src/librustc_mir/borrow_check/move_errors.rs

   1 use core::unicode::property::Pattern_White_Space;
   2
   3 use rustc::mir::*;
   4 use rustc::ty;
   5 use rustc_errors::{DiagnosticBuilder,Applicability};
   6 use syntax_pos::Span;
   7
   8 use crate::borrow_check::MirBorrowckCtxt;
   9 use crate::borrow_check::prefixes::PrefixSet;
  10 use crate::borrow_check::error_reporting::UseSpans;
  11 use crate::dataflow::move_paths::{
  12     IllegalMoveOrigin, IllegalMoveOriginKind,
  13     LookupResult, MoveError, MovePathIndex,
  14 };
  15 use crate::util::borrowck_errors::BorrowckErrors;
  16
  17 // Often when desugaring a pattern match we may have many individual moves in
  18 // MIR that are all part of one operation from the user's point-of-view. For
  19 // example:
  20 //
  21 // let (x, y) = foo()
  22 //
  23 // would move x from the 0 field of some temporary, and y from the 1 field. We
  24 // group such errors together for cleaner error reporting.
  25 //
  26 // Errors are kept separate if they are from places with different parent move
  27 // paths. For example, this generates two errors:
  28 //
  29 // let (&x, &y) = (&String::new(), &String::new());
  30 #[derive(Debug)]
  31 enum GroupedMoveError<'tcx> {
  32     // Place expression can't be moved from,
  33     // e.g., match x[0] { s => (), } where x: &[String]
  34     MovesFromPlace {
  35         original_path: Place<'tcx>,
  36         span: Span,
  37         move_from: Place<'tcx>,
  38         kind: IllegalMoveOriginKind<'tcx>,
  39         binds_to: Vec<Local>,
  40     },
  41     // Part of a value expression can't be moved from,
  42     // e.g., match &String::new() { &x => (), }
  43     MovesFromValue {
  44         original_path: Place<'tcx>,
  45         span: Span,
  46         move_from: MovePathIndex,
  47         kind: IllegalMoveOriginKind<'tcx>,
  48         binds_to: Vec<Local>,
  49     },
  50     // Everything that isn't from pattern matching.
  51     OtherIllegalMove {
  52         original_path: Place<'tcx>,
  53         use_spans: UseSpans,
  54         kind: IllegalMoveOriginKind<'tcx>,
  55     },
  56 }
  57
  58 impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
  59     pub(crate) fn report_move_errors(&mut self, move_errors: Vec<(Place<'tcx>, MoveError<'tcx>)>) {
  60         let grouped_errors = self.group_move_errors(move_errors);
  61         for error in grouped_errors {
  62             self.report(error);
  63         }
  64     }
  65
  66     fn group_move_errors(
  67         &self,
  68         errors: Vec<(Place<'tcx>, MoveError<'tcx>)>
  69     ) -> Vec<GroupedMoveError<'tcx>> {
  70         let mut grouped_errors = Vec::new();
  71         for (original_path, error) in errors {
  72             self.append_to_grouped_errors(&mut grouped_errors, original_path, error);
  73         }
  74         grouped_errors
  75     }
  76
  77     fn append_to_grouped_errors(
  78         &self,
  79         grouped_errors: &mut Vec<GroupedMoveError<'tcx>>,
  80         original_path: Place<'tcx>,
  81         error: MoveError<'tcx>,
  82     ) {
  83         match error {
  84             MoveError::UnionMove { .. } => {
  85                 unimplemented!("don't know how to report union move errors yet.")
  86             }
  87             MoveError::IllegalMove {
  88                 cannot_move_out_of: IllegalMoveOrigin { location, kind },
  89             } => {
  90                 // Note: that the only time we assign a place isn't a temporary
  91                 // to a user variable is when initializing it.
  92                 // If that ever stops being the case, then the ever initialized
  93                 // flow could be used.
