src/librustc_mir/borrow_check/error_reporting.rs

   1 use rustc::hir;
   2 use rustc::hir::def::Namespace;
   3 use rustc::hir::def_id::DefId;
   4 use rustc::hir::GeneratorKind;
   5 use rustc::mir::{
   6     AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand,
   7     Place, PlaceBase, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind,
   8     Static, StaticKind, Terminator, TerminatorKind,
   9 };
  10 use rustc::ty::{self, DefIdTree, Ty, TyCtxt};
  11 use rustc::ty::layout::VariantIdx;
  12 use rustc::ty::print::Print;
  13 use rustc_errors::DiagnosticBuilder;
  14 use syntax_pos::Span;
  15
  16 use super::borrow_set::BorrowData;
  17 use super::MirBorrowckCtxt;
  18 use crate::dataflow::move_paths::{InitLocation, LookupResult};
  19
  20 pub(super) struct IncludingDowncast(pub(super) bool);
  21
  22 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  23     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  24     /// is moved after being invoked.
  25     ///
  26     /// ```text
  27     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  28     ///       its environment
  29     ///   --> $DIR/issue-42065.rs:16:29
  30     ///    |
  31     /// LL |         for (key, value) in dict {
  32     ///    |                             ^^^^
  33     /// ```
  34     pub(super) fn add_moved_or_invoked_closure_note(
  35         &self,
  36         location: Location,
  37         place: PlaceRef<'cx, 'tcx>,
  38         diag: &mut DiagnosticBuilder<'_>,
  39     ) {
  40         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  41         let mut target = place.local_or_deref_local();
  42         for stmt in &self.body_cache[location.block].statements[location.statement_index..] {
  43             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  44             if let StatementKind::Assign(box(into, Rvalue::Use(from))) = &stmt.kind {
  45                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  46                 match from {
  47                     Operand::Copy(ref place) |
  48                     Operand::Move(ref place) if target == place.local_or_deref_local() =>
  49                         target = into.local_or_deref_local(),
  50                     _ => {},
  51                 }
  52             }
  53         }
  54
  55         // Check if we are attempting to call a closure after it has been invoked.
  56         let terminator = self.body_cache[location.block].terminator();
  57         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  58         if let TerminatorKind::Call {
  59             func: Operand::Constant(box Constant {
  60                 literal: ty::Const {
  61                     ty: &ty::TyS { kind: ty::FnDef(id, _), ..  },
  62                     ..
  63                 },
  64                 ..
  65             }),
  66             args,
  67             ..
  68         } = &terminator.kind {
  69             debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  70             if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  71                 let closure = match args.first() {
  72                     Some(Operand::Copy(ref place)) |
  73                     Some(Operand::Move(ref place)) if target == place.local_or_deref_local() =>
  74                         place.local_or_deref_local().unwrap(),
  75                     _ => return,
  76                 };
  77
  78                 debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
  79                 if let ty::Closure(did, _) = self.body_cache.local_decls[closure].ty.kind {
  80                     let hir_id = self.infcx.tcx.hir().as_local_hir_id(did).unwrap();
  81
  82                     if let Some((span, name)) = self.infcx.tcx.typeck_tables_of(did)
  83                         .closure_kind_origins()
  84                         .get(hir_id)
  85                     {
  86                         diag.span_note(
  87                             *span,
  88                             &format!(
  89                                 "closure cannot be invoked more than once because it moves the \
  90                                  variable `{}` out of its environment",
  91                                 name,
  92                             ),
  93                         );
  94                         return;
  95                     }
  96                 }
  97             }
  98         }
  99
 100         // Check if we are just moving a closure after it has been invoked.
 101         if let Some(target) = target {
 102             if let ty::Closure(did, _) = self.body_cache.local_decls[target].ty.kind {
 103                 let hir_id = self.infcx.tcx.hir().as_local_hir_id(did).unwrap();
 104
 105                 if let Some((span, name)) = self.infcx.tcx.typeck_tables_of(did)
 106                     .closure_kind_origins()
 107                     .get(hir_id)
 108                 {
 109                     diag.span_note(
 110                         *span,
 111                         &format!(
 112                             "closure cannot be moved more than once as it is not `Copy` due to \
 113                              moving the variable `{}` out of its environment",
 114                              name
 115                         ),
 116                     );
 117                 }
 118             }
 119         }
 120     }
 121
 122     /// End-user visible description of `place` if one can be found. If the
 123     /// place is a temporary for instance, None will be returned.
