584         //    We know that an error is being reported. So the arguments and return type
1585         //    must satisfy the elision rules. Therefore, if there is a single argument
1586         //    then that means the return type and first (and only) argument have the same
1587         //    lifetime and the borrow isn't meeting that, we can highlight the argument
1588         //    and return type.
1589         //
1590         //    If there are multiple arguments then the first argument must be self (else
1591         //    it would not satisfy the elision rules), so we can highlight self and the
1592         //    return type.
1593         // 3. The return type is not a reference. In this case, we don't highlight
1594         //    anything.
1595         let return_ty = sig.output();
1596         match return_ty.skip_binder().sty {
1597             ty::TyKind::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
1598                 // This is case 1 from above, return type is a named reference so we need to
1599                 // search for relevant arguments.
1600                 let mut arguments = Vec::new();
1601                 for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
1602                     if let ty::TyKind::Ref(argument_region, _, _) = argument.sty {
1603                         if argument_region == return_region {
1604                             // Need to use the `rustc::ty` types to compare against the
1605                             // `return_region`. Then use the `rustc::hir` type to get only
1606                             // the lifetime span.
1607                             match &fn_decl.inputs[index].node {
1608                                 hir::TyKind::Rptr(lifetime, _) => {
1609                                     // With access to the lifetime, we can get
1610                                     // the span of it.
1611                                     arguments.push((*argument, lifetime.span));
1612                                 }
1613                                 _ => bug!("ty type is a ref but hir type is not"),
1614                             }
1615                         }
1616                     }
1617                 }
1618
1619                 // We need to have arguments. This shouldn't happen, but it's worth checking.
1620                 if arguments.is_empty() {
1621                     return None;
1622                 }
1623
1624                 // We use a mix of the HIR and the Ty types to get information
1625                 // as the HIR doesn't have full types for closure arguments.
1626                 let return_ty = *sig.output().skip_binder();
1627                 let mut return_span = fn_decl.output.span();
1628                 if let hir::FunctionRetTy::Return(ty) = fn_decl.output {
1629                     if let hir::TyKind::Rptr(lifetime, _) = ty.into_inner().node {
1630                         return_span = lifetime.span;
1631                     }
1632                 }
1633
1634                 Some(AnnotatedBorrowFnSignature::NamedFunction {
1635                     arguments,
1636                     return_ty,
1637                     return_span,
1638                 })
1639             }
1640             ty::TyKind::Ref(_, _, _) if is_closure => {
1641                 // This is case 2 from above but only for closures, return type is anonymous
1642                 // reference so we select
1643                 // the first argument.
1644                 let argument_span = fn_decl.inputs.first()?.span;
1645                 let argument_ty = sig.inputs().skip_binder().first()?;
1646
1647                 // Closure arguments are wrapped in a tuple, so we need to get the first
1648                 // from that.
1649                 if let ty::TyKind::Tuple(elems) = argument_ty.sty {
1650                     let argument_ty = elems.first()?;
1651                     if let ty::TyKind::Ref(_, _, _) = argument_ty.sty {
1652                         return Some(AnnotatedBorrowFnSignature::Closure {
1653                             argument_ty,
1654                             argument_span,
1655                         });
1656                     }
1657                 }
1658
1659                 None
1660             }
1661             ty::TyKind::Ref(_, _, _) => {
1662                 // This is also case 2 from above but for functions, return type is still an
1663                 // anonymous reference so we select the first argument.
1664                 let argument_span = fn_decl.inputs.first()?.span;
1665                 let argument_ty = sig.inputs().skip_binder().first()?;
1666
1667                 let return_span = fn_decl.output.span();
1668                 let return_ty = *sig.output().skip_binder();
1669
1670                 // We expect the first argument to be a reference.
