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     ) -> bool {
  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 false,
 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 true;
 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                     return true;
 153                 }
 154             }
 155         }
 156         false
 157     }
 158
 159     /// End-user visible description of `place` if one can be found.
 160     /// If the place is a temporary for instance, `"value"` will be returned.
 161     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 162         match self.describe_place(place_ref) {
 163             Some(mut descr) => {
 164                 // Surround descr with `backticks`.
 165                 descr.reserve(2);
 166                 descr.insert(0, '`');
 167                 descr.push('`');
 168                 descr
 169             }
 170             None => "value".to_string(),
 171         }
 172     }
 173
 174     /// End-user visible description of `place` if one can be found.
 175     /// If the place is a temporary for instance, `None` will be returned.
 176     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 177         self.describe_place_with_options(
 178             place_ref,
 179             DescribePlaceOpt { including_downcast: false, including_tuple_field: true },
 180         )
 181     }
 182
 183     /// End-user visible description of `place` if one can be found. If the place is a temporary
 184     /// for instance, `None` will be returned.
 185     /// `IncludingDowncast` parameter makes the function return `None` if `ProjectionElem` is
 186     /// `Downcast` and `IncludingDowncast` is true
 187     pub(super) fn describe_place_with_options(
 188         &self,
 189         place: PlaceRef<'tcx>,
 190         opt: DescribePlaceOpt,
 191     ) -> Option<String> {
 192         let local = place.local;
 193         let mut autoderef_index = None;
 194         let mut buf = String::new();
 195         let mut ok = self.append_local_to_string(local, &mut buf);
 196
 197         for (index, elem) in place.projection.into_iter().enumerate() {
 198             match elem {
 199                 ProjectionElem::Deref => {
 200                     if index == 0 {
 201                         if self.body.local_decls[local].is_ref_for_guard() {
 202                             continue;
 203                         }
 204                         if let Some(box LocalInfo::StaticRef { def_id, .. }) =
 205                             &self.body.local_decls[local].local_info
 206                         {
 207                             buf.push_str(self.infcx.tcx.item_name(*def_id).as_str());
 208                             ok = Ok(());
 209                             continue;
 210                         }
 211                     }
 212                     if let Some(field) = self.is_upvar_field_projection(PlaceRef {
 213                         local,
 214                         projection: place.projection.split_at(index + 1).0,
 215                     }) {
 216                         let var_index = field.index();
 217                         buf = self.upvars[var_index].place.to_string(self.infcx.tcx);
 218                         ok = Ok(());
 219                         if !self.upvars[var_index].by_ref {
 220                             buf.insert(0, '*');
 221                         }
 222                     } else {
 223                         if autoderef_index.is_none() {
 224                             autoderef_index =
 225                                 match place.projection.into_iter().rev().find_position(|elem| {
 226                                     !matches!(
 227                                         elem,
 228                                         ProjectionElem::Deref | ProjectionElem::Downcast(..)
 229                                     )
 230                                 }) {
 231                                     Some((index, _)) => Some(place.projection.len() - index),
 232                                     None => Some(0),
 233                                 };
 234                         }
 235                         if index >= autoderef_index.unwrap() {
 236                             buf.insert(0, '*');
 237                         }
 238                     }
 239                 }
 240                 ProjectionElem::Downcast(..) if opt.including_downcast => return None,
 241                 ProjectionElem::Downcast(..) => (),
 242                 ProjectionElem::OpaqueCast(..) => (),
 243                 ProjectionElem::Field(field, _ty) => {
 244                     // FIXME(project-rfc_2229#36): print capture precisely here.
