compiler/rustc_borrowck/src/diagnostics/mod.rs

   1 //! Borrow checker diagnostics.
   2
   3 use itertools::Itertools;
   4 use rustc_const_eval::util::{call_kind, CallDesugaringKind};
   5 use rustc_errors::{Applicability, Diagnostic};
   6 use rustc_hir as hir;
   7 use rustc_hir::def::{CtorKind, Namespace};
   8 use rustc_hir::GeneratorKind;
   9 use rustc_infer::infer::TyCtxtInferExt;
  10 use rustc_middle::mir::tcx::PlaceTy;
  11 use rustc_middle::mir::{
  12     AggregateKind, Constant, FakeReadCause, Field, Local, LocalInfo, LocalKind, Location, Operand,
  13     Place, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
  14 };
  15 use rustc_middle::ty::print::Print;
  16 use rustc_middle::ty::{self, DefIdTree, Instance, Ty, TyCtxt};
  17 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
  18 use rustc_span::def_id::LocalDefId;
  19 use rustc_span::{symbol::sym, Span, Symbol, DUMMY_SP};
  20 use rustc_target::abi::VariantIdx;
  21 use rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions;
  22
  23 use super::borrow_set::BorrowData;
  24 use super::MirBorrowckCtxt;
  25
  26 mod find_all_local_uses;
  27 mod find_use;
  28 mod outlives_suggestion;
  29 mod region_name;
  30 mod var_name;
  31
  32 mod bound_region_errors;
  33 mod conflict_errors;
  34 mod explain_borrow;
  35 mod move_errors;
  36 mod mutability_errors;
  37 mod region_errors;
  38
  39 pub(crate) use bound_region_errors::{ToUniverseInfo, UniverseInfo};
  40 pub(crate) use mutability_errors::AccessKind;
  41 pub(crate) use outlives_suggestion::OutlivesSuggestionBuilder;
  42 pub(crate) use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
  43 pub(crate) use region_name::{RegionName, RegionNameSource};
  44 pub(crate) use rustc_const_eval::util::CallKind;
  45
  46 pub(super) struct DescribePlaceOpt {
  47     pub including_downcast: bool,
  48
  49     /// Enable/Disable tuple fields.
  50     /// For example `x` tuple. if it's `true` `x.0`. Otherwise `x`
  51     pub including_tuple_field: bool,
  52 }
  53
  54 pub(super) struct IncludingTupleField(pub(super) bool);
  55
  56 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  57     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  58     /// is moved after being invoked.
  59     ///
  60     /// ```text
  61     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  62     ///       its environment
  63     ///   --> $DIR/issue-42065.rs:16:29
  64     ///    |
  65     /// LL |         for (key, value) in dict {
  66     ///    |                             ^^^^
  67     /// ```
  68     pub(super) fn add_moved_or_invoked_closure_note(
  69         &self,
  70         location: Location,
  71         place: PlaceRef<'tcx>,
  72         diag: &mut Diagnostic,
  73     ) {
  74         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  75         let mut target = place.local_or_deref_local();
  76         for stmt in &self.body[location.block].statements[location.statement_index..] {
  77             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  78             if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
  79                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  80                 match from {
  81                     Operand::Copy(ref place) | Operand::Move(ref place)
  82                         if target == place.local_or_deref_local() =>
  83                     {
  84                         target = into.local_or_deref_local()
  85                     }
  86                     _ => {}
  87                 }
  88             }
  89         }
  90
  91         // Check if we are attempting to call a closure after it has been invoked.
  92         let terminator = self.body[location.block].terminator();
  93         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  94         if let TerminatorKind::Call {
  95             func: Operand::Constant(box Constant { literal, .. }),
  96             args,
  97             ..
  98         } = &terminator.kind
  99         {
 100             if let ty::FnDef(id, _) = *literal.ty().kind() {
 101                 debug!("add_moved_or_invoked_closure_note: id={:?}", id);
 102                 if Some(self.infcx.tcx.parent(id)) == self.infcx.tcx.lang_items().fn_once_trait() {
 103                     let closure = match args.first() {
 104                         Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
 105                             if target == place.local_or_deref_local() =>
 106                         {
 107                             place.local_or_deref_local().unwrap()
 108                         }
 109                         _ => return,
 110                     };
 111
 112                     debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
 113                     if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind() {
 114                         let did = did.expect_local();
 115                         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 116
 117                         if let Some((span, hir_place)) =
 118                             self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 119                         {
 120                             diag.span_note(
 121                                 *span,
 122                                 &format!(
 123                                     "closure cannot be invoked more than once because it moves the \
 124                                     variable `{}` out of its environment",
 125                                     ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
 126                                 ),
 127                             );
 128                             return;
 129                         }
 130                     }
 131                 }
 132             }
 133         }
 134
 135         // Check if we are just moving a closure after it has been invoked.
