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::mir::{
   5     AggregateKind, Constant, Field, Local, LocalKind, Location, Operand,
   6     Place, PlaceBase, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind,
   7     Static, StaticKind, Terminator, TerminatorKind,
   8 };
   9 use rustc::ty::{self, DefIdTree, Ty, TyCtxt};
  10 use rustc::ty::layout::VariantIdx;
  11 use rustc::ty::print::Print;
  12 use rustc_errors::DiagnosticBuilder;
  13 use syntax_pos::Span;
  14 use syntax::symbol::sym;
  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[location.block].statements[location.statement_index..] {
  43             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  44             if let StatementKind::Assign(into, box 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[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 { sty: 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.local_decls[closure].ty.sty {
  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.local_decls[target].ty.sty {
 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: None,
 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: None,
 166             } => {
 167                 buf.push_str("promoted");
 168             }
 169             PlaceRef {
 170                 base:
 171                     PlaceBase::Static(box Static {
 172                         kind: StaticKind::Static(def_id),
 173                         ..
 174                     }),
 175                 projection: None,
 176             } => {
 177                 buf.push_str(&self.infcx.tcx.item_name(*def_id).to_string());
 178             }
 179             PlaceRef {
 180                 base,
 181                 projection: Some(ref proj),
 182             } => {
 183                 match proj.elem {
 184                     ProjectionElem::Deref => {
 185                         let upvar_field_projection =
 186                             self.is_upvar_field_projection(place);
 187                         if let Some(field) = upvar_field_projection {
 188                             let var_index = field.index();
 189                             let name = self.upvars[var_index].name.to_string();
 190                             if self.upvars[var_index].by_ref {
 191                                 buf.push_str(&name);
 192                             } else {
 193                                 buf.push_str(&format!("*{}", &name));
 194                             }
 195                         } else {
 196                             if autoderef {
 197                                 // FIXME turn this recursion into iteration
 198                                 self.append_place_to_string(
 199                                     PlaceRef {
 200                                         base,
 201                                         projection: &proj.base,
 202                                     },
 203                                     buf,
 204                                     autoderef,
 205                                     &including_downcast,
 206                                 )?;
 207                             } else {
 208                                 match (&proj.base, base) {
 209                                     (None, PlaceBase::Local(local)) => {
 210                                         if self.body.local_decls[*local].is_ref_for_guard() {
 211                                             self.append_place_to_string(
 212                                                 PlaceRef {
 213                                                     base,
 214                                                     projection: &proj.base,
 215                                                 },
 216                                                 buf,
 217                                                 autoderef,
 218                                                 &including_downcast,
 219                                             )?;
 220                                         } else {
 221                                             // FIXME deduplicate this and the _ => body below
 222                                             buf.push_str(&"*");
 223                                             self.append_place_to_string(
 224                                                 PlaceRef {
 225                                                     base,
 226                                                     projection: &proj.base,
 227                                                 },
 228                                                 buf,
 229                                                 autoderef,
 230                                                 &including_downcast,
 231                                             )?;
 232                                         }
 233                                     }
 234
 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_index: Local, buf: &mut String) -> Result<(), ()> {
 335         let local = &self.body.local_decls[local_index];
 336         match local.name {
 337             Some(name) if !local.from_compiler_desugaring() => {
 338                 buf.push_str(name.as_str().get());
 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: None,
 352             } => {
 353                 let local = &self.body.local_decls[*local];
 354                 self.describe_field_from_ty(&local.ty, field, None)
 355             }
 356             PlaceRef {
 357                 base: PlaceBase::Static(static_),
 358                 projection: None,
 359             } =>
 360                 self.describe_field_from_ty(&static_.ty, field, None),
 361             PlaceRef {
 362                 base,
 363                 projection: Some(proj),
 364             } => match proj.elem {
 365                 ProjectionElem::Deref => self.describe_field(PlaceRef {
 366                     base,
 367                     projection: &proj.base,
 368                 }, field),
 369                 ProjectionElem::Downcast(_, variant_index) => {
 370                     let base_ty =
 371                         Place::ty_from(place.base, place.projection, self.body, self.infcx.tcx).ty;
 372                     self.describe_field_from_ty(&base_ty, field, Some(variant_index))
 373                 }
 374                 ProjectionElem::Field(_, field_type) => {
 375                     self.describe_field_from_ty(&field_type, field, None)
