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         (moved_place, used_place, span): (&Place<'tcx>, &Place<'tcx>, Span),
  55         mpi: MovePathIndex,
  56     ) {
  57         debug!(
  58             "report_use_of_moved_or_uninitialized: context={:?} desired_action={:?} \
  59              moved_place={:?} used_place={:?} span={:?} mpi={:?}",
  60             context, desired_action, moved_place, used_place, span, mpi
  61         );
  62
  63         let use_spans = self.move_spans(moved_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(&used_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(used_place,
  93                                                                   IncludingDowncast(true)) {
  94                 Some(name) => format!("`{}`", name),
  95                 None => "value".to_owned(),
  96             };
  97             let mut err = self.infcx.tcx.cannot_act_on_uninitialized_variable(
  98                 span,
  99                 desired_action.as_noun(),
 100                 &self.describe_place_with_options(moved_place, IncludingDowncast(true))
 101                     .unwrap_or("_".to_owned()),
 102                 Origin::Mir,
 103             );
 104             err.span_label(span, format!("use of possibly uninitialized {}", item_msg));
 105
 106             use_spans.var_span_label(
 107                 &mut err,
 108                 format!("{} occurs due to use in closure", desired_action.as_noun()),
 109             );
 110
 111             err.buffer(&mut self.errors_buffer);
 112         } else {
 113             if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
 114                 if self.prefixes(&reported_place, PrefixSet::All)
 115                     .any(|p| p == used_place)
 116                 {
 117                     debug!(
 118                         "report_use_of_moved_or_uninitialized place: error suppressed \
 119                          mois={:?}",
 120                         move_out_indices
 121                     );
 122                     return;
 123                 }
 124             }
 125
 126             let msg = ""; //FIXME: add "partially " or "collaterally "
 127
 128             let mut err = self.infcx.tcx.cannot_act_on_moved_value(
 129                 span,
 130                 desired_action.as_noun(),
 131                 msg,
 132                 self.describe_place_with_options(&moved_place, IncludingDowncast(true)),
 133                 Origin::Mir,
 134             );
 135
 136             let mut is_loop_move = false;
 137             for move_site in &move_site_vec {
 138                 let move_out = self.move_data.moves[(*move_site).moi];
 139                 let moved_place = &self.move_data.move_paths[move_out.path].place;
 140
 141                 let move_spans = self.move_spans(moved_place, move_out.source);
 142                 let move_span = move_spans.args_or_use();
 143
 144                 let move_msg = if move_spans.for_closure() {
 145                     " into closure"
 146                 } else {
 147                     ""
 148                 };
 149
 150                 if span == move_span {
 151                     err.span_label(
 152                         span,
 153                         format!("value moved{} here, in previous iteration of loop", move_msg),
 154                     );
 155                     is_loop_move = true;
 156                 } else if move_site.traversed_back_edge {
 157                     err.span_label(
 158                         move_span,
 159                         format!(
 160                             "value moved{} here, in previous iteration of loop",
 161                             move_msg
 162                         ),
 163                     );
 164                 } else {
 165                     err.span_label(move_span, format!("value moved{} here", move_msg));
 166                     move_spans.var_span_label(&mut err, "variable moved due to use in closure");
 167                 };
 168             }
 169
 170             use_spans.var_span_label(
 171                 &mut err,
 172                 format!("{} occurs due to use in closure", desired_action.as_noun()),
 173             );
 174
 175             if !is_loop_move {
 176                 err.span_label(
 177                     span,
 178                     format!(
 179                         "value {} here after move",
 180                         desired_action.as_verb_in_past_tense()
 181                     ),
 182                 );
 183             }
 184
 185             if let Some(ty) = self.retrieve_type_for_place(used_place) {
 186                 let needs_note = match ty.sty {
 187                     ty::Closure(id, _) => {
 188                         let tables = self.infcx.tcx.typeck_tables_of(id);
 189                         let node_id = self.infcx.tcx.hir.as_local_node_id(id).unwrap();
 190                         let hir_id = self.infcx.tcx.hir.node_to_hir_id(node_id);
 191                         if tables.closure_kind_origins().get(hir_id).is_some() {
 192                             false
 193                         } else {
 194                             true
 195                         }
 196                     }
 197                     _ => true,
 198                 };
 199
 200                 if needs_note {
 201                     let mpi = self.move_data.moves[move_out_indices[0]].path;
 202                     let place = &self.move_data.move_paths[mpi].place;
 203
 204                     if let Some(ty) = self.retrieve_type_for_place(place) {
 205                         let note_msg = match self.describe_place_with_options(
 206                             place,
 207                             IncludingDowncast(true),
 208                         ) {
 209                             Some(name) => format!("`{}`", name),
 210                             None => "value".to_owned(),
 211                         };
 212
 213                         err.note(&format!(
 214                             "move occurs because {} has type `{}`, \
 215                              which does not implement the `Copy` trait",
 216                             note_msg, ty
 217                         ));
 218                     }
 219                 }
 220             }
 221
 222             if let Some((_, mut old_err)) = self.move_error_reported
 223                 .insert(move_out_indices, (used_place.clone(), err))
 224             {
 225                 // Cancel the old error so it doesn't ICE.
 226                 old_err.cancel();
 227             }
 228         }
 229     }
 230
 231     pub(super) fn report_move_out_while_borrowed(
 232         &mut self,
 233         context: Context,
 234         (place, _span): (&Place<'tcx>, Span),
 235         borrow: &BorrowData<'tcx>,
 236     ) {
 237         let tcx = self.infcx.tcx;
 238         let value_msg = match self.describe_place(place) {
 239             Some(name) => format!("`{}`", name),
 240             None => "value".to_owned(),
 241         };
 242         let borrow_msg = match self.describe_place(&borrow.borrowed_place) {
 243             Some(name) => format!("`{}`", name),
 244             None => "value".to_owned(),
 245         };
 246
 247         let borrow_spans = self.retrieve_borrow_spans(borrow);
 248         let borrow_span = borrow_spans.args_or_use();
 249
 250         let move_spans = self.move_spans(place, context.loc);
 251         let span = move_spans.args_or_use();
 252
 253         let mut err = tcx.cannot_move_when_borrowed(
 254             span,
 255             &self.describe_place(place).unwrap_or("_".to_owned()),
 256             Origin::Mir,
 257         );
 258         err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
 259         err.span_label(span, format!("move out of {} occurs here", value_msg));
 260
 261         borrow_spans.var_span_label(&mut err, "borrow occurs due to use in closure");
 262
 263         move_spans.var_span_label(&mut err, "move occurs due to use in closure");
 264
 265         self.explain_why_borrow_contains_point(context, borrow, None)
 266             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 267         err.buffer(&mut self.errors_buffer);
 268     }
 269
 270     pub(super) fn report_use_while_mutably_borrowed(
 271         &mut self,
 272         context: Context,
 273         (place, _span): (&Place<'tcx>, Span),
 274         borrow: &BorrowData<'tcx>,
 275     ) {
 276         let tcx = self.infcx.tcx;
 277
 278         let borrow_spans = self.retrieve_borrow_spans(borrow);
 279         let borrow_span = borrow_spans.args_or_use();
 280
 281         // Conflicting borrows are reported separately, so only check for move
 282         // captures.
