src/librustc_mir/borrow_check/error_reporting.rs

   1 use borrow_check::nll::explain_borrow::BorrowExplanation;
   2 use borrow_check::nll::region_infer::{RegionName, RegionNameSource};
   3 use borrow_check::prefixes::IsPrefixOf;
   4 use borrow_check::WriteKind;
   5 use rustc::hir;
   6 use rustc::hir::def_id::DefId;
   7 use rustc::middle::region::ScopeTree;
   8 use rustc::mir::{
   9     self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, Constant,
  10     ConstraintCategory, Field, Local, LocalDecl, LocalKind, Location, Operand,
  11     Place, PlaceProjection, ProjectionElem, Rvalue, Statement, StatementKind,
  12     TerminatorKind, VarBindingForm,
  13 };
  14 use rustc::ty::{self, DefIdTree};
  15 use rustc::util::ppaux::RegionHighlightMode;
  16 use rustc_data_structures::fx::FxHashSet;
  17 use rustc_data_structures::indexed_vec::Idx;
  18 use rustc_data_structures::sync::Lrc;
  19 use rustc_errors::{Applicability, DiagnosticBuilder};
  20 use syntax_pos::Span;
  21
  22 use super::borrow_set::BorrowData;
  23 use super::{Context, MirBorrowckCtxt};
  24 use super::{InitializationRequiringAction, PrefixSet};
  25 use dataflow::drop_flag_effects;
  26 use dataflow::move_paths::indexes::MoveOutIndex;
  27 use dataflow::move_paths::MovePathIndex;
  28 use util::borrowck_errors::{BorrowckErrors, Origin};
  29
  30 #[derive(Debug)]
  31 struct MoveSite {
  32     /// Index of the "move out" that we found. The `MoveData` can
  33     /// then tell us where the move occurred.
  34     moi: MoveOutIndex,
  35
  36     /// True if we traversed a back edge while walking from the point
  37     /// of error to the move site.
  38     traversed_back_edge: bool
  39 }
  40
  41 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
  42     pub(super) fn report_use_of_moved_or_uninitialized(
  43         &mut self,
  44         context: Context,
  45         desired_action: InitializationRequiringAction,
  46         (moved_place, used_place, span): (&Place<'tcx>, &Place<'tcx>, Span),
  47         mpi: MovePathIndex,
  48     ) {
  49         debug!(
  50             "report_use_of_moved_or_uninitialized: context={:?} desired_action={:?} \
  51              moved_place={:?} used_place={:?} span={:?} mpi={:?}",
  52             context, desired_action, moved_place, used_place, span, mpi
  53         );
  54
  55         let use_spans = self.move_spans(moved_place, context.loc)
  56             .or_else(|| self.borrow_spans(span, context.loc));
  57         let span = use_spans.args_or_use();
  58
  59         let move_site_vec = self.get_moved_indexes(context, mpi);
  60         debug!(
  61             "report_use_of_moved_or_uninitialized: move_site_vec={:?}",
  62             move_site_vec
  63         );
  64         let move_out_indices: Vec<_> = move_site_vec
  65             .iter()
  66             .map(|move_site| move_site.moi)
  67             .collect();
  68
  69         if move_out_indices.is_empty() {
  70             let root_place = self.prefixes(&used_place, PrefixSet::All).last().unwrap();
  71
  72             if self.uninitialized_error_reported.contains(root_place) {
  73                 debug!(
  74                     "report_use_of_moved_or_uninitialized place: error about {:?} suppressed",
  75                     root_place
  76                 );
  77                 return;
  78             }
  79
  80             self.uninitialized_error_reported.insert(root_place.clone());
  81
  82             let item_msg = match self.describe_place_with_options(used_place,
  83                                                                   IncludingDowncast(true)) {
  84                 Some(name) => format!("`{}`", name),
  85                 None => "value".to_owned(),
  86             };
  87             let mut err = self.infcx.tcx.cannot_act_on_uninitialized_variable(
  88                 span,
  89                 desired_action.as_noun(),
  90                 &self.describe_place_with_options(moved_place, IncludingDowncast(true))
  91                     .unwrap_or_else(|| "_".to_owned()),
  92                 Origin::Mir,
  93             );
  94             err.span_label(span, format!("use of possibly uninitialized {}", item_msg));
  95
  96             use_spans.var_span_label(
  97                 &mut err,
  98                 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
  99             );
 100
 101             err.buffer(&mut self.errors_buffer);
 102         } else {
 103             if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
 104                 if self.prefixes(&reported_place, PrefixSet::All)
 105                     .any(|p| p == used_place)
 106                 {
 107                     debug!(
 108                         "report_use_of_moved_or_uninitialized place: error suppressed \
 109                          mois={:?}",
 110                         move_out_indices
 111                     );
 112                     return;
 113                 }
 114             }
 115
 116             let msg = ""; //FIXME: add "partially " or "collaterally "
 117
 118             let mut err = self.infcx.tcx.cannot_act_on_moved_value(
 119                 span,
 120                 desired_action.as_noun(),
 121                 msg,
 122                 self.describe_place_with_options(&moved_place, IncludingDowncast(true)),
 123                 Origin::Mir,
 124             );
 125
 126             self.add_closure_invoked_twice_with_moved_variable_suggestion(
 127                 context.loc,
 128                 used_place,
 129                 &mut err,
 130             );
 131
 132             let mut is_loop_move = false;
 133             for move_site in &move_site_vec {
 134                 let move_out = self.move_data.moves[(*move_site).moi];
 135                 let moved_place = &self.move_data.move_paths[move_out.path].place;
 136
 137                 let move_spans = self.move_spans(moved_place, move_out.source);
 138                 let move_span = move_spans.args_or_use();
 139
 140                 let move_msg = if move_spans.for_closure() {
 141                     " into closure"
 142                 } else {
 143                     ""
 144                 };
 145
 146                 if span == move_span {
 147                     err.span_label(
 148                         span,
 149                         format!("value moved{} here, in previous iteration of loop", move_msg),
 150                     );
 151                     is_loop_move = true;
 152                 } else if move_site.traversed_back_edge {
 153                     err.span_label(
 154                         move_span,
 155                         format!(
 156                             "value moved{} here, in previous iteration of loop",
 157                             move_msg
 158                         ),
 159                     );
 160                 } else {
 161                     err.span_label(move_span, format!("value moved{} here", move_msg));
 162                     move_spans.var_span_label(
 163                         &mut err,
 164                         format!("variable moved due to use{}", move_spans.describe()),
 165                     );
 166                 };
 167             }
 168
 169             use_spans.var_span_label(
 170                 &mut err,
 171                 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
 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             let ty = used_place.ty(self.mir, self.infcx.tcx).to_ty(self.infcx.tcx);
 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
 191                     tables.closure_kind_origins().get(hir_id).is_none()
 192                 }
 193                 _ => true,
 194             };
 195
 196             if needs_note {
 197                 let mpi = self.move_data.moves[move_out_indices[0]].path;
 198                 let place = &self.move_data.move_paths[mpi].place;
 199
 200                 let ty = place.ty(self.mir, self.infcx.tcx).to_ty(self.infcx.tcx);
 201                 let note_msg = match self.describe_place_with_options(
 202                     place,
 203                     IncludingDowncast(true),
 204                 ) {
 205                     Some(name) => format!("`{}`", name),
 206                     None => "value".to_owned(),
 207                 };
 208
 209                 err.note(&format!(
 210                     "move occurs because {} has type `{}`, \
 211                      which does not implement the `Copy` trait",
 212                     note_msg, ty
 213                 ));
 214             }
 215
 216             if let Some((_, mut old_err)) = self.move_error_reported
 217                 .insert(move_out_indices, (used_place.clone(), err))
 218             {
 219                 // Cancel the old error so it doesn't ICE.
 220                 old_err.cancel();
 221             }
 222         }
 223     }
 224
 225     pub(super) fn report_move_out_while_borrowed(
 226         &mut self,
 227         context: Context,
 228         (place, span): (&Place<'tcx>, Span),
 229         borrow: &BorrowData<'tcx>,
 230     ) {
 231         debug!(
 232             "report_move_out_while_borrowed: context={:?} place={:?} span={:?} borrow={:?}",
 233             context, place, span, borrow
 234         );
 235         let tcx = self.infcx.tcx;
 236         let value_msg = match self.describe_place(place) {
 237             Some(name) => format!("`{}`", name),
 238             None => "value".to_owned(),
 239         };
 240         let borrow_msg = match self.describe_place(&borrow.borrowed_place) {
 241             Some(name) => format!("`{}`", name),
 242             None => "value".to_owned(),
 243         };
 244
 245         let borrow_spans = self.retrieve_borrow_spans(borrow);
 246         let borrow_span = borrow_spans.args_or_use();
 247
 248         let move_spans = self.move_spans(place, context.loc);
 249         let span = move_spans.args_or_use();
 250
 251         let mut err = tcx.cannot_move_when_borrowed(
 252             span,
 253             &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
 254             Origin::Mir,
 255         );
 256         err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
 257         err.span_label(span, format!("move out of {} occurs here", value_msg));
 258
 259         borrow_spans.var_span_label(
 260             &mut err,
 261             format!("borrow occurs due to use{}", borrow_spans.describe())
 262         );
 263
 264         move_spans.var_span_label(
 265             &mut err,
 266             format!("move occurs due to use{}", move_spans.describe())
 267         );
 268
 269         self.explain_why_borrow_contains_point(context, borrow, None)
 270             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 271         err.buffer(&mut self.errors_buffer);
 272     }
 273
 274     pub(super) fn report_use_while_mutably_borrowed(
 275         &mut self,
 276         context: Context,
 277         (place, _span): (&Place<'tcx>, Span),
 278         borrow: &BorrowData<'tcx>,
 279     ) {
 280         let tcx = self.infcx.tcx;
 281
 282         let borrow_spans = self.retrieve_borrow_spans(borrow);
 283         let borrow_span = borrow_spans.args_or_use();
 284
 285         // Conflicting borrows are reported separately, so only check for move
 286         // captures.
