src/librustc_mir/borrow_check/diagnostics/mod.rs

   1 //! Borrow checker diagnostics.
   2
   3 use rustc_errors::DiagnosticBuilder;
   4 use rustc_hir as hir;
   5 use rustc_hir::def::Namespace;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_hir::GeneratorKind;
   8 use rustc_middle::mir::{
   9     AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
  10     PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
  11 };
  12 use rustc_middle::ty::print::Print;
  13 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt};
  14 use rustc_span::{symbol::sym, Span};
  15 use rustc_target::abi::VariantIdx;
  16
  17 use super::borrow_set::BorrowData;
  18 use super::MirBorrowckCtxt;
  19 use crate::dataflow::move_paths::{InitLocation, LookupResult};
  20
  21 mod find_use;
  22 mod outlives_suggestion;
  23 mod region_name;
  24 mod var_name;
  25
  26 mod conflict_errors;
  27 mod explain_borrow;
  28 mod move_errors;
  29 mod mutability_errors;
  30 mod region_errors;
  31
  32 crate use mutability_errors::AccessKind;
  33 crate use outlives_suggestion::OutlivesSuggestionBuilder;
  34 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
  35 crate use region_name::{RegionName, RegionNameSource};
  36
  37 pub(super) struct IncludingDowncast(pub(super) bool);
  38
  39 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  40     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  41     /// is moved after being invoked.
  42     ///
  43     /// ```text
  44     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  45     ///       its environment
  46     ///   --> $DIR/issue-42065.rs:16:29
  47     ///    |
  48     /// LL |         for (key, value) in dict {
  49     ///    |                             ^^^^
  50     /// ```
  51     pub(super) fn add_moved_or_invoked_closure_note(
  52         &self,
  53         location: Location,
  54         place: PlaceRef<'tcx>,
  55         diag: &mut DiagnosticBuilder<'_>,
  56     ) {
  57         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  58         let mut target = place.local_or_deref_local();
  59         for stmt in &self.body[location.block].statements[location.statement_index..] {
  60             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  61             if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
  62                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  63                 match from {
  64                     Operand::Copy(ref place) | Operand::Move(ref place)
  65                         if target == place.local_or_deref_local() =>
  66                     {
  67                         target = into.local_or_deref_local()
  68                     }
  69                     _ => {}
  70                 }
  71             }
  72         }
  73
  74         // Check if we are attempting to call a closure after it has been invoked.
  75         let terminator = self.body[location.block].terminator();
  76         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  77         if let TerminatorKind::Call {
  78             func:
  79                 Operand::Constant(box Constant {
  80                     literal: ty::Const { ty: &ty::TyS { kind: ty::FnDef(id, _), .. }, .. },
  81                     ..
  82                 }),
  83             args,
  84             ..
  85         } = &terminator.kind
  86         {
  87             debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  88             if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  89                 let closure = match args.first() {
  90                     Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
  91                         if target == place.local_or_deref_local() =>
  92                     {
  93                         place.local_or_deref_local().unwrap()
  94                     }
  95                     _ => return,
  96                 };
  97
  98                 debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
  99                 if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind {
 100                     let did = did.expect_local();
 101                     let hir_id = self.infcx.tcx.hir().as_local_hir_id(did);
 102
 103                     if let Some((span, name)) =
 104                         self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
 105                     {
 106                         diag.span_note(
 107                             *span,
 108                             &format!(
 109                                 "closure cannot be invoked more than once because it moves the \
 110                                  variable `{}` out of its environment",
 111                                 name,
 112                             ),
 113                         );
 114                         return;
 115                     }
 116                 }
 117             }
 118         }
 119
 120         // Check if we are just moving a closure after it has been invoked.
 121         if let Some(target) = target {
 122             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind {
 123                 let did = did.expect_local();
 124                 let hir_id = self.infcx.tcx.hir().as_local_hir_id(did);
 125
 126                 if let Some((span, name)) =
 127                     self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
 128                 {
 129                     diag.span_note(
 130                         *span,
 131                         &format!(
 132                             "closure cannot be moved more than once as it is not `Copy` due to \
 133                              moving the variable `{}` out of its environment",
 134                             name
 135                         ),
 136                     );
 137                 }
 138             }
 139         }
 140     }
 141
 142     /// End-user visible description of `place` if one can be found.
