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::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, 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:
  85                 Operand::Constant(box Constant {
  86                     literal: ty::Const { ty: &ty::TyS { kind: ty::FnDef(id, _), .. }, .. },
  87                     ..
  88                 }),
  89             args,
  90             ..
  91         } = &terminator.kind
  92         {
  93             debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  94             if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  95                 let closure = match args.first() {
  96                     Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
  97                         if target == place.local_or_deref_local() =>
  98                     {
  99                         place.local_or_deref_local().unwrap()
 100                     }
 101                     _ => return,
 102                 };
 103
 104                 debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
 105                 if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind {
 106                     let did = did.expect_local();
 107                     let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 108
 109                     if let Some((span, name)) =
 110                         self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 111                     {
 112                         diag.span_note(
 113                             *span,
 114                             &format!(
 115                                 "closure cannot be invoked more than once because it moves the \
 116                                  variable `{}` out of its environment",
 117                                 name,
 118                             ),
 119                         );
 120                         return;
 121                     }
 122                 }
 123             }
 124         }
 125
 126         // Check if we are just moving a closure after it has been invoked.
 127         if let Some(target) = target {
 128             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind {
 129                 let did = did.expect_local();
 130                 let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 131
 132                 if let Some((span, name)) =
 133                     self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 134                 {
 135                     diag.span_note(
 136                         *span,
 137                         &format!(
 138                             "closure cannot be moved more than once as it is not `Copy` due to \
 139                              moving the variable `{}` out of its environment",
 140                             name
 141                         ),
 142                     );
 143                 }
 144             }
 145         }
 146     }
 147
 148     /// End-user visible description of `place` if one can be found.
 149     /// If the place is a temporary for instance, `"value"` will be returned.
 150     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 151         match self.describe_place(place_ref) {
 152             Some(mut descr) => {
 153                 // Surround descr with `backticks`.
 154                 descr.reserve(2);
 155                 descr.insert_str(0, "`");
 156                 descr.push_str("`");
 157                 descr
 158             }
 159             None => "value".to_string(),
 160         }
 161     }
 162
 163     /// End-user visible description of `place` if one can be found.
 164     /// If the place is a temporary for instance, None will be returned.
 165     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 166         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 167     }
 168
 169     /// End-user visible description of `place` if one can be found. If the
 170     /// place is a temporary for instance, None will be returned.
 171     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 172     /// `Downcast` and `IncludingDowncast` is true
 173     pub(super) fn describe_place_with_options(
 174         &self,
 175         place: PlaceRef<'tcx>,
 176         including_downcast: IncludingDowncast,
 177     ) -> Option<String> {
 178         let mut buf = String::new();
 179         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 180             Ok(()) => Some(buf),
 181             Err(()) => None,
 182         }
 183     }
 184
 185     /// Appends end-user visible description of `place` to `buf`.
 186     fn append_place_to_string(
 187         &self,
 188         place: PlaceRef<'tcx>,
 189         buf: &mut String,
 190         mut autoderef: bool,
 191         including_downcast: &IncludingDowncast,
 192     ) -> Result<(), ()> {
 193         match place {
 194             PlaceRef { local, projection: [] } => {
 195                 self.append_local_to_string(local, buf)?;
 196             }
 197             PlaceRef { local, projection: [ProjectionElem::Deref] }
 198                 if self.body.local_decls[local].is_ref_for_guard() =>
 199             {
 200                 self.append_place_to_string(
 201                     PlaceRef { local, projection: &[] },
 202                     buf,
 203                     autoderef,
 204                     &including_downcast,
 205                 )?;
 206             }
 207             PlaceRef { local, projection: [ProjectionElem::Deref] }
 208                 if self.body.local_decls[local].is_ref_to_static() =>
 209             {
 210                 let local_info = &self.body.local_decls[local].local_info;
 211                 if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
 212                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 213                 } else {