  94                 if let Some(StatementKind::Assign(
  95                     Place::Base(PlaceBase::Local(local)),
  96                     box Rvalue::Use(Operand::Move(move_from)),
  97                 )) = self.body.basic_blocks()[location.block]
  98                     .statements
  99                     .get(location.statement_index)
 100                     .map(|stmt| &stmt.kind)
 101                 {
 102                     let local_decl = &self.body.local_decls[*local];
 103                     // opt_match_place is the
 104                     // match_span is the span of the expression being matched on
 105                     // match *x.y { ... }        match_place is Some(*x.y)
 106                     //       ^^^^                match_span is the span of *x.y
 107                     //
 108                     // opt_match_place is None for let [mut] x = ... statements,
 109                     // whether or not the right-hand side is a place expression
 110                     if let Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
 111                         opt_match_place: Some((ref opt_match_place, match_span)),
 112                         binding_mode: _,
 113                         opt_ty_info: _,
 114                         pat_span: _,
 115                     }))) = local_decl.is_user_variable
 116                     {
 117                         let stmt_source_info = self.body.source_info(location);
 118                         self.append_binding_error(
 119                             grouped_errors,
 120                             kind,
 121                             original_path,
 122                             move_from,
 123                             *local,
 124                             opt_match_place,
 125                             match_span,
 126                             stmt_source_info.span,
 127                         );
 128                         return;
 129                     }
 130                 }
 131
 132                 let move_spans = self.move_spans(&original_path, location);
 133                 grouped_errors.push(GroupedMoveError::OtherIllegalMove {
 134                     use_spans: move_spans,
 135                     original_path,
 136                     kind,
 137                 });
 138             }
 139         }
 140     }
 141
 142     fn append_binding_error(
 143         &self,
 144         grouped_errors: &mut Vec<GroupedMoveError<'tcx>>,
 145         kind: IllegalMoveOriginKind<'tcx>,
 146         original_path: Place<'tcx>,
 147         move_from: &Place<'tcx>,
 148         bind_to: Local,
 149         match_place: &Option<Place<'tcx>>,
 150         match_span: Span,
 151         statement_span: Span,
 152     ) {
 153         debug!(
 154             "append_binding_error(match_place={:?}, match_span={:?})",
 155             match_place, match_span
 156         );
 157
 158         let from_simple_let = match_place.is_none();
 159         let match_place = match_place.as_ref().unwrap_or(move_from);
 160
 161         match self.move_data.rev_lookup.find(match_place) {
 162             // Error with the match place
 163             LookupResult::Parent(_) => {
 164                 for ge in &mut *grouped_errors {
 165                     if let GroupedMoveError::MovesFromPlace { span, binds_to, .. } = ge {
 166                         if match_span == *span {
 167                             debug!("appending local({:?}) to list", bind_to);
 168                             if !binds_to.is_empty() {
 169                                 binds_to.push(bind_to);
 170                             }
 171                             return;
 172                         }
 173                     }
 174                 }
 175                 debug!("found a new move error location");
 176
 177                 // Don't need to point to x in let x = ... .
 178                 let (binds_to, span) = if from_simple_let {
 179                     (vec![], statement_span)
 180                 } else {
 181                     (vec![bind_to], match_span)
 182                 };
 183                 grouped_errors.push(GroupedMoveError::MovesFromPlace {
 184                     span,
 185                     move_from: match_place.clone(),
 186                     original_path,
 187                     kind,
 188                     binds_to,
 189                 });
 190             }
 191             // Error with the pattern
 192             LookupResult::Exact(_) => {
 193                 let mpi = match self.move_data.rev_lookup.find(move_from) {
 194                     LookupResult::Parent(Some(mpi)) => mpi,
 195                     // move_from should be a projection from match_place.
 196                     _ => unreachable!("Probably not unreachable..."),
 197                 };
 198                 for ge in &mut *grouped_errors {
 199                     if let GroupedMoveError::MovesFromValue {
 200                         span,
 201                         move_from: other_mpi,
 202                         binds_to,
 203                         ..