1671                 match argument_ty.sty {
1672                     ty::TyKind::Ref(_, _, _) => {}
1673                     _ => return None,
1674                 }
1675
1676                 Some(AnnotatedBorrowFnSignature::AnonymousFunction {
1677                     argument_ty,
1678                     argument_span,
1679                     return_ty,
1680                     return_span,
1681                 })
1682             }
1683             _ => {
1684                 // This is case 3 from above, return type is not a reference so don't highlight
1685                 // anything.
1686                 None
1687             }
1688         }
1689     }
1690 }
1691
1692 #[derive(Debug)]
1693 enum AnnotatedBorrowFnSignature<'tcx> {
1694     NamedFunction {
1695         arguments: Vec<(ty::Ty<'tcx>, Span)>,
1696         return_ty: ty::Ty<'tcx>,
1697         return_span: Span,
1698     },
1699     AnonymousFunction {
1700         argument_ty: ty::Ty<'tcx>,
1701         argument_span: Span,
1702         return_ty: ty::Ty<'tcx>,
1703         return_span: Span,
1704     },
1705     Closure {
1706         argument_ty: ty::Ty<'tcx>,
1707         argument_span: Span,
1708     },
1709 }
1710
1711 impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
1712     /// Annotate the provided diagnostic with information about borrow from the fn signature that
1713     /// helps explain.
1714     fn emit(&self, diag: &mut DiagnosticBuilder<'_>) -> String {
1715         match self {
1716             AnnotatedBorrowFnSignature::Closure {
1717                 argument_ty,
1718                 argument_span,
1719             } => {
1720                 diag.span_label(
1721                     *argument_span,
1722                     format!("has type `{}`", self.get_name_for_ty(argument_ty, 0)),
1723                 );
1724
1725                 self.get_region_name_for_ty(argument_ty, 0)
1726             }
1727             AnnotatedBorrowFnSignature::AnonymousFunction {
1728                 argument_ty,
1729                 argument_span,
1730                 return_ty,
1731                 return_span,
1732             } => {
1733                 let argument_ty_name = self.get_name_for_ty(argument_ty, 0);
1734                 diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
1735
1736                 let return_ty_name = self.get_name_for_ty(return_ty, 0);
1737                 let types_equal = return_ty_name == argument_ty_name;
1738                 diag.span_label(
1739                     *return_span,
1740                     format!(
1741                         "{}has type `{}`",
1742                         if types_equal { "also " } else { "" },
1743                         return_ty_name,
1744                     ),
1745                 );
1746
1747                 diag.note(
1748                     "argument and return type have the same lifetime due to lifetime elision rules",
1749                 );
1750                 diag.note(
1751                     "to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch10-03-\
1752                      lifetime-syntax.html#lifetime-elision>",
1753                 );
1754
1755                 self.get_region_name_for_ty(return_ty, 0)
1756             }
1757             AnnotatedBorrowFnSignature::NamedFunction {
1758                 arguments,
1759                 return_ty,
1760                 return_span,
1761             } => {
1762                 // Region of return type and arguments checked to be the same earlier.
1763                 let region_name = self.get_region_name_for_ty(return_ty, 0);
1764                 for (_, argument_span) in arguments {
1765                     diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
1766                 }
1767
1768                 diag.span_label(
1769                     *return_span,
1770                     format!("also has lifetime `{}`", region_name,),
1771                 );
1772
1773                 diag.help(&format!(
1774                     "use data from the highlighted arguments which match the `{}` lifetime of \
1775                      the return type",
1776                     region_name,
1777                 ));
1778
1779                 region_name
1780             }
1781         }
1782     }
1783
1784     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
1785     /// name where required.
1786     fn get_name_for_ty(&self, ty: ty::Ty<'tcx>, counter: usize) -> String {
1787         // We need to add synthesized lifetimes where appropriate. We do
1788         // this by hooking into the pretty printer and telling it to label the
1789         // lifetimes without names with the value `'0`.
