compiler/rustc_borrowck/src/diagnostics/mod.rs

   1 //! Borrow checker diagnostics.
   2
   3 use rustc_const_eval::util::{call_kind, CallDesugaringKind};
   4 use rustc_errors::{Applicability, Diagnostic};
   5 use rustc_hir as hir;
   6 use rustc_hir::def::Namespace;
   7 use rustc_hir::def_id::DefId;
   8 use rustc_hir::GeneratorKind;
   9 use rustc_infer::infer::TyCtxtInferExt;
  10 use rustc_middle::mir::{
  11     AggregateKind, Constant, FakeReadCause, Field, Local, LocalInfo, LocalKind, Location, Operand,
  12     Place, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
  13 };
  14 use rustc_middle::ty::print::Print;
  15 use rustc_middle::ty::{self, DefIdTree, Instance, Ty, TyCtxt};
  16 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
  17 use rustc_span::{symbol::sym, Span, DUMMY_SP};
  18 use rustc_target::abi::VariantIdx;
  19 use rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions;
  20
  21 use super::borrow_set::BorrowData;
  22 use super::MirBorrowckCtxt;
  23
  24 mod find_all_local_uses;
  25 mod find_use;
  26 mod outlives_suggestion;
  27 mod region_name;
  28 mod var_name;
  29
  30 mod bound_region_errors;
  31 mod conflict_errors;
  32 mod explain_borrow;
  33 mod move_errors;
  34 mod mutability_errors;
  35 mod region_errors;
  36
  37 crate use bound_region_errors::{ToUniverseInfo, UniverseInfo};
  38 crate use mutability_errors::AccessKind;
  39 crate use outlives_suggestion::OutlivesSuggestionBuilder;
  40 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
  41 crate use region_name::{RegionName, RegionNameSource};
  42 crate use rustc_const_eval::util::CallKind;
  43
  44 pub(super) struct IncludingDowncast(pub(super) bool);
  45
  46 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  47     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  48     /// is moved after being invoked.
  49     ///
  50     /// ```text
  51     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  52     ///       its environment
  53     ///   --> $DIR/issue-42065.rs:16:29
  54     ///    |
  55     /// LL |         for (key, value) in dict {
  56     ///    |                             ^^^^
  57     /// ```
  58     pub(super) fn add_moved_or_invoked_closure_note(
  59         &self,
  60         location: Location,
  61         place: PlaceRef<'tcx>,
  62         diag: &mut Diagnostic,
  63     ) {
  64         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  65         let mut target = place.local_or_deref_local();
  66         for stmt in &self.body[location.block].statements[location.statement_index..] {
  67             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  68             if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
  69                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  70                 match from {
  71                     Operand::Copy(ref place) | Operand::Move(ref place)
  72                         if target == place.local_or_deref_local() =>
  73                     {
  74                         target = into.local_or_deref_local()
  75                     }
  76                     _ => {}
  77                 }
  78             }
  79         }
  80
  81         // Check if we are attempting to call a closure after it has been invoked.
  82         let terminator = self.body[location.block].terminator();
  83         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  84         if let TerminatorKind::Call {
  85             func: Operand::Constant(box Constant { literal, .. }),
  86             args,
  87             ..
  88         } = &terminator.kind
  89         {
  90             if let ty::FnDef(id, _) = *literal.ty().kind() {
  91                 debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  92                 if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  93                     let closure = match args.first() {
  94                         Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
  95                             if target == place.local_or_deref_local() =>
  96                         {
  97                             place.local_or_deref_local().unwrap()
  98                         }
  99                         _ => return,
 100                     };
 101
 102                     debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
 103                     if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind() {
 104                         let did = did.expect_local();
 105                         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 106
 107                         if let Some((span, hir_place)) =
 108                             self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 109                         {
 110                             diag.span_note(
 111                                 *span,
 112                                 &format!(
 113                                     "closure cannot be invoked more than once because it moves the \
 114                                     variable `{}` out of its environment",
 115                                     ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
 116                                 ),
 117                             );
 118                             return;
 119                         }
 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().local_def_id_to_hir_id(did);
 130
 131                 if let Some((span, hir_place)) =
 132                     self.infcx.tcx.typeck(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                             ty::place_to_string_for_capture(self.infcx.tcx, hir_place)
 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(0, '`');
 155                 descr.push('`');
 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].place.to_string(self.infcx.tcx);
 223                             if self.upvars[var_index].by_ref {
 224                                 buf.push_str(&name);
 225                             } else {
 226                                 buf.push('*');
 227                                 buf.push_str(&name);
 228                             }
 229                         } else {
 230                             if autoderef {
 231                                 // FIXME turn this recursion into iteration
 232                                 self.append_place_to_string(
 233                                     PlaceRef { local, projection: proj_base },
 234                                     buf,
 235                                     autoderef,
 236                                     &including_downcast,
 237                                 )?;
 238                             } else {
 239                                 buf.push('*');
 240                                 self.append_place_to_string(
 241                                     PlaceRef { local, projection: proj_base },
 242                                     buf,
 243                                     autoderef,
 244                                     &including_downcast,
 245                                 )?;
 246                             }
 247                         }
 248                     }
 249                     ProjectionElem::Downcast(..) => {
 250                         self.append_place_to_string(
 251                             PlaceRef { local, projection: proj_base },
 252                             buf,
 253                             autoderef,
 254                             &including_downcast,
 255                         )?;
 256                         if including_downcast.0 {
 257                             return Err(());
 258                         }
 259                     }
 260                     ProjectionElem::Field(field, _ty) => {
 261                         autoderef = true;
 262
 263                         // FIXME(project-rfc_2229#36): print capture precisely here.
