src/librustc_mir/borrow_check/diagnostics/mod.rs

   1 //! Borrow checker diagnostics.
   2
   3 use rustc_errors::DiagnosticBuilder;
   4 use rustc_hir as hir;
   5 use rustc_hir::def::Namespace;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_hir::GeneratorKind;
   8 use rustc_middle::mir::{
   9     AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
  10     PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
  11 };
  12 use rustc_middle::ty::print::Print;
  13 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt};
  14 use rustc_span::{
  15     hygiene::{DesugaringKind, ForLoopLoc},
  16     symbol::sym,
  17     Span,
  18 };
  19 use rustc_target::abi::VariantIdx;
  20
  21 use super::borrow_set::BorrowData;
  22 use super::MirBorrowckCtxt;
  23 use crate::dataflow::move_paths::{InitLocation, LookupResult};
  24
  25 mod find_use;
  26 mod outlives_suggestion;
  27 mod region_name;
  28 mod var_name;
  29
  30 mod conflict_errors;
  31 mod explain_borrow;
  32 mod move_errors;
  33 mod mutability_errors;
  34 mod region_errors;
  35
  36 crate use mutability_errors::AccessKind;
  37 crate use outlives_suggestion::OutlivesSuggestionBuilder;
  38 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
  39 crate use region_name::{RegionName, RegionNameSource};
  40 use rustc_span::symbol::Ident;
  41
  42 pub(super) struct IncludingDowncast(pub(super) bool);
  43
  44 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  45     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  46     /// is moved after being invoked.
  47     ///
  48     /// ```text
  49     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  50     ///       its environment
  51     ///   --> $DIR/issue-42065.rs:16:29
  52     ///    |
  53     /// LL |         for (key, value) in dict {
  54     ///    |                             ^^^^
  55     /// ```
  56     pub(super) fn add_moved_or_invoked_closure_note(
  57         &self,
  58         location: Location,
  59         place: PlaceRef<'tcx>,
  60         diag: &mut DiagnosticBuilder<'_>,
  61     ) {
  62         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  63         let mut target = place.local_or_deref_local();
  64         for stmt in &self.body[location.block].statements[location.statement_index..] {
  65             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  66             if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
  67                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  68                 match from {
  69                     Operand::Copy(ref place) | Operand::Move(ref place)
  70                         if target == place.local_or_deref_local() =>
  71                     {
  72                         target = into.local_or_deref_local()
  73                     }
  74                     _ => {}
  75                 }
  76             }
  77         }
  78
  79         // Check if we are attempting to call a closure after it has been invoked.
  80         let terminator = self.body[location.block].terminator();
  81         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  82         if let TerminatorKind::Call {
  83             func:
  84                 Operand::Constant(box Constant {
  85                     literal: ty::Const { ty: &ty::TyS { kind: ty::FnDef(id, _), .. }, .. },
  86                     ..
  87                 }),
  88             args,
  89             ..
  90         } = &terminator.kind
  91         {
  92             debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  93             if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  94                 let closure = match args.first() {
  95                     Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
  96                         if target == place.local_or_deref_local() =>
  97                     {
  98                         place.local_or_deref_local().unwrap()
  99                     }
 100                     _ => return,
 101                 };
 102
 103                 debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
 104                 if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind {
 105                     let did = did.expect_local();
 106                     let hir_id = self.infcx.tcx.hir().as_local_hir_id(did);
 107
 108                     if let Some((span, name)) =
 109                         self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
 110                     {
 111                         diag.span_note(
 112                             *span,
 113                             &format!(
 114                                 "closure cannot be invoked more than once because it moves the \
 115                                  variable `{}` out of its environment",
 116                                 name,
 117                             ),
 118                         );
 119                         return;
 120                     }
 121                 }
 122             }
 123         }
 124
 125         // Check if we are just moving a closure after it has been invoked.