 214                     unreachable!();
 215                 }
 216             }
 217             PlaceRef { local, projection: [proj_base @ .., elem] } => {
 218                 match elem {
 219                     ProjectionElem::Deref => {
 220                         let upvar_field_projection = self.is_upvar_field_projection(place);
 221                         if let Some(field) = upvar_field_projection {
 222                             let var_index = field.index();
 223                             let name = self.upvars[var_index].name.to_string();
 224                             if self.upvars[var_index].by_ref {
 225                                 buf.push_str(&name);
 226                             } else {
 227                                 buf.push_str(&format!("*{}", &name));
 228                             }
 229                         } else {
 230                             if autoderef {
 231                                 // FIXME turn this recursion into iteration
 232                                 self.append_place_to_string(
 233                                     PlaceRef { local, projection: proj_base },
 234                                     buf,
 235                                     autoderef,
 236                                     &including_downcast,
 237                                 )?;
 238                             } else {
 239                                 buf.push_str(&"*");
 240                                 self.append_place_to_string(
 241                                     PlaceRef { local, projection: proj_base },
 242                                     buf,
 243                                     autoderef,
 244                                     &including_downcast,
 245                                 )?;
 246                             }
 247                         }
 248                     }
 249                     ProjectionElem::Downcast(..) => {
 250                         self.append_place_to_string(
 251                             PlaceRef { local, projection: proj_base },
 252                             buf,
 253                             autoderef,
 254                             &including_downcast,
 255                         )?;
 256                         if including_downcast.0 {
 257                             return Err(());
 258                         }
 259                     }
 260                     ProjectionElem::Field(field, _ty) => {
 261                         autoderef = true;
 262
 263                         let upvar_field_projection = self.is_upvar_field_projection(place);
 264                         if let Some(field) = upvar_field_projection {
 265                             let var_index = field.index();
 266                             let name = self.upvars[var_index].name.to_string();
 267                             buf.push_str(&name);
 268                         } else {
 269                             let field_name = self
 270                                 .describe_field(PlaceRef { local, projection: proj_base }, *field);
 271                             self.append_place_to_string(
 272                                 PlaceRef { local, projection: proj_base },
 273                                 buf,
 274                                 autoderef,
 275                                 &including_downcast,
 276                             )?;
 277                             buf.push_str(&format!(".{}", 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_str("[");
 290                         if self.append_local_to_string(*index, buf).is_err() {
 291                             buf.push_str("_");
 292                         }
 293                         buf.push_str("]");
 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                     // `tcx.upvars_mentioned(def_id)` returns an `Option`, which is `None` in case
 387                     // the closure comes from another crate. But in that case we wouldn't
 388                     // be borrowck'ing it, so we can just unwrap:
 389                     let (&var_id, _) = self
 390                         .infcx
 391                         .tcx
 392                         .upvars_mentioned(def_id)
 393                         .unwrap()
 394                         .get_index(field.index())
 395                         .unwrap();
 396
 397                     self.infcx.tcx.hir().name(var_id).to_string()
 398                 }
 399                 _ => {
 400                     // Might need a revision when the fields in trait RFC is implemented
 401                     // (https://github.com/rust-lang/rfcs/pull/1546)
 402                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 403                 }
 404             }
 405         }
 406     }
 407
 408     /// Add a note that a type does not implement `Copy`
 409     pub(super) fn note_type_does_not_implement_copy(
 410         &self,
 411         err: &mut DiagnosticBuilder<'a>,
 412         place_desc: &str,
 413         ty: Ty<'tcx>,
 414         span: Option<Span>,
 415     ) {
 416         let message = format!(
 417             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 418             place_desc, ty,
 419         );
 420         if let Some(span) = span {
 421             err.span_label(span, message);
 422         } else {
 423             err.note(&message);
 424         }
 425     }
 426
 427     pub(super) fn borrowed_content_source(
 428         &self,
 429         deref_base: PlaceRef<'tcx>,
 430     ) -> BorrowedContentSource<'tcx> {
 431         let tcx = self.infcx.tcx;
 432
 433         // Look up the provided place and work out the move path index for it,
 434         // we'll use this to check whether it was originally from an overloaded
 435         // operator.