 283         let use_spans = self.move_spans(place, context.loc);
 284         let span = use_spans.var_or_use();
 285
 286         let mut err = tcx.cannot_use_when_mutably_borrowed(
 287             span,
 288             &self.describe_place(place).unwrap_or("_".to_owned()),
 289             borrow_span,
 290             &self.describe_place(&borrow.borrowed_place)
 291                 .unwrap_or("_".to_owned()),
 292             Origin::Mir,
 293         );
 294
 295         borrow_spans.var_span_label(&mut err, {
 296             let place = &borrow.borrowed_place;
 297             let desc_place = self.describe_place(place).unwrap_or("_".to_owned());
 298
 299             format!("borrow occurs due to use of `{}` in closure", desc_place)
 300         });
 301
 302         self.explain_why_borrow_contains_point(context, borrow, None)
 303             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 304         err.buffer(&mut self.errors_buffer);
 305     }
 306
 307     pub(super) fn report_conflicting_borrow(
 308         &mut self,
 309         context: Context,
 310         (place, span): (&Place<'tcx>, Span),
 311         gen_borrow_kind: BorrowKind,
 312         issued_borrow: &BorrowData<'tcx>,
 313     ) {
 314         let issued_spans = self.retrieve_borrow_spans(issued_borrow);
 315         let issued_span = issued_spans.args_or_use();
 316
 317         let borrow_spans = self.borrow_spans(span, context.loc);
 318         let span = borrow_spans.args_or_use();
 319
 320         let desc_place = self.describe_place(place).unwrap_or("_".to_owned());
 321         let tcx = self.infcx.tcx;
 322
 323         let first_borrow_desc;
 324
 325         // FIXME: supply non-"" `opt_via` when appropriate
 326         let mut err = match (
 327             gen_borrow_kind,
 328             "immutable",
 329             "mutable",
 330             issued_borrow.kind,
 331             "immutable",
 332             "mutable",
 333         ) {
 334             (BorrowKind::Shared, lft, _, BorrowKind::Mut { .. }, _, rgt) => {
 335                 first_borrow_desc = "mutable ";
 336                 tcx.cannot_reborrow_already_borrowed(
 337                     span,
 338                     &desc_place,
 339                     "",
 340                     lft,
 341                     issued_span,
 342                     "it",
 343                     rgt,
 344                     "",
 345                     None,
 346                     Origin::Mir,
 347                 )
 348             }
 349             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Shared, rgt, _) => {
 350                 first_borrow_desc = "immutable ";
 351                 tcx.cannot_reborrow_already_borrowed(
 352                     span,
 353                     &desc_place,
 354                     "",
 355                     lft,
 356                     issued_span,
 357                     "it",
 358                     rgt,
 359                     "",
 360                     None,
 361                     Origin::Mir,
 362                 )
 363             }
 364
 365             (BorrowKind::Mut { .. }, _, _, BorrowKind::Mut { .. }, _, _) => {
 366                 first_borrow_desc = "first ";
 367                 tcx.cannot_mutably_borrow_multiply(
 368                     span,
 369                     &desc_place,
 370                     "",
 371                     issued_span,
 372                     "",
 373                     None,
 374                     Origin::Mir,
 375                 )
 376             }
 377
 378             (BorrowKind::Unique, _, _, BorrowKind::Unique, _, _) => {
 379                 first_borrow_desc = "first ";
 380                 tcx.cannot_uniquely_borrow_by_two_closures(
 381                     span,
 382                     &desc_place,
 383                     issued_span,
 384                     None,
 385                     Origin::Mir,
 386                 )
 387             }
 388
 389             (BorrowKind::Mut { .. }, _, _, BorrowKind::Shallow, _, _)
 390             | (BorrowKind::Unique, _, _, BorrowKind::Shallow, _, _) => {
 391                 let mut err = tcx.cannot_mutate_in_match_guard(
 392                     span,
 393                     issued_span,
 394                     &desc_place,
 395                     "mutably borrow",
 396                     Origin::Mir,
 397                 );
 398                 borrow_spans.var_span_label(
 399                     &mut err,
 400                     format!("borrow occurs due to use of `{}` in closure", desc_place),
 401                 );
 402                 err.buffer(&mut self.errors_buffer);
 403
 404                 return;
 405             }
 406
 407             (BorrowKind::Unique, _, _, _, _, _) => {
 408                 first_borrow_desc = "first ";
 409                 tcx.cannot_uniquely_borrow_by_one_closure(
 410                     span,
 411                     &desc_place,
 412                     "",
 413                     issued_span,
 414                     "it",
 415                     "",
 416                     None,
 417                     Origin::Mir,
 418                 )
 419             },
 420
 421             (BorrowKind::Shared, lft, _, BorrowKind::Unique, _, _) => {
 422                 first_borrow_desc = "first ";
 423                 tcx.cannot_reborrow_already_uniquely_borrowed(
 424                     span,
 425                     &desc_place,
 426                     "",
 427                     lft,
 428                     issued_span,
 429                     "",
 430                     None,
 431                     Origin::Mir,
 432                 )
 433             }
 434
 435             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Unique, _, _) => {
 436                 first_borrow_desc = "first ";
 437                 tcx.cannot_reborrow_already_uniquely_borrowed(
 438                     span,
 439                     &desc_place,
 440                     "",
 441                     lft,
 442                     issued_span,
 443                     "",
 444                     None,
 445                     Origin::Mir,
 446                 )
 447             }
 448
 449             (BorrowKind::Shallow, _, _, BorrowKind::Unique, _, _)
 450             | (BorrowKind::Shallow, _, _, BorrowKind::Mut { .. }, _, _) => {
 451                 // Shallow borrows are uses from the user's point of view.
 452                 self.report_use_while_mutably_borrowed(context, (place, span), issued_borrow);
 453                 return;
 454             }
 455             (BorrowKind::Shared, _, _, BorrowKind::Shared, _, _)
 456             | (BorrowKind::Shared, _, _, BorrowKind::Shallow, _, _)
 457             | (BorrowKind::Shallow, _, _, BorrowKind::Shared, _, _)
 458             | (BorrowKind::Shallow, _, _, BorrowKind::Shallow, _, _) => unreachable!(),
 459         };
 460
 461         if issued_spans == borrow_spans {
 462             borrow_spans.var_span_label(
 463                 &mut err,
 464                 format!("borrows occur due to use of `{}` in closure", desc_place),
 465             );
 466         } else {
 467             let borrow_place = &issued_borrow.borrowed_place;
 468             let borrow_place_desc = self.describe_place(borrow_place).unwrap_or("_".to_owned());
 469             issued_spans.var_span_label(
 470                 &mut err,
 471                 format!(
 472                     "first borrow occurs due to use of `{}` in closure",
 473                     borrow_place_desc
 474                 ),
 475             );
 476
 477             borrow_spans.var_span_label(
 478                 &mut err,
 479                 format!(
 480                     "second borrow occurs due to use of `{}` in closure",
 481                     desc_place
 482                 ),
 483             );
 484         }
 485
 486         self.explain_why_borrow_contains_point(context, issued_borrow, None)
 487             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, first_borrow_desc);
 488
 489         err.buffer(&mut self.errors_buffer);
 490     }
 491
 492     /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
 493     ///
 494     /// This means that some data referenced by `borrow` needs to live
 495     /// past the point where the StorageDeadOrDrop of `place` occurs.
 496     /// This is usually interpreted as meaning that `place` has too
 497     /// short a lifetime. (But sometimes it is more useful to report
 498     /// it as a more direct conflict between the execution of a
 499     /// `Drop::drop` with an aliasing borrow.)
 500     pub(super) fn report_borrowed_value_does_not_live_long_enough(
 501         &mut self,
 502         context: Context,
 503         borrow: &BorrowData<'tcx>,
 504         place_span: (&Place<'tcx>, Span),
 505         kind: Option<WriteKind>,
 506     ) {
 507         debug!(
 508             "report_borrowed_value_does_not_live_long_enough(\
 509              {:?}, {:?}, {:?}, {:?}\
 510              )",
 511             context, borrow, place_span, kind
 512         );
 513
 514         let drop_span = place_span.1;
 515         let scope_tree = self.infcx.tcx.region_scope_tree(self.mir_def_id);
 516         let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
 517             .last()
 518             .unwrap();
 519
 520         let borrow_spans = self.retrieve_borrow_spans(borrow);
 521         let borrow_span = borrow_spans.var_or_use();
 522
 523         let proper_span = match *root_place {
 524             Place::Local(local) => self.mir.local_decls[local].source_info.span,
 525             _ => drop_span,
 526         };
 527
 528         if self.access_place_error_reported
 529             .contains(&(root_place.clone(), borrow_span))
 530         {
 531             debug!(
 532                 "suppressing access_place error when borrow doesn't live long enough for {:?}",
 533                 borrow_span
 534             );
 535             return;
 536         }
 537
 538         self.access_place_error_reported
 539             .insert((root_place.clone(), borrow_span));
 540
 541         if let StorageDeadOrDrop::Destructor(dropped_ty) =
 542             self.classify_drop_access_kind(&borrow.borrowed_place)
 543         {
 544             // If a borrow of path `B` conflicts with drop of `D` (and
 545             // we're not in the uninteresting case where `B` is a
 546             // prefix of `D`), then report this as a more interesting
 547             // destructor conflict.
