compiler/rustc_typeck/src/check/upvar.rs

   1 //! ### Inferring borrow kinds for upvars
   2 //!
   3 //! Whenever there is a closure expression, we need to determine how each
   4 //! upvar is used. We do this by initially assigning each upvar an
   5 //! immutable "borrow kind" (see `ty::BorrowKind` for details) and then
   6 //! "escalating" the kind as needed. The borrow kind proceeds according to
   7 //! the following lattice:
   8 //!
   9 //!     ty::ImmBorrow -> ty::UniqueImmBorrow -> ty::MutBorrow
  10 //!
  11 //! So, for example, if we see an assignment `x = 5` to an upvar `x`, we
  12 //! will promote its borrow kind to mutable borrow. If we see an `&mut x`
  13 //! we'll do the same. Naturally, this applies not just to the upvar, but
  14 //! to everything owned by `x`, so the result is the same for something
  15 //! like `x.f = 5` and so on (presuming `x` is not a borrowed pointer to a
  16 //! struct). These adjustments are performed in
  17 //! `adjust_upvar_borrow_kind()` (you can trace backwards through the code
  18 //! from there).
  19 //!
  20 //! The fact that we are inferring borrow kinds as we go results in a
  21 //! semi-hacky interaction with mem-categorization. In particular,
  22 //! mem-categorization will query the current borrow kind as it
  23 //! categorizes, and we'll return the *current* value, but this may get
  24 //! adjusted later. Therefore, in this module, we generally ignore the
  25 //! borrow kind (and derived mutabilities) that are returned from
  26 //! mem-categorization, since they may be inaccurate. (Another option
  27 //! would be to use a unification scheme, where instead of returning a
  28 //! concrete borrow kind like `ty::ImmBorrow`, we return a
  29 //! `ty::InferBorrow(upvar_id)` or something like that, but this would
  30 //! then mean that all later passes would have to check for these figments
  31 //! and report an error, and it just seems like more mess in the end.)
  32
  33 use super::FnCtxt;
  34
  35 use crate::expr_use_visitor as euv;
  36 use rustc_data_structures::fx::FxIndexMap;
  37 use rustc_hir as hir;
  38 use rustc_hir::def_id::DefId;
  39 use rustc_hir::def_id::LocalDefId;
  40 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  41 use rustc_infer::infer::UpvarRegion;
  42 use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, ProjectionKind};
  43 use rustc_middle::ty::{self, Ty, TyCtxt, UpvarSubsts};
  44 use rustc_span::sym;
  45 use rustc_span::{MultiSpan, Span, Symbol};
  46
  47 /// Describe the relationship between the paths of two places
  48 /// eg:
  49 /// - `foo` is ancestor of `foo.bar.baz`
  50 /// - `foo.bar.baz` is an descendant of `foo.bar`
  51 /// - `foo.bar` and `foo.baz` are divergent
  52 enum PlaceAncestryRelation {
  53     Ancestor,
  54     Descendant,
  55     Divergent,
  56 }
  57
  58 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  59     pub fn closure_analyze(&self, body: &'tcx hir::Body<'tcx>) {
  60         InferBorrowKindVisitor { fcx: self }.visit_body(body);
  61
  62         // it's our job to process these.
  63         assert!(self.deferred_call_resolutions.borrow().is_empty());
  64     }
  65 }
  66
  67 struct InferBorrowKindVisitor<'a, 'tcx> {
  68     fcx: &'a FnCtxt<'a, 'tcx>,
  69 }
  70
  71 impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
  72     type Map = intravisit::ErasedMap<'tcx>;
  73
  74     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
  75         NestedVisitorMap::None
  76     }
  77
  78     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
  79         if let hir::ExprKind::Closure(cc, _, body_id, _, _) = expr.kind {
  80             let body = self.fcx.tcx.hir().body(body_id);
  81             self.visit_body(body);
  82             self.fcx.analyze_closure(expr.hir_id, expr.span, body, cc);
  83         }
  84
  85         intravisit::walk_expr(self, expr);
  86     }
  87 }
  88
  89 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  90     /// Analysis starting point.
  91     fn analyze_closure(
  92         &self,
  93         closure_hir_id: hir::HirId,
  94         span: Span,
  95         body: &hir::Body<'_>,
  96         capture_clause: hir::CaptureBy,
  97     ) {
  98         debug!("analyze_closure(id={:?}, body.id={:?})", closure_hir_id, body.id());
  99
 100         // Extract the type of the closure.
