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         move_prefix: &str,
 416     ) {
 417         let message = format!(
 418             "{}move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 419             move_prefix, place_desc, ty,
 420         );
 421         if let Some(span) = span {
 422             err.span_label(span, message);
 423         } else {
 424             err.note(&message);
 425         }
 426     }
 427
 428     pub(super) fn borrowed_content_source(
 429         &self,
 430         deref_base: PlaceRef<'tcx>,
 431     ) -> BorrowedContentSource<'tcx> {
 432         let tcx = self.infcx.tcx;
 433
 434         // Look up the provided place and work out the move path index for it,
 435         // we'll use this to check whether it was originally from an overloaded
 436         // operator.
 437         match self.move_data.rev_lookup.find(deref_base) {
 438             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 439                 debug!("borrowed_content_source: mpi={:?}", mpi);
 440
 441                 for i in &self.move_data.init_path_map[mpi] {
 442                     let init = &self.move_data.inits[*i];
 443                     debug!("borrowed_content_source: init={:?}", init);
 444                     // We're only interested in statements that initialized a value, not the
 445                     // initializations from arguments.
 446                     let loc = match init.location {
 447                         InitLocation::Statement(stmt) => stmt,
 448                         _ => continue,
 449                     };
 450
 451                     let bbd = &self.body[loc.block];
 452                     let is_terminator = bbd.statements.len() == loc.statement_index;
 453                     debug!(
 454                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 455                         loc, is_terminator,
 456                     );
 457                     if !is_terminator {
 458                         continue;
 459                     } else if let Some(Terminator {
 460                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 461                         ..
 462                     }) = bbd.terminator
 463                     {
 464                         if let Some(source) =
 465                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 466                         {
 467                             return source;
 468                         }
 469                     }
 470                 }
 471             }
 472             // Base is a `static` so won't be from an overloaded operator
 473             _ => (),
 474         };
 475
 476         // If we didn't find an overloaded deref or index, then assume it's a
 477         // built in deref and check the type of the base.
 478         let base_ty = Place::ty_from(deref_base.local, deref_base.projection, self.body, tcx).ty;
 479         if base_ty.is_unsafe_ptr() {
 480             BorrowedContentSource::DerefRawPointer
 481         } else if base_ty.is_mutable_ptr() {
 482             BorrowedContentSource::DerefMutableRef
 483         } else {
 484             BorrowedContentSource::DerefSharedRef
 485         }
 486     }
 487 }
 488
 489 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 490     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 491     /// name where required.
 492     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 493         let mut s = String::new();
 494         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 495
 496         // We need to add synthesized lifetimes where appropriate. We do
 497         // this by hooking into the pretty printer and telling it to label the
 498         // lifetimes without names with the value `'0`.
 499         match ty.kind {
 500             ty::Ref(
 501                 ty::RegionKind::ReLateBound(_, br)
 502                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 503                 _,
 504                 _,
 505             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 506             _ => {}
 507         }
 508
 509         let _ = ty.print(printer);
 510         s
 511     }
 512
 513     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 514     /// synthesized lifetime name where required.
 515     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 516         let mut s = String::new();
 517         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 518
 519         let region = match ty.kind {
 520             ty::Ref(region, _, _) => {
 521                 match region {
 522                     ty::RegionKind::ReLateBound(_, br)
 523                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 524                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 525                     }
 526                     _ => {}
 527                 }
 528
 529                 region
 530             }
 531             _ => bug!("ty for annotation of borrow region is not a reference"),
 532         };
 533
 534         let _ = region.print(printer);
 535         s
 536     }
 537 }
 538
 539 /// The span(s) associated to a use of a place.
 540 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 541 pub(super) enum UseSpans {
 542     /// The access is caused by capturing a variable for a closure.
 543     ClosureUse {
 544         /// This is true if the captured variable was from a generator.
 545         generator_kind: Option<GeneratorKind>,
 546         /// The span of the args of the closure, including the `move` keyword if
 547         /// it's present.
 548         args_span: Span,
 549         /// The span of the first use of the captured variable inside the closure.