 548             if !borrow.borrowed_place.is_prefix_of(place_span.0) {
 549                 self.report_borrow_conflicts_with_destructor(
 550                     context, borrow, place_span, kind, dropped_ty,
 551                 );
 552                 return;
 553             }
 554         }
 555
 556         let err = match &self.describe_place(&borrow.borrowed_place) {
 557             Some(_) if self.is_place_thread_local(root_place) => {
 558                 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span)
 559             }
 560             Some(name) => self.report_local_value_does_not_live_long_enough(
 561                 context,
 562                 name,
 563                 &scope_tree,
 564                 &borrow,
 565                 drop_span,
 566                 borrow_spans,
 567                 kind.map(|k| (k, place_span.0)),
 568             ),
 569             None => self.report_temporary_value_does_not_live_long_enough(
 570                 context,
 571                 &scope_tree,
 572                 &borrow,
 573                 drop_span,
 574                 borrow_spans,
 575                 proper_span,
 576             ),
 577         };
 578
 579         err.buffer(&mut self.errors_buffer);
 580     }
 581
 582     fn report_local_value_does_not_live_long_enough(
 583         &mut self,
 584         context: Context,
 585         name: &String,
 586         scope_tree: &Lrc<ScopeTree>,
 587         borrow: &BorrowData<'tcx>,
 588         drop_span: Span,
 589         borrow_spans: UseSpans,
 590         kind_place: Option<(WriteKind, &Place<'tcx>)>,
 591     ) -> DiagnosticBuilder<'cx> {
 592         debug!(
 593             "report_local_value_does_not_live_long_enough(\
 594              {:?}, {:?}, {:?}, {:?}, {:?}, {:?}\
 595              )",
 596             context, name, scope_tree, borrow, drop_span, borrow_spans
 597         );
 598
 599         let borrow_span = borrow_spans.var_or_use();
 600         let mut err = self.infcx.tcx.path_does_not_live_long_enough(
 601             borrow_span,
 602             &format!("`{}`", name),
 603             Origin::Mir,
 604         );
 605
 606         let explanation = self.explain_why_borrow_contains_point(context, borrow, kind_place);
 607         if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
 608             let region_name = annotation.emit(&mut err);
 609
 610             err.span_label(
 611                 borrow_span,
 612                 format!("`{}` would have to be valid for `{}`...", name, region_name),
 613             );
 614
 615             if let Some(fn_node_id) = self.infcx.tcx.hir.as_local_node_id(self.mir_def_id) {
 616                 err.span_label(
 617                     drop_span,
 618                     format!(
 619                         "...but `{}` will be dropped here, when the function `{}` returns",
 620                         name,
 621                         self.infcx.tcx.hir.name(fn_node_id),
 622                     ),
 623                 );
 624
 625                 err.note(
 626                     "functions cannot return a borrow to data owned within the function's scope, \
 627                      functions can only return borrows to data passed as arguments",
 628                 );
 629                 err.note(
 630                     "to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch04-02-\
 631                      references-and-borrowing.html#dangling-references>",
 632                 );
 633             } else {
 634                 err.span_label(
 635                     drop_span,
 636                     format!("...but `{}` dropped here while still borrowed", name),
 637                 );
 638             }
 639
 640             if let BorrowExplanation::MustBeValidFor(..) = explanation {
 641             } else {
 642                 explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 643             }
 644         } else {
 645             err.span_label(borrow_span, "borrowed value does not live long enough");
 646             err.span_label(
 647                 drop_span,
 648                 format!("`{}` dropped here while still borrowed", name),
 649             );
 650
 651             borrow_spans.args_span_label(&mut err, "value captured here");
 652
 653             explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 654         }
 655
 656         err
 657     }
 658
 659     pub(super) fn report_borrow_conflicts_with_destructor(
 660         &mut self,
 661         context: Context,
 662         borrow: &BorrowData<'tcx>,
 663         (place, drop_span): (&Place<'tcx>, Span),
 664         kind: Option<WriteKind>,
 665         dropped_ty: ty::Ty<'tcx>,
 666     ) {
 667         debug!(
 668             "report_borrow_conflicts_with_destructor(\
 669              {:?}, {:?}, ({:?}, {:?}), {:?}\
 670              )",
 671             context, borrow, place, drop_span, kind,
 672         );
 673
 674         let borrow_spans = self.retrieve_borrow_spans(borrow);
 675         let borrow_span = borrow_spans.var_or_use();
 676
 677         let mut err = self.infcx
 678             .tcx
 679             .cannot_borrow_across_destructor(borrow_span, Origin::Mir);
 680
 681         let what_was_dropped = match self.describe_place(place) {
 682             Some(name) => format!("`{}`", name.as_str()),
 683             None => format!("temporary value"),
 684         };
 685
 686         let label = match self.describe_place(&borrow.borrowed_place) {
 687             Some(borrowed) => format!(
 688                 "here, drop of {D} needs exclusive access to `{B}`, \
 689                  because the type `{T}` implements the `Drop` trait",
 690                 D = what_was_dropped,
 691                 T = dropped_ty,
 692                 B = borrowed
 693             ),
 694             None => format!(
 695                 "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
 696                 D = what_was_dropped,
 697                 T = dropped_ty
 698             ),
 699         };
 700         err.span_label(drop_span, label);
 701
 702         // Only give this note and suggestion if they could be relevant.
 703         let explanation =
 704             self.explain_why_borrow_contains_point(context, borrow, kind.map(|k| (k, place)));
 705         match explanation {
 706             BorrowExplanation::UsedLater { .. }
 707             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
 708                 err.note("consider using a `let` binding to create a longer lived value");
 709             }
 710             _ => {}
 711         }
 712
 713         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 714
 715         err.buffer(&mut self.errors_buffer);
 716     }
 717
 718     fn report_thread_local_value_does_not_live_long_enough(
 719         &mut self,
 720         drop_span: Span,
 721         borrow_span: Span,
 722     ) -> DiagnosticBuilder<'cx> {
 723         debug!(
 724             "report_thread_local_value_does_not_live_long_enough(\
 725              {:?}, {:?}\
 726              )",
 727             drop_span, borrow_span
 728         );
 729
 730         let mut err = self.infcx
 731             .tcx
 732             .thread_local_value_does_not_live_long_enough(borrow_span, Origin::Mir);
 733
 734         err.span_label(
 735             borrow_span,
 736             "thread-local variables cannot be borrowed beyond the end of the function",
 737         );
 738         err.span_label(drop_span, "end of enclosing function is here");
 739
 740         err
 741     }
 742
 743     fn report_temporary_value_does_not_live_long_enough(
 744         &mut self,
 745         context: Context,
 746         scope_tree: &Lrc<ScopeTree>,
 747         borrow: &BorrowData<'tcx>,
 748         drop_span: Span,
 749         borrow_spans: UseSpans,
 750         proper_span: Span,
 751     ) -> DiagnosticBuilder<'cx> {
 752         debug!(
 753             "report_temporary_value_does_not_live_long_enough(\
 754              {:?}, {:?}, {:?}, {:?}, {:?}\
 755              )",
 756             context, scope_tree, borrow, drop_span, proper_span
 757         );
 758
 759         let tcx = self.infcx.tcx;
 760         let mut err = tcx.temporary_value_borrowed_for_too_long(proper_span, Origin::Mir);
 761         err.span_label(
 762             proper_span,
 763             "creates a temporary which is freed while still in use",
 764         );
 765         err.span_label(
 766             drop_span,
 767             "temporary value is freed at the end of this statement",
 768         );
 769
 770         let explanation = self.explain_why_borrow_contains_point(context, borrow, None);
 771         match explanation {
 772             BorrowExplanation::UsedLater(..)
 773             | BorrowExplanation::UsedLaterInLoop(..)
 774             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
 775                 // Only give this note and suggestion if it could be relevant.
 776                 err.note("consider using a `let` binding to create a longer lived value");
 777             }
 778             _ => {}
 779         }
 780         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 781
 782         borrow_spans.args_span_label(&mut err, "value captured here");
 783
 784         err
 785     }
 786
 787     fn get_moved_indexes(&mut self, context: Context, mpi: MovePathIndex) -> Vec<MoveSite> {
 788         let mir = self.mir;
 789
 790         let mut stack = Vec::new();
 791         stack.extend(mir.predecessor_locations(context.loc).map(|predecessor| {
 792             let is_back_edge = context.loc.dominates(predecessor, &self.dominators);
 793             (predecessor, is_back_edge)
 794         }));
 795
 796         let mut visited = FxHashSet();
 797         let mut result = vec![];
 798
 799         'dfs: while let Some((location, is_back_edge)) = stack.pop() {
 800             debug!(
 801                 "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
 802                 location, is_back_edge
 803             );
 804
 805             if !visited.insert(location) {
 806                 continue;
 807             }
 808
 809             // check for moves
 810             let stmt_kind = mir[location.block]
 811                 .statements
 812                 .get(location.statement_index)
 813                 .map(|s| &s.kind);
 814             if let Some(StatementKind::StorageDead(..)) = stmt_kind {
 815                 // this analysis only tries to find moves explicitly
 816                 // written by the user, so we ignore the move-outs
 817                 // created by `StorageDead` and at the beginning
 818                 // of a function.