 287         let use_spans = self.move_spans(place, context.loc);
 288         let span = use_spans.var_or_use();
 289
 290         let mut err = tcx.cannot_use_when_mutably_borrowed(
 291             span,
 292             &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
 293             borrow_span,
 294             &self.describe_place(&borrow.borrowed_place)
 295                 .unwrap_or_else(|| "_".to_owned()),
 296             Origin::Mir,
 297         );
 298
 299         borrow_spans.var_span_label(&mut err, {
 300             let place = &borrow.borrowed_place;
 301             let desc_place = self.describe_place(place).unwrap_or_else(|| "_".to_owned());
 302
 303             format!("borrow occurs due to use of `{}`{}", desc_place, borrow_spans.describe())
 304         });
 305
 306         self.explain_why_borrow_contains_point(context, borrow, None)
 307             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 308         err.buffer(&mut self.errors_buffer);
 309     }
 310
 311     pub(super) fn report_conflicting_borrow(
 312         &mut self,
 313         context: Context,
 314         (place, span): (&Place<'tcx>, Span),
 315         gen_borrow_kind: BorrowKind,
 316         issued_borrow: &BorrowData<'tcx>,
 317     ) {
 318         let issued_spans = self.retrieve_borrow_spans(issued_borrow);
 319         let issued_span = issued_spans.args_or_use();
 320
 321         let borrow_spans = self.borrow_spans(span, context.loc);
 322         let span = borrow_spans.args_or_use();
 323
 324         let container_name = if issued_spans.for_generator() || borrow_spans.for_generator() {
 325             "generator"
 326         } else {
 327             "closure"
 328         };
 329
 330         let desc_place = self.describe_place(place).unwrap_or_else(|| "_".to_owned());
 331         let tcx = self.infcx.tcx;
 332
 333         let first_borrow_desc;
 334
 335         let explanation = self.explain_why_borrow_contains_point(context, issued_borrow, None);
 336         let second_borrow_desc = if explanation.is_explained() {
 337             "second "
 338         } else {
 339             ""
 340         };
 341
 342         // FIXME: supply non-"" `opt_via` when appropriate
 343         let mut err = match (
 344             gen_borrow_kind,
 345             "immutable",
 346             "mutable",
 347             issued_borrow.kind,
 348             "immutable",
 349             "mutable",
 350         ) {
 351             (BorrowKind::Shared, lft, _, BorrowKind::Mut { .. }, _, rgt) => {
 352                 first_borrow_desc = "mutable ";
 353                 tcx.cannot_reborrow_already_borrowed(
 354                     span,
 355                     &desc_place,
 356                     "",
 357                     lft,
 358                     issued_span,
 359                     "it",
 360                     rgt,
 361                     "",
 362                     None,
 363                     Origin::Mir,
 364                 )
 365             }
 366             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Shared, rgt, _) => {
 367                 first_borrow_desc = "immutable ";
 368                 tcx.cannot_reborrow_already_borrowed(
 369                     span,
 370                     &desc_place,
 371                     "",
 372                     lft,
 373                     issued_span,
 374                     "it",
 375                     rgt,
 376                     "",
 377                     None,
 378                     Origin::Mir,
 379                 )
 380             }
 381
 382             (BorrowKind::Mut { .. }, _, _, BorrowKind::Mut { .. }, _, _) => {
 383                 first_borrow_desc = "first ";
 384                 tcx.cannot_mutably_borrow_multiply(
 385                     span,
 386                     &desc_place,
 387                     "",
 388                     issued_span,
 389                     "",
 390                     None,
 391                     Origin::Mir,
 392                 )
 393             }
 394
 395             (BorrowKind::Unique, _, _, BorrowKind::Unique, _, _) => {
 396                 first_borrow_desc = "first ";
 397                 tcx.cannot_uniquely_borrow_by_two_closures(
 398                     span,
 399                     &desc_place,
 400                     issued_span,
 401                     None,
 402                     Origin::Mir,
 403                 )
 404             }
 405
 406             (BorrowKind::Mut { .. }, _, _, BorrowKind::Shallow, _, _)
 407             | (BorrowKind::Unique, _, _, BorrowKind::Shallow, _, _) => {
 408                 let mut err = tcx.cannot_mutate_in_match_guard(
 409                     span,
 410                     issued_span,
 411                     &desc_place,
 412                     "mutably borrow",
 413                     Origin::Mir,
 414                 );
 415                 borrow_spans.var_span_label(
 416                     &mut err,
 417                     format!(
 418                         "borrow occurs due to use of `{}`{}", desc_place, borrow_spans.describe()
 419                     ),
 420                 );
 421                 err.buffer(&mut self.errors_buffer);
 422
 423                 return;
 424             }
 425
 426             (BorrowKind::Unique, _, _, _, _, _) => {
 427                 first_borrow_desc = "first ";
 428                 tcx.cannot_uniquely_borrow_by_one_closure(
 429                     span,
 430                     container_name,
 431                     &desc_place,
 432                     "",
 433                     issued_span,
 434                     "it",
 435                     "",
 436                     None,
 437                     Origin::Mir,
 438                 )
 439             },
 440
 441             (BorrowKind::Shared, lft, _, BorrowKind::Unique, _, _) => {
 442                 first_borrow_desc = "first ";
 443                 tcx.cannot_reborrow_already_uniquely_borrowed(
 444                     span,
 445                     container_name,
 446                     &desc_place,
 447                     "",
 448                     lft,
 449                     issued_span,
 450                     "",
 451                     None,
 452                     second_borrow_desc,
 453                     Origin::Mir,
 454                 )
 455             }
 456
 457             (BorrowKind::Mut { .. }, _, lft, BorrowKind::Unique, _, _) => {
 458                 first_borrow_desc = "first ";
 459                 tcx.cannot_reborrow_already_uniquely_borrowed(
 460                     span,
 461                     container_name,
 462                     &desc_place,
 463                     "",
 464                     lft,
 465                     issued_span,
 466                     "",
 467                     None,
 468                     second_borrow_desc,
 469                     Origin::Mir,
 470                 )
 471             }
 472
 473             (BorrowKind::Shallow, _, _, BorrowKind::Unique, _, _)
 474             | (BorrowKind::Shallow, _, _, BorrowKind::Mut { .. }, _, _) => {
 475                 // Shallow borrows are uses from the user's point of view.
 476                 self.report_use_while_mutably_borrowed(context, (place, span), issued_borrow);
 477                 return;
 478             }
 479             (BorrowKind::Shared, _, _, BorrowKind::Shared, _, _)
 480             | (BorrowKind::Shared, _, _, BorrowKind::Shallow, _, _)
 481             | (BorrowKind::Shallow, _, _, BorrowKind::Shared, _, _)
 482             | (BorrowKind::Shallow, _, _, BorrowKind::Shallow, _, _) => unreachable!(),
 483         };
 484
 485         if issued_spans == borrow_spans {
 486             borrow_spans.var_span_label(
 487                 &mut err,
 488                 format!("borrows occur due to use of `{}`{}", desc_place, borrow_spans.describe()),
 489             );
 490         } else {
 491             let borrow_place = &issued_borrow.borrowed_place;
 492             let borrow_place_desc = self.describe_place(borrow_place)
 493                                         .unwrap_or_else(|| "_".to_owned());
 494             issued_spans.var_span_label(
 495                 &mut err,
 496                 format!(
 497                     "first borrow occurs due to use of `{}`{}",
 498                     borrow_place_desc,
 499                     issued_spans.describe(),
 500                 ),
 501             );
 502
 503             borrow_spans.var_span_label(
 504                 &mut err,
 505                 format!(
 506                     "second borrow occurs due to use of `{}`{}",
 507                     desc_place,
 508                     borrow_spans.describe(),
 509                 ),
 510             );
 511         }
 512
 513         explanation
 514             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, first_borrow_desc);
 515
 516         err.buffer(&mut self.errors_buffer);
 517     }
 518
 519     /// Reports StorageDeadOrDrop of `place` conflicts with `borrow`.
 520     ///
 521     /// This means that some data referenced by `borrow` needs to live
 522     /// past the point where the StorageDeadOrDrop of `place` occurs.
 523     /// This is usually interpreted as meaning that `place` has too
 524     /// short a lifetime. (But sometimes it is more useful to report
 525     /// it as a more direct conflict between the execution of a
 526     /// `Drop::drop` with an aliasing borrow.)
 527     pub(super) fn report_borrowed_value_does_not_live_long_enough(
 528         &mut self,
 529         context: Context,
 530         borrow: &BorrowData<'tcx>,
 531         place_span: (&Place<'tcx>, Span),
 532         kind: Option<WriteKind>,
 533     ) {
 534         debug!(
 535             "report_borrowed_value_does_not_live_long_enough(\
 536              {:?}, {:?}, {:?}, {:?}\
 537              )",
 538             context, borrow, place_span, kind
 539         );
 540
 541         let drop_span = place_span.1;
 542         let scope_tree = self.infcx.tcx.region_scope_tree(self.mir_def_id);
 543         let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
 544             .last()
 545             .unwrap();
 546
 547         let borrow_spans = self.retrieve_borrow_spans(borrow);
 548         let borrow_span = borrow_spans.var_or_use();
 549
 550         let proper_span = match *root_place {
 551             Place::Local(local) => self.mir.local_decls[local].source_info.span,
 552             _ => drop_span,
 553         };
 554
 555         if self.access_place_error_reported
 556             .contains(&(root_place.clone(), borrow_span))
 557         {
 558             debug!(
 559                 "suppressing access_place error when borrow doesn't live long enough for {:?}",
 560                 borrow_span
 561             );
 562             return;
 563         }
 564
 565         self.access_place_error_reported
 566             .insert((root_place.clone(), borrow_span));
 567
 568         if let StorageDeadOrDrop::Destructor(dropped_ty) =
 569             self.classify_drop_access_kind(&borrow.borrowed_place)
 570         {
 571             // If a borrow of path `B` conflicts with drop of `D` (and
 572             // we're not in the uninteresting case where `B` is a
 573             // prefix of `D`), then report this as a more interesting
 574             // destructor conflict.
 575             if !borrow.borrowed_place.is_prefix_of(place_span.0) {
 576                 self.report_borrow_conflicts_with_destructor(
 577                     context, borrow, place_span, kind, dropped_ty,
 578                 );
 579                 return;
 580             }
 581         }
 582
 583         let place_desc = self.describe_place(&borrow.borrowed_place);
 584
 585         let kind_place = kind.filter(|_| place_desc.is_some()).map(|k| (k, place_span.0));
 586         let explanation = self.explain_why_borrow_contains_point(context, &borrow, kind_place);
 587
 588         let err = match (place_desc, explanation) {
 589             (Some(_), _) if self.is_place_thread_local(root_place) => {
 590                 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span)
 591             }
 592             // If the outlives constraint comes from inside the closure,
 593             // for example:
 594             //
 595             // let x = 0;
 596             // let y = &x;
 597             // Box::new(|| y) as Box<Fn() -> &'static i32>
 598             //
 599             // then just use the normal error. The closure isn't escaping
 600             // and `move` will not help here.
 601             (
 602                 Some(ref name),
 603                 BorrowExplanation::MustBeValidFor {
 604                     category: category @ ConstraintCategory::Return,
 605                     from_closure: false,
 606                     ref region_name,
 607                     span,
 608                     ..