 264                         let upvar_field_projection = self.is_upvar_field_projection(place);
 265                         if let Some(field) = upvar_field_projection {
 266                             let var_index = field.index();
 267                             let name = self.upvars[var_index].place.to_string(self.infcx.tcx);
 268                             buf.push_str(&name);
 269                         } else {
 270                             let field_name = self
 271                                 .describe_field(PlaceRef { local, projection: proj_base }, *field);
 272                             self.append_place_to_string(
 273                                 PlaceRef { local, projection: proj_base },
 274                                 buf,
 275                                 autoderef,
 276                                 &including_downcast,
 277                             )?;
 278                             buf.push('.');
 279                             buf.push_str(&field_name);
 280                         }
 281                     }
 282                     ProjectionElem::Index(index) => {
 283                         autoderef = true;
 284
 285                         self.append_place_to_string(
 286                             PlaceRef { local, projection: proj_base },
 287                             buf,
 288                             autoderef,
 289                             &including_downcast,
 290                         )?;
 291                         buf.push('[');
 292                         if self.append_local_to_string(*index, buf).is_err() {
 293                             buf.push('_');
 294                         }
 295                         buf.push(']');
 296                     }
 297                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 298                         autoderef = true;
 299                         // Since it isn't possible to borrow an element on a particular index and
 300                         // then use another while the borrow is held, don't output indices details
 301                         // to avoid confusing the end-user
 302                         self.append_place_to_string(
 303                             PlaceRef { local, projection: proj_base },
 304                             buf,
 305                             autoderef,
 306                             &including_downcast,
 307                         )?;
 308                         buf.push_str("[..]");
 309                     }
 310                 };
 311             }
 312         }
 313
 314         Ok(())
 315     }
 316
 317     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 318     /// a name, or its name was generated by the compiler, then `Err` is returned
 319     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 320         let decl = &self.body.local_decls[local];
 321         match self.local_names[local] {
 322             Some(name) if !decl.from_compiler_desugaring() => {
 323                 buf.push_str(name.as_str());
 324                 Ok(())
 325             }
 326             _ => Err(()),
 327         }
 328     }
 329
 330     /// End-user visible description of the `field`nth field of `base`
 331     fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
 332         // FIXME Place2 Make this work iteratively
 333         match place {
 334             PlaceRef { local, projection: [] } => {
 335                 let local = &self.body.local_decls[local];
 336                 self.describe_field_from_ty(local.ty, field, None)
 337             }
 338             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 339                 ProjectionElem::Deref => {
 340                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 341                 }
 342                 ProjectionElem::Downcast(_, variant_index) => {
 343                     let base_ty = place.ty(self.body, self.infcx.tcx).ty;
 344                     self.describe_field_from_ty(base_ty, field, Some(*variant_index))
 345                 }
 346                 ProjectionElem::Field(_, field_type) => {
 347                     self.describe_field_from_ty(*field_type, field, None)