 124     pub(super) fn describe_place(&self, place_ref: PlaceRef<'cx, 'tcx>) -> Option<String> {
 125         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 126     }
 127
 128     /// End-user visible description of `place` if one can be found. If the
 129     /// place is a temporary for instance, None will be returned.
 130     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 131     /// `Downcast` and `IncludingDowncast` is true
 132     pub(super) fn describe_place_with_options(
 133         &self,
 134         place: PlaceRef<'cx, 'tcx>,
 135         including_downcast: IncludingDowncast,
 136     ) -> Option<String> {
 137         let mut buf = String::new();
 138         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 139             Ok(()) => Some(buf),
 140             Err(()) => None,
 141         }
 142     }
 143
 144     /// Appends end-user visible description of `place` to `buf`.
 145     fn append_place_to_string(
 146         &self,
 147         place: PlaceRef<'cx, 'tcx>,
 148         buf: &mut String,
 149         mut autoderef: bool,
 150         including_downcast: &IncludingDowncast,
 151     ) -> Result<(), ()> {
 152         match place {
 153             PlaceRef {
 154                 base: PlaceBase::Local(local),
 155                 projection: [],
 156             } => {
 157                 self.append_local_to_string(*local, buf)?;
 158             }
 159             PlaceRef {
 160                 base:
 161                     PlaceBase::Static(box Static {
 162                         kind: StaticKind::Promoted(..),
 163                         ..
 164                     }),
 165                 projection: [],
 166             } => {
 167                 buf.push_str("promoted");
 168             }
 169             PlaceRef {
 170                 base:
 171                     PlaceBase::Static(box Static {
 172                         kind: StaticKind::Static,
 173                         def_id,
 174                         ..
 175                     }),
 176                 projection: [],
 177             } => {
 178                 buf.push_str(&self.infcx.tcx.item_name(*def_id).to_string());
 179             }
 180             PlaceRef {
 181                 base: &PlaceBase::Local(local),
 182                 projection: [ProjectionElem::Deref]
 183             } if self.body.local_decls[local].is_ref_for_guard() => {
 184                 self.append_place_to_string(
 185                     PlaceRef {
 186                         base: &PlaceBase::Local(local),
 187                         projection: &[],
 188                     },
 189                     buf,
 190                     autoderef,
 191                     &including_downcast,
 192                 )?;
 193             },
 194             PlaceRef {
 195                 base: &PlaceBase::Local(local),
 196                 projection: [ProjectionElem::Deref]
 197             } if self.body.local_decls[local].is_ref_to_static() => {
 198                 let local_info = &self.body.local_decls[local].local_info;
 199                 if let LocalInfo::StaticRef { def_id, .. } = *local_info {
 200                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 201                 } else {
 202                     unreachable!();
 203                 }
 204             },
 205             PlaceRef {
 206                 base,
 207                 projection: [proj_base @ .., elem],
 208             } => {
 209                 match elem {
 210                     ProjectionElem::Deref => {
 211                         let upvar_field_projection =
 212                             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 {
 226                                         base,
 227                                         projection: proj_base,
 228                                     },
 229                                     buf,
 230                                     autoderef,
 231                                     &including_downcast,
 232                                 )?;
 233                             } else {
 234                                 match (proj_base, base) {
 235                                     _ => {
 236                                         buf.push_str(&"*");
 237                                         self.append_place_to_string(
 238                                             PlaceRef {
 239                                                 base,
 240                                                 projection: proj_base,
 241                                             },
 242                                             buf,
 243                                             autoderef,
 244                                             &including_downcast,
 245                                         )?;
 246                                     }
 247                                 }
 248                             }
 249                         }
 250                     }
 251                     ProjectionElem::Downcast(..) => {
 252                         self.append_place_to_string(
 253                             PlaceRef {
 254                                 base,
 255                                 projection: proj_base,
 256                             },
 257                             buf,
 258                             autoderef,
 259                             &including_downcast,
 260                         )?;
