compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs

   1 //! Borrow checker diagnostics.
   2
   3 use rustc_errors::DiagnosticBuilder;
   4 use rustc_hir as hir;
   5 use rustc_hir::def::Namespace;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_hir::lang_items::LangItemGroup;
   8 use rustc_hir::GeneratorKind;
   9 use rustc_middle::mir::{
  10     AggregateKind, Constant, Field, Local, LocalInfo, LocalKind, Location, Operand, Place,
  11     PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
  12 };
  13 use rustc_middle::ty::print::Print;
  14 use rustc_middle::ty::{self, DefIdTree, Instance, Ty, TyCtxt};
  15 use rustc_span::{
  16     hygiene::{DesugaringKind, ForLoopLoc},
  17     symbol::sym,
  18     Span,
  19 };
  20 use rustc_target::abi::VariantIdx;
  21
  22 use super::borrow_set::BorrowData;
  23 use super::MirBorrowckCtxt;
  24 use crate::dataflow::move_paths::{InitLocation, LookupResult};
  25
  26 mod find_use;
  27 mod outlives_suggestion;
  28 mod region_name;
  29 mod var_name;
  30
  31 mod conflict_errors;
  32 mod explain_borrow;
  33 mod move_errors;
  34 mod mutability_errors;
  35 mod region_errors;
  36
  37 crate use mutability_errors::AccessKind;
  38 crate use outlives_suggestion::OutlivesSuggestionBuilder;
  39 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
  40 crate use region_name::{RegionName, RegionNameSource};
  41 use rustc_span::symbol::Ident;
  42
  43 pub(super) struct IncludingDowncast(pub(super) bool);
  44
  45 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
  46     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
  47     /// is moved after being invoked.
  48     ///
  49     /// ```text
  50     /// note: closure cannot be invoked more than once because it moves the variable `dict` out of
  51     ///       its environment
  52     ///   --> $DIR/issue-42065.rs:16:29
  53     ///    |
  54     /// LL |         for (key, value) in dict {
  55     ///    |                             ^^^^
  56     /// ```
  57     pub(super) fn add_moved_or_invoked_closure_note(
  58         &self,
  59         location: Location,
  60         place: PlaceRef<'tcx>,
  61         diag: &mut DiagnosticBuilder<'_>,
  62     ) {
  63         debug!("add_moved_or_invoked_closure_note: location={:?} place={:?}", location, place);
  64         let mut target = place.local_or_deref_local();
  65         for stmt in &self.body[location.block].statements[location.statement_index..] {
  66             debug!("add_moved_or_invoked_closure_note: stmt={:?} target={:?}", stmt, target);
  67             if let StatementKind::Assign(box (into, Rvalue::Use(from))) = &stmt.kind {
  68                 debug!("add_fnonce_closure_note: into={:?} from={:?}", into, from);
  69                 match from {
  70                     Operand::Copy(ref place) | Operand::Move(ref place)
  71                         if target == place.local_or_deref_local() =>
  72                     {
  73                         target = into.local_or_deref_local()
  74                     }
  75                     _ => {}
  76                 }
  77             }
  78         }
  79
  80         // Check if we are attempting to call a closure after it has been invoked.
  81         let terminator = self.body[location.block].terminator();
  82         debug!("add_moved_or_invoked_closure_note: terminator={:?}", terminator);
  83         if let TerminatorKind::Call {
  84             func: Operand::Constant(box Constant { literal: ty::Const { ty: const_ty, .. }, .. }),
  85             args,
  86             ..
  87         } = &terminator.kind
  88         {
  89             if let ty::FnDef(id, _) = *const_ty.kind() {
  90                 debug!("add_moved_or_invoked_closure_note: id={:?}", id);
  91                 if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
  92                     let closure = match args.first() {
  93                         Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
  94                             if target == place.local_or_deref_local() =>
  95                         {
  96                             place.local_or_deref_local().unwrap()
  97                         }
  98                         _ => return,
  99                     };
 100
 101                     debug!("add_moved_or_invoked_closure_note: closure={:?}", closure);
 102                     if let ty::Closure(did, _) = self.body.local_decls[closure].ty.kind() {
 103                         let did = did.expect_local();
 104                         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 105
 106                         if let Some((span, name)) =
 107                             self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 108                         {
 109                             diag.span_note(
 110                                 *span,
 111                                 &format!(
 112                                     "closure cannot be invoked more than once because it moves the \
 113                                     variable `{}` out of its environment",
 114                                     name,
 115                                 ),
 116                             );
 117                             return;
 118                         }
 119                     }
 120                 }
 121             }
 122         }
 123
 124         // Check if we are just moving a closure after it has been invoked.
