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                         if match_span == *span {
 162                             debug!("appending local({:?}) to list", bind_to);
 163                             if !binds_to.is_empty() {
 164                                 binds_to.push(bind_to);
 165                             }
 166                             return;
 167                         }
 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): (
 222                 Span,
 223                 Option<UseSpans<'tcx>>,
 224                 Place<'tcx>,
 225                 &IllegalMoveOriginKind<'_>,
 226             ) = match error {
 227                 GroupedMoveError::MovesFromPlace { span, original_path, ref kind, .. }
 228                 | GroupedMoveError::MovesFromValue { span, original_path, ref kind, .. } => {
 229                     (span, None, original_path, kind)
 230                 }
 231                 GroupedMoveError::OtherIllegalMove { use_spans, original_path, ref kind } => {
 232                     (use_spans.args_or_use(), Some(use_spans), original_path, kind)
 233                 }
 234             };
 235             debug!(
 236                 "report: original_path={:?} span={:?}, kind={:?} \
 237                    original_path.is_upvar_field_projection={:?}",
 238                 original_path,
 239                 span,
 240                 kind,
 241                 self.is_upvar_field_projection(original_path.as_ref())
 242             );
 243             (
 244                 match kind {
 245                     &IllegalMoveOriginKind::BorrowedContent { target_place } => self
 246                         .report_cannot_move_from_borrowed_content(
 247                             original_path,
 248                             target_place,
 249                             span,
 250                             use_spans,
 251                         ),
 252                     &IllegalMoveOriginKind::InteriorOfTypeWithDestructor { container_ty: ty } => {
 253                         self.cannot_move_out_of_interior_of_drop(span, ty)
 254                     }
 255                     &IllegalMoveOriginKind::InteriorOfSliceOrArray { ty, is_index } => {
 256                         self.cannot_move_out_of_interior_noncopy(span, ty, Some(is_index))
 257                     }
 258                 },
 259                 span,
 260             )
 261         };
 262
 263         self.add_move_hints(error, &mut err, err_span);
 264         self.buffer_error(err);
 265     }
 266
 267     fn report_cannot_move_from_static(
 268         &mut self,
 269         place: Place<'tcx>,
 270         span: Span,
 271     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 272         let description = if place.projection.len() == 1 {
 273             format!("static item {}", self.describe_any_place(place.as_ref()))
 274         } else {
 275             let base_static = PlaceRef { local: place.local, projection: &[ProjectionElem::Deref] };
 276
 277             format!(
 278                 "{} as {} is a static item",
 279                 self.describe_any_place(place.as_ref()),
 280                 self.describe_any_place(base_static),
 281             )
 282         };
 283
 284         self.cannot_move_out_of(span, &description)
 285     }
 286
 287     fn report_cannot_move_from_borrowed_content(
 288         &mut self,
 289         move_place: Place<'tcx>,
 290         deref_target_place: Place<'tcx>,
 291         span: Span,
 292         use_spans: Option<UseSpans<'tcx>>,
 293     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 294         // Inspect the type of the content behind the
 295         // borrow to provide feedback about why this
 296         // was a move rather than a copy.