 376                 }
 377                 ProjectionElem::Index(..)
 378                 | ProjectionElem::ConstantIndex { .. }
 379                 | ProjectionElem::Subslice { .. } => {
 380                     self.describe_field(PlaceRef {
 381                         base,
 382                         projection: &proj.base,
 383                     }, field)
 384                 }
 385             },
 386         }
 387     }
 388
 389     /// End-user visible description of the `field_index`nth field of `ty`
 390     fn describe_field_from_ty(
 391         &self,
 392         ty: Ty<'_>,
 393         field: Field,
 394         variant_index: Option<VariantIdx>
 395     ) -> String {
 396         if ty.is_box() {
 397             // If the type is a box, the field is described from the boxed type
 398             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 399         } else {
 400             match ty.sty {
 401                 ty::Adt(def, _) => {
 402                     let variant = if let Some(idx) = variant_index {
 403                         assert!(def.is_enum());
 404                         &def.variants[idx]
 405                     } else {
 406                         def.non_enum_variant()
 407                     };
 408                     variant.fields[field.index()]
 409                         .ident
 410                         .to_string()
 411                 },
 412                 ty::Tuple(_) => field.index().to_string(),
 413                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 414                     self.describe_field_from_ty(&ty, field, variant_index)
 415                 }
 416                 ty::Array(ty, _) | ty::Slice(ty) =>
 417                     self.describe_field_from_ty(&ty, field, variant_index),
 418                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 419                     // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
 420                     // the closure comes from another crate. But in that case we wouldn't
 421                     // be borrowck'ing it, so we can just unwrap:
 422                     let (&var_id, _) = self.infcx.tcx.upvars(def_id).unwrap()
 423                         .get_index(field.index()).unwrap();
 424
 425                     self.infcx.tcx.hir().name(var_id).to_string()
 426                 }
 427                 _ => {
 428                     // Might need a revision when the fields in trait RFC is implemented
 429                     // (https://github.com/rust-lang/rfcs/pull/1546)
 430                     bug!(
 431                         "End-user description not implemented for field access on `{:?}`",
 432                         ty
 433                     );
 434                 }
 435             }
 436         }
 437     }
 438
 439     /// Checks if a place is a thread-local static.
 440     pub fn is_place_thread_local(&self, place_ref: PlaceRef<'cx, 'tcx>) -> bool {
 441         if let PlaceRef {
 442             base: PlaceBase::Static(box Static {
 443                 kind: StaticKind::Static(def_id),
 444                 ..
 445             }),
 446             projection: None,
 447         } = place_ref {
 448             let attrs = self.infcx.tcx.get_attrs(*def_id);
 449             let is_thread_local = attrs.iter().any(|attr| attr.check_name(sym::thread_local));
 450
 451             debug!(
 452                 "is_place_thread_local: attrs={:?} is_thread_local={:?}",
 453                 attrs, is_thread_local
 454             );
 455             is_thread_local
 456         } else {
 457             debug!("is_place_thread_local: no");
 458             false
 459         }
 460     }
 461
 462     /// Add a note that a type does not implement `Copy`
 463     pub(super) fn note_type_does_not_implement_copy(
 464         &self,
 465         err: &mut DiagnosticBuilder<'a>,
 466         place_desc: &str,
 467         ty: Ty<'tcx>,
 468         span: Option<Span>,
 469     ) {
 470         let message = format!(
 471             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 472             place_desc,
 473             ty,
 474         );
 475         if let Some(span) = span {
 476             err.span_label(span, message);
 477         } else {
 478             err.note(&message);
 479         }
 480     }
 481
 482     pub(super) fn borrowed_content_source(
 483         &self,
 484         deref_base: PlaceRef<'cx, 'tcx>,
 485     ) -> BorrowedContentSource<'tcx> {
 486         let tcx = self.infcx.tcx;
 487
 488         // Look up the provided place and work out the move path index for it,
 489         // we'll use this to check whether it was originally from an overloaded
 490         // operator.
 491         match self.move_data.rev_lookup.find(deref_base) {
 492             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 493                 debug!("borrowed_content_source: mpi={:?}", mpi);
 494
 495                 for i in &self.move_data.init_path_map[mpi] {
 496                     let init = &self.move_data.inits[*i];
 497                     debug!("borrowed_content_source: init={:?}", init);
 498                     // We're only interested in statements that initialized a value, not the
 499                     // initializations from arguments.