 348                 }
 349                 ProjectionElem::Index(..)
 350                 | ProjectionElem::ConstantIndex { .. }
 351                 | ProjectionElem::Subslice { .. } => {
 352                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 353                 }
 354             },
 355         }
 356     }
 357
 358     /// End-user visible description of the `field_index`nth field of `ty`
 359     fn describe_field_from_ty(
 360         &self,
 361         ty: Ty<'_>,
 362         field: Field,
 363         variant_index: Option<VariantIdx>,
 364     ) -> String {
 365         if ty.is_box() {
 366             // If the type is a box, the field is described from the boxed type
 367             self.describe_field_from_ty(ty.boxed_ty(), field, variant_index)
 368         } else {
 369             match *ty.kind() {
 370                 ty::Adt(def, _) => {
 371                     let variant = if let Some(idx) = variant_index {
 372                         assert!(def.is_enum());
 373                         &def.variant(idx)
 374                     } else {
 375                         def.non_enum_variant()
 376                     };
 377                     variant.fields[field.index()].name.to_string()
 378                 }
 379                 ty::Tuple(_) => field.index().to_string(),
 380                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 381                     self.describe_field_from_ty(ty, field, variant_index)
 382                 }
 383                 ty::Array(ty, _) | ty::Slice(ty) => {
 384                     self.describe_field_from_ty(ty, field, variant_index)
 385                 }
 386                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 387                     // We won't be borrowck'ing here if the closure came from another crate,
 388                     // so it's safe to call `expect_local`.
 389                     //
 390                     // We know the field exists so it's safe to call operator[] and `unwrap` here.
 391                     let var_id = self
 392                         .infcx
 393                         .tcx
 394                         .typeck(def_id.expect_local())
 395                         .closure_min_captures_flattened(def_id)
 396                         .nth(field.index())
 397                         .unwrap()
 398                         .get_root_variable();
 399
 400                     self.infcx.tcx.hir().name(var_id).to_string()
 401                 }
 402                 _ => {
 403                     // Might need a revision when the fields in trait RFC is implemented
 404                     // (https://github.com/rust-lang/rfcs/pull/1546)
 405                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 406                 }
 407             }
 408         }
 409     }
 410
 411     /// Add a note that a type does not implement `Copy`
 412     pub(super) fn note_type_does_not_implement_copy(
 413         &self,
 414         err: &mut Diagnostic,
 415         place_desc: &str,
 416         ty: Ty<'tcx>,
 417         span: Option<Span>,
 418         move_prefix: &str,
 419     ) {
 420         let message = format!(
 421             "{}move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 422             move_prefix, place_desc, ty,
 423         );
 424         if let Some(span) = span {
 425             err.span_label(span, message);
 426         } else {
 427             err.note(&message);
 428         }
 429     }
 430
 431     pub(super) fn borrowed_content_source(
 432         &self,
 433         deref_base: PlaceRef<'tcx>,
 434     ) -> BorrowedContentSource<'tcx> {
 435         let tcx = self.infcx.tcx;
 436
 437         // Look up the provided place and work out the move path index for it,
 438         // we'll use this to check whether it was originally from an overloaded
 439         // operator.
 440         match self.move_data.rev_lookup.find(deref_base) {
 441             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 442                 debug!("borrowed_content_source: mpi={:?}", mpi);
 443
 444                 for i in &self.move_data.init_path_map[mpi] {
 445                     let init = &self.move_data.inits[*i];
 446                     debug!("borrowed_content_source: init={:?}", init);
 447                     // We're only interested in statements that initialized a value, not the
 448                     // initializations from arguments.
 449                     let InitLocation::Statement(loc) = init.location else { continue };
 450
 451                     let bbd = &self.body[loc.block];
 452                     let is_terminator = bbd.statements.len() == loc.statement_index;
 453                     debug!(
 454                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 455                         loc, is_terminator,
 456                     );
 457                     if !is_terminator {
 458                         continue;
 459                     } else if let Some(Terminator {
 460                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 461                         ..
 462                     }) = bbd.terminator
 463                     {
 464                         if let Some(source) =
 465                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 466                         {
 467                             return source;
 468                         }
 469                     }
 470                 }
 471             }
 472             // Base is a `static` so won't be from an overloaded operator
 473             _ => (),
 474         };
 475
 476         // If we didn't find an overloaded deref or index, then assume it's a
 477         // built in deref and check the type of the base.
 478         let base_ty = deref_base.ty(self.body, tcx).ty;
 479         if base_ty.is_unsafe_ptr() {
 480             BorrowedContentSource::DerefRawPointer
 481         } else if base_ty.is_mutable_ptr() {
 482             BorrowedContentSource::DerefMutableRef
 483         } else {
 484             BorrowedContentSource::DerefSharedRef
 485         }
 486     }
 487
 488     /// 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 printer = ty::print::FmtPrinter::new(self.infcx.tcx, Namespace::TypeNS);
 492
 493         // We need to add synthesized lifetimes where appropriate. We do
 494         // this by hooking into the pretty printer and telling it to label the
 495         // lifetimes without names with the value `'0`.
