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: [],
 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,
 182                 projection: [proj_base @ .., elem],
 183             } => {
 184                 match 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                                     ([], 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());
 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: [],
 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: [],
 360             } =>
 361                 self.describe_field_from_ty(&static_.ty, field, None),
 362             PlaceRef {
 363                 base,
 364                 projection: [proj_base @ .., elem],
 365             } => match elem {
 366                 ProjectionElem::Deref => {
 367                     self.describe_field(PlaceRef {
 368                         base,
 369                         projection: proj_base,
 370                     }, field)
 371                 }
 372                 ProjectionElem::Downcast(_, variant_index) => {
 373                     let base_ty =
 374                         Place::ty_from(place.base, place.projection, self.body, self.infcx.tcx).ty;
 375                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 376                 }
 377                 ProjectionElem::Field(_, field_type) => {
 378                     self.describe_field_from_ty(&field_type, field, None)
 379                 }
 380                 ProjectionElem::Index(..)
 381                 | ProjectionElem::ConstantIndex { .. }
 382                 | ProjectionElem::Subslice { .. } => {
 383                     self.describe_field(PlaceRef {
 384                         base,
 385                         projection: proj_base,
 386                     }, field)
 387                 }
 388             },
 389         }
 390     }
 391
 392     /// End-user visible description of the `field_index`nth field of `ty`
 393     fn describe_field_from_ty(
 394         &self,
 395         ty: Ty<'_>,
 396         field: Field,
 397         variant_index: Option<VariantIdx>
 398     ) -> String {
 399         if ty.is_box() {
 400             // If the type is a box, the field is described from the boxed type
 401             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 402         } else {
 403             match ty.sty {
 404                 ty::Adt(def, _) => {
 405                     let variant = if let Some(idx) = variant_index {
 406                         assert!(def.is_enum());
 407                         &def.variants[idx]
 408                     } else {
 409                         def.non_enum_variant()
 410                     };
 411                     variant.fields[field.index()]
 412                         .ident
 413                         .to_string()
 414                 },
 415                 ty::Tuple(_) => field.index().to_string(),
 416                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 417                     self.describe_field_from_ty(&ty, field, variant_index)
 418                 }
 419                 ty::Array(ty, _) | ty::Slice(ty) =>
 420                     self.describe_field_from_ty(&ty, field, variant_index),
 421                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 422                     // `tcx.upvars(def_id)` returns an `Option`, which is `None` in case
 423                     // the closure comes from another crate. But in that case we wouldn't
 424                     // be borrowck'ing it, so we can just unwrap:
 425                     let (&var_id, _) = self.infcx.tcx.upvars(def_id).unwrap()
 426                         .get_index(field.index()).unwrap();
 427
 428                     self.infcx.tcx.hir().name(var_id).to_string()
 429                 }
 430                 _ => {
 431                     // Might need a revision when the fields in trait RFC is implemented
 432                     // (https://github.com/rust-lang/rfcs/pull/1546)
 433                     bug!(
 434                         "End-user description not implemented for field access on `{:?}`",
 435                         ty
 436                     );
 437                 }
 438             }
 439         }
 440     }
 441
 442     /// Checks if a place is a thread-local static.
 443     pub fn is_place_thread_local(&self, place_ref: PlaceRef<'cx, 'tcx>) -> bool {
 444         if let PlaceRef {
 445             base: PlaceBase::Static(box Static {
 446                 kind: StaticKind::Static,
 447                 def_id,
 448                 ..
 449             }),
 450             projection: [],
 451         } = place_ref {
 452             let attrs = self.infcx.tcx.get_attrs(*def_id);
 453             let is_thread_local = attrs.iter().any(|attr| attr.check_name(sym::thread_local));
 454
 455             debug!(
 456                 "is_place_thread_local: attrs={:?} is_thread_local={:?}",
 457                 attrs, is_thread_local
 458             );
 459             is_thread_local
 460         } else {
 461             debug!("is_place_thread_local: no");
 462             false
 463         }
 464     }
 465
 466     /// Add a note that a type does not implement `Copy`
 467     pub(super) fn note_type_does_not_implement_copy(
 468         &self,
 469         err: &mut DiagnosticBuilder<'a>,
 470         place_desc: &str,
 471         ty: Ty<'tcx>,
 472         span: Option<Span>,
 473     ) {
 474         let message = format!(
 475             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 476             place_desc,
 477             ty,
 478         );
 479         if let Some(span) = span {
 480             err.span_label(span, message);
 481         } else {
 482             err.note(&message);
 483         }
 484     }
 485
 486     pub(super) fn borrowed_content_source(
 487         &self,
 488         deref_base: PlaceRef<'cx, 'tcx>,
 489     ) -> BorrowedContentSource<'tcx> {
 490         let tcx = self.infcx.tcx;
 491
 492         // Look up the provided place and work out the move path index for it,
 493         // we'll use this to check whether it was originally from an overloaded
 494         // operator.