 245                     if let Some(field) = self.is_upvar_field_projection(PlaceRef {
 246                         local,
 247                         projection: place.projection.split_at(index + 1).0,
 248                     }) {
 249                         buf = self.upvars[field.index()].place.to_string(self.infcx.tcx);
 250                         ok = Ok(());
 251                     } else {
 252                         let field_name = self.describe_field(
 253                             PlaceRef { local, projection: place.projection.split_at(index).0 },
 254                             *field,
 255                             IncludingTupleField(opt.including_tuple_field),
 256                         );
 257                         if let Some(field_name_str) = field_name {
 258                             buf.push('.');
 259                             buf.push_str(&field_name_str);
 260                         }
 261                     }
 262                 }
 263                 ProjectionElem::Index(index) => {
 264                     buf.push('[');
 265                     if self.append_local_to_string(*index, &mut buf).is_err() {
 266                         buf.push('_');
 267                     }
 268                     buf.push(']');
 269                 }
 270                 ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 271                     // Since it isn't possible to borrow an element on a particular index and
 272                     // then use another while the borrow is held, don't output indices details
 273                     // to avoid confusing the end-user
 274                     buf.push_str("[..]");
 275                 }
 276             }
 277         }
 278         ok.ok().map(|_| buf)
 279     }
 280
 281     fn describe_name(&self, place: PlaceRef<'tcx>) -> Option<Symbol> {
 282         for elem in place.projection.into_iter() {
 283             match elem {
 284                 ProjectionElem::Downcast(Some(name), _) => {
 285                     return Some(*name);
 286                 }
 287                 _ => {}
 288             }
 289         }
 290         None
 291     }
 292
 293     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 294     /// a name, or its name was generated by the compiler, then `Err` is returned
 295     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 296         let decl = &self.body.local_decls[local];
 297         match self.local_names[local] {
 298             Some(name) if !decl.from_compiler_desugaring() => {
 299                 buf.push_str(name.as_str());
 300                 Ok(())
 301             }
 302             _ => Err(()),
 303         }
 304     }
 305
 306     /// End-user visible description of the `field`nth field of `base`
 307     fn describe_field(
 308         &self,
 309         place: PlaceRef<'tcx>,
 310         field: Field,
 311         including_tuple_field: IncludingTupleField,
 312     ) -> Option<String> {
 313         let place_ty = match place {
 314             PlaceRef { local, projection: [] } => PlaceTy::from_ty(self.body.local_decls[local].ty),
 315             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 316                 ProjectionElem::Deref
 317                 | ProjectionElem::Index(..)
 318                 | ProjectionElem::ConstantIndex { .. }
 319                 | ProjectionElem::Subslice { .. } => {
 320                     PlaceRef { local, projection: proj_base }.ty(self.body, self.infcx.tcx)
 321                 }
 322                 ProjectionElem::Downcast(..) => place.ty(self.body, self.infcx.tcx),
 323                 ProjectionElem::OpaqueCast(ty) => PlaceTy::from_ty(*ty),
 324                 ProjectionElem::Field(_, field_type) => PlaceTy::from_ty(*field_type),
 325             },
 326         };
 327         self.describe_field_from_ty(
 328             place_ty.ty,
 329             field,
 330             place_ty.variant_index,
 331             including_tuple_field,
 332         )
 333     }
 334
 335     /// End-user visible description of the `field_index`nth field of `ty`
 336     fn describe_field_from_ty(
 337         &self,
 338         ty: Ty<'_>,
 339         field: Field,
 340         variant_index: Option<VariantIdx>,
 341         including_tuple_field: IncludingTupleField,
 342     ) -> Option<String> {
 343         if ty.is_box() {
 344             // If the type is a box, the field is described from the boxed type
 345             self.describe_field_from_ty(ty.boxed_ty(), field, variant_index, including_tuple_field)
 346         } else {
 347             match *ty.kind() {
 348                 ty::Adt(def, _) => {
 349                     let variant = if let Some(idx) = variant_index {
 350                         assert!(def.is_enum());
 351                         &def.variant(idx)
 352                     } else {
 353                         def.non_enum_variant()
 354                     };
 355                     if !including_tuple_field.0 && variant.ctor_kind() == Some(CtorKind::Fn) {
 356                         return None;
 357                     }
 358                     Some(variant.fields[field.index()].name.to_string())
 359                 }
 360                 ty::Tuple(_) => Some(field.index().to_string()),
 361                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 362                     self.describe_field_from_ty(ty, field, variant_index, including_tuple_field)
 363                 }
 364                 ty::Array(ty, _) | ty::Slice(ty) => {
 365                     self.describe_field_from_ty(ty, field, variant_index, including_tuple_field)
 366                 }
 367                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 368                     // We won't be borrowck'ing here if the closure came from another crate,
 369                     // so it's safe to call `expect_local`.
 370                     //
 371                     // We know the field exists so it's safe to call operator[] and `unwrap` here.