 261                         if including_downcast.0 {
 262                             return Err(());
 263                         }
 264                     }
 265                     ProjectionElem::Field(field, _ty) => {
 266                         autoderef = true;
 267
 268                         let upvar_field_projection =
 269                             self.is_upvar_field_projection(place);
 270                         if let Some(field) = upvar_field_projection {
 271                             let var_index = field.index();
 272                             let name = self.upvars[var_index].name.to_string();
 273                             buf.push_str(&name);
 274                         } else {
 275                             let field_name = self.describe_field(PlaceRef {
 276                                 base,
 277                                 projection: proj_base,
 278                             }, *field);
 279                             self.append_place_to_string(
 280                                 PlaceRef {
 281                                     base,
 282                                     projection: proj_base,
 283                                 },
 284                                 buf,
 285                                 autoderef,
 286                                 &including_downcast,
 287                             )?;
 288                             buf.push_str(&format!(".{}", field_name));
 289                         }
 290                     }
 291                     ProjectionElem::Index(index) => {
 292                         autoderef = true;
 293
 294                         self.append_place_to_string(
 295                             PlaceRef {
 296                                 base,
 297                                 projection: proj_base,
 298                             },
 299                             buf,
 300                             autoderef,
 301                             &including_downcast,
 302                         )?;
 303                         buf.push_str("[");
 304                         if self.append_local_to_string(*index, buf).is_err() {
 305                             buf.push_str("_");
 306                         }
 307                         buf.push_str("]");
 308                     }
 309                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 310                         autoderef = true;
 311                         // Since it isn't possible to borrow an element on a particular index and
 312                         // then use another while the borrow is held, don't output indices details
 313                         // to avoid confusing the end-user
 314                         self.append_place_to_string(
 315                             PlaceRef {
 316                                 base,
 317                                 projection: proj_base,
 318                             },
 319                             buf,
 320                             autoderef,
 321                             &including_downcast,
 322                         )?;
 323                         buf.push_str(&"[..]");
 324                     }
 325                 };
 326             }
 327         }
 328
 329         Ok(())
 330     }
 331
 332     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 333     /// a name, or its name was generated by the compiler, then `Err` is returned
 334     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 335         let decl = &self.body_cache.local_decls[local];
 336         match self.local_names[local] {
 337             Some(name) if !decl.from_compiler_desugaring() => {
 338                 buf.push_str(&name.as_str());
 339                 Ok(())
 340             }
 341             _ => Err(()),
 342         }
 343     }
 344
 345     /// End-user visible description of the `field`nth field of `base`
 346     fn describe_field(&self, place: PlaceRef<'cx, 'tcx>, field: Field) -> String {
 347         // FIXME Place2 Make this work iteratively
 348         match place {
 349             PlaceRef {
 350                 base: PlaceBase::Local(local),
 351                 projection: [],
 352             } => {
 353                 let local = &self.body_cache.local_decls[*local];
 354                 self.describe_field_from_ty(&local.ty, field, None)
 355             }
 356             PlaceRef {
 357                 base: PlaceBase::Static(static_),
 358                 projection: [],
 359             } =>
 360                 self.describe_field_from_ty(&static_.ty, field, None),
 361             PlaceRef {
 362                 base,
 363                 projection: [proj_base @ .., elem],
 364             } => match elem {
 365                 ProjectionElem::Deref => {
 366                     self.describe_field(PlaceRef {
 367                         base,
 368                         projection: proj_base,
 369                     }, field)
 370                 }
 371                 ProjectionElem::Downcast(_, variant_index) => {
 372                     let base_ty =
 373                         Place::ty_from(place.base, place.projection, self.body_cache.body(), self.infcx.tcx).ty;
 374                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 375                 }
 376                 ProjectionElem::Field(_, field_type) => {
 377                     self.describe_field_from_ty(&field_type, field, None)