 125         if let Some(target) = target {
 126             if let ty::Closure(did, _) = self.body.local_decls[target].ty.kind() {
 127                 let did = did.expect_local();
 128                 let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(did);
 129
 130                 if let Some((span, name)) =
 131                     self.infcx.tcx.typeck(did).closure_kind_origins().get(hir_id)
 132                 {
 133                     diag.span_note(
 134                         *span,
 135                         &format!(
 136                             "closure cannot be moved more than once as it is not `Copy` due to \
 137                              moving the variable `{}` out of its environment",
 138                             name
 139                         ),
 140                     );
 141                 }
 142             }
 143         }
 144     }
 145
 146     /// End-user visible description of `place` if one can be found.
 147     /// If the place is a temporary for instance, `"value"` will be returned.
 148     pub(super) fn describe_any_place(&self, place_ref: PlaceRef<'tcx>) -> String {
 149         match self.describe_place(place_ref) {
 150             Some(mut descr) => {
 151                 // Surround descr with `backticks`.
 152                 descr.reserve(2);
 153                 descr.insert(0, '`');
 154                 descr.push('`');
 155                 descr
 156             }
 157             None => "value".to_string(),
 158         }
 159     }
 160
 161     /// End-user visible description of `place` if one can be found.
 162     /// If the place is a temporary for instance, None will be returned.
 163     pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
 164         self.describe_place_with_options(place_ref, IncludingDowncast(false))
 165     }
 166
 167     /// End-user visible description of `place` if one can be found. If the
 168     /// place is a temporary for instance, None will be returned.
 169     /// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
 170     /// `Downcast` and `IncludingDowncast` is true
 171     pub(super) fn describe_place_with_options(
 172         &self,
 173         place: PlaceRef<'tcx>,
 174         including_downcast: IncludingDowncast,
 175     ) -> Option<String> {
 176         let mut buf = String::new();
 177         match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
 178             Ok(()) => Some(buf),
 179             Err(()) => None,
 180         }
 181     }
 182
 183     /// Appends end-user visible description of `place` to `buf`.
 184     fn append_place_to_string(
 185         &self,
 186         place: PlaceRef<'tcx>,
 187         buf: &mut String,
 188         mut autoderef: bool,
 189         including_downcast: &IncludingDowncast,
 190     ) -> Result<(), ()> {
 191         match place {
 192             PlaceRef { local, projection: [] } => {
 193                 self.append_local_to_string(local, buf)?;
 194             }
 195             PlaceRef { local, projection: [ProjectionElem::Deref] }
 196                 if self.body.local_decls[local].is_ref_for_guard() =>
 197             {
 198                 self.append_place_to_string(
 199                     PlaceRef { local, projection: &[] },
 200                     buf,
 201                     autoderef,
 202                     &including_downcast,
 203                 )?;
 204             }
 205             PlaceRef { local, projection: [ProjectionElem::Deref] }
 206                 if self.body.local_decls[local].is_ref_to_static() =>
 207             {
 208                 let local_info = &self.body.local_decls[local].local_info;
 209                 if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
 210                     buf.push_str(&self.infcx.tcx.item_name(def_id).as_str());
 211                 } else {
 212                     unreachable!();
 213                 }
 214             }
 215             PlaceRef { local, projection: [proj_base @ .., elem] } => {
 216                 match elem {
 217                     ProjectionElem::Deref => {
 218                         let upvar_field_projection = self.is_upvar_field_projection(place);
 219                         if let Some(field) = upvar_field_projection {
 220                             let var_index = field.index();
 221                             let name = self.upvars[var_index].name.to_string();
 222                             if self.upvars[var_index].by_ref {
 223                                 buf.push_str(&name);
 224                             } else {
 225                                 buf.push('*');
 226                                 buf.push_str(&name);
 227                             }
 228                         } else {
 229                             if autoderef {
 230                                 // FIXME turn this recursion into iteration
 231                                 self.append_place_to_string(
 232                                     PlaceRef { local, projection: proj_base },
 233                                     buf,
 234                                     autoderef,
 235                                     &including_downcast,
 236                                 )?;
 237                             } else {
 238                                 buf.push('*');
 239                                 self.append_place_to_string(
 240                                     PlaceRef { local, projection: proj_base },
 241                                     buf,
 242                                     autoderef,
 243                                     &including_downcast,
 244                                 )?;
 245                             }
 246                         }
 247                     }
 248                     ProjectionElem::Downcast(..) => {
 249                         self.append_place_to_string(
 250                             PlaceRef { local, projection: proj_base },
 251                             buf,
 252                             autoderef,
 253                             &including_downcast,
 254                         )?;
 255                         if including_downcast.0 {
 256                             return Err(());
 257                         }
 258                     }
 259                     ProjectionElem::Field(field, _ty) => {
 260                         autoderef = true;
 261
 262                         let upvar_field_projection = self.is_upvar_field_projection(place);
 263                         if let Some(field) = upvar_field_projection {
 264                             let var_index = field.index();
 265                             let name = self.upvars[var_index].name.to_string();
 266                             buf.push_str(&name);
 267                         } else {
 268                             let field_name = self
 269                                 .describe_field(PlaceRef { local, projection: proj_base }, *field);
 270                             self.append_place_to_string(
 271                                 PlaceRef { local, projection: proj_base },
 272                                 buf,
 273                                 autoderef,
 274                                 &including_downcast,
 275                             )?;