 372                     let def_id = def_id.expect_local();
 373                     let var_id = self
 374                         .infcx
 375                         .tcx
 376                         .typeck(def_id)
 377                         .closure_min_captures_flattened(def_id)
 378                         .nth(field.index())
 379                         .unwrap()
 380                         .get_root_variable();
 381
 382                     Some(self.infcx.tcx.hir().name(var_id).to_string())
 383                 }
 384                 _ => {
 385                     // Might need a revision when the fields in trait RFC is implemented
 386                     // (https://github.com/rust-lang/rfcs/pull/1546)
 387                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 388                 }
 389             }
 390         }
 391     }
 392
 393     /// Add a note that a type does not implement `Copy`
 394     pub(super) fn note_type_does_not_implement_copy(
 395         &self,
 396         err: &mut Diagnostic,
 397         place_desc: &str,
 398         ty: Ty<'tcx>,
 399         span: Option<Span>,
 400         move_prefix: &str,
 401     ) {
 402         let message = format!(
 403             "{}move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 404             move_prefix, place_desc, ty,
 405         );
 406         if let Some(span) = span {
 407             err.span_label(span, message);
 408         } else {
 409             err.note(&message);
 410         }
 411     }
 412
 413     pub(super) fn borrowed_content_source(
 414         &self,
 415         deref_base: PlaceRef<'tcx>,
 416     ) -> BorrowedContentSource<'tcx> {
 417         let tcx = self.infcx.tcx;
 418
 419         // Look up the provided place and work out the move path index for it,
 420         // we'll use this to check whether it was originally from an overloaded
 421         // operator.
 422         match self.move_data.rev_lookup.find(deref_base) {
 423             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 424                 debug!("borrowed_content_source: mpi={:?}", mpi);
 425
 426                 for i in &self.move_data.init_path_map[mpi] {
 427                     let init = &self.move_data.inits[*i];
 428                     debug!("borrowed_content_source: init={:?}", init);
 429                     // We're only interested in statements that initialized a value, not the
 430                     // initializations from arguments.
 431                     let InitLocation::Statement(loc) = init.location else { continue };
 432
 433                     let bbd = &self.body[loc.block];
 434                     let is_terminator = bbd.statements.len() == loc.statement_index;
 435                     debug!(
 436                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 437                         loc, is_terminator,
 438                     );
 439                     if !is_terminator {
 440                         continue;
 441                     } else if let Some(Terminator {
 442                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 443                         ..
 444                     }) = bbd.terminator
 445                     {
 446                         if let Some(source) =
 447                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 448                         {
 449                             return source;
 450                         }
 451                     }
 452                 }
 453             }
 454             // Base is a `static` so won't be from an overloaded operator
 455             _ => (),
 456         };
 457
 458         // If we didn't find an overloaded deref or index, then assume it's a
 459         // built in deref and check the type of the base.
 460         let base_ty = deref_base.ty(self.body, tcx).ty;
 461         if base_ty.is_unsafe_ptr() {
 462             BorrowedContentSource::DerefRawPointer
 463         } else if base_ty.is_mutable_ptr() {
 464             BorrowedContentSource::DerefMutableRef
 465         } else {
 466             BorrowedContentSource::DerefSharedRef
 467         }
 468     }
 469
 470     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 471     /// name where required.
 472     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 473         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, Namespace::TypeNS);
 474
 475         // We need to add synthesized lifetimes where appropriate. We do
 476         // this by hooking into the pretty printer and telling it to label the
 477         // lifetimes without names with the value `'0`.
 478         if let ty::Ref(region, ..) = ty.kind() {
 479             match **region {
 480                 ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
 481                 | ty::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 482                     printer.region_highlight_mode.highlighting_bound_region(br, counter)
 483                 }
 484                 _ => {}
 485             }
 486         }
 487
 488         ty.print(printer).unwrap().into_buffer()
 489     }
 490
 491     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 492     /// synthesized lifetime name where required.
 493     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 494         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, Namespace::TypeNS);
 495
 496         let region = 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             region
 505         } else {
 506             bug!("ty for annotation of borrow region is not a reference");
 507         };
 508
 509         region.print(printer).unwrap().into_buffer()
 510     }
 511 }
 512
 513 /// The span(s) associated to a use of a place.
 514 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 515 pub(super) enum UseSpans<'tcx> {
 516     /// The access is caused by capturing a variable for a closure.
 517     ClosureUse {
 518         /// This is true if the captured variable was from a generator.
 519         generator_kind: Option<GeneratorKind>,
 520         /// The span of the args of the closure, including the `move` keyword if
 521         /// it's present.
 522         args_span: Span,
 523         /// The span of the use resulting in capture kind
 524         /// Check `ty::CaptureInfo` for more details
 525         capture_kind_span: Span,
 526         /// The span of the use resulting in the captured path
 527         /// Check `ty::CaptureInfo` for more details
 528         path_span: Span,
 529     },
 530     /// The access is caused by using a variable as the receiver of a method
 531     /// that takes 'self'
 532     FnSelfUse {
 533         /// The span of the variable being moved
 534         var_span: Span,
 535         /// The span of the method call on the variable
 536         fn_call_span: Span,
 537         /// The definition span of the method being called
 538         fn_span: Span,
 539         kind: CallKind<'tcx>,
 540     },
 541     /// This access is caused by a `match` or `if let` pattern.