 378                 }
 379                 ProjectionElem::Index(..)
 380                 | ProjectionElem::ConstantIndex { .. }
 381                 | ProjectionElem::Subslice { .. } => {
 382                     self.describe_field(PlaceRef {
 383                         base,
 384                         projection: proj_base,
 385                     }, field)
 386                 }
 387             },
 388         }
 389     }
 390
 391     /// End-user visible description of the `field_index`nth field of `ty`
 392     fn describe_field_from_ty(
 393         &self,
 394         ty: Ty<'_>,
 395         field: Field,
 396         variant_index: Option<VariantIdx>
 397     ) -> String {
 398         if ty.is_box() {
 399             // If the type is a box, the field is described from the boxed type
 400             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 401         } else {
 402             match ty.kind {
 403                 ty::Adt(def, _) => {
 404                     let variant = if let Some(idx) = variant_index {
 405                         assert!(def.is_enum());
 406                         &def.variants[idx]
 407                     } else {
 408                         def.non_enum_variant()
 409                     };
 410                     variant.fields[field.index()]
 411                         .ident
 412                         .to_string()
 413                 },
 414                 ty::Tuple(_) => field.index().to_string(),
 415                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 416                     self.describe_field_from_ty(&ty, field, variant_index)
 417                 }
 418                 ty::Array(ty, _) | ty::Slice(ty) =>
 419                     self.describe_field_from_ty(&ty, field, variant_index),
 420                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 421                     // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
 422                     // the closure comes from another crate. But in that case we wouldn't
 423                     // be borrowck'ing it, so we can just unwrap:
 424                     let (&var_id, _) = self.infcx.tcx.upvars(def_id).unwrap()
 425                         .get_index(field.index()).unwrap();
 426
 427                     self.infcx.tcx.hir().name(var_id).to_string()
 428                 }
 429                 _ => {
 430                     // Might need a revision when the fields in trait RFC is implemented
 431                     // (https://github.com/rust-lang/rfcs/pull/1546)
 432                     bug!(
 433                         "End-user description not implemented for field access on `{:?}`",
 434                         ty
 435                     );
 436                 }
 437             }
 438         }
 439     }
 440
 441     /// Add a note that a type does not implement `Copy`
 442     pub(super) fn note_type_does_not_implement_copy(
 443         &self,
 444         err: &mut DiagnosticBuilder<'a>,
 445         place_desc: &str,
 446         ty: Ty<'tcx>,
 447         span: Option<Span>,
 448     ) {
 449         let message = format!(
 450             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 451             place_desc,
 452             ty,
 453         );
 454         if let Some(span) = span {
 455             err.span_label(span, message);
 456         } else {
 457             err.note(&message);
 458         }
 459     }
 460
 461     pub(super) fn borrowed_content_source(
 462         &self,
 463         deref_base: PlaceRef<'cx, 'tcx>,
 464     ) -> BorrowedContentSource<'tcx> {
 465         let tcx = self.infcx.tcx;
 466
 467         // Look up the provided place and work out the move path index for it,
 468         // we'll use this to check whether it was originally from an overloaded
 469         // operator.
 470         match self.move_data.rev_lookup.find(deref_base) {
 471             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 472                 debug!("borrowed_content_source: mpi={:?}", mpi);
 473
 474                 for i in &self.move_data.init_path_map[mpi] {
 475                     let init = &self.move_data.inits[*i];
 476                     debug!("borrowed_content_source: init={:?}", init);
 477                     // We're only interested in statements that initialized a value, not the
 478                     // initializations from arguments.
 479                     let loc = match init.location {
 480                         InitLocation::Statement(stmt) => stmt,
 481                         _ => continue,
 482                     };
 483
 484                     let bbd = &self.body_cache[loc.block];
 485                     let is_terminator = bbd.statements.len() == loc.statement_index;
 486                     debug!(
 487                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 488                         loc,
 489                         is_terminator,
 490                     );
 491                     if !is_terminator {
 492                         continue;
 493                     } else if let Some(Terminator {
 494                         kind: TerminatorKind::Call {
 495                             ref func,
 496                             from_hir_call: false,
 497                             ..
 498                         },
 499                         ..