 204                     } = ge
 205                     {
 206                         if match_span == *span && mpi == *other_mpi {
 207                             debug!("appending local({:?}) to list", bind_to);
 208                             binds_to.push(bind_to);
 209                             return;
 210                         }
 211                     }
 212                 }
 213                 debug!("found a new move error location");
 214                 grouped_errors.push(GroupedMoveError::MovesFromValue {
 215                     span: match_span,
 216                     move_from: mpi,
 217                     original_path,
 218                     kind,
 219                     binds_to: vec![bind_to],
 220                 });
 221             }
 222         };
 223     }
 224
 225     fn report(&mut self, error: GroupedMoveError<'tcx>) {
 226         let (mut err, err_span) = {
 227             let (span, original_path, kind): (Span, &Place<'tcx>, &IllegalMoveOriginKind<'_>) =
 228                 match error {
 229                     GroupedMoveError::MovesFromPlace { span, ref original_path, ref kind, .. } |
 230                     GroupedMoveError::MovesFromValue { span, ref original_path, ref kind, .. } => {
 231                         (span, original_path, kind)
 232                     }
 233                     GroupedMoveError::OtherIllegalMove {
 234                         use_spans,
 235                         ref original_path,
 236                         ref kind
 237                     } => {
 238                         (use_spans.args_or_use(), original_path, kind)
 239                     },
 240                 };
 241             debug!("report: original_path={:?} span={:?}, kind={:?} \
 242                    original_path.is_upvar_field_projection={:?}", original_path, span, kind,
 243                    self.is_upvar_field_projection(original_path));
 244             (
 245                 match kind {
 246                     IllegalMoveOriginKind::Static => {
 247                         self.report_cannot_move_from_static(original_path, span)
 248                     }
 249                     IllegalMoveOriginKind::BorrowedContent { target_place } => {
 250                         self.report_cannot_move_from_borrowed_content(
 251                             original_path,
 252                             target_place,
 253                             span,
 254                         )
 255                     }
 256                     IllegalMoveOriginKind::InteriorOfTypeWithDestructor { container_ty: ty } => {
 257                         self.infcx.tcx
 258                             .cannot_move_out_of_interior_of_drop(span, ty)
 259                     }
 260                     IllegalMoveOriginKind::InteriorOfSliceOrArray { ty, is_index } =>
 261                         self.infcx.tcx.cannot_move_out_of_interior_noncopy(
 262                             span, ty, Some(*is_index),
 263                         ),
 264                 },
 265                 span,
 266             )
 267         };
 268
 269         self.add_move_hints(error, &mut err, err_span);
 270         err.buffer(&mut self.errors_buffer);
 271     }
 272
 273     fn report_cannot_move_from_static(
 274         &mut self,
 275         place: &Place<'tcx>,
 276         span: Span
 277     ) -> DiagnosticBuilder<'a> {
 278         let mut base_static = place;
 279         loop {
 280             match base_static {
 281                 Place::Base(_) => break,
 282                 Place::Projection(box Projection { base, .. }) => base_static = base,
 283             }
 284         }
 285
 286         let description = if let Place::Base(_) = place {
 287             format!("static item `{}`", self.describe_place(place).unwrap())
 288         } else {
 289             format!(
 290                 "`{:?}` as `{:?}` is a static item",
 291                 self.describe_place(place).unwrap(),
 292                 self.describe_place(base_static).unwrap(),
 293             )
 294         };
 295
 296         self.infcx.tcx.cannot_move_out_of(span, &description)
 297     }
 298
 299     fn report_cannot_move_from_borrowed_content(
 300         &mut self,
 301         move_place: &Place<'tcx>,
 302         deref_target_place: &Place<'tcx>,
 303         span: Span,
 304     ) -> DiagnosticBuilder<'a> {
 305         // Inspect the type of the content behind the
 306         // borrow to provide feedback about why this
 307         // was a move rather than a copy.
 308         let ty = deref_target_place.ty(self.body, self.infcx.tcx).ty;
 309         let upvar_field = self.prefixes(&move_place, PrefixSet::All)
 310             .find_map(|p| self.is_upvar_field_projection(p));
 311
 312         let deref_base = match deref_target_place {
 313             Place::Projection(box Projection { base, elem: ProjectionElem::Deref }) => base,
 314             _ => bug!("deref_target_place is not a deref projection"),
 315         };
 316
 317         if let Place::Base(PlaceBase::Local(local)) = *deref_base {
 318             let decl = &self.body.local_decls[local];
 319             if decl.is_ref_for_guard() {
 320                 let mut err = self.infcx.tcx.cannot_move_out_of(
 321                     span,
 322                     &format!("`{}` in pattern guard", decl.name.unwrap()),
 323                 );
 324                 err.note(
 325                     "variables bound in patterns cannot be moved from \
 326                      until after the end of the pattern guard");
 327                 return err;
 328             }
 329         }
 330
 331         debug!("report: ty={:?}", ty);
 332         let mut err = match ty.sty {
 333             ty::Array(..) | ty::Slice(..) =>
 334                 self.infcx.tcx.cannot_move_out_of_interior_noncopy(span, ty, None),