 542     PatUse(Span),
 543     /// This access has a single span associated to it: common case.
 544     OtherUse(Span),
 545 }
 546
 547 impl UseSpans<'_> {
 548     pub(super) fn args_or_use(self) -> Span {
 549         match self {
 550             UseSpans::ClosureUse { args_span: span, .. }
 551             | UseSpans::PatUse(span)
 552             | UseSpans::OtherUse(span) => span,
 553             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 554                 fn_call_span
 555             }
 556             UseSpans::FnSelfUse { var_span, .. } => var_span,
 557         }
 558     }
 559
 560     /// Returns the span of `self`, in the case of a `ClosureUse` returns the `path_span`
 561     pub(super) fn var_or_use_path_span(self) -> Span {
 562         match self {
 563             UseSpans::ClosureUse { path_span: span, .. }
 564             | UseSpans::PatUse(span)
 565             | UseSpans::OtherUse(span) => span,
 566             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 567                 fn_call_span
 568             }
 569             UseSpans::FnSelfUse { var_span, .. } => var_span,
 570         }
 571     }
 572
 573     /// Returns the span of `self`, in the case of a `ClosureUse` returns the `capture_kind_span`
 574     pub(super) fn var_or_use(self) -> Span {
 575         match self {
 576             UseSpans::ClosureUse { capture_kind_span: span, .. }
 577             | UseSpans::PatUse(span)
 578             | UseSpans::OtherUse(span) => span,
 579             UseSpans::FnSelfUse { fn_call_span, kind: CallKind::DerefCoercion { .. }, .. } => {
 580                 fn_call_span
 581             }
 582             UseSpans::FnSelfUse { var_span, .. } => var_span,
 583         }
 584     }
 585
 586     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 587         match self {
 588             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 589             _ => None,
 590         }
 591     }
 592
 593     /// Add a span label to the arguments of the closure, if it exists.
 594     pub(super) fn args_span_label(self, err: &mut Diagnostic, message: impl Into<String>) {
 595         if let UseSpans::ClosureUse { args_span, .. } = self {
 596             err.span_label(args_span, message);
 597         }
 598     }
 599
 600     /// Add a span label to the use of the captured variable, if it exists.
 601     /// only adds label to the `path_span`
 602     pub(super) fn var_path_only_subdiag(
 603         self,
 604         err: &mut Diagnostic,
 605         action: crate::InitializationRequiringAction,
 606     ) {
 607         use crate::session_diagnostics::CaptureVarPathUseCause::*;
 608         use crate::InitializationRequiringAction::*;
 609         if let UseSpans::ClosureUse { generator_kind, path_span, .. } = self {
 610             match generator_kind {
 611                 Some(_) => {
 612                     err.subdiagnostic(match action {
 613                         Borrow => BorrowInGenerator { path_span },
 614                         MatchOn | Use => UseInGenerator { path_span },
 615                         Assignment => AssignInGenerator { path_span },
 616                         PartialAssignment => AssignPartInGenerator { path_span },
 617                     });
 618                 }
 619                 None => {
 620                     err.subdiagnostic(match action {
 621                         Borrow => BorrowInClosure { path_span },
 622                         MatchOn | Use => UseInClosure { path_span },
 623                         Assignment => AssignInClosure { path_span },
 624                         PartialAssignment => AssignPartInClosure { path_span },
 625                     });
 626                 }
 627             }
 628         }
 629     }
 630
 631     /// Add a span label to the use of the captured variable, if it exists.
 632     pub(super) fn var_span_label(
 633         self,
 634         err: &mut Diagnostic,
 635         message: impl Into<String>,
 636         kind_desc: impl Into<String>,
 637     ) {
 638         if let UseSpans::ClosureUse { capture_kind_span, path_span, .. } = self {
 639             if capture_kind_span == path_span {
 640                 err.span_label(capture_kind_span, message);
 641             } else {
 642                 let capture_kind_label =
 643                     format!("capture is {} because of use here", kind_desc.into());
 644                 let path_label = message;
 645                 err.span_label(capture_kind_span, capture_kind_label);
 646                 err.span_label(path_span, path_label);
 647             }
 648         }
 649     }
 650
 651     /// Add a subdiagnostic to the use of the captured variable, if it exists.