 143     /// If the place is a temporary for instance, `"value"` will be returned.
 144     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 145         match self.describe_place(place_ref) {
 146             Some(mut descr) => {
 147                 // Surround descr with `backticks`.
 148                 descr.reserve(2);
 149                 descr.insert_str(0, "`");
 150                 descr.push_str("`");
 151                 descr
 152             }
 153             None => "value".to_string(),
 154         }
 155     }
 156
 157     /// End-user visible description of `place` if one can be found.
 158     /// If the place is a temporary for instance, None will be returned.
 159     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 160         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 161     }
 162
 163     /// End-user visible description of `place` if one can be found. If the
 164     /// place is a temporary for instance, None will be returned.
 165     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 166     /// `Downcast` and `IncludingDowncast` is true
 167     pub(super) fn describe_place_with_options(
 168         &self,
 169         place: PlaceRef<'tcx>,
 170         including_downcast: IncludingDowncast,
 171     ) -> Option<String> {
 172         let mut buf = String::new();
 173         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 174             Ok(()) => Some(buf),
 175             Err(()) => None,
 176         }
 177     }
 178
 179     /// Appends end-user visible description of `place` to `buf`.
 180     fn append_place_to_string(
 181         &self,
 182         place: PlaceRef<'tcx>,
 183         buf: &mut String,
 184         mut autoderef: bool,
 185         including_downcast: &IncludingDowncast,
 186     ) -> Result<(), ()> {
 187         match place {
 188             PlaceRef { local, projection: [] } => {
 189                 self.append_local_to_string(local, buf)?;
 190             }
 191             PlaceRef { local, projection: [ProjectionElem::Deref] }
 192                 if self.body.local_decls[local].is_ref_for_guard() =>
 193             {
 194                 self.append_place_to_string(
 195                     PlaceRef { local, projection: &[] },
 196                     buf,
 197                     autoderef,
 198                     &including_downcast,
 199                 )?;
 200             }
 201             PlaceRef { local, projection: [ProjectionElem::Deref] }
 202                 if self.body.local_decls[local].is_ref_to_static() =>
 203             {
 204                 let local_info = &self.body.local_decls[local].local_info;
 205                 if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
 206                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 207                 } else {
 208                     unreachable!();
 209                 }
 210             }
 211             PlaceRef { local, projection: [proj_base @ .., elem] } => {
 212                 match elem {
 213                     ProjectionElem::Deref => {
 214                         let upvar_field_projection = self.is_upvar_field_projection(place);
 215                         if let Some(field) = upvar_field_projection {
 216                             let var_index = field.index();
 217                             let name = self.upvars[var_index].name.to_string();
 218                             if self.upvars[var_index].by_ref {
 219                                 buf.push_str(&name);
 220                             } else {
 221                                 buf.push_str(&format!("*{}", &name));
 222                             }
 223                         } else {
 224                             if autoderef {
 225                                 // FIXME turn this recursion into iteration
 226                                 self.append_place_to_string(
 227                                     PlaceRef { local, projection: proj_base },
 228                                     buf,
 229                                     autoderef,
 230                                     &including_downcast,
 231                                 )?;
 232                             } else {
 233                                 buf.push_str(&"*");
 234                                 self.append_place_to_string(
 235                                     PlaceRef { local, projection: proj_base },
 236                                     buf,
 237                                     autoderef,
 238                                     &including_downcast,
 239                                 )?;
 240                             }
 241                         }
 242                     }
 243                     ProjectionElem::Downcast(..) => {
 244                         self.append_place_to_string(
 245                             PlaceRef { local, projection: proj_base },
 246                             buf,
 247                             autoderef,
 248                             &including_downcast,
 249                         )?;
 250                         if including_downcast.0 {
 251                             return Err(());
 252                         }
 253                     }
 254                     ProjectionElem::Field(field, _ty) => {
 255                         autoderef = true;
 256
 257                         let upvar_field_projection = self.is_upvar_field_projection(place);
 258                         if let Some(field) = upvar_field_projection {
 259                             let var_index = field.index();
 260                             let name = self.upvars[var_index].name.to_string();
 261                             buf.push_str(&name);
 262                         } else {
 263                             let field_name = self
 264                                 .describe_field(PlaceRef { local, projection: proj_base }, *field);
 265                             self.append_place_to_string(
 266                                 PlaceRef { local, projection: proj_base },
 267                                 buf,
 268                                 autoderef,
 269                                 &including_downcast,
 270                             )?;
 271                             buf.push_str(&format!(".{}", field_name));
 272                         }
 273                     }
 274                     ProjectionElem::Index(index) => {
 275                         autoderef = true;
 276
 277                         self.append_place_to_string(
 278                             PlaceRef { local, projection: proj_base },
 279                             buf,