 297         let ty = deref_target_place.ty(self.body, self.infcx.tcx).ty;
 298         let upvar_field = self
 299             .prefixes(move_place.as_ref(), PrefixSet::All)
 300             .find_map(|p| self.is_upvar_field_projection(p));
 301
 302         let deref_base = match deref_target_place.projection.as_ref() {
 303             [proj_base @ .., ProjectionElem::Deref] => {
 304                 PlaceRef { local: deref_target_place.local, projection: &proj_base }
 305             }
 306             _ => bug!("deref_target_place is not a deref projection"),
 307         };
 308
 309         if let PlaceRef { local, projection: [] } = deref_base {
 310             let decl = &self.body.local_decls[local];
 311             if decl.is_ref_for_guard() {
 312                 let mut err = self.cannot_move_out_of(
 313                     span,
 314                     &format!("`{}` in pattern guard", self.local_names[local].unwrap()),
 315                 );
 316                 err.note(
 317                     "variables bound in patterns cannot be moved from \
 318                      until after the end of the pattern guard",
 319                 );
 320                 return err;
 321             } else if decl.is_ref_to_static() {
 322                 return self.report_cannot_move_from_static(move_place, span);
 323             }
 324         }
 325
 326         debug!("report: ty={:?}", ty);
 327         let mut err = match ty.kind() {
 328             ty::Array(..) | ty::Slice(..) => {
 329                 self.cannot_move_out_of_interior_noncopy(span, ty, None)
 330             }
 331             ty::Closure(def_id, closure_substs)
 332                 if def_id.as_local() == Some(self.mir_def_id()) && upvar_field.is_some() =>
 333             {
 334                 let closure_kind_ty = closure_substs.as_closure().kind_ty();
 335                 let closure_kind = match closure_kind_ty.to_opt_closure_kind() {
 336                     Some(kind @ (ty::ClosureKind::Fn | ty::ClosureKind::FnMut)) => kind,
 337                     Some(ty::ClosureKind::FnOnce) => {
 338                         bug!("closure kind does not match first argument type")
 339                     }
 340                     None => bug!("closure kind not inferred by borrowck"),
 341                 };
 342                 let capture_description =
 343                     format!("captured variable in an `{}` closure", closure_kind);
 344
 345                 let upvar = &self.upvars[upvar_field.unwrap().index()];
 346                 let upvar_hir_id = upvar.place.get_root_variable();
 347                 let upvar_name = upvar.place.to_string(self.infcx.tcx);
 348                 let upvar_span = self.infcx.tcx.hir().span(upvar_hir_id);
 349
 350                 let place_name = self.describe_any_place(move_place.as_ref());
 351
 352                 let place_description =
 353                     if self.is_upvar_field_projection(move_place.as_ref()).is_some() {
 354                         format!("{}, a {}", place_name, capture_description)
 355                     } else {
 356                         format!("{}, as `{}` is a {}", place_name, upvar_name, capture_description)
 357                     };
 358
 359                 debug!(
 360                     "report: closure_kind_ty={:?} closure_kind={:?} place_description={:?}",
 361                     closure_kind_ty, closure_kind, place_description,
 362                 );
 363
 364                 let mut diag = self.cannot_move_out_of(span, &place_description);
 365
 366                 diag.span_label(upvar_span, "captured outer variable");
 367                 diag.span_label(
 368                     self.body.span,
 369                     format!("captured by this `{}` closure", closure_kind),
 370                 );
 371
 372                 diag
 373             }
 374             _ => {
 375                 let source = self.borrowed_content_source(deref_base);
 376                 match (self.describe_place(move_place.as_ref()), source.describe_for_named_place())
 377                 {
 378                     (Some(place_desc), Some(source_desc)) => self.cannot_move_out_of(
 379                         span,
 380                         &format!("`{}` which is behind a {}", place_desc, source_desc),
 381                     ),
 382                     (_, _) => self.cannot_move_out_of(
 383                         span,
 384                         &source.describe_for_unnamed_place(self.infcx.tcx),
 385                     ),
 386                 }
 387             }
 388         };
 389         let ty = move_place.ty(self.body, self.infcx.tcx).ty;
 390         let def_id = match *ty.kind() {
 391             ty::Adt(self_def, _) => self_def.did(),
 392             ty::Foreign(def_id)
 393             | ty::FnDef(def_id, _)
 394             | ty::Closure(def_id, _)
 395             | ty::Generator(def_id, ..)
 396             | ty::Opaque(def_id, _) => def_id,
 397             _ => return err,
 398         };
 399         let diag_name = self.infcx.tcx.get_diagnostic_name(def_id);
 400         if matches!(diag_name, Some(sym::Option | sym::Result))
 401             && use_spans.map_or(true, |v| !v.for_closure())
 402         {
 403             err.span_suggestion_verbose(
 404                 span.shrink_to_hi(),
 405                 &format!("consider borrowing the `{}`'s content", diag_name.unwrap()),
 406                 ".as_ref()".to_string(),
 407                 Applicability::MaybeIncorrect,
 408             );
 409         } else if let Some(use_spans) = use_spans {
 410             self.explain_captures(
 411                 &mut err, span, span, use_spans, move_place, None, "", "", "", false, true,
 412             );
 413         }
 414         err
 415     }
 416
 417     fn add_move_hints(&self, error: GroupedMoveError<'tcx>, err: &mut Diagnostic, span: Span) {
 418         match error {
 419             GroupedMoveError::MovesFromPlace { mut binds_to, move_from, .. } => {
 420                 if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) {
 421                     err.span_suggestion(
 422                         span,
 423                         "consider borrowing here",
 424                         format!("&{}", snippet),
 425                         Applicability::Unspecified,
 426                     );
 427                 }
 428
 429                 if binds_to.is_empty() {
 430                     let place_ty = move_from.ty(self.body, self.infcx.tcx).ty;
 431                     let place_desc = match self.describe_place(move_from.as_ref()) {
 432                         Some(desc) => format!("`{}`", desc),
 433                         None => "value".to_string(),
 434                     };
 435
 436                     self.note_type_does_not_implement_copy(
 437                         err,
 438                         &place_desc,
 439                         place_ty,
 440                         Some(span),
 441                         "",
 442                     );
 443                 } else {
 444                     binds_to.sort();
 445                     binds_to.dedup();
 446
 447                     self.add_move_error_details(err, &binds_to);
 448                 }
 449             }
 450             GroupedMoveError::MovesFromValue { mut binds_to, .. } => {
 451                 binds_to.sort();
 452                 binds_to.dedup();
 453                 self.add_move_error_suggestions(err, &binds_to);
 454                 self.add_move_error_details(err, &binds_to);
 455             }
 456             // No binding. Nothing to suggest.
