src/librustc_mir/borrow_check/diagnostics/mod.rs

   1 //! Borrow checker diagnostics.
   2
   3 use rustc::mir::{
   4     AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
   5     PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
   6 };
   7 use rustc::ty::layout::VariantIdx;
   8 use rustc::ty::print::Print;
   9 use rustc::ty::{self, DefIdTree, Ty, TyCtxt};
  10 use rustc_errors::DiagnosticBuilder;
  11 use rustc_hir as hir;
  12 use rustc_hir::def::Namespace;
  13 use rustc_hir::def_id::DefId;
  14 use rustc_hir::GeneratorKind;
  15 use rustc_span::Span;
  16
  17 use super::borrow_set::BorrowData;
  18 use super::MirBorrowckCtxt;
  19 use crate::dataflow::move_paths::{InitLocation, LookupResult};
  20
  21 mod find_use;
  22 mod outlives_suggestion;
  23 mod region_name;
  24 mod var_name;
  25
  26 mod conflict_errors;
  27 mod explain_borrow;
  28 mod move_errors;
  29 mod mutability_errors;
  30 mod region_errors;
  31
  32 crate use mutability_errors::AccessKind;
  33 crate use outlives_suggestion::OutlivesSuggestionBuilder;
  34 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
  35 crate use region_name::{RegionName, RegionNameSource};
  36
  37 pub(super) struct IncludingDowncast(pub(super) bool);
  38
  39 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  40     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  41     /// is moved after being invoked.
  42     ///
  43     /// ```text
  44     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  45     ///       its environment
  46     ///   --> $DIR/issue-42065.rs:16:29
  47     ///    |
  48     /// LL |         for (key, value) in dict {
  49     ///    |                             ^^^^
  50     /// ```
  51     pub(super) fn add_moved_or_invoked_closure_note(
  52         &self,
  53         location: Location,
  54         place: PlaceRef<'cx, 'tcx>,
  55         diag: &mut DiagnosticBuilder<'_>,
  56     ) {
  57         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  58         let mut target = place.local_or_deref_local();
  59         for stmt in &self.body[location.block].statements[location.statement_index..] {
  60             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  61             if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
  62                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  63                 match from {
  64                     Operand::Copy(ref place) | Operand::Move(ref place)
  65                         if target == place.local_or_deref_local() =>
  66                     {
  67                         target = into.local_or_deref_local()
  68                     }
  69                     _ => {}
  70                 }
  71             }
  72         }
  73
  74         // Check if we are attempting to call a closure after it has been invoked.
  75         let terminator = self.body[location.block].terminator();
  76         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  77         if let TerminatorKind::Call {
  78             func:
  79                 Operand::Constant(box Constant {
  80                     literal: ty::Const { ty: &ty::TyS { kind: ty::FnDef(id, _), .. }, .. },
  81                     ..
  82                 }),
  83             args,
  84             ..
  85         } = &terminator.kind
  86         {
  87             debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  88             if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  89                 let closure = match args.first() {
  90                     Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
  91                         if target == place.local_or_deref_local() =>
  92                     {
  93                         place.local_or_deref_local().unwrap()
  94                     }
  95                     _ => return,
  96                 };
  97
  98                 debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
  99                 if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind {
 100                     let hir_id = self.infcx.tcx.hir().as_local_hir_id(did).unwrap();
 101
 102                     if let Some((span, name)) =
 103                         self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
 104                     {
 105                         diag.span_note(
 106                             *span,
 107                             &format!(
 108                                 "closure cannot be invoked more than once because it moves the \
 109                                  variable `{}` out of its environment",
 110                                 name,
 111                             ),
 112                         );
 113                         return;
 114                     }
 115                 }
 116             }
 117         }
 118
 119         // Check if we are just moving a closure after it has been invoked.
 120         if let Some(target) = target {
 121             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind {
 122                 let hir_id = self.infcx.tcx.hir().as_local_hir_id(did).unwrap();
 123
 124                 if let Some((span, name)) =
 125                     self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
 126                 {
 127                     diag.span_note(
 128                         *span,
 129                         &format!(
 130                             "closure cannot be moved more than once as it is not `Copy` due to \
 131                              moving the variable `{}` out of its environment",
 132                             name
 133                         ),
 134                     );
 135                 }
 136             }
 137         }
 138     }
 139
 140     /// End-user visible description of `place` if one can be found. If the
 141     /// place is a temporary for instance, None will be returned.