 495         match self.move_data.rev_lookup.find(deref_base) {
 496             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 497                 debug!("borrowed_content_source: mpi={:?}", mpi);
 498
 499                 for i in &self.move_data.init_path_map[mpi] {
 500                     let init = &self.move_data.inits[*i];
 501                     debug!("borrowed_content_source: init={:?}", init);
 502                     // We're only interested in statements that initialized a value, not the
 503                     // initializations from arguments.
 504                     let loc = match init.location {
 505                         InitLocation::Statement(stmt) => stmt,
 506                         _ => continue,
 507                     };
 508
 509                     let bbd = &self.body[loc.block];
 510                     let is_terminator = bbd.statements.len() == loc.statement_index;
 511                     debug!(
 512                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 513                         loc,
 514                         is_terminator,
 515                     );
 516                     if !is_terminator {
 517                         continue;
 518                     } else if let Some(Terminator {
 519                         kind: TerminatorKind::Call {
 520                             ref func,
 521                             from_hir_call: false,
 522                             ..
 523                         },
 524                         ..
 525                     }) = bbd.terminator {
 526                         if let Some(source)
 527                             = BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 528                         {
 529                             return source;
 530                         }
 531                     }
 532                 }
 533             }
 534             // Base is a `static` so won't be from an overloaded operator
 535             _ => (),
 536         };
 537
 538         // If we didn't find an overloaded deref or index, then assume it's a
 539         // built in deref and check the type of the base.
 540         let base_ty = Place::ty_from(deref_base.base, deref_base.projection, self.body, tcx).ty;
 541         if base_ty.is_unsafe_ptr() {
 542             BorrowedContentSource::DerefRawPointer
 543         } else if base_ty.is_mutable_ptr() {
 544             BorrowedContentSource::DerefMutableRef
 545         } else {
 546             BorrowedContentSource::DerefSharedRef
 547         }
 548     }
 549 }
 550
 551 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 552     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 553     /// name where required.
 554     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 555         let mut s = String::new();
 556         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 557
 558         // We need to add synthesized lifetimes where appropriate. We do
 559         // this by hooking into the pretty printer and telling it to label the
 560         // lifetimes without names with the value `'0`.
 561         match ty.sty {
 562             ty::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
 563             | ty::Ref(
 564                 ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 565                 _,
 566                 _,
 567             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 568             _ => {}
 569         }
 570
 571         let _ = ty.print(printer);
 572         s
 573     }
 574
 575     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 576     /// synthesized lifetime name where required.
 577     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 578         let mut s = String::new();
 579         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 580
 581         let region = match ty.sty {
 582             ty::Ref(region, _, _) => {
 583                 match region {
 584                     ty::RegionKind::ReLateBound(_, br)
 585                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 586                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 587                     }
 588                     _ => {}
 589                 }
 590
 591                 region
 592             }
 593             _ => bug!("ty for annotation of borrow region is not a reference"),
 594         };
 595
 596         let _ = region.print(printer);
 597         s
 598     }
 599 }
 600
 601 // The span(s) associated to a use of a place.
 602 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 603 pub(super) enum UseSpans {
 604     // The access is caused by capturing a variable for a closure.
 605     ClosureUse {
 606         // This is true if the captured variable was from a generator.
 607         is_generator: bool,
 608         // The span of the args of the closure, including the `move` keyword if
 609         // it's present.
 610         args_span: Span,
 611         // The span of the first use of the captured variable inside the closure.
 612         var_span: Span,
 613     },
 614     // This access has a single span associated to it: common case.
 615     OtherUse(Span),
 616 }
 617
 618 impl UseSpans {
 619     pub(super) fn args_or_use(self) -> Span {
 620         match self {
 621             UseSpans::ClosureUse {
 622                 args_span: span, ..
 623             }
 624             | UseSpans::OtherUse(span) => span,
 625         }
 626     }
 627
 628     pub(super) fn var_or_use(self) -> Span {
 629         match self {
 630             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
 631         }
 632     }
 633
 634     // Add a span label to the arguments of the closure, if it exists.