 550         var_span: Span,
 551     },
 552     /// The access is caused by using a variable as the receiver of a method
 553     /// that takes 'self'
 554     FnSelfUse {
 555         /// The span of the variable being moved
 556         var_span: Span,
 557         /// The span of the method call on the variable
 558         fn_call_span: Span,
 559         /// The definition span of the method being called
 560         fn_span: Span,
 561         kind: FnSelfUseKind,
 562     },
 563     /// This access is caused by a `match` or `if let` pattern.
 564     PatUse(Span),
 565     /// This access has a single span associated to it: common case.
 566     OtherUse(Span),
 567 }
 568
 569 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 570 pub(super) enum FnSelfUseKind {
 571     /// A normal method call of the form `receiver.foo(a, b, c)`
 572     Normal { self_arg: Ident, implicit_into_iter: bool },
 573     /// A call to `FnOnce::call_once`, desugared from `my_closure(a, b, c)`
 574     FnOnceCall,
 575     /// A call to an operator trait, desuraged from operator syntax (e.g. `a << b`)
 576     Operator { self_arg: Ident },
 577 }
 578
 579 impl UseSpans {
 580     pub(super) fn args_or_use(self) -> Span {
 581         match self {
 582             UseSpans::ClosureUse { args_span: span, .. }
 583             | UseSpans::PatUse(span)
 584             | UseSpans::FnSelfUse { var_span: span, .. }
 585             | UseSpans::OtherUse(span) => span,
 586         }
 587     }
 588
 589     pub(super) fn var_or_use(self) -> Span {
 590         match self {
 591             UseSpans::ClosureUse { var_span: span, .. }
 592             | UseSpans::PatUse(span)
 593             | UseSpans::FnSelfUse { var_span: span, .. }
 594             | UseSpans::OtherUse(span) => span,
 595         }
 596     }
 597
 598     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 599         match self {
 600             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 601             _ => None,
 602         }
 603     }
 604
 605     // Add a span label to the arguments of the closure, if it exists.
 606     pub(super) fn args_span_label(
 607         self,
 608         err: &mut DiagnosticBuilder<'_>,
 609         message: impl Into<String>,
 610     ) {
 611         if let UseSpans::ClosureUse { args_span, .. } = self {
 612             err.span_label(args_span, message);
 613         }
 614     }
 615
 616     // Add a span label to the use of the captured variable, if it exists.
 617     pub(super) fn var_span_label(
 618         self,
 619         err: &mut DiagnosticBuilder<'_>,
 620         message: impl Into<String>,
 621     ) {
 622         if let UseSpans::ClosureUse { var_span, .. } = self {
 623             err.span_label(var_span, message);
 624         }
 625     }
 626
 627     /// Returns `false` if this place is not used in a closure.
 628     pub(super) fn for_closure(&self) -> bool {
 629         match *self {
 630             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 631             _ => false,
 632         }
 633     }
 634
 635     /// Returns `false` if this place is not used in a generator.
 636     pub(super) fn for_generator(&self) -> bool {
 637         match *self {
 638             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 639             _ => false,
 640         }
 641     }
 642
 643     /// Describe the span associated with a use of a place.
 644     pub(super) fn describe(&self) -> String {
 645         match *self {
 646             UseSpans::ClosureUse { generator_kind, .. } => {
 647                 if generator_kind.is_some() {
 648                     " in generator".to_string()
 649                 } else {
 650                     " in closure".to_string()
 651                 }
 652             }
 653             _ => "".to_string(),
 654         }
 655     }
 656
 657     pub(super) fn or_else<F>(self, if_other: F) -> Self
 658     where
 659         F: FnOnce() -> Self,
 660     {
 661         match self {
 662             closure @ UseSpans::ClosureUse { .. } => closure,
 663             UseSpans::PatUse(_) | UseSpans::OtherUse(_) => if_other(),
 664             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 665         }
 666     }
 667 }
 668
 669 pub(super) enum BorrowedContentSource<'tcx> {
 670     DerefRawPointer,
 671     DerefMutableRef,
 672     DerefSharedRef,
 673     OverloadedDeref(Ty<'tcx>),
 674     OverloadedIndex(Ty<'tcx>),
 675 }
 676
 677 impl BorrowedContentSource<'tcx> {
 678     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 679         match *self {
 680             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 681             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 682             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 683             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 684                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 685                     "an `Rc`".to_string()
 686                 }
 687                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 688                     "an `Arc`".to_string()
 689                 }
 690                 _ => format!("dereference of `{}`", ty),
 691             },
 692             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 693         }
 694     }
 695
 696     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 697         match *self {
 698             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 699             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 700             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 701             // Overloaded deref and index operators should be evaluated into a
 702             // temporary. So we don't need a description here.
