compiler/rustc_mir/src/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::lang_items::LangItemGroup;
   8 use rustc_hir::GeneratorKind;
   9 use rustc_middle::mir::{
  10     AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
  11     PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
  12 };
  13 use rustc_middle::ty::print::Print;
  14 use rustc_middle::ty::{self, DefIdTree, Instance, Ty, TyCtxt};
  15 use rustc_span::{
  16     hygiene::{DesugaringKind, ForLoopLoc},
  17     symbol::sym,
  18     Span,
  19 };
  20 use rustc_target::abi::VariantIdx;
  21
  22 use super::borrow_set::BorrowData;
  23 use super::MirBorrowckCtxt;
  24 use crate::dataflow::move_paths::{InitLocation, LookupResult};
  25
  26 mod find_use;
  27 mod outlives_suggestion;
  28 mod region_name;
  29 mod var_name;
  30
  31 mod conflict_errors;
  32 mod explain_borrow;
  33 mod move_errors;
  34 mod mutability_errors;
  35 mod region_errors;
  36
  37 crate use mutability_errors::AccessKind;
  38 crate use outlives_suggestion::OutlivesSuggestionBuilder;
  39 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
  40 crate use region_name::{RegionName, RegionNameSource};
  41 use rustc_span::symbol::Ident;
  42
  43 pub(super) struct IncludingDowncast(pub(super) bool);
  44
  45 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  46     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  47     /// is moved after being invoked.
  48     ///
  49     /// ```text
  50     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  51     ///       its environment
  52     ///   --> $DIR/issue-42065.rs:16:29
  53     ///    |
  54     /// LL |         for (key, value) in dict {
  55     ///    |                             ^^^^
  56     /// ```
  57     pub(super) fn add_moved_or_invoked_closure_note(
  58         &self,
  59         location: Location,
  60         place: PlaceRef<'tcx>,
  61         diag: &mut DiagnosticBuilder<'_>,
  62     ) {
  63         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  64         let mut target = place.local_or_deref_local();
  65         for stmt in &self.body[location.block].statements[location.statement_index..] {
  66             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  67             if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
  68                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  69                 match from {
  70                     Operand::Copy(ref place) | Operand::Move(ref place)
  71                         if target == place.local_or_deref_local() =>
  72                     {
  73                         target = into.local_or_deref_local()
  74                     }
  75                     _ => {}
  76                 }
  77             }
  78         }
  79
  80         // Check if we are attempting to call a closure after it has been invoked.
  81         let terminator = self.body[location.block].terminator();
  82         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  83         if let TerminatorKind::Call {
  84             func: Operand::Constant(box Constant { literal: ty::Const { ty: const_ty, .. }, .. }),
  85             args,
  86             ..
  87         } = &terminator.kind
  88         {
  89             if let ty::FnDef(id, _) = *const_ty.kind() {
  90                 debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  91                 if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  92                     let closure = match args.first() {
  93                         Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
  94                             if target == place.local_or_deref_local() =>
  95                         {
  96                             place.local_or_deref_local().unwrap()
  97                         }
  98                         _ => return,
  99                     };
 100
 101                     debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
 102                     if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind() {
 103                         let did = did.expect_local();
 104                         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 105
 106                         if let Some((span, hir_place)) =
 107                             self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 108                         {
 109                             diag.span_note(
 110                                 *span,
 111                                 &format!(
 112                                     "closure cannot be invoked more than once because it moves the \
 113                                     variable `{}` out of its environment",
 114                                     ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
 115                                 ),
 116                             );
 117                             return;
 118                         }
 119                     }
 120                 }
 121             }
 122         }
 123
 124         // Check if we are just moving a closure after it has been invoked.
 125         if let Some(target) = target {
 126             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind() {
 127                 let did = did.expect_local();
 128                 let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 129
 130                 if let Some((span, hir_place)) =
 131                     self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 132                 {
 133                     diag.span_note(
 134                         *span,
 135                         &format!(
 136                             "closure cannot be moved more than once as it is not `Copy` due to \
 137                              moving the variable `{}` out of its environment",
 138                             ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
 139                         ),
 140                     );
 141                 }
 142             }
 143         }
 144     }
 145
 146     /// End-user visible description of `place` if one can be found.