 500                     let loc = match init.location {
 501                         InitLocation::Statement(stmt) => stmt,
 502                         _ => continue,
 503                     };
 504
 505                     let bbd = &self.body[loc.block];
 506                     let is_terminator = bbd.statements.len() == loc.statement_index;
 507                     debug!(
 508                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 509                         loc,
 510                         is_terminator,
 511                     );
 512                     if !is_terminator {
 513                         continue;
 514                     } else if let Some(Terminator {
 515                         kind: TerminatorKind::Call {
 516                             ref func,
 517                             from_hir_call: false,
 518                             ..
 519                         },
 520                         ..
 521                     }) = bbd.terminator {
 522                         if let Some(source)
 523                             = BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 524                         {
 525                             return source;
 526                         }
 527                     }
 528                 }
 529             }
 530             // Base is a `static` so won't be from an overloaded operator
 531             _ => (),
 532         };
 533
 534         // If we didn't find an overloaded deref or index, then assume it's a
 535         // built in deref and check the type of the base.
 536         let base_ty = Place::ty_from(deref_base.base, deref_base.projection, self.body, tcx).ty;
 537         if base_ty.is_unsafe_ptr() {
 538             BorrowedContentSource::DerefRawPointer
 539         } else if base_ty.is_mutable_ptr() {
 540             BorrowedContentSource::DerefMutableRef
 541         } else {
 542             BorrowedContentSource::DerefSharedRef
 543         }
 544     }
 545 }
 546
 547 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 548     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 549     /// name where required.
 550     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 551         let mut s = String::new();
 552         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 553
 554         // We need to add synthesized lifetimes where appropriate. We do
 555         // this by hooking into the pretty printer and telling it to label the
 556         // lifetimes without names with the value `'0`.
 557         match ty.sty {
 558             ty::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
 559             | ty::Ref(
 560                 ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 561                 _,
 562                 _,
 563             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 564             _ => {}
 565         }
 566
 567         let _ = ty.print(printer);
 568         s
 569     }
 570
 571     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 572     /// synthesized lifetime name where required.
 573     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 574         let mut s = String::new();
 575         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 576
 577         let region = match ty.sty {
 578             ty::Ref(region, _, _) => {
 579                 match region {
 580                     ty::RegionKind::ReLateBound(_, br)
 581                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 582                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 583                     }
 584                     _ => {}
 585                 }
 586
 587                 region
 588             }
 589             _ => bug!("ty for annotation of borrow region is not a reference"),
 590         };
 591
 592         let _ = region.print(printer);
 593         s
 594     }
 595 }
 596
 597 // The span(s) associated to a use of a place.
 598 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 599 pub(super) enum UseSpans {
 600     // The access is caused by capturing a variable for a closure.
 601     ClosureUse {
 602         // This is true if the captured variable was from a generator.
 603         is_generator: bool,
 604         // The span of the args of the closure, including the `move` keyword if
 605         // it's present.
 606         args_span: Span,
 607         // The span of the first use of the captured variable inside the closure.
 608         var_span: Span,
 609     },
 610     // This access has a single span associated to it: common case.
 611     OtherUse(Span),
 612 }
 613
 614 impl UseSpans {
 615     pub(super) fn args_or_use(self) -> Span {
 616         match self {
 617             UseSpans::ClosureUse {
 618                 args_span: span, ..
 619             }
 620             | UseSpans::OtherUse(span) => span,
 621         }
 622     }
 623
 624     pub(super) fn var_or_use(self) -> Span {
 625         match self {
 626             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
 627         }
 628     }
 629
 630     // Add a span label to the arguments of the closure, if it exists.
 631     pub(super) fn args_span_label(
 632         self,
 633         err: &mut DiagnosticBuilder<'_>,
 634         message: impl Into<String>,
 635     ) {
 636         if let UseSpans::ClosureUse { args_span, .. } = self {
 637             err.span_label(args_span, message);
 638         }
 639     }
 640
 641     // Add a span label to the use of the captured variable, if it exists.
