src/librustc_mir/borrow_check/diagnostics/mod.rs

   1 //! Borrow checker diagnostics.
   2
   3 use rustc_errors::DiagnosticBuilder;
   4 use rustc_hir as hir;
   5 use rustc_hir::def::Namespace;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_hir::GeneratorKind;
   8 use rustc_middle::mir::{
   9     AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
  10     PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
  11 };
  12 use rustc_middle::ty::print::Print;
  13 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt};
  14 use rustc_span::{symbol::sym, Span};
  15 use rustc_target::abi::VariantIdx;
  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<'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.
 141     /// If the place is a temporary for instance, `"value"` will be returned.
 142     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 143         match self.describe_place(place_ref) {
 144             Some(mut descr) => {
 145                 // Surround descr with `backticks`.
 146                 descr.reserve(2);
 147                 descr.insert_str(0, "`");
 148                 descr.push_str("`");
 149                 descr
 150             }
 151             None => "value".to_string(),
 152         }
 153     }
 154
 155     /// End-user visible description of `place` if one can be found.
 156     /// If the place is a temporary for instance, None will be returned.
 157     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 158         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 159     }
 160
 161     /// End-user visible description of `place` if one can be found. If the
 162     /// place is a temporary for instance, None will be returned.
 163     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 164     /// `Downcast` and `IncludingDowncast` is true
 165     pub(super) fn describe_place_with_options(
 166         &self,
 167         place: PlaceRef<'tcx>,
 168         including_downcast: IncludingDowncast,
 169     ) -> Option<String> {
 170         let mut buf = String::new();
 171         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 172             Ok(()) => Some(buf),
 173             Err(()) => None,
 174         }
 175     }
 176
 177     /// Appends end-user visible description of `place` to `buf`.
 178     fn append_place_to_string(
 179         &self,
 180         place: PlaceRef<'tcx>,
 181         buf: &mut String,
 182         mut autoderef: bool,
 183         including_downcast: &IncludingDowncast,
 184     ) -> Result<(), ()> {
 185         match place {
 186             PlaceRef { local, projection: [] } => {
 187                 self.append_local_to_string(local, buf)?;
 188             }
 189             PlaceRef { local, projection: [ProjectionElem::Deref] }
 190                 if self.body.local_decls[local].is_ref_for_guard() =>
 191             {
 192                 self.append_place_to_string(
 193                     PlaceRef { local, projection: &[] },
 194                     buf,
 195                     autoderef,
 196                     &including_downcast,
 197                 )?;
 198             }
 199             PlaceRef { local, projection: [ProjectionElem::Deref] }
 200                 if self.body.local_decls[local].is_ref_to_static() =>
 201             {
 202                 let local_info = &self.body.local_decls[local].local_info;
 203                 if let LocalInfo::StaticRef { def_id, .. } = *local_info {
 204                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 205                 } else {
 206                     unreachable!();
 207                 }
 208             }
 209             PlaceRef { local, projection: [proj_base @ .., elem] } => {
 210                 match elem {
 211                     ProjectionElem::Deref => {
 212                         let upvar_field_projection = self.is_upvar_field_projection(place);
 213                         if let Some(field) = upvar_field_projection {
 214                             let var_index = field.index();
 215                             let name = self.upvars[var_index].name.to_string();
 216                             if self.upvars[var_index].by_ref {
 217                                 buf.push_str(&name);
 218                             } else {
 219                                 buf.push_str(&format!("*{}", &name));
 220                             }
 221                         } else {
 222                             if autoderef {
 223                                 // FIXME turn this recursion into iteration
 224                                 self.append_place_to_string(
 225                                     PlaceRef { local, projection: proj_base },
 226                                     buf,
 227                                     autoderef,
 228                                     &including_downcast,
 229                                 )?;
 230                             } else {
 231                                 buf.push_str(&"*");
 232                                 self.append_place_to_string(
 233                                     PlaceRef { local, projection: proj_base },