 652     pub(super) fn var_subdiag(
 653         self,
 654         err: &mut Diagnostic,
 655         kind: Option<rustc_middle::mir::BorrowKind>,
 656         f: impl Fn(Option<GeneratorKind>, Span) -> crate::session_diagnostics::CaptureVarCause,
 657     ) {
 658         use crate::session_diagnostics::CaptureVarKind::*;
 659         if let UseSpans::ClosureUse { generator_kind, capture_kind_span, path_span, .. } = self {
 660             if capture_kind_span != path_span {
 661                 err.subdiagnostic(match kind {
 662                     Some(kd) => match kd {
 663                         rustc_middle::mir::BorrowKind::Shared
 664                         | rustc_middle::mir::BorrowKind::Shallow
 665                         | rustc_middle::mir::BorrowKind::Unique => {
 666                             Immute { kind_span: capture_kind_span }
 667                         }
 668
 669                         rustc_middle::mir::BorrowKind::Mut { .. } => {
 670                             Mut { kind_span: capture_kind_span }
 671                         }
 672                     },
 673                     None => Move { kind_span: capture_kind_span },
 674                 });
 675             };
 676             err.subdiagnostic(f(generator_kind, path_span));
 677         }
 678     }
 679
 680     /// Returns `false` if this place is not used in a closure.
 681     pub(super) fn for_closure(&self) -> bool {
 682         match *self {
 683             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 684             _ => false,
 685         }
 686     }
 687
 688     /// Returns `false` if this place is not used in a generator.
 689     pub(super) fn for_generator(&self) -> bool {
 690         match *self {
 691             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 692             _ => false,
 693         }
 694     }
 695
 696     /// Describe the span associated with a use of a place.
 697     pub(super) fn describe(&self) -> &str {
 698         match *self {
 699             UseSpans::ClosureUse { generator_kind, .. } => {
 700                 if generator_kind.is_some() {
 701                     " in generator"
 702                 } else {
 703                     " in closure"
 704                 }
 705             }
 706             _ => "",
 707         }
 708     }
 709
 710     pub(super) fn or_else<F>(self, if_other: F) -> Self
 711     where
 712         F: FnOnce() -> Self,
 713     {
 714         match self {
 715             closure @ UseSpans::ClosureUse { .. } => closure,
 716             UseSpans::PatUse(_) | UseSpans::OtherUse(_) => if_other(),
 717             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 718         }
 719     }
 720 }
 721
 722 pub(super) enum BorrowedContentSource<'tcx> {
 723     DerefRawPointer,
 724     DerefMutableRef,
 725     DerefSharedRef,
 726     OverloadedDeref(Ty<'tcx>),
 727     OverloadedIndex(Ty<'tcx>),
 728 }
 729
 730 impl<'tcx> BorrowedContentSource<'tcx> {
 731     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 732         match *self {
 733             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 734             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 735             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 736             BorrowedContentSource::OverloadedDeref(ty) => ty
 737                 .ty_adt_def()
 738                 .and_then(|adt| match tcx.get_diagnostic_name(adt.did())? {
 739                     name @ (sym::Rc | sym::Arc) => Some(format!("an `{}`", name)),
 740                     _ => None,
 741                 })
 742                 .unwrap_or_else(|| format!("dereference of `{}`", ty)),
 743             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 744         }
 745     }
 746
 747     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 748         match *self {
 749             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 750             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 751             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 752             // Overloaded deref and index operators should be evaluated into a
 753             // temporary. So we don't need a description here.
 754             BorrowedContentSource::OverloadedDeref(_)
 755             | BorrowedContentSource::OverloadedIndex(_) => None,
 756         }
 757     }
 758
 759     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 760         match *self {
 761             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 762             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 763             BorrowedContentSource::DerefMutableRef => {
 764                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 765             }
 766             BorrowedContentSource::OverloadedDeref(ty) => ty
 767                 .ty_adt_def()
 768                 .and_then(|adt| match tcx.get_diagnostic_name(adt.did())? {
 769                     name @ (sym::Rc | sym::Arc) => Some(format!("an `{}`", name)),
 770                     _ => None,
 771                 })
 772                 .unwrap_or_else(|| format!("dereference of `{}`", ty)),
 773             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 774         }
 775     }
 776
 777     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 778         match *func.kind() {
 779             ty::FnDef(def_id, substs) => {
 780                 let trait_id = tcx.trait_of_item(def_id)?;
 781
 782                 let lang_items = tcx.lang_items();
 783                 if Some(trait_id) == lang_items.deref_trait()
 784                     || Some(trait_id) == lang_items.deref_mut_trait()
 785                 {
 786                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 787                 } else if Some(trait_id) == lang_items.index_trait()
 788                     || Some(trait_id) == lang_items.index_mut_trait()
 789                 {
 790                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 791                 } else {
 792                     None
 793                 }
 794             }
 795             _ => None,
 796         }
 797     }
 798 }
 799
 800 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 801     /// Finds the spans associated to a move or copy of move_place at location.