 819             } else {
 820                 // If we are found a use of a.b.c which was in error, then we want to look for
 821                 // moves not only of a.b.c but also a.b and a.
 822                 //
 823                 // Note that the moves data already includes "parent" paths, so we don't have to
 824                 // worry about the other case: that is, if there is a move of a.b.c, it is already
 825                 // marked as a move of a.b and a as well, so we will generate the correct errors
 826                 // there.
 827                 let mut mpis = vec![mpi];
 828                 let move_paths = &self.move_data.move_paths;
 829                 mpis.extend(move_paths[mpi].parents(move_paths));
 830
 831                 for moi in &self.move_data.loc_map[location] {
 832                     debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
 833                     if mpis.contains(&self.move_data.moves[*moi].path) {
 834                         debug!("report_use_of_moved_or_uninitialized: found");
 835                         result.push(MoveSite {
 836                             moi: *moi,
 837                             traversed_back_edge: is_back_edge,
 838                         });
 839
 840                         // Strictly speaking, we could continue our DFS here. There may be
 841                         // other moves that can reach the point of error. But it is kind of
 842                         // confusing to highlight them.
 843                         //
 844                         // Example:
 845                         //
 846                         // ```
 847                         // let a = vec![];
 848                         // let b = a;
 849                         // let c = a;
 850                         // drop(a); // <-- current point of error
 851                         // ```
 852                         //
 853                         // Because we stop the DFS here, we only highlight `let c = a`,
 854                         // and not `let b = a`. We will of course also report an error at
 855                         // `let c = a` which highlights `let b = a` as the move.
 856                         continue 'dfs;
 857                     }
 858                 }
 859             }
 860
 861             // check for inits
 862             let mut any_match = false;
 863             drop_flag_effects::for_location_inits(
 864                 self.infcx.tcx,
 865                 self.mir,
 866                 self.move_data,
 867                 location,
 868                 |m| {
 869                     if m == mpi {
 870                         any_match = true;
 871                     }
 872                 },
 873             );
 874             if any_match {
 875                 continue 'dfs;
 876             }
 877
 878             stack.extend(mir.predecessor_locations(location).map(|predecessor| {
 879                 let back_edge = location.dominates(predecessor, &self.dominators);
 880                 (predecessor, is_back_edge || back_edge)
 881             }));
 882         }
 883
 884         result
 885     }
 886
 887     pub(super) fn report_illegal_mutation_of_borrowed(
 888         &mut self,
 889         context: Context,
 890         (place, span): (&Place<'tcx>, Span),
 891         loan: &BorrowData<'tcx>,
 892     ) {
 893         let loan_spans = self.retrieve_borrow_spans(loan);
 894         let loan_span = loan_spans.args_or_use();
 895
 896         let tcx = self.infcx.tcx;
 897         let mut err = if loan.kind == BorrowKind::Shallow {
 898             tcx.cannot_mutate_in_match_guard(
 899                 span,
 900                 loan_span,
 901                 &self.describe_place(place).unwrap_or("_".to_owned()),
 902                 "assign",
 903                 Origin::Mir,
 904             )
 905         } else {
 906             tcx.cannot_assign_to_borrowed(
 907                 span,
 908                 loan_span,
 909                 &self.describe_place(place).unwrap_or("_".to_owned()),
 910                 Origin::Mir,
 911             )
 912         };
 913
 914         loan_spans.var_span_label(&mut err, "borrow occurs due to use in closure");
 915
 916         self.explain_why_borrow_contains_point(context, loan, None)
 917             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 918
 919         err.buffer(&mut self.errors_buffer);
 920     }
 921
 922     /// Reports an illegal reassignment; for example, an assignment to
 923     /// (part of) a non-`mut` local that occurs potentially after that
 924     /// local has already been initialized. `place` is the path being
 925     /// assigned; `err_place` is a place providing a reason why
 926     /// `place` is not mutable (e.g. the non-`mut` local `x` in an
 927     /// assignment to `x.f`).
 928     pub(super) fn report_illegal_reassignment(
 929         &mut self,
 930         _context: Context,
 931         (place, span): (&Place<'tcx>, Span),
 932         assigned_span: Span,
 933         err_place: &Place<'tcx>,
 934     ) {
 935         let (from_arg, local_decl) = if let Place::Local(local) = *err_place {
 936             if let LocalKind::Arg = self.mir.local_kind(local) {
 937                 (true, Some(&self.mir.local_decls[local]))
 938             } else {
 939                 (false, Some(&self.mir.local_decls[local]))
 940             }
 941         } else {
 942             (false, None)
 943         };
 944
 945         // If root local is initialized immediately (everything apart from let
 946         // PATTERN;) then make the error refer to that local, rather than the
 947         // place being assigned later.
 948         let (place_description, assigned_span) = match local_decl {
 949             Some(LocalDecl {
 950                 is_user_variable: Some(ClearCrossCrate::Clear),
 951                 ..
 952             })
 953             | Some(LocalDecl {
 954                 is_user_variable:
 955                     Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
 956                         opt_match_place: None,
 957                         ..
 958                     }))),
 959                 ..
 960             })
 961             | Some(LocalDecl {
 962                 is_user_variable: None,
 963                 ..
 964             })
 965             | None => (self.describe_place(place), assigned_span),
 966             Some(decl) => (self.describe_place(err_place), decl.source_info.span),
 967         };
 968
 969         let mut err = self.infcx.tcx.cannot_reassign_immutable(
 970             span,
 971             place_description.as_ref().map(AsRef::as_ref).unwrap_or("_"),
 972             from_arg,
 973             Origin::Mir,
 974         );
 975         let msg = if from_arg {
 976             "cannot assign to immutable argument"
 977         } else {
 978             "cannot assign twice to immutable variable"
 979         };
 980         if span != assigned_span {
 981             if !from_arg {
 982                 let value_msg = match place_description {
 983                     Some(name) => format!("`{}`", name),
 984                     None => "value".to_owned(),
 985                 };
 986                 err.span_label(assigned_span, format!("first assignment to {}", value_msg));
 987             }
 988         }
 989         if let Some(decl) = local_decl {
 990             if let Some(name) = decl.name {
 991                 if decl.can_be_made_mutable() {
 992                     err.span_suggestion_with_applicability(
 993                         decl.source_info.span,
 994                         "make this binding mutable",
 995                         format!("mut {}", name),
 996                         Applicability::MachineApplicable,
 997                     );
 998                 }
 999             }
1000         }
1001         err.span_label(span, msg);
1002         err.buffer(&mut self.errors_buffer);
1003     }
1004 }
1005
1006 pub(super) struct IncludingDowncast(bool);
1007
1008 /// Which case a StorageDeadOrDrop is for.
1009 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
1010 enum StorageDeadOrDrop<'tcx> {
1011     LocalStorageDead,
1012     BoxedStorageDead,
1013     Destructor(ty::Ty<'tcx>),
1014 }
1015
1016 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1017     // End-user visible description of `place` if one can be found. If the
1018     // place is a temporary for instance, None will be returned.
1019     pub(super) fn describe_place(&self, place: &Place<'tcx>) -> Option<String> {
1020         self.describe_place_with_options(place, IncludingDowncast(false))
1021     }
1022
1023     // End-user visible description of `place` if one can be found. If the
1024     // place is a temporary for instance, None will be returned.
1025     // `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
1026     // `Downcast` and `IncludingDowncast` is true
1027     pub(super) fn describe_place_with_options(
1028         &self,
1029         place: &Place<'tcx>,
1030         including_downcast: IncludingDowncast,
1031     ) -> Option<String> {
1032         let mut buf = String::new();
1033         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
1034             Ok(()) => Some(buf),
1035             Err(()) => None,
1036         }
1037     }
1038
1039     // Appends end-user visible description of `place` to `buf`.