 126         if let Some(target) = target {
 127             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind {
 128                 let did = did.expect_local();
 129                 let hir_id = self.infcx.tcx.hir().as_local_hir_id(did);
 130
 131                 if let Some((span, name)) =
 132                     self.infcx.tcx.typeck_tables_of(did).closure_kind_origins().get(hir_id)
 133                 {
 134                     diag.span_note(
 135                         *span,
 136                         &format!(
 137                             "closure cannot be moved more than once as it is not `Copy` due to \
 138                              moving the variable `{}` out of its environment",
 139                             name
 140                         ),
 141                     );
 142                 }
 143             }
 144         }
 145     }
 146
 147     /// End-user visible description of `place` if one can be found.
 148     /// If the place is a temporary for instance, `"value"` will be returned.
 149     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 150         match self.describe_place(place_ref) {
 151             Some(mut descr) => {
 152                 // Surround descr with `backticks`.
 153                 descr.reserve(2);
 154                 descr.insert_str(0, "`");
 155                 descr.push_str("`");
 156                 descr
 157             }
 158             None => "value".to_string(),
 159         }
 160     }
 161
 162     /// End-user visible description of `place` if one can be found.
 163     /// If the place is a temporary for instance, None will be returned.
 164     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 165         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 166     }
 167
 168     /// End-user visible description of `place` if one can be found. If the
 169     /// place is a temporary for instance, None will be returned.
 170     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 171     /// `Downcast` and `IncludingDowncast` is true
 172     pub(super) fn describe_place_with_options(
 173         &self,
 174         place: PlaceRef<'tcx>,
 175         including_downcast: IncludingDowncast,
 176     ) -> Option<String> {
 177         let mut buf = String::new();
 178         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 179             Ok(()) => Some(buf),
 180             Err(()) => None,
 181         }
 182     }
 183
 184     /// Appends end-user visible description of `place` to `buf`.
 185     fn append_place_to_string(
 186         &self,
 187         place: PlaceRef<'tcx>,
 188         buf: &mut String,
 189         mut autoderef: bool,
 190         including_downcast: &IncludingDowncast,
 191     ) -> Result<(), ()> {
 192         match place {
 193             PlaceRef { local, projection: [] } => {
 194                 self.append_local_to_string(local, buf)?;
 195             }
 196             PlaceRef { local, projection: [ProjectionElem::Deref] }
 197                 if self.body.local_decls[local].is_ref_for_guard() =>
 198             {
 199                 self.append_place_to_string(
 200                     PlaceRef { local, projection: &[] },
 201                     buf,
 202                     autoderef,
 203                     &including_downcast,
 204                 )?;
 205             }
 206             PlaceRef { local, projection: [ProjectionElem::Deref] }
 207                 if self.body.local_decls[local].is_ref_to_static() =>
 208             {
 209                 let local_info = &self.body.local_decls[local].local_info;
 210                 if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
 211                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 212                 } else {
 213                     unreachable!();
 214                 }
 215             }
 216             PlaceRef { local, projection: [proj_base @ .., elem] } => {
 217                 match elem {
 218                     ProjectionElem::Deref => {
 219                         let upvar_field_projection = self.is_upvar_field_projection(place);
 220                         if let Some(field) = upvar_field_projection {
 221                             let var_index = field.index();
 222                             let name = self.upvars[var_index].name.to_string();
 223                             if self.upvars[var_index].by_ref {
 224                                 buf.push_str(&name);
 225                             } else {
 226                                 buf.push_str(&format!("*{}", &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_str(&"*");
 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_str(&format!(".{}", field_name));
 277                         }
 278                     }
 279                     ProjectionElem::Index(index) => {
 280                         autoderef = true;
 281
 282                         self.append_place_to_string(
 283                             PlaceRef { local, projection: proj_base },
 284                             buf,
 285                             autoderef,
 286                             &including_downcast,
 287                         )?;
 288                         buf.push_str("[");
 289                         if self.append_local_to_string(*index, buf).is_err() {
 290                             buf.push_str("_");
 291                         }
 292                         buf.push_str("]");
 293                     }
 294                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 295                         autoderef = true;
 296                         // Since it isn't possible to borrow an element on a particular index and