 280                             autoderef,
 281                             &including_downcast,
 282                         )?;
 283                         buf.push_str("[");
 284                         if self.append_local_to_string(*index, buf).is_err() {
 285                             buf.push_str("_");
 286                         }
 287                         buf.push_str("]");
 288                     }
 289                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 290                         autoderef = true;
 291                         // Since it isn't possible to borrow an element on a particular index and
 292                         // then use another while the borrow is held, don't output indices details
 293                         // to avoid confusing the end-user
 294                         self.append_place_to_string(
 295                             PlaceRef { local, projection: proj_base },
 296                             buf,
 297                             autoderef,
 298                             &including_downcast,
 299                         )?;
 300                         buf.push_str(&"[..]");
 301                     }
 302                 };
 303             }
 304         }
 305
 306         Ok(())
 307     }
 308
 309     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 310     /// a name, or its name was generated by the compiler, then `Err` is returned
 311     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 312         let decl = &self.body.local_decls[local];
 313         match self.local_names[local] {
 314             Some(name) if !decl.from_compiler_desugaring() => {
 315                 buf.push_str(&name.as_str());
 316                 Ok(())
 317             }
 318             _ => Err(()),
 319         }
 320     }
 321
 322     /// End-user visible description of the `field`nth field of `base`
 323     fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
 324         // FIXME Place2 Make this work iteratively
 325         match place {
 326             PlaceRef { local, projection: [] } => {
 327                 let local = &self.body.local_decls[local];
 328                 self.describe_field_from_ty(&local.ty, field, None)
 329             }
 330             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 331                 ProjectionElem::Deref => {
 332                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 333                 }
 334                 ProjectionElem::Downcast(_, variant_index) => {
 335                     let base_ty =
 336                         Place::ty_from(place.local, place.projection, self.body, self.infcx.tcx).ty;
 337                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 338                 }
 339                 ProjectionElem::Field(_, field_type) => {
 340                     self.describe_field_from_ty(&field_type, field, None)
 341                 }
 342                 ProjectionElem::Index(..)
 343                 | ProjectionElem::ConstantIndex { .. }
 344                 | ProjectionElem::Subslice { .. } => {
 345                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 346                 }
 347             },
 348         }
 349     }
 350
 351     /// End-user visible description of the `field_index`nth field of `ty`
 352     fn describe_field_from_ty(
 353         &self,
 354         ty: Ty<'_>,
 355         field: Field,
 356         variant_index: Option<VariantIdx>,
 357     ) -> String {
 358         if ty.is_box() {
 359             // If the type is a box, the field is described from the boxed type
 360             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 361         } else {
 362             match ty.kind {
 363                 ty::Adt(def, _) => {
 364                     let variant = if let Some(idx) = variant_index {
 365                         assert!(def.is_enum());
 366                         &def.variants[idx]
 367                     } else {
 368                         def.non_enum_variant()
 369                     };
 370                     variant.fields[field.index()].ident.to_string()
 371                 }
 372                 ty::Tuple(_) => field.index().to_string(),
 373                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 374                     self.describe_field_from_ty(&ty, field, variant_index)
 375                 }
 376                 ty::Array(ty, _) | ty::Slice(ty) => {
 377                     self.describe_field_from_ty(&ty, field, variant_index)
 378                 }
 379                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 380                     // `tcx.upvars_mentioned(def_id)` returns an `Option`, which is `None` in case
 381                     // the closure comes from another crate. But in that case we wouldn't
 382                     // be borrowck'ing it, so we can just unwrap:
 383                     let (&var_id, _) = self
 384                         .infcx
 385                         .tcx
 386                         .upvars_mentioned(def_id)
 387                         .unwrap()
 388                         .get_index(field.index())
 389                         .unwrap();
 390
 391                     self.infcx.tcx.hir().name(var_id).to_string()
 392                 }
 393                 _ => {
 394                     // Might need a revision when the fields in trait RFC is implemented
 395                     // (https://github.com/rust-lang/rfcs/pull/1546)
 396                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 397                 }
 398             }
 399         }
 400     }
 401
 402     /// Add a note that a type does not implement `Copy`
 403     pub(super) fn note_type_does_not_implement_copy(
 404         &self,
 405         err: &mut DiagnosticBuilder<'a>,
 406         place_desc: &str,
 407         ty: Ty<'tcx>,
 408         span: Option<Span>,
 409     ) {
 410         let message = format!(
 411             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 412             place_desc, ty,
 413         );
 414         if let Some(span) = span {
 415             err.span_label(span, message);
 416         } else {
 417             err.note(&message);
 418         }
 419     }
 420
 421     pub(super) fn borrowed_content_source(
 422         &self,
 423         deref_base: PlaceRef<'tcx>,
 424     ) -> BorrowedContentSource<'tcx> {
 425         let tcx = self.infcx.tcx;
 426
 427         // Look up the provided place and work out the move path index for it,
 428         // we'll use this to check whether it was originally from an overloaded
 429         // operator.