 101         let ty = self.node_ty(closure_hir_id);
 102         let (closure_def_id, substs) = match *ty.kind() {
 103             ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
 104             ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
 105             ty::Error(_) => {
 106                 // #51714: skip analysis when we have already encountered type errors
 107                 return;
 108             }
 109             _ => {
 110                 span_bug!(
 111                     span,
 112                     "type of closure expr {:?} is not a closure {:?}",
 113                     closure_hir_id,
 114                     ty
 115                 );
 116             }
 117         };
 118
 119         let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
 120             self.closure_kind(closure_substs).is_none().then_some(closure_substs)
 121         } else {
 122             None
 123         };
 124
 125         let local_def_id = closure_def_id.expect_local();
 126
 127         let mut capture_information: FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>> =
 128             Default::default();
 129         if !self.tcx.features().capture_disjoint_fields {
 130             if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
 131                 for (&var_hir_id, _) in upvars.iter() {
 132                     let place = self.place_for_root_variable(local_def_id, var_hir_id);
 133
 134                     debug!("seed place {:?}", place);
 135
 136                     let upvar_id = ty::UpvarId::new(var_hir_id, local_def_id);
 137                     let capture_kind = self.init_capture_kind(capture_clause, upvar_id, span);
 138                     let info = ty::CaptureInfo {
 139                         capture_kind_expr_id: None,
 140                         path_expr_id: None,
 141                         capture_kind,
 142                     };
 143
 144                     capture_information.insert(place, info);
 145                 }
 146             }
 147         }
 148
 149         let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
 150         assert_eq!(body_owner_def_id.to_def_id(), closure_def_id);
 151         let mut delegate = InferBorrowKind {
 152             fcx: self,
 153             closure_def_id,
 154             closure_span: span,
 155             capture_clause,
 156             current_closure_kind: ty::ClosureKind::LATTICE_BOTTOM,
 157             current_origin: None,
 158             capture_information,
 159         };
 160         euv::ExprUseVisitor::new(
 161             &mut delegate,
 162             &self.infcx,
 163             body_owner_def_id,
 164             self.param_env,
 165             &self.typeck_results.borrow(),
 166         )
 167         .consume_body(body);
 168
 169         debug!(
 170             "For closure={:?}, capture_information={:#?}",
 171             closure_def_id, delegate.capture_information
 172         );
 173         self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
 174
 175         if let Some(closure_substs) = infer_kind {
 176             // Unify the (as yet unbound) type variable in the closure
 177             // substs with the kind we inferred.
 178             let inferred_kind = delegate.current_closure_kind;
 179             let closure_kind_ty = closure_substs.as_closure().kind_ty();
 180             self.demand_eqtype(span, inferred_kind.to_ty(self.tcx), closure_kind_ty);
 181
 182             // If we have an origin, store it.
 183             if let Some(origin) = delegate.current_origin.clone() {
 184                 let origin = if self.tcx.features().capture_disjoint_fields {
 185                     origin
 186                 } else {
 187                     // FIXME(project-rfc-2229#26): Once rust-lang#80092 is merged, we should restrict the
 188                     // precision of origin as well. Otherwise, this will cause issues when project-rfc-2229#26
 189                     // is fixed as we might see Index projections in the origin, which we can't print because
 190                     // we don't store enough information.
 191                     (origin.0, Place { projections: vec![], ..origin.1 })
 192                 };
 193
 194                 self.typeck_results
 195                     .borrow_mut()
 196                     .closure_kind_origins_mut()
 197                     .insert(closure_hir_id, origin);
 198             }
 199         }
 200
 201         self.compute_min_captures(closure_def_id, delegate);
 202         self.log_closure_min_capture_info(closure_def_id, span);
 203
 204         self.min_captures_to_closure_captures_bridge(closure_def_id);
 205
 206         // Now that we've analyzed the closure, we know how each
 207         // variable is borrowed, and we know what traits the closure
 208         // implements (Fn vs FnMut etc). We now have some updates to do
 209         // with that information.
 210         //
 211         // Note that no closure type C may have an upvar of type C
 212         // (though it may reference itself via a trait object). This
 213         // results from the desugaring of closures to a struct like
 214         // `Foo<..., UV0...UVn>`. If one of those upvars referenced
 215         // C, then the type would have infinite size (and the
 216         // inference algorithm will reject it).
 217
 218         // Equate the type variables for the upvars with the actual types.
 219         let final_upvar_tys = self.final_upvar_tys(closure_def_id);
 220         debug!(
 221             "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
 222             closure_hir_id, substs, final_upvar_tys
 223         );
 224
 225         // Build a tuple (U0..Un) of the final upvar types U0..Un
 226         // and unify the upvar tupe type in the closure with it:
 227         let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
 228         self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
 229
 230         // If we are also inferred the closure kind here,
 231         // process any deferred resolutions.
 232         let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
 233         for deferred_call_resolution in deferred_call_resolutions {
 234             deferred_call_resolution.resolve(self);
 235         }
 236     }
 237
 238     // Returns a list of `Ty`s for each upvar.