 609                 },
 610             )
 611             | (
 612                 Some(ref name),
 613                 BorrowExplanation::MustBeValidFor {
 614                     category: category @ ConstraintCategory::CallArgument,
 615                     from_closure: false,
 616                     ref region_name,
 617                     span,
 618                     ..
 619                 },
 620             ) if borrow_spans.for_closure() => self.report_escaping_closure_capture(
 621                 borrow_spans.args_or_use(),
 622                 borrow_span,
 623                 region_name,
 624                 category,
 625                 span,
 626                 &format!("`{}`", name),
 627             ),
 628             (
 629                 ref name,
 630                 BorrowExplanation::MustBeValidFor {
 631                     category: ConstraintCategory::Assignment,
 632                     from_closure: false,
 633                     region_name: RegionName {
 634                         source: RegionNameSource::AnonRegionFromUpvar(upvar_span, ref upvar_name),
 635                         ..
 636                     },
 637                     span,
 638                     ..
 639                 },
 640             ) => self.report_escaping_data(borrow_span, name, upvar_span, upvar_name, span),
 641             (Some(name), explanation) => self.report_local_value_does_not_live_long_enough(
 642                 context,
 643                 &name,
 644                 &scope_tree,
 645                 &borrow,
 646                 drop_span,
 647                 borrow_spans,
 648                 explanation,
 649             ),
 650             (None, explanation) => self.report_temporary_value_does_not_live_long_enough(
 651                 context,
 652                 &scope_tree,
 653                 &borrow,
 654                 drop_span,
 655                 borrow_spans,
 656                 proper_span,
 657                 explanation,
 658             ),
 659         };
 660
 661         err.buffer(&mut self.errors_buffer);
 662     }
 663
 664     fn report_local_value_does_not_live_long_enough(
 665         &mut self,
 666         context: Context,
 667         name: &str,
 668         scope_tree: &Lrc<ScopeTree>,
 669         borrow: &BorrowData<'tcx>,
 670         drop_span: Span,
 671         borrow_spans: UseSpans,
 672         explanation: BorrowExplanation,
 673     ) -> DiagnosticBuilder<'cx> {
 674         debug!(
 675             "report_local_value_does_not_live_long_enough(\
 676              {:?}, {:?}, {:?}, {:?}, {:?}, {:?}\
 677              )",
 678             context, name, scope_tree, borrow, drop_span, borrow_spans
 679         );
 680
 681         let borrow_span = borrow_spans.var_or_use();
 682         if let BorrowExplanation::MustBeValidFor {
 683             category: ConstraintCategory::Return,
 684             span,
 685             ref opt_place_desc,
 686             from_closure: false,
 687             ..
 688         } = explanation {
 689             return self.report_cannot_return_reference_to_local(
 690                 borrow,
 691                 borrow_span,
 692                 span,
 693                 opt_place_desc.as_ref(),
 694             );
 695         }
 696
 697         let mut err = self.infcx.tcx.path_does_not_live_long_enough(
 698             borrow_span,
 699             &format!("`{}`", name),
 700             Origin::Mir,
 701         );
 702
 703         if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
 704             let region_name = annotation.emit(&mut err);
 705
 706             err.span_label(
 707                 borrow_span,
 708                 format!("`{}` would have to be valid for `{}`...", name, region_name),
 709             );
 710
 711             if let Some(fn_node_id) = self.infcx.tcx.hir().as_local_node_id(self.mir_def_id) {
 712                 err.span_label(
 713                     drop_span,
 714                     format!(
 715                         "...but `{}` will be dropped here, when the function `{}` returns",
 716                         name,
 717                         self.infcx.tcx.hir().name(fn_node_id),
 718                     ),
 719                 );
 720
 721                 err.note(
 722                     "functions cannot return a borrow to data owned within the function's scope, \
 723                      functions can only return borrows to data passed as arguments",
 724                 );
 725                 err.note(
 726                     "to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch04-02-\
 727                      references-and-borrowing.html#dangling-references>",
 728                 );
 729             } else {
 730                 err.span_label(
 731                     drop_span,
 732                     format!("...but `{}` dropped here while still borrowed", name),
 733                 );
 734             }
 735
 736             if let BorrowExplanation::MustBeValidFor { .. } = explanation {
 737             } else {
 738                 explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 739             }
 740         } else {
 741             err.span_label(borrow_span, "borrowed value does not live long enough");
 742             err.span_label(
 743                 drop_span,
 744                 format!("`{}` dropped here while still borrowed", name),
 745             );
 746
 747             let within = if borrow_spans.for_generator() {
 748                 " by generator"
 749             } else {
 750                 ""
 751             };
 752
 753             borrow_spans.args_span_label(
 754                 &mut err,
 755                 format!("value captured here{}", within),
 756             );
 757
 758             explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 759         }
 760
 761         err
 762     }
 763
 764     fn report_borrow_conflicts_with_destructor(
 765         &mut self,
 766         context: Context,
 767         borrow: &BorrowData<'tcx>,
 768         (place, drop_span): (&Place<'tcx>, Span),
 769         kind: Option<WriteKind>,
 770         dropped_ty: ty::Ty<'tcx>,
 771     ) {
 772         debug!(
 773             "report_borrow_conflicts_with_destructor(\
 774              {:?}, {:?}, ({:?}, {:?}), {:?}\
 775              )",
 776             context, borrow, place, drop_span, kind,
 777         );
 778
 779         let borrow_spans = self.retrieve_borrow_spans(borrow);
 780         let borrow_span = borrow_spans.var_or_use();
 781
 782         let mut err = self.infcx
 783             .tcx
 784             .cannot_borrow_across_destructor(borrow_span, Origin::Mir);
 785
 786         let what_was_dropped = match self.describe_place(place) {
 787             Some(name) => format!("`{}`", name.as_str()),
 788             None => String::from("temporary value"),
 789         };
 790
 791         let label = match self.describe_place(&borrow.borrowed_place) {
 792             Some(borrowed) => format!(
 793                 "here, drop of {D} needs exclusive access to `{B}`, \
 794                  because the type `{T}` implements the `Drop` trait",
 795                 D = what_was_dropped,
 796                 T = dropped_ty,
 797                 B = borrowed
 798             ),
 799             None => format!(
 800                 "here is drop of {D}; whose type `{T}` implements the `Drop` trait",
 801                 D = what_was_dropped,
 802                 T = dropped_ty
 803             ),
 804         };
 805         err.span_label(drop_span, label);
 806
 807         // Only give this note and suggestion if they could be relevant.
 808         let explanation =
 809             self.explain_why_borrow_contains_point(context, borrow, kind.map(|k| (k, place)));
 810         match explanation {
 811             BorrowExplanation::UsedLater { .. }
 812             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
 813                 err.note("consider using a `let` binding to create a longer lived value");
 814             }
 815             _ => {}
 816         }
 817
 818         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 819
 820         err.buffer(&mut self.errors_buffer);
 821     }
 822
 823     fn report_thread_local_value_does_not_live_long_enough(
 824         &mut self,
 825         drop_span: Span,
 826         borrow_span: Span,
 827     ) -> DiagnosticBuilder<'cx> {
 828         debug!(
 829             "report_thread_local_value_does_not_live_long_enough(\
 830              {:?}, {:?}\
 831              )",
 832             drop_span, borrow_span
 833         );
 834
 835         let mut err = self.infcx
 836             .tcx
 837             .thread_local_value_does_not_live_long_enough(borrow_span, Origin::Mir);
 838
 839         err.span_label(
 840             borrow_span,
 841             "thread-local variables cannot be borrowed beyond the end of the function",
 842         );
 843         err.span_label(drop_span, "end of enclosing function is here");
 844
 845         err
 846     }
 847
 848     fn report_temporary_value_does_not_live_long_enough(
 849         &mut self,
 850         context: Context,
 851         scope_tree: &Lrc<ScopeTree>,
 852         borrow: &BorrowData<'tcx>,
 853         drop_span: Span,
 854         borrow_spans: UseSpans,
 855         proper_span: Span,
 856         explanation: BorrowExplanation,
 857     ) -> DiagnosticBuilder<'cx> {
 858         debug!(
 859             "report_temporary_value_does_not_live_long_enough(\
 860              {:?}, {:?}, {:?}, {:?}, {:?}\
 861              )",
 862             context, scope_tree, borrow, drop_span, proper_span
 863         );
 864
 865         if let BorrowExplanation::MustBeValidFor {
 866             category: ConstraintCategory::Return,
 867             span,
 868             from_closure: false,
 869             ..
 870         } = explanation {
 871             return self.report_cannot_return_reference_to_local(
 872                 borrow,
 873                 proper_span,
 874                 span,
 875                 None,
 876             );
 877         }
 878
 879         let tcx = self.infcx.tcx;
 880         let mut err = tcx.temporary_value_borrowed_for_too_long(proper_span, Origin::Mir);
 881         err.span_label(
 882             proper_span,
 883             "creates a temporary which is freed while still in use",
 884         );
 885         err.span_label(
 886             drop_span,
 887             "temporary value is freed at the end of this statement",
 888         );
 889
 890         match explanation {
 891             BorrowExplanation::UsedLater(..)
 892             | BorrowExplanation::UsedLaterInLoop(..)
 893             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
 894                 // Only give this note and suggestion if it could be relevant.