 142     pub(super) fn describe_place(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<String> {
 143         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 144     }
 145
 146     /// End-user visible description of `place` if one can be found. If the
 147     /// place is a temporary for instance, None will be returned.
 148     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 149     /// `Downcast` and `IncludingDowncast` is true
 150     pub(super) fn describe_place_with_options(
 151         &self,
 152         place: PlaceRef<'cx, 'tcx>,
 153         including_downcast: IncludingDowncast,
 154     ) -> Option<String> {
 155         let mut buf = String::new();
 156         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 157             Ok(()) => Some(buf),
 158             Err(()) => None,
 159         }
 160     }
 161
 162     /// Appends end-user visible description of `place` to `buf`.
 163     fn append_place_to_string(
 164         &self,
 165         place: PlaceRef<'cx, 'tcx>,
 166         buf: &mut String,
 167         mut autoderef: bool,
 168         including_downcast: &IncludingDowncast,
 169     ) -> Result<(), ()> {
 170         match place {
 171             PlaceRef { local, projection: [] } => {
 172                 self.append_local_to_string(local, buf)?;
 173             }
 174             PlaceRef { local, projection: [ProjectionElem::Deref] }
 175                 if self.body.local_decls[local].is_ref_for_guard() =>
 176             {
 177                 self.append_place_to_string(
 178                     PlaceRef { local: local, projection: &[] },
 179                     buf,
 180                     autoderef,
 181                     &including_downcast,
 182                 )?;
 183             }
 184             PlaceRef { local, projection: [ProjectionElem::Deref] }
 185                 if self.body.local_decls[local].is_ref_to_static() =>
 186             {
 187                 let local_info = &self.body.local_decls[local].local_info;
 188                 if let LocalInfo::StaticRef { def_id, .. } = *local_info {
 189                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 190                 } else {
 191                     unreachable!();
 192                 }
 193             }
 194             PlaceRef { local, projection: [proj_base @ .., elem] } => {
 195                 match elem {
 196                     ProjectionElem::Deref => {
 197                         let upvar_field_projection = self.is_upvar_field_projection(place);
 198                         if let Some(field) = upvar_field_projection {
 199                             let var_index = field.index();
 200                             let name = self.upvars[var_index].name.to_string();
 201                             if self.upvars[var_index].by_ref {
 202                                 buf.push_str(&name);
 203                             } else {
 204                                 buf.push_str(&format!("*{}", &name));
 205                             }
 206                         } else {
 207                             if autoderef {
 208                                 // FIXME turn this recursion into iteration
 209                                 self.append_place_to_string(
 210                                     PlaceRef { local, projection: proj_base },
 211                                     buf,
 212                                     autoderef,
 213                                     &including_downcast,
 214                                 )?;
 215                             } else {
 216                                 buf.push_str(&"*");
 217                                 self.append_place_to_string(
 218                                     PlaceRef { local, projection: proj_base },
 219                                     buf,
 220                                     autoderef,
 221                                     &including_downcast,
 222                                 )?;
 223                             }
 224                         }
 225                     }
 226                     ProjectionElem::Downcast(..) => {
 227                         self.append_place_to_string(
 228                             PlaceRef { local, projection: proj_base },
 229                             buf,
 230                             autoderef,
 231                             &including_downcast,
 232                         )?;
 233                         if including_downcast.0 {
 234                             return Err(());
 235                         }
 236                     }
 237                     ProjectionElem::Field(field, _ty) => {
 238                         autoderef = true;
 239
 240                         let upvar_field_projection = self.is_upvar_field_projection(place);
 241                         if let Some(field) = upvar_field_projection {
 242                             let var_index = field.index();
 243                             let name = self.upvars[var_index].name.to_string();
 244                             buf.push_str(&name);
 245                         } else {
 246                             let field_name = self
 247                                 .describe_field(PlaceRef { local, projection: proj_base }, *field);
 248                             self.append_place_to_string(
 249                                 PlaceRef { local, projection: proj_base },
 250                                 buf,
 251                                 autoderef,
 252                                 &including_downcast,
 253                             )?;
 254                             buf.push_str(&format!(".{}", field_name));
 255                         }
 256                     }
 257                     ProjectionElem::Index(index) => {
 258                         autoderef = true;
 259
 260                         self.append_place_to_string(
 261                             PlaceRef { local, projection: proj_base },
 262                             buf,
 263                             autoderef,
 264                             &including_downcast,
 265                         )?;
 266                         buf.push_str("[");
 267                         if self.append_local_to_string(*index, buf).is_err() {