 147     /// If the place is a temporary for instance, `"value"` will be returned.
 148     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 149         match self.describe_place(place_ref) {
 150             Some(mut descr) => {
 151                 // Surround descr with `backticks`.
 152                 descr.reserve(2);
 153                 descr.insert(0, '`');
 154                 descr.push('`');
 155                 descr
 156             }
 157             None => "value".to_string(),
 158         }
 159     }
 160
 161     /// End-user visible description of `place` if one can be found.
 162     /// If the place is a temporary for instance, None will be returned.
 163     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 164         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 165     }
 166
 167     /// End-user visible description of `place` if one can be found. If the
 168     /// place is a temporary for instance, None will be returned.
 169     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 170     /// `Downcast` and `IncludingDowncast` is true
 171     pub(super) fn describe_place_with_options(
 172         &self,
 173         place: PlaceRef<'tcx>,
 174         including_downcast: IncludingDowncast,
 175     ) -> Option<String> {
 176         let mut buf = String::new();
 177         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 178             Ok(()) => Some(buf),
 179             Err(()) => None,
 180         }
 181     }
 182
 183     /// Appends end-user visible description of `place` to `buf`.
 184     fn append_place_to_string(
 185         &self,
 186         place: PlaceRef<'tcx>,
 187         buf: &mut String,
 188         mut autoderef: bool,
 189         including_downcast: &IncludingDowncast,
 190     ) -> Result<(), ()> {
 191         match place {
 192             PlaceRef { local, projection: [] } => {
 193                 self.append_local_to_string(local, buf)?;
 194             }
 195             PlaceRef { local, projection: [ProjectionElem::Deref] }
 196                 if self.body.local_decls[local].is_ref_for_guard() =>
 197             {
 198                 self.append_place_to_string(
 199                     PlaceRef { local, projection: &[] },
 200                     buf,
 201                     autoderef,
 202                     &including_downcast,
 203                 )?;
 204             }
 205             PlaceRef { local, projection: [ProjectionElem::Deref] }
 206                 if self.body.local_decls[local].is_ref_to_static() =>
 207             {
 208                 let local_info = &self.body.local_decls[local].local_info;
 209                 if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
 210                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 211                 } else {
 212                     unreachable!();
 213                 }
 214             }
 215             PlaceRef { local, projection: [proj_base @ .., elem] } => {
 216                 match elem {
 217                     ProjectionElem::Deref => {
 218                         let upvar_field_projection = self.is_upvar_field_projection(place);
 219                         if let Some(field) = upvar_field_projection {
 220                             let var_index = field.index();
 221                             let name = self.upvars[var_index].name.to_string();
 222                             if self.upvars[var_index].by_ref {
 223                                 buf.push_str(&name);
 224                             } else {
 225                                 buf.push('*');
 226                                 buf.push_str(&name);
 227                             }
 228                         } else {
 229                             if autoderef {
 230                                 // FIXME turn this recursion into iteration
 231                                 self.append_place_to_string(
 232                                     PlaceRef { local, projection: proj_base },
 233                                     buf,
 234                                     autoderef,
 235                                     &including_downcast,
 236                                 )?;
 237                             } else {
 238                                 buf.push('*');
 239                                 self.append_place_to_string(
 240                                     PlaceRef { local, projection: proj_base },
 241                                     buf,
 242                                     autoderef,
 243                                     &including_downcast,
 244                                 )?;
 245                             }
 246                         }
 247                     }
 248                     ProjectionElem::Downcast(..) => {
 249                         self.append_place_to_string(
 250                             PlaceRef { local, projection: proj_base },
 251                             buf,
 252                             autoderef,
 253                             &including_downcast,
 254                         )?;
 255                         if including_downcast.0 {
 256                             return Err(());
 257                         }
 258                     }
 259                     ProjectionElem::Field(field, _ty) => {
 260                         autoderef = true;
 261
 262                         let upvar_field_projection = self.is_upvar_field_projection(place);
 263                         if let Some(field) = upvar_field_projection {
 264                             let var_index = field.index();
 265                             let name = self.upvars[var_index].name.to_string();
 266                             buf.push_str(&name);