1790         match ty.sty {
1791             ty::TyKind::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
1792             | ty::TyKind::Ref(
1793                 ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }),
1794                 _,
1795                 _,
1796             ) => with_highlight_region_for_bound_region(*br, counter, || format!("{}", ty)),
1797             _ => format!("{}", ty),
1798         }
1799     }
1800
1801     /// Return the name of the provided `Ty` (that must be a reference)'s region with a
1802     /// synthesized lifetime name where required.
1803     fn get_region_name_for_ty(&self, ty: ty::Ty<'tcx>, counter: usize) -> String {
1804         match ty.sty {
1805             ty::TyKind::Ref(region, _, _) => match region {
1806                 ty::RegionKind::ReLateBound(_, br)
1807                 | ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }) => {
1808                     with_highlight_region_for_bound_region(*br, counter, || format!("{}", region))
1809                 }
1810                 _ => format!("{}", region),
1811             },
1812             _ => bug!("ty for annotation of borrow region is not a reference"),
1813         }
1814     }
1815 }
1816
1817 // The span(s) associated to a use of a place.
1818 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
1819 pub(super) enum UseSpans {
1820     // The access is caused by capturing a variable for a closure.
1821     ClosureUse {
1822         // The span of the args of the closure, including the `move` keyword if
1823         // it's present.
1824         args_span: Span,
1825         // The span of the first use of the captured variable inside the closure.
1826         var_span: Span,
1827     },
1828     // This access has a single span associated to it: common case.
1829     OtherUse(Span),
1830 }
1831
1832 impl UseSpans {
1833     pub(super) fn args_or_use(self) -> Span {
1834         match self {
1835             UseSpans::ClosureUse {
1836                 args_span: span, ..
1837             }
1838             | UseSpans::OtherUse(span) => span,
1839         }
1840     }
1841
1842     pub(super) fn var_or_use(self) -> Span {
1843         match self {
1844             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
1845         }
1846     }
1847
1848     // Add a span label to the arguments of the closure, if it exists.
1849     pub(super) fn args_span_label(self, err: &mut DiagnosticBuilder, message: impl Into<String>) {
1850         if let UseSpans::ClosureUse { args_span, .. } = self {
1851             err.span_label(args_span, message);
1852         }
1853     }
1854
1855     // Add a span label to the use of the captured variable, if it exists.
1856     pub(super) fn var_span_label(self, err: &mut DiagnosticBuilder, message: impl Into<String>) {
1857         if let UseSpans::ClosureUse { var_span, .. } = self {
1858             err.span_label(var_span, message);
1859         }
1860     }
1861
1862     pub(super) fn for_closure(self) -> bool {
1863         match self {
1864             UseSpans::ClosureUse { .. } => true,
1865             UseSpans::OtherUse(_) => false,
1866         }
1867     }
1868
1869     pub(super) fn or_else<F>(self, if_other: F) -> Self
1870     where
1871         F: FnOnce() -> Self,
1872     {
1873         match self {
1874             closure @ UseSpans::ClosureUse { .. } => closure,
1875             UseSpans::OtherUse(_) => if_other(),
1876         }
1877     }
1878 }
1879
1880 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1881     /// Finds the spans associated to a move or copy of move_place at location.
1882     pub(super) fn move_spans(
1883         &self,
1884         moved_place: &Place<'tcx>, // Could also be an upvar.