 268                             buf.push_str("_");
 269                         }
 270                         buf.push_str("]");
 271                     }
 272                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 273                         autoderef = true;
 274                         // Since it isn't possible to borrow an element on a particular index and
 275                         // then use another while the borrow is held, don't output indices details
 276                         // to avoid confusing the end-user
 277                         self.append_place_to_string(
 278                             PlaceRef { local, projection: proj_base },
 279                             buf,
 280                             autoderef,
 281                             &including_downcast,
 282                         )?;
 283                         buf.push_str(&"[..]");
 284                     }
 285                 };
 286             }
 287         }
 288
 289         Ok(())
 290     }
 291
 292     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 293     /// a name, or its name was generated by the compiler, then `Err` is returned
 294     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 295         let decl = &self.body.local_decls[local];
 296         match self.local_names[local] {
 297             Some(name) if !decl.from_compiler_desugaring() => {
 298                 buf.push_str(&name.as_str());
 299                 Ok(())
 300             }
 301             _ => Err(()),
 302         }
 303     }
 304
 305     /// End-user visible description of the `field`nth field of `base`
 306     fn describe_field(&self, place: PlaceRef<'cx, 'tcx>, field: Field) -> String {
 307         // FIXME Place2 Make this work iteratively
 308         match place {
 309             PlaceRef { local, projection: [] } => {
 310                 let local = &self.body.local_decls[local];
 311                 self.describe_field_from_ty(&local.ty, field, None)
 312             }
 313             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 314                 ProjectionElem::Deref => {
 315                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 316                 }
 317                 ProjectionElem::Downcast(_, variant_index) => {
 318                     let base_ty =
 319                         Place::ty_from(place.local, place.projection, *self.body, self.infcx.tcx)
 320                             .ty;
 321                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 322                 }
 323                 ProjectionElem::Field(_, field_type) => {
 324                     self.describe_field_from_ty(&field_type, field, None)
 325                 }
 326                 ProjectionElem::Index(..)
 327                 | ProjectionElem::ConstantIndex { .. }
 328                 | ProjectionElem::Subslice { .. } => {
 329                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 330                 }
 331             },
 332         }
 333     }
 334
 335     /// End-user visible description of the `field_index`nth field of `ty`
 336     fn describe_field_from_ty(
 337         &self,
 338         ty: Ty<'_>,
 339         field: Field,
 340         variant_index: Option<VariantIdx>,
 341     ) -> String {
 342         if ty.is_box() {
 343             // If the type is a box, the field is described from the boxed type
 344             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 345         } else {
 346             match ty.kind {
 347                 ty::Adt(def, _) => {
 348                     let variant = if let Some(idx) = variant_index {
 349                         assert!(def.is_enum());
 350                         &def.variants[idx]
 351                     } else {
 352                         def.non_enum_variant()
 353                     };
 354                     variant.fields[field.index()].ident.to_string()
 355                 }
 356                 ty::Tuple(_) => field.index().to_string(),
 357                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 358                     self.describe_field_from_ty(&ty, field, variant_index)
 359                 }
 360                 ty::Array(ty, _) | ty::Slice(ty) => {
 361                     self.describe_field_from_ty(&ty, field, variant_index)
 362                 }
 363                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 364                     // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
 365                     // the closure comes from another crate. But in that case we wouldn't
 366                     // be borrowck'ing it, so we can just unwrap:
 367                     let (&var_id, _) =
 368                         self.infcx.tcx.upvars(def_id).unwrap().get_index(field.index()).unwrap();
 369
 370                     self.infcx.tcx.hir().name(var_id).to_string()
 371                 }
 372                 _ => {
 373                     // Might need a revision when the fields in trait RFC is implemented
 374                     // (https://github.com/rust-lang/rfcs/pull/1546)
 375                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 376                 }
 377             }
 378         }
 379     }
 380
 381     /// Add a note that a type does not implement `Copy`
 382     pub(super) fn note_type_does_not_implement_copy(
 383         &self,
 384         err: &mut DiagnosticBuilder<'a>,
 385         place_desc: &str,
 386         ty: Ty<'tcx>,
 387         span: Option<Span>,
 388     ) {
 389         let message = format!(
 390             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 391             place_desc, ty,
 392         );
 393         if let Some(span) = span {
 394             err.span_label(span, message);
 395         } else {
 396             err.note(&message);
 397         }
 398     }
 399
 400     pub(super) fn borrowed_content_source(
 401         &self,
 402         deref_base: PlaceRef<'cx, 'tcx>,
 403     ) -> BorrowedContentSource<'tcx> {
 404         let tcx = self.infcx.tcx;
 405
 406         // Look up the provided place and work out the move path index for it,
 407         // we'll use this to check whether it was originally from an overloaded
 408         // operator.
