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,
 173                         def_id,
 174                         ..
 175                     }),
 176                 projection: None,
 177             } => {
 178                 buf.push_str(&self.infcx.tcx.item_name(*def_id).to_string());
 179             }
 180             PlaceRef {
 181                 base,
 182                 projection: Some(ref proj),
 183             } => {
 184                 match proj.elem {
 185                     ProjectionElem::Deref => {
 186                         let upvar_field_projection =
 187                             self.is_upvar_field_projection(place);
 188                         if let Some(field) = upvar_field_projection {
 189                             let var_index = field.index();
 190                             let name = self.upvars[var_index].name.to_string();
 191                             if self.upvars[var_index].by_ref {
 192                                 buf.push_str(&name);
 193                             } else {
 194                                 buf.push_str(&format!("*{}", &name));
 195                             }
 196                         } else {
 197                             if autoderef {
 198                                 // FIXME turn this recursion into iteration
 199                                 self.append_place_to_string(
 200                                     PlaceRef {
 201                                         base,
 202                                         projection: &proj.base,
 203                                     },
 204                                     buf,
 205                                     autoderef,
 206                                     &including_downcast,
 207                                 )?;
 208                             } else {
 209                                 match (&proj.base, base) {
 210                                     (None, PlaceBase::Local(local)) => {
 211                                         if self.body.local_decls[*local].is_ref_for_guard() {
 212                                             self.append_place_to_string(
 213                                                 PlaceRef {
 214                                                     base,
 215                                                     projection: &proj.base,
 216                                                 },
 217                                                 buf,
 218                                                 autoderef,
 219                                                 &including_downcast,
 220                                             )?;
 221                                         } else {
 222                                             // FIXME deduplicate this and the _ => body below
 223                                             buf.push_str(&"*");
 224                                             self.append_place_to_string(
 225                                                 PlaceRef {
 226                                                     base,
 227                                                     projection: &proj.base,
 228                                                 },
 229                                                 buf,
 230                                                 autoderef,
 231                                                 &including_downcast,
 232                                             )?;
 233                                         }
 234                                     }
 235
 236                                     _ => {
 237                                         buf.push_str(&"*");
 238                                         self.append_place_to_string(
 239                                             PlaceRef {
 240                                                 base,
 241                                                 projection: &proj.base,
 242                                             },
 243                                             buf,
 244                                             autoderef,
 245                                             &including_downcast,
 246                                         )?;
 247                                     }
 248                                 }
 249                             }
 250                         }
 251                     }
 252                     ProjectionElem::Downcast(..) => {
 253                         self.append_place_to_string(
 254                             PlaceRef {
 255                                 base,
 256                                 projection: &proj.base,
 257                             },
 258                             buf,
 259                             autoderef,
 260                             &including_downcast,
 261                         )?;
 262                         if including_downcast.0 {
 263                             return Err(());
 264                         }
 265                     }
 266                     ProjectionElem::Field(field, _ty) => {
 267                         autoderef = true;
 268
 269                         let upvar_field_projection =
 270                             self.is_upvar_field_projection(place);
 271                         if let Some(field) = upvar_field_projection {
 272                             let var_index = field.index();
 273                             let name = self.upvars[var_index].name.to_string();
 274                             buf.push_str(&name);
 275                         } else {
 276                             let field_name = self.describe_field(PlaceRef {
 277                                 base,
 278                                 projection: &proj.base,
 279                             }, field);
 280                             self.append_place_to_string(
 281                                 PlaceRef {
 282                                     base,
 283                                     projection: &proj.base,
 284                                 },
 285                                 buf,
 286                                 autoderef,
 287                                 &including_downcast,
 288                             )?;
 289                             buf.push_str(&format!(".{}", field_name));
 290                         }
 291                     }
 292                     ProjectionElem::Index(index) => {
 293                         autoderef = true;
 294
 295                         self.append_place_to_string(