 895                 err.note("consider using a `let` binding to create a longer lived value");
 896             }
 897             _ => {}
 898         }
 899         explanation.add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
 900
 901         let within = if borrow_spans.for_generator() {
 902             " by generator"
 903         } else {
 904             ""
 905         };
 906
 907         borrow_spans.args_span_label(
 908             &mut err,
 909             format!("value captured here{}", within),
 910         );
 911
 912         err
 913     }
 914
 915     fn report_cannot_return_reference_to_local(
 916         &self,
 917         borrow: &BorrowData<'tcx>,
 918         borrow_span: Span,
 919         return_span: Span,
 920         opt_place_desc: Option<&String>,
 921     ) -> DiagnosticBuilder<'cx> {
 922         let tcx = self.infcx.tcx;
 923
 924         // FIXME use a better heuristic than Spans
 925         let reference_desc = if return_span == self.mir.source_info(borrow.reserve_location).span {
 926             "reference to"
 927         } else {
 928             "value referencing"
 929         };
 930
 931         let (place_desc, note) = if let Some(place_desc) = opt_place_desc {
 932             let local_kind = match borrow.borrowed_place {
 933                 Place::Local(local) => {
 934                     match self.mir.local_kind(local) {
 935                         LocalKind::ReturnPointer
 936                         | LocalKind::Temp => bug!("temporary or return pointer with a name"),
 937                         LocalKind::Var => "local variable ",
 938                         LocalKind::Arg
 939                         if !self.mir.upvar_decls.is_empty()
 940                             && local == Local::new(1) => {
 941                             "variable captured by `move` "
 942                         }
 943                         LocalKind::Arg => {
 944                             "function parameter "
 945                         }
 946                     }
 947                 }
 948                 _ => "local data ",
 949             };
 950             (
 951                 format!("{}`{}`", local_kind, place_desc),
 952                 format!("`{}` is borrowed here", place_desc),
 953             )
 954         } else {
 955             let root_place = self.prefixes(&borrow.borrowed_place, PrefixSet::All)
 956                 .last()
 957                 .unwrap();
 958             let local = if let Place::Local(local) = *root_place {
 959                 local
 960             } else {
 961                 bug!("report_cannot_return_reference_to_local: not a local")
 962             };
 963             match self.mir.local_kind(local) {
 964                 LocalKind::ReturnPointer | LocalKind::Temp => {
 965                     (
 966                         "temporary value".to_string(),
 967                         "temporary value created here".to_string(),
 968                     )
 969                 }
 970                 LocalKind::Arg => {
 971                     (
 972                         "function parameter".to_string(),
 973                         "function parameter borrowed here".to_string(),
 974                     )
 975                 },
 976                 LocalKind::Var => bug!("local variable without a name"),
 977             }
 978         };
 979
 980         let mut err = tcx.cannot_return_reference_to_local(
 981             return_span,
 982             reference_desc,
 983             &place_desc,
 984             Origin::Mir,
 985         );
 986
 987         if return_span != borrow_span {
 988             err.span_label(borrow_span, note);
 989         }
 990
 991         err
 992     }
 993
 994     fn report_escaping_closure_capture(
 995         &mut self,
 996         args_span: Span,
 997         var_span: Span,
 998         fr_name: &RegionName,
 999         category: ConstraintCategory,
1000         constraint_span: Span,
1001         captured_var: &str,
1002     ) -> DiagnosticBuilder<'cx> {
1003         let tcx = self.infcx.tcx;
1004
1005         let mut err = tcx.cannot_capture_in_long_lived_closure(
1006             args_span,
1007             captured_var,
1008             var_span,
1009           Origin::Mir,
1010         );
1011
1012         let suggestion = match tcx.sess.source_map().span_to_snippet(args_span) {
1013             Ok(string) => format!("move {}", string),
1014             Err(_) => "move |<args>| <body>".to_string()
1015         };
1016
1017         err.span_suggestion_with_applicability(
1018             args_span,
1019             &format!("to force the closure to take ownership of {} (and any \
1020                       other referenced variables), use the `move` keyword",
1021                       captured_var),
1022             suggestion,
1023             Applicability::MachineApplicable,
1024         );
1025
1026         match category {
1027             ConstraintCategory::Return => {
1028                 err.span_note(constraint_span, "closure is returned here");
1029             }
1030             ConstraintCategory::CallArgument => {
1031                 fr_name.highlight_region_name(&mut err);
1032                 err.span_note(
1033                     constraint_span,
1034                     &format!("function requires argument type to outlive `{}`", fr_name),
1035                 );
1036             }
1037             _ => bug!("report_escaping_closure_capture called with unexpected constraint \
1038                        category: `{:?}`", category),
1039         }
1040         err
1041     }
1042
1043     fn report_escaping_data(
1044         &mut self,
1045         borrow_span: Span,
1046         name: &Option<String>,
1047         upvar_span: Span,
1048         upvar_name: &str,
1049         escape_span: Span,
1050     ) -> DiagnosticBuilder<'cx> {
1051         let tcx = self.infcx.tcx;
1052
1053         let escapes_from = if tcx.is_closure(self.mir_def_id) {
1054             let tables = tcx.typeck_tables_of(self.mir_def_id);
1055             let mir_hir_id = tcx.hir().def_index_to_hir_id(self.mir_def_id.index);
1056             match tables.node_id_to_type(mir_hir_id).sty {
1057                 ty::Closure(..) => "closure",
1058                 ty::Generator(..) => "generator",
1059                 _ => bug!("Closure body doesn't have a closure or generator type"),
1060             }
1061         } else {
1062             "function"
1063         };
1064
1065         let mut err = tcx.borrowed_data_escapes_closure(escape_span, escapes_from, Origin::Mir);
1066
1067         err.span_label(
1068             upvar_span,
1069             format!(
1070                 "`{}` is declared here, outside of the {} body",
1071                 upvar_name, escapes_from
1072             ),
1073         );
1074
1075         err.span_label(
1076             borrow_span,
1077             format!(
1078                 "borrow is only valid in the {} body",
1079                 escapes_from
1080             ),
1081         );
1082
1083         if let Some(name) = name {
1084             err.span_label(
1085                 escape_span,
1086                 format!("reference to `{}` escapes the {} body here", name, escapes_from),
1087             );
1088         } else {
1089             err.span_label(
1090                 escape_span,
1091                 format!("reference escapes the {} body here", escapes_from),
1092             );
1093         }
1094
1095         err
1096     }
1097
1098     fn get_moved_indexes(&mut self, context: Context, mpi: MovePathIndex) -> Vec<MoveSite> {
1099         let mir = self.mir;
1100
1101         let mut stack = Vec::new();
1102         stack.extend(mir.predecessor_locations(context.loc).map(|predecessor| {
1103             let is_back_edge = context.loc.dominates(predecessor, &self.dominators);
1104             (predecessor, is_back_edge)
1105         }));
1106
1107         let mut visited = FxHashSet::default();
1108         let mut result = vec![];
1109
1110         'dfs: while let Some((location, is_back_edge)) = stack.pop() {
1111             debug!(
1112                 "report_use_of_moved_or_uninitialized: (current_location={:?}, back_edge={})",
1113                 location, is_back_edge
1114             );
1115
1116             if !visited.insert(location) {
1117                 continue;
1118             }
1119
1120             // check for moves
1121             let stmt_kind = mir[location.block]
1122                 .statements
1123                 .get(location.statement_index)
1124                 .map(|s| &s.kind);
1125             if let Some(StatementKind::StorageDead(..)) = stmt_kind {
1126                 // this analysis only tries to find moves explicitly
1127                 // written by the user, so we ignore the move-outs
1128                 // created by `StorageDead` and at the beginning
1129                 // of a function.
1130             } else {
1131                 // If we are found a use of a.b.c which was in error, then we want to look for
1132                 // moves not only of a.b.c but also a.b and a.
1133                 //
1134                 // Note that the moves data already includes "parent" paths, so we don't have to
1135                 // worry about the other case: that is, if there is a move of a.b.c, it is already
1136                 // marked as a move of a.b and a as well, so we will generate the correct errors
1137                 // there.
1138                 let mut mpis = vec![mpi];
1139                 let move_paths = &self.move_data.move_paths;
1140                 mpis.extend(move_paths[mpi].parents(move_paths));
1141
1142                 for moi in &self.move_data.loc_map[location] {
1143                     debug!("report_use_of_moved_or_uninitialized: moi={:?}", moi);
1144                     if mpis.contains(&self.move_data.moves[*moi].path) {
1145                         debug!("report_use_of_moved_or_uninitialized: found");
1146                         result.push(MoveSite {
1147                             moi: *moi,
1148                             traversed_back_edge: is_back_edge,
1149                         });
1150
1151                         // Strictly speaking, we could continue our DFS here. There may be
1152                         // other moves that can reach the point of error. But it is kind of
1153                         // confusing to highlight them.
1154                         //
1155                         // Example:
1156                         //
1157                         // ```
1158                         // let a = vec![];
1159                         // let b = a;
1160                         // let c = a;
1161                         // drop(a); // <-- current point of error
1162                         // ```
1163                         //
1164                         // Because we stop the DFS here, we only highlight `let c = a`,
1165                         // and not `let b = a`. We will of course also report an error at
1166                         // `let c = a` which highlights `let b = a` as the move.
1167                         continue 'dfs;
1168                     }
1169                 }
1170             }
1171
1172             // check for inits
1173             let mut any_match = false;
1174             drop_flag_effects::for_location_inits(
1175                 self.infcx.tcx,
1176                 self.mir,
1177                 self.move_data,
1178                 location,
1179                 |m| {
1180                     if m == mpi {
1181                         any_match = true;
1182                     }
1183                 },
1184             );
1185             if any_match {
1186                 continue 'dfs;
1187             }
1188
1189             stack.extend(mir.predecessor_locations(location).map(|predecessor| {
1190                 let back_edge = location.dominates(predecessor, &self.dominators);
1191                 (predecessor, is_back_edge || back_edge)
1192             }));
1193         }
1194
1195         result
1196     }
1197
1198     pub(super) fn report_illegal_mutation_of_borrowed(
1199         &mut self,
1200         context: Context,
1201         (place, span): (&Place<'tcx>, Span),
1202         loan: &BorrowData<'tcx>,
1203     ) {
1204         let loan_spans = self.retrieve_borrow_spans(loan);
1205         let loan_span = loan_spans.args_or_use();
1206
1207         let tcx = self.infcx.tcx;
1208         let mut err = if loan.kind == BorrowKind::Shallow {
1209             tcx.cannot_mutate_in_match_guard(
1210                 span,
1211                 loan_span,
1212                 &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
1213                 "assign",
1214                 Origin::Mir,
1215             )
1216         } else {
1217             tcx.cannot_assign_to_borrowed(
1218                 span,
1219                 loan_span,
1220                 &self.describe_place(place).unwrap_or_else(|| "_".to_owned()),
1221                 Origin::Mir,
1222             )
1223         };
1224
1225         loan_spans.var_span_label(
1226             &mut err,
1227             format!("borrow occurs due to use{}", loan_spans.describe()),
1228         );
1229
1230         self.explain_why_borrow_contains_point(context, loan, None)
1231             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, "");
1232
1233         err.buffer(&mut self.errors_buffer);
1234     }
1235
1236     /// Reports an illegal reassignment; for example, an assignment to
1237     /// (part of) a non-`mut` local that occurs potentially after that
1238     /// local has already been initialized. `place` is the path being
1239     /// assigned; `err_place` is a place providing a reason why
1240     /// `place` is not mutable (e.g., the non-`mut` local `x` in an
1241     /// assignment to `x.f`).