 297                         // then use another while the borrow is held, don't output indices details
 298                         // to avoid confusing the end-user
 299                         self.append_place_to_string(
 300                             PlaceRef { local, projection: proj_base },
 301                             buf,
 302                             autoderef,
 303                             &including_downcast,
 304                         )?;
 305                         buf.push_str(&"[..]");
 306                     }
 307                 };
 308             }
 309         }
 310
 311         Ok(())
 312     }
 313
 314     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 315     /// a name, or its name was generated by the compiler, then `Err` is returned
 316     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 317         let decl = &self.body.local_decls[local];
 318         match self.local_names[local] {
 319             Some(name) if !decl.from_compiler_desugaring() => {
 320                 buf.push_str(&name.as_str());
 321                 Ok(())
 322             }
 323             _ => Err(()),
 324         }
 325     }
 326
 327     /// End-user visible description of the `field`nth field of `base`
 328     fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
 329         // FIXME Place2 Make this work iteratively
 330         match place {
 331             PlaceRef { local, projection: [] } => {
 332                 let local = &self.body.local_decls[local];
 333                 self.describe_field_from_ty(&local.ty, field, None)
 334             }
 335             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 336                 ProjectionElem::Deref => {
 337                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 338                 }
 339                 ProjectionElem::Downcast(_, variant_index) => {
 340                     let base_ty =
 341                         Place::ty_from(place.local, place.projection, self.body, self.infcx.tcx).ty;
 342                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 343                 }
 344                 ProjectionElem::Field(_, field_type) => {
 345                     self.describe_field_from_ty(&field_type, field, None)
 346                 }
 347                 ProjectionElem::Index(..)
 348                 | ProjectionElem::ConstantIndex { .. }
 349                 | ProjectionElem::Subslice { .. } => {
 350                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 351                 }
 352             },
 353         }
 354     }
 355
 356     /// End-user visible description of the `field_index`nth field of `ty`
 357     fn describe_field_from_ty(
 358         &self,
 359         ty: Ty<'_>,
 360         field: Field,
 361         variant_index: Option<VariantIdx>,
 362     ) -> String {
 363         if ty.is_box() {
 364             // If the type is a box, the field is described from the boxed type
 365             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 366         } else {
 367             match ty.kind {
 368                 ty::Adt(def, _) => {
 369                     let variant = if let Some(idx) = variant_index {
 370                         assert!(def.is_enum());
 371                         &def.variants[idx]
 372                     } else {
 373                         def.non_enum_variant()
 374                     };
 375                     variant.fields[field.index()].ident.to_string()
 376                 }
 377                 ty::Tuple(_) => field.index().to_string(),
 378                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 379                     self.describe_field_from_ty(&ty, field, variant_index)
 380                 }
 381                 ty::Array(ty, _) | ty::Slice(ty) => {
 382                     self.describe_field_from_ty(&ty, field, variant_index)
 383                 }
 384                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 385                     // `tcx.upvars_mentioned(def_id)` returns an `Option`, which is `None` in case
 386                     // the closure comes from another crate. But in that case we wouldn't
 387                     // be borrowck'ing it, so we can just unwrap:
 388                     let (&var_id, _) = self
 389                         .infcx
 390                         .tcx
 391                         .upvars_mentioned(def_id)
 392                         .unwrap()
 393                         .get_index(field.index())
 394                         .unwrap();
 395
 396                     self.infcx.tcx.hir().name(var_id).to_string()
 397                 }
 398                 _ => {
 399                     // Might need a revision when the fields in trait RFC is implemented
 400                     // (https://github.com/rust-lang/rfcs/pull/1546)
 401                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 402                 }
 403             }
 404         }
 405     }
 406
 407     /// Add a note that a type does not implement `Copy`
 408     pub(super) fn note_type_does_not_implement_copy(
 409         &self,
 410         err: &mut DiagnosticBuilder<'a>,
 411         place_desc: &str,
 412         ty: Ty<'tcx>,
 413         span: Option<Span>,
 414     ) {
 415         let message = format!(
 416             "move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 417             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(_, 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(_, 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 {
 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,
 560     },
 561     // This access has a single span associated to it: common case.