 267                         } else {
 268                             let field_name = self
 269                                 .describe_field(PlaceRef { local, projection: proj_base }, *field);
 270                             self.append_place_to_string(
 271                                 PlaceRef { local, projection: proj_base },
 272                                 buf,
 273                                 autoderef,
 274                                 &including_downcast,
 275                             )?;
 276                             buf.push('.');
 277                             buf.push_str(&field_name);
 278                         }
 279                     }
 280                     ProjectionElem::Index(index) => {
 281                         autoderef = true;
 282
 283                         self.append_place_to_string(
 284                             PlaceRef { local, projection: proj_base },
 285                             buf,
 286                             autoderef,
 287                             &including_downcast,
 288                         )?;
 289                         buf.push('[');
 290                         if self.append_local_to_string(*index, buf).is_err() {
 291                             buf.push('_');
 292                         }
 293                         buf.push(']');
 294                     }
 295                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 296                         autoderef = true;
 297                         // Since it isn't possible to borrow an element on a particular index and
 298                         // then use another while the borrow is held, don't output indices details
 299                         // to avoid confusing the end-user
 300                         self.append_place_to_string(
 301                             PlaceRef { local, projection: proj_base },
 302                             buf,
 303                             autoderef,
 304                             &including_downcast,
 305                         )?;
 306                         buf.push_str("[..]");
 307                     }
 308                 };
 309             }
 310         }
 311
 312         Ok(())
 313     }
 314
 315     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 316     /// a name, or its name was generated by the compiler, then `Err` is returned
 317     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 318         let decl = &self.body.local_decls[local];
 319         match self.local_names[local] {
 320             Some(name) if !decl.from_compiler_desugaring() => {
 321                 buf.push_str(&name.as_str());
 322                 Ok(())
 323             }
 324             _ => Err(()),
 325         }
 326     }
 327
 328     /// End-user visible description of the `field`nth field of `base`
 329     fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
 330         // FIXME Place2 Make this work iteratively
 331         match place {
 332             PlaceRef { local, projection: [] } => {
 333                 let local = &self.body.local_decls[local];
 334                 self.describe_field_from_ty(&local.ty, field, None)
 335             }
 336             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 337                 ProjectionElem::Deref => {
 338                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 339                 }
 340                 ProjectionElem::Downcast(_, variant_index) => {
 341                     let base_ty =
 342                         Place::ty_from(place.local, place.projection, self.body, self.infcx.tcx).ty;
 343                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 344                 }
 345                 ProjectionElem::Field(_, field_type) => {
 346                     self.describe_field_from_ty(&field_type, field, None)
 347                 }
 348                 ProjectionElem::Index(..)
 349                 | ProjectionElem::ConstantIndex { .. }
 350                 | ProjectionElem::Subslice { .. } => {
 351                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 352                 }
 353             },
 354         }
 355     }
 356
 357     /// End-user visible description of the `field_index`nth field of `ty`
 358     fn describe_field_from_ty(
 359         &self,
 360         ty: Ty<'_>,
 361         field: Field,
 362         variant_index: Option<VariantIdx>,
 363     ) -> String {
 364         if ty.is_box() {
 365             // If the type is a box, the field is described from the boxed type
 366             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 367         } else {
 368             match *ty.kind() {
 369                 ty::Adt(def, _) => {
 370                     let variant = if let Some(idx) = variant_index {
 371                         assert!(def.is_enum());
 372                         &def.variants[idx]
 373                     } else {
 374                         def.non_enum_variant()
 375                     };
 376                     variant.fields[field.index()].ident.to_string()
 377                 }
 378                 ty::Tuple(_) => field.index().to_string(),
 379                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 380                     self.describe_field_from_ty(&ty, field, variant_index)
 381                 }
 382                 ty::Array(ty, _) | ty::Slice(ty) => {
 383                     self.describe_field_from_ty(&ty, field, variant_index)
 384                 }
 385                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 386                     // We won't be borrowck'ing here if the closure came from another crate,
 387                     // so it's safe to call `expect_local`.