1242     pub(super) fn report_illegal_reassignment(
1243         &mut self,
1244         _context: Context,
1245         (place, span): (&Place<'tcx>, Span),
1246         assigned_span: Span,
1247         err_place: &Place<'tcx>,
1248     ) {
1249         let (from_arg, local_decl) = if let Place::Local(local) = *err_place {
1250             if let LocalKind::Arg = self.mir.local_kind(local) {
1251                 (true, Some(&self.mir.local_decls[local]))
1252             } else {
1253                 (false, Some(&self.mir.local_decls[local]))
1254             }
1255         } else {
1256             (false, None)
1257         };
1258
1259         // If root local is initialized immediately (everything apart from let
1260         // PATTERN;) then make the error refer to that local, rather than the
1261         // place being assigned later.
1262         let (place_description, assigned_span) = match local_decl {
1263             Some(LocalDecl {
1264                 is_user_variable: Some(ClearCrossCrate::Clear),
1265                 ..
1266             })
1267             | Some(LocalDecl {
1268                 is_user_variable:
1269                     Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
1270                         opt_match_place: None,
1271                         ..
1272                     }))),
1273                 ..
1274             })
1275             | Some(LocalDecl {
1276                 is_user_variable: None,
1277                 ..
1278             })
1279             | None => (self.describe_place(place), assigned_span),
1280             Some(decl) => (self.describe_place(err_place), decl.source_info.span),
1281         };
1282
1283         let mut err = self.infcx.tcx.cannot_reassign_immutable(
1284             span,
1285             place_description.as_ref().map(AsRef::as_ref).unwrap_or("_"),
1286             from_arg,
1287             Origin::Mir,
1288         );
1289         let msg = if from_arg {
1290             "cannot assign to immutable argument"
1291         } else {
1292             "cannot assign twice to immutable variable"
1293         };
1294         if span != assigned_span {
1295             if !from_arg {
1296                 let value_msg = match place_description {
1297                     Some(name) => format!("`{}`", name),
1298                     None => "value".to_owned(),
1299                 };
1300                 err.span_label(assigned_span, format!("first assignment to {}", value_msg));
1301             }
1302         }
1303         if let Some(decl) = local_decl {
1304             if let Some(name) = decl.name {
1305                 if decl.can_be_made_mutable() {
1306                     err.span_suggestion_with_applicability(
1307                         decl.source_info.span,
1308                         "make this binding mutable",
1309                         format!("mut {}", name),
1310                         Applicability::MachineApplicable,
1311                     );
1312                 }
1313             }
1314         }
1315         err.span_label(span, msg);
1316         err.buffer(&mut self.errors_buffer);
1317     }
1318 }
1319
1320 pub(super) struct IncludingDowncast(bool);
1321
1322 /// Which case a StorageDeadOrDrop is for.
1323 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
1324 enum StorageDeadOrDrop<'tcx> {
1325     LocalStorageDead,
1326     BoxedStorageDead,
1327     Destructor(ty::Ty<'tcx>),
1328 }
1329
1330 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
1331
1332     /// Adds a suggestion when a closure is invoked twice with a moved variable.
1333     ///
1334     /// ```text
1335     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
1336     ///       its environment
1337     ///   --> $DIR/issue-42065.rs:16:29
1338     ///    |
1339     /// LL |         for (key, value) in dict {
1340     ///    |                             ^^^^
1341     /// ```
1342     pub(super) fn add_closure_invoked_twice_with_moved_variable_suggestion(
1343         &self,
1344         location: Location,
1345         place: &Place<'tcx>,
1346         diag: &mut DiagnosticBuilder<'_>,
1347     ) {
1348         let mut target = place.local();
1349         debug!(
1350             "add_closure_invoked_twice_with_moved_variable_suggestion: location={:?} place={:?} \
1351              target={:?}",
1352              location, place, target,
1353         );
1354         for stmt in &self.mir[location.block].statements[location.statement_index..] {
1355             debug!(
1356                 "add_closure_invoked_twice_with_moved_variable_suggestion: stmt={:?} \
1357                  target={:?}",
1358                  stmt, target,
1359             );
1360             if let StatementKind::Assign(into, box Rvalue::Use(from)) = &stmt.kind {
1361                 debug!(
1362                     "add_closure_invoked_twice_with_moved_variable_suggestion: into={:?} \
1363                      from={:?}",
1364                      into, from,
1365                 );
1366                 match from {
1367                     Operand::Copy(ref place) |
1368                     Operand::Move(ref place) if target == place.local() =>
1369                         target = into.local(),
1370                     _ => {},
1371                 }
1372             }
1373         }
1374
1375
1376         let terminator = self.mir[location.block].terminator();
1377         debug!(
1378             "add_closure_invoked_twice_with_moved_variable_suggestion: terminator={:?}",
1379             terminator,
1380         );
1381         if let TerminatorKind::Call {
1382             func: Operand::Constant(box Constant {
1383                 literal: ty::Const { ty: &ty::TyS { sty: ty::TyKind::FnDef(id, _), ..  }, ..  },
1384                 ..
1385             }),
1386             args,
1387             ..
1388         } = &terminator.kind {
1389             debug!("add_closure_invoked_twice_with_moved_variable_suggestion: id={:?}", id);
1390             if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
1391                 let closure = match args.first() {
1392                     Some(Operand::Copy(ref place)) |
1393                     Some(Operand::Move(ref place)) if target == place.local() =>
1394                         place.local().unwrap(),
1395                     _ => return,
1396                 };
1397                 debug!(
1398                     "add_closure_invoked_twice_with_moved_variable_suggestion: closure={:?}",
1399                      closure,
1400                 );
1401
1402                 if let ty::TyKind::Closure(did, _substs) = self.mir.local_decls[closure].ty.sty {
1403                     let node_id = match self.infcx.tcx.hir().as_local_node_id(did) {
1404                         Some(node_id) => node_id,
1405                         _ => return,
1406                     };
1407                     let hir_id = self.infcx.tcx.hir().node_to_hir_id(node_id);
1408
1409                     if let Some((
1410                         span, name
1411                     )) = self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id) {
1412                         diag.span_note(
1413                             *span,
1414                             &format!(
1415                                 "closure cannot be invoked more than once because it \
1416                                  moves the variable `{}` out of its environment",
1417                                  name,
1418                             ),
1419                         );
1420                     }
1421                 }
1422             }
1423         }
1424     }
1425
1426     /// End-user visible description of `place` if one can be found. If the
1427     /// place is a temporary for instance, None will be returned.
1428     pub(super) fn describe_place(&self, place: &Place<'tcx>) -> Option<String> {
1429         self.describe_place_with_options(place, IncludingDowncast(false))
1430     }
1431
1432     /// End-user visible description of `place` if one can be found. If the
1433     /// place is a temporary for instance, None will be returned.
1434     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
1435     /// `Downcast` and `IncludingDowncast` is true
1436     pub(super) fn describe_place_with_options(
1437         &self,
1438         place: &Place<'tcx>,
1439         including_downcast: IncludingDowncast,
1440     ) -> Option<String> {
1441         let mut buf = String::new();
1442         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
1443             Ok(()) => Some(buf),
1444             Err(()) => None,
1445         }
1446     }
1447
1448     /// Appends end-user visible description of `place` to `buf`.
1449     fn append_place_to_string(
1450         &self,
1451         place: &Place<'tcx>,
1452         buf: &mut String,
1453         mut autoderef: bool,
1454         including_downcast: &IncludingDowncast,
1455     ) -> Result<(), ()> {
1456         match *place {
1457             Place::Promoted(_) => {
1458                 buf.push_str("promoted");
1459             }
1460             Place::Local(local) => {
1461                 self.append_local_to_string(local, buf)?;
1462             }
1463             Place::Static(ref static_) => {
1464                 buf.push_str(&self.infcx.tcx.item_name(static_.def_id).to_string());
1465             }
1466             Place::Projection(ref proj) => {
1467                 match proj.elem {
1468                     ProjectionElem::Deref => {
1469                         let upvar_field_projection =
1470                             place.is_upvar_field_projection(self.mir, &self.infcx.tcx);
1471                         if let Some(field) = upvar_field_projection {
1472                             let var_index = field.index();
1473                             let name = self.mir.upvar_decls[var_index].debug_name.to_string();
1474                             if self.mir.upvar_decls[var_index].by_ref {
1475                                 buf.push_str(&name);
1476                             } else {
1477                                 buf.push_str(&format!("*{}", &name));
1478                             }
1479                         } else {
1480                             if autoderef {
1481                                 self.append_place_to_string(
1482                                     &proj.base,
1483                                     buf,
1484                                     autoderef,
1485                                     &including_downcast,
1486                                 )?;
1487                             } else if let Place::Local(local) = proj.base {
1488                                 if let Some(ClearCrossCrate::Set(BindingForm::RefForGuard)) =
1489                                     self.mir.local_decls[local].is_user_variable
1490                                 {
1491                                     self.append_place_to_string(
1492                                         &proj.base,
1493                                         buf,
1494                                         autoderef,
1495                                         &including_downcast,
1496                                     )?;
1497                                 } else {
1498                                     buf.push_str(&"*");
1499                                     self.append_place_to_string(
1500                                         &proj.base,
1501                                         buf,
1502                                         autoderef,
1503                                         &including_downcast,
1504                                     )?;
1505                                 }
1506                             } else {
1507                                 buf.push_str(&"*");
1508                                 self.append_place_to_string(
1509                                     &proj.base,
1510                                     buf,
1511                                     autoderef,
1512                                     &including_downcast,
1513                                 )?;
1514                             }
1515                         }
1516                     }
1517                     ProjectionElem::Downcast(..) => {
1518                         self.append_place_to_string(
1519                             &proj.base,
1520                             buf,
1521                             autoderef,
1522                             &including_downcast,
1523                         )?;
1524                         if including_downcast.0 {
1525                             return Err(());
1526                         }
1527                     }
1528                     ProjectionElem::Field(field, _ty) => {
1529                         autoderef = true;
1530
1531                         let upvar_field_projection =
1532                             place.is_upvar_field_projection(self.mir, &self.infcx.tcx);
1533                         if let Some(field) = upvar_field_projection {
1534                             let var_index = field.index();
1535                             let name = self.mir.upvar_decls[var_index].debug_name.to_string();
1536                             buf.push_str(&name);
1537                         } else {
1538                             let field_name = self.describe_field(&proj.base, field);
1539                             self.append_place_to_string(
1540                                 &proj.base,
1541                                 buf,
1542                                 autoderef,
1543                                 &including_downcast,
1544                             )?;
1545                             buf.push_str(&format!(".{}", field_name));
1546                         }
1547                     }
1548                     ProjectionElem::Index(index) => {
1549                         autoderef = true;
1550
1551                         self.append_place_to_string(
1552                             &proj.base,
1553                             buf,
1554                             autoderef,
1555                             &including_downcast,
1556                         )?;
1557                         buf.push_str("[");
1558                         if self.append_local_to_string(index, buf).is_err() {
1559                             buf.push_str("_");
1560                         }
1561                         buf.push_str("]");
1562                     }
1563                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
1564                         autoderef = true;
1565                         // Since it isn't possible to borrow an element on a particular index and
1566                         // then use another while the borrow is held, don't output indices details
1567                         // to avoid confusing the end-user
1568                         self.append_place_to_string(
1569                             &proj.base,
1570                             buf,
1571                             autoderef,
1572                             &including_downcast,
1573                         )?;
1574                         buf.push_str(&"[..]");
1575                     }
1576                 };
1577             }
1578         }
1579
1580         Ok(())
1581     }
1582
1583     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
1584     /// a name, then `Err` is returned
1585     fn append_local_to_string(&self, local_index: Local, buf: &mut String) -> Result<(), ()> {
1586         let local = &self.mir.local_decls[local_index];
1587         match local.name {
1588             Some(name) => {
1589                 buf.push_str(&name.to_string());
1590                 Ok(())
1591             }
1592             None => Err(()),
1593         }
1594     }
1595
1596     /// End-user visible description of the `field`nth field of `base`
1597     fn describe_field(&self, base: &Place, field: Field) -> String {
1598         match *base {
1599             Place::Local(local) => {
1600                 let local = &self.mir.local_decls[local];
1601                 self.describe_field_from_ty(&local.ty, field)
1602             }
1603             Place::Promoted(ref prom) => self.describe_field_from_ty(&prom.1, field),
1604             Place::Static(ref static_) => self.describe_field_from_ty(&static_.ty, field),
1605             Place::Projection(ref proj) => match proj.elem {
1606                 ProjectionElem::Deref => self.describe_field(&proj.base, field),
1607                 ProjectionElem::Downcast(def, variant_index) =>
1608                     def.variants[variant_index].fields[field.index()].ident.to_string(),
1609                 ProjectionElem::Field(_, field_type) => {
1610                     self.describe_field_from_ty(&field_type, field)