 500                     }) = bbd.terminator {
 501                         if let Some(source)
 502                             = BorrowedContentSource::from_call(func.ty(self.body_cache.body(), tcx), tcx)
 503                         {
 504                             return source;
 505                         }
 506                     }
 507                 }
 508             }
 509             // Base is a `static` so won't be from an overloaded operator
 510             _ => (),
 511         };
 512
 513         // If we didn't find an overloaded deref or index, then assume it's a
 514         // built in deref and check the type of the base.
 515         let base_ty = Place::ty_from(deref_base.base, deref_base.projection, self.body_cache.body(), tcx).ty;
 516         if base_ty.is_unsafe_ptr() {
 517             BorrowedContentSource::DerefRawPointer
 518         } else if base_ty.is_mutable_ptr() {
 519             BorrowedContentSource::DerefMutableRef
 520         } else {
 521             BorrowedContentSource::DerefSharedRef
 522         }
 523     }
 524 }
 525
 526 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 527     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 528     /// name where required.
 529     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 530         let mut s = String::new();
 531         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 532
 533         // We need to add synthesized lifetimes where appropriate. We do
 534         // this by hooking into the pretty printer and telling it to label the
 535         // lifetimes without names with the value `'0`.
 536         match ty.kind {
 537             ty::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
 538             | ty::Ref(
 539                 ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 540                 _,
 541                 _,
 542             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 543             _ => {}
 544         }
 545
 546         let _ = ty.print(printer);
 547         s
 548     }
 549
 550     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 551     /// synthesized lifetime name where required.
 552     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 553         let mut s = String::new();
 554         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 555
 556         let region = match ty.kind {
 557             ty::Ref(region, _, _) => {
 558                 match region {
 559                     ty::RegionKind::ReLateBound(_, br)
 560                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 561                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 562                     }
 563                     _ => {}
 564                 }
 565
 566                 region
 567             }
 568             _ => bug!("ty for annotation of borrow region is not a reference"),
 569         };
 570
 571         let _ = region.print(printer);
 572         s
 573     }
 574 }
 575
 576 // The span(s) associated to a use of a place.
 577 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 578 pub(super) enum UseSpans {
 579     // The access is caused by capturing a variable for a closure.
 580     ClosureUse {
 581         // This is true if the captured variable was from a generator.
 582         generator_kind: Option<GeneratorKind>,
 583         // The span of the args of the closure, including the `move` keyword if
 584         // it's present.
 585         args_span: Span,
 586         // The span of the first use of the captured variable inside the closure.
 587         var_span: Span,
 588     },
 589     // This access has a single span associated to it: common case.
 590     OtherUse(Span),
 591 }
 592
 593 impl UseSpans {
 594     pub(super) fn args_or_use(self) -> Span {
 595         match self {
 596             UseSpans::ClosureUse {
 597                 args_span: span, ..
 598             }
 599             | UseSpans::OtherUse(span) => span,
 600         }
 601     }
 602
 603     pub(super) fn var_or_use(self) -> Span {
 604         match self {
 605             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
 606         }
 607     }
 608
 609     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 610         match self {
 611             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 612             _ => None,
 613         }
 614     }
 615
 616     // Add a span label to the arguments of the closure, if it exists.
 617     pub(super) fn args_span_label(
 618         self,
 619         err: &mut DiagnosticBuilder<'_>,
 620         message: impl Into<String>,
 621     ) {
 622         if let UseSpans::ClosureUse { args_span, .. } = self {
 623             err.span_label(args_span, message);
 624         }
 625     }
 626
 627     // Add a span label to the use of the captured variable, if it exists.
 628     pub(super) fn var_span_label(
 629         self,
 630         err: &mut DiagnosticBuilder<'_>,
 631         message: impl Into<String>,
 632     ) {
 633         if let UseSpans::ClosureUse { var_span, .. } = self {
 634             err.span_label(var_span, message);
 635         }
 636     }
 637
 638     /// Returns `false` if this place is not used in a closure.
 639     pub(super) fn for_closure(&self) -> bool {
 640         match *self {
 641             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 642             _ => false,
 643         }
 644     }
 645
 646     /// Returns `false` if this place is not used in a generator.