 436         match self.move_data.rev_lookup.find(deref_base) {
 437             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 438                 debug!("borrowed_content_source: mpi={:?}", mpi);
 439
 440                 for i in &self.move_data.init_path_map[mpi] {
 441                     let init = &self.move_data.inits[*i];
 442                     debug!("borrowed_content_source: init={:?}", init);
 443                     // We're only interested in statements that initialized a value, not the
 444                     // initializations from arguments.
 445                     let loc = match init.location {
 446                         InitLocation::Statement(stmt) => stmt,
 447                         _ => continue,
 448                     };
 449
 450                     let bbd = &self.body[loc.block];
 451                     let is_terminator = bbd.statements.len() == loc.statement_index;
 452                     debug!(
 453                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 454                         loc, is_terminator,
 455                     );
 456                     if !is_terminator {
 457                         continue;
 458                     } else if let Some(Terminator {
 459                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 460                         ..
 461                     }) = bbd.terminator
 462                     {
 463                         if let Some(source) =
 464                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 465                         {
 466                             return source;
 467                         }
 468                     }
 469                 }
 470             }
 471             // Base is a `static` so won't be from an overloaded operator
 472             _ => (),
 473         };
 474
 475         // If we didn't find an overloaded deref or index, then assume it's a
 476         // built in deref and check the type of the base.
 477         let base_ty = Place::ty_from(deref_base.local, deref_base.projection, self.body, tcx).ty;
 478         if base_ty.is_unsafe_ptr() {
 479             BorrowedContentSource::DerefRawPointer
 480         } else if base_ty.is_mutable_ptr() {
 481             BorrowedContentSource::DerefMutableRef
 482         } else {
 483             BorrowedContentSource::DerefSharedRef
 484         }
 485     }
 486 }
 487
 488 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 489     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 490     /// name where required.
 491     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 492         let mut s = String::new();
 493         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 494
 495         // We need to add synthesized lifetimes where appropriate. We do
 496         // this by hooking into the pretty printer and telling it to label the
 497         // lifetimes without names with the value `'0`.
 498         match ty.kind {
 499             ty::Ref(
 500                 ty::RegionKind::ReLateBound(_, br)
 501                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 502                 _,
 503                 _,
 504             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 505             _ => {}
 506         }
 507
 508         let _ = ty.print(printer);
 509         s
 510     }
 511
 512     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 513     /// synthesized lifetime name where required.
 514     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 515         let mut s = String::new();
 516         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 517
 518         let region = match ty.kind {
 519             ty::Ref(region, _, _) => {
 520                 match region {
 521                     ty::RegionKind::ReLateBound(_, br)
 522                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 523                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 524                     }
 525                     _ => {}
 526                 }
 527
 528                 region
 529             }
 530             _ => bug!("ty for annotation of borrow region is not a reference"),
 531         };
 532
 533         let _ = region.print(printer);
 534         s
 535     }
 536 }
 537
 538 /// The span(s) associated to a use of a place.
 539 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 540 pub(super) enum UseSpans {
 541     /// The access is caused by capturing a variable for a closure.
 542     ClosureUse {
 543         /// This is true if the captured variable was from a generator.
 544         generator_kind: Option<GeneratorKind>,
 545         /// The span of the args of the closure, including the `move` keyword if
 546         /// it's present.
 547         args_span: Span,
 548         /// The span of the first use of the captured variable inside the closure.
 549         var_span: Span,
 550     },
 551     /// The access is caused by using a variable as the receiver of a method
 552     /// that takes 'self'
 553     FnSelfUse {
 554         /// The span of the variable being moved
 555         var_span: Span,
 556         /// The span of the method call on the variable
 557         fn_call_span: Span,
 558         /// The definition span of the method being called
 559         fn_span: Span,
 560         kind: FnSelfUseKind,
 561     },
 562     /// This access is caused by a `match` or `if let` pattern.
 563     PatUse(Span),
 564     /// This access has a single span associated to it: common case.