 136         if let Some(target) = target {
 137             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind() {
 138                 let did = did.expect_local();
 139                 let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 140
 141                 if let Some((span, hir_place)) =
 142                     self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 143                 {
 144                     diag.span_note(
 145                         *span,
 146                         &format!(
 147                             "closure cannot be moved more than once as it is not `Copy` due to \
 148                              moving the variable `{}` out of its environment",
 149                             ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
 150                         ),
 151                     );
 152                 }
 153             }
 154         }
 155     }
 156
 157     /// End-user visible description of `place` if one can be found.
 158     /// If the place is a temporary for instance, `"value"` will be returned.
 159     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 160         match self.describe_place(place_ref) {
 161             Some(mut descr) => {
 162                 // Surround descr with `backticks`.
 163                 descr.reserve(2);
 164                 descr.insert(0, '`');
 165                 descr.push('`');
 166                 descr
 167             }
 168             None => "value".to_string(),
 169         }
 170     }
 171
 172     /// End-user visible description of `place` if one can be found.
 173     /// If the place is a temporary for instance, `None` will be returned.
 174     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 175         self.describe_place_with_options(
 176             place_ref,
 177             DescribePlaceOpt { including_downcast: false, including_tuple_field: true },
 178         )
 179     }
 180
 181     /// End-user visible description of `place` if one can be found. If the place is a temporary
 182     /// for instance, `None` will be returned.
 183     /// `IncludingDowncast` parameter makes the function return `None` if `ProjectionElem` is
 184     /// `Downcast` and `IncludingDowncast` is true
 185     pub(super) fn describe_place_with_options(
 186         &self,
 187         place: PlaceRef<'tcx>,
 188         opt: DescribePlaceOpt,
 189     ) -> Option<String> {
 190         let local = place.local;
 191         let mut autoderef_index = None;
 192         let mut buf = String::new();
 193         let mut ok = self.append_local_to_string(local, &mut buf);
 194
 195         for (index, elem) in place.projection.into_iter().enumerate() {
 196             match elem {
 197                 ProjectionElem::Deref => {
 198                     if index == 0 {
 199                         if self.body.local_decls[local].is_ref_for_guard() {
 200                             continue;
 201                         }
 202                         if let Some(box LocalInfo::StaticRef { def_id, .. }) =
 203                             &self.body.local_decls[local].local_info
 204                         {
 205                             buf.push_str(self.infcx.tcx.item_name(*def_id).as_str());
 206                             ok = Ok(());
 207                             continue;
 208                         }
 209                     }
 210                     if let Some(field) = self.is_upvar_field_projection(PlaceRef {
 211                         local,
 212                         projection: place.projection.split_at(index + 1).0,
 213                     }) {
 214                         let var_index = field.index();
 215                         buf = self.upvars[var_index].place.to_string(self.infcx.tcx);
 216                         ok = Ok(());
 217                         if !self.upvars[var_index].by_ref {
 218                             buf.insert(0, '*');
 219                         }
 220                     } else {
 221                         if autoderef_index.is_none() {
 222                             autoderef_index =
 223                                 match place.projection.into_iter().rev().find_position(|elem| {
 224                                     !matches!(
 225                                         elem,
 226                                         ProjectionElem::Deref | ProjectionElem::Downcast(..)
 227                                     )
 228                                 }) {
 229                                     Some((index, _)) => Some(place.projection.len() - index),
 230                                     None => Some(0),
 231                                 };
 232                         }
 233                         if index >= autoderef_index.unwrap() {
 234                             buf.insert(0, '*');
 235                         }
 236                     }
 237                 }
 238                 ProjectionElem::Downcast(..) if opt.including_downcast => return None,
 239                 ProjectionElem::Downcast(..) => (),
 240                 ProjectionElem::Field(field, _ty) => {
 241                     // FIXME(project-rfc_2229#36): print capture precisely here.