 239     fn final_upvar_tys(&self, closure_id: DefId) -> Vec<Ty<'tcx>> {
 240         // Presently an unboxed closure type cannot "escape" out of a
 241         // function, so we will only encounter ones that originated in the
 242         // local crate or were inlined into it along with some function.
 243         // This may change if abstract return types of some sort are
 244         // implemented.
 245         let tcx = self.tcx;
 246
 247         self.typeck_results
 248             .borrow()
 249             .closure_min_captures_flattened(closure_id)
 250             .map(|captured_place| {
 251                 let upvar_ty = captured_place.place.ty();
 252                 let capture = captured_place.info.capture_kind;
 253
 254                 debug!(
 255                     "place={:?} upvar_ty={:?} capture={:?}",
 256                     captured_place.place, upvar_ty, capture
 257                 );
 258
 259                 match capture {
 260                     ty::UpvarCapture::ByValue(_) => upvar_ty,
 261                     ty::UpvarCapture::ByRef(borrow) => tcx.mk_ref(
 262                         borrow.region,
 263                         ty::TypeAndMut { ty: upvar_ty, mutbl: borrow.kind.to_mutbl_lossy() },
 264                     ),
 265                 }
 266             })
 267             .collect()
 268     }
 269
 270     /// Bridge for closure analysis
 271     /// ----------------------------
 272     ///
 273     /// For closure with DefId `c`, the bridge converts structures required for supporting RFC 2229,
 274     /// to structures currently used in the compiler for handling closure captures.
 275     ///
 276     /// For example the following structure will be converted:
 277     ///
 278     /// closure_min_captures
 279     /// foo -> [ {foo.x, ImmBorrow}, {foo.y, MutBorrow} ]
 280     /// bar -> [ {bar.z, ByValue}, {bar.q, MutBorrow} ]
 281     ///
 282     /// to
 283     ///
 284     /// 1. closure_captures
 285     /// foo -> UpvarId(foo, c), bar -> UpvarId(bar, c)
 286     ///
 287     /// 2. upvar_capture_map
 288     /// UpvarId(foo,c) -> MutBorrow, UpvarId(bar, c) -> ByValue
 289     fn min_captures_to_closure_captures_bridge(&self, closure_def_id: DefId) {
 290         let mut closure_captures: FxIndexMap<hir::HirId, ty::UpvarId> = Default::default();
 291         let mut upvar_capture_map = ty::UpvarCaptureMap::default();
 292
 293         if let Some(min_captures) =
 294             self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
 295         {
 296             for (var_hir_id, min_list) in min_captures.iter() {
 297                 for captured_place in min_list {
 298                     let place = &captured_place.place;
 299                     let capture_info = captured_place.info;
 300
 301                     let upvar_id = match place.base {
 302                         PlaceBase::Upvar(upvar_id) => upvar_id,
 303                         base => bug!("Expected upvar, found={:?}", base),
 304                     };
 305
 306                     assert_eq!(upvar_id.var_path.hir_id, *var_hir_id);
 307                     assert_eq!(upvar_id.closure_expr_id, closure_def_id.expect_local());
 308
 309                     closure_captures.insert(*var_hir_id, upvar_id);
 310
 311                     let new_capture_kind =
 312                         if let Some(capture_kind) = upvar_capture_map.get(&upvar_id) {
 313                             // upvar_capture_map only stores the UpvarCapture (CaptureKind),
 314                             // so we create a fake capture info with no expression.
 315                             let fake_capture_info = ty::CaptureInfo {
 316                                 capture_kind_expr_id: None,
 317                                 path_expr_id: None,
 318                                 capture_kind: *capture_kind,
 319                             };
 320                             determine_capture_info(fake_capture_info, capture_info).capture_kind
 321                         } else {
 322                             capture_info.capture_kind
 323                         };
 324                     upvar_capture_map.insert(upvar_id, new_capture_kind);
 325                 }
 326             }
 327         }
 328         debug!("For closure_def_id={:?}, closure_captures={:#?}", closure_def_id, closure_captures);
 329         debug!(
 330             "For closure_def_id={:?}, upvar_capture_map={:#?}",
 331             closure_def_id, upvar_capture_map
 332         );
 333
 334         if !closure_captures.is_empty() {
 335             self.typeck_results
 336                 .borrow_mut()
 337                 .closure_captures
 338                 .insert(closure_def_id, closure_captures);
 339
 340             self.typeck_results.borrow_mut().upvar_capture_map.extend(upvar_capture_map);
 341         }
 342     }
 343
 344     /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
 345     /// Places (and corresponding capture kind) that we need to keep track of to support all
 346     /// the required captured paths.
 347     ///
 348     /// Eg:
 349     /// ```rust,no_run
 350     /// struct Point { x: i32, y: i32 }
 351     ///
 352     /// let s: String;  // hir_id_s
 353     /// let mut p: Point; // his_id_p
 354     /// let c = || {
 355     ///        println!("{}", s);  // L1
 356     ///        p.x += 10;  // L2
 357     ///        println!("{}" , p.y) // L3
 358     ///        println!("{}", p) // L4
 359     ///        drop(s);   // L5
 360     /// };
 361     /// ```
 362     /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
 363     /// the lines L1..5 respectively.