 565     OtherUse(Span),
 566 }
 567
 568 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 569 pub(super) enum FnSelfUseKind {
 570     /// A normal method call of the form `receiver.foo(a, b, c)`
 571     Normal { self_arg: Ident, implicit_into_iter: bool },
 572     /// A call to `FnOnce::call_once`, desugared from `my_closure(a, b, c)`
 573     FnOnceCall,
 574     /// A call to an operator trait, desuraged from operator syntax (e.g. `a << b`)
 575     Operator { self_arg: Ident },
 576 }
 577
 578 impl UseSpans {
 579     pub(super) fn args_or_use(self) -> Span {
 580         match self {
 581             UseSpans::ClosureUse { args_span: span, .. }
 582             | UseSpans::PatUse(span)
 583             | UseSpans::FnSelfUse { var_span: span, .. }
 584             | UseSpans::OtherUse(span) => span,
 585         }
 586     }
 587
 588     pub(super) fn var_or_use(self) -> Span {
 589         match self {
 590             UseSpans::ClosureUse { var_span: span, .. }
 591             | UseSpans::PatUse(span)
 592             | UseSpans::FnSelfUse { var_span: span, .. }
 593             | UseSpans::OtherUse(span) => span,
 594         }
 595     }
 596
 597     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 598         match self {
 599             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 600             _ => None,
 601         }
 602     }
 603
 604     // Add a span label to the arguments of the closure, if it exists.
 605     pub(super) fn args_span_label(
 606         self,
 607         err: &mut DiagnosticBuilder<'_>,
 608         message: impl Into<String>,
 609     ) {
 610         if let UseSpans::ClosureUse { args_span, .. } = self {
 611             err.span_label(args_span, message);
 612         }
 613     }
 614
 615     // Add a span label to the use of the captured variable, if it exists.
 616     pub(super) fn var_span_label(
 617         self,
 618         err: &mut DiagnosticBuilder<'_>,
 619         message: impl Into<String>,
 620     ) {
 621         if let UseSpans::ClosureUse { var_span, .. } = self {
 622             err.span_label(var_span, message);
 623         }
 624     }
 625
 626     /// Returns `false` if this place is not used in a closure.
 627     pub(super) fn for_closure(&self) -> bool {
 628         match *self {
 629             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 630             _ => false,
 631         }
 632     }
 633
 634     /// Returns `false` if this place is not used in a generator.
 635     pub(super) fn for_generator(&self) -> bool {
 636         match *self {
 637             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 638             _ => false,
 639         }
 640     }
 641
 642     /// Describe the span associated with a use of a place.
 643     pub(super) fn describe(&self) -> String {
 644         match *self {
 645             UseSpans::ClosureUse { generator_kind, .. } => {
 646                 if generator_kind.is_some() {
 647                     " in generator".to_string()
 648                 } else {
 649                     " in closure".to_string()
 650                 }
 651             }
 652             _ => "".to_string(),
 653         }
 654     }
 655
 656     pub(super) fn or_else<F>(self, if_other: F) -> Self
 657     where
 658         F: FnOnce() -> Self,
 659     {
 660         match self {
 661             closure @ UseSpans::ClosureUse { .. } => closure,
 662             UseSpans::PatUse(_) | UseSpans::OtherUse(_) => if_other(),
 663             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 664         }
 665     }
 666 }
 667
 668 pub(super) enum BorrowedContentSource<'tcx> {
 669     DerefRawPointer,
 670     DerefMutableRef,
 671     DerefSharedRef,
 672     OverloadedDeref(Ty<'tcx>),
 673     OverloadedIndex(Ty<'tcx>),
 674 }
 675
 676 impl BorrowedContentSource<'tcx> {
 677     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 678         match *self {
 679             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 680             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 681             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 682             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 683                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 684                     "an `Rc`".to_string()
 685                 }
 686                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 687                     "an `Arc`".to_string()
 688                 }
 689                 _ => format!("dereference of `{}`", ty),
 690             },
 691             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 692         }
 693     }
 694
 695     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 696         match *self {
 697             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 698             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 699             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 700             // Overloaded deref and index operators should be evaluated into a
 701             // temporary. So we don't need a description here.