 296                             PlaceRef {
 297                                 base,
 298                                 projection: &proj.base,
 299                             },
 300                             buf,
 301                             autoderef,
 302                             &including_downcast,
 303                         )?;
 304                         buf.push_str("[");
 305                         if self.append_local_to_string(index, buf).is_err() {
 306                             buf.push_str("_");
 307                         }
 308                         buf.push_str("]");
 309                     }
 310                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 311                         autoderef = true;
 312                         // Since it isn't possible to borrow an element on a particular index and
 313                         // then use another while the borrow is held, don't output indices details
 314                         // to avoid confusing the end-user
 315                         self.append_place_to_string(
 316                             PlaceRef {
 317                                 base,
 318                                 projection: &proj.base,
 319                             },
 320                             buf,
 321                             autoderef,
 322                             &including_downcast,
 323                         )?;
 324                         buf.push_str(&"[..]");
 325                     }
 326                 };
 327             }
 328         }
 329
 330         Ok(())
 331     }
 332
 333     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 334     /// a name, or its name was generated by the compiler, then `Err` is returned
 335     fn append_local_to_string(&self, local_index: Local, buf: &mut String) -> Result<(), ()> {
 336         let local = &self.body.local_decls[local_index];
 337         match local.name {
 338             Some(name) if !local.from_compiler_desugaring() => {
 339                 buf.push_str(name.as_str().get());
 340                 Ok(())
 341             }
 342             _ => Err(()),
 343         }
 344     }
 345
 346     /// End-user visible description of the `field`nth field of `base`
 347     fn describe_field(&self, place: PlaceRef<'cx, 'tcx>, field: Field) -> String {
 348         // FIXME Place2 Make this work iteratively
 349         match place {
 350             PlaceRef {
 351                 base: PlaceBase::Local(local),
 352                 projection: None,
 353             } => {
 354                 let local = &self.body.local_decls[*local];
 355                 self.describe_field_from_ty(&local.ty, field, None)
 356             }
 357             PlaceRef {
 358                 base: PlaceBase::Static(static_),
 359                 projection: None,
 360             } =>
 361                 self.describe_field_from_ty(&static_.ty, field, None),
 362             PlaceRef {
 363                 base,
 364                 projection: Some(proj),
 365             } => match proj.elem {
 366                 ProjectionElem::Deref => self.describe_field(PlaceRef {
 367                     base,
 368                     projection: &proj.base,
 369                 }, field),
 370                 ProjectionElem::Downcast(_, variant_index) => {
 371                     let base_ty =
 372                         Place::ty_from(place.base, place.projection, self.body, self.infcx.tcx).ty;
 373                     self.describe_field_from_ty(&base_ty, field, Some(variant_index))
 374                 }
 375                 ProjectionElem::Field(_, field_type) => {
 376                     self.describe_field_from_ty(&field_type, field, None)
 377                 }
 378                 ProjectionElem::Index(..)
 379                 | ProjectionElem::ConstantIndex { .. }
 380                 | ProjectionElem::Subslice { .. } => {
 381                     self.describe_field(PlaceRef {
 382                         base,
 383                         projection: &proj.base,
 384                     }, field)
 385                 }
 386             },
 387         }
 388     }
 389
 390     /// End-user visible description of the `field_index`nth field of `ty`
 391     fn describe_field_from_ty(
 392         &self,
 393         ty: Ty<'_>,
 394         field: Field,
 395         variant_index: Option<VariantIdx>
 396     ) -> String {
 397         if ty.is_box() {
 398             // If the type is a box, the field is described from the boxed type
 399             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 400         } else {
 401             match ty.sty {
 402                 ty::Adt(def, _) => {
 403                     let variant = if let Some(idx) = variant_index {
 404                         assert!(def.is_enum());
 405                         &def.variants[idx]
 406                     } else {
 407                         def.non_enum_variant()
 408                     };
 409                     variant.fields[field.index()]
 410                         .ident
 411                         .to_string()
 412                 },
 413                 ty::Tuple(_) => field.index().to_string(),
 414                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 415                     self.describe_field_from_ty(&ty, field, variant_index)
 416                 }
 417                 ty::Array(ty, _) | ty::Slice(ty) =>
 418                     self.describe_field_from_ty(&ty, field, variant_index),
 419                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 420                     // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
 421                     // the closure comes from another crate. But in that case we wouldn't
 422                     // be borrowck'ing it, so we can just unwrap:
 423                     let (&var_id, _) = self.infcx.tcx.upvars(def_id).unwrap()
 424                         .get_index(field.index()).unwrap();
 425
 426                     self.infcx.tcx.hir().name(var_id).to_string()
 427                 }
 428                 _ => {
 429                     // Might need a revision when the fields in trait RFC is implemented
 430                     // (https://github.com/rust-lang/rfcs/pull/1546)
 431                     bug!(
 432                         "End-user description not implemented for field access on `{:?}`",
 433                         ty
 434                     );
 435                 }
 436             }
 437         }
 438     }
 439
 440     /// Checks if a place is a thread-local static.