 647     pub(super) fn for_generator(&self) -> bool {
 648         match *self {
 649             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 650             _ => false,
 651         }
 652     }
 653
 654     /// Describe the span associated with a use of a place.
 655     pub(super) fn describe(&self) -> String {
 656         match *self {
 657             UseSpans::ClosureUse { generator_kind, .. } => if generator_kind.is_some() {
 658                 " in generator".to_string()
 659             } else {
 660                 " in closure".to_string()
 661             },
 662             _ => "".to_string(),
 663         }
 664     }
 665
 666     pub(super) fn or_else<F>(self, if_other: F) -> Self
 667     where
 668         F: FnOnce() -> Self,
 669     {
 670         match self {
 671             closure @ UseSpans::ClosureUse { .. } => closure,
 672             UseSpans::OtherUse(_) => if_other(),
 673         }
 674     }
 675 }
 676
 677 pub(super) enum BorrowedContentSource<'tcx> {
 678     DerefRawPointer,
 679     DerefMutableRef,
 680     DerefSharedRef,
 681     OverloadedDeref(Ty<'tcx>),
 682     OverloadedIndex(Ty<'tcx>),
 683 }
 684
 685 impl BorrowedContentSource<'tcx> {
 686     pub(super) fn describe_for_unnamed_place(&self) -> String {
 687         match *self {
 688             BorrowedContentSource::DerefRawPointer => format!("a raw pointer"),
 689             BorrowedContentSource::DerefSharedRef => format!("a shared reference"),
 690             BorrowedContentSource::DerefMutableRef => {
 691                 format!("a mutable reference")
 692             }
 693             BorrowedContentSource::OverloadedDeref(ty) => {
 694                 if ty.is_rc() {
 695                    format!("an `Rc`")
 696                 } else if ty.is_arc() {
 697                     format!("an `Arc`")
 698                 } else {
 699                     format!("dereference of `{}`", ty)
 700                 }
 701             }
 702             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 703         }
 704     }
 705
 706     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 707         match *self {
 708             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 709             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 710             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 711             // Overloaded deref and index operators should be evaluated into a
 712             // temporary. So we don't need a description here.
 713             BorrowedContentSource::OverloadedDeref(_)
 714             | BorrowedContentSource::OverloadedIndex(_) => None
 715         }
 716     }
 717
 718     pub(super) fn describe_for_immutable_place(&self) -> String {
 719         match *self {
 720             BorrowedContentSource::DerefRawPointer => format!("a `*const` pointer"),
 721             BorrowedContentSource::DerefSharedRef => format!("a `&` reference"),
 722             BorrowedContentSource::DerefMutableRef => {
 723                  bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 724             },
 725             BorrowedContentSource::OverloadedDeref(ty) => {
 726                 if ty.is_rc() {
 727                    format!("an `Rc`")
 728                 } else if ty.is_arc() {
 729                     format!("an `Arc`")
 730                 } else {
 731                     format!("a dereference of `{}`", ty)
 732                 }
 733             }
 734             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 735         }
 736     }
 737
 738     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 739         match func.kind {
 740             ty::FnDef(def_id, substs) => {
 741                 let trait_id = tcx.trait_of_item(def_id)?;
 742
 743                 let lang_items = tcx.lang_items();
 744                 if Some(trait_id) == lang_items.deref_trait()
 745                     || Some(trait_id) == lang_items.deref_mut_trait()
 746                 {
 747                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 748                 } else if Some(trait_id) == lang_items.index_trait()
 749                     || Some(trait_id) == lang_items.index_mut_trait()
 750                 {
 751                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 752                 } else {
 753                     None
 754                 }
 755             }
 756             _ => None,
 757         }
 758     }
 759 }
 760
 761 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 762     /// Finds the spans associated to a move or copy of move_place at location.
 763     pub(super) fn move_spans(
 764         &self,
 765         moved_place: PlaceRef<'cx, 'tcx>, // Could also be an upvar.