1040     fn append_place_to_string(
1041         &self,
1042         place: &Place<'tcx>,
1043         buf: &mut String,
1044         mut autoderef: bool,
1045         including_downcast: &IncludingDowncast,
1046     ) -> Result<(), ()> {
1047         match *place {
1048             Place::Promoted(_) => {
1049                 buf.push_str("promoted");
1050             }
1051             Place::Local(local) => {
1052                 self.append_local_to_string(local, buf)?;
1053             }
1054             Place::Static(ref static_) => {
1055                 buf.push_str(&self.infcx.tcx.item_name(static_.def_id).to_string());
1056             }
1057             Place::Projection(ref proj) => {
1058                 match proj.elem {
1059                     ProjectionElem::Deref => {
1060                         let upvar_field_projection =
1061                             place.is_upvar_field_projection(self.mir, &self.infcx.tcx);
1062                         if let Some(field) = upvar_field_projection {
1063                             let var_index = field.index();
1064                             let name = self.mir.upvar_decls[var_index].debug_name.to_string();
1065                             if self.mir.upvar_decls[var_index].by_ref {
1066                                 buf.push_str(&name);
1067                             } else {
1068                                 buf.push_str(&format!("*{}", &name));
1069                             }
1070                         } else {
1071                             if autoderef {
1072                                 self.append_place_to_string(
1073                                     &proj.base,
1074                                     buf,
1075                                     autoderef,
1076                                     &including_downcast,
1077                                 )?;
1078                             } else if let Place::Local(local) = proj.base {
1079                                 if let Some(ClearCrossCrate::Set(BindingForm::RefForGuard)) =
1080                                     self.mir.local_decls[local].is_user_variable
1081                                 {
1082                                     self.append_place_to_string(
1083                                         &proj.base,
1084                                         buf,
1085                                         autoderef,
1086                                         &including_downcast,
1087                                     )?;
1088                                 } else {
1089                                     buf.push_str(&"*");
1090                                     self.append_place_to_string(
1091                                         &proj.base,
1092                                         buf,
1093                                         autoderef,
1094                                         &including_downcast,
1095                                     )?;
1096                                 }
1097                             } else {
1098                                 buf.push_str(&"*");
1099                                 self.append_place_to_string(
1100                                     &proj.base,
1101                                     buf,
1102                                     autoderef,
1103                                     &including_downcast,
1104                                 )?;
1105                             }
1106                         }
1107                     }
1108                     ProjectionElem::Downcast(..) => {
1109                         self.append_place_to_string(
1110                             &proj.base,
1111                             buf,
1112                             autoderef,
1113                             &including_downcast,
1114                         )?;
1115                         if including_downcast.0 {
1116                             return Err(());
1117                         }
1118                     }
1119                     ProjectionElem::Field(field, _ty) => {
1120                         autoderef = true;
1121
1122                         let upvar_field_projection =
1123                             place.is_upvar_field_projection(self.mir, &self.infcx.tcx);
1124                         if let Some(field) = upvar_field_projection {
1125                             let var_index = field.index();
1126                             let name = self.mir.upvar_decls[var_index].debug_name.to_string();
1127                             buf.push_str(&name);
1128                         } else {
1129                             let field_name = self.describe_field(&proj.base, field);
1130                             self.append_place_to_string(
1131                                 &proj.base,
1132                                 buf,
1133                                 autoderef,
1134                                 &including_downcast,
1135                             )?;
1136                             buf.push_str(&format!(".{}", field_name));
1137                         }
1138                     }
1139                     ProjectionElem::Index(index) => {
1140                         autoderef = true;
1141
1142                         self.append_place_to_string(
1143                             &proj.base,
1144                             buf,
1145                             autoderef,
1146                             &including_downcast,
1147                         )?;
1148                         buf.push_str("[");
1149                         if self.append_local_to_string(index, buf).is_err() {
1150                             buf.push_str("..");
1151                         }
1152                         buf.push_str("]");
1153                     }
1154                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
1155                         autoderef = true;
1156                         // Since it isn't possible to borrow an element on a particular index and
1157                         // then use another while the borrow is held, don't output indices details
1158                         // to avoid confusing the end-user
1159                         self.append_place_to_string(
1160                             &proj.base,
1161                             buf,
1162                             autoderef,
1163                             &including_downcast,
1164                         )?;
1165                         buf.push_str(&"[..]");
1166                     }
1167                 };
1168             }
1169         }
1170
1171         Ok(())
1172     }
1173
1174     // Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
1175     // a name, then `Err` is returned
1176     fn append_local_to_string(&self, local_index: Local, buf: &mut String) -> Result<(), ()> {
1177         let local = &self.mir.local_decls[local_index];
1178         match local.name {
1179             Some(name) => {
1180                 buf.push_str(&name.to_string());
1181                 Ok(())
1182             }
1183             None => Err(()),
1184         }
1185     }
1186
1187     // End-user visible description of the `field`nth field of `base`
1188     fn describe_field(&self, base: &Place, field: Field) -> String {
1189         match *base {
1190             Place::Local(local) => {
1191                 let local = &self.mir.local_decls[local];
1192                 self.describe_field_from_ty(&local.ty, field)
1193             }
1194             Place::Promoted(ref prom) => self.describe_field_from_ty(&prom.1, field),
1195             Place::Static(ref static_) => self.describe_field_from_ty(&static_.ty, field),
1196             Place::Projection(ref proj) => match proj.elem {
1197                 ProjectionElem::Deref => self.describe_field(&proj.base, field),
1198                 ProjectionElem::Downcast(def, variant_index) => format!(
1199                     "{}",
1200                     def.variants[variant_index].fields[field.index()].ident
1201                 ),
1202                 ProjectionElem::Field(_, field_type) => {
1203                     self.describe_field_from_ty(&field_type, field)
1204                 }
1205                 ProjectionElem::Index(..)
1206                 | ProjectionElem::ConstantIndex { .. }
1207                 | ProjectionElem::Subslice { .. } => {
1208                     self.describe_field(&proj.base, field).to_string()
1209                 }
1210             },
1211         }
1212     }
1213
1214     // End-user visible description of the `field_index`nth field of `ty`
1215     fn describe_field_from_ty(&self, ty: &ty::Ty, field: Field) -> String {
1216         if ty.is_box() {
1217             // If the type is a box, the field is described from the boxed type
1218             self.describe_field_from_ty(&ty.boxed_ty(), field)
1219         } else {
1220             match ty.sty {
1221                 ty::Adt(def, _) => if def.is_enum() {
1222                     field.index().to_string()
1223                 } else {
1224                     def.non_enum_variant().fields[field.index()]
1225                         .ident
1226                         .to_string()
1227                 },
1228                 ty::Tuple(_) => field.index().to_string(),
1229                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
1230                     self.describe_field_from_ty(&ty, field)
1231                 }
1232                 ty::Array(ty, _) | ty::Slice(ty) => self.describe_field_from_ty(&ty, field),
1233                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
1234                     // Convert the def-id into a node-id. node-ids are only valid for
1235                     // the local code in the current crate, so this returns an `Option` in case
1236                     // the closure comes from another crate. But in that case we wouldn't
1237                     // be borrowck'ing it, so we can just unwrap:
1238                     let node_id = self.infcx.tcx.hir.as_local_node_id(def_id).unwrap();
1239                     let freevar = self.infcx
1240                         .tcx
1241                         .with_freevars(node_id, |fv| fv[field.index()]);
1242
1243                     self.infcx.tcx.hir.name(freevar.var_id()).to_string()
1244                 }
1245                 _ => {
1246                     // Might need a revision when the fields in trait RFC is implemented
1247                     // (https://github.com/rust-lang/rfcs/pull/1546)
1248                     bug!(
1249                         "End-user description not implemented for field access on `{:?}`",
1250                         ty.sty
1251                     );
1252                 }
1253             }
1254         }
1255     }
1256
1257     // Retrieve type of a place for the current MIR representation
1258     fn retrieve_type_for_place(&self, place: &Place<'tcx>) -> Option<ty::Ty> {
1259         match place {
1260             Place::Local(local) => {
1261                 let local = &self.mir.local_decls[*local];
1262                 Some(local.ty)
1263             }
1264             Place::Promoted(ref prom) => Some(prom.1),
1265             Place::Static(ref st) => Some(st.ty),
1266             Place::Projection(ref proj) => match proj.elem {
1267                 ProjectionElem::Field(_, ty) => Some(ty),
1268                 _ => None,
1269             },
1270         }
1271     }
1272
1273     /// Check if a place is a thread-local static.