 364     ///
 365     /// InferBorrowKind results in a structure like this:
 366     ///
 367     /// ```
 368     /// {
 369     ///       Place(base: hir_id_s, projections: [], ....) -> {
 370     ///                                                            capture_kind_expr: hir_id_L5,
 371     ///                                                            path_expr_id: hir_id_L5,
 372     ///                                                            capture_kind: ByValue
 373     ///                                                       },
 374     ///       Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
 375     ///                                                                     capture_kind_expr: hir_id_L2,
 376     ///                                                                     path_expr_id: hir_id_L2,
 377     ///                                                                     capture_kind: ByValue
 378     ///                                                                 },
 379     ///       Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
 380     ///                                                                     capture_kind_expr: hir_id_L3,
 381     ///                                                                     path_expr_id: hir_id_L3,
 382     ///                                                                     capture_kind: ByValue
 383     ///                                                                 },
 384     ///       Place(base: hir_id_p, projections: [], ...) -> {
 385     ///                                                          capture_kind_expr: hir_id_L4,
 386     ///                                                          path_expr_id: hir_id_L4,
 387     ///                                                          capture_kind: ByValue
 388     ///                                                      },
 389     /// ```
 390     ///
 391     /// After the min capture analysis, we get:
 392     /// ```
 393     /// {
 394     ///       hir_id_s -> [
 395     ///            Place(base: hir_id_s, projections: [], ....) -> {
 396     ///                                                                capture_kind_expr: hir_id_L5,
 397     ///                                                                path_expr_id: hir_id_L5,
 398     ///                                                                capture_kind: ByValue
 399     ///                                                            },
 400     ///       ],
 401     ///       hir_id_p -> [
 402     ///            Place(base: hir_id_p, projections: [], ...) -> {
 403     ///                                                               capture_kind_expr: hir_id_L2,
 404     ///                                                               path_expr_id: hir_id_L4,
 405     ///                                                               capture_kind: ByValue
 406     ///                                                           },
 407     ///       ],
 408     /// ```
 409     fn compute_min_captures(
 410         &self,
 411         closure_def_id: DefId,
 412         inferred_info: InferBorrowKind<'_, 'tcx>,
 413     ) {
 414         let mut root_var_min_capture_list: ty::RootVariableMinCaptureList<'_> = Default::default();
 415
 416         for (place, capture_info) in inferred_info.capture_information.into_iter() {
 417             let var_hir_id = match place.base {
 418                 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
 419                 base => bug!("Expected upvar, found={:?}", base),
 420             };
 421
 422             // Arrays are captured in entirety, drop Index projections and projections
 423             // after Index projections.
 424             let first_index_projection =
 425                 place.projections.split(|proj| ProjectionKind::Index == proj.kind).next();
 426             let place = Place {
 427                 base_ty: place.base_ty,
 428                 base: place.base,
 429                 projections: first_index_projection.map_or(Vec::new(), |p| p.to_vec()),
 430             };
 431
 432             let min_cap_list = match root_var_min_capture_list.get_mut(&var_hir_id) {
 433                 None => {
 434                     let min_cap_list = vec![ty::CapturedPlace { place, info: capture_info }];
 435                     root_var_min_capture_list.insert(var_hir_id, min_cap_list);
 436                     continue;
 437                 }
 438                 Some(min_cap_list) => min_cap_list,
 439             };
 440
 441             // Go through each entry in the current list of min_captures
 442             // - if ancestor is found, update it's capture kind to account for current place's
 443             // capture information.
 444             //
 445             // - if descendant is found, remove it from the list, and update the current place's
 446             // capture information to account for the descendants's capture kind.
 447             //
 448             // We can never be in a case where the list contains both an ancestor and a descendant
 449             // Also there can only be ancestor but in case of descendants there might be
 450             // multiple.
 451
 452             let mut descendant_found = false;
 453             let mut updated_capture_info = capture_info;
 454             min_cap_list.retain(|possible_descendant| {
 455                 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
 456                     // current place is ancestor of possible_descendant
 457                     PlaceAncestryRelation::Ancestor => {
 458                         descendant_found = true;
 459                         let backup_path_expr_id = updated_capture_info.path_expr_id;
 460
 461                         updated_capture_info =
 462                             determine_capture_info(updated_capture_info, possible_descendant.info);
 463
 464                         // we need to keep the ancestor's `path_expr_id`
 465                         updated_capture_info.path_expr_id = backup_path_expr_id;
 466                         false
 467                     }
 468
 469                     _ => true,
 470                 }
 471             });
 472
 473             let mut ancestor_found = false;
 474             if !descendant_found {
 475                 for possible_ancestor in min_cap_list.iter_mut() {
 476                     match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
 477                         // current place is descendant of possible_ancestor
 478                         PlaceAncestryRelation::Descendant => {
 479                             ancestor_found = true;
 480                             let backup_path_expr_id = possible_ancestor.info.path_expr_id;
 481                             possible_ancestor.info =
 482                                 determine_capture_info(possible_ancestor.info, capture_info);
 483
 484                             // we need to keep the ancestor's `path_expr_id`
 485                             possible_ancestor.info.path_expr_id = backup_path_expr_id;
 486
 487                             // Only one ancestor of the current place will be in the list.