 276                             buf.push('.');
 277                             buf.push_str(&field_name);
 278                         }
 279                     }
 280                     ProjectionElem::Index(index) => {
 281                         autoderef = true;
 282
 283                         self.append_place_to_string(
 284                             PlaceRef { local, projection: proj_base },
 285                             buf,
 286                             autoderef,
 287                             &including_downcast,
 288                         )?;
 289                         buf.push('[');
 290                         if self.append_local_to_string(*index, buf).is_err() {
 291                             buf.push('_');
 292                         }
 293                         buf.push(']');
 294                     }
 295                     ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
 296                         autoderef = true;
 297                         // Since it isn't possible to borrow an element on a particular index and
 298                         // then use another while the borrow is held, don't output indices details
 299                         // to avoid confusing the end-user
 300                         self.append_place_to_string(
 301                             PlaceRef { local, projection: proj_base },
 302                             buf,
 303                             autoderef,
 304                             &including_downcast,
 305                         )?;
 306                         buf.push_str("[..]");
 307                     }
 308                 };
 309             }
 310         }
 311
 312         Ok(())
 313     }
 314
 315     /// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
 316     /// a name, or its name was generated by the compiler, then `Err` is returned
 317     fn append_local_to_string(&self, local: Local, buf: &mut String) -> Result<(), ()> {
 318         let decl = &self.body.local_decls[local];
 319         match self.local_names[local] {
 320             Some(name) if !decl.from_compiler_desugaring() => {
 321                 buf.push_str(&name.as_str());
 322                 Ok(())
 323             }
 324             _ => Err(()),
 325         }
 326     }
 327
 328     /// End-user visible description of the `field`nth field of `base`
 329     fn describe_field(&self, place: PlaceRef<'tcx>, field: Field) -> String {
 330         // FIXME Place2 Make this work iteratively
 331         match place {
 332             PlaceRef { local, projection: [] } => {
 333                 let local = &self.body.local_decls[local];
 334                 self.describe_field_from_ty(&local.ty, field, None)
 335             }
 336             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
 337                 ProjectionElem::Deref => {
 338                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 339                 }
 340                 ProjectionElem::Downcast(_, variant_index) => {
 341                     let base_ty =
 342                         Place::ty_from(place.local, place.projection, self.body, self.infcx.tcx).ty;
 343                     self.describe_field_from_ty(&base_ty, field, Some(*variant_index))
 344                 }
 345                 ProjectionElem::Field(_, field_type) => {
 346                     self.describe_field_from_ty(&field_type, field, None)
 347                 }
 348                 ProjectionElem::Index(..)
 349                 | ProjectionElem::ConstantIndex { .. }
 350                 | ProjectionElem::Subslice { .. } => {
 351                     self.describe_field(PlaceRef { local, projection: proj_base }, field)
 352                 }
 353             },
 354         }
 355     }
 356
 357     /// End-user visible description of the `field_index`nth field of `ty`
 358     fn describe_field_from_ty(
 359         &self,
 360         ty: Ty<'_>,
 361         field: Field,
 362         variant_index: Option<VariantIdx>,
 363     ) -> String {
 364         if ty.is_box() {
 365             // If the type is a box, the field is described from the boxed type
 366             self.describe_field_from_ty(&ty.boxed_ty(), field, variant_index)
 367         } else {
 368             match *ty.kind() {
 369                 ty::Adt(def, _) => {
 370                     let variant = if let Some(idx) = variant_index {
 371                         assert!(def.is_enum());
 372                         &def.variants[idx]
 373                     } else {
 374                         def.non_enum_variant()
 375                     };
 376                     variant.fields[field.index()].ident.to_string()
 377                 }
 378                 ty::Tuple(_) => field.index().to_string(),
 379                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 380                     self.describe_field_from_ty(&ty, field, variant_index)
 381                 }
 382                 ty::Array(ty, _) | ty::Slice(ty) => {
 383                     self.describe_field_from_ty(&ty, field, variant_index)
 384                 }
 385                 ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 386                     // `tcx.upvars_mentioned(def_id)` returns an `Option`, which is `None` in case
 387                     // the closure comes from another crate. But in that case we wouldn't
 388                     // be borrowck'ing it, so we can just unwrap:
 389                     let (&var_id, _) = self
 390                         .infcx
 391                         .tcx
 392                         .upvars_mentioned(def_id)
 393                         .unwrap()
 394                         .get_index(field.index())
 395                         .unwrap();
 396
 397                     self.infcx.tcx.hir().name(var_id).to_string()
 398                 }
 399                 _ => {
 400                     // Might need a revision when the fields in trait RFC is implemented
 401                     // (https://github.com/rust-lang/rfcs/pull/1546)
 402                     bug!("End-user description not implemented for field access on `{:?}`", ty);
 403                 }
 404             }
 405         }
 406     }
 407
 408     /// Add a note that a type does not implement `Copy`
 409     pub(super) fn note_type_does_not_implement_copy(
 410         &self,
 411         err: &mut DiagnosticBuilder<'a>,
 412         place_desc: &str,
 413         ty: Ty<'tcx>,
 414         span: Option<Span>,
 415         move_prefix: &str,
 416     ) {
 417         let message = format!(
 418             "{}move occurs because {} has type `{}`, which does not implement the `Copy` trait",
 419             move_prefix, place_desc, ty,
 420         );
 421         if let Some(span) = span {
 422             err.span_label(span, message);
 423         } else {
 424             err.note(&message);
 425         }
 426     }
 427
 428     pub(super) fn borrowed_content_source(
 429         &self,
 430         deref_base: PlaceRef<'tcx>,
 431     ) -> BorrowedContentSource<'tcx> {
 432         let tcx = self.infcx.tcx;
 433
 434         // Look up the provided place and work out the move path index for it,
 435         // we'll use this to check whether it was originally from an overloaded
 436         // operator.