1274     pub fn is_place_thread_local(&self, place: &Place<'tcx>) -> bool {
1275         if let Place::Static(statik) = place {
1276             let attrs = self.infcx.tcx.get_attrs(statik.def_id);
1277             let is_thread_local = attrs.iter().any(|attr| attr.check_name("thread_local"));
1278
1279             debug!(
1280                 "is_place_thread_local: attrs={:?} is_thread_local={:?}",
1281                 attrs, is_thread_local
1282             );
1283             is_thread_local
1284         } else {
1285             debug!("is_place_thread_local: no");
1286             false
1287         }
1288     }
1289
1290     fn classify_drop_access_kind(&self, place: &Place<'tcx>) -> StorageDeadOrDrop<'tcx> {
1291         let tcx = self.infcx.tcx;
1292         match place {
1293             Place::Local(_) | Place::Static(_) | Place::Promoted(_) => {
1294                 StorageDeadOrDrop::LocalStorageDead
1295             }
1296             Place::Projection(box PlaceProjection { base, elem }) => {
1297                 let base_access = self.classify_drop_access_kind(base);
1298                 match elem {
1299                     ProjectionElem::Deref => match base_access {
1300                         StorageDeadOrDrop::LocalStorageDead
1301                         | StorageDeadOrDrop::BoxedStorageDead => {
1302                             assert!(
1303                                 base.ty(self.mir, tcx).to_ty(tcx).is_box(),
1304                                 "Drop of value behind a reference or raw pointer"
1305                             );
1306                             StorageDeadOrDrop::BoxedStorageDead
1307                         }
1308                         StorageDeadOrDrop::Destructor(_) => base_access,
1309                     },
1310                     ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
1311                         let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
1312                         match base_ty.sty {
1313                             ty::Adt(def, _) if def.has_dtor(tcx) => {
1314                                 // Report the outermost adt with a destructor
1315                                 match base_access {
1316                                     StorageDeadOrDrop::Destructor(_) => base_access,
1317                                     StorageDeadOrDrop::LocalStorageDead
1318                                     | StorageDeadOrDrop::BoxedStorageDead => {
1319                                         StorageDeadOrDrop::Destructor(base_ty)
1320                                     }
1321                                 }
1322                             }
1323                             _ => base_access,
1324                         }
1325                     }
1326
1327                     ProjectionElem::ConstantIndex { .. }
1328                     | ProjectionElem::Subslice { .. }
1329                     | ProjectionElem::Index(_) => base_access,
1330                 }
1331             }
1332         }
1333     }
1334
1335     /// Annotate argument and return type of function and closure with (synthesized) lifetime for
1336     /// borrow of local value that does not live long enough.
1337     fn annotate_argument_and_return_for_borrow(
1338         &self,
1339         borrow: &BorrowData<'tcx>,
1340     ) -> Option<AnnotatedBorrowFnSignature> {
1341         // Define a fallback for when we can't match a closure.
1342         let fallback = || {
1343             let is_closure = self.infcx.tcx.is_closure(self.mir_def_id);
1344             if is_closure {
1345                 None
1346             } else {
1347                 let ty = self.infcx.tcx.type_of(self.mir_def_id);
1348                 match ty.sty {
1349                     ty::TyKind::FnDef(_, _) | ty::TyKind::FnPtr(_) => self.annotate_fn_sig(
1350                         self.mir_def_id,
1351                         self.infcx.tcx.fn_sig(self.mir_def_id),
1352                     ),
1353                     _ => None,
1354                 }
1355             }
1356         };
1357
1358         // In order to determine whether we need to annotate, we need to check whether the reserve
1359         // place was an assignment into a temporary.
1360         //
1361         // If it was, we check whether or not that temporary is eventually assigned into the return
1362         // place. If it was, we can add annotations about the function's return type and arguments
1363         // and it'll make sense.
1364         let location = borrow.reserve_location;
1365         debug!(
1366             "annotate_argument_and_return_for_borrow: location={:?}",
1367             location
1368         );
1369         match &self.mir[location.block]
1370             .statements
1371             .get(location.statement_index)
1372         {
1373             Some(&Statement {
1374                 kind: StatementKind::Assign(ref reservation, _),
1375                 ..
1376             }) => {
1377                 debug!(
1378                     "annotate_argument_and_return_for_borrow: reservation={:?}",
1379                     reservation
1380                 );
1381                 // Check that the initial assignment of the reserve location is into a temporary.
1382                 let mut target = *match reservation {
1383                     Place::Local(local) if self.mir.local_kind(*local) == LocalKind::Temp => local,
1384                     _ => return None,
1385                 };
1386
1387                 // Next, look through the rest of the block, checking if we are assigning the
1388                 // `target` (that is, the place that contains our borrow) to anything.
1389                 let mut annotated_closure = None;
1390                 for stmt in &self.mir[location.block].statements[location.statement_index + 1..] {
1391                     debug!(
1392                         "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
1393                         target, stmt
1394                     );
1395                     if let StatementKind::Assign(Place::Local(assigned_to), box rvalue) = &stmt.kind
1396                     {
1397                         debug!(
1398                             "annotate_argument_and_return_for_borrow: assigned_to={:?} \
1399                              rvalue={:?}",
1400                             assigned_to, rvalue
1401                         );
1402                         // Check if our `target` was captured by a closure.
1403                         if let Rvalue::Aggregate(
1404                             box AggregateKind::Closure(def_id, substs),
1405                             operands,
1406                         ) = rvalue
1407                         {
1408                             for operand in operands {
1409                                 let assigned_from = match operand {
1410                                     Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1411                                         assigned_from
1412                                     }
1413                                     _ => continue,
1414                                 };
1415                                 debug!(
1416                                     "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1417                                     assigned_from
1418                                 );
1419
1420                                 // Find the local from the operand.
1421                                 let assigned_from_local = match assigned_from.local() {
1422                                     Some(local) => local,
1423                                     None => continue,
1424                                 };
1425
1426                                 if assigned_from_local != target {
1427                                     continue;
1428                                 }
1429
1430                                 // If a closure captured our `target` and then assigned
1431                                 // into a place then we should annotate the closure in
1432                                 // case it ends up being assigned into the return place.
1433                                 annotated_closure = self.annotate_fn_sig(
1434                                     *def_id,
1435                                     self.infcx.closure_sig(*def_id, *substs),
1436                                 );
1437                                 debug!(
1438                                     "annotate_argument_and_return_for_borrow: \
1439                                      annotated_closure={:?} assigned_from_local={:?} \
1440                                      assigned_to={:?}",
1441                                     annotated_closure, assigned_from_local, assigned_to
1442                                 );
1443
1444                                 if *assigned_to == mir::RETURN_PLACE {
1445                                     // If it was assigned directly into the return place, then
1446                                     // return now.
1447                                     return annotated_closure;
1448                                 } else {
1449                                     // Otherwise, update the target.
1450                                     target = *assigned_to;
1451                                 }
1452                             }
1453
1454                             // If none of our closure's operands matched, then skip to the next
1455                             // statement.
1456                             continue;
1457                         }
1458
1459                         // Otherwise, look at other types of assignment.
1460                         let assigned_from = match rvalue {
1461                             Rvalue::Ref(_, _, assigned_from) => assigned_from,
1462                             Rvalue::Use(operand) => match operand {
1463                                 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1464                                     assigned_from
1465                                 }
1466                                 _ => continue,
1467                             },
1468                             _ => continue,
1469                         };
1470                         debug!(
1471                             "annotate_argument_and_return_for_borrow: \
1472                              assigned_from={:?}",
1473                             assigned_from,
1474                         );
1475
1476                         // Find the local from the rvalue.
1477                         let assigned_from_local = match assigned_from.local() {
1478                             Some(local) => local,
1479                             None => continue,
1480                         };
1481                         debug!(
1482                             "annotate_argument_and_return_for_borrow: \
1483                              assigned_from_local={:?}",
1484                             assigned_from_local,
1485                         );
1486
1487                         // Check if our local matches the target - if so, we've assigned our
1488                         // borrow to a new place.
1489                         if assigned_from_local != target {
1490                             continue;
1491                         }
1492
1493                         // If we assigned our `target` into a new place, then we should
1494                         // check if it was the return place.
1495                         debug!(
1496                             "annotate_argument_and_return_for_borrow: \
1497                              assigned_from_local={:?} assigned_to={:?}",
1498                             assigned_from_local, assigned_to
1499                         );
1500                         if *assigned_to == mir::RETURN_PLACE {
1501                             // If it was then return the annotated closure if there was one,
1502                             // else, annotate this function.
1503                             return annotated_closure.or_else(fallback);
1504                         }
1505
1506                         // If we didn't assign into the return place, then we just update
1507                         // the target.
1508                         target = *assigned_to;
1509                     }
1510                 }
1511
1512                 // Check the terminator if we didn't find anything in the statements.
1513                 let terminator = &self.mir[location.block].terminator();
1514                 debug!(
1515                     "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
1516                     target, terminator
1517                 );
1518                 if let TerminatorKind::Call {
1519                     destination: Some((Place::Local(assigned_to), _)),
1520                     args,
1521                     ..