 234                                     buf,
 235                                     autoderef,
 236                                     &including_downcast,
 237                                 )?;
 238                             }
 239                         }
 240                     }
 241                     ProjectionElem::Downcast(..) => {
 242                         self.append_place_to_string(
 243                             PlaceRef { local, projection: proj_base },
 244                             buf,
 245                             autoderef,
 246                             &including_downcast,
 247                         )?;
 248                         if including_downcast.0 {
 249                             return Err(());
 250                         }
 251                     }
 252                     ProjectionElem::Field(field, _ty) => {
 253                         autoderef = true;
 254
 255                         let upvar_field_projection = self.is_upvar_field_projection(place);
 256                         if let Some(field) = upvar_field_projection {
 257                             let var_index = field.index();
 258                             let name = self.upvars[var_index].name.to_string();
 259                             buf.push_str(&name);
 260                         } else {
 261                             let field_name = self
 262                                 .describe_field(PlaceRef { local, projection: proj_base }, *field);
 263                             self.append_place_to_string(
 264                                 PlaceRef { local, projection: proj_base },
 265                                 buf,
 266                                 autoderef,
 267                                 &including_downcast,
 268                             )?;
 269                             buf.push_str(&format!(".{}", field_name));
 270                         }
 271                     }
 272                     ProjectionElem::Index(index) => {
 273                         autoderef = true;
 274
 275                         self.append_place_to_string(
 276                             PlaceRef { local, projection: proj_base },
 277                             buf,
 278                             autoderef,
 279                             &including_downcast,
 280                         )?;
 281                         buf.push_str("[");
 282                         if self.append_local_to_string(*index, buf).is_err() {
 283                             buf.push_str("_");
 284                         }
 285                         buf.push_str("]");
 286                     }
 287                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 288                         autoderef = true;
 289                         // Since it isn't possible to borrow an element on a particular index and
 290                         // then use another while the borrow is held, don't output indices details
 291                         // to avoid confusing the end-user
 292                         self.append_place_to_string(
 293                             PlaceRef { local, projection: proj_base },
 294                             buf,
 295                             autoderef,
 296                             &including_downcast,
 297                         )?;
 298                         buf.push_str(&"[..]");
 299                     }
 300                 };
 301             }
 302         }
 303
 304         Ok(())
 305     }
 306
 307     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 308     /// a name, or its name was generated by the compiler, then `Err` is returned
 309     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 310         let decl = &self.body.local_decls[local];
 311         match self.local_names[local] {
 312             Some(name) if !decl.from_compiler_desugaring() => {
 313                 buf.push_str(&name.as_str());
 314                 Ok(())
 315             }
 316             _ => Err(()),
 317         }
 318     }
 319
 320     /// End-user visible description of the `field`nth field of `base`
 321     fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
 322         // FIXME Place2 Make this work iteratively
 323         match place {
 324             PlaceRef { local, projection: [] } => {
 325                 let local = &self.body.local_decls[local];
 326                 self.describe_field_from_ty(&local.ty, field, None)
 327             }
 328             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 329                 ProjectionElem::Deref => {
 330                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 331                 }
 332                 ProjectionElem::Downcast(_, variant_index) => {
 333                     let base_ty =
 334                         Place::ty_from(place.local, place.projection, self.body, self.infcx.tcx).ty;
 335                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 336                 }
 337                 ProjectionElem::Field(_, field_type) => {
 338                     self.describe_field_from_ty(&field_type, field, None)