1611                 }
1612                 ProjectionElem::Index(..)
1613                 | ProjectionElem::ConstantIndex { .. }
1614                 | ProjectionElem::Subslice { .. } => {
1615                     self.describe_field(&proj.base, field)
1616                 }
1617             },
1618         }
1619     }
1620
1621     /// End-user visible description of the `field_index`nth field of `ty`
1622     fn describe_field_from_ty(&self, ty: &ty::Ty, field: Field) -> String {
1623         if ty.is_box() {
1624             // If the type is a box, the field is described from the boxed type
1625             self.describe_field_from_ty(&ty.boxed_ty(), field)
1626         } else {
1627             match ty.sty {
1628                 ty::Adt(def, _) => if def.is_enum() {
1629                     field.index().to_string()
1630                 } else {
1631                     def.non_enum_variant().fields[field.index()]
1632                         .ident
1633                         .to_string()
1634                 },
1635                 ty::Tuple(_) => field.index().to_string(),
1636                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
1637                     self.describe_field_from_ty(&ty, field)
1638                 }
1639                 ty::Array(ty, _) | ty::Slice(ty) => self.describe_field_from_ty(&ty, field),
1640                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
1641                     // Convert the def-id into a node-id. node-ids are only valid for
1642                     // the local code in the current crate, so this returns an `Option` in case
1643                     // the closure comes from another crate. But in that case we wouldn't
1644                     // be borrowck'ing it, so we can just unwrap:
1645                     let node_id = self.infcx.tcx.hir().as_local_node_id(def_id).unwrap();
1646                     let freevar = self.infcx
1647                         .tcx
1648                         .with_freevars(node_id, |fv| fv[field.index()]);
1649
1650                     self.infcx.tcx.hir().name(freevar.var_id()).to_string()
1651                 }
1652                 _ => {
1653                     // Might need a revision when the fields in trait RFC is implemented
1654                     // (https://github.com/rust-lang/rfcs/pull/1546)
1655                     bug!(
1656                         "End-user description not implemented for field access on `{:?}`",
1657                         ty.sty
1658                     );
1659                 }
1660             }
1661         }
1662     }
1663
1664     /// Check if a place is a thread-local static.
1665     pub fn is_place_thread_local(&self, place: &Place<'tcx>) -> bool {
1666         if let Place::Static(statik) = place {
1667             let attrs = self.infcx.tcx.get_attrs(statik.def_id);
1668             let is_thread_local = attrs.iter().any(|attr| attr.check_name("thread_local"));
1669
1670             debug!(
1671                 "is_place_thread_local: attrs={:?} is_thread_local={:?}",
1672                 attrs, is_thread_local
1673             );
1674             is_thread_local
1675         } else {
1676             debug!("is_place_thread_local: no");
1677             false
1678         }
1679     }
1680
1681     fn classify_drop_access_kind(&self, place: &Place<'tcx>) -> StorageDeadOrDrop<'tcx> {
1682         let tcx = self.infcx.tcx;
1683         match place {
1684             Place::Local(_) | Place::Static(_) | Place::Promoted(_) => {
1685                 StorageDeadOrDrop::LocalStorageDead
1686             }
1687             Place::Projection(box PlaceProjection { base, elem }) => {
1688                 let base_access = self.classify_drop_access_kind(base);
1689                 match elem {
1690                     ProjectionElem::Deref => match base_access {
1691                         StorageDeadOrDrop::LocalStorageDead
1692                         | StorageDeadOrDrop::BoxedStorageDead => {
1693                             assert!(
1694                                 base.ty(self.mir, tcx).to_ty(tcx).is_box(),
1695                                 "Drop of value behind a reference or raw pointer"
1696                             );
1697                             StorageDeadOrDrop::BoxedStorageDead
1698                         }
1699                         StorageDeadOrDrop::Destructor(_) => base_access,
1700                     },
1701                     ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
1702                         let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
1703                         match base_ty.sty {
1704                             ty::Adt(def, _) if def.has_dtor(tcx) => {
1705                                 // Report the outermost adt with a destructor
1706                                 match base_access {
1707                                     StorageDeadOrDrop::Destructor(_) => base_access,
1708                                     StorageDeadOrDrop::LocalStorageDead
1709                                     | StorageDeadOrDrop::BoxedStorageDead => {
1710                                         StorageDeadOrDrop::Destructor(base_ty)
1711                                     }
1712                                 }
1713                             }
1714                             _ => base_access,
1715                         }
1716                     }
1717
1718                     ProjectionElem::ConstantIndex { .. }
1719                     | ProjectionElem::Subslice { .. }
1720                     | ProjectionElem::Index(_) => base_access,
1721                 }
1722             }
1723         }
1724     }
1725
1726     /// Annotate argument and return type of function and closure with (synthesized) lifetime for
1727     /// borrow of local value that does not live long enough.
1728     fn annotate_argument_and_return_for_borrow(
1729         &self,
1730         borrow: &BorrowData<'tcx>,
1731     ) -> Option<AnnotatedBorrowFnSignature> {
1732         // Define a fallback for when we can't match a closure.
1733         let fallback = || {
1734             let is_closure = self.infcx.tcx.is_closure(self.mir_def_id);
1735             if is_closure {
1736                 None
1737             } else {
1738                 let ty = self.infcx.tcx.type_of(self.mir_def_id);
1739                 match ty.sty {
1740                     ty::TyKind::FnDef(_, _) | ty::TyKind::FnPtr(_) => self.annotate_fn_sig(
1741                         self.mir_def_id,
1742                         self.infcx.tcx.fn_sig(self.mir_def_id),
1743                     ),
1744                     _ => None,
1745                 }
1746             }
1747         };
1748
1749         // In order to determine whether we need to annotate, we need to check whether the reserve
1750         // place was an assignment into a temporary.
1751         //
1752         // If it was, we check whether or not that temporary is eventually assigned into the return
1753         // place. If it was, we can add annotations about the function's return type and arguments
1754         // and it'll make sense.
1755         let location = borrow.reserve_location;
1756         debug!(
1757             "annotate_argument_and_return_for_borrow: location={:?}",
1758             location
1759         );
1760         if let Some(&Statement { kind: StatementKind::Assign(ref reservation, _), ..})
1761              = &self.mir[location.block].statements.get(location.statement_index)
1762         {
1763             debug!(
1764                 "annotate_argument_and_return_for_borrow: reservation={:?}",
1765                 reservation
1766             );
1767             // Check that the initial assignment of the reserve location is into a temporary.
1768             let mut target = *match reservation {
1769                 Place::Local(local) if self.mir.local_kind(*local) == LocalKind::Temp => local,
1770                 _ => return None,
1771             };
1772
1773             // Next, look through the rest of the block, checking if we are assigning the
1774             // `target` (that is, the place that contains our borrow) to anything.
1775             let mut annotated_closure = None;
1776             for stmt in &self.mir[location.block].statements[location.statement_index + 1..] {
1777                 debug!(
1778                     "annotate_argument_and_return_for_borrow: target={:?} stmt={:?}",
1779                     target, stmt
1780                 );
1781                 if let StatementKind::Assign(Place::Local(assigned_to), box rvalue) = &stmt.kind
1782                 {
1783                     debug!(
1784                         "annotate_argument_and_return_for_borrow: assigned_to={:?} \
1785                          rvalue={:?}",
1786                         assigned_to, rvalue
1787                     );
1788                     // Check if our `target` was captured by a closure.
1789                     if let Rvalue::Aggregate(
1790                         box AggregateKind::Closure(def_id, substs),
1791                         operands,
1792                     ) = rvalue
1793                     {
1794                         for operand in operands {
1795                             let assigned_from = match operand {
1796                                 Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1797                                     assigned_from
1798                                 }
1799                                 _ => continue,
1800                             };
1801                             debug!(
1802                                 "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1803                                 assigned_from
1804                             );
1805
1806                             // Find the local from the operand.
1807                             let assigned_from_local = match assigned_from.local() {
1808                                 Some(local) => local,
1809                                 None => continue,
1810                             };
1811
1812                             if assigned_from_local != target {
1813                                 continue;
1814                             }
1815
1816                             // If a closure captured our `target` and then assigned
1817                             // into a place then we should annotate the closure in
1818                             // case it ends up being assigned into the return place.
1819                             annotated_closure = self.annotate_fn_sig(
1820                                 *def_id,
1821                                 self.infcx.closure_sig(*def_id, *substs),
1822                             );
1823                             debug!(
1824                                 "annotate_argument_and_return_for_borrow: \
1825                                  annotated_closure={:?} assigned_from_local={:?} \
1826                                  assigned_to={:?}",
1827                                 annotated_closure, assigned_from_local, assigned_to
1828                             );
1829
1830                             if *assigned_to == mir::RETURN_PLACE {
1831                                 // If it was assigned directly into the return place, then
1832                                 // return now.