 496         if let ty::Ref(region, ..) = ty.kind() {
 497             match **region {
 498                 ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
 499                 | ty::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 500                     printer.region_highlight_mode.highlighting_bound_region(br, counter)
 501                 }
 502                 _ => {}
 503             }
 504         }
 505
 506         ty.print(printer).unwrap().into_buffer()
 507     }
 508
 509     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 510     /// synthesized lifetime name where required.
 511     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 512         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, Namespace::TypeNS);
 513
 514         let region = if let ty::Ref(region, ..) = ty.kind() {
 515             match **region {
 516                 ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
 517                 | ty::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 518                     printer.region_highlight_mode.highlighting_bound_region(br, counter)
 519                 }
 520                 _ => {}
 521             }
 522             region
 523         } else {
 524             bug!("ty for annotation of borrow region is not a reference");
 525         };
 526
 527         region.print(printer).unwrap().into_buffer()
 528     }
 529 }
 530
 531 /// The span(s) associated to a use of a place.
 532 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 533 pub(super) enum UseSpans<'tcx> {
 534     /// The access is caused by capturing a variable for a closure.
 535     ClosureUse {
 536         /// This is true if the captured variable was from a generator.
 537         generator_kind: Option<GeneratorKind>,
 538         /// The span of the args of the closure, including the `move` keyword if
 539         /// it's present.
 540         args_span: Span,
 541         /// The span of the use resulting in capture kind
 542         /// Check `ty::CaptureInfo` for more details
 543         capture_kind_span: Span,
 544         /// The span of the use resulting in the captured path
 545         /// Check `ty::CaptureInfo` for more details
 546         path_span: Span,
 547     },
 548     /// The access is caused by using a variable as the receiver of a method
 549     /// that takes 'self'
 550     FnSelfUse {
 551         /// The span of the variable being moved
 552         var_span: Span,
 553         /// The span of the method call on the variable
 554         fn_call_span: Span,
 555         /// The definition span of the method being called
 556         fn_span: Span,
 557         kind: CallKind<'tcx>,
 558     },
 559     /// This access is caused by a `match` or `if let` pattern.
 560     PatUse(Span),
 561     /// This access has a single span associated to it: common case.
 562     OtherUse(Span),
 563 }
 564
 565 impl UseSpans<'_> {
 566     pub(super) fn args_or_use(self) -> Span {
 567         match self {
 568             UseSpans::ClosureUse { args_span: span, .. }
 569             | UseSpans::PatUse(span)
 570             | UseSpans::OtherUse(span) => span,
 571             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 572                 fn_call_span
 573             }
 574             UseSpans::FnSelfUse { var_span, .. } => var_span,
 575         }
 576     }
 577
 578     /// Returns the span of `self`, in the case of a `ClosureUse` returns the `path_span`
 579     pub(super) fn var_or_use_path_span(self) -> Span {
 580         match self {
 581             UseSpans::ClosureUse { path_span: span, .. }
 582             | UseSpans::PatUse(span)
 583             | UseSpans::OtherUse(span) => span,
 584             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 585                 fn_call_span
 586             }
 587             UseSpans::FnSelfUse { var_span, .. } => var_span,
 588         }
 589     }
 590
 591     /// Returns the span of `self`, in the case of a `ClosureUse` returns the `capture_kind_span`
 592     pub(super) fn var_or_use(self) -> Span {
 593         match self {
 594             UseSpans::ClosureUse { capture_kind_span: span, .. }
 595             | UseSpans::PatUse(span)
 596             | UseSpans::OtherUse(span) => span,
 597             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 598                 fn_call_span
 599             }
 600             UseSpans::FnSelfUse { var_span, .. } => var_span,
 601         }
 602     }
 603
 604     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 605         match self {
 606             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 607             _ => None,
 608         }
 609     }
 610
 611     // Add a span label to the arguments of the closure, if it exists.
 612     pub(super) fn args_span_label(self, err: &mut Diagnostic, message: impl Into<String>) {
 613         if let UseSpans::ClosureUse { args_span, .. } = self {
 614             err.span_label(args_span, message);
 615         }
 616     }
 617
 618     // Add a span label to the use of the captured variable, if it exists.