 388                     //
 389                     // We know the field exists so it's safe to call operator[] and `unwrap` here.
 390                     let (&var_id, _) =
 391                         self.infcx.tcx.typeck(def_id.expect_local()).closure_captures[&def_id]
 392                             .get_index(field.index())
 393                             .unwrap();
 394
 395                     self.infcx.tcx.hir().name(var_id).to_string()
 396                 }
 397                 _ => {
 398                     // Might need a revision when the fields in trait RFC is implemented
 399                     // (https://github.com/rust-lang/rfcs/pull/1546)
 400                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 401                 }
 402             }
 403         }
 404     }
 405
 406     /// Add a note that a type does not implement `Copy`
 407     pub(super) fn note_type_does_not_implement_copy(
 408         &self,
 409         err: &mut DiagnosticBuilder<'a>,
 410         place_desc: &str,
 411         ty: Ty<'tcx>,
 412         span: Option<Span>,
 413         move_prefix: &str,
 414     ) {
 415         let message = format!(
 416             "{}move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 417             move_prefix, place_desc, ty,
 418         );
 419         if let Some(span) = span {
 420             err.span_label(span, message);
 421         } else {
 422             err.note(&message);
 423         }
 424     }
 425
 426     pub(super) fn borrowed_content_source(
 427         &self,
 428         deref_base: PlaceRef<'tcx>,
 429     ) -> BorrowedContentSource<'tcx> {
 430         let tcx = self.infcx.tcx;
 431
 432         // Look up the provided place and work out the move path index for it,
 433         // we'll use this to check whether it was originally from an overloaded
 434         // operator.
 435         match self.move_data.rev_lookup.find(deref_base) {
 436             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 437                 debug!("borrowed_content_source: mpi={:?}", mpi);
 438
 439                 for i in &self.move_data.init_path_map[mpi] {
 440                     let init = &self.move_data.inits[*i];
 441                     debug!("borrowed_content_source: init={:?}", init);
 442                     // We're only interested in statements that initialized a value, not the
 443                     // initializations from arguments.
 444                     let loc = match init.location {
 445                         InitLocation::Statement(stmt) => stmt,
 446                         _ => continue,
 447                     };
 448
 449                     let bbd = &self.body[loc.block];
 450                     let is_terminator = bbd.statements.len() == loc.statement_index;
 451                     debug!(
 452                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 453                         loc, is_terminator,
 454                     );
 455                     if !is_terminator {
 456                         continue;
 457                     } else if let Some(Terminator {
 458                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 459                         ..
 460                     }) = bbd.terminator
 461                     {
 462                         if let Some(source) =
 463                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 464                         {
 465                             return source;
 466                         }
 467                     }
 468                 }
 469             }
 470             // Base is a `static` so won't be from an overloaded operator
 471             _ => (),
 472         };
 473
 474         // If we didn't find an overloaded deref or index, then assume it's a
 475         // built in deref and check the type of the base.
 476         let base_ty = Place::ty_from(deref_base.local, deref_base.projection, self.body, tcx).ty;
 477         if base_ty.is_unsafe_ptr() {
 478             BorrowedContentSource::DerefRawPointer
 479         } else if base_ty.is_mutable_ptr() {
 480             BorrowedContentSource::DerefMutableRef
 481         } else {
 482             BorrowedContentSource::DerefSharedRef
 483         }
 484     }
 485 }
 486
 487 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 488     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 489     /// name where required.
 490     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 491         let mut s = String::new();
 492         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 493
 494         // We need to add synthesized lifetimes where appropriate. We do
 495         // this by hooking into the pretty printer and telling it to label the
 496         // lifetimes without names with the value `'0`.
 497         match ty.kind() {
 498             ty::Ref(
 499                 ty::RegionKind::ReLateBound(_, ty::BoundRegion { kind: br })
 500                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 501                 _,
 502                 _,
 503             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 504             _ => {}
 505         }
 506
 507         let _ = ty.print(printer);
 508         s
 509     }
 510
 511     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 512     /// synthesized lifetime name where required.