1833                                 return annotated_closure;
1834                             } else {
1835                                 // Otherwise, update the target.
1836                                 target = *assigned_to;
1837                             }
1838                         }
1839
1840                         // If none of our closure's operands matched, then skip to the next
1841                         // statement.
1842                         continue;
1843                     }
1844
1845                     // Otherwise, look at other types of assignment.
1846                     let assigned_from = match rvalue {
1847                         Rvalue::Ref(_, _, assigned_from) => assigned_from,
1848                         Rvalue::Use(operand) => match operand {
1849                             Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1850                                 assigned_from
1851                             }
1852                             _ => continue,
1853                         },
1854                         _ => continue,
1855                     };
1856                     debug!(
1857                         "annotate_argument_and_return_for_borrow: \
1858                          assigned_from={:?}",
1859                         assigned_from,
1860                     );
1861
1862                     // Find the local from the rvalue.
1863                     let assigned_from_local = match assigned_from.local() {
1864                         Some(local) => local,
1865                         None => continue,
1866                     };
1867                     debug!(
1868                         "annotate_argument_and_return_for_borrow: \
1869                          assigned_from_local={:?}",
1870                         assigned_from_local,
1871                     );
1872
1873                     // Check if our local matches the target - if so, we've assigned our
1874                     // borrow to a new place.
1875                     if assigned_from_local != target {
1876                         continue;
1877                     }
1878
1879                     // If we assigned our `target` into a new place, then we should
1880                     // check if it was the return place.
1881                     debug!(
1882                         "annotate_argument_and_return_for_borrow: \
1883                          assigned_from_local={:?} assigned_to={:?}",
1884                         assigned_from_local, assigned_to
1885                     );
1886                     if *assigned_to == mir::RETURN_PLACE {
1887                         // If it was then return the annotated closure if there was one,
1888                         // else, annotate this function.
1889                         return annotated_closure.or_else(fallback);
1890                     }
1891
1892                     // If we didn't assign into the return place, then we just update
1893                     // the target.
1894                     target = *assigned_to;
1895                 }
1896             }
1897
1898             // Check the terminator if we didn't find anything in the statements.
1899             let terminator = &self.mir[location.block].terminator();
1900             debug!(
1901                 "annotate_argument_and_return_for_borrow: target={:?} terminator={:?}",
1902                 target, terminator
1903             );
1904             if let TerminatorKind::Call {
1905                 destination: Some((Place::Local(assigned_to), _)),
1906                 args,
1907                 ..
1908             } = &terminator.kind
1909             {
1910                 debug!(
1911                     "annotate_argument_and_return_for_borrow: assigned_to={:?} args={:?}",
1912                     assigned_to, args
1913                 );
1914                 for operand in args {
1915                     let assigned_from = match operand {
1916                         Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
1917                             assigned_from
1918                         }
1919                         _ => continue,
1920                     };
1921                     debug!(
1922                         "annotate_argument_and_return_for_borrow: assigned_from={:?}",
1923                         assigned_from,
1924                     );
1925
1926                     if let Some(assigned_from_local) = assigned_from.local() {
1927                         debug!(
1928                             "annotate_argument_and_return_for_borrow: assigned_from_local={:?}",
1929                             assigned_from_local,
1930                         );
1931
1932                         if *assigned_to == mir::RETURN_PLACE && assigned_from_local == target {
1933                             return annotated_closure.or_else(fallback);
1934                         }
1935                     }
1936                 }
1937             }
1938         }
1939
1940         // If we haven't found an assignment into the return place, then we need not add
1941         // any annotations.
1942         debug!("annotate_argument_and_return_for_borrow: none found");
1943         None
1944     }
1945
1946     /// Annotate the first argument and return type of a function signature if they are
1947     /// references.
1948     fn annotate_fn_sig(
1949         &self,
1950         did: DefId,
1951         sig: ty::PolyFnSig<'tcx>,
1952     ) -> Option<AnnotatedBorrowFnSignature> {
1953         debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
1954         let is_closure = self.infcx.tcx.is_closure(did);
1955         let fn_node_id = self.infcx.tcx.hir().as_local_node_id(did)?;
1956         let fn_decl = self.infcx.tcx.hir().fn_decl(fn_node_id)?;
1957
1958         // We need to work out which arguments to highlight. We do this by looking
1959         // at the return type, where there are three cases:
1960         //
1961         // 1. If there are named arguments, then we should highlight the return type and
1962         //    highlight any of the arguments that are also references with that lifetime.
1963         //    If there are no arguments that have the same lifetime as the return type,
1964         //    then don't highlight anything.
1965         // 2. The return type is a reference with an anonymous lifetime. If this is
1966         //    the case, then we can take advantage of (and teach) the lifetime elision
1967         //    rules.
1968         //
1969         //    We know that an error is being reported. So the arguments and return type
1970         //    must satisfy the elision rules. Therefore, if there is a single argument
1971         //    then that means the return type and first (and only) argument have the same
1972         //    lifetime and the borrow isn't meeting that, we can highlight the argument
1973         //    and return type.
1974         //
1975         //    If there are multiple arguments then the first argument must be self (else
1976         //    it would not satisfy the elision rules), so we can highlight self and the
1977         //    return type.
1978         // 3. The return type is not a reference. In this case, we don't highlight
1979         //    anything.
1980         let return_ty = sig.output();
1981         match return_ty.skip_binder().sty {
1982             ty::TyKind::Ref(return_region, _, _) if return_region.has_name() && !is_closure => {
1983                 // This is case 1 from above, return type is a named reference so we need to
1984                 // search for relevant arguments.
1985                 let mut arguments = Vec::new();
1986                 for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
1987                     if let ty::TyKind::Ref(argument_region, _, _) = argument.sty {
1988                         if argument_region == return_region {
1989                             // Need to use the `rustc::ty` types to compare against the
1990                             // `return_region`. Then use the `rustc::hir` type to get only
1991                             // the lifetime span.
1992                             if let hir::TyKind::Rptr(lifetime, _) = &fn_decl.inputs[index].node {
1993                                 // With access to the lifetime, we can get
1994                                 // the span of it.
1995                                 arguments.push((*argument, lifetime.span));
1996                             } else {
1997                                 bug!("ty type is a ref but hir type is not");
1998                             }
1999                         }
2000                     }
2001                 }
2002
2003                 // We need to have arguments. This shouldn't happen, but it's worth checking.
2004                 if arguments.is_empty() {
2005                     return None;
2006                 }
2007
2008                 // We use a mix of the HIR and the Ty types to get information
2009                 // as the HIR doesn't have full types for closure arguments.
2010                 let return_ty = *sig.output().skip_binder();
2011                 let mut return_span = fn_decl.output.span();
2012                 if let hir::FunctionRetTy::Return(ty) = fn_decl.output {
2013                     if let hir::TyKind::Rptr(lifetime, _) = ty.into_inner().node {
2014                         return_span = lifetime.span;
2015                     }
2016                 }
2017
2018                 Some(AnnotatedBorrowFnSignature::NamedFunction {
2019                     arguments,
2020                     return_ty,
2021                     return_span,
2022                 })
2023             }
2024             ty::TyKind::Ref(_, _, _) if is_closure => {
2025                 // This is case 2 from above but only for closures, return type is anonymous
2026                 // reference so we select
2027                 // the first argument.
2028                 let argument_span = fn_decl.inputs.first()?.span;
2029                 let argument_ty = sig.inputs().skip_binder().first()?;
2030
2031                 // Closure arguments are wrapped in a tuple, so we need to get the first
2032                 // from that.
2033                 if let ty::TyKind::Tuple(elems) = argument_ty.sty {
2034                     let argument_ty = elems.first()?;
2035                     if let ty::TyKind::Ref(_, _, _) = argument_ty.sty {
2036                         return Some(AnnotatedBorrowFnSignature::Closure {
2037                             argument_ty,
2038                             argument_span,
2039                         });
2040                     }
2041                 }
2042
2043                 None
2044             }
2045             ty::TyKind::Ref(_, _, _) => {
2046                 // This is also case 2 from above but for functions, return type is still an
2047                 // anonymous reference so we select the first argument.
2048                 let argument_span = fn_decl.inputs.first()?.span;
2049                 let argument_ty = sig.inputs().skip_binder().first()?;
2050
2051                 let return_span = fn_decl.output.span();
2052                 let return_ty = *sig.output().skip_binder();
2053
2054                 // We expect the first argument to be a reference.
2055                 match argument_ty.sty {
2056                     ty::TyKind::Ref(_, _, _) => {}
2057                     _ => return None,
2058                 }
2059
2060                 Some(AnnotatedBorrowFnSignature::AnonymousFunction {
2061                     argument_ty,
2062                     argument_span,
2063                     return_ty,
2064                     return_span,
2065                 })
2066             }
2067             _ => {
2068                 // This is case 3 from above, return type is not a reference so don't highlight
2069                 // anything.
2070                 None
2071             }
2072         }
2073     }
2074 }
2075
2076 #[derive(Debug)]
2077 enum AnnotatedBorrowFnSignature<'tcx> {
2078     NamedFunction {
2079         arguments: Vec<(ty::Ty<'tcx>, Span)>,
2080         return_ty: ty::Ty<'tcx>,
2081         return_span: Span,
2082     },
2083     AnonymousFunction {
2084         argument_ty: ty::Ty<'tcx>,
2085         argument_span: Span,
2086         return_ty: ty::Ty<'tcx>,
2087         return_span: Span,
2088     },
2089     Closure {
2090         argument_ty: ty::Ty<'tcx>,
2091         argument_span: Span,
2092     },
2093 }
2094
2095 impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
2096     /// Annotate the provided diagnostic with information about borrow from the fn signature that
2097     /// helps explain.