 430         match self.move_data.rev_lookup.find(deref_base) {
 431             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 432                 debug!("borrowed_content_source: mpi={:?}", mpi);
 433
 434                 for i in &self.move_data.init_path_map[mpi] {
 435                     let init = &self.move_data.inits[*i];
 436                     debug!("borrowed_content_source: init={:?}", init);
 437                     // We're only interested in statements that initialized a value, not the
 438                     // initializations from arguments.
 439                     let loc = match init.location {
 440                         InitLocation::Statement(stmt) => stmt,
 441                         _ => continue,
 442                     };
 443
 444                     let bbd = &self.body[loc.block];
 445                     let is_terminator = bbd.statements.len() == loc.statement_index;
 446                     debug!(
 447                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 448                         loc, is_terminator,
 449                     );
 450                     if !is_terminator {
 451                         continue;
 452                     } else if let Some(Terminator {
 453                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 454                         ..
 455                     }) = bbd.terminator
 456                     {
 457                         if let Some(source) =
 458                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 459                         {
 460                             return source;
 461                         }
 462                     }
 463                 }
 464             }
 465             // Base is a `static` so won't be from an overloaded operator
 466             _ => (),
 467         };
 468
 469         // If we didn't find an overloaded deref or index, then assume it's a
 470         // built in deref and check the type of the base.
 471         let base_ty = Place::ty_from(deref_base.local, deref_base.projection, self.body, tcx).ty;
 472         if base_ty.is_unsafe_ptr() {
 473             BorrowedContentSource::DerefRawPointer
 474         } else if base_ty.is_mutable_ptr() {
 475             BorrowedContentSource::DerefMutableRef
 476         } else {
 477             BorrowedContentSource::DerefSharedRef
 478         }
 479     }
 480 }
 481
 482 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 483     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 484     /// name where required.
 485     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 486         let mut s = String::new();
 487         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 488
 489         // We need to add synthesized lifetimes where appropriate. We do
 490         // this by hooking into the pretty printer and telling it to label the
 491         // lifetimes without names with the value `'0`.
 492         match ty.kind {
 493             ty::Ref(
 494                 ty::RegionKind::ReLateBound(_, br)
 495                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 496                 _,
 497                 _,
 498             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 499             _ => {}
 500         }
 501
 502         let _ = ty.print(printer);
 503         s
 504     }
 505
 506     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 507     /// synthesized lifetime name where required.
 508     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 509         let mut s = String::new();
 510         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 511
 512         let region = match ty.kind {
 513             ty::Ref(region, _, _) => {
 514                 match region {
 515                     ty::RegionKind::ReLateBound(_, br)
 516                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 517                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 518                     }
 519                     _ => {}
 520                 }
 521
 522                 region
 523             }
 524             _ => bug!("ty for annotation of borrow region is not a reference"),
 525         };
 526
 527         let _ = region.print(printer);
 528         s
 529     }
 530 }
 531
 532 // The span(s) associated to a use of a place.
 533 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 534 pub(super) enum UseSpans {
 535     // The access is caused by capturing a variable for a closure.
 536     ClosureUse {
 537         // This is true if the captured variable was from a generator.