 441     pub fn is_place_thread_local(&self, place_ref: PlaceRef<'cx, 'tcx>) -> bool {
 442         if let PlaceRef {
 443             base: PlaceBase::Static(box Static {
 444                 kind: StaticKind::Static,
 445                 def_id,
 446                 ..
 447             }),
 448             projection: None,
 449         } = place_ref {
 450             let attrs = self.infcx.tcx.get_attrs(*def_id);
 451             let is_thread_local = attrs.iter().any(|attr| attr.check_name(sym::thread_local));
 452
 453             debug!(
 454                 "is_place_thread_local: attrs={:?} is_thread_local={:?}",
 455                 attrs, is_thread_local
 456             );
 457             is_thread_local
 458         } else {
 459             debug!("is_place_thread_local: no");
 460             false
 461         }
 462     }
 463
 464     /// Add a note that a type does not implement `Copy`
 465     pub(super) fn note_type_does_not_implement_copy(
 466         &self,
 467         err: &mut DiagnosticBuilder<'a>,
 468         place_desc: &str,
 469         ty: Ty<'tcx>,
 470         span: Option<Span>,
 471     ) {
 472         let message = format!(
 473             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 474             place_desc,
 475             ty,
 476         );
 477         if let Some(span) = span {
 478             err.span_label(span, message);
 479         } else {
 480             err.note(&message);
 481         }
 482     }
 483
 484     pub(super) fn borrowed_content_source(
 485         &self,
 486         deref_base: PlaceRef<'cx, 'tcx>,
 487     ) -> BorrowedContentSource<'tcx> {
 488         let tcx = self.infcx.tcx;
 489
 490         // Look up the provided place and work out the move path index for it,
 491         // we'll use this to check whether it was originally from an overloaded
 492         // operator.
 493         match self.move_data.rev_lookup.find(deref_base) {
 494             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 495                 debug!("borrowed_content_source: mpi={:?}", mpi);
 496
 497                 for i in &self.move_data.init_path_map[mpi] {
 498                     let init = &self.move_data.inits[*i];
 499                     debug!("borrowed_content_source: init={:?}", init);
 500                     // We're only interested in statements that initialized a value, not the
 501                     // initializations from arguments.
 502                     let loc = match init.location {
 503                         InitLocation::Statement(stmt) => stmt,
 504                         _ => continue,
 505                     };
 506
 507                     let bbd = &self.body[loc.block];
 508                     let is_terminator = bbd.statements.len() == loc.statement_index;
 509                     debug!(
 510                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 511                         loc,
 512                         is_terminator,
 513                     );
 514                     if !is_terminator {
 515                         continue;
 516                     } else if let Some(Terminator {
 517                         kind: TerminatorKind::Call {
 518                             ref func,
 519                             from_hir_call: false,
 520                             ..
 521                         },
 522                         ..