1522                 } = &terminator.kind
1523                 {
1524                     debug!(
1525                         "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
1526                         assigned_to, args
1527                     );
1528                     for operand in args {
1529                         let assigned_from = match operand {
1530                             Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1531                                 assigned_from
1532                             }
1533                             _ => continue,
1534                         };
1535                         debug!(
1536                             "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1537                             assigned_from,
1538                         );
1539
1540                         if let Some(assigned_from_local) = assigned_from.local() {
1541                             debug!(
1542                                 "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
1543                                 assigned_from_local,
1544                             );
1545
1546                             if *assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
1547                                 return annotated_closure.or_else(fallback);
1548                             }
1549                         }
1550                     }
1551                 }
1552             }
1553             _ => {}
1554         }
1555
1556         // If we haven't found an assignment into the return place, then we need not add
1557         // any annotations.
1558         debug!("annotate_argument_and_return_for_borrow: none found");
1559         None
1560     }
1561
1562     /// Annotate the first argument and return type of a function signature if they are
1563     /// references.
1564     fn annotate_fn_sig(
1565         &self,
1566         did: DefId,
1567         sig: ty::PolyFnSig<'tcx>,
1568     ) -> Option<AnnotatedBorrowFnSignature> {
1569         debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
1570         let is_closure = self.infcx.tcx.is_closure(did);
1571         let fn_node_id = self.infcx.tcx.hir.as_local_node_id(did)?;
1572         let fn_decl = self.infcx.tcx.hir.fn_decl(fn_node_id)?;
1573
1574         // We need to work out which arguments to highlight. We do this by looking
1575         // at the return type, where there are three cases:
1576         //
1577         // 1. If there are named arguments, then we should highlight the return type and
1578         //    highlight any of the arguments that are also references with that lifetime.
1579         //    If there are no arguments that have the same lifetime as the return type,
1580         //    then don't highlight anything.
1581         // 2. The return type is a reference with an anonymous lifetime. If this is
1582         //    the case, then we can take advantage of (and teach) the lifetime elision
1583         //    rules.
1584         //
1585         //    We know that an error is being reported. So the arguments and return type
1586         //    must satisfy the elision rules. Therefore, if there is a single argument
1587         //    then that means the return type and first (and only) argument have the same
1588         //    lifetime and the borrow isn't meeting that, we can highlight the argument
1589         //    and return type.
1590         //
1591         //    If there are multiple arguments then the first argument must be self (else
1592         //    it would not satisfy the elision rules), so we can highlight self and the
1593         //    return type.
1594         // 3. The return type is not a reference. In this case, we don't highlight
1595         //    anything.
1596         let return_ty = sig.output();
1597         match return_ty.skip_binder().sty {
1598             ty::TyKind::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
1599                 // This is case 1 from above, return type is a named reference so we need to
1600                 // search for relevant arguments.
1601                 let mut arguments = Vec::new();
1602                 for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
1603                     if let ty::TyKind::Ref(argument_region, _, _) = argument.sty {
1604                         if argument_region == return_region {
1605                             // Need to use the `rustc::ty` types to compare against the
1606                             // `return_region`. Then use the `rustc::hir` type to get only
1607                             // the lifetime span.
1608                             match &fn_decl.inputs[index].node {
1609                                 hir::TyKind::Rptr(lifetime, _) => {
1610                                     // With access to the lifetime, we can get
1611                                     // the span of it.
1612                                     arguments.push((*argument, lifetime.span));
1613                                 }
1614                                 _ => bug!("ty type is a ref but hir type is not"),
1615                             }
1616                         }
1617                     }
1618                 }
1619
1620                 // We need to have arguments. This shouldn't happen, but it's worth checking.
1621                 if arguments.is_empty() {
1622                     return None;
1623                 }
1624
1625                 // We use a mix of the HIR and the Ty types to get information
1626                 // as the HIR doesn't have full types for closure arguments.
1627                 let return_ty = *sig.output().skip_binder();
1628                 let mut return_span = fn_decl.output.span();
1629                 if let hir::FunctionRetTy::Return(ty) = fn_decl.output {
1630                     if let hir::TyKind::Rptr(lifetime, _) = ty.into_inner().node {
1631                         return_span = lifetime.span;
1632                     }
1633                 }
1634
1635                 Some(AnnotatedBorrowFnSignature::NamedFunction {
1636                     arguments,
1637                     return_ty,
1638                     return_span,
1639                 })
1640             }
1641             ty::TyKind::Ref(_, _, _) if is_closure => {
1642                 // This is case 2 from above but only for closures, return type is anonymous
1643                 // reference so we select
1644                 // the first argument.
1645                 let argument_span = fn_decl.inputs.first()?.span;
1646                 let argument_ty = sig.inputs().skip_binder().first()?;
1647
1648                 // Closure arguments are wrapped in a tuple, so we need to get the first
1649                 // from that.
1650                 if let ty::TyKind::Tuple(elems) = argument_ty.sty {
1651                     let argument_ty = elems.first()?;
1652                     if let ty::TyKind::Ref(_, _, _) = argument_ty.sty {
1653                         return Some(AnnotatedBorrowFnSignature::Closure {
1654                             argument_ty,
1655                             argument_span,
1656                         });
1657                     }
1658                 }
1659
1660                 None
1661             }
1662             ty::TyKind::Ref(_, _, _) => {
1663                 // This is also case 2 from above but for functions, return type is still an
1664                 // anonymous reference so we select the first argument.
1665                 let argument_span = fn_decl.inputs.first()?.span;
1666                 let argument_ty = sig.inputs().skip_binder().first()?;
1667
1668                 let return_span = fn_decl.output.span();
1669                 let return_ty = *sig.output().skip_binder();
1670
1671                 // We expect the first argument to be a reference.
1672                 match argument_ty.sty {
1673                     ty::TyKind::Ref(_, _, _) => {}
1674                     _ => return None,
1675                 }
1676
1677                 Some(AnnotatedBorrowFnSignature::AnonymousFunction {
1678                     argument_ty,
1679                     argument_span,
1680                     return_ty,
1681                     return_span,
1682                 })
1683             }
1684             _ => {
1685                 // This is case 3 from above, return type is not a reference so don't highlight
1686                 // anything.
1687                 None
1688             }
1689         }
1690     }
1691 }
1692
1693 #[derive(Debug)]
1694 enum AnnotatedBorrowFnSignature<'tcx> {
1695     NamedFunction {
1696         arguments: Vec<(ty::Ty<'tcx>, Span)>,
1697         return_ty: ty::Ty<'tcx>,
1698         return_span: Span,
1699     },
1700     AnonymousFunction {
1701         argument_ty: ty::Ty<'tcx>,
1702         argument_span: Span,
1703         return_ty: ty::Ty<'tcx>,
1704         return_span: Span,
1705     },
1706     Closure {
1707         argument_ty: ty::Ty<'tcx>,
1708         argument_span: Span,
1709     },
1710 }
1711
1712 impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
1713     /// Annotate the provided diagnostic with information about borrow from the fn signature that
1714     /// helps explain.
1715     fn emit(&self, diag: &mut DiagnosticBuilder<'_>) -> String {
1716         match self {
1717             AnnotatedBorrowFnSignature::Closure {
1718                 argument_ty,
1719                 argument_span,
1720             } => {
1721                 diag.span_label(
1722                     *argument_span,
1723                     format!("has type `{}`", self.get_name_for_ty(argument_ty, 0)),
1724                 );
1725
1726                 self.get_region_name_for_ty(argument_ty, 0)
1727             }
1728             AnnotatedBorrowFnSignature::AnonymousFunction {
1729                 argument_ty,
1730                 argument_span,
1731                 return_ty,
1732                 return_span,
1733             } => {
1734                 let argument_ty_name = self.get_name_for_ty(argument_ty, 0);
1735                 diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
1736
1737                 let return_ty_name = self.get_name_for_ty(return_ty, 0);
1738                 let types_equal = return_ty_name == argument_ty_name;
1739                 diag.span_label(
1740                     *return_span,
1741                     format!(
1742                         "{}has type `{}`",
1743                         if types_equal { "also " } else { "" },
1744                         return_ty_name,
1745                     ),
1746                 );
1747
1748                 diag.note(
1749                     "argument and return type have the same lifetime due to lifetime elision rules",
1750                 );
1751                 diag.note(
1752                     "to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch10-03-\
1753                      lifetime-syntax.html#lifetime-elision>",
1754                 );
1755
1756                 self.get_region_name_for_ty(return_ty, 0)
1757             }
1758             AnnotatedBorrowFnSignature::NamedFunction {
1759                 arguments,
1760                 return_ty,
1761                 return_span,
1762             } => {
1763                 // Region of return type and arguments checked to be the same earlier.