2098     fn emit(&self, diag: &mut DiagnosticBuilder<'_>) -> String {
2099         match self {
2100             AnnotatedBorrowFnSignature::Closure {
2101                 argument_ty,
2102                 argument_span,
2103             } => {
2104                 diag.span_label(
2105                     *argument_span,
2106                     format!("has type `{}`", self.get_name_for_ty(argument_ty, 0)),
2107                 );
2108
2109                 self.get_region_name_for_ty(argument_ty, 0)
2110             }
2111             AnnotatedBorrowFnSignature::AnonymousFunction {
2112                 argument_ty,
2113                 argument_span,
2114                 return_ty,
2115                 return_span,
2116             } => {
2117                 let argument_ty_name = self.get_name_for_ty(argument_ty, 0);
2118                 diag.span_label(*argument_span, format!("has type `{}`", argument_ty_name));
2119
2120                 let return_ty_name = self.get_name_for_ty(return_ty, 0);
2121                 let types_equal = return_ty_name == argument_ty_name;
2122                 diag.span_label(
2123                     *return_span,
2124                     format!(
2125                         "{}has type `{}`",
2126                         if types_equal { "also " } else { "" },
2127                         return_ty_name,
2128                     ),
2129                 );
2130
2131                 diag.note(
2132                     "argument and return type have the same lifetime due to lifetime elision rules",
2133                 );
2134                 diag.note(
2135                     "to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch10-03-\
2136                      lifetime-syntax.html#lifetime-elision>",
2137                 );
2138
2139                 self.get_region_name_for_ty(return_ty, 0)
2140             }
2141             AnnotatedBorrowFnSignature::NamedFunction {
2142                 arguments,
2143                 return_ty,
2144                 return_span,
2145             } => {
2146                 // Region of return type and arguments checked to be the same earlier.
2147                 let region_name = self.get_region_name_for_ty(return_ty, 0);
2148                 for (_, argument_span) in arguments {
2149                     diag.span_label(*argument_span, format!("has lifetime `{}`", region_name));
2150                 }
2151
2152                 diag.span_label(
2153                     *return_span,
2154                     format!("also has lifetime `{}`", region_name,),
2155                 );
2156
2157                 diag.help(&format!(
2158                     "use data from the highlighted arguments which match the `{}` lifetime of \
2159                      the return type",
2160                     region_name,
2161                 ));
2162
2163                 region_name
2164             }
2165         }
2166     }
2167
2168     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
2169     /// name where required.
2170     fn get_name_for_ty(&self, ty: ty::Ty<'tcx>, counter: usize) -> String {
2171         // We need to add synthesized lifetimes where appropriate. We do
2172         // this by hooking into the pretty printer and telling it to label the
2173         // lifetimes without names with the value `'0`.
2174         match ty.sty {
2175             ty::TyKind::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
2176             | ty::TyKind::Ref(
2177                 ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
2178                 _,
2179                 _,
2180             ) => RegionHighlightMode::highlighting_bound_region(*br, counter, || ty.to_string()),
2181             _ => ty.to_string(),
2182         }
2183     }
2184
2185     /// Return the name of the provided `Ty` (that must be a reference)'s region with a
2186     /// synthesized lifetime name where required.
2187     fn get_region_name_for_ty(&self, ty: ty::Ty<'tcx>, counter: usize) -> String {
2188         match ty.sty {
2189             ty::TyKind::Ref(region, _, _) => match region {
2190                 ty::RegionKind::ReLateBound(_, br)
2191                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
2192                     RegionHighlightMode::highlighting_bound_region(
2193                         *br,
2194                         counter,
2195                         || region.to_string(),
2196                     )
2197                 }
2198                 _ => region.to_string(),
2199             },
2200             _ => bug!("ty for annotation of borrow region is not a reference"),
2201         }
2202     }
2203 }
2204
2205 // The span(s) associated to a use of a place.
2206 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
2207 pub(super) enum UseSpans {
2208     // The access is caused by capturing a variable for a closure.
2209     ClosureUse {
2210         // This is true if the captured variable was from a generator.
2211         is_generator: bool,
2212         // The span of the args of the closure, including the `move` keyword if
2213         // it's present.
2214         args_span: Span,
2215         // The span of the first use of the captured variable inside the closure.
2216         var_span: Span,
2217     },
2218     // This access has a single span associated to it: common case.
2219     OtherUse(Span),
2220 }
2221
2222 impl UseSpans {
2223     pub(super) fn args_or_use(self) -> Span {
2224         match self {
2225             UseSpans::ClosureUse {
2226                 args_span: span, ..
2227             }
2228             | UseSpans::OtherUse(span) => span,
2229         }
2230     }
2231
2232     pub(super) fn var_or_use(self) -> Span {
2233         match self {
2234             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
2235         }
2236     }
2237
2238     // Add a span label to the arguments of the closure, if it exists.
2239     pub(super) fn args_span_label(self, err: &mut DiagnosticBuilder, message: impl Into<String>) {
2240         if let UseSpans::ClosureUse { args_span, .. } = self {
2241             err.span_label(args_span, message);
2242         }
2243     }
2244
2245     // Add a span label to the use of the captured variable, if it exists.
2246     pub(super) fn var_span_label(self, err: &mut DiagnosticBuilder, message: impl Into<String>) {
2247         if let UseSpans::ClosureUse { var_span, .. } = self {
2248             err.span_label(var_span, message);
2249         }
2250     }
2251
2252     /// Return `false` if this place is not used in a closure.
2253     fn for_closure(&self) -> bool {
2254         match *self {
2255             UseSpans::ClosureUse { is_generator, .. } => !is_generator,
2256             _ => false,
2257         }
2258     }
2259
2260     /// Return `false` if this place is not used in a generator.
2261     fn for_generator(&self) -> bool {
2262         match *self {
2263             UseSpans::ClosureUse { is_generator, .. } => is_generator,
2264             _ => false,
2265         }
2266     }
2267
2268     /// Describe the span associated with a use of a place.
2269     fn describe(&self) -> String {
2270         match *self {
2271             UseSpans::ClosureUse { is_generator, .. } => if is_generator {
2272                 " in generator".to_string()
2273             } else {
2274                 " in closure".to_string()
2275             },
2276             _ => "".to_string(),
2277         }
2278     }
2279
2280     pub(super) fn or_else<F>(self, if_other: F) -> Self
2281     where
2282         F: FnOnce() -> Self,
2283     {
2284         match self {
2285             closure @ UseSpans::ClosureUse { .. } => closure,
2286             UseSpans::OtherUse(_) => if_other(),
2287         }
2288     }
2289 }
2290
2291 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
2292     /// Finds the spans associated to a move or copy of move_place at location.
2293     pub(super) fn move_spans(
2294         &self,
2295         moved_place: &Place<'tcx>, // Could also be an upvar.
2296         location: Location,
2297     ) -> UseSpans {
2298         use self::UseSpans::*;
2299
2300         let stmt = match self.mir[location.block].statements.get(location.statement_index) {
2301             Some(stmt) => stmt,
2302             None => return OtherUse(self.mir.source_info(location).span),
2303         };
2304
2305         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
2306         if let  StatementKind::Assign(
2307             _,
2308             box Rvalue::Aggregate(ref kind, ref places)
2309         ) = stmt.kind {
2310             let (def_id, is_generator) = match kind {
2311                 box AggregateKind::Closure(def_id, _) => (def_id, false),
2312                 box AggregateKind::Generator(def_id, _, _) => (def_id, true),
2313                 _ => return OtherUse(stmt.source_info.span),
2314             };
2315
2316             debug!(
2317                 "move_spans: def_id={:?} is_generator={:?} places={:?}",
2318                 def_id, is_generator, places
2319             );
2320             if let Some((args_span, var_span)) = self.closure_span(*def_id, moved_place, places) {
2321                 return ClosureUse {
2322                     is_generator,
2323                     args_span,
2324                     var_span,
2325                 };
2326             }
2327         }
2328
2329         OtherUse(stmt.source_info.span)
2330     }
2331
2332     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
2333     /// and its usage of the local assigned at `location`.
2334     /// This is done by searching in statements succeeding `location`
2335     /// and originating from `maybe_closure_span`.
2336     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
2337         use self::UseSpans::*;
2338         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
2339
2340         let target = match self.mir[location.block]
2341             .statements
2342             .get(location.statement_index)
2343         {
2344             Some(&Statement {
2345                 kind: StatementKind::Assign(Place::Local(local), _),
2346                 ..
2347             }) => local,
2348             _ => return OtherUse(use_span),
2349         };
2350
2351         if self.mir.local_kind(target) != LocalKind::Temp {
2352             // operands are always temporaries.
2353             return OtherUse(use_span);
2354         }
2355
2356         for stmt in &self.mir[location.block].statements[location.statement_index + 1..] {
2357             if let StatementKind::Assign(
2358                 _, box Rvalue::Aggregate(ref kind, ref places)
2359             ) = stmt.kind {
2360                 let (def_id, is_generator) = match kind {
2361                     box AggregateKind::Closure(def_id, _) => (def_id, false),
2362                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
2363                     _ => continue,
2364                 };
2365
2366                 debug!(
2367                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
2368                     def_id, is_generator, places
2369                 );
2370                 if let Some((args_span, var_span)) = self.closure_span(
2371                     *def_id, &Place::Local(target), places
2372                 ) {
2373                     return ClosureUse {
2374                         is_generator,
2375                         args_span,
2376                         var_span,
2377                     };
2378                 } else {
2379                     return OtherUse(use_span);
2380                 }
2381             }
2382
2383             if use_span != stmt.source_info.span {
2384                 break;
2385             }
2386         }
2387
2388         OtherUse(use_span)
2389     }
2390
2391     /// Finds the span of a captured variable within a closure or generator.
2392     fn closure_span(
2393         &self,
2394         def_id: DefId,
2395         target_place: &Place<'tcx>,
2396         places: &Vec<Operand<'tcx>>,
2397     ) -> Option<(Span, Span)> {
2398         debug!(
2399             "closure_span: def_id={:?} target_place={:?} places={:?}",
2400             def_id, target_place, places
2401         );
2402         let node_id = self.infcx.tcx.hir().as_local_node_id(def_id)?;
2403         let expr = &self.infcx.tcx.hir().expect_expr(node_id).node;
2404         debug!("closure_span: node_id={:?} expr={:?}", node_id, expr);
2405         if let hir::ExprKind::Closure(
2406             .., args_span, _
2407         ) = expr {
2408             let var_span = self.infcx.tcx.with_freevars(
2409                 node_id,
2410                 |freevars| {
2411                     for (v, place) in freevars.iter().zip(places) {
2412                         match place {
2413                             Operand::Copy(place) |
2414                             Operand::Move(place) if target_place == place => {
2415                                 debug!("closure_span: found captured local {:?}", place);
2416                                 return Some(v.span);
2417                             },
2418                             _ => {}
2419                         }
2420                     }
2421
2422                     None
2423                 },
2424             )?;
2425
2426             Some((*args_span, var_span))
2427         } else {
2428             None
2429         }
2430     }
2431
2432     /// Helper to retrieve span(s) of given borrow from the current MIR
2433     /// representation
2434     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData) -> UseSpans {
2435         let span = self.mir.source_info(borrow.reserve_location).span;
2436         self.borrow_spans(span, borrow.reserve_location)
2437     }
2438 }