 703             BorrowedContentSource::OverloadedDeref(_)
 704             | BorrowedContentSource::OverloadedIndex(_) => None,
 705         }
 706     }
 707
 708     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 709         match *self {
 710             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 711             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 712             BorrowedContentSource::DerefMutableRef => {
 713                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 714             }
 715             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 716                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 717                     "an `Rc`".to_string()
 718                 }
 719                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 720                     "an `Arc`".to_string()
 721                 }
 722                 _ => format!("a dereference of `{}`", ty),
 723             },
 724             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 725         }
 726     }
 727
 728     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 729         match func.kind {
 730             ty::FnDef(def_id, substs) => {
 731                 let trait_id = tcx.trait_of_item(def_id)?;
 732
 733                 let lang_items = tcx.lang_items();
 734                 if Some(trait_id) == lang_items.deref_trait()
 735                     || Some(trait_id) == lang_items.deref_mut_trait()
 736                 {
 737                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 738                 } else if Some(trait_id) == lang_items.index_trait()
 739                     || Some(trait_id) == lang_items.index_mut_trait()
 740                 {
 741                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 742                 } else {
 743                     None
 744                 }
 745             }
 746             _ => None,
 747         }
 748     }
 749 }
 750
 751 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 752     /// Finds the spans associated to a move or copy of move_place at location.
 753     pub(super) fn move_spans(
 754         &self,
 755         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 756         location: Location,
 757     ) -> UseSpans {
 758         use self::UseSpans::*;
 759
 760         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 761             Some(stmt) => stmt,
 762             None => return OtherUse(self.body.source_info(location).span),
 763         };
 764
 765         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 766         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 767             match kind {
 768                 box AggregateKind::Closure(def_id, _)
 769                 | box AggregateKind::Generator(def_id, _, _) => {
 770                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 771                     if let Some((args_span, generator_kind, var_span)) =
 772                         self.closure_span(*def_id, moved_place, places)
 773                     {
 774                         return ClosureUse { generator_kind, args_span, var_span };
 775                     }
 776                 }
 777                 _ => {}
 778             }
 779         }
 780
 781         let normal_ret =
 782             if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
 783                 PatUse(stmt.source_info.span)
 784             } else {
 785                 OtherUse(stmt.source_info.span)
 786             };
 787
 788         // We are trying to find MIR of the form:
 789         // ```
 790         // _temp = _moved_val;
 791         // ...
 792         // FnSelfCall(_temp, ...)
 793         // ```
 794         //
 795         // where `_moved_val` is the place we generated the move error for,
 796         // `_temp` is some other local, and `FnSelfCall` is a function
 797         // that has a `self` parameter.
 798
 799         let target_temp = match stmt.kind {
 800             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 801                 temp.as_local().unwrap()
 802             }
 803             _ => return normal_ret,
 804         };
 805
 806         debug!("move_spans: target_temp = {:?}", target_temp);
 807
 808         if let Some(Terminator {
 809             kind: TerminatorKind::Call { func, args, fn_span, from_hir_call, .. },
 810             ..