 335             ty::Closure(def_id, closure_substs)
 336                 if def_id == self.mir_def_id && upvar_field.is_some()
 337             => {
 338                 let closure_kind_ty = closure_substs.closure_kind_ty(def_id, self.infcx.tcx);
 339                 let closure_kind = closure_kind_ty.to_opt_closure_kind();
 340                 let capture_description = match closure_kind {
 341                     Some(ty::ClosureKind::Fn) => {
 342                         "captured variable in an `Fn` closure"
 343                     }
 344                     Some(ty::ClosureKind::FnMut) => {
 345                         "captured variable in an `FnMut` closure"
 346                     }
 347                     Some(ty::ClosureKind::FnOnce) => {
 348                         bug!("closure kind does not match first argument type")
 349                     }
 350                     None => bug!("closure kind not inferred by borrowck"),
 351                 };
 352
 353                 let upvar = &self.upvars[upvar_field.unwrap().index()];
 354                 let upvar_hir_id = upvar.var_hir_id;
 355                 let upvar_name = upvar.name;
 356                 let upvar_span = self.infcx.tcx.hir().span(upvar_hir_id);
 357
 358                 let place_name = self.describe_place(move_place).unwrap();
 359
 360                 let place_description = if self.is_upvar_field_projection(move_place).is_some() {
 361                     format!("`{}`, a {}", place_name, capture_description)
 362                 } else {
 363                     format!(
 364                         "`{}`, as `{}` is a {}",
 365                         place_name,
 366                         upvar_name,
 367                         capture_description,
 368                     )
 369                 };
 370
 371                 debug!(
 372                     "report: closure_kind_ty={:?} closure_kind={:?} place_description={:?}",
 373                     closure_kind_ty, closure_kind, place_description,
 374                 );
 375
 376                 let mut diag = self.infcx.tcx.cannot_move_out_of(span, &place_description);
 377
 378                 diag.span_label(upvar_span, "captured outer variable");
 379
 380                 diag
 381             }
 382             _ => {
 383                 let source = self.borrowed_content_source(deref_base);
 384                 match (self.describe_place(move_place), source.describe_for_named_place()) {
 385                     (Some(place_desc), Some(source_desc)) => {
 386                         self.infcx.tcx.cannot_move_out_of(
 387                             span,
 388                             &format!("`{}` which is behind a {}", place_desc, source_desc),
 389                         )
 390                     }
 391                     (_, _) => {
 392                         self.infcx.tcx.cannot_move_out_of(
 393                             span,
 394                             &source.describe_for_unnamed_place(),
 395                         )
 396                     }
 397                 }
 398             },
 399         };
 400         let move_ty = format!(
 401             "{:?}",
 402             move_place.ty(self.body, self.infcx.tcx).ty,
 403         );
 404         let snippet = self.infcx.tcx.sess.source_map().span_to_snippet(span).unwrap();
 405         let is_option = move_ty.starts_with("std::option::Option");
 406         let is_result = move_ty.starts_with("std::result::Result");
 407         if  is_option || is_result {
 408             err.span_suggestion(
 409                 span,
 410                 &format!("consider borrowing the `{}`'s content", if is_option {
 411                     "Option"
 412                 } else {
 413                     "Result"
 414                 }),
 415                 format!("{}.as_ref()", snippet),
 416                 Applicability::MaybeIncorrect,
 417             );
 418         }
 419         err
 420     }
 421
 422     fn add_move_hints(
 423         &self,
 424         error: GroupedMoveError<'tcx>,
 425         err: &mut DiagnosticBuilder<'a>,
 426         span: Span,
 427     ) {
 428         let snippet = self.infcx.tcx.sess.source_map().span_to_snippet(span).unwrap();
 429         match error {
 430             GroupedMoveError::MovesFromPlace {
 431                 mut binds_to,
 432                 move_from,
 433                 ..
 434             } => {
 435                 err.span_suggestion(
 436                     span,
 437                     "consider borrowing here",
 438                     format!("&{}", snippet),
 439                     Applicability::Unspecified,
 440                 );
 441
 442                 if binds_to.is_empty() {
 443                     let place_ty = move_from.ty(self.body, self.infcx.tcx).ty;
 444                     let place_desc = match self.describe_place(&move_from) {
 445                         Some(desc) => format!("`{}`", desc),
 446                         None => format!("value"),
 447                     };
 448
 449                     self.note_type_does_not_implement_copy(
 450                         err,
 451                         &place_desc,
 452                         place_ty,
 453                         Some(span)
 454                     );
 455                 } else {
 456                     binds_to.sort();
 457                     binds_to.dedup();
 458
 459                     self.add_move_error_details(err, &binds_to);
 460                 }
 461             }
 462             GroupedMoveError::MovesFromValue { mut binds_to, .. } => {
 463                 binds_to.sort();
 464                 binds_to.dedup();
 465                 self.add_move_error_suggestions(err, &binds_to);
 466                 self.add_move_error_details(err, &binds_to);
 467             }
 468             // No binding. Nothing to suggest.