 242                     if let Some(field) = self.is_upvar_field_projection(PlaceRef {
 243                         local,
 244                         projection: place.projection.split_at(index + 1).0,
 245                     }) {
 246                         buf = self.upvars[field.index()].place.to_string(self.infcx.tcx);
 247                         ok = Ok(());
 248                     } else {
 249                         let field_name = self.describe_field(
 250                             PlaceRef { local, projection: place.projection.split_at(index).0 },
 251                             *field,
 252                             IncludingTupleField(opt.including_tuple_field),
 253                         );
 254                         if let Some(field_name_str) = field_name {
 255                             buf.push('.');
 256                             buf.push_str(&field_name_str);
 257                         }
 258                     }
 259                 }
 260                 ProjectionElem::Index(index) => {
 261                     buf.push('[');
 262                     if self.append_local_to_string(*index, &mut buf).is_err() {
 263                         buf.push('_');
 264                     }
 265                     buf.push(']');
 266                 }
 267                 ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 268                     // Since it isn't possible to borrow an element on a particular index and
 269                     // then use another while the borrow is held, don't output indices details
 270                     // to avoid confusing the end-user
 271                     buf.push_str("[..]");
 272                 }
 273             }
 274         }
 275         ok.ok().map(|_| buf)
 276     }
 277
 278     fn describe_name(&self, place: PlaceRef<'tcx>) -> Option<Symbol> {
 279         for elem in place.projection.into_iter() {
 280             match elem {
 281                 ProjectionElem::Downcast(Some(name), _) => {
 282                     return Some(*name);
 283                 }
 284                 _ => {}
 285             }
 286         }
 287         None
 288     }
 289
 290     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 291     /// a name, or its name was generated by the compiler, then `Err` is returned
 292     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 293         let decl = &self.body.local_decls[local];
 294         match self.local_names[local] {
 295             Some(name) if !decl.from_compiler_desugaring() => {
 296                 buf.push_str(name.as_str());
 297                 Ok(())
 298             }
 299             _ => Err(()),
 300         }
 301     }
 302
 303     /// End-user visible description of the `field`nth field of `base`
 304     fn describe_field(
 305         &self,
 306         place: PlaceRef<'tcx>,
 307         field: Field,
 308         including_tuple_field: IncludingTupleField,
 309     ) -> Option<String> {
 310         let place_ty = match place {
 311             PlaceRef { local, projection: [] } => PlaceTy::from_ty(self.body.local_decls[local].ty),
 312             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 313                 ProjectionElem::Deref
 314                 | ProjectionElem::Index(..)
 315                 | ProjectionElem::ConstantIndex { .. }
 316                 | ProjectionElem::Subslice { .. } => {
 317                     PlaceRef { local, projection: proj_base }.ty(self.body, self.infcx.tcx)
 318                 }
 319                 ProjectionElem::Downcast(..) => place.ty(self.body, self.infcx.tcx),
 320                 ProjectionElem::Field(_, field_type) => PlaceTy::from_ty(*field_type),
 321             },
 322         };
 323         self.describe_field_from_ty(
 324             place_ty.ty,
 325             field,
 326             place_ty.variant_index,
 327             including_tuple_field,
 328         )
 329     }
 330
 331     /// End-user visible description of the `field_index`nth field of `ty`
 332     fn describe_field_from_ty(
 333         &self,
 334         ty: Ty<'_>,
 335         field: Field,
 336         variant_index: Option<VariantIdx>,
 337         including_tuple_field: IncludingTupleField,
 338     ) -> Option<String> {
 339         if ty.is_box() {
 340             // If the type is a box, the field is described from the boxed type
 341             self.describe_field_from_ty(ty.boxed_ty(), field, variant_index, including_tuple_field)
 342         } else {
 343             match *ty.kind() {
 344                 ty::Adt(def, _) => {
 345                     let variant = if let Some(idx) = variant_index {
 346                         assert!(def.is_enum());
 347                         &def.variant(idx)
 348                     } else {
 349                         def.non_enum_variant()
 350                     };
 351                     if !including_tuple_field.0 && variant.ctor_kind == CtorKind::Fn {
 352                         return None;
 353                     }
 354                     Some(variant.fields[field.index()].name.to_string())
 355                 }
 356                 ty::Tuple(_) => Some(field.index().to_string()),
 357                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 358                     self.describe_field_from_ty(ty, field, variant_index, including_tuple_field)
 359                 }
 360                 ty::Array(ty, _) | ty::Slice(ty) => {
 361                     self.describe_field_from_ty(ty, field, variant_index, including_tuple_field)
 362                 }
 363                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 364                     // We won't be borrowck'ing here if the closure came from another crate,
 365                     // so it's safe to call `expect_local`.
 366                     //
 367                     // We know the field exists so it's safe to call operator[] and `unwrap` here.
 368                     let def_id = def_id.expect_local();
 369                     let var_id = self
 370                         .infcx
 371                         .tcx
 372                         .typeck(def_id)
 373                         .closure_min_captures_flattened(def_id)
 374                         .nth(field.index())
 375                         .unwrap()
 376                         .get_root_variable();
 377
 378                     Some(self.infcx.tcx.hir().name(var_id).to_string())
 379                 }
 380                 _ => {
 381                     // Might need a revision when the fields in trait RFC is implemented
 382                     // (https://github.com/rust-lang/rfcs/pull/1546)
 383                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 384                 }
 385             }
 386         }
 387     }
 388
 389     /// Add a note that a type does not implement `Copy`
 390     pub(super) fn note_type_does_not_implement_copy(
 391         &self,
 392         err: &mut Diagnostic,
 393         place_desc: &str,
 394         ty: Ty<'tcx>,
 395         span: Option<Span>,
 396         move_prefix: &str,
 397     ) {
 398         let message = format!(
 399             "{}move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 400             move_prefix, place_desc, ty,
 401         );
 402         if let Some(span) = span {
 403             err.span_label(span, message);
 404         } else {
 405             err.note(&message);
 406         }
 407     }
 408
 409     pub(super) fn borrowed_content_source(
 410         &self,
 411         deref_base: PlaceRef<'tcx>,
 412     ) -> BorrowedContentSource<'tcx> {
 413         let tcx = self.infcx.tcx;
 414
 415         // Look up the provided place and work out the move path index for it,
 416         // we'll use this to check whether it was originally from an overloaded
 417         // operator.