 437         match self.move_data.rev_lookup.find(deref_base) {
 438             LookupResult::Exact(mpi) | LookupResult::Parent(Some(mpi)) => {
 439                 debug!("borrowed_content_source: mpi={:?}", mpi);
 440
 441                 for i in &self.move_data.init_path_map[mpi] {
 442                     let init = &self.move_data.inits[*i];
 443                     debug!("borrowed_content_source: init={:?}", init);
 444                     // We're only interested in statements that initialized a value, not the
 445                     // initializations from arguments.
 446                     let loc = match init.location {
 447                         InitLocation::Statement(stmt) => stmt,
 448                         _ => continue,
 449                     };
 450
 451                     let bbd = &self.body[loc.block];
 452                     let is_terminator = bbd.statements.len() == loc.statement_index;
 453                     debug!(
 454                         "borrowed_content_source: loc={:?} is_terminator={:?}",
 455                         loc, is_terminator,
 456                     );
 457                     if !is_terminator {
 458                         continue;
 459                     } else if let Some(Terminator {
 460                         kind: TerminatorKind::Call { ref func, from_hir_call: false, .. },
 461                         ..
 462                     }) = bbd.terminator
 463                     {
 464                         if let Some(source) =
 465                             BorrowedContentSource::from_call(func.ty(self.body, tcx), tcx)
 466                         {
 467                             return source;
 468                         }
 469                     }
 470                 }
 471             }
 472             // Base is a `static` so won't be from an overloaded operator
 473             _ => (),
 474         };
 475
 476         // If we didn't find an overloaded deref or index, then assume it's a
 477         // built in deref and check the type of the base.
 478         let base_ty = Place::ty_from(deref_base.local, deref_base.projection, self.body, tcx).ty;
 479         if base_ty.is_unsafe_ptr() {
 480             BorrowedContentSource::DerefRawPointer
 481         } else if base_ty.is_mutable_ptr() {
 482             BorrowedContentSource::DerefMutableRef
 483         } else {
 484             BorrowedContentSource::DerefSharedRef
 485         }
 486     }
 487 }
 488
 489 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 490     /// Return the name of the provided `Ty` (that must be a reference) with a synthesized lifetime
 491     /// name where required.
 492     pub(super) fn get_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 493         let mut s = String::new();
 494         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 495
 496         // We need to add synthesized lifetimes where appropriate. We do
 497         // this by hooking into the pretty printer and telling it to label the
 498         // lifetimes without names with the value `'0`.
 499         match ty.kind() {
 500             ty::Ref(
 501                 ty::RegionKind::ReLateBound(_, br)
 502                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
 503                 _,
 504                 _,
 505             ) => printer.region_highlight_mode.highlighting_bound_region(*br, counter),
 506             _ => {}
 507         }
 508
 509         let _ = ty.print(printer);
 510         s
 511     }
 512
 513     /// Returns the name of the provided `Ty` (that must be a reference)'s region with a
 514     /// synthesized lifetime name where required.
 515     pub(super) fn get_region_name_for_ty(&self, ty: Ty<'tcx>, counter: usize) -> String {
 516         let mut s = String::new();
 517         let mut printer = ty::print::FmtPrinter::new(self.infcx.tcx, &mut s, Namespace::TypeNS);
 518
 519         let region = match ty.kind() {
 520             ty::Ref(region, _, _) => {
 521                 match region {
 522                     ty::RegionKind::ReLateBound(_, br)
 523                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
 524                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
 525                     }
 526                     _ => {}
 527                 }
 528
 529                 region
 530             }
 531             _ => bug!("ty for annotation of borrow region is not a reference"),
 532         };
 533
 534         let _ = region.print(printer);
 535         s
 536     }
 537 }
 538
 539 /// The span(s) associated to a use of a place.