 538         generator_kind: Option<GeneratorKind>,
 539         // The span of the args of the closure, including the `move` keyword if
 540         // it's present.
 541         args_span: Span,
 542         // The span of the first use of the captured variable inside the closure.
 543         var_span: Span,
 544     },
 545     // This access has a single span associated to it: common case.
 546     OtherUse(Span),
 547 }
 548
 549 impl UseSpans {
 550     pub(super) fn args_or_use(self) -> Span {
 551         match self {
 552             UseSpans::ClosureUse { args_span: span, .. } | UseSpans::OtherUse(span) => span,
 553         }
 554     }
 555
 556     pub(super) fn var_or_use(self) -> Span {
 557         match self {
 558             UseSpans::ClosureUse { var_span: span, .. } | UseSpans::OtherUse(span) => span,
 559         }
 560     }
 561
 562     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 563         match self {
 564             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 565             _ => None,
 566         }
 567     }
 568
 569     // Add a span label to the arguments of the closure, if it exists.
 570     pub(super) fn args_span_label(
 571         self,
 572         err: &mut DiagnosticBuilder<'_>,
 573         message: impl Into<String>,
 574     ) {
 575         if let UseSpans::ClosureUse { args_span, .. } = self {
 576             err.span_label(args_span, message);
 577         }
 578     }
 579
 580     // Add a span label to the use of the captured variable, if it exists.
 581     pub(super) fn var_span_label(
 582         self,
 583         err: &mut DiagnosticBuilder<'_>,
 584         message: impl Into<String>,
 585     ) {
 586         if let UseSpans::ClosureUse { var_span, .. } = self {
 587             err.span_label(var_span, message);
 588         }
 589     }
 590
 591     /// Returns `false` if this place is not used in a closure.
 592     pub(super) fn for_closure(&self) -> bool {
 593         match *self {
 594             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 595             _ => false,
 596         }
 597     }
 598
 599     /// Returns `false` if this place is not used in a generator.
 600     pub(super) fn for_generator(&self) -> bool {
 601         match *self {
 602             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 603             _ => false,
 604         }
 605     }
 606
 607     /// Describe the span associated with a use of a place.
 608     pub(super) fn describe(&self) -> String {
 609         match *self {
 610             UseSpans::ClosureUse { generator_kind, .. } => {
 611                 if generator_kind.is_some() {
 612                     " in generator".to_string()
 613                 } else {
 614                     " in closure".to_string()
 615                 }
 616             }
 617             _ => "".to_string(),
 618         }
 619     }
 620
 621     pub(super) fn or_else<F>(self, if_other: F) -> Self
 622     where
 623         F: FnOnce() -> Self,
 624     {
 625         match self {
 626             closure @ UseSpans::ClosureUse { .. } => closure,
 627             UseSpans::OtherUse(_) => if_other(),
 628         }
 629     }
 630 }
 631
 632 pub(super) enum BorrowedContentSource<'tcx> {
 633     DerefRawPointer,
 634     DerefMutableRef,
 635     DerefSharedRef,
 636     OverloadedDeref(Ty<'tcx>),
 637     OverloadedIndex(Ty<'tcx>),
 638 }
 639
 640 impl BorrowedContentSource<'tcx> {
 641     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 642         match *self {
 643             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 644             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 645             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 646             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 647                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 648                     "an `Rc`".to_string()
 649                 }
 650                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 651                     "an `Arc`".to_string()
 652                 }
 653                 _ => format!("dereference of `{}`", ty),
 654             },
 655             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 656         }
 657     }
 658
 659     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 660         match *self {
 661             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 662             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 663             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 664             // Overloaded deref and index operators should be evaluated into a
 665             // temporary. So we don't need a description here.