 418         match self.move_data.rev_lookup.find(deref_base) {
 419             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 420                 debug!("borrowed_content_source: mpi={:?}", mpi);
 421
 422                 for i in &self.move_data.init_path_map[mpi] {
 423                     let init = &self.move_data.inits[*i];
 424                     debug!("borrowed_content_source: init={:?}", init);
 425                     // We're only interested in statements that initialized a value, not the
 426                     // initializations from arguments.
 427                     let InitLocation::Statement(loc) = init.location else { continue };
 428
 429                     let bbd = &self.body[loc.block];
 430                     let is_terminator = bbd.statements.len() == loc.statement_index;
 431                     debug!(
 432                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 433                         loc, is_terminator,
 434                     );
 435                     if !is_terminator {
 436                         continue;
 437                     } else if let Some(Terminator {
 438                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 439                         ..
 440                     }) = bbd.terminator
 441                     {
 442                         if let Some(source) =
 443                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 444                         {
 445                             return source;
 446                         }
 447                     }
 448                 }
 449             }
 450             // Base is a `static` so won't be from an overloaded operator
 451             _ => (),
 452         };
 453
 454         // If we didn't find an overloaded deref or index, then assume it's a
 455         // built in deref and check the type of the base.
 456         let base_ty = deref_base.ty(self.body, tcx).ty;
 457         if base_ty.is_unsafe_ptr() {
 458             BorrowedContentSource::DerefRawPointer
 459         } else if base_ty.is_mutable_ptr() {
 460             BorrowedContentSource::DerefMutableRef
 461         } else {
 462             BorrowedContentSource::DerefSharedRef
 463         }
 464     }
 465
 466     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 467     /// name where required.
 468     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 469         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, Namespace::TypeNS);
 470
 471         // We need to add synthesized lifetimes where appropriate. We do
 472         // this by hooking into the pretty printer and telling it to label the
 473         // lifetimes without names with the value `'0`.
 474         if let ty::Ref(region, ..) = ty.kind() {
 475             match **region {
 476                 ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
 477                 | ty::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 478                     printer.region_highlight_mode.highlighting_bound_region(br, counter)
 479                 }
 480                 _ => {}
 481             }
 482         }
 483
 484         ty.print(printer).unwrap().into_buffer()
 485     }
 486
 487     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 488     /// synthesized lifetime name where required.
 489     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 490         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, Namespace::TypeNS);
 491
 492         let region = if let ty::Ref(region, ..) = ty.kind() {
 493             match **region {
 494                 ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
 495                 | ty::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 496                     printer.region_highlight_mode.highlighting_bound_region(br, counter)
 497                 }
 498                 _ => {}
 499             }
 500             region
 501         } else {
 502             bug!("ty for annotation of borrow region is not a reference");
 503         };
 504
 505         region.print(printer).unwrap().into_buffer()
 506     }
 507 }
 508
 509 /// The span(s) associated to a use of a place.
 510 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 511 pub(super) enum UseSpans<'tcx> {
 512     /// The access is caused by capturing a variable for a closure.
 513     ClosureUse {
 514         /// This is true if the captured variable was from a generator.
 515         generator_kind: Option<GeneratorKind>,
 516         /// The span of the args of the closure, including the `move` keyword if
 517         /// it's present.
 518         args_span: Span,
 519         /// The span of the use resulting in capture kind
 520         /// Check `ty::CaptureInfo` for more details
 521         capture_kind_span: Span,
 522         /// The span of the use resulting in the captured path
 523         /// Check `ty::CaptureInfo` for more details
 524         path_span: Span,
 525     },
 526     /// The access is caused by using a variable as the receiver of a method
 527     /// that takes 'self'
 528     FnSelfUse {
 529         /// The span of the variable being moved
 530         var_span: Span,
 531         /// The span of the method call on the variable
 532         fn_call_span: Span,
 533         /// The definition span of the method being called
 534         fn_span: Span,
 535         kind: CallKind<'tcx>,
 536     },
 537     /// This access is caused by a `match` or `if let` pattern.
 538     PatUse(Span),
 539     /// This access has a single span associated to it: common case.