 488                             break;
 489                         }
 490                         _ => {}
 491                     }
 492                 }
 493             }
 494
 495             // Only need to insert when we don't have an ancestor in the existing min capture list
 496             if !ancestor_found {
 497                 let captured_place =
 498                     ty::CapturedPlace { place: place.clone(), info: updated_capture_info };
 499                 min_cap_list.push(captured_place);
 500             }
 501         }
 502
 503         debug!("For closure={:?}, min_captures={:#?}", closure_def_id, root_var_min_capture_list);
 504
 505         if !root_var_min_capture_list.is_empty() {
 506             self.typeck_results
 507                 .borrow_mut()
 508                 .closure_min_captures
 509                 .insert(closure_def_id, root_var_min_capture_list);
 510         }
 511     }
 512
 513     fn init_capture_kind(
 514         &self,
 515         capture_clause: hir::CaptureBy,
 516         upvar_id: ty::UpvarId,
 517         closure_span: Span,
 518     ) -> ty::UpvarCapture<'tcx> {
 519         match capture_clause {
 520             hir::CaptureBy::Value => ty::UpvarCapture::ByValue(None),
 521             hir::CaptureBy::Ref => {
 522                 let origin = UpvarRegion(upvar_id, closure_span);
 523                 let upvar_region = self.next_region_var(origin);
 524                 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
 525                 ty::UpvarCapture::ByRef(upvar_borrow)
 526             }
 527         }
 528     }
 529
 530     fn place_for_root_variable(
 531         &self,
 532         closure_def_id: LocalDefId,
 533         var_hir_id: hir::HirId,
 534     ) -> Place<'tcx> {
 535         let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
 536
 537         Place {
 538             base_ty: self.node_ty(var_hir_id),
 539             base: PlaceBase::Upvar(upvar_id),
 540             projections: Default::default(),
 541         }
 542     }
 543
 544     fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
 545         self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
 546     }
 547
 548     fn log_capture_analysis_first_pass(
 549         &self,
 550         closure_def_id: rustc_hir::def_id::DefId,
 551         capture_information: &FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>,
 552         closure_span: Span,
 553     ) {
 554         if self.should_log_capture_analysis(closure_def_id) {
 555             let mut diag =
 556                 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
 557             for (place, capture_info) in capture_information {
 558                 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
 559                 let output_str = format!("Capturing {}", capture_str);
 560
 561                 let span =
 562                     capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
 563                 diag.span_note(span, &output_str);
 564             }
 565             diag.emit();
 566         }
 567     }
 568
 569     fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
 570         if self.should_log_capture_analysis(closure_def_id) {
 571             if let Some(min_captures) =
 572                 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
 573             {
 574                 let mut diag =
 575                     self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
 576
 577                 for (_, min_captures_for_var) in min_captures {
 578                     for capture in min_captures_for_var {
 579                         let place = &capture.place;
 580                         let capture_info = &capture.info;
 581
 582                         let capture_str =
 583                             construct_capture_info_string(self.tcx, place, capture_info);
 584                         let output_str = format!("Min Capture {}", capture_str);
 585
 586                         if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
 587                             let path_span = capture_info
 588                                 .path_expr_id
 589                                 .map_or(closure_span, |e| self.tcx.hir().span(e));
 590                             let capture_kind_span = capture_info
 591                                 .capture_kind_expr_id
 592                                 .map_or(closure_span, |e| self.tcx.hir().span(e));
 593
 594                             let mut multi_span: MultiSpan =
 595                                 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
 596
 597                             let capture_kind_label =
 598                                 construct_capture_kind_reason_string(self.tcx, place, capture_info);
 599                             let path_label = construct_path_string(self.tcx, place);
 600
 601                             multi_span.push_span_label(path_span, path_label);
 602                             multi_span.push_span_label(capture_kind_span, capture_kind_label);
 603
 604                             diag.span_note(multi_span, &output_str);
 605                         } else {
 606                             let span = capture_info
 607                                 .path_expr_id
 608                                 .map_or(closure_span, |e| self.tcx.hir().span(e));
 609
 610                             diag.span_note(span, &output_str);
 611                         };
 612                     }
 613                 }
 614                 diag.emit();
 615             }
 616         }
 617     }
 618 }
 619
 620 struct InferBorrowKind<'a, 'tcx> {
 621     fcx: &'a FnCtxt<'a, 'tcx>,
 622
 623     // The def-id of the closure whose kind and upvar accesses are being inferred.