 642     pub(super) fn var_span_label(
 643         self,
 644         err: &mut DiagnosticBuilder<'_>,
 645         message: impl Into<String>,
 646     ) {
 647         if let UseSpans::ClosureUse { var_span, .. } = self {
 648             err.span_label(var_span, message);
 649         }
 650     }
 651
 652     /// Returns `false` if this place is not used in a closure.
 653     pub(super) fn for_closure(&self) -> bool {
 654         match *self {
 655             UseSpans::ClosureUse { is_generator, .. } => !is_generator,
 656             _ => false,
 657         }
 658     }
 659
 660     /// Returns `false` if this place is not used in a generator.
 661     pub(super) fn for_generator(&self) -> bool {
 662         match *self {
 663             UseSpans::ClosureUse { is_generator, .. } => is_generator,
 664             _ => false,
 665         }
 666     }
 667
 668     /// Describe the span associated with a use of a place.
 669     pub(super) fn describe(&self) -> String {
 670         match *self {
 671             UseSpans::ClosureUse { is_generator, .. } => if is_generator {
 672                 " in generator".to_string()
 673             } else {
 674                 " in closure".to_string()
 675             },
 676             _ => "".to_string(),
 677         }
 678     }
 679
 680     pub(super) fn or_else<F>(self, if_other: F) -> Self
 681     where
 682         F: FnOnce() -> Self,
 683     {
 684         match self {
 685             closure @ UseSpans::ClosureUse { .. } => closure,
 686             UseSpans::OtherUse(_) => if_other(),
 687         }
 688     }
 689 }
 690
 691 pub(super) enum BorrowedContentSource<'tcx> {
 692     DerefRawPointer,
 693     DerefMutableRef,
 694     DerefSharedRef,
 695     OverloadedDeref(Ty<'tcx>),
 696     OverloadedIndex(Ty<'tcx>),
 697 }
 698
 699 impl BorrowedContentSource<'tcx> {
 700     pub(super) fn describe_for_unnamed_place(&self) -> String {
 701         match *self {
 702             BorrowedContentSource::DerefRawPointer => format!("a raw pointer"),
 703             BorrowedContentSource::DerefSharedRef => format!("a shared reference"),
 704             BorrowedContentSource::DerefMutableRef => {
 705                 format!("a mutable reference")
 706             }
 707             BorrowedContentSource::OverloadedDeref(ty) => {
 708                 if ty.is_rc() {
 709                    format!("an `Rc`")
 710                 } else if ty.is_arc() {
 711                     format!("an `Arc`")
 712                 } else {
 713                     format!("dereference of `{}`", ty)
 714                 }
 715             }
 716             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 717         }
 718     }
 719
 720     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 721         match *self {
 722             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 723             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 724             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 725             // Overloaded deref and index operators should be evaluated into a
 726             // temporary. So we don't need a description here.
 727             BorrowedContentSource::OverloadedDeref(_)
 728             | BorrowedContentSource::OverloadedIndex(_) => None
 729         }
 730     }
 731
 732     pub(super) fn describe_for_immutable_place(&self) -> String {
 733         match *self {
 734             BorrowedContentSource::DerefRawPointer => format!("a `*const` pointer"),
 735             BorrowedContentSource::DerefSharedRef => format!("a `&` reference"),
 736             BorrowedContentSource::DerefMutableRef => {
 737                  bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 738             },
 739             BorrowedContentSource::OverloadedDeref(ty) => {
 740                 if ty.is_rc() {
 741                    format!("an `Rc`")
 742                 } else if ty.is_arc() {
 743                     format!("an `Arc`")
 744                 } else {
 745                     format!("a dereference of `{}`", ty)
 746                 }
 747             }
 748             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 749         }
 750     }
 751
 752     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 753         match func.sty {
 754             ty::FnDef(def_id, substs) => {
 755                 let trait_id = tcx.trait_of_item(def_id)?;
 756
 757                 let lang_items = tcx.lang_items();
 758                 if Some(trait_id) == lang_items.deref_trait()
 759                     || Some(trait_id) == lang_items.deref_mut_trait()
 760                 {
 761                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 762                 } else if Some(trait_id) == lang_items.index_trait()
 763                     || Some(trait_id) == lang_items.index_mut_trait()
 764                 {
 765                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 766                 } else {
 767                     None
 768                 }
 769             }
 770             _ => None,
 771         }
 772     }
 773 }
 774
 775 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 776     /// Finds the spans associated to a move or copy of move_place at location.