 540 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 541 pub(super) enum UseSpans<'tcx> {
 542     /// The access is caused by capturing a variable for a closure.
 543     ClosureUse {
 544         /// This is true if the captured variable was from a generator.
 545         generator_kind: Option<GeneratorKind>,
 546         /// The span of the args of the closure, including the `move` keyword if
 547         /// it's present.
 548         args_span: Span,
 549         /// The span of the first use of the captured variable inside the closure.
 550         var_span: Span,
 551     },
 552     /// The access is caused by using a variable as the receiver of a method
 553     /// that takes 'self'
 554     FnSelfUse {
 555         /// The span of the variable being moved
 556         var_span: Span,
 557         /// The span of the method call on the variable
 558         fn_call_span: Span,
 559         /// The definition span of the method being called
 560         fn_span: Span,
 561         kind: FnSelfUseKind<'tcx>,
 562     },
 563     /// This access is caused by a `match` or `if let` pattern.
 564     PatUse(Span),
 565     /// This access has a single span associated to it: common case.
 566     OtherUse(Span),
 567 }
 568
 569 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 570 pub(super) enum FnSelfUseKind<'tcx> {
 571     /// A normal method call of the form `receiver.foo(a, b, c)`
 572     Normal { self_arg: Ident, implicit_into_iter: bool },
 573     /// A call to `FnOnce::call_once`, desugared from `my_closure(a, b, c)`
 574     FnOnceCall,
 575     /// A call to an operator trait, desuraged from operator syntax (e.g. `a << b`)
 576     Operator { self_arg: Ident },
 577     DerefCoercion {
 578         /// The `Span` of the `Target` associated type
 579         /// in the `Deref` impl we are using.
 580         deref_target: Span,
 581         /// The type `T::Deref` we are dereferencing to
 582         deref_target_ty: Ty<'tcx>,
 583     },
 584 }
 585
 586 impl UseSpans<'_> {
 587     pub(super) fn args_or_use(self) -> Span {
 588         match self {
 589             UseSpans::ClosureUse { args_span: span, .. }
 590             | UseSpans::PatUse(span)
 591             | UseSpans::OtherUse(span) => span,
 592             UseSpans::FnSelfUse {
 593                 fn_call_span, kind: FnSelfUseKind::DerefCoercion { .. }, ..
 594             } => fn_call_span,
 595             UseSpans::FnSelfUse { var_span, .. } => var_span,
 596         }
 597     }
 598
 599     pub(super) fn var_or_use(self) -> Span {
 600         match self {
 601             UseSpans::ClosureUse { var_span: span, .. }
 602             | UseSpans::PatUse(span)
 603             | UseSpans::OtherUse(span) => span,
 604             UseSpans::FnSelfUse {
 605                 fn_call_span, kind: FnSelfUseKind::DerefCoercion { .. }, ..
 606             } => fn_call_span,
 607             UseSpans::FnSelfUse { var_span, .. } => var_span,
 608         }
 609     }
 610
 611     pub(super) fn generator_kind(self) -> Option<GeneratorKind> {
 612         match self {
 613             UseSpans::ClosureUse { generator_kind, .. } => generator_kind,
 614             _ => None,
 615         }
 616     }
 617
 618     // Add a span label to the arguments of the closure, if it exists.
 619     pub(super) fn args_span_label(
 620         self,
 621         err: &mut DiagnosticBuilder<'_>,
 622         message: impl Into<String>,
 623     ) {
 624         if let UseSpans::ClosureUse { args_span, .. } = self {
 625             err.span_label(args_span, message);
 626         }
 627     }
 628
 629     // Add a span label to the use of the captured variable, if it exists.
 630     pub(super) fn var_span_label(
 631         self,
 632         err: &mut DiagnosticBuilder<'_>,
 633         message: impl Into<String>,
 634     ) {
 635         if let UseSpans::ClosureUse { var_span, .. } = self {
 636             err.span_label(var_span, message);
 637         }
 638     }
 639
 640     /// Returns `false` if this place is not used in a closure.
 641     pub(super) fn for_closure(&self) -> bool {
 642         match *self {
 643             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_none(),
 644             _ => false,
 645         }
 646     }
 647
 648     /// Returns `false` if this place is not used in a generator.
 649     pub(super) fn for_generator(&self) -> bool {
 650         match *self {
 651             UseSpans::ClosureUse { generator_kind, .. } => generator_kind.is_some(),
 652             _ => false,
 653         }
 654     }
 655
 656     /// Describe the span associated with a use of a place.