 619     // only adds label to the `path_span`
 620     pub(super) fn var_span_label_path_only(self, err: &mut Diagnostic, message: impl Into<String>) {
 621         if let UseSpans::ClosureUse { path_span, .. } = self {
 622             err.span_label(path_span, message);
 623         }
 624     }
 625
 626     // Add a span label to the use of the captured variable, if it exists.
 627     pub(super) fn var_span_label(
 628         self,
 629         err: &mut Diagnostic,
 630         message: impl Into<String>,
 631         kind_desc: impl Into<String>,
 632     ) {
 633         if let UseSpans::ClosureUse { capture_kind_span, path_span, .. } = self {
 634             if capture_kind_span == path_span {
 635                 err.span_label(capture_kind_span, message);
 636             } else {
 637                 let capture_kind_label =
 638                     format!("capture is {} because of use here", kind_desc.into());
 639                 let path_label = message;
 640                 err.span_label(capture_kind_span, capture_kind_label);
 641                 err.span_label(path_span, path_label);
 642             }
 643         }
 644     }
 645
 646     /// Returns `false` if this place is not used in a closure.
 647     pub(super) fn for_closure(&self) -> bool {
 648         match *self {
 649             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 650             _ => false,
 651         }
 652     }
 653
 654     /// Returns `false` if this place is not used in a generator.
 655     pub(super) fn for_generator(&self) -> bool {
 656         match *self {
 657             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 658             _ => false,
 659         }
 660     }
 661
 662     /// Describe the span associated with a use of a place.
 663     pub(super) fn describe(&self) -> String {
 664         match *self {
 665             UseSpans::ClosureUse { generator_kind, .. } => {
 666                 if generator_kind.is_some() {
 667                     " in generator".to_string()
 668                 } else {
 669                     " in closure".to_string()
 670                 }
 671             }
 672             _ => String::new(),
 673         }
 674     }
 675
 676     pub(super) fn or_else<F>(self, if_other: F) -> Self
 677     where
 678         F: FnOnce() -> Self,
 679     {
 680         match self {
 681             closure @ UseSpans::ClosureUse { .. } => closure,
 682             UseSpans::PatUse(_) | UseSpans::OtherUse(_) => if_other(),
 683             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 684         }
 685     }
 686 }
 687
 688 pub(super) enum BorrowedContentSource<'tcx> {
 689     DerefRawPointer,
 690     DerefMutableRef,
 691     DerefSharedRef,
 692     OverloadedDeref(Ty<'tcx>),
 693     OverloadedIndex(Ty<'tcx>),
 694 }
 695
 696 impl<'tcx> BorrowedContentSource<'tcx> {
 697     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 698         match *self {
 699             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 700             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 701             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 702             BorrowedContentSource::OverloadedDeref(ty) => ty
 703                 .ty_adt_def()
 704                 .and_then(|adt| match tcx.get_diagnostic_name(adt.did())? {
 705                     name @ (sym::Rc | sym::Arc) => Some(format!("an `{}`", name)),
 706                     _ => None,
 707                 })
 708                 .unwrap_or_else(|| format!("dereference of `{}`", ty)),
 709             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 710         }
 711     }
 712
 713     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 714         match *self {
 715             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 716             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 717             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 718             // Overloaded deref and index operators should be evaluated into a
 719             // temporary. So we don't need a description here.
 720             BorrowedContentSource::OverloadedDeref(_)
 721             | BorrowedContentSource::OverloadedIndex(_) => None,
 722         }
 723     }
 724
 725     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 726         match *self {
 727             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 728             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 729             BorrowedContentSource::DerefMutableRef => {
 730                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 731             }
 732             BorrowedContentSource::OverloadedDeref(ty) => ty
 733                 .ty_adt_def()
 734                 .and_then(|adt| match tcx.get_diagnostic_name(adt.did())? {
 735                     name @ (sym::Rc | sym::Arc) => Some(format!("an `{}`", name)),
 736                     _ => None,
 737                 })
 738                 .unwrap_or_else(|| format!("dereference of `{}`", ty)),
 739             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 740         }
 741     }
 742
 743     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 744         match *func.kind() {
 745             ty::FnDef(def_id, substs) => {
 746                 let trait_id = tcx.trait_of_item(def_id)?;
 747
 748                 let lang_items = tcx.lang_items();
 749                 if Some(trait_id) == lang_items.deref_trait()
 750                     || Some(trait_id) == lang_items.deref_mut_trait()
 751                 {
 752                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 753                 } else if Some(trait_id) == lang_items.index_trait()
 754                     || Some(trait_id) == lang_items.index_mut_trait()
 755                 {
 756                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 757                 } else {
 758                     None
 759                 }
 760             }
 761             _ => None,
 762         }
 763     }
 764 }
 765
 766 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 767     /// Finds the spans associated to a move or copy of move_place at location.