 702             BorrowedContentSource::OverloadedDeref(_)
 703             | BorrowedContentSource::OverloadedIndex(_) => None,
 704         }
 705     }
 706
 707     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 708         match *self {
 709             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 710             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 711             BorrowedContentSource::DerefMutableRef => {
 712                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 713             }
 714             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 715                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 716                     "an `Rc`".to_string()
 717                 }
 718                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 719                     "an `Arc`".to_string()
 720                 }
 721                 _ => format!("a dereference of `{}`", ty),
 722             },
 723             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 724         }
 725     }
 726
 727     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 728         match func.kind {
 729             ty::FnDef(def_id, substs) => {
 730                 let trait_id = tcx.trait_of_item(def_id)?;
 731
 732                 let lang_items = tcx.lang_items();
 733                 if Some(trait_id) == lang_items.deref_trait()
 734                     || Some(trait_id) == lang_items.deref_mut_trait()
 735                 {
 736                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 737                 } else if Some(trait_id) == lang_items.index_trait()
 738                     || Some(trait_id) == lang_items.index_mut_trait()
 739                 {
 740                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 741                 } else {
 742                     None
 743                 }
 744             }
 745             _ => None,
 746         }
 747     }
 748 }
 749
 750 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 751     /// Finds the spans associated to a move or copy of move_place at location.
 752     pub(super) fn move_spans(
 753         &self,
 754         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 755         location: Location,
 756     ) -> UseSpans {
 757         use self::UseSpans::*;
 758
 759         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 760             Some(stmt) => stmt,
 761             None => return OtherUse(self.body.source_info(location).span),
 762         };
 763
 764         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 765         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 766             match kind {
 767                 box AggregateKind::Closure(def_id, _)
 768                 | box AggregateKind::Generator(def_id, _, _) => {
 769                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 770                     if let Some((args_span, generator_kind, var_span)) =
 771                         self.closure_span(*def_id, moved_place, places)
 772                     {
 773                         return ClosureUse { generator_kind, args_span, var_span };
 774                     }
 775                 }
 776                 _ => {}
 777             }
 778         }
 779
 780         let normal_ret =
 781             if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
 782                 PatUse(stmt.source_info.span)
 783             } else {
 784                 OtherUse(stmt.source_info.span)
 785             };
 786
 787         // We are trying to find MIR of the form:
 788         // ```
 789         // _temp = _moved_val;
 790         // ...
 791         // FnSelfCall(_temp, ...)
 792         // ```
 793         //
 794         // where `_moved_val` is the place we generated the move error for,
 795         // `_temp` is some other local, and `FnSelfCall` is a function
 796         // that has a `self` parameter.
 797
 798         let target_temp = match stmt.kind {
 799             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 800                 temp.as_local().unwrap()
 801             }
 802             _ => return normal_ret,
 803         };
 804
 805         debug!("move_spans: target_temp = {:?}", target_temp);
 806
 807         if let Some(Terminator {
 808             kind: TerminatorKind::Call { func, args, fn_span, from_hir_call, .. },
 809             ..