 339                 }
 340                 ProjectionElem::Index(..)
 341                 | ProjectionElem::ConstantIndex { .. }
 342                 | ProjectionElem::Subslice { .. } => {
 343                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 344                 }
 345             },
 346         }
 347     }
 348
 349     /// End-user visible description of the `field_index`nth field of `ty`
 350     fn describe_field_from_ty(
 351         &self,
 352         ty: Ty<'_>,
 353         field: Field,
 354         variant_index: Option<VariantIdx>,
 355     ) -> String {
 356         if ty.is_box() {
 357             // If the type is a box, the field is described from the boxed type
 358             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 359         } else {
 360             match ty.kind {
 361                 ty::Adt(def, _) => {
 362                     let variant = if let Some(idx) = variant_index {
 363                         assert!(def.is_enum());
 364                         &def.variants[idx]
 365                     } else {
 366                         def.non_enum_variant()
 367                     };
 368                     variant.fields[field.index()].ident.to_string()
 369                 }
 370                 ty::Tuple(_) => field.index().to_string(),
 371                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 372                     self.describe_field_from_ty(&ty, field, variant_index)
 373                 }
 374                 ty::Array(ty, _) | ty::Slice(ty) => {
 375                     self.describe_field_from_ty(&ty, field, variant_index)
 376                 }
 377                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 378                     // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
 379                     // the closure comes from another crate. But in that case we wouldn't
 380                     // be borrowck'ing it, so we can just unwrap:
 381                     let (&var_id, _) =
 382                         self.infcx.tcx.upvars(def_id).unwrap().get_index(field.index()).unwrap();
 383
 384                     self.infcx.tcx.hir().name(var_id).to_string()
 385                 }
 386                 _ => {
 387                     // Might need a revision when the fields in trait RFC is implemented
 388                     // (https://github.com/rust-lang/rfcs/pull/1546)
 389                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 390                 }
 391             }
 392         }
 393     }
 394
 395     /// Add a note that a type does not implement `Copy`
 396     pub(super) fn note_type_does_not_implement_copy(
 397         &self,
 398         err: &mut DiagnosticBuilder<'a>,
 399         place_desc: &str,
 400         ty: Ty<'tcx>,
 401         span: Option<Span>,
 402     ) {
 403         let message = format!(
 404             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 405             place_desc, ty,
 406         );
 407         if let Some(span) = span {
 408             err.span_label(span, message);
 409         } else {
 410             err.note(&message);
 411         }
 412     }
 413
 414     pub(super) fn borrowed_content_source(
 415         &self,
 416         deref_base: PlaceRef<'tcx>,
 417     ) -> BorrowedContentSource<'tcx> {
 418         let tcx = self.infcx.tcx;
 419
 420         // Look up the provided place and work out the move path index for it,
 421         // we'll use this to check whether it was originally from an overloaded
 422         // operator.
 423         match self.move_data.rev_lookup.find(deref_base) {
 424             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 425                 debug!("borrowed_content_source: mpi={:?}", mpi);
 426
 427                 for i in &self.move_data.init_path_map[mpi] {
 428                     let init = &self.move_data.inits[*i];
 429                     debug!("borrowed_content_source: init={:?}", init);
 430                     // We're only interested in statements that initialized a value, not the
 431                     // initializations from arguments.
 432                     let loc = match init.location {
 433                         InitLocation::Statement(stmt) => stmt,
 434                         _ => continue,
 435                     };
 436
 437                     let bbd = &self.body[loc.block];
 438                     let is_terminator = bbd.statements.len() == loc.statement_index;
 439                     debug!(
 440                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 441                         loc, is_terminator,
 442                     );
 443                     if !is_terminator {
 444                         continue;
 445                     } else if let Some(Terminator {
 446                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 447                         ..
 448                     }) = bbd.terminator
 449                     {
 450                         if let Some(source) =
 451                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 452                         {
 453                             return source;
 454                         }
 455                     }
 456                 }
 457             }
 458             // Base is a `static` so won't be from an overloaded operator
 459             _ => (),
 460         };
 461
 462         // If we didn't find an overloaded deref or index, then assume it's a
 463         // built in deref and check the type of the base.
 464         let base_ty = Place::ty_from(deref_base.local, deref_base.projection, self.body, tcx).ty;
 465         if base_ty.is_unsafe_ptr() {
 466             BorrowedContentSource::DerefRawPointer
 467         } else if base_ty.is_mutable_ptr() {
 468             BorrowedContentSource::DerefMutableRef
 469         } else {
 470             BorrowedContentSource::DerefSharedRef
 471         }
 472     }
 473 }
 474
 475 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 476     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 477     /// name where required.
 478     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 479         let mut s = String::new();
 480         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 481
 482         // We need to add synthesized lifetimes where appropriate. We do
 483         // this by hooking into the pretty printer and telling it to label the
 484         // lifetimes without names with the value `'0`.
 485         match ty.kind {
 486             ty::Ref(
 487                 ty::RegionKind::ReLateBound(_, br)
 488                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 489                 _,
 490                 _,
 491             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 492             _ => {}
 493         }
 494
 495         let _ = ty.print(printer);
 496         s
 497     }
 498
 499     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 500     /// synthesized lifetime name where required.
 501     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 502         let mut s = String::new();
 503         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 504
 505         let region = match ty.kind {
 506             ty::Ref(region, _, _) => {
 507                 match region {
 508                     ty::RegionKind::ReLateBound(_, br)
 509                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 510                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 511                     }
 512                     _ => {}
 513                 }
 514
 515                 region
 516             }
 517             _ => bug!("ty for annotation of borrow region is not a reference"),
 518         };
 519
 520         let _ = region.print(printer);
 521         s
 522     }
 523 }
 524
 525 // The span(s) associated to a use of a place.