 457             GroupedMoveError::OtherIllegalMove { ref original_path, use_spans, .. } => {
 458                 let span = use_spans.var_or_use();
 459                 let place_ty = original_path.ty(self.body, self.infcx.tcx).ty;
 460                 let place_desc = match self.describe_place(original_path.as_ref()) {
 461                     Some(desc) => format!("`{}`", desc),
 462                     None => "value".to_string(),
 463                 };
 464                 self.note_type_does_not_implement_copy(err, &place_desc, place_ty, Some(span), "");
 465
 466                 use_spans.args_span_label(err, format!("move out of {} occurs here", place_desc));
 467             }
 468         }
 469     }
 470
 471     fn add_move_error_suggestions(&self, err: &mut Diagnostic, binds_to: &[Local]) {
 472         let mut suggestions: Vec<(Span, &str, String)> = Vec::new();
 473         for local in binds_to {
 474             let bind_to = &self.body.local_decls[*local];
 475             if let Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
 476                 VarBindingForm { pat_span, .. },
 477             )))) = bind_to.local_info
 478             {
 479                 if let Ok(pat_snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(pat_span)
 480                 {
 481                     if let Some(stripped) = pat_snippet.strip_prefix('&') {
 482                         let pat_snippet = stripped.trim_start();
 483                         let (suggestion, to_remove) = if pat_snippet.starts_with("mut")
 484                             && pat_snippet["mut".len()..].starts_with(rustc_lexer::is_whitespace)
 485                         {
 486                             (pat_snippet["mut".len()..].trim_start(), "&mut")
 487                         } else {
 488                             (pat_snippet, "&")
 489                         };
 490                         suggestions.push((pat_span, to_remove, suggestion.to_owned()));
 491                     }
 492                 }
 493             }
 494         }
 495         suggestions.sort_unstable_by_key(|&(span, _, _)| span);
 496         suggestions.dedup_by_key(|&mut (span, _, _)| span);
 497         for (span, to_remove, suggestion) in suggestions {
 498             err.span_suggestion(
 499                 span,
 500                 &format!("consider removing the `{}`", to_remove),
 501                 suggestion,
 502                 Applicability::MachineApplicable,
 503             );
 504         }
 505     }
 506
 507     fn add_move_error_details(&self, err: &mut Diagnostic, binds_to: &[Local]) {
 508         for (j, local) in binds_to.iter().enumerate() {
 509             let bind_to = &self.body.local_decls[*local];
 510             let binding_span = bind_to.source_info.span;
 511
 512             if j == 0 {
 513                 err.span_label(binding_span, "data moved here");
 514             } else {
 515                 err.span_label(binding_span, "...and here");
 516             }
 517
 518             if binds_to.len() == 1 {
 519                 self.note_type_does_not_implement_copy(
 520                     err,
 521                     &format!("`{}`", self.local_names[*local].unwrap()),
 522                     bind_to.ty,
 523                     Some(binding_span),
 524                     "",
 525                 );
 526             }
 527         }
 528
 529         if binds_to.len() > 1 {
 530             err.note(
 531                 "move occurs because these variables have types that \
 532                       don't implement the `Copy` trait",
 533             );
 534         }
 535     }
 536 }