 802     pub(super) fn move_spans(
 803         &self,
 804         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 805         location: Location,
 806     ) -> UseSpans<'tcx> {
 807         use self::UseSpans::*;
 808
 809         let Some(stmt) = self.body[location.block].statements.get(location.statement_index) else {
 810             return OtherUse(self.body.source_info(location).span);
 811         };
 812
 813         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 814         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 815             match **kind {
 816                 AggregateKind::Closure(def_id, _) | AggregateKind::Generator(def_id, _, _) => {
 817                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 818                     if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 819                         self.closure_span(def_id, moved_place, places)
 820                     {
 821                         return ClosureUse {
 822                             generator_kind,
 823                             args_span,
 824                             capture_kind_span,
 825                             path_span,
 826                         };
 827                     }
 828                 }
 829                 _ => {}
 830             }
 831         }
 832
 833         // StatementKind::FakeRead only contains a def_id if they are introduced as a result
 834         // of pattern matching within a closure.
 835         if let StatementKind::FakeRead(box (cause, ref place)) = stmt.kind {
 836             match cause {
 837                 FakeReadCause::ForMatchedPlace(Some(closure_def_id))
 838                 | FakeReadCause::ForLet(Some(closure_def_id)) => {
 839                     debug!("move_spans: def_id={:?} place={:?}", closure_def_id, place);
 840                     let places = &[Operand::Move(*place)];
 841                     if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 842                         self.closure_span(closure_def_id, moved_place, places)
 843                     {
 844                         return ClosureUse {
 845                             generator_kind,
 846                             args_span,
 847                             capture_kind_span,
 848                             path_span,
 849                         };
 850                     }
 851                 }
 852                 _ => {}
 853             }
 854         }
 855
 856         let normal_ret =
 857             if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
 858                 PatUse(stmt.source_info.span)
 859             } else {
 860                 OtherUse(stmt.source_info.span)
 861             };
 862
 863         // We are trying to find MIR of the form:
 864         // ```
 865         // _temp = _moved_val;
 866         // ...
 867         // FnSelfCall(_temp, ...)
 868         // ```
 869         //
 870         // where `_moved_val` is the place we generated the move error for,
 871         // `_temp` is some other local, and `FnSelfCall` is a function
 872         // that has a `self` parameter.
 873
 874         let target_temp = match stmt.kind {
 875             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 876                 temp.as_local().unwrap()
 877             }
 878             _ => return normal_ret,
 879         };
 880
 881         debug!("move_spans: target_temp = {:?}", target_temp);
 882
 883         if let Some(Terminator {
 884             kind: TerminatorKind::Call { fn_span, from_hir_call, .. }, ..
 885         }) = &self.body[location.block].terminator
 886         {
 887             let Some((method_did, method_substs)) =
 888                 rustc_const_eval::util::find_self_call(
 889                     self.infcx.tcx,
 890                     &self.body,
 891                     target_temp,
 892                     location.block,
 893                 )
 894             else {
 895                 return normal_ret;
 896             };
 897
 898             let kind = call_kind(
 899                 self.infcx.tcx,
 900                 self.param_env,
 901                 method_did,
 902                 method_substs,
 903                 *fn_span,
 904                 *from_hir_call,
 905                 Some(self.infcx.tcx.fn_arg_names(method_did)[0]),
 906             );
 907
 908             return FnSelfUse {
 909                 var_span: stmt.source_info.span,
 910                 fn_call_span: *fn_span,
 911                 fn_span: self.infcx.tcx.def_span(method_did),
 912                 kind,
 913             };
 914         }
 915         normal_ret
 916     }
 917
 918     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 919     /// and its usage of the local assigned at `location`.
 920     /// This is done by searching in statements succeeding `location`
 921     /// and originating from `maybe_closure_span`.