 513     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 514         let mut s = String::new();
 515         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 516
 517         let region = match ty.kind() {
 518             ty::Ref(region, _, _) => {
 519                 match region {
 520                     ty::RegionKind::ReLateBound(_, ty::BoundRegion { kind: br })
 521                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 522                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 523                     }
 524                     _ => {}
 525                 }
 526
 527                 region
 528             }
 529             _ => bug!("ty for annotation of borrow region is not a reference"),
 530         };
 531
 532         let _ = region.print(printer);
 533         s
 534     }
 535 }
 536
 537 /// The span(s) associated to a use of a place.
 538 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 539 pub(super) enum UseSpans<'tcx> {
 540     /// The access is caused by capturing a variable for a closure.
 541     ClosureUse {
 542         /// This is true if the captured variable was from a generator.
 543         generator_kind: Option<GeneratorKind>,
 544         /// The span of the args of the closure, including the `move` keyword if
 545         /// it's present.
 546         args_span: Span,
 547         /// The span of the first use of the captured variable inside the closure.
 548         var_span: Span,
 549     },
 550     /// The access is caused by using a variable as the receiver of a method
 551     /// that takes 'self'
 552     FnSelfUse {
 553         /// The span of the variable being moved
 554         var_span: Span,
 555         /// The span of the method call on the variable
 556         fn_call_span: Span,
 557         /// The definition span of the method being called
 558         fn_span: Span,
 559         kind: FnSelfUseKind<'tcx>,
 560     },
 561     /// This access is caused by a `match` or `if let` pattern.
 562     PatUse(Span),
 563     /// This access has a single span associated to it: common case.
 564     OtherUse(Span),
 565 }
 566
 567 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 568 pub(super) enum FnSelfUseKind<'tcx> {
 569     /// A normal method call of the form `receiver.foo(a, b, c)`
 570     Normal { self_arg: Ident, implicit_into_iter: bool },
 571     /// A call to `FnOnce::call_once`, desugared from `my_closure(a, b, c)`
 572     FnOnceCall,
 573     /// A call to an operator trait, desuraged from operator syntax (e.g. `a << b`)
 574     Operator { self_arg: Ident },
 575     DerefCoercion {
 576         /// The `Span` of the `Target` associated type
 577         /// in the `Deref` impl we are using.
 578         deref_target: Span,
 579         /// The type `T::Deref` we are dereferencing to
 580         deref_target_ty: Ty<'tcx>,
 581     },
 582 }
 583
 584 impl UseSpans<'_> {
 585     pub(super) fn args_or_use(self) -> Span {
 586         match self {
 587             UseSpans::ClosureUse { args_span: span, .. }
 588             | UseSpans::PatUse(span)
 589             | UseSpans::OtherUse(span) => span,
 590             UseSpans::FnSelfUse {
 591                 fn_call_span, kind: FnSelfUseKind::DerefCoercion { .. }, ..
 592             } => fn_call_span,
 593             UseSpans::FnSelfUse { var_span, .. } => var_span,
 594         }
 595     }
 596
 597     pub(super) fn var_or_use(self) -> Span {
 598         match self {
 599             UseSpans::ClosureUse { var_span: span, .. }
 600             | UseSpans::PatUse(span)
 601             | UseSpans::OtherUse(span) => span,
 602             UseSpans::FnSelfUse {
 603                 fn_call_span, kind: FnSelfUseKind::DerefCoercion { .. }, ..
 604             } => fn_call_span,
 605             UseSpans::FnSelfUse { var_span, .. } => var_span,
 606         }
 607     }
 608
 609     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 610         match self {
 611             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 612             _ => None,
 613         }
 614     }
 615
 616     // Add a span label to the arguments of the closure, if it exists.
 617     pub(super) fn args_span_label(
 618         self,
 619         err: &mut DiagnosticBuilder<'_>,
 620         message: impl Into<String>,
 621     ) {
 622         if let UseSpans::ClosureUse { args_span, .. } = self {
 623             err.span_label(args_span, message);
 624         }
 625     }
 626
 627     // Add a span label to the use of the captured variable, if it exists.