 540     OtherUse(Span),
 541 }
 542
 543 impl UseSpans<'_> {
 544     pub(super) fn args_or_use(self) -> Span {
 545         match self {
 546             UseSpans::ClosureUse { args_span: span, .. }
 547             | UseSpans::PatUse(span)
 548             | UseSpans::OtherUse(span) => span,
 549             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 550                 fn_call_span
 551             }
 552             UseSpans::FnSelfUse { var_span, .. } => var_span,
 553         }
 554     }
 555
 556     /// Returns the span of `self`, in the case of a `ClosureUse` returns the `path_span`
 557     pub(super) fn var_or_use_path_span(self) -> Span {
 558         match self {
 559             UseSpans::ClosureUse { path_span: span, .. }
 560             | UseSpans::PatUse(span)
 561             | UseSpans::OtherUse(span) => span,
 562             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 563                 fn_call_span
 564             }
 565             UseSpans::FnSelfUse { var_span, .. } => var_span,
 566         }
 567     }
 568
 569     /// Returns the span of `self`, in the case of a `ClosureUse` returns the `capture_kind_span`
 570     pub(super) fn var_or_use(self) -> Span {
 571         match self {
 572             UseSpans::ClosureUse { capture_kind_span: span, .. }
 573             | UseSpans::PatUse(span)
 574             | UseSpans::OtherUse(span) => span,
 575             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 576                 fn_call_span
 577             }
 578             UseSpans::FnSelfUse { var_span, .. } => var_span,
 579         }
 580     }
 581
 582     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 583         match self {
 584             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 585             _ => None,
 586         }
 587     }
 588
 589     // Add a span label to the arguments of the closure, if it exists.
 590     pub(super) fn args_span_label(self, err: &mut Diagnostic, message: impl Into<String>) {
 591         if let UseSpans::ClosureUse { args_span, .. } = self {
 592             err.span_label(args_span, message);
 593         }
 594     }
 595
 596     // Add a span label to the use of the captured variable, if it exists.
 597     // only adds label to the `path_span`
 598     pub(super) fn var_span_label_path_only(self, err: &mut Diagnostic, message: impl Into<String>) {
 599         if let UseSpans::ClosureUse { path_span, .. } = self {
 600             err.span_label(path_span, message);
 601         }
 602     }
 603
 604     // Add a span label to the use of the captured variable, if it exists.
 605     pub(super) fn var_span_label(
 606         self,
 607         err: &mut Diagnostic,
 608         message: impl Into<String>,
 609         kind_desc: impl Into<String>,
 610     ) {
 611         if let UseSpans::ClosureUse { capture_kind_span, path_span, .. } = self {
 612             if capture_kind_span == path_span {
 613                 err.span_label(capture_kind_span, message);
 614             } else {
 615                 let capture_kind_label =
 616                     format!("capture is {} because of use here", kind_desc.into());
 617                 let path_label = message;
 618                 err.span_label(capture_kind_span, capture_kind_label);
 619                 err.span_label(path_span, path_label);
 620             }
 621         }
 622     }
 623
 624     /// Returns `false` if this place is not used in a closure.
 625     pub(super) fn for_closure(&self) -> bool {
 626         match *self {
 627             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 628             _ => false,
 629         }
 630     }
 631
 632     /// Returns `false` if this place is not used in a generator.
 633     pub(super) fn for_generator(&self) -> bool {
 634         match *self {
 635             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 636             _ => false,
 637         }
 638     }
 639
 640     /// Describe the span associated with a use of a place.
 641     pub(super) fn describe(&self) -> &str {
 642         match *self {
 643             UseSpans::ClosureUse { generator_kind, .. } => {
 644                 if generator_kind.is_some() {
 645                     " in generator"
 646                 } else {
 647                     " in closure"
 648                 }
 649             }
 650             _ => "",
 651         }
 652     }
 653
 654     pub(super) fn or_else<F>(self, if_other: F) -> Self
 655     where
 656         F: FnOnce() -> Self,
 657     {
 658         match self {
 659             closure @ UseSpans::ClosureUse { .. } => closure,
 660             UseSpans::PatUse(_) | UseSpans::OtherUse(_) => if_other(),
 661             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 662         }
 663     }
 664 }
 665
 666 pub(super) enum BorrowedContentSource<'tcx> {
 667     DerefRawPointer,
 668     DerefMutableRef,
 669     DerefSharedRef,
 670     OverloadedDeref(Ty<'tcx>),
 671     OverloadedIndex(Ty<'tcx>),
 672 }
 673
 674 impl<'tcx> BorrowedContentSource<'tcx> {
 675     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 676         match *self {
 677             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 678             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 679             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 680             BorrowedContentSource::OverloadedDeref(ty) => ty
 681                 .ty_adt_def()
 682                 .and_then(|adt| match tcx.get_diagnostic_name(adt.did())? {
 683                     name @ (sym::Rc | sym::Arc) => Some(format!("an `{}`", name)),
 684                     _ => None,
 685                 })
 686                 .unwrap_or_else(|| format!("dereference of `{}`", ty)),
 687             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 688         }
 689     }
 690
 691     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 692         match *self {
 693             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 694             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 695             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 696             // Overloaded deref and index operators should be evaluated into a
 697             // temporary. So we don't need a description here.