 768     pub(super) fn move_spans(
 769         &self,
 770         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 771         location: Location,
 772     ) -> UseSpans<'tcx> {
 773         use self::UseSpans::*;
 774
 775         let Some(stmt) = self.body[location.block].statements.get(location.statement_index) else {
 776             return OtherUse(self.body.source_info(location).span);
 777         };
 778
 779         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 780         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 781             match kind {
 782                 box AggregateKind::Closure(def_id, _)
 783                 | box AggregateKind::Generator(def_id, _, _) => {
 784                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 785                     if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 786                         self.closure_span(*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         // StatementKind::FakeRead only contains a def_id if they are introduced as a result
 801         // of pattern matching within a closure.
 802         if let StatementKind::FakeRead(box (cause, ref place)) = stmt.kind {
 803             match cause {
 804                 FakeReadCause::ForMatchedPlace(Some(closure_def_id))
 805                 | FakeReadCause::ForLet(Some(closure_def_id)) => {
 806                     debug!("move_spans: def_id={:?} place={:?}", closure_def_id, place);
 807                     let places = &[Operand::Move(*place)];
 808                     if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 809                         self.closure_span(closure_def_id, moved_place, places)
 810                     {
 811                         return ClosureUse {
 812                             generator_kind,
 813                             args_span,
 814                             capture_kind_span,
 815                             path_span,
 816                         };
 817                     }
 818                 }
 819                 _ => {}
 820             }
 821         }
 822
 823         let normal_ret =
 824             if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
 825                 PatUse(stmt.source_info.span)
 826             } else {
 827                 OtherUse(stmt.source_info.span)
 828             };
 829
 830         // We are trying to find MIR of the form:
 831         // ```
 832         // _temp = _moved_val;
 833         // ...
 834         // FnSelfCall(_temp, ...)
 835         // ```
 836         //
 837         // where `_moved_val` is the place we generated the move error for,
 838         // `_temp` is some other local, and `FnSelfCall` is a function
 839         // that has a `self` parameter.
 840
 841         let target_temp = match stmt.kind {
 842             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 843                 temp.as_local().unwrap()
 844             }
 845             _ => return normal_ret,
 846         };
 847
 848         debug!("move_spans: target_temp = {:?}", target_temp);
 849
 850         if let Some(Terminator {
 851             kind: TerminatorKind::Call { fn_span, from_hir_call, .. }, ..
 852         }) = &self.body[location.block].terminator
 853         {
 854             let Some((method_did, method_substs)) =
 855                 rustc_const_eval::util::find_self_call(
 856                     self.infcx.tcx,
 857                     &self.body,
 858                     target_temp,
 859                     location.block,
 860                 )
 861             else {
 862                 return normal_ret;
 863             };
 864
 865             let kind = call_kind(
 866                 self.infcx.tcx,
 867                 self.param_env,
 868                 method_did,
 869                 method_substs,
 870                 *fn_span,
 871                 *from_hir_call,
 872                 Some(self.infcx.tcx.fn_arg_names(method_did)[0]),
 873             );
 874
 875             return FnSelfUse {
 876                 var_span: stmt.source_info.span,
 877                 fn_call_span: *fn_span,
 878                 fn_span: self
 879                     .infcx
 880                     .tcx
 881                     .sess
 882                     .source_map()
 883                     .guess_head_span(self.infcx.tcx.def_span(method_did)),
 884                 kind,
 885             };
 886         }
 887         normal_ret
 888     }
 889
 890     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 891     /// and its usage of the local assigned at `location`.
 892     /// This is done by searching in statements succeeding `location`
 893     /// and originating from `maybe_closure_span`.
 894     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans<'tcx> {
 895         use self::UseSpans::*;
 896         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 897
 898         let target = match self.body[location.block].statements.get(location.statement_index) {
 899             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 900                 if let Some(local) = place.as_local() {
 901                     local
 902                 } else {
 903                     return OtherUse(use_span);
 904                 }
 905             }
 906             _ => return OtherUse(use_span),
 907         };
 908
 909         if self.body.local_kind(target) != LocalKind::Temp {
 910             // operands are always temporaries.