 469             GroupedMoveError::OtherIllegalMove { ref original_path, use_spans, .. } => {
 470                 let span = use_spans.var_or_use();
 471                 let place_ty = original_path.ty(self.body, self.infcx.tcx).ty;
 472                 let place_desc = match self.describe_place(original_path) {
 473                     Some(desc) => format!("`{}`", desc),
 474                     None => format!("value"),
 475                 };
 476                 self.note_type_does_not_implement_copy(
 477                     err,
 478                     &place_desc,
 479                     place_ty,
 480                     Some(span),
 481                 );
 482
 483                 use_spans.args_span_label(err, format!("move out of {} occurs here", place_desc));
 484                 use_spans.var_span_label(
 485                     err,
 486                     format!("move occurs due to use{}", use_spans.describe()),
 487                 );
 488             },
 489         }
 490     }
 491
 492     fn add_move_error_suggestions(
 493         &self,
 494         err: &mut DiagnosticBuilder<'a>,
 495         binds_to: &[Local],
 496     ) {
 497         let mut suggestions: Vec<(Span, &str, String)> = Vec::new();
 498         for local in binds_to {
 499             let bind_to = &self.body.local_decls[*local];
 500             if let Some(
 501                 ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
 502                     pat_span,
 503                     ..
 504                 }))
 505             ) = bind_to.is_user_variable {
 506                 let pat_snippet = self.infcx.tcx.sess.source_map()
 507                     .span_to_snippet(pat_span)
 508                     .unwrap();
 509                 if pat_snippet.starts_with('&') {
 510                     let pat_snippet = pat_snippet[1..].trim_start();
 511                     let suggestion;
 512                     let to_remove;
 513                     if pat_snippet.starts_with("mut")
 514                         && pat_snippet["mut".len()..].starts_with(Pattern_White_Space)
 515                     {
 516                         suggestion = pat_snippet["mut".len()..].trim_start();
 517                         to_remove = "&mut";
 518                     } else {
 519                         suggestion = pat_snippet;
 520                         to_remove = "&";
 521                     }
 522                     suggestions.push((
 523                         pat_span,
 524                         to_remove,
 525                         suggestion.to_owned(),
 526                     ));
 527                 }
 528             }
 529         }
 530         suggestions.sort_unstable_by_key(|&(span, _, _)| span);
 531         suggestions.dedup_by_key(|&mut (span, _, _)| span);
 532         for (span, to_remove, suggestion) in suggestions {
 533             err.span_suggestion(
 534                 span,
 535                 &format!("consider removing the `{}`", to_remove),
 536                 suggestion,
 537                 Applicability::MachineApplicable,
 538             );
 539         }
 540     }
 541
 542     fn add_move_error_details(
 543         &self,
 544         err: &mut DiagnosticBuilder<'a>,
 545         binds_to: &[Local],
 546     ) {
 547         let mut noncopy_var_spans = Vec::new();
 548         for (j, local) in binds_to.into_iter().enumerate() {
 549             let bind_to = &self.body.local_decls[*local];
 550             let binding_span = bind_to.source_info.span;
 551
 552             if j == 0 {
 553                 err.span_label(binding_span, "data moved here");
 554             } else {
 555                 err.span_label(binding_span, "...and here");
 556             }
 557
 558             if binds_to.len() == 1 {
 559                 self.note_type_does_not_implement_copy(
 560                     err,
 561                     &format!("`{}`", bind_to.name.unwrap()),
 562                     bind_to.ty,
 563                     Some(binding_span)
 564                 );
 565             } else {
 566                 noncopy_var_spans.push(binding_span);
 567             }
 568         }
 569
 570         if binds_to.len() > 1 {
 571             err.span_note(
 572                 noncopy_var_spans,
 573                 "move occurs because these variables have types that \
 574                     don't implement the `Copy` trait",
 575             );
 576         }
 577     }
 578 }