 698             BorrowedContentSource::OverloadedDeref(_)
 699             | BorrowedContentSource::OverloadedIndex(_) => None,
 700         }
 701     }
 702
 703     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 704         match *self {
 705             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 706             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 707             BorrowedContentSource::DerefMutableRef => {
 708                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 709             }
 710             BorrowedContentSource::OverloadedDeref(ty) => ty
 711                 .ty_adt_def()
 712                 .and_then(|adt| match tcx.get_diagnostic_name(adt.did())? {
 713                     name @ (sym::Rc | sym::Arc) => Some(format!("an `{}`", name)),
 714                     _ => None,
 715                 })
 716                 .unwrap_or_else(|| format!("dereference of `{}`", ty)),
 717             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 718         }
 719     }
 720
 721     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 722         match *func.kind() {
 723             ty::FnDef(def_id, substs) => {
 724                 let trait_id = tcx.trait_of_item(def_id)?;
 725
 726                 let lang_items = tcx.lang_items();
 727                 if Some(trait_id) == lang_items.deref_trait()
 728                     || Some(trait_id) == lang_items.deref_mut_trait()
 729                 {
 730                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 731                 } else if Some(trait_id) == lang_items.index_trait()
 732                     || Some(trait_id) == lang_items.index_mut_trait()
 733                 {
 734                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 735                 } else {
 736                     None
 737                 }
 738             }
 739             _ => None,
 740         }
 741     }
 742 }
 743
 744 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 745     /// Finds the spans associated to a move or copy of move_place at location.
 746     pub(super) fn move_spans(
 747         &self,
 748         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 749         location: Location,
 750     ) -> UseSpans<'tcx> {
 751         use self::UseSpans::*;
 752
 753         let Some(stmt) = self.body[location.block].statements.get(location.statement_index) else {
 754             return OtherUse(self.body.source_info(location).span);
 755         };
 756
 757         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 758         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 759             match **kind {
 760                 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
 761                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 762                     if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 763                         self.closure_span(def_id, moved_place, places)
 764                     {
 765                         return ClosureUse {
 766                             generator_kind,
 767                             args_span,
 768                             capture_kind_span,
 769                             path_span,
 770                         };
 771                     }
 772                 }
 773                 _ => {}
 774             }
 775         }
 776
 777         // StatementKind::FakeRead only contains a def_id if they are introduced as a result
 778         // of pattern matching within a closure.
 779         if let StatementKind::FakeRead(box (cause, ref place)) = stmt.kind {
 780             match cause {
 781                 FakeReadCause::ForMatchedPlace(Some(closure_def_id))
 782                 | FakeReadCause::ForLet(Some(closure_def_id)) => {
 783                     debug!("move_spans: def_id={:?} place={:?}", closure_def_id, place);
 784                     let places = &[Operand::Move(*place)];
 785                     if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 786                         self.closure_span(closure_def_id, moved_place, places)
 787                     {
 788                         return ClosureUse {
 789                             generator_kind,
 790                             args_span,
 791                             capture_kind_span,
 792                             path_span,
 793                         };
 794                     }
 795                 }
 796                 _ => {}
 797             }
 798         }
 799
 800         let normal_ret =
 801             if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
 802                 PatUse(stmt.source_info.span)
 803             } else {
 804                 OtherUse(stmt.source_info.span)
 805             };
 806
 807         // We are trying to find MIR of the form:
 808         // ```
 809         // _temp = _moved_val;
 810         // ...
 811         // FnSelfCall(_temp, ...)
 812         // ```
 813         //
 814         // where `_moved_val` is the place we generated the move error for,
 815         // `_temp` is some other local, and `FnSelfCall` is a function
 816         // that has a `self` parameter.
 817
 818         let target_temp = match stmt.kind {
 819             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 820                 temp.as_local().unwrap()
 821             }
 822             _ => return normal_ret,
 823         };
 824
 825         debug!("move_spans: target_temp = {:?}", target_temp);
 826
 827         if let Some(Terminator {
 828             kind: TerminatorKind::Call { fn_span, from_hir_call, .. }, ..
 829         }) = &self.body[location.block].terminator
 830         {
 831             let Some((method_did, method_substs)) =
 832                 rustc_const_eval::util::find_self_call(
 833                     self.infcx.tcx,
 834                     &self.body,
 835                     target_temp,
 836                     location.block,
 837                 )
 838             else {
 839                 return normal_ret;
 840             };
 841
 842             let kind = call_kind(
 843                 self.infcx.tcx,
 844                 self.param_env,
 845                 method_did,
 846                 method_substs,
 847                 *fn_span,
 848                 *from_hir_call,
 849                 Some(self.infcx.tcx.fn_arg_names(method_did)[0]),
 850             );
 851
 852             return FnSelfUse {
 853                 var_span: stmt.source_info.span,
 854                 fn_call_span: *fn_span,
 855                 fn_span: self.infcx.tcx.def_span(method_did),
 856                 kind,
 857             };
 858         }
 859         normal_ret
 860     }
 861
 862     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 863     /// and its usage of the local assigned at `location`.