 777     pub(super) fn move_spans(
 778         &self,
 779         moved_place: PlaceRef<'cx, 'tcx>, // Could also be an upvar.
 780         location: Location,
 781     ) -> UseSpans {
 782         use self::UseSpans::*;
 783
 784         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 785             Some(stmt) => stmt,
 786             None => return OtherUse(self.body.source_info(location).span),
 787         };
 788
 789         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 790         if let  StatementKind::Assign(
 791             _,
 792             box Rvalue::Aggregate(ref kind, ref places)
 793         ) = stmt.kind {
 794             let (def_id, is_generator) = match kind {
 795                 box AggregateKind::Closure(def_id, _) => (def_id, false),
 796                 box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 797                 _ => return OtherUse(stmt.source_info.span),
 798             };
 799
 800             debug!(
 801                 "move_spans: def_id={:?} is_generator={:?} places={:?}",
 802                 def_id, is_generator, places
 803             );
 804             if let Some((args_span, var_span)) = self.closure_span(*def_id, moved_place, places) {
 805                 return ClosureUse {
 806                     is_generator,
 807                     args_span,
 808                     var_span,
 809                 };
 810             }
 811         }
 812
 813         OtherUse(stmt.source_info.span)
 814     }
 815
 816     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 817     /// and its usage of the local assigned at `location`.
 818     /// This is done by searching in statements succeeding `location`
 819     /// and originating from `maybe_closure_span`.
 820     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 821         use self::UseSpans::*;
 822         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 823
 824         let target = match self.body[location.block]
 825             .statements
 826             .get(location.statement_index)
 827         {
 828             Some(&Statement {
 829                 kind: StatementKind::Assign(Place {
 830                     base: PlaceBase::Local(local),
 831                     projection: None,
 832                 }, _),
 833                 ..
 834             }) => local,
 835             _ => return OtherUse(use_span),
 836         };
 837
 838         if self.body.local_kind(target) != LocalKind::Temp {
 839             // operands are always temporaries.
 840             return OtherUse(use_span);
 841         }
 842
 843         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 844             if let StatementKind::Assign(
 845                 _, box Rvalue::Aggregate(ref kind, ref places)
 846             ) = stmt.kind {
 847                 let (def_id, is_generator) = match kind {
 848                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 849                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 850                     _ => continue,
 851                 };
 852
 853                 debug!(
 854                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 855                     def_id, is_generator, places
 856                 );
 857                 if let Some((args_span, var_span)) = self.closure_span(
 858                     *def_id, Place::from(target).as_ref(), places
 859                 ) {
 860                     return ClosureUse {
 861                         is_generator,
 862                         args_span,
 863                         var_span,
 864                     };
 865                 } else {
 866                     return OtherUse(use_span);
 867                 }
 868             }
 869
 870             if use_span != stmt.source_info.span {
 871                 break;
 872             }
 873         }
 874
 875         OtherUse(use_span)
 876     }
 877
 878     /// Finds the span of a captured variable within a closure or generator.
 879     fn closure_span(
 880         &self,
 881         def_id: DefId,
 882         target_place: PlaceRef<'cx, 'tcx>,
 883         places: &Vec<Operand<'tcx>>,
 884     ) -> Option<(Span, Span)> {
 885         debug!(
 886             "closure_span: def_id={:?} target_place={:?} places={:?}",
 887             def_id, target_place, places
 888         );
 889         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
 890         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).node;
 891         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 892         if let hir::ExprKind::Closure(
 893             .., args_span, _
 894         ) = expr {
 895             for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
 896                 match place {
 897                     Operand::Copy(place) |
 898                     Operand::Move(place) if target_place == place.as_ref() => {
 899                         debug!("closure_span: found captured local {:?}", place);
 900                         return Some((*args_span, upvar.span));
 901                     },
 902                     _ => {}
 903                 }
 904             }
 905
 906         }
 907         None
 908     }
 909
 910     /// Helper to retrieve span(s) of given borrow from the current MIR
 911     /// representation
 912     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 913         let span = self.body.source_info(borrow.reserve_location).span;
 914         self.borrow_spans(span, borrow.reserve_location)
 915     }
 916 }