 911             return OtherUse(use_span);
 912         }
 913
 914         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 915             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 916                 stmt.kind
 917             {
 918                 let (def_id, is_generator) = match kind {
 919                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 920                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 921                     _ => continue,
 922                 };
 923
 924                 debug!(
 925                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 926                     def_id, is_generator, places
 927                 );
 928                 if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 929                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 930                 {
 931                     return ClosureUse { generator_kind, args_span, capture_kind_span, path_span };
 932                 } else {
 933                     return OtherUse(use_span);
 934                 }
 935             }
 936
 937             if use_span != stmt.source_info.span {
 938                 break;
 939             }
 940         }
 941
 942         OtherUse(use_span)
 943     }
 944
 945     /// Finds the spans of a captured place within a closure or generator.
 946     /// The first span is the location of the use resulting in the capture kind of the capture
 947     /// The second span is the location the use resulting in the captured path of the capture
 948     fn closure_span(
 949         &self,
 950         def_id: DefId,
 951         target_place: PlaceRef<'tcx>,
 952         places: &[Operand<'tcx>],
 953     ) -> Option<(Span, Option<GeneratorKind>, Span, Span)> {
 954         debug!(
 955             "closure_span: def_id={:?} target_place={:?} places={:?}",
 956             def_id, target_place, places
 957         );
 958         let local_did = def_id.as_local()?;
 959         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(local_did);
 960         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 961         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 962         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 963             for (captured_place, place) in self
 964                 .infcx
 965                 .tcx
 966                 .typeck(def_id.expect_local())
 967                 .closure_min_captures_flattened(def_id)
 968                 .zip(places)
 969             {
 970                 match place {
 971                     Operand::Copy(place) | Operand::Move(place)
 972                         if target_place == place.as_ref() =>
 973                     {
 974                         debug!("closure_span: found captured local {:?}", place);
 975                         let body = self.infcx.tcx.hir().body(*body_id);
 976                         let generator_kind = body.generator_kind();
 977
 978                         return Some((
 979                             *args_span,
 980                             generator_kind,
 981                             captured_place.get_capture_kind_span(self.infcx.tcx),
 982                             captured_place.get_path_span(self.infcx.tcx),
 983                         ));
 984                     }
 985                     _ => {}
 986                 }
 987             }
 988         }
 989         None
 990     }
 991
 992     /// Helper to retrieve span(s) of given borrow from the current MIR
 993     /// representation
 994     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans<'tcx> {
 995         let span = self.body.source_info(borrow.reserve_location).span;
 996         self.borrow_spans(span, borrow.reserve_location)
 997     }
 998
 999     fn explain_captures(
1000         &mut self,
1001         err: &mut Diagnostic,
1002         span: Span,
1003         move_span: Span,
1004         move_spans: UseSpans<'tcx>,
1005         moved_place: Place<'tcx>,
1006         used_place: Option<PlaceRef<'tcx>>,
1007         partially_str: &str,
1008         loop_message: &str,
1009         move_msg: &str,
1010         is_loop_move: bool,
1011         maybe_reinitialized_locations_is_empty: bool,
1012     ) {
1013         if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
1014             let place_name = self
1015                 .describe_place(moved_place.as_ref())
1016                 .map(|n| format!("`{}`", n))
1017                 .unwrap_or_else(|| "value".to_owned());
1018             match kind {
1019                 CallKind::FnCall { fn_trait_id, .. }
1020                     if Some(fn_trait_id) == self.infcx.tcx.lang_items().fn_once_trait() =>
1021                 {
1022                     err.span_label(
1023                         fn_call_span,
1024                         &format!(
1025                             "{} {}moved due to this call{}",
1026                             place_name, partially_str, loop_message
1027                         ),
1028                     );
1029                     err.span_note(
1030                         var_span,
1031                         "this value implements `FnOnce`, which causes it to be moved when called",
1032                     );
1033                 }
1034                 CallKind::Operator { self_arg, .. } => {
1035                     let self_arg = self_arg.unwrap();
1036                     err.span_label(
1037                         fn_call_span,
1038                         &format!(
1039                             "{} {}moved due to usage in operator{}",
1040                             place_name, partially_str, loop_message
1041                         ),
1042                     );
1043                     if self.fn_self_span_reported.insert(fn_span) {
1044                         err.span_note(
1045                             // Check whether the source is accessible
1046                             if self
1047                                 .infcx
1048                                 .tcx
1049                                 .sess
1050                                 .source_map()
1051                                 .span_to_snippet(self_arg.span)