 864     /// This is done by searching in statements succeeding `location`
 865     /// and originating from `maybe_closure_span`.
 866     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans<'tcx> {
 867         use self::UseSpans::*;
 868         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 869
 870         let target = match self.body[location.block].statements.get(location.statement_index) {
 871             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 872                 if let Some(local) = place.as_local() {
 873                     local
 874                 } else {
 875                     return OtherUse(use_span);
 876                 }
 877             }
 878             _ => return OtherUse(use_span),
 879         };
 880
 881         if self.body.local_kind(target) != LocalKind::Temp {
 882             // operands are always temporaries.
 883             return OtherUse(use_span);
 884         }
 885
 886         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 887             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 888                 stmt.kind
 889             {
 890                 let (&def_id, is_generator) = match kind {
 891                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 892                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 893                     _ => continue,
 894                 };
 895
 896                 debug!(
 897                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 898                     def_id, is_generator, places
 899                 );
 900                 if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 901                     self.closure_span(def_id, Place::from(target).as_ref(), places)
 902                 {
 903                     return ClosureUse { generator_kind, args_span, capture_kind_span, path_span };
 904                 } else {
 905                     return OtherUse(use_span);
 906                 }
 907             }
 908
 909             if use_span != stmt.source_info.span {
 910                 break;
 911             }
 912         }
 913
 914         OtherUse(use_span)
 915     }
 916
 917     /// Finds the spans of a captured place within a closure or generator.
 918     /// The first span is the location of the use resulting in the capture kind of the capture
 919     /// The second span is the location the use resulting in the captured path of the capture
 920     fn closure_span(
 921         &self,
 922         def_id: LocalDefId,
 923         target_place: PlaceRef<'tcx>,
 924         places: &[Operand<'tcx>],
 925     ) -> Option<(Span, Option<GeneratorKind>, Span, Span)> {
 926         debug!(
 927             "closure_span: def_id={:?} target_place={:?} places={:?}",
 928             def_id, target_place, places
 929         );
 930         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(def_id);
 931         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 932         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 933         if let hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }) = expr {
 934             for (captured_place, place) in
 935                 self.infcx.tcx.typeck(def_id).closure_min_captures_flattened(def_id).zip(places)
 936             {
 937                 match place {
 938                     Operand::Copy(place) | Operand::Move(place)
 939                         if target_place == place.as_ref() =>
 940                     {
 941                         debug!("closure_span: found captured local {:?}", place);
 942                         let body = self.infcx.tcx.hir().body(body);
 943                         let generator_kind = body.generator_kind();
 944
 945                         return Some((
 946                             fn_decl_span,
 947                             generator_kind,
 948                             captured_place.get_capture_kind_span(self.infcx.tcx),
 949                             captured_place.get_path_span(self.infcx.tcx),
 950                         ));
 951                     }
 952                     _ => {}
 953                 }
 954             }
 955         }
 956         None
 957     }
 958
 959     /// Helper to retrieve span(s) of given borrow from the current MIR
 960     /// representation
 961     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans<'tcx> {
 962         let span = self.body.source_info(borrow.reserve_location).span;
 963         self.borrow_spans(span, borrow.reserve_location)
 964     }
 965
 966     fn explain_captures(
 967         &mut self,
 968         err: &mut Diagnostic,
 969         span: Span,
 970         move_span: Span,
 971         move_spans: UseSpans<'tcx>,
 972         moved_place: Place<'tcx>,
 973         used_place: Option<PlaceRef<'tcx>>,
 974         partially_str: &str,
 975         loop_message: &str,
 976         move_msg: &str,
 977         is_loop_move: bool,
 978         maybe_reinitialized_locations_is_empty: bool,
 979     ) {
 980         if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
 981             let place_name = self
 982                 .describe_place(moved_place.as_ref())
 983                 .map(|n| format!("`{}`", n))
 984                 .unwrap_or_else(|| "value".to_owned());
 985             match kind {
 986                 CallKind::FnCall { fn_trait_id, .. }
 987                     if Some(fn_trait_id) == self.infcx.tcx.lang_items().fn_once_trait() =>
 988                 {
 989                     err.span_label(
 990                         fn_call_span,
 991                         &format!(
 992                             "{} {}moved due to this call{}",
 993                             place_name, partially_str, loop_message
 994                         ),
 995                     );
 996                     err.span_note(
 997                         var_span,
 998                         "this value implements `FnOnce`, which causes it to be moved when called",
 999                     );
1000                 }
1001                 CallKind::Operator { self_arg, .. } => {
1002                     let self_arg = self_arg.unwrap();
1003                     err.span_label(
1004                         fn_call_span,
1005                         &format!(
1006                             "{} {}moved due to usage in operator{}",
1007                             place_name, partially_str, loop_message
1008                         ),
