compiler/rustc_borrowck/src/diagnostics/move_errors.rs

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