1052                                 .is_ok()
1053                             {
1054                                 self_arg.span
1055                             } else {
1056                                 fn_call_span
1057                             },
1058                             "calling this operator moves the left-hand side",
1059                         );
1060                     }
1061                 }
1062                 CallKind::Normal { self_arg, desugaring, is_option_or_result } => {
1063                     let self_arg = self_arg.unwrap();
1064                     if let Some((CallDesugaringKind::ForLoopIntoIter, _)) = desugaring {
1065                         let ty = moved_place.ty(self.body, self.infcx.tcx).ty;
1066                         let suggest = match self.infcx.tcx.get_diagnostic_item(sym::IntoIterator) {
1067                             Some(def_id) => self.infcx.tcx.infer_ctxt().enter(|infcx| {
1068                                 type_known_to_meet_bound_modulo_regions(
1069                                     &infcx,
1070                                     self.param_env,
1071                                     infcx.tcx.mk_imm_ref(
1072                                         infcx.tcx.lifetimes.re_erased,
1073                                         infcx.tcx.erase_regions(ty),
1074                                     ),
1075                                     def_id,
1076                                     DUMMY_SP,
1077                                 )
1078                             }),
1079                             _ => false,
1080                         };
1081                         if suggest {
1082                             err.span_suggestion_verbose(
1083                                 move_span.shrink_to_lo(),
1084                                 &format!(
1085                                     "consider iterating over a slice of the `{}`'s content to \
1086                                      avoid moving into the `for` loop",
1087                                     ty,
1088                                 ),
1089                                 "&".to_string(),
1090                                 Applicability::MaybeIncorrect,
1091                             );
1092                         }
1093
1094                         err.span_label(
1095                             fn_call_span,
1096                             &format!(
1097                                 "{} {}moved due to this implicit call to `.into_iter()`{}",
1098                                 place_name, partially_str, loop_message
1099                             ),
1100                         );
1101                         // If we have a `&mut` ref, we need to reborrow.
1102                         if let Some(ty::Ref(_, _, hir::Mutability::Mut)) = used_place
1103                             .map(|used_place| used_place.ty(self.body, self.infcx.tcx).ty.kind())
1104                         {
1105                             // If we are in a loop this will be suggested later.
1106                             if !is_loop_move {
1107                                 err.span_suggestion_verbose(
1108                                     move_span.shrink_to_lo(),
1109                                     &format!(
1110                                         "consider creating a fresh reborrow of {} here",
1111                                         self.describe_place(moved_place.as_ref())
1112                                             .map(|n| format!("`{}`", n))
1113                                             .unwrap_or_else(|| "the mutable reference".to_string()),
1114                                     ),
1115                                     "&mut *".to_string(),
1116                                     Applicability::MachineApplicable,
1117                                 );
1118                             }
1119                         }
1120                     } else {
1121                         err.span_label(
1122                             fn_call_span,
1123                             &format!(
1124                                 "{} {}moved due to this method call{}",
1125                                 place_name, partially_str, loop_message
1126                             ),
1127                         );
1128                     }
1129                     if is_option_or_result && maybe_reinitialized_locations_is_empty {
1130                         err.span_suggestion_verbose(
1131                             fn_call_span.shrink_to_lo(),
1132                             "consider calling `.as_ref()` to borrow the type's contents",
1133                             "as_ref().".to_string(),
1134                             Applicability::MachineApplicable,
1135                         );
1136                     }
1137                     // Avoid pointing to the same function in multiple different
1138                     // error messages.
1139                     if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span) {
1140                         err.span_note(
1141                             self_arg.span,
1142                             &format!("this function takes ownership of the receiver `self`, which moves {}", place_name)
1143                         );
1144                     }
1145                 }
1146                 // Other desugarings takes &self, which cannot cause a move
1147                 _ => {}
1148             }
1149         } else {
1150             if move_span != span || !loop_message.is_empty() {
1151                 err.span_label(
1152                     move_span,
1153                     format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
1154                 );
1155             }
1156             // If the move error occurs due to a loop, don't show
1157             // another message for the same span
1158             if loop_message.is_empty() {
1159                 move_spans.var_span_label(
1160                     err,
1161                     format!("variable {}moved due to use{}", partially_str, move_spans.describe()),
1162                     "moved",
1163                 );
1164             }
1165         }
1166     }
1167 }