 624     closure_def_id: DefId,
 625
 626     closure_span: Span,
 627
 628     capture_clause: hir::CaptureBy,
 629
 630     // The kind that we have inferred that the current closure
 631     // requires. Note that we *always* infer a minimal kind, even if
 632     // we don't always *use* that in the final result (i.e., sometimes
 633     // we've taken the closure kind from the expectations instead, and
 634     // for generators we don't even implement the closure traits
 635     // really).
 636     current_closure_kind: ty::ClosureKind,
 637
 638     // If we modified `current_closure_kind`, this field contains a `Some()` with the
 639     // variable access that caused us to do so.
 640     current_origin: Option<(Span, Place<'tcx>)>,
 641
 642     /// For each Place that is captured by the closure, we track the minimal kind of
 643     /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
 644     ///
 645     /// Consider closure where s.str1 is captured via an ImmutableBorrow and
 646     /// s.str2 via a MutableBorrow
 647     ///
 648     /// ```rust,no_run
 649     /// struct SomeStruct { str1: String, str2: String }
 650     ///
 651     /// // Assume that the HirId for the variable definition is `V1`
 652     /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
 653     ///
 654     /// let fix_s = |new_s2| {
 655     ///     // Assume that the HirId for the expression `s.str1` is `E1`
 656     ///     println!("Updating SomeStruct with str1=", s.str1);
 657     ///     // Assume that the HirId for the expression `*s.str2` is `E2`
 658     ///     s.str2 = new_s2;
 659     /// };
 660     /// ```
 661     ///
 662     /// For closure `fix_s`, (at a high level) the map contains
 663     ///
 664     /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
 665     /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
 666     capture_information: FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>,
 667 }
 668
 669 impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
 670     fn adjust_upvar_borrow_kind_for_consume(
 671         &mut self,
 672         place_with_id: &PlaceWithHirId<'tcx>,
 673         diag_expr_id: hir::HirId,
 674         mode: euv::ConsumeMode,
 675     ) {
 676         debug!(
 677             "adjust_upvar_borrow_kind_for_consume(place_with_id={:?}, diag_expr_id={:?}, mode={:?})",
 678             place_with_id, diag_expr_id, mode
 679         );
 680
 681         // we only care about moves
 682         match mode {
 683             euv::Copy => {
 684                 return;
 685             }
 686             euv::Move => {}
 687         }
 688
 689         let tcx = self.fcx.tcx;
 690         let upvar_id = if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
 691             upvar_id
 692         } else {
 693             return;
 694         };
 695
 696         debug!("adjust_upvar_borrow_kind_for_consume: upvar={:?}", upvar_id);
 697
 698         let usage_span = tcx.hir().span(diag_expr_id);
 699
 700         // To move out of an upvar, this must be a FnOnce closure
 701         self.adjust_closure_kind(
 702             upvar_id.closure_expr_id,
 703             ty::ClosureKind::FnOnce,
 704             usage_span,
 705             place_with_id.place.clone(),
 706         );
 707
 708         let capture_info = ty::CaptureInfo {
 709             capture_kind_expr_id: Some(diag_expr_id),
 710             path_expr_id: Some(diag_expr_id),
 711             capture_kind: ty::UpvarCapture::ByValue(Some(usage_span)),
 712         };
 713
 714         let curr_info = self.capture_information[&place_with_id.place];
 715         let updated_info = determine_capture_info(curr_info, capture_info);
 716
 717         self.capture_information[&place_with_id.place] = updated_info;
 718     }
 719
 720     /// Indicates that `place_with_id` is being directly mutated (e.g., assigned
 721     /// to). If the place is based on a by-ref upvar, this implies that
 722     /// the upvar must be borrowed using an `&mut` borrow.
 723     fn adjust_upvar_borrow_kind_for_mut(
 724         &mut self,
 725         place_with_id: &PlaceWithHirId<'tcx>,
 726         diag_expr_id: hir::HirId,
 727     ) {
 728         debug!(
 729             "adjust_upvar_borrow_kind_for_mut(place_with_id={:?}, diag_expr_id={:?})",
 730             place_with_id, diag_expr_id
 731         );
 732
 733         if let PlaceBase::Upvar(_) = place_with_id.place.base {
 734             let mut borrow_kind = ty::MutBorrow;
 735             for pointer_ty in place_with_id.place.deref_tys() {
 736                 match pointer_ty.kind() {
 737                     // Raw pointers don't inherit mutability.