 562     OtherUse(Span),
 563 }
 564
 565 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 566 pub(super) enum FnSelfUseKind {
 567     /// A normal method call of the form `receiver.foo(a, b, c)`
 568     Normal { self_arg: Ident, implicit_into_iter: bool },
 569     /// A call to `FnOnce::call_once`, desugared from `my_closure(a, b, c)`
 570     FnOnceCall,
 571     /// A call to an operator trait, desuraged from operator syntax (e.g. `a << b`)
 572     Operator { self_arg: Ident },
 573 }
 574
 575 impl UseSpans {
 576     pub(super) fn args_or_use(self) -> Span {
 577         match self {
 578             UseSpans::ClosureUse { args_span: span, .. }
 579             | UseSpans::FnSelfUse { var_span: span, .. }
 580             | UseSpans::OtherUse(span) => span,
 581         }
 582     }
 583
 584     pub(super) fn var_or_use(self) -> Span {
 585         match self {
 586             UseSpans::ClosureUse { var_span: span, .. }
 587             | UseSpans::FnSelfUse { var_span: span, .. }
 588             | UseSpans::OtherUse(span) => span,
 589         }
 590     }
 591
 592     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 593         match self {
 594             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 595             _ => None,
 596         }
 597     }
 598
 599     // Add a span label to the arguments of the closure, if it exists.
 600     pub(super) fn args_span_label(
 601         self,
 602         err: &mut DiagnosticBuilder<'_>,
 603         message: impl Into<String>,
 604     ) {
 605         if let UseSpans::ClosureUse { args_span, .. } = self {
 606             err.span_label(args_span, message);
 607         }
 608     }
 609
 610     // Add a span label to the use of the captured variable, if it exists.
 611     pub(super) fn var_span_label(
 612         self,
 613         err: &mut DiagnosticBuilder<'_>,
 614         message: impl Into<String>,
 615     ) {
 616         if let UseSpans::ClosureUse { var_span, .. } = self {
 617             err.span_label(var_span, message);
 618         }
 619     }
 620
 621     /// Returns `false` if this place is not used in a closure.
 622     pub(super) fn for_closure(&self) -> bool {
 623         match *self {
 624             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 625             _ => false,
 626         }
 627     }
 628
 629     /// Returns `false` if this place is not used in a generator.
 630     pub(super) fn for_generator(&self) -> bool {
 631         match *self {
 632             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 633             _ => false,
 634         }
 635     }
 636
 637     /// Describe the span associated with a use of a place.
 638     pub(super) fn describe(&self) -> String {
 639         match *self {
 640             UseSpans::ClosureUse { generator_kind, .. } => {
 641                 if generator_kind.is_some() {
 642                     " in generator".to_string()
 643                 } else {
 644                     " in closure".to_string()
 645                 }
 646             }
 647             _ => "".to_string(),
 648         }
 649     }
 650
 651     pub(super) fn or_else<F>(self, if_other: F) -> Self
 652     where
 653         F: FnOnce() -> Self,
 654     {
 655         match self {
 656             closure @ UseSpans::ClosureUse { .. } => closure,
 657             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 658             UseSpans::OtherUse(_) => if_other(),
 659         }
 660     }
 661 }
 662
 663 pub(super) enum BorrowedContentSource<'tcx> {
 664     DerefRawPointer,
 665     DerefMutableRef,
 666     DerefSharedRef,
 667     OverloadedDeref(Ty<'tcx>),
 668     OverloadedIndex(Ty<'tcx>),
 669 }
 670
 671 impl BorrowedContentSource<'tcx> {
 672     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 673         match *self {
 674             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 675             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 676             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 677             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 678                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 679                     "an `Rc`".to_string()
 680                 }
 681                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 682                     "an `Arc`".to_string()
 683                 }
 684                 _ => format!("dereference of `{}`", ty),
 685             },
 686             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 687         }
 688     }
 689
 690     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 691         match *self {
 692             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 693             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 694             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 695             // Overloaded deref and index operators should be evaluated into a
 696             // temporary. So we don't need a description here.