1885         location: Location,
1886     ) -> UseSpans {
1887         use self::UseSpans::*;
1888         use rustc::hir::ExprKind::Closure;
1889         use rustc::mir::AggregateKind;
1890
1891         let stmt = match self.mir[location.block]
1892             .statements
1893             .get(location.statement_index)
1894         {
1895             Some(stmt) => stmt,
1896             None => return OtherUse(self.mir.source_info(location).span),
1897         };
1898
1899         if let StatementKind::Assign(_, box Rvalue::Aggregate(ref kind, ref places)) = stmt.kind {
1900             if let AggregateKind::Closure(def_id, _) = **kind {
1901                 debug!("find_closure_move_span: found closure {:?}", places);
1902
1903                 if let Some(node_id) = self.infcx.tcx.hir.as_local_node_id(def_id) {
1904                     if let Closure(_, _, _, args_span, _) =
1905                         self.infcx.tcx.hir.expect_expr(node_id).node
1906                     {
1907                         if let Some(var_span) = self.infcx.tcx.with_freevars(node_id, |freevars| {
1908                             for (v, place) in freevars.iter().zip(places) {
1909                                 match place {
1910                                     Operand::Copy(place) | Operand::Move(place)
1911                                         if moved_place == place =>
1912                                     {
1913                                         debug!(
1914                                             "find_closure_move_span: found captured local {:?}",
1915                                             place
1916                                         );
1917                                         return Some(v.span);
1918                                     }
1919                                     _ => {}
1920                                 }
1921                             }
1922                             None
1923                         }) {
1924                             return ClosureUse {
1925                                 args_span,
1926                                 var_span,
1927                             };
1928                         }
1929                     }
1930                 }
1931             }
1932         }
1933
1934         return OtherUse(stmt.source_info.span);
1935     }
1936
1937     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
1938     /// and its usage of the local assigned at `location`.
1939     /// This is done by searching in statements succeeding `location`
1940     /// and originating from `maybe_closure_span`.
1941     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
1942         use self::UseSpans::*;
1943         use rustc::hir::ExprKind::Closure;
1944
1945         let local = match self.mir[location.block]
1946             .statements
1947             .get(location.statement_index)
1948         {
1949             Some(&Statement {
1950                 kind: StatementKind::Assign(Place::Local(local), _),
1951                 ..
1952             }) => local,
1953             _ => return OtherUse(use_span),
1954         };
1955
1956         if self.mir.local_kind(local) != LocalKind::Temp {
1957             // operands are always temporaries.
1958             return OtherUse(use_span);
1959         }
1960
1961         for stmt in &self.mir[location.block].statements[location.statement_index + 1..] {
1962             if let StatementKind::Assign(_, box Rvalue::Aggregate(ref kind, ref places)) = stmt.kind
1963             {
1964                 if let AggregateKind::Closure(def_id, _) = **kind {
1965                     debug!("find_closure_borrow_span: found closure {:?}", places);
1966
1967                     return if let Some(node_id) = self.infcx.tcx.hir.as_local_node_id(def_id) {
1968                         let args_span = if let Closure(_, _, _, span, _) =
1969                             self.infcx.tcx.hir.expect_expr(node_id).node
1970                         {
1971                             span
1972                         } else {
1973                             return OtherUse(use_span);
1974                         };
1975
1976                         self.infcx
1977                             .tcx
1978                             .with_freevars(node_id, |freevars| {
1979                                 for (v, place) in freevars.iter().zip(places) {
1980                                     match *place {
1981                                         Operand::Copy(Place::Local(l))
1982                                         | Operand::Move(Place::Local(l)) if local == l =>
1983                                         {
1984                                             debug!(
1985                                                 "find_closure_borrow_span: found captured local \
1986                                                  {:?}",
1987                                                 l
1988                                             );
1989                                             return Some(v.span);
1990                                         }
1991                                         _ => {}
1992                                     }
1993                                 }
1994                                 None
1995                             })
1996                             .map(|var_span| ClosureUse {
1997                                 args_span,
1998                                 var_span,
1999                             })
2000                             .unwrap_or(OtherUse(use_span))
2001                     } else {
2002                         OtherUse(use_span)
2003                     };
2004                 }
2005             }
2006
2007             if use_span != stmt.source_info.span {
2008                 break;
2009             }
2010         }
2011
2012         OtherUse(use_span)
2013     }
2014
2015     /// Helper to retrieve span(s) of given borrow from the current MIR
2016     /// representation
2017     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData) -> UseSpans {
2018         let span = self.mir.source_info(borrow.reserve_location).span;
2019         self.borrow_spans(span, borrow.reserve_location)
2020     }
2021 }