 766         location: Location,
 767     ) -> UseSpans {
 768         use self::UseSpans::*;
 769
 770         let stmt = match self.body_cache[location.block].statements.get(location.statement_index) {
 771             Some(stmt) => stmt,
 772             None => return OtherUse(self.body_cache.source_info(location).span),
 773         };
 774
 775         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 776         if let  StatementKind::Assign(
 777             box(_, Rvalue::Aggregate(ref kind, ref places))
 778         ) = stmt.kind {
 779             let def_id = match kind {
 780                 box AggregateKind::Closure(def_id, _)
 781                 | box AggregateKind::Generator(def_id, _, _) => def_id,
 782                 _ => return OtherUse(stmt.source_info.span),
 783             };
 784
 785             debug!(
 786                 "move_spans: def_id={:?} places={:?}",
 787                 def_id, places
 788             );
 789             if let Some((args_span, generator_kind, var_span))
 790                 = self.closure_span(*def_id, moved_place, places) {
 791                 return ClosureUse {
 792                     generator_kind,
 793                     args_span,
 794                     var_span,
 795                 };
 796             }
 797         }
 798
 799         OtherUse(stmt.source_info.span)
 800     }
 801
 802     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 803     /// and its usage of the local assigned at `location`.
 804     /// This is done by searching in statements succeeding `location`
 805     /// and originating from `maybe_closure_span`.
 806     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 807         use self::UseSpans::*;
 808         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 809
 810         let target = match self.body_cache[location.block]
 811             .statements
 812             .get(location.statement_index)
 813         {
 814             Some(&Statement {
 815                 kind: StatementKind::Assign(box(ref place, _)),
 816                 ..
 817             }) => {
 818                 if let Some(local) = place.as_local() {
 819                     local
 820                 } else {
 821                     return OtherUse(use_span);
 822                 }
 823             }
 824             _ => return OtherUse(use_span),
 825         };
 826
 827         if self.body_cache.local_kind(target) != LocalKind::Temp {
 828             // operands are always temporaries.
 829             return OtherUse(use_span);
 830         }
 831
 832         for stmt in &self.body_cache[location.block].statements[location.statement_index + 1..] {
 833             if let StatementKind::Assign(
 834                 box(_, Rvalue::Aggregate(ref kind, ref places))
 835             ) = stmt.kind {
 836                 let (def_id, is_generator) = match kind {
 837                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 838                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 839                     _ => continue,
 840                 };
 841
 842                 debug!(
 843                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 844                     def_id, is_generator, places
 845                 );
 846                 if let Some((args_span, generator_kind, var_span)) = self.closure_span(
 847                     *def_id, Place::from(target).as_ref(), places
 848                 ) {
 849                     return ClosureUse {
 850                         generator_kind,
 851                         args_span,
 852                         var_span,
 853                     };
 854                 } else {
 855                     return OtherUse(use_span);
 856                 }
 857             }
 858
 859             if use_span != stmt.source_info.span {
 860                 break;
 861             }
 862         }
 863
 864         OtherUse(use_span)
 865     }
 866
 867     /// Finds the span of a captured variable within a closure or generator.
 868     fn closure_span(
 869         &self,
 870         def_id: DefId,
 871         target_place: PlaceRef<'cx, 'tcx>,
 872         places: &Vec<Operand<'tcx>>,
 873     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 874         debug!(
 875             "closure_span: def_id={:?} target_place={:?} places={:?}",
 876             def_id, target_place, places
 877         );
 878         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
 879         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 880         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 881         if let hir::ExprKind::Closure(
 882             .., body_id, args_span, _
 883         ) = expr {
 884             for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
 885                 match place {
 886                     Operand::Copy(place) |
 887                     Operand::Move(place) if target_place == place.as_ref() => {
 888                         debug!("closure_span: found captured local {:?}", place);
 889                         let body = self.infcx.tcx.hir().body(*body_id);
 890                         let generator_kind = body.generator_kind();
 891                         return Some((*args_span, generator_kind, upvar.span));
 892                     },
 893                     _ => {}
 894                 }
 895             }
 896
 897         }
 898         None
 899     }
 900
 901     /// Helper to retrieve span(s) of given borrow from the current MIR
 902     /// representation
 903     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 904         let span = self.body_cache.source_info(borrow.reserve_location).span;
 905         self.borrow_spans(span, borrow.reserve_location)
 906     }
 907 }