 526 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 527 pub(super) enum UseSpans {
 528     // The access is caused by capturing a variable for a closure.
 529     ClosureUse {
 530         // This is true if the captured variable was from a generator.
 531         generator_kind: Option<GeneratorKind>,
 532         // The span of the args of the closure, including the `move` keyword if
 533         // it's present.
 534         args_span: Span,
 535         // The span of the first use of the captured variable inside the closure.
 536         var_span: Span,
 537     },
 538     // This access has a single span associated to it: common case.
 539     OtherUse(Span),
 540 }
 541
 542 impl UseSpans {
 543     pub(super) fn args_or_use(self) -> Span {
 544         match self {
 545             UseSpans::ClosureUse { args_span: span, .. } | UseSpans::OtherUse(span) => span,
 546         }
 547     }
 548
 549     pub(super) fn var_or_use(self) -> Span {
 550         match self {
 551             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
 552         }
 553     }
 554
 555     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 556         match self {
 557             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 558             _ => None,
 559         }
 560     }
 561
 562     // Add a span label to the arguments of the closure, if it exists.
 563     pub(super) fn args_span_label(
 564         self,
 565         err: &mut DiagnosticBuilder<'_>,
 566         message: impl Into<String>,
 567     ) {
 568         if let UseSpans::ClosureUse { args_span, .. } = self {
 569             err.span_label(args_span, message);
 570         }
 571     }
 572
 573     // Add a span label to the use of the captured variable, if it exists.
 574     pub(super) fn var_span_label(
 575         self,
 576         err: &mut DiagnosticBuilder<'_>,
 577         message: impl Into<String>,
 578     ) {
 579         if let UseSpans::ClosureUse { var_span, .. } = self {
 580             err.span_label(var_span, message);
 581         }
 582     }
 583
 584     /// Returns `false` if this place is not used in a closure.
 585     pub(super) fn for_closure(&self) -> bool {
 586         match *self {
 587             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 588             _ => false,
 589         }
 590     }
 591
 592     /// Returns `false` if this place is not used in a generator.
 593     pub(super) fn for_generator(&self) -> bool {
 594         match *self {
 595             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 596             _ => false,
 597         }
 598     }
 599
 600     /// Describe the span associated with a use of a place.
 601     pub(super) fn describe(&self) -> String {
 602         match *self {
 603             UseSpans::ClosureUse { generator_kind, .. } => {
 604                 if generator_kind.is_some() {
 605                     " in generator".to_string()
 606                 } else {
 607                     " in closure".to_string()
 608                 }
 609             }
 610             _ => "".to_string(),
 611         }
 612     }
 613
 614     pub(super) fn or_else<F>(self, if_other: F) -> Self
 615     where
 616         F: FnOnce() -> Self,
 617     {
 618         match self {
 619             closure @ UseSpans::ClosureUse { .. } => closure,
 620             UseSpans::OtherUse(_) => if_other(),
 621         }
 622     }
 623 }
 624
 625 pub(super) enum BorrowedContentSource<'tcx> {
 626     DerefRawPointer,
 627     DerefMutableRef,
 628     DerefSharedRef,
 629     OverloadedDeref(Ty<'tcx>),
 630     OverloadedIndex(Ty<'tcx>),
 631 }
 632
 633 impl BorrowedContentSource<'tcx> {
 634     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 635         match *self {
 636             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 637             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 638             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 639             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 640                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 641                     "an `Rc`".to_string()
 642                 }
 643                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 644                     "an `Arc`".to_string()
 645                 }
 646                 _ => format!("dereference of `{}`", ty),
 647             },
 648             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 649         }
 650     }
 651
 652     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 653         match *self {
 654             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 655             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 656             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 657             // Overloaded deref and index operators should be evaluated into a
 658             // temporary. So we don't need a description here.