 922     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans<'tcx> {
 923         use self::UseSpans::*;
 924         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 925
 926         let target = match self.body[location.block].statements.get(location.statement_index) {
 927             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 928                 if let Some(local) = place.as_local() {
 929                     local
 930                 } else {
 931                     return OtherUse(use_span);
 932                 }
 933             }
 934             _ => return OtherUse(use_span),
 935         };
 936
 937         if self.body.local_kind(target) != LocalKind::Temp {
 938             // operands are always temporaries.
 939             return OtherUse(use_span);
 940         }
 941
 942         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 943             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 944                 stmt.kind
 945             {
 946                 let (&def_id, is_generator) = match kind {
 947                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 948                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 949                     _ => continue,
 950                 };
 951
 952                 debug!(
 953                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 954                     def_id, is_generator, places
 955                 );
 956                 if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
 957                     self.closure_span(def_id, Place::from(target).as_ref(), places)
 958                 {
 959                     return ClosureUse { generator_kind, args_span, capture_kind_span, path_span };
 960                 } else {
 961                     return OtherUse(use_span);
 962                 }
 963             }
 964
 965             if use_span != stmt.source_info.span {
 966                 break;
 967             }
 968         }
 969
 970         OtherUse(use_span)
 971     }
 972
 973     /// Finds the spans of a captured place within a closure or generator.
 974     /// The first span is the location of the use resulting in the capture kind of the capture
 975     /// The second span is the location the use resulting in the captured path of the capture
 976     fn closure_span(
 977         &self,
 978         def_id: LocalDefId,
 979         target_place: PlaceRef<'tcx>,
 980         places: &[Operand<'tcx>],
 981     ) -> Option<(Span, Option<GeneratorKind>, Span, Span)> {
 982         debug!(
 983             "closure_span: def_id={:?} target_place={:?} places={:?}",
 984             def_id, target_place, places
 985         );
 986         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(def_id);
 987         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 988         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 989         if let hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }) = expr {
 990             for (captured_place, place) in
 991                 self.infcx.tcx.typeck(def_id).closure_min_captures_flattened(def_id).zip(places)
 992             {
 993                 match place {
 994                     Operand::Copy(place) | Operand::Move(place)
 995                         if target_place == place.as_ref() =>
 996                     {
 997                         debug!("closure_span: found captured local {:?}", place);
 998                         let body = self.infcx.tcx.hir().body(body);
 999                         let generator_kind = body.generator_kind();
1000
1001                         return Some((
1002                             fn_decl_span,
1003                             generator_kind,
1004                             captured_place.get_capture_kind_span(self.infcx.tcx),
1005                             captured_place.get_path_span(self.infcx.tcx),
1006                         ));
1007                     }
1008                     _ => {}
1009                 }
1010             }
1011         }
1012         None
1013     }
1014
1015     /// Helper to retrieve span(s) of given borrow from the current MIR
1016     /// representation
1017     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans<'tcx> {
1018         let span = self.body.source_info(borrow.reserve_location).span;
1019         self.borrow_spans(span, borrow.reserve_location)
1020     }
1021
1022     fn explain_captures(
1023         &mut self,
1024         err: &mut Diagnostic,
1025         span: Span,
1026         move_span: Span,
1027         move_spans: UseSpans<'tcx>,
1028         moved_place: Place<'tcx>,
1029         partially_str: &str,
1030         loop_message: &str,
1031         move_msg: &str,
1032         is_loop_move: bool,
1033         maybe_reinitialized_locations_is_empty: bool,
1034     ) {
1035         if let UseSpans::FnSelfUse { var_span, fn_call_span, fn_span, kind } = move_spans {
1036             let place_name = self
1037                 .describe_place(moved_place.as_ref())
1038                 .map(|n| format!("`{}`", n))
1039                 .unwrap_or_else(|| "value".to_owned());
1040             match kind {
1041                 CallKind::FnCall { fn_trait_id, .. }
1042                     if Some(fn_trait_id) == self.infcx.tcx.lang_items().fn_once_trait() =>
1043                 {
1044                     err.span_label(
1045                         fn_call_span,
1046                         &format!(
1047                             "{} {}moved due to this call{}",
1048                             place_name, partially_str, loop_message
1049                         ),
1050                     );
1051                     err.span_note(
1052                         var_span,
1053                         "this value implements `FnOnce`, which causes it to be moved when called",
1054                     );
1055                 }
1056                 CallKind::Operator { self_arg, .. } => {
1057                     let self_arg = self_arg.unwrap();
1058                     err.span_label(
1059                         fn_call_span,
1060                         &format!(
1061                             "{} {}moved due to usage in operator{}",
1062                             place_name, partially_str, loop_message
1063                         ),
1064                     );
1065                     if self.fn_self_span_reported.insert(fn_span) {