 409         match self.move_data.rev_lookup.find(deref_base) {
 410             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 411                 debug!("borrowed_content_source: mpi={:?}", mpi);
 412
 413                 for i in &self.move_data.init_path_map[mpi] {
 414                     let init = &self.move_data.inits[*i];
 415                     debug!("borrowed_content_source: init={:?}", init);
 416                     // We're only interested in statements that initialized a value, not the
 417                     // initializations from arguments.
 418                     let loc = match init.location {
 419                         InitLocation::Statement(stmt) => stmt,
 420                         _ => continue,
 421                     };
 422
 423                     let bbd = &self.body[loc.block];
 424                     let is_terminator = bbd.statements.len() == loc.statement_index;
 425                     debug!(
 426                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 427                         loc, is_terminator,
 428                     );
 429                     if !is_terminator {
 430                         continue;
 431                     } else if let Some(Terminator {
 432                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 433                         ..
 434                     }) = bbd.terminator
 435                     {
 436                         if let Some(source) =
 437                             BorrowedContentSource::from_call(func.ty(*self.body, tcx), tcx)
 438                         {
 439                             return source;
 440                         }
 441                     }
 442                 }
 443             }
 444             // Base is a `static` so won't be from an overloaded operator
 445             _ => (),
 446         };
 447
 448         // If we didn't find an overloaded deref or index, then assume it's a
 449         // built in deref and check the type of the base.
 450         let base_ty = Place::ty_from(deref_base.local, deref_base.projection, *self.body, tcx).ty;
 451         if base_ty.is_unsafe_ptr() {
 452             BorrowedContentSource::DerefRawPointer
 453         } else if base_ty.is_mutable_ptr() {
 454             BorrowedContentSource::DerefMutableRef
 455         } else {
 456             BorrowedContentSource::DerefSharedRef
 457         }
 458     }
 459 }
 460
 461 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 462     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 463     /// name where required.
 464     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 465         let mut s = String::new();
 466         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 467
 468         // We need to add synthesized lifetimes where appropriate. We do
 469         // this by hooking into the pretty printer and telling it to label the
 470         // lifetimes without names with the value `'0`.
 471         match ty.kind {
 472             ty::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
 473             | ty::Ref(
 474                 ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 475                 _,
 476                 _,
 477             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 478             _ => {}
 479         }
 480
 481         let _ = ty.print(printer);
 482         s
 483     }
 484
 485     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 486     /// synthesized lifetime name where required.
 487     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 488         let mut s = String::new();
 489         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 490
 491         let region = match ty.kind {
 492             ty::Ref(region, _, _) => {
 493                 match region {
 494                     ty::RegionKind::ReLateBound(_, br)
 495                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 496                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 497                     }
 498                     _ => {}
 499                 }
 500
 501                 region
 502             }
 503             _ => bug!("ty for annotation of borrow region is not a reference"),
 504         };
 505
 506         let _ = region.print(printer);
 507         s
 508     }
 509 }
 510
 511 // The span(s) associated to a use of a place.
 512 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 513 pub(super) enum UseSpans {
 514     // The access is caused by capturing a variable for a closure.
 515     ClosureUse {
 516         // This is true if the captured variable was from a generator.
 517         generator_kind: Option<GeneratorKind>,
 518         // The span of the args of the closure, including the `move` keyword if
 519         // it's present.
 520         args_span: Span,
 521         // The span of the first use of the captured variable inside the closure.
 522         var_span: Span,
 523     },
 524     // This access has a single span associated to it: common case.