 666             BorrowedContentSource::OverloadedDeref(_)
 667             | BorrowedContentSource::OverloadedIndex(_) => None,
 668         }
 669     }
 670
 671     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 672         match *self {
 673             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 674             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 675             BorrowedContentSource::DerefMutableRef => {
 676                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 677             }
 678             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 679                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 680                     "an `Rc`".to_string()
 681                 }
 682                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 683                     "an `Arc`".to_string()
 684                 }
 685                 _ => format!("a dereference of `{}`", ty),
 686             },
 687             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 688         }
 689     }
 690
 691     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 692         match func.kind {
 693             ty::FnDef(def_id, substs) => {
 694                 let trait_id = tcx.trait_of_item(def_id)?;
 695
 696                 let lang_items = tcx.lang_items();
 697                 if Some(trait_id) == lang_items.deref_trait()
 698                     || Some(trait_id) == lang_items.deref_mut_trait()
 699                 {
 700                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 701                 } else if Some(trait_id) == lang_items.index_trait()
 702                     || Some(trait_id) == lang_items.index_mut_trait()
 703                 {
 704                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 705                 } else {
 706                     None
 707                 }
 708             }
 709             _ => None,
 710         }
 711     }
 712 }
 713
 714 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 715     /// Finds the spans associated to a move or copy of move_place at location.
 716     pub(super) fn move_spans(
 717         &self,
 718         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 719         location: Location,
 720     ) -> UseSpans {
 721         use self::UseSpans::*;
 722
 723         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 724             Some(stmt) => stmt,
 725             None => return OtherUse(self.body.source_info(location).span),
 726         };
 727
 728         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 729         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 730             let def_id = match kind {
 731                 box AggregateKind::Closure(def_id, _)
 732                 | box AggregateKind::Generator(def_id, _, _) => def_id,
 733                 _ => return OtherUse(stmt.source_info.span),
 734             };
 735
 736             debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 737             if let Some((args_span, generator_kind, var_span)) =
 738                 self.closure_span(*def_id, moved_place, places)
 739             {
 740                 return ClosureUse { generator_kind, args_span, var_span };
 741             }
 742         }
 743
 744         OtherUse(stmt.source_info.span)
 745     }
 746
 747     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 748     /// and its usage of the local assigned at `location`.
 749     /// This is done by searching in statements succeeding `location`
 750     /// and originating from `maybe_closure_span`.
 751     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 752         use self::UseSpans::*;
 753         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 754
 755         let target = match self.body[location.block].statements.get(location.statement_index) {
 756             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 757                 if let Some(local) = place.as_local() {
 758                     local
 759                 } else {
 760                     return OtherUse(use_span);
 761                 }
 762             }
 763             _ => return OtherUse(use_span),
 764         };
 765
 766         if self.body.local_kind(target) != LocalKind::Temp {
 767             // operands are always temporaries.
 768             return OtherUse(use_span);
 769         }
 770
 771         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 772             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 773                 stmt.kind
 774             {
 775                 let (def_id, is_generator) = match kind {
 776                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 777                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 778                     _ => continue,
 779                 };
 780
 781                 debug!(
 782                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 783                     def_id, is_generator, places
 784                 );
 785                 if let Some((args_span, generator_kind, var_span)) =
 786                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 787                 {
 788                     return ClosureUse { generator_kind, args_span, var_span };
 789                 } else {
 790                     return OtherUse(use_span);
 791                 }
 792             }
 793
 794             if use_span != stmt.source_info.span {
 795                 break;
 796             }
 797         }
 798
 799         OtherUse(use_span)
 800     }
 801
 802     /// Finds the span of a captured variable within a closure or generator.
 803     fn closure_span(
 804         &self,
 805         def_id: DefId,
 806         target_place: PlaceRef<'tcx>,
 807         places: &Vec<Operand<'tcx>>,
 808     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 809         debug!(
 810             "closure_span: def_id={:?} target_place={:?} places={:?}",
 811             def_id, target_place, places
 812         );
 813         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id.as_local()?);
 814         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 815         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 816         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 817             for (upvar, place) in self.infcx.tcx.upvars_mentioned(def_id)?.values().zip(places) {
 818                 match place {
 819                     Operand::Copy(place) | Operand::Move(place)
 820                         if target_place == place.as_ref() =>
 821                     {
 822                         debug!("closure_span: found captured local {:?}", place);
 823                         let body = self.infcx.tcx.hir().body(*body_id);
 824                         let generator_kind = body.generator_kind();
 825                         return Some((*args_span, generator_kind, upvar.span));
 826                     }
 827                     _ => {}
 828                 }
 829             }
 830         }
 831         None
 832     }
 833
 834     /// Helper to retrieve span(s) of given borrow from the current MIR
 835     /// representation
 836     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 837         let span = self.body.source_info(borrow.reserve_location).span;
 838         self.borrow_spans(span, borrow.reserve_location)
 839     }
 840 }