 657     pub(super) fn describe(&self) -> String {
 658         match *self {
 659             UseSpans::ClosureUse { generator_kind, .. } => {
 660                 if generator_kind.is_some() {
 661                     " in generator".to_string()
 662                 } else {
 663                     " in closure".to_string()
 664                 }
 665             }
 666             _ => String::new(),
 667         }
 668     }
 669
 670     pub(super) fn or_else<F>(self, if_other: F) -> Self
 671     where
 672         F: FnOnce() -> Self,
 673     {
 674         match self {
 675             closure @ UseSpans::ClosureUse { .. } => closure,
 676             UseSpans::PatUse(_) | UseSpans::OtherUse(_) => if_other(),
 677             fn_self @ UseSpans::FnSelfUse { .. } => fn_self,
 678         }
 679     }
 680 }
 681
 682 pub(super) enum BorrowedContentSource<'tcx> {
 683     DerefRawPointer,
 684     DerefMutableRef,
 685     DerefSharedRef,
 686     OverloadedDeref(Ty<'tcx>),
 687     OverloadedIndex(Ty<'tcx>),
 688 }
 689
 690 impl BorrowedContentSource<'tcx> {
 691     pub(super) fn describe_for_unnamed_place(&self, tcx: TyCtxt<'_>) -> String {
 692         match *self {
 693             BorrowedContentSource::DerefRawPointer => "a raw pointer".to_string(),
 694             BorrowedContentSource::DerefSharedRef => "a shared reference".to_string(),
 695             BorrowedContentSource::DerefMutableRef => "a mutable reference".to_string(),
 696             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind() {
 697                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 698                     "an `Rc`".to_string()
 699                 }
 700                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 701                     "an `Arc`".to_string()
 702                 }
 703                 _ => format!("dereference of `{}`", ty),
 704             },
 705             BorrowedContentSource::OverloadedIndex(ty) => format!("index of `{}`", ty),
 706         }
 707     }
 708
 709     pub(super) fn describe_for_named_place(&self) -> Option<&'static str> {
 710         match *self {
 711             BorrowedContentSource::DerefRawPointer => Some("raw pointer"),
 712             BorrowedContentSource::DerefSharedRef => Some("shared reference"),
 713             BorrowedContentSource::DerefMutableRef => Some("mutable reference"),
 714             // Overloaded deref and index operators should be evaluated into a
 715             // temporary. So we don't need a description here.
 716             BorrowedContentSource::OverloadedDeref(_)
 717             | BorrowedContentSource::OverloadedIndex(_) => None,
 718         }
 719     }
 720
 721     pub(super) fn describe_for_immutable_place(&self, tcx: TyCtxt<'_>) -> String {
 722         match *self {
 723             BorrowedContentSource::DerefRawPointer => "a `*const` pointer".to_string(),
 724             BorrowedContentSource::DerefSharedRef => "a `&` reference".to_string(),
 725             BorrowedContentSource::DerefMutableRef => {
 726                 bug!("describe_for_immutable_place: DerefMutableRef isn't immutable")
 727             }
 728             BorrowedContentSource::OverloadedDeref(ty) => match ty.kind() {
 729                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Rc, def.did) => {
 730                     "an `Rc`".to_string()
 731                 }
 732                 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::Arc, def.did) => {
 733                     "an `Arc`".to_string()
 734                 }
 735                 _ => format!("a dereference of `{}`", ty),
 736             },
 737             BorrowedContentSource::OverloadedIndex(ty) => format!("an index of `{}`", ty),
 738         }
 739     }
 740
 741     fn from_call(func: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Self> {
 742         match *func.kind() {
 743             ty::FnDef(def_id, substs) => {
 744                 let trait_id = tcx.trait_of_item(def_id)?;
 745
 746                 let lang_items = tcx.lang_items();
 747                 if Some(trait_id) == lang_items.deref_trait()
 748                     || Some(trait_id) == lang_items.deref_mut_trait()
 749                 {
 750                     Some(BorrowedContentSource::OverloadedDeref(substs.type_at(0)))
 751                 } else if Some(trait_id) == lang_items.index_trait()
 752                     || Some(trait_id) == lang_items.index_mut_trait()
 753                 {
 754                     Some(BorrowedContentSource::OverloadedIndex(substs.type_at(0)))
 755                 } else {
 756                     None
 757                 }
 758             }
 759             _ => None,
 760         }
 761     }
 762 }
 763
 764 impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 765     /// Finds the spans associated to a move or copy of move_place at location.
 766     pub(super) fn move_spans(
 767         &self,
 768         moved_place: PlaceRef<'tcx>, // Could also be an upvar.