 525     OtherUse(Span),
 526 }
 527
 528 impl UseSpans {
 529     pub(super) fn args_or_use(self) -> Span {
 530         match self {
 531             UseSpans::ClosureUse { args_span: span, .. } | UseSpans::OtherUse(span) => span,
 532         }
 533     }
 534
 535     pub(super) fn var_or_use(self) -> Span {
 536         match self {
 537             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
 538         }
 539     }
 540
 541     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 542         match self {
 543             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 544             _ => None,
 545         }
 546     }
 547
 548     // Add a span label to the arguments of the closure, if it exists.
 549     pub(super) fn args_span_label(
 550         self,
 551         err: &mut DiagnosticBuilder<'_>,
 552         message: impl Into<String>,
 553     ) {
 554         if let UseSpans::ClosureUse { args_span, .. } = self {
 555             err.span_label(args_span, message);
 556         }
 557     }
 558
 559     // Add a span label to the use of the captured variable, if it exists.
 560     pub(super) fn var_span_label(
 561         self,
 562         err: &mut DiagnosticBuilder<'_>,
 563         message: impl Into<String>,
 564     ) {
 565         if let UseSpans::ClosureUse { var_span, .. } = self {
 566             err.span_label(var_span, message);
 567         }
 568     }
 569
 570     /// Returns `false` if this place is not used in a closure.
 571     pub(super) fn for_closure(&self) -> bool {
 572         match *self {
 573             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 574             _ => false,
 575         }
 576     }
 577
 578     /// Returns `false` if this place is not used in a generator.
 579     pub(super) fn for_generator(&self) -> bool {
 580         match *self {
 581             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 582             _ => false,
 583         }
 584     }
 585
 586     /// Describe the span associated with a use of a place.
 587     pub(super) fn describe(&self) -> String {
 588         match *self {
 589             UseSpans::ClosureUse { generator_kind, .. } => {
 590                 if generator_kind.is_some() {
 591                     " in generator".to_string()
 592                 } else {
 593                     " in closure".to_string()
 594                 }
 595             }
 596             _ => "".to_string(),
 597         }
 598     }
 599
 600     pub(super) fn or_else<F>(self, if_other: F) -> Self
 601     where
 602         F: FnOnce() -> Self,
 603     {
 604         match self {
 605             closure @ UseSpans::ClosureUse { .. } => closure,
 606             UseSpans::OtherUse(_) => if_other(),
 607         }
 608     }
 609 }
 610
 611 pub(super) enum BorrowedContentSource<'tcx> {
 612     DerefRawPointer,
 613     DerefMutableRef,
 614     DerefSharedRef,
 615     OverloadedDeref(Ty<'tcx>),
 616     OverloadedIndex(Ty<'tcx>),
 617 }
 618
 619 impl BorrowedContentSource<'tcx> {
 620     pub(super) fn describe_for_unnamed_place(&self) -> String {
 621         match *self {
 622             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 623             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 624             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 625             BorrowedContentSource::OverloadedDeref(ty) => {
 626                 if ty.is_rc() {
 627                     "an `Rc`".to_string()
 628                 } else if ty.is_arc() {
 629                     "an `Arc`".to_string()
 630                 } else {
 631                     format!("dereference of `{}`", ty)
 632                 }
 633             }
 634             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 635         }
 636     }
 637
 638     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 639         match *self {
 640             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 641             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 642             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 643             // Overloaded deref and index operators should be evaluated into a
 644             // temporary. So we don't need a description here.
 645             BorrowedContentSource::OverloadedDeref(_)
 646             | BorrowedContentSource::OverloadedIndex(_) => None,
 647         }
 648     }
 649
 650     pub(super) fn describe_for_immutable_place(&self) -> String {
 651         match *self {
 652             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 653             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 654             BorrowedContentSource::DerefMutableRef => {
 655                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 656             }
 657             BorrowedContentSource::OverloadedDeref(ty) => {
 658                 if ty.is_rc() {
 659                     "an `Rc`".to_string()
 660                 } else if ty.is_arc() {
 661                     "an `Arc`".to_string()
 662                 } else {
 663                     format!("a dereference of `{}`", ty)
 664                 }
 665             }
 666             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 667         }
 668     }
 669
 670     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 671         match func.kind {
 672             ty::FnDef(def_id, substs) => {
 673                 let trait_id = tcx.trait_of_item(def_id)?;
 674
 675                 let lang_items = tcx.lang_items();
 676                 if Some(trait_id) == lang_items.deref_trait()
 677                     || Some(trait_id) == lang_items.deref_mut_trait()
 678                 {
 679                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 680                 } else if Some(trait_id) == lang_items.index_trait()
 681                     || Some(trait_id) == lang_items.index_mut_trait()
 682                 {
 683                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 684                 } else {
 685                     None
 686                 }
 687             }
 688             _ => None,
 689         }
 690     }
 691 }
 692
 693 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 694     /// Finds the spans associated to a move or copy of move_place at location.