 811         }) = &self.body[location.block].terminator
 812         {
 813             let mut method_did = None;
 814             if let Operand::Constant(box Constant { literal: ty::Const { ty, .. }, .. }) = func {
 815                 if let ty::FnDef(def_id, _) = ty.kind {
 816                     debug!("move_spans: fn = {:?}", def_id);
 817                     if let Some(ty::AssocItem { fn_has_self_parameter, .. }) =
 818                         self.infcx.tcx.opt_associated_item(def_id)
 819                     {
 820                         if *fn_has_self_parameter {
 821                             method_did = Some(def_id);
 822                         }
 823                     }
 824                 }
 825             }
 826
 827             let tcx = self.infcx.tcx;
 828             let method_did = if let Some(did) = method_did { did } else { return normal_ret };
 829
 830             if let [Operand::Move(self_place), ..] = **args {
 831                 if self_place.as_local() == Some(target_temp) {
 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| {
 836                             tcx.lang_items().group(LangItemGroup::Op).contains(&p)
 837                         });
 838                     let fn_call_span = *fn_span;
 839
 840                     let self_arg = tcx.fn_arg_names(method_did)[0];
 841
 842                     let kind = if is_fn_once {
 843                         FnSelfUseKind::FnOnceCall
 844                     } else if is_operator {
 845                         FnSelfUseKind::Operator { self_arg }
 846                     } else {
 847                         debug!(
 848                             "move_spans: method_did={:?}, fn_call_span={:?}",
 849                             method_did, fn_call_span
 850                         );
 851                         let implicit_into_iter = matches!(
 852                             fn_call_span.desugaring_kind(),
 853                             Some(DesugaringKind::ForLoop(ForLoopLoc::IntoIter))
 854                         );
 855                         FnSelfUseKind::Normal { self_arg, implicit_into_iter }
 856                     };
 857
 858                     return FnSelfUse {
 859                         var_span: stmt.source_info.span,
 860                         fn_call_span,
 861                         fn_span: self
 862                             .infcx
 863                             .tcx
 864                             .sess
 865                             .source_map()
 866                             .guess_head_span(self.infcx.tcx.def_span(method_did)),
 867                         kind,
 868                     };
 869                 }
 870             }
 871         }
 872         normal_ret
 873     }
 874
 875     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 876     /// and its usage of the local assigned at `location`.
 877     /// This is done by searching in statements succeeding `location`
 878     /// and originating from `maybe_closure_span`.
 879     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 880         use self::UseSpans::*;
 881         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 882
 883         let target = match self.body[location.block].statements.get(location.statement_index) {
 884             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 885                 if let Some(local) = place.as_local() {
 886                     local
 887                 } else {
 888                     return OtherUse(use_span);
 889                 }
 890             }
 891             _ => return OtherUse(use_span),
 892         };
 893
 894         if self.body.local_kind(target) != LocalKind::Temp {
 895             // operands are always temporaries.
 896             return OtherUse(use_span);
 897         }
 898
 899         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 900             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 901                 stmt.kind
 902             {
 903                 let (def_id, is_generator) = match kind {
 904                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 905                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 906                     _ => continue,
 907                 };
 908
 909                 debug!(
 910                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 911                     def_id, is_generator, places
 912                 );
 913                 if let Some((args_span, generator_kind, var_span)) =
 914                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 915                 {
 916                     return ClosureUse { generator_kind, args_span, var_span };
 917                 } else {
 918                     return OtherUse(use_span);
 919                 }
 920             }
 921
 922             if use_span != stmt.source_info.span {
 923                 break;
 924             }
 925         }
 926
 927         OtherUse(use_span)
 928     }
 929
 930     /// Finds the span of a captured variable within a closure or generator.
 931     fn closure_span(
 932         &self,
 933         def_id: DefId,
 934         target_place: PlaceRef<'tcx>,
 935         places: &Vec<Operand<'tcx>>,
 936     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 937         debug!(
 938             "closure_span: def_id={:?} target_place={:?} places={:?}",
 939             def_id, target_place, places
 940         );
 941         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(def_id.as_local()?);
 942         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 943         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 944         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 945             for (upvar, place) in self.infcx.tcx.upvars_mentioned(def_id)?.values().zip(places) {
 946                 match place {
 947                     Operand::Copy(place) | Operand::Move(place)
 948                         if target_place == place.as_ref() =>
 949                     {
 950                         debug!("closure_span: found captured local {:?}", place);
 951                         let body = self.infcx.tcx.hir().body(*body_id);
 952                         let generator_kind = body.generator_kind();
 953                         return Some((*args_span, generator_kind, upvar.span));
 954                     }
 955                     _ => {}
 956                 }
 957             }
 958         }
 959         None
 960     }
 961
 962     /// Helper to retrieve span(s) of given borrow from the current MIR
 963     /// representation
 964     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 965         let span = self.body.source_info(borrow.reserve_location).span;
 966         self.borrow_spans(span, borrow.reserve_location)
 967     }
 968 }