 697             BorrowedContentSource::OverloadedDeref(_)
 698             | BorrowedContentSource::OverloadedIndex(_) => None,
 699         }
 700     }
 701
 702     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 703         match *self {
 704             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 705             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 706             BorrowedContentSource::DerefMutableRef => {
 707                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 708             }
 709             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind {
 710                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 711                     "an `Rc`".to_string()
 712                 }
 713                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 714                     "an `Arc`".to_string()
 715                 }
 716                 _ => format!("a dereference of `{}`", ty),
 717             },
 718             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 719         }
 720     }
 721
 722     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 723         match func.kind {
 724             ty::FnDef(def_id, substs) => {
 725                 let trait_id = tcx.trait_of_item(def_id)?;
 726
 727                 let lang_items = tcx.lang_items();
 728                 if Some(trait_id) == lang_items.deref_trait()
 729                     || Some(trait_id) == lang_items.deref_mut_trait()
 730                 {
 731                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 732                 } else if Some(trait_id) == lang_items.index_trait()
 733                     || Some(trait_id) == lang_items.index_mut_trait()
 734                 {
 735                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 736                 } else {
 737                     None
 738                 }
 739             }
 740             _ => None,
 741         }
 742     }
 743 }
 744
 745 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 746     /// Finds the spans associated to a move or copy of move_place at location.
 747     pub(super) fn move_spans(
 748         &self,
 749         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 750         location: Location,
 751     ) -> UseSpans {
 752         use self::UseSpans::*;
 753
 754         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 755             Some(stmt) => stmt,
 756             None => return OtherUse(self.body.source_info(location).span),
 757         };
 758
 759         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 760         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 761             match kind {
 762                 box AggregateKind::Closure(def_id, _)
 763                 | box AggregateKind::Generator(def_id, _, _) => {
 764                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 765                     if let Some((args_span, generator_kind, var_span)) =
 766                         self.closure_span(*def_id, moved_place, places)
 767                     {
 768                         return ClosureUse { generator_kind, args_span, var_span };
 769                     }
 770                 }
 771                 _ => {}
 772             }
 773         }
 774
 775         let normal_ret = OtherUse(stmt.source_info.span);
 776
 777         // We are trying to find MIR of the form:
 778         // ```
 779         // _temp = _moved_val;
 780         // ...
 781         // FnSelfCall(_temp, ...)
 782         // ```
 783         //
 784         // where `_moved_val` is the place we generated the move error for,
 785         // `_temp` is some other local, and `FnSelfCall` is a function
 786         // that has a `self` parameter.
 787
 788         let target_temp = match stmt.kind {
 789             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 790                 temp.as_local().unwrap()
 791             }
 792             _ => return normal_ret,
 793         };
 794
 795         debug!("move_spans: target_temp = {:?}", target_temp);
 796
 797         if let Some(Terminator { kind: TerminatorKind::Call { func, args, fn_span, .. }, .. }) =
 798             &self.body[location.block].terminator
 799         {
 800             let mut method_did = None;
 801             if let Operand::Constant(box Constant { literal: ty::Const { ty, .. }, .. }) = func {
 802                 if let ty::FnDef(def_id, _) = ty.kind {
 803                     debug!("move_spans: fn = {:?}", def_id);
 804                     if let Some(ty::AssocItem { fn_has_self_parameter, .. }) =
 805                         self.infcx.tcx.opt_associated_item(def_id)
 806                     {
 807                         if *fn_has_self_parameter {
 808                             method_did = Some(def_id);
 809                         }
 810                     }
 811                 }
 812             }
 813
 814             let tcx = self.infcx.tcx;
 815             let method_did = if let Some(did) = method_did { did } else { return normal_ret };
 816
 817             if let [Operand::Move(self_place), ..] = **args {
 818                 if self_place.as_local() == Some(target_temp) {
 819                     let is_fn_once = tcx.parent(method_did) == tcx.lang_items().fn_once_trait();
 820                     let fn_call_span = *fn_span;
 821
 822                     let self_arg = tcx.fn_arg_names(method_did)[0];
 823
 824                     let kind = if is_fn_once {