 635     pub(super) fn args_span_label(
 636         self,
 637         err: &mut DiagnosticBuilder<'_>,
 638         message: impl Into<String>,
 639     ) {
 640         if let UseSpans::ClosureUse { args_span, .. } = self {
 641             err.span_label(args_span, message);
 642         }
 643     }
 644
 645     // Add a span label to the use of the captured variable, if it exists.
 646     pub(super) fn var_span_label(
 647         self,
 648         err: &mut DiagnosticBuilder<'_>,
 649         message: impl Into<String>,
 650     ) {
 651         if let UseSpans::ClosureUse { var_span, .. } = self {
 652             err.span_label(var_span, message);
 653         }
 654     }
 655
 656     /// Returns `false` if this place is not used in a closure.
 657     pub(super) fn for_closure(&self) -> bool {
 658         match *self {
 659             UseSpans::ClosureUse { is_generator, .. } => !is_generator,
 660             _ => false,
 661         }
 662     }
 663
 664     /// Returns `false` if this place is not used in a generator.
 665     pub(super) fn for_generator(&self) -> bool {
 666         match *self {
 667             UseSpans::ClosureUse { is_generator, .. } => is_generator,
 668             _ => false,
 669         }
 670     }
 671
 672     /// Describe the span associated with a use of a place.
 673     pub(super) fn describe(&self) -> String {
 674         match *self {
 675             UseSpans::ClosureUse { is_generator, .. } => if is_generator {
 676                 " in generator".to_string()
 677             } else {
 678                 " in closure".to_string()
 679             },
 680             _ => "".to_string(),
 681         }
 682     }
 683
 684     pub(super) fn or_else<F>(self, if_other: F) -> Self
 685     where
 686         F: FnOnce() -> Self,
 687     {
 688         match self {
 689             closure @ UseSpans::ClosureUse { .. } => closure,
 690             UseSpans::OtherUse(_) => if_other(),
 691         }
 692     }
 693 }
 694
 695 pub(super) enum BorrowedContentSource<'tcx> {
 696     DerefRawPointer,
 697     DerefMutableRef,
 698     DerefSharedRef,
 699     OverloadedDeref(Ty<'tcx>),
 700     OverloadedIndex(Ty<'tcx>),
 701 }
 702
 703 impl BorrowedContentSource<'tcx> {
 704     pub(super) fn describe_for_unnamed_place(&self) -> String {
 705         match *self {
 706             BorrowedContentSource::DerefRawPointer => format!("a raw pointer"),
 707             BorrowedContentSource::DerefSharedRef => format!("a shared reference"),
 708             BorrowedContentSource::DerefMutableRef => {
 709                 format!("a mutable reference")
 710             }
 711             BorrowedContentSource::OverloadedDeref(ty) => {
 712                 if ty.is_rc() {
 713                    format!("an `Rc`")
 714                 } else if ty.is_arc() {
 715                     format!("an `Arc`")
 716                 } else {
 717                     format!("dereference of `{}`", ty)
 718                 }
 719             }
 720             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 721         }
 722     }
 723
 724     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 725         match *self {
 726             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 727             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 728             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 729             // Overloaded deref and index operators should be evaluated into a
 730             // temporary. So we don't need a description here.
 731             BorrowedContentSource::OverloadedDeref(_)
 732             | BorrowedContentSource::OverloadedIndex(_) => None
 733         }
 734     }
 735
 736     pub(super) fn describe_for_immutable_place(&self) -> String {
 737         match *self {
 738             BorrowedContentSource::DerefRawPointer => format!("a `*const` pointer"),
 739             BorrowedContentSource::DerefSharedRef => format!("a `&` reference"),
 740             BorrowedContentSource::DerefMutableRef => {
 741                  bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 742             },
 743             BorrowedContentSource::OverloadedDeref(ty) => {
 744                 if ty.is_rc() {
 745                    format!("an `Rc`")
 746                 } else if ty.is_arc() {
 747                     format!("an `Arc`")
 748                 } else {
 749                     format!("a dereference of `{}`", ty)
 750                 }
 751             }
 752             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 753         }
 754     }
 755
 756     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 757         match func.sty {
 758             ty::FnDef(def_id, substs) => {
 759                 let trait_id = tcx.trait_of_item(def_id)?;
 760
 761                 let lang_items = tcx.lang_items();
 762                 if Some(trait_id) == lang_items.deref_trait()
 763                     || Some(trait_id) == lang_items.deref_mut_trait()
 764                 {
 765                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 766                 } else if Some(trait_id) == lang_items.index_trait()
 767                     || Some(trait_id) == lang_items.index_mut_trait()
 768                 {
 769                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 770                 } else {
 771                     None
 772                 }
 773             }
 774             _ => None,
 775         }
 776     }
 777 }
 778
 779 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 780     /// Finds the spans associated to a move or copy of move_place at location.