 628     pub(super) fn var_span_label(
 629         self,
 630         err: &mut DiagnosticBuilder<'_>,
 631         message: impl Into<String>,
 632     ) {
 633         if let UseSpans::ClosureUse { var_span, .. } = self {
 634             err.span_label(var_span, message);
 635         }
 636     }
 637
 638     /// Returns `false` if this place is not used in a closure.
 639     pub(super) fn for_closure(&self) -> bool {
 640         match *self {
 641             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 642             _ => false,
 643         }
 644     }
 645
 646     /// Returns `false` if this place is not used in a generator.
 647     pub(super) fn for_generator(&self) -> bool {
 648         match *self {
 649             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 650             _ => false,
 651         }
 652     }
 653
 654     /// Describe the span associated with a use of a place.
 655     pub(super) fn describe(&self) -> String {
 656         match *self {
 657             UseSpans::ClosureUse { generator_kind, .. } => {
 658                 if generator_kind.is_some() {
 659                     " in generator".to_string()
 660                 } else {
 661                     " in closure".to_string()
 662                 }
 663             }
 664             _ => String::new(),
 665         }
 666     }
 667
 668     pub(super) fn or_else<F>(self, if_other: F) -> Self
 669     where
 670         F: FnOnce() -> Self,
 671     {
 672         match self {
 673             closure @ UseSpans::ClosureUse { .. } => closure,
 674             UseSpans::PatUse(_) | UseSpans::OtherUse(_) => if_other(),
 675             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 676         }
 677     }
 678 }
 679
 680 pub(super) enum BorrowedContentSource<'tcx> {
 681     DerefRawPointer,
 682     DerefMutableRef,
 683     DerefSharedRef,
 684     OverloadedDeref(Ty<'tcx>),
 685     OverloadedIndex(Ty<'tcx>),
 686 }
 687
 688 impl BorrowedContentSource<'tcx> {
 689     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 690         match *self {
 691             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 692             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 693             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 694             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind() {
 695                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 696                     "an `Rc`".to_string()
 697                 }
 698                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 699                     "an `Arc`".to_string()
 700                 }
 701                 _ => format!("dereference of `{}`", ty),
 702             },
 703             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 704         }
 705     }
 706
 707     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 708         match *self {
 709             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 710             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 711             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 712             // Overloaded deref and index operators should be evaluated into a
 713             // temporary. So we don't need a description here.
 714             BorrowedContentSource::OverloadedDeref(_)
 715             | BorrowedContentSource::OverloadedIndex(_) => None,
 716         }
 717     }
 718
 719     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 720         match *self {
 721             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 722             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 723             BorrowedContentSource::DerefMutableRef => {
 724                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 725             }
 726             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind() {
 727                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 728                     "an `Rc`".to_string()
 729                 }
 730                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 731                     "an `Arc`".to_string()
 732                 }
 733                 _ => format!("a dereference of `{}`", ty),
 734             },
 735             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 736         }
 737     }
 738
 739     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 740         match *func.kind() {
 741             ty::FnDef(def_id, substs) => {
 742                 let trait_id = tcx.trait_of_item(def_id)?;
 743
 744                 let lang_items = tcx.lang_items();
 745                 if Some(trait_id) == lang_items.deref_trait()
 746                     || Some(trait_id) == lang_items.deref_mut_trait()
 747                 {
 748                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 749                 } else if Some(trait_id) == lang_items.index_trait()
 750                     || Some(trait_id) == lang_items.index_mut_trait()
 751                 {
 752                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 753                 } else {
 754                     None
 755                 }
 756             }
 757             _ => None,
 758         }
 759     }
 760 }
 761
 762 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 763     /// Finds the spans associated to a move or copy of move_place at location.