 738                     ty::RawPtr(_) => return,
 739                     // assignment to deref of an `&mut`
 740                     // borrowed pointer implies that the
 741                     // pointer itself must be unique, but not
 742                     // necessarily *mutable*
 743                     ty::Ref(.., hir::Mutability::Mut) => borrow_kind = ty::UniqueImmBorrow,
 744                     _ => (),
 745                 }
 746             }
 747             self.adjust_upvar_deref(place_with_id, diag_expr_id, borrow_kind);
 748         }
 749     }
 750
 751     fn adjust_upvar_borrow_kind_for_unique(
 752         &mut self,
 753         place_with_id: &PlaceWithHirId<'tcx>,
 754         diag_expr_id: hir::HirId,
 755     ) {
 756         debug!(
 757             "adjust_upvar_borrow_kind_for_unique(place_with_id={:?}, diag_expr_id={:?})",
 758             place_with_id, diag_expr_id
 759         );
 760
 761         if let PlaceBase::Upvar(_) = place_with_id.place.base {
 762             if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
 763                 // Raw pointers don't inherit mutability.
 764                 return;
 765             }
 766             // for a borrowed pointer to be unique, its base must be unique
 767             self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::UniqueImmBorrow);
 768         }
 769     }
 770
 771     fn adjust_upvar_deref(
 772         &mut self,
 773         place_with_id: &PlaceWithHirId<'tcx>,
 774         diag_expr_id: hir::HirId,
 775         borrow_kind: ty::BorrowKind,
 776     ) {
 777         assert!(match borrow_kind {
 778             ty::MutBorrow => true,
 779             ty::UniqueImmBorrow => true,
 780
 781             // imm borrows never require adjusting any kinds, so we don't wind up here
 782             ty::ImmBorrow => false,
 783         });
 784
 785         let tcx = self.fcx.tcx;
 786
 787         // if this is an implicit deref of an
 788         // upvar, then we need to modify the
 789         // borrow_kind of the upvar to make sure it
 790         // is inferred to mutable if necessary
 791         self.adjust_upvar_borrow_kind(place_with_id, diag_expr_id, borrow_kind);
 792
 793         if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
 794             self.adjust_closure_kind(
 795                 upvar_id.closure_expr_id,
 796                 ty::ClosureKind::FnMut,
 797                 tcx.hir().span(diag_expr_id),
 798                 place_with_id.place.clone(),
 799             );
 800         }
 801     }
 802
 803     /// We infer the borrow_kind with which to borrow upvars in a stack closure.
 804     /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
 805     /// moving from left to right as needed (but never right to left).
 806     /// Here the argument `mutbl` is the borrow_kind that is required by
 807     /// some particular use.
 808     fn adjust_upvar_borrow_kind(
 809         &mut self,
 810         place_with_id: &PlaceWithHirId<'tcx>,
 811         diag_expr_id: hir::HirId,
 812         kind: ty::BorrowKind,
 813     ) {
 814         let curr_capture_info = self.capture_information[&place_with_id.place];
 815
 816         debug!(
 817             "adjust_upvar_borrow_kind(place={:?}, diag_expr_id={:?}, capture_info={:?}, kind={:?})",
 818             place_with_id, diag_expr_id, curr_capture_info, kind
 819         );
 820
 821         if let ty::UpvarCapture::ByValue(_) = curr_capture_info.capture_kind {
 822             // It's already captured by value, we don't need to do anything here
 823             return;
 824         } else if let ty::UpvarCapture::ByRef(curr_upvar_borrow) = curr_capture_info.capture_kind {
 825             // Use the same region as the current capture information
 826             // Doesn't matter since only one of the UpvarBorrow will be used.
 827             let new_upvar_borrow = ty::UpvarBorrow { kind, region: curr_upvar_borrow.region };
 828
 829             let capture_info = ty::CaptureInfo {
 830                 capture_kind_expr_id: Some(diag_expr_id),
 831                 path_expr_id: Some(diag_expr_id),
 832                 capture_kind: ty::UpvarCapture::ByRef(new_upvar_borrow),
 833             };
 834             let updated_info = determine_capture_info(curr_capture_info, capture_info);
 835             self.capture_information[&place_with_id.place] = updated_info;
 836         };
 837     }
 838
 839     fn adjust_closure_kind(
 840         &mut self,
 841         closure_id: LocalDefId,
 842         new_kind: ty::ClosureKind,
 843         upvar_span: Span,
 844         place: Place<'tcx>,
 845     ) {
 846         debug!(
 847             "adjust_closure_kind(closure_id={:?}, new_kind={:?}, upvar_span={:?}, place={:?})",
 848             closure_id, new_kind, upvar_span, place
 849         );
 850
 851         // Is this the closure whose kind is currently being inferred?
 852         if closure_id.to_def_id() != self.closure_def_id {
 853             debug!("adjust_closure_kind: not current closure");
 854             return;
 855         }
 856
 857         // closures start out as `Fn`.