1066                         err.span_note(
1067                             // Check whether the source is accessible
1068                             if self.infcx.tcx.sess.source_map().is_span_accessible(self_arg.span) {
1069                                 self_arg.span
1070                             } else {
1071                                 fn_call_span
1072                             },
1073                             "calling this operator moves the left-hand side",
1074                         );
1075                     }
1076                 }
1077                 CallKind::Normal { self_arg, desugaring, is_option_or_result } => {
1078                     let self_arg = self_arg.unwrap();
1079                     if let Some((CallDesugaringKind::ForLoopIntoIter, _)) = desugaring {
1080                         let ty = moved_place.ty(self.body, self.infcx.tcx).ty;
1081                         let suggest = match self.infcx.tcx.get_diagnostic_item(sym::IntoIterator) {
1082                             Some(def_id) => {
1083                                 let infcx = self.infcx.tcx.infer_ctxt().build();
1084                                 type_known_to_meet_bound_modulo_regions(
1085                                     &infcx,
1086                                     self.param_env,
1087                                     infcx.tcx.mk_imm_ref(
1088                                         infcx.tcx.lifetimes.re_erased,
1089                                         infcx.tcx.erase_regions(ty),
1090                                     ),
1091                                     def_id,
1092                                     DUMMY_SP,
1093                                 )
1094                             }
1095                             _ => false,
1096                         };
1097                         if suggest {
1098                             err.span_suggestion_verbose(
1099                                 move_span.shrink_to_lo(),
1100                                 &format!(
1101                                     "consider iterating over a slice of the `{}`'s content to \
1102                                      avoid moving into the `for` loop",
1103                                     ty,
1104                                 ),
1105                                 "&",
1106                                 Applicability::MaybeIncorrect,
1107                             );
1108                         }
1109
1110                         err.span_label(
1111                             fn_call_span,
1112                             &format!(
1113                                 "{} {}moved due to this implicit call to `.into_iter()`{}",
1114                                 place_name, partially_str, loop_message
1115                             ),
1116                         );
1117                         // If the moved place was a `&mut` ref, then we can
1118                         // suggest to reborrow it where it was moved, so it
1119                         // will still be valid by the time we get to the usage.
1120                         if let ty::Ref(_, _, hir::Mutability::Mut) =
1121                             moved_place.ty(self.body, self.infcx.tcx).ty.kind()
1122                         {
1123                             // If we are in a loop this will be suggested later.
1124                             if !is_loop_move {
1125                                 err.span_suggestion_verbose(
1126                                     move_span.shrink_to_lo(),
1127                                     &format!(
1128                                         "consider creating a fresh reborrow of {} here",
1129                                         self.describe_place(moved_place.as_ref())
1130                                             .map(|n| format!("`{}`", n))
1131                                             .unwrap_or_else(|| "the mutable reference".to_string()),
1132                                     ),
1133                                     "&mut *",
1134                                     Applicability::MachineApplicable,
1135                                 );
1136                             }
1137                         }
1138                     } else {
1139                         err.span_label(
1140                             fn_call_span,
1141                             &format!(
1142                                 "{} {}moved due to this method call{}",
1143                                 place_name, partially_str, loop_message
1144                             ),
1145                         );
1146                     }
1147                     // Avoid pointing to the same function in multiple different
1148                     // error messages.
1149                     if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span) {
1150                         err.span_note(
1151                             self_arg.span,
1152                             &format!("this function takes ownership of the receiver `self`, which moves {}", place_name)
1153                         );
1154                     }
1155                     if is_option_or_result && maybe_reinitialized_locations_is_empty {
1156                         err.span_label(
1157                             var_span,
1158                             "help: consider calling `.as_ref()` or `.as_mut()` to borrow the type's contents",
1159                         );
1160                     }
1161                 }
1162                 // Other desugarings takes &self, which cannot cause a move
1163                 _ => {}
1164             }
1165         } else {
1166             if move_span != span || !loop_message.is_empty() {
1167                 err.span_label(
1168                     move_span,
1169                     format!("value {}moved{} here{}", partially_str, move_msg, loop_message),
1170                 );
1171             }
1172             // If the move error occurs due to a loop, don't show
1173             // another message for the same span
1174             if loop_message.is_empty() {
1175                 move_spans.var_span_label(
1176                     err,
1177                     format!("variable {}moved due to use{}", partially_str, move_spans.describe()),
1178                     "moved",
1179                 );
1180             }
1181         }
1182     }
1183 }