 764     pub(super) fn move_spans(
 765         &self,
 766         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 767         location: Location,
 768     ) -> UseSpans<'tcx> {
 769         use self::UseSpans::*;
 770
 771         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 772             Some(stmt) => stmt,
 773             None => return OtherUse(self.body.source_info(location).span),
 774         };
 775
 776         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 777         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 778             match kind {
 779                 box AggregateKind::Closure(def_id, _)
 780                 | box AggregateKind::Generator(def_id, _, _) => {
 781                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 782                     if let Some((args_span, generator_kind, var_span)) =
 783                         self.closure_span(*def_id, moved_place, places)
 784                     {
 785                         return ClosureUse { generator_kind, args_span, var_span };
 786                     }
 787                 }
 788                 _ => {}
 789             }
 790         }
 791
 792         let normal_ret =
 793             if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
 794                 PatUse(stmt.source_info.span)
 795             } else {
 796                 OtherUse(stmt.source_info.span)
 797             };
 798
 799         // We are trying to find MIR of the form:
 800         // ```
 801         // _temp = _moved_val;
 802         // ...
 803         // FnSelfCall(_temp, ...)
 804         // ```
 805         //
 806         // where `_moved_val` is the place we generated the move error for,
 807         // `_temp` is some other local, and `FnSelfCall` is a function
 808         // that has a `self` parameter.
 809
 810         let target_temp = match stmt.kind {
 811             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 812                 temp.as_local().unwrap()
 813             }
 814             _ => return normal_ret,
 815         };
 816
 817         debug!("move_spans: target_temp = {:?}", target_temp);
 818
 819         if let Some(Terminator {
 820             kind: TerminatorKind::Call { fn_span, from_hir_call, .. }, ..
 821         }) = &self.body[location.block].terminator
 822         {
 823             let (method_did, method_substs) = if let Some(info) =
 824                 crate::util::find_self_call(self.infcx.tcx, &self.body, target_temp, location.block)
 825             {
 826                 info
 827             } else {
 828                 return normal_ret;
 829             };
 830
 831             let tcx = self.infcx.tcx;
 832             let parent = tcx.parent(method_did);
 833             let is_fn_once = parent == tcx.lang_items().fn_once_trait();
 834             let is_operator = !from_hir_call
 835                 && parent.map_or(false, |p| tcx.lang_items().group(LangItemGroup::Op).contains(&p));
 836             let is_deref = !from_hir_call && tcx.is_diagnostic_item(sym::deref_method, method_did);
 837             let fn_call_span = *fn_span;
 838
 839             let self_arg = tcx.fn_arg_names(method_did)[0];
 840
 841             debug!(
 842                 "terminator = {:?} from_hir_call={:?}",
 843                 self.body[location.block].terminator, from_hir_call
 844             );
 845
 846             // Check for a 'special' use of 'self' -
 847             // an FnOnce call, an operator (e.g. `<<`), or a
 848             // deref coercion.
 849             let kind = if is_fn_once {
 850                 Some(FnSelfUseKind::FnOnceCall)
 851             } else if is_operator {
 852                 Some(FnSelfUseKind::Operator { self_arg })
 853             } else if is_deref {
 854                 let deref_target =
 855                     tcx.get_diagnostic_item(sym::deref_target).and_then(|deref_target| {
 856                         Instance::resolve(tcx, self.param_env, deref_target, method_substs)
 857                             .transpose()
 858                     });
 859                 if let Some(Ok(instance)) = deref_target {
 860                     let deref_target_ty = instance.ty(tcx, self.param_env);
 861                     Some(FnSelfUseKind::DerefCoercion {
 862                         deref_target: tcx.def_span(instance.def_id()),
 863                         deref_target_ty,
 864                     })
 865                 } else {
 866                     None
 867                 }
 868             } else {
 869                 None
 870             };
 871
 872             let kind = kind.unwrap_or_else(|| {
 873                 // This isn't a 'special' use of `self`
 874                 debug!("move_spans: method_did={:?}, fn_call_span={:?}", method_did, fn_call_span);
 875                 let implicit_into_iter = matches!(
 876                     fn_call_span.desugaring_kind(),
 877                     Some(DesugaringKind::ForLoop(ForLoopLoc::IntoIter))
 878                 );
 879                 FnSelfUseKind::Normal { self_arg, implicit_into_iter }
 880             });
 881
 882             return FnSelfUse {
 883                 var_span: stmt.source_info.span,
 884                 fn_call_span,
 885                 fn_span: self
 886                     .infcx
 887                     .tcx
 888                     .sess
 889                     .source_map()
 890                     .guess_head_span(self.infcx.tcx.def_span(method_did)),
 891                 kind,
 892             };
 893         }
 894         normal_ret
 895     }
 896
 897     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 898     /// and its usage of the local assigned at `location`.