 781     pub(super) fn move_spans(
 782         &self,
 783         moved_place: PlaceRef<'cx, 'tcx>, // Could also be an upvar.
 784         location: Location,
 785     ) -> UseSpans {
 786         use self::UseSpans::*;
 787
 788         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 789             Some(stmt) => stmt,
 790             None => return OtherUse(self.body.source_info(location).span),
 791         };
 792
 793         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 794         if let  StatementKind::Assign(
 795             _,
 796             box Rvalue::Aggregate(ref kind, ref places)
 797         ) = stmt.kind {
 798             let (def_id, is_generator) = match kind {
 799                 box AggregateKind::Closure(def_id, _) => (def_id, false),
 800                 box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 801                 _ => return OtherUse(stmt.source_info.span),
 802             };
 803
 804             debug!(
 805                 "move_spans: def_id={:?} is_generator={:?} places={:?}",
 806                 def_id, is_generator, places
 807             );
 808             if let Some((args_span, var_span)) = self.closure_span(*def_id, moved_place, places) {
 809                 return ClosureUse {
 810                     is_generator,
 811                     args_span,
 812                     var_span,
 813                 };
 814             }
 815         }
 816
 817         OtherUse(stmt.source_info.span)
 818     }
 819
 820     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 821     /// and its usage of the local assigned at `location`.
 822     /// This is done by searching in statements succeeding `location`
 823     /// and originating from `maybe_closure_span`.
 824     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 825         use self::UseSpans::*;
 826         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 827
 828         let target = match self.body[location.block]
 829             .statements
 830             .get(location.statement_index)
 831         {
 832             Some(&Statement {
 833                 kind: StatementKind::Assign(Place {
 834                     base: PlaceBase::Local(local),
 835                     projection: box [],
 836                 }, _),
 837                 ..
 838             }) => local,
 839             _ => return OtherUse(use_span),
 840         };
 841
 842         if self.body.local_kind(target) != LocalKind::Temp {
 843             // operands are always temporaries.
 844             return OtherUse(use_span);
 845         }
 846
 847         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 848             if let StatementKind::Assign(
 849                 _, box Rvalue::Aggregate(ref kind, ref places)
 850             ) = stmt.kind {
 851                 let (def_id, is_generator) = match kind {
 852                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 853                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 854                     _ => continue,
 855                 };
 856
 857                 debug!(
 858                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 859                     def_id, is_generator, places
 860                 );
 861                 if let Some((args_span, var_span)) = self.closure_span(
 862                     *def_id, Place::from(target).as_ref(), places
 863                 ) {
 864                     return ClosureUse {
 865                         is_generator,
 866                         args_span,
 867                         var_span,
 868                     };
 869                 } else {
 870                     return OtherUse(use_span);
 871                 }
 872             }
 873
 874             if use_span != stmt.source_info.span {
 875                 break;
 876             }
 877         }
 878
 879         OtherUse(use_span)
 880     }
 881
 882     /// Finds the span of a captured variable within a closure or generator.
 883     fn closure_span(
 884         &self,
 885         def_id: DefId,
 886         target_place: PlaceRef<'cx, 'tcx>,
 887         places: &Vec<Operand<'tcx>>,
 888     ) -> Option<(Span, Span)> {
 889         debug!(
 890             "closure_span: def_id={:?} target_place={:?} places={:?}",
 891             def_id, target_place, places
 892         );
 893         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id)?;
 894         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).node;
 895         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 896         if let hir::ExprKind::Closure(
 897             .., args_span, _
 898         ) = expr {
 899             for (upvar, place) in self.infcx.tcx.upvars(def_id)?.values().zip(places) {
 900                 match place {
 901                     Operand::Copy(place) |
 902                     Operand::Move(place) if target_place == place.as_ref() => {
 903                         debug!("closure_span: found captured local {:?}", place);
 904                         return Some((*args_span, upvar.span));
 905                     },
 906                     _ => {}
 907                 }
 908             }
 909
 910         }
 911         None
 912     }
 913
 914     /// Helper to retrieve span(s) of given borrow from the current MIR
 915     /// representation
 916     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 917         let span = self.body.source_info(borrow.reserve_location).span;
 918         self.borrow_spans(span, borrow.reserve_location)
 919     }
 920 }