 810         }) = &self.body[location.block].terminator
 811         {
 812             let mut method_did = None;
 813             if let Operand::Constant(box Constant { literal: ty::Const { ty, .. }, .. }) = func {
 814                 if let ty::FnDef(def_id, _) = ty.kind {
 815                     debug!("move_spans: fn = {:?}", def_id);
 816                     if let Some(ty::AssocItem { fn_has_self_parameter, .. }) =
 817                         self.infcx.tcx.opt_associated_item(def_id)
 818                     {
 819                         if *fn_has_self_parameter {
 820                             method_did = Some(def_id);
 821                         }
 822                     }
 823                 }
 824             }
 825
 826             let tcx = self.infcx.tcx;
 827             let method_did = if let Some(did) = method_did { did } else { return normal_ret };
 828
 829             if let [Operand::Move(self_place), ..] = **args {
 830                 if self_place.as_local() == Some(target_temp) {
 831                     let parent = tcx.parent(method_did);
 832                     let is_fn_once = parent == tcx.lang_items().fn_once_trait();
 833                     let is_operator = !from_hir_call
 834                         && parent.map_or(false, |p| {
 835                             tcx.lang_items().group(LangItemGroup::Op).contains(&p)
 836                         });
 837                     let fn_call_span = *fn_span;
 838
 839                     let self_arg = tcx.fn_arg_names(method_did)[0];
 840
 841                     let kind = if is_fn_once {
 842                         FnSelfUseKind::FnOnceCall
 843                     } else if is_operator {
 844                         FnSelfUseKind::Operator { self_arg }
 845                     } else {
 846                         debug!(
 847                             "move_spans: method_did={:?}, fn_call_span={:?}",
 848                             method_did, fn_call_span
 849                         );
 850                         let implicit_into_iter = matches!(
 851                             fn_call_span.desugaring_kind(),
 852                             Some(DesugaringKind::ForLoop(ForLoopLoc::IntoIter))
 853                         );
 854                         FnSelfUseKind::Normal { self_arg, implicit_into_iter }
 855                     };
 856
 857                     return FnSelfUse {
 858                         var_span: stmt.source_info.span,
 859                         fn_call_span,
 860                         fn_span: self
 861                             .infcx
 862                             .tcx
 863                             .sess
 864                             .source_map()
 865                             .guess_head_span(self.infcx.tcx.def_span(method_did)),
 866                         kind,
 867                     };
 868                 }
 869             }
 870         }
 871         normal_ret
 872     }
 873
 874     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 875     /// and its usage of the local assigned at `location`.
 876     /// This is done by searching in statements succeeding `location`
 877     /// and originating from `maybe_closure_span`.
 878     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 879         use self::UseSpans::*;
 880         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 881
 882         let target = match self.body[location.block].statements.get(location.statement_index) {
 883             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 884                 if let Some(local) = place.as_local() {
 885                     local
 886                 } else {
 887                     return OtherUse(use_span);
 888                 }
 889             }
 890             _ => return OtherUse(use_span),
 891         };
 892
 893         if self.body.local_kind(target) != LocalKind::Temp {
 894             // operands are always temporaries.
 895             return OtherUse(use_span);
 896         }
 897
 898         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 899             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 900                 stmt.kind
 901             {
 902                 let (def_id, is_generator) = match kind {
 903                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 904                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 905                     _ => continue,
 906                 };
 907
 908                 debug!(
 909                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 910                     def_id, is_generator, places
 911                 );
 912                 if let Some((args_span, generator_kind, var_span)) =
 913                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 914                 {
 915                     return ClosureUse { generator_kind, args_span, var_span };
 916                 } else {
 917                     return OtherUse(use_span);
 918                 }
 919             }
 920
 921             if use_span != stmt.source_info.span {
 922                 break;
 923             }
 924         }
 925
 926         OtherUse(use_span)
 927     }
 928
 929     /// Finds the span of a captured variable within a closure or generator.
 930     fn closure_span(
 931         &self,
 932         def_id: DefId,
 933         target_place: PlaceRef<'tcx>,
 934         places: &Vec<Operand<'tcx>>,
 935     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 936         debug!(
 937             "closure_span: def_id={:?} target_place={:?} places={:?}",
 938             def_id, target_place, places
 939         );
 940         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(def_id.as_local()?);
 941         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 942         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 943         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 944             for (upvar, place) in self.infcx.tcx.upvars_mentioned(def_id)?.values().zip(places) {
 945                 match place {
 946                     Operand::Copy(place) | Operand::Move(place)
 947                         if target_place == place.as_ref() =>
 948                     {
 949                         debug!("closure_span: found captured local {:?}", place);
 950                         let body = self.infcx.tcx.hir().body(*body_id);
 951                         let generator_kind = body.generator_kind();
 952                         return Some((*args_span, generator_kind, upvar.span));
 953                     }
 954                     _ => {}
 955                 }
 956             }
 957         }
 958         None
 959     }
 960
 961     /// Helper to retrieve span(s) of given borrow from the current MIR
 962     /// representation
 963     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 964         let span = self.body.source_info(borrow.reserve_location).span;
 965         self.borrow_spans(span, borrow.reserve_location)
 966     }
 967 }