 825                         FnSelfUseKind::FnOnceCall
 826                     } else if fn_call_span.is_desugaring(DesugaringKind::Operator) {
 827                         FnSelfUseKind::Operator { self_arg }
 828                     } else {
 829                         debug!(
 830                             "move_spans: method_did={:?}, fn_call_span={:?}",
 831                             method_did, fn_call_span
 832                         );
 833                         let implicit_into_iter = matches!(
 834                             fn_call_span.desugaring_kind(),
 835                             Some(DesugaringKind::ForLoop(ForLoopLoc::IntoIter))
 836                         );
 837                         FnSelfUseKind::Normal { self_arg, implicit_into_iter }
 838                     };
 839
 840                     return FnSelfUse {
 841                         var_span: stmt.source_info.span,
 842                         fn_call_span,
 843                         fn_span: self
 844                             .infcx
 845                             .tcx
 846                             .sess
 847                             .source_map()
 848                             .guess_head_span(self.infcx.tcx.def_span(method_did)),
 849                         kind,
 850                     };
 851                 }
 852             }
 853         }
 854         return normal_ret;
 855     }
 856
 857     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 858     /// and its usage of the local assigned at `location`.
 859     /// This is done by searching in statements succeeding `location`
 860     /// and originating from `maybe_closure_span`.
 861     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans {
 862         use self::UseSpans::*;
 863         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 864
 865         let target = match self.body[location.block].statements.get(location.statement_index) {
 866             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 867                 if let Some(local) = place.as_local() {
 868                     local
 869                 } else {
 870                     return OtherUse(use_span);
 871                 }
 872             }
 873             _ => return OtherUse(use_span),
 874         };
 875
 876         if self.body.local_kind(target) != LocalKind::Temp {
 877             // operands are always temporaries.
 878             return OtherUse(use_span);
 879         }
 880
 881         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 882             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 883                 stmt.kind
 884             {
 885                 let (def_id, is_generator) = match kind {
 886                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 887                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 888                     _ => continue,
 889                 };
 890
 891                 debug!(
 892                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 893                     def_id, is_generator, places
 894                 );
 895                 if let Some((args_span, generator_kind, var_span)) =
 896                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 897                 {
 898                     return ClosureUse { generator_kind, args_span, var_span };
 899                 } else {
 900                     return OtherUse(use_span);
 901                 }
 902             }
 903
 904             if use_span != stmt.source_info.span {
 905                 break;
 906             }
 907         }
 908
 909         OtherUse(use_span)
 910     }
 911
 912     /// Finds the span of a captured variable within a closure or generator.
 913     fn closure_span(
 914         &self,
 915         def_id: DefId,
 916         target_place: PlaceRef<'tcx>,
 917         places: &Vec<Operand<'tcx>>,
 918     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 919         debug!(
 920             "closure_span: def_id={:?} target_place={:?} places={:?}",
 921             def_id, target_place, places
 922         );
 923         let hir_id = self.infcx.tcx.hir().as_local_hir_id(def_id.as_local()?);
 924         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 925         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 926         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 927             for (upvar, place) in self.infcx.tcx.upvars_mentioned(def_id)?.values().zip(places) {
 928                 match place {
 929                     Operand::Copy(place) | Operand::Move(place)
 930                         if target_place == place.as_ref() =>
 931                     {
 932                         debug!("closure_span: found captured local {:?}", place);
 933                         let body = self.infcx.tcx.hir().body(*body_id);
 934                         let generator_kind = body.generator_kind();
 935                         return Some((*args_span, generator_kind, upvar.span));
 936                     }
 937                     _ => {}
 938                 }
 939             }
 940         }
 941         None
 942     }
 943
 944     /// Helper to retrieve span(s) of given borrow from the current MIR
 945     /// representation
 946     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans {
 947         let span = self.body.source_info(borrow.reserve_location).span;
 948         self.borrow_spans(span, borrow.reserve_location)
 949     }
 950 }