 523                     }) = bbd.terminator {
 524                         if let Some(source)
 525                             = BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 526                         {
 527                             return source;
 528                         }
 529                     }
 530                 }
 531             }
 532             // Base is a `static` so won't be from an overloaded operator
 533             _ => (),
 534         };
 535
 536         // If we didn't find an overloaded deref or index, then assume it's a
 537         // built in deref and check the type of the base.
 538         let base_ty = Place::ty_from(deref_base.base, deref_base.projection, self.body, tcx).ty;
 539         if base_ty.is_unsafe_ptr() {
 540             BorrowedContentSource::DerefRawPointer
 541         } else if base_ty.is_mutable_ptr() {
 542             BorrowedContentSource::DerefMutableRef
 543         } else {
 544             BorrowedContentSource::DerefSharedRef
 545         }
 546     }
 547 }
 548
 549 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 550     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 551     /// name where required.
 552     pub(super) fn get_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         // We need to add synthesized lifetimes where appropriate. We do
 557         // this by hooking into the pretty printer and telling it to label the
 558         // lifetimes without names with the value `'0`.
 559         match ty.sty {
 560             ty::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
 561             | ty::Ref(
 562                 ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 563                 _,
 564                 _,
 565             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 566             _ => {}
 567         }
 568
 569         let _ = ty.print(printer);
 570         s
 571     }
 572
 573     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 574     /// synthesized lifetime name where required.
 575     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 576         let mut s = String::new();
 577         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 578
 579         let region = match ty.sty {
 580             ty::Ref(region, _, _) => {
 581                 match region {
 582                     ty::RegionKind::ReLateBound(_, br)
 583                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 584                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 585                     }
 586                     _ => {}
 587                 }
 588
 589                 region
 590             }
 591             _ => bug!("ty for annotation of borrow region is not a reference"),
 592         };
 593
 594         let _ = region.print(printer);
 595         s
 596     }
 597 }
 598
 599 // The span(s) associated to a use of a place.
 600 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 601 pub(super) enum UseSpans {
 602     // The access is caused by capturing a variable for a closure.
 603     ClosureUse {
 604         // This is true if the captured variable was from a generator.
 605         is_generator: bool,
 606         // The span of the args of the closure, including the `move` keyword if
 607         // it's present.
 608         args_span: Span,
 609         // The span of the first use of the captured variable inside the closure.
 610         var_span: Span,
 611     },
 612     // This access has a single span associated to it: common case.
 613     OtherUse(Span),
 614 }
 615
 616 impl UseSpans {
 617     pub(super) fn args_or_use(self) -> Span {
 618         match self {
 619             UseSpans::ClosureUse {
 620                 args_span: span, ..
 621             }
 622             | UseSpans::OtherUse(span) => span,
 623         }
 624     }
 625
 626     pub(super) fn var_or_use(self) -> Span {
 627         match self {
 628             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
 629         }
 630     }
 631
 632     // Add a span label to the arguments of the closure, if it exists.
 633     pub(super) fn args_span_label(
 634         self,
 635         err: &mut DiagnosticBuilder<'_>,
 636         message: impl Into<String>,
 637     ) {
 638         if let UseSpans::ClosureUse { args_span, .. } = self {
 639             err.span_label(args_span, message);
 640         }
 641     }
 642
 643     // Add a span label to the use of the captured variable, if it exists.
 644     pub(super) fn var_span_label(
 645         self,
 646         err: &mut DiagnosticBuilder<'_>,
 647         message: impl Into<String>,
 648     ) {
 649         if let UseSpans::ClosureUse { var_span, .. } = self {
 650             err.span_label(var_span, message);
 651         }
 652     }
 653
 654     /// Returns `false` if this place is not used in a closure.
 655     pub(super) fn for_closure(&self) -> bool {
 656         match *self {
 657             UseSpans::ClosureUse { is_generator, .. } => !is_generator,
 658             _ => false,
 659         }
 660     }
 661
 662     /// Returns `false` if this place is not used in a generator.