 695     pub(super) fn move_spans(
 696         &self,
 697         moved_place: PlaceRef<'cx, 'tcx>, // Could also be an upvar.
 698         location: Location,
 699     ) -> UseSpans {
 700         use self::UseSpans::*;
 701
 702         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 703             Some(stmt) => stmt,
 704             None => return OtherUse(self.body.source_info(location).span),
 705         };
 706
 707         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 708         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 709             let def_id = match kind {
 710                 box AggregateKind::Closure(def_id, _)
 711                 | box AggregateKind::Generator(def_id, _, _) => def_id,
 712                 _ => return OtherUse(stmt.source_info.span),
 713             };
 714
 715             debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 716             if let Some((args_span, generator_kind, var_span)) =
 717                 self.closure_span(*def_id, moved_place, places)
 718             {
 719                 return ClosureUse { generator_kind, args_span, var_span };
 720             }
 721         }
 722
 723         OtherUse(stmt.source_info.span)
 724     }
 725
 726     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 727     /// and its usage of the local assigned at `location`.
 728     /// This is done by searching in statements succeeding `location`
 729     /// and originating from `maybe_closure_span`.
 730     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 731         use self::UseSpans::*;
 732         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 733
 734         let target = match self.body[location.block].statements.get(location.statement_index) {
 735             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 736                 if let Some(local) = place.as_local() {
 737                     local
 738                 } else {
 739                     return OtherUse(use_span);
 740                 }
 741             }
 742             _ => return OtherUse(use_span),
 743         };
 744
 745         if self.body.local_kind(target) != LocalKind::Temp {
 746             // operands are always temporaries.
 747             return OtherUse(use_span);
 748         }
 749
 750         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 751             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 752                 stmt.kind
 753             {
 754                 let (def_id, is_generator) = match kind {
 755                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 756                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 757                     _ => continue,
 758                 };
 759
 760                 debug!(
 761                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 762                     def_id, is_generator, places
 763                 );
 764                 if let Some((args_span, generator_kind, var_span)) =
 765                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 766                 {
 767                     return ClosureUse { generator_kind, args_span, var_span };
 768                 } else {
 769                     return OtherUse(use_span);
 770                 }
 771             }
 772
 773             if use_span != stmt.source_info.span {
 774                 break;
 775             }
 776         }
 777
 778         OtherUse(use_span)
 779     }
 780
 781     /// Finds the span of a captured variable within a closure or generator.
 782     fn closure_span(
 783         &self,
 784         def_id: DefId,
 785         target_place: PlaceRef<'cx, 'tcx>,
 786         places: &Vec<Operand<'tcx>>,
 787     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 788         debug!(
 789             "closure_span: def_id={:?} target_place={:?} places={:?}",
 790             def_id, target_place, places
 791         );
 792         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
 793         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 794         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 795         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 796             for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
 797                 match place {
 798                     Operand::Copy(place) | Operand::Move(place)
 799                         if target_place == place.as_ref() =>
 800                     {
 801                         debug!("closure_span: found captured local {:?}", place);
 802                         let body = self.infcx.tcx.hir().body(*body_id);
 803                         let generator_kind = body.generator_kind();
 804                         return Some((*args_span, generator_kind, upvar.span));
 805                     }
 806                     _ => {}
 807                 }
 808             }
 809         }
 810         None
 811     }
 812
 813     /// Helper to retrieve span(s) of given borrow from the current MIR
 814     /// representation
 815     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 816         let span = self.body.source_info(borrow.reserve_location).span;
 817         self.borrow_spans(span, borrow.reserve_location)
 818     }
 819 }