 899     /// This is done by searching in statements succeeding `location`
 900     /// and originating from `maybe_closure_span`.
 901     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans<'tcx> {
 902         use self::UseSpans::*;
 903         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 904
 905         let target = match self.body[location.block].statements.get(location.statement_index) {
 906             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 907                 if let Some(local) = place.as_local() {
 908                     local
 909                 } else {
 910                     return OtherUse(use_span);
 911                 }
 912             }
 913             _ => return OtherUse(use_span),
 914         };
 915
 916         if self.body.local_kind(target) != LocalKind::Temp {
 917             // operands are always temporaries.
 918             return OtherUse(use_span);
 919         }
 920
 921         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 922             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 923                 stmt.kind
 924             {
 925                 let (def_id, is_generator) = match kind {
 926                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 927                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 928                     _ => continue,
 929                 };
 930
 931                 debug!(
 932                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 933                     def_id, is_generator, places
 934                 );
 935                 if let Some((args_span, generator_kind, var_span)) =
 936                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 937                 {
 938                     return ClosureUse { generator_kind, args_span, var_span };
 939                 } else {
 940                     return OtherUse(use_span);
 941                 }
 942             }
 943
 944             if use_span != stmt.source_info.span {
 945                 break;
 946             }
 947         }
 948
 949         OtherUse(use_span)
 950     }
 951
 952     /// Finds the span of a captured variable within a closure or generator.
 953     fn closure_span(
 954         &self,
 955         def_id: DefId,
 956         target_place: PlaceRef<'tcx>,
 957         places: &Vec<Operand<'tcx>>,
 958     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 959         debug!(
 960             "closure_span: def_id={:?} target_place={:?} places={:?}",
 961             def_id, target_place, places
 962         );
 963         let local_did = def_id.as_local()?;
 964         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(local_did);
 965         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 966         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 967         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 968             for (upvar_hir_id, place) in
 969                 self.infcx.tcx.typeck(def_id.expect_local()).closure_captures[&def_id]
 970                     .keys()
 971                     .zip(places)
 972             {
 973                 let span = self.infcx.tcx.upvars_mentioned(local_did)?[upvar_hir_id].span;
 974                 match place {
 975                     Operand::Copy(place) | Operand::Move(place)
 976                         if target_place == place.as_ref() =>
 977                     {
 978                         debug!("closure_span: found captured local {:?}", place);
 979                         let body = self.infcx.tcx.hir().body(*body_id);
 980                         let generator_kind = body.generator_kind();
 981                         let upvar_id = ty::UpvarId {
 982                             var_path: ty::UpvarPath { hir_id: *upvar_hir_id },
 983                             closure_expr_id: local_did,
 984                         };
 985
 986                         // If we have a more specific span available, point to that.
 987                         // We do this even though this span might be part of a borrow error
 988                         // message rather than a move error message. Our goal is to point
 989                         // to a span that shows why the upvar is used in the closure,
 990                         // so a move-related span is as good as any (and potentially better,
 991                         // if the overall error is due to a move of the upvar).
 992                         let usage_span =
 993                             match self.infcx.tcx.typeck(local_did).upvar_capture(upvar_id) {
 994                                 ty::UpvarCapture::ByValue(Some(span)) => span,
 995                                 _ => span,
 996                             };
 997                         return Some((*args_span, generator_kind, usage_span));
 998                     }
 999                     _ => {}
1000                 }
1001             }
1002         }
1003         None
1004     }
1005
1006     /// Helper to retrieve span(s) of given borrow from the current MIR
1007     /// representation
1008     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans<'tcx> {
1009         let span = self.body.source_info(borrow.reserve_location).span;
1010         self.borrow_spans(span, borrow.reserve_location)
1011     }
1012 }