 663     pub(super) fn for_generator(&self) -> bool {
 664         match *self {
 665             UseSpans::ClosureUse { is_generator, .. } => is_generator,
 666             _ => false,
 667         }
 668     }
 669
 670     /// Describe the span associated with a use of a place.
 671     pub(super) fn describe(&self) -> String {
 672         match *self {
 673             UseSpans::ClosureUse { is_generator, .. } => if is_generator {
 674                 " in generator".to_string()
 675             } else {
 676                 " in closure".to_string()
 677             },
 678             _ => "".to_string(),
 679         }
 680     }
 681
 682     pub(super) fn or_else<F>(self, if_other: F) -> Self
 683     where
 684         F: FnOnce() -> Self,
 685     {
 686         match self {
 687             closure @ UseSpans::ClosureUse { .. } => closure,
 688             UseSpans::OtherUse(_) => if_other(),
 689         }
 690     }
 691 }
 692
 693 pub(super) enum BorrowedContentSource<'tcx> {
 694     DerefRawPointer,
 695     DerefMutableRef,
 696     DerefSharedRef,
 697     OverloadedDeref(Ty<'tcx>),
 698     OverloadedIndex(Ty<'tcx>),
 699 }
 700
 701 impl BorrowedContentSource<'tcx> {
 702     pub(super) fn describe_for_unnamed_place(&self) -> String {
 703         match *self {
 704             BorrowedContentSource::DerefRawPointer => format!("a raw pointer"),
 705             BorrowedContentSource::DerefSharedRef => format!("a shared reference"),
 706             BorrowedContentSource::DerefMutableRef => {
 707                 format!("a mutable reference")
 708             }
 709             BorrowedContentSource::OverloadedDeref(ty) => {
 710                 if ty.is_rc() {
 711                    format!("an `Rc`")
 712                 } else if ty.is_arc() {
 713                     format!("an `Arc`")
 714                 } else {
 715                     format!("dereference of `{}`", ty)
 716                 }
 717             }
 718             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 719         }
 720     }
 721
 722     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 723         match *self {
 724             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 725             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 726             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 727             // Overloaded deref and index operators should be evaluated into a
 728             // temporary. So we don't need a description here.
 729             BorrowedContentSource::OverloadedDeref(_)
 730             | BorrowedContentSource::OverloadedIndex(_) => None
 731         }
 732     }
 733
 734     pub(super) fn describe_for_immutable_place(&self) -> String {
 735         match *self {
 736             BorrowedContentSource::DerefRawPointer => format!("a `*const` pointer"),
 737             BorrowedContentSource::DerefSharedRef => format!("a `&` reference"),
 738             BorrowedContentSource::DerefMutableRef => {
 739                  bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 740             },
 741             BorrowedContentSource::OverloadedDeref(ty) => {
 742                 if ty.is_rc() {
 743                    format!("an `Rc`")
 744                 } else if ty.is_arc() {
 745                     format!("an `Arc`")
 746                 } else {
 747                     format!("a dereference of `{}`", ty)
 748                 }
 749             }
 750             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 751         }
 752     }
 753
 754     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 755         match func.sty {
 756             ty::FnDef(def_id, substs) => {
 757                 let trait_id = tcx.trait_of_item(def_id)?;
 758
 759                 let lang_items = tcx.lang_items();
 760                 if Some(trait_id) == lang_items.deref_trait()
 761                     || Some(trait_id) == lang_items.deref_mut_trait()
 762                 {
 763                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 764                 } else if Some(trait_id) == lang_items.index_trait()
 765                     || Some(trait_id) == lang_items.index_mut_trait()
 766                 {
 767                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 768                 } else {
 769                     None
 770                 }
 771             }
 772             _ => None,
 773         }
 774     }
 775 }
 776
 777 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 778     /// Finds the spans associated to a move or copy of move_place at location.
 779     pub(super) fn move_spans(
 780         &self,
 781         moved_place: PlaceRef<'cx, 'tcx>, // Could also be an upvar.