1764                 let region_name = self.get_region_name_for_ty(return_ty, 0);
1765                 for (_, argument_span) in arguments {
1766                     diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
1767                 }
1768
1769                 diag.span_label(
1770                     *return_span,
1771                     format!("also has lifetime `{}`", region_name,),
1772                 );
1773
1774                 diag.help(&format!(
1775                     "use data from the highlighted arguments which match the `{}` lifetime of \
1776                      the return type",
1777                     region_name,
1778                 ));
1779
1780                 region_name
1781             }
1782         }
1783     }
1784
1785     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
1786     /// name where required.
1787     fn get_name_for_ty(&self, ty: ty::Ty<'tcx>, counter: usize) -> String {
1788         // We need to add synthesized lifetimes where appropriate. We do
1789         // this by hooking into the pretty printer and telling it to label the
1790         // lifetimes without names with the value `'0`.
1791         match ty.sty {
1792             ty::TyKind::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
1793             | ty::TyKind::Ref(
1794                 ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }),
1795                 _,
1796                 _,
1797             ) => with_highlight_region_for_bound_region(*br, counter, || format!("{}", ty)),
1798             _ => format!("{}", ty),
1799         }
1800     }
1801
1802     /// Return the name of the provided `Ty` (that must be a reference)'s region with a
1803     /// synthesized lifetime name where required.
1804     fn get_region_name_for_ty(&self, ty: ty::Ty<'tcx>, counter: usize) -> String {
1805         match ty.sty {
1806             ty::TyKind::Ref(region, _, _) => match region {
1807                 ty::RegionKind::ReLateBound(_, br)
1808                 | ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }) => {
1809                     with_highlight_region_for_bound_region(*br, counter, || format!("{}", region))
1810                 }
1811                 _ => format!("{}", region),
1812             },
1813             _ => bug!("ty for annotation of borrow region is not a reference"),
1814         }
1815     }
1816 }
1817
1818 // The span(s) associated to a use of a place.
1819 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
1820 pub(super) enum UseSpans {
1821     // The access is caused by capturing a variable for a closure.
1822     ClosureUse {
1823         // The span of the args of the closure, including the `move` keyword if
1824         // it's present.
1825         args_span: Span,
1826         // The span of the first use of the captured variable inside the closure.
1827         var_span: Span,
1828     },
1829     // This access has a single span associated to it: common case.
1830     OtherUse(Span),
1831 }
1832
1833 impl UseSpans {
1834     pub(super) fn args_or_use(self) -> Span {
1835         match self {
1836             UseSpans::ClosureUse {
1837                 args_span: span, ..
1838             }
1839             | UseSpans::OtherUse(span) => span,
1840         }
1841     }
1842
1843     pub(super) fn var_or_use(self) -> Span {
1844         match self {
1845             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
1846         }
1847     }
1848
1849     // Add a span label to the arguments of the closure, if it exists.
1850     pub(super) fn args_span_label(self, err: &mut DiagnosticBuilder, message: impl Into<String>) {
1851         if let UseSpans::ClosureUse { args_span, .. } = self {
1852             err.span_label(args_span, message);
1853         }
1854     }
1855
1856     // Add a span label to the use of the captured variable, if it exists.
1857     pub(super) fn var_span_label(self, err: &mut DiagnosticBuilder, message: impl Into<String>) {
1858         if let UseSpans::ClosureUse { var_span, .. } = self {
1859             err.span_label(var_span, message);
1860         }
1861     }
1862
1863     pub(super) fn for_closure(self) -> bool {
1864         match self {
1865             UseSpans::ClosureUse { .. } => true,
1866             UseSpans::OtherUse(_) => false,
1867         }
1868     }
1869
1870     pub(super) fn or_else<F>(self, if_other: F) -> Self
1871     where
1872         F: FnOnce() -> Self,
1873     {
1874         match self {
1875             closure @ UseSpans::ClosureUse { .. } => closure,
1876             UseSpans::OtherUse(_) => if_other(),
1877         }
1878     }
1879 }
1880
1881 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1882     /// Finds the spans associated to a move or copy of move_place at location.
1883     pub(super) fn move_spans(
1884         &self,
1885         moved_place: &Place<'tcx>, // Could also be an upvar.
1886         location: Location,
1887     ) -> UseSpans {
1888         use self::UseSpans::*;
1889         use rustc::hir::ExprKind::Closure;
1890         use rustc::mir::AggregateKind;
1891
1892         let stmt = match self.mir[location.block]
1893             .statements
1894             .get(location.statement_index)
1895         {
1896             Some(stmt) => stmt,
1897             None => return OtherUse(self.mir.source_info(location).span),
1898         };
1899
1900         if let StatementKind::Assign(_, box Rvalue::Aggregate(ref kind, ref places)) = stmt.kind {
1901             if let AggregateKind::Closure(def_id, _) = **kind {
1902                 debug!("find_closure_move_span: found closure {:?}", places);
1903
1904                 if let Some(node_id) = self.infcx.tcx.hir.as_local_node_id(def_id) {
1905                     if let Closure(_, _, _, args_span, _) =
1906                         self.infcx.tcx.hir.expect_expr(node_id).node
1907                     {
1908                         if let Some(var_span) = self.infcx.tcx.with_freevars(node_id, |freevars| {
1909                             for (v, place) in freevars.iter().zip(places) {
1910                                 match place {
1911                                     Operand::Copy(place) | Operand::Move(place)
1912                                         if moved_place == place =>
1913                                     {
1914                                         debug!(
1915                                             "find_closure_move_span: found captured local {:?}",
1916                                             place
1917                                         );
1918                                         return Some(v.span);
1919                                     }
1920                                     _ => {}
1921                                 }
1922                             }
1923                             None
1924                         }) {
1925                             return ClosureUse {
1926                                 args_span,
1927                                 var_span,
1928                             };
1929                         }
1930                     }
1931                 }
1932             }
1933         }
1934
1935         return OtherUse(stmt.source_info.span);
1936     }
1937
1938     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
1939     /// and its usage of the local assigned at `location`.
1940     /// This is done by searching in statements succeeding `location`
1941     /// and originating from `maybe_closure_span`.
1942     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
1943         use self::UseSpans::*;
1944         use rustc::hir::ExprKind::Closure;
1945
1946         let local = match self.mir[location.block]
1947             .statements
1948             .get(location.statement_index)
1949         {
1950             Some(&Statement {
1951                 kind: StatementKind::Assign(Place::Local(local), _),
1952                 ..
1953             }) => local,
1954             _ => return OtherUse(use_span),
1955         };
1956
1957         if self.mir.local_kind(local) != LocalKind::Temp {
1958             // operands are always temporaries.
1959             return OtherUse(use_span);
1960         }
1961
1962         for stmt in &self.mir[location.block].statements[location.statement_index + 1..] {
1963             if let StatementKind::Assign(_, box Rvalue::Aggregate(ref kind, ref places)) = stmt.kind
1964             {
1965                 if let AggregateKind::Closure(def_id, _) = **kind {
1966                     debug!("find_closure_borrow_span: found closure {:?}", places);
1967
1968                     return if let Some(node_id) = self.infcx.tcx.hir.as_local_node_id(def_id) {
1969                         let args_span = if let Closure(_, _, _, span, _) =
1970                             self.infcx.tcx.hir.expect_expr(node_id).node
1971                         {
1972                             span
1973                         } else {
1974                             return OtherUse(use_span);
1975                         };
1976
1977                         self.infcx
1978                             .tcx
1979                             .with_freevars(node_id, |freevars| {
1980                                 for (v, place) in freevars.iter().zip(places) {
1981                                     match *place {
1982                                         Operand::Copy(Place::Local(l))
1983                                         | Operand::Move(Place::Local(l)) if local == l =>
1984                                         {
1985                                             debug!(
1986                                                 "find_closure_borrow_span: found captured local \
1987                                                  {:?}",
1988                                                 l
1989                                             );
1990                                             return Some(v.span);
1991                                         }
1992                                         _ => {}
1993                                     }
1994                                 }
1995                                 None
1996                             })
1997                             .map(|var_span| ClosureUse {
1998                                 args_span,
1999                                 var_span,
2000                             })
2001                             .unwrap_or(OtherUse(use_span))
2002                     } else {
2003                         OtherUse(use_span)
2004                     };
2005                 }
2006             }
2007
2008             if use_span != stmt.source_info.span {
2009                 break;
2010             }
2011         }
2012
2013         OtherUse(use_span)
2014     }
2015
2016     /// Helper to retrieve span(s) of given borrow from the current MIR
2017     /// representation
2018     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData) -> UseSpans {
2019         let span = self.mir.source_info(borrow.reserve_location).span;
2020         self.borrow_spans(span, borrow.reserve_location)
2021     }
2022 }