 659             BorrowedContentSource::OverloadedDeref(_)
 660             | BorrowedContentSource::OverloadedIndex(_) => None,
 661         }
 662     }
 663
 664     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 665         match *self {
 666             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 667             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 668             BorrowedContentSource::DerefMutableRef => {
 669                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 670             }
 671             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 672                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 673                     "an `Rc`".to_string()
 674                 }
 675                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 676                     "an `Arc`".to_string()
 677                 }
 678                 _ => format!("a dereference of `{}`", ty),
 679             },
 680             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 681         }
 682     }
 683
 684     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 685         match func.kind {
 686             ty::FnDef(def_id, substs) => {
 687                 let trait_id = tcx.trait_of_item(def_id)?;
 688
 689                 let lang_items = tcx.lang_items();
 690                 if Some(trait_id) == lang_items.deref_trait()
 691                     || Some(trait_id) == lang_items.deref_mut_trait()
 692                 {
 693                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 694                 } else if Some(trait_id) == lang_items.index_trait()
 695                     || Some(trait_id) == lang_items.index_mut_trait()
 696                 {
 697                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 698                 } else {
 699                     None
 700                 }
 701             }
 702             _ => None,
 703         }
 704     }
 705 }
 706
 707 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 708     /// Finds the spans associated to a move or copy of move_place at location.
 709     pub(super) fn move_spans(
 710         &self,
 711         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 712         location: Location,
 713     ) -> UseSpans {
 714         use self::UseSpans::*;
 715
 716         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 717             Some(stmt) => stmt,
 718             None => return OtherUse(self.body.source_info(location).span),
 719         };
 720
 721         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 722         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 723             let def_id = match kind {
 724                 box AggregateKind::Closure(def_id, _)
 725                 | box AggregateKind::Generator(def_id, _, _) => def_id,
 726                 _ => return OtherUse(stmt.source_info.span),
 727             };
 728
 729             debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 730             if let Some((args_span, generator_kind, var_span)) =
 731                 self.closure_span(*def_id, moved_place, places)
 732             {
 733                 return ClosureUse { generator_kind, args_span, var_span };
 734             }
 735         }
 736
 737         OtherUse(stmt.source_info.span)
 738     }
 739
 740     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 741     /// and its usage of the local assigned at `location`.
 742     /// This is done by searching in statements succeeding `location`
 743     /// and originating from `maybe_closure_span`.
 744     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 745         use self::UseSpans::*;
 746         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 747
 748         let target = match self.body[location.block].statements.get(location.statement_index) {
 749             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 750                 if let Some(local) = place.as_local() {
 751                     local
 752                 } else {
 753                     return OtherUse(use_span);
 754                 }
 755             }
 756             _ => return OtherUse(use_span),
 757         };
 758
 759         if self.body.local_kind(target) != LocalKind::Temp {
 760             // operands are always temporaries.
 761             return OtherUse(use_span);
 762         }
 763
 764         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 765             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 766                 stmt.kind
 767             {
 768                 let (def_id, is_generator) = match kind {
 769                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 770                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 771                     _ => continue,
 772                 };
 773
 774                 debug!(
 775                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 776                     def_id, is_generator, places
 777                 );
 778                 if let Some((args_span, generator_kind, var_span)) =
 779                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 780                 {
 781                     return ClosureUse { generator_kind, args_span, var_span };
 782                 } else {
 783                     return OtherUse(use_span);
 784                 }
 785             }
 786
 787             if use_span != stmt.source_info.span {
 788                 break;
 789             }
 790         }
 791
 792         OtherUse(use_span)
 793     }
 794
 795     /// Finds the span of a captured variable within a closure or generator.
 796     fn closure_span(
 797         &self,
 798         def_id: DefId,
 799         target_place: PlaceRef<'tcx>,
 800         places: &Vec<Operand<'tcx>>,
 801     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 802         debug!(
 803             "closure_span: def_id={:?} target_place={:?} places={:?}",
 804             def_id, target_place, places
 805         );
 806         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
 807         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 808         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 809         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 810             for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
 811                 match place {
 812                     Operand::Copy(place) | Operand::Move(place)
 813                         if target_place == place.as_ref() =>
 814                     {
 815                         debug!("closure_span: found captured local {:?}", place);
 816                         let body = self.infcx.tcx.hir().body(*body_id);
 817                         let generator_kind = body.generator_kind();
 818                         return Some((*args_span, generator_kind, upvar.span));
 819                     }
 820                     _ => {}
 821                 }
 822             }
 823         }
 824         None
 825     }
 826
 827     /// Helper to retrieve span(s) of given borrow from the current MIR
 828     /// representation
 829     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 830         let span = self.body.source_info(borrow.reserve_location).span;
 831         self.borrow_spans(span, borrow.reserve_location)
 832     }
 833 }