 769         location: Location,
 770     ) -> UseSpans<'tcx> {
 771         use self::UseSpans::*;
 772
 773         let stmt = match self.body[location.block].statements.get(location.statement_index) {
 774             Some(stmt) => stmt,
 775             None => return OtherUse(self.body.source_info(location).span),
 776         };
 777
 778         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);
 779         if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) = stmt.kind {
 780             match kind {
 781                 box AggregateKind::Closure(def_id, _)
 782                 | box AggregateKind::Generator(def_id, _, _) => {
 783                     debug!("move_spans: def_id={:?} places={:?}", def_id, places);
 784                     if let Some((args_span, generator_kind, var_span)) =
 785                         self.closure_span(*def_id, moved_place, places)
 786                     {
 787                         return ClosureUse { generator_kind, args_span, var_span };
 788                     }
 789                 }
 790                 _ => {}
 791             }
 792         }
 793
 794         let normal_ret =
 795             if moved_place.projection.iter().any(|p| matches!(p, ProjectionElem::Downcast(..))) {
 796                 PatUse(stmt.source_info.span)
 797             } else {
 798                 OtherUse(stmt.source_info.span)
 799             };
 800
 801         // We are trying to find MIR of the form:
 802         // ```
 803         // _temp = _moved_val;
 804         // ...
 805         // FnSelfCall(_temp, ...)
 806         // ```
 807         //
 808         // where `_moved_val` is the place we generated the move error for,
 809         // `_temp` is some other local, and `FnSelfCall` is a function
 810         // that has a `self` parameter.
 811
 812         let target_temp = match stmt.kind {
 813             StatementKind::Assign(box (temp, _)) if temp.as_local().is_some() => {
 814                 temp.as_local().unwrap()
 815             }
 816             _ => return normal_ret,
 817         };
 818
 819         debug!("move_spans: target_temp = {:?}", target_temp);
 820
 821         if let Some(Terminator {
 822             kind: TerminatorKind::Call { fn_span, from_hir_call, .. }, ..
 823         }) = &self.body[location.block].terminator
 824         {
 825             let (method_did, method_substs) = if let Some(info) =
 826                 crate::util::find_self_call(self.infcx.tcx, &self.body, target_temp, location.block)
 827             {
 828                 info
 829             } else {
 830                 return normal_ret;
 831             };
 832
 833             let tcx = self.infcx.tcx;
 834             let parent = tcx.parent(method_did);
 835             let is_fn_once = parent == tcx.lang_items().fn_once_trait();
 836             let is_operator = !from_hir_call
 837                 && parent.map_or(false, |p| tcx.lang_items().group(LangItemGroup::Op).contains(&p));
 838             let is_deref = !from_hir_call && tcx.is_diagnostic_item(sym::deref_method, method_did);
 839             let fn_call_span = *fn_span;
 840
 841             let self_arg = tcx.fn_arg_names(method_did)[0];
 842
 843             debug!(
 844                 "terminator = {:?} from_hir_call={:?}",
 845                 self.body[location.block].terminator, from_hir_call
 846             );
 847
 848             // Check for a 'special' use of 'self' -
 849             // an FnOnce call, an operator (e.g. `<<`), or a
 850             // deref coercion.
 851             let kind = if is_fn_once {
 852                 Some(FnSelfUseKind::FnOnceCall)
 853             } else if is_operator {
 854                 Some(FnSelfUseKind::Operator { self_arg })
 855             } else if is_deref {
 856                 let deref_target =
 857                     tcx.get_diagnostic_item(sym::deref_target).and_then(|deref_target| {
 858                         Instance::resolve(tcx, self.param_env, deref_target, method_substs)
 859                             .transpose()
 860                     });
 861                 if let Some(Ok(instance)) = deref_target {
 862                     let deref_target_ty = instance.ty(tcx, self.param_env);
 863                     Some(FnSelfUseKind::DerefCoercion {
 864                         deref_target: tcx.def_span(instance.def_id()),
 865                         deref_target_ty,
 866                     })
 867                 } else {
 868                     None
 869                 }
 870             } else {
 871                 None
 872             };
 873
 874             let kind = kind.unwrap_or_else(|| {
 875                 // This isn't a 'special' use of `self`
 876                 debug!("move_spans: method_did={:?}, fn_call_span={:?}", method_did, fn_call_span);
 877                 let implicit_into_iter = matches!(
 878                     fn_call_span.desugaring_kind(),
 879                     Some(DesugaringKind::ForLoop(ForLoopLoc::IntoIter))
 880                 );
 881                 FnSelfUseKind::Normal { self_arg, implicit_into_iter }
 882             });
 883
 884             return FnSelfUse {
 885                 var_span: stmt.source_info.span,
 886                 fn_call_span,
 887                 fn_span: self
 888                     .infcx
 889                     .tcx
 890                     .sess
 891                     .source_map()
 892                     .guess_head_span(self.infcx.tcx.def_span(method_did)),
 893                 kind,
 894             };
 895         }
 896         normal_ret
 897     }
 898
 899     /// Finds the span of arguments of a closure (within `maybe_closure_span`)
 900     /// and its usage of the local assigned at `location`.