 782         location: Location,
 783     ) -> UseSpans {
 784         use self::UseSpans::*;
 785
 786         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 787             Some(stmt) => stmt,
 788             None => return OtherUse(self.body.source_info(location).span),
 789         };
 790
 791         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 792         if let  StatementKind::Assign(
 793             _,
 794             box Rvalue::Aggregate(ref kind, ref places)
 795         ) = stmt.kind {
 796             let (def_id, is_generator) = match kind {
 797                 box AggregateKind::Closure(def_id, _) => (def_id, false),
 798                 box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 799                 _ => return OtherUse(stmt.source_info.span),
 800             };
 801
 802             debug!(
 803                 "move_spans: def_id={:?} is_generator={:?} places={:?}",
 804                 def_id, is_generator, places
 805             );
 806             if let Some((args_span, var_span)) = self.closure_span(*def_id, moved_place, places) {
 807                 return ClosureUse {
 808                     is_generator,
 809                     args_span,
 810                     var_span,
 811                 };
 812             }
 813         }
 814
 815         OtherUse(stmt.source_info.span)
 816     }
 817
 818     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 819     /// and its usage of the local assigned at `location`.
 820     /// This is done by searching in statements succeeding `location`
 821     /// and originating from `maybe_closure_span`.
 822     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 823         use self::UseSpans::*;
 824         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 825
 826         let target = match self.body[location.block]
 827             .statements
 828             .get(location.statement_index)
 829         {
 830             Some(&Statement {
 831                 kind: StatementKind::Assign(Place {
 832                     base: PlaceBase::Local(local),
 833                     projection: None,
 834                 }, _),
 835                 ..
 836             }) => local,
 837             _ => return OtherUse(use_span),
 838         };
 839
 840         if self.body.local_kind(target) != LocalKind::Temp {
 841             // operands are always temporaries.
 842             return OtherUse(use_span);
 843         }
 844
 845         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 846             if let StatementKind::Assign(
 847                 _, box Rvalue::Aggregate(ref kind, ref places)
 848             ) = stmt.kind {
 849                 let (def_id, is_generator) = match kind {
 850                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 851                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 852                     _ => continue,
 853                 };
 854
 855                 debug!(
 856                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 857                     def_id, is_generator, places
 858                 );
 859                 if let Some((args_span, var_span)) = self.closure_span(
 860                     *def_id, Place::from(target).as_ref(), places
 861                 ) {
 862                     return ClosureUse {
 863                         is_generator,
 864                         args_span,
 865                         var_span,
 866                     };
 867                 } else {
 868                     return OtherUse(use_span);
 869                 }
 870             }
 871
 872             if use_span != stmt.source_info.span {
 873                 break;
 874             }
 875         }
 876
 877         OtherUse(use_span)
 878     }
 879
 880     /// Finds the span of a captured variable within a closure or generator.
 881     fn closure_span(
 882         &self,
 883         def_id: DefId,
 884         target_place: PlaceRef<'cx, 'tcx>,
 885         places: &Vec<Operand<'tcx>>,
 886     ) -> Option<(Span, Span)> {
 887         debug!(
 888             "closure_span: def_id={:?} target_place={:?} places={:?}",
 889             def_id, target_place, places
 890         );
 891         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
 892         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).node;
 893         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 894         if let hir::ExprKind::Closure(
 895             .., args_span, _
 896         ) = expr {
 897             for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
 898                 match place {
 899                     Operand::Copy(place) |
 900                     Operand::Move(place) if target_place == place.as_ref() => {
 901                         debug!("closure_span: found captured local {:?}", place);
 902                         return Some((*args_span, upvar.span));
 903                     },
 904                     _ => {}
 905                 }
 906             }
 907
 908         }
 909         None
 910     }
 911
 912     /// Helper to retrieve span(s) of given borrow from the current MIR
 913     /// representation
 914     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 915         let span = self.body.source_info(borrow.reserve_location).span;
 916         self.borrow_spans(span, borrow.reserve_location)
 917     }
 918 }