1009                     );
1010                     if self.fn_self_span_reported.insert(fn_span) {
1011                         err.span_note(
1012                             // Check whether the source is accessible
1013                             if self.infcx.tcx.sess.source_map().is_span_accessible(self_arg.span) {
1014                                 self_arg.span
1015                             } else {
1016                                 fn_call_span
1017                             },
1018                             "calling this operator moves the left-hand side",
1019                         );
1020                     }
1021                 }
1022                 CallKind::Normal { self_arg, desugaring, is_option_or_result } => {
1023                     let self_arg = self_arg.unwrap();
1024                     if let Some((CallDesugaringKind::ForLoopIntoIter, _)) = desugaring {
1025                         let ty = moved_place.ty(self.body, self.infcx.tcx).ty;
1026                         let suggest = match self.infcx.tcx.get_diagnostic_item(sym::IntoIterator) {
1027                             Some(def_id) => self.infcx.tcx.infer_ctxt().enter(|infcx| {
1028                                 type_known_to_meet_bound_modulo_regions(
1029                                     &infcx,
1030                                     self.param_env,
1031                                     infcx.tcx.mk_imm_ref(
1032                                         infcx.tcx.lifetimes.re_erased,
1033                                         infcx.tcx.erase_regions(ty),
1034                                     ),
1035                                     def_id,
1036                                     DUMMY_SP,
1037                                 )
1038                             }),
1039                             _ => false,
1040                         };
1041                         if suggest {
1042                             err.span_suggestion_verbose(
1043                                 move_span.shrink_to_lo(),
1044                                 &format!(
1045                                     "consider iterating over a slice of the `{}`'s content to \
1046                                      avoid moving into the `for` loop",
1047                                     ty,
1048                                 ),
1049                                 "&",
1050                                 Applicability::MaybeIncorrect,
1051                             );
1052                         }
1053
1054                         err.span_label(
1055                             fn_call_span,
1056                             &format!(
1057                                 "{} {}moved due to this implicit call to `.into_iter()`{}",
1058                                 place_name, partially_str, loop_message
1059                             ),
1060                         );
1061                         // If we have a `&mut` ref, we need to reborrow.
1062                         if let Some(ty::Ref(_, _, hir::Mutability::Mut)) = used_place
1063                             .map(|used_place| used_place.ty(self.body, self.infcx.tcx).ty.kind())
1064                         {
1065                             // If we are in a loop this will be suggested later.
1066                             if !is_loop_move {
1067                                 err.span_suggestion_verbose(
1068                                     move_span.shrink_to_lo(),
1069                                     &format!(
1070                                         "consider creating a fresh reborrow of {} here",
1071                                         self.describe_place(moved_place.as_ref())
1072                                             .map(|n| format!("`{}`", n))
1073                                             .unwrap_or_else(|| "the mutable reference".to_string()),
1074                                     ),
1075                                     "&mut *",
1076                                     Applicability::MachineApplicable,
1077                                 );
1078                             }
1079                         }
1080                     } else {
1081                         err.span_label(
1082                             fn_call_span,
1083                             &format!(
1084                                 "{} {}moved due to this method call{}",
1085                                 place_name, partially_str, loop_message
1086                             ),
1087                         );
1088                     }
1089                     if is_option_or_result && maybe_reinitialized_locations_is_empty {
1090                         err.span_suggestion_verbose(
1091                             fn_call_span.shrink_to_lo(),
1092                             "consider calling `.as_ref()` to borrow the type's contents",
1093                             "as_ref().",
1094                             Applicability::MachineApplicable,
1095                         );
1096                     }
1097                     // Avoid pointing to the same function in multiple different
1098                     // error messages.
1099                     if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span) {
1100                         err.span_note(
1101                             self_arg.span,
1102                             &format!("this function takes ownership of the receiver `self`, which moves {}", place_name)
1103                         );
1104                     }
1105                 }
1106                 // Other desugarings takes &self, which cannot cause a move
1107                 _ => {}
1108             }
1109         } else {
1110             if move_span != span || !loop_message.is_empty() {
1111                 err.span_label(
1112                     move_span,
1113                     format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
1114                 );
1115             }
1116             // If the move error occurs due to a loop, don't show
1117             // another message for the same span
1118             if loop_message.is_empty() {
1119                 move_spans.var_span_label(
1120                     err,
1121                     format!("variable {}moved due to use{}", partially_str, move_spans.describe()),
1122                     "moved",
1123                 );
1124             }
1125         }
1126     }
1127 }