 901     /// This is done by searching in statements succeeding `location`
 902     /// and originating from `maybe_closure_span`.
 903     pub(super) fn borrow_spans(&self, use_span: Span, location: Location) -> UseSpans<'tcx> {
 904         use self::UseSpans::*;
 905         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 906
 907         let target = match self.body[location.block].statements.get(location.statement_index) {
 908             Some(&Statement { kind: StatementKind::Assign(box (ref place, _)), .. }) => {
 909                 if let Some(local) = place.as_local() {
 910                     local
 911                 } else {
 912                     return OtherUse(use_span);
 913                 }
 914             }
 915             _ => return OtherUse(use_span),
 916         };
 917
 918         if self.body.local_kind(target) != LocalKind::Temp {
 919             // operands are always temporaries.
 920             return OtherUse(use_span);
 921         }
 922
 923         for stmt in &self.body[location.block].statements[location.statement_index + 1..] {
 924             if let StatementKind::Assign(box (_, Rvalue::Aggregate(ref kind, ref places))) =
 925                 stmt.kind
 926             {
 927                 let (def_id, is_generator) = match kind {
 928                     box AggregateKind::Closure(def_id, _) => (def_id, false),
 929                     box AggregateKind::Generator(def_id, _, _) => (def_id, true),
 930                     _ => continue,
 931                 };
 932
 933                 debug!(
 934                     "borrow_spans: def_id={:?} is_generator={:?} places={:?}",
 935                     def_id, is_generator, places
 936                 );
 937                 if let Some((args_span, generator_kind, var_span)) =
 938                     self.closure_span(*def_id, Place::from(target).as_ref(), places)
 939                 {
 940                     return ClosureUse { generator_kind, args_span, var_span };
 941                 } else {
 942                     return OtherUse(use_span);
 943                 }
 944             }
 945
 946             if use_span != stmt.source_info.span {
 947                 break;
 948             }
 949         }
 950
 951         OtherUse(use_span)
 952     }
 953
 954     /// Finds the span of a captured variable within a closure or generator.
 955     fn closure_span(
 956         &self,
 957         def_id: DefId,
 958         target_place: PlaceRef<'tcx>,
 959         places: &Vec<Operand<'tcx>>,
 960     ) -> Option<(Span, Option<GeneratorKind>, Span)> {
 961         debug!(
 962             "closure_span: def_id={:?} target_place={:?} places={:?}",
 963             def_id, target_place, places
 964         );
 965         let local_did = def_id.as_local()?;
 966         let hir_id = self.infcx.tcx.hir().local_def_id_to_hir_id(local_did);
 967         let expr = &self.infcx.tcx.hir().expect_expr(hir_id).kind;
 968         debug!("closure_span: hir_id={:?} expr={:?}", hir_id, expr);
 969         if let hir::ExprKind::Closure(.., body_id, args_span, _) = expr {
 970             for ((upvar_hir_id, upvar), place) in
 971                 self.infcx.tcx.upvars_mentioned(def_id)?.iter().zip(places)
 972             {
 973                 match place {
 974                     Operand::Copy(place) | Operand::Move(place)
 975                         if target_place == place.as_ref() =>
 976                     {
 977                         debug!("closure_span: found captured local {:?}", place);
 978                         let body = self.infcx.tcx.hir().body(*body_id);
 979                         let generator_kind = body.generator_kind();
 980                         let upvar_id = ty::UpvarId {
 981                             var_path: ty::UpvarPath { hir_id: *upvar_hir_id },
 982                             closure_expr_id: local_did,
 983                         };
 984
 985                         // If we have a more specific span available, point to that.
 986                         // We do this even though this span might be part of a borrow error
 987                         // message rather than a move error message. Our goal is to point
 988                         // to a span that shows why the upvar is used in the closure,
 989                         // so a move-related span is as good as any (and potentially better,
 990                         // if the overall error is due to a move of the upvar).
 991                         let usage_span =
 992                             match self.infcx.tcx.typeck(local_did).upvar_capture(upvar_id) {
 993                                 ty::UpvarCapture::ByValue(Some(span)) => span,
 994                                 _ => upvar.span,
 995                             };
 996                         return Some((*args_span, generator_kind, usage_span));
 997                     }
 998                     _ => {}
 999                 }
1000             }
1001         }
1002         None
1003     }
1004
1005     /// Helper to retrieve span(s) of given borrow from the current MIR
1006     /// representation
1007     pub(super) fn retrieve_borrow_spans(&self, borrow: &BorrowData<'_>) -> UseSpans<'tcx> {
1008         let span = self.body.source_info(borrow.reserve_location).span;
1009         self.borrow_spans(span, borrow.reserve_location)
1010     }
1011 }