 858         let existing_kind = self.current_closure_kind;
 859
 860         debug!(
 861             "adjust_closure_kind: closure_id={:?}, existing_kind={:?}, new_kind={:?}",
 862             closure_id, existing_kind, new_kind
 863         );
 864
 865         match (existing_kind, new_kind) {
 866             (ty::ClosureKind::Fn, ty::ClosureKind::Fn)
 867             | (ty::ClosureKind::FnMut, ty::ClosureKind::Fn | ty::ClosureKind::FnMut)
 868             | (ty::ClosureKind::FnOnce, _) => {
 869                 // no change needed
 870             }
 871
 872             (ty::ClosureKind::Fn, ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce)
 873             | (ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => {
 874                 // new kind is stronger than the old kind
 875                 self.current_closure_kind = new_kind;
 876                 self.current_origin = Some((upvar_span, place));
 877             }
 878         }
 879     }
 880
 881     fn init_capture_info_for_place(
 882         &mut self,
 883         place_with_id: &PlaceWithHirId<'tcx>,
 884         diag_expr_id: hir::HirId,
 885     ) {
 886         if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
 887             assert_eq!(self.closure_def_id.expect_local(), upvar_id.closure_expr_id);
 888
 889             let capture_kind =
 890                 self.fcx.init_capture_kind(self.capture_clause, upvar_id, self.closure_span);
 891
 892             let expr_id = Some(diag_expr_id);
 893             let capture_info = ty::CaptureInfo {
 894                 capture_kind_expr_id: expr_id,
 895                 path_expr_id: expr_id,
 896                 capture_kind,
 897             };
 898
 899             debug!("Capturing new place {:?}, capture_info={:?}", place_with_id, capture_info);
 900
 901             self.capture_information.insert(place_with_id.place.clone(), capture_info);
 902         } else {
 903             debug!("Not upvar: {:?}", place_with_id);
 904         }
 905     }
 906 }
 907
 908 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
 909     fn consume(
 910         &mut self,
 911         place_with_id: &PlaceWithHirId<'tcx>,
 912         diag_expr_id: hir::HirId,
 913         mode: euv::ConsumeMode,
 914     ) {
 915         debug!(
 916             "consume(place_with_id={:?}, diag_expr_id={:?}, mode={:?})",
 917             place_with_id, diag_expr_id, mode
 918         );
 919         if !self.capture_information.contains_key(&place_with_id.place) {
 920             self.init_capture_info_for_place(place_with_id, diag_expr_id);
 921         }
 922
 923         self.adjust_upvar_borrow_kind_for_consume(place_with_id, diag_expr_id, mode);
 924     }
 925
 926     fn borrow(
 927         &mut self,
 928         place_with_id: &PlaceWithHirId<'tcx>,
 929         diag_expr_id: hir::HirId,
 930         bk: ty::BorrowKind,
 931     ) {
 932         debug!(
 933             "borrow(place_with_id={:?}, diag_expr_id={:?}, bk={:?})",
 934             place_with_id, diag_expr_id, bk
 935         );
 936
 937         if !self.capture_information.contains_key(&place_with_id.place) {
 938             self.init_capture_info_for_place(place_with_id, diag_expr_id);
 939         }
 940
 941         match bk {
 942             ty::ImmBorrow => {}
 943             ty::UniqueImmBorrow => {
 944                 self.adjust_upvar_borrow_kind_for_unique(&place_with_id, diag_expr_id);
 945             }
 946             ty::MutBorrow => {
 947                 self.adjust_upvar_borrow_kind_for_mut(&place_with_id, diag_expr_id);
 948             }
 949         }
 950     }
 951
 952     fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
 953         debug!("mutate(assignee_place={:?}, diag_expr_id={:?})", assignee_place, diag_expr_id);
 954
 955         if !self.capture_information.contains_key(&assignee_place.place) {
 956             self.init_capture_info_for_place(assignee_place, diag_expr_id);
 957         }
 958
 959         self.adjust_upvar_borrow_kind_for_mut(assignee_place, diag_expr_id);
 960     }
 961 }
 962
 963 fn construct_place_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
 964     let variable_name = match place.base {
 965         PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
 966         _ => bug!("Capture_information should only contain upvars"),
 967     };
 968
 969     let mut projections_str = String::new();
 970     for (i, item) in place.projections.iter().enumerate() {
 971         let proj = match item.kind {
 972             ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
 973             ProjectionKind::Deref => String::from("Deref"),
 974             ProjectionKind::Index => String::from("Index"),
 975             ProjectionKind::Subslice => String::from("Subslice"),
 976         };
 977         if i != 0 {
 978             projections_str.push_str(",");
 979         }
 980         projections_str.push_str(proj.as_str());
 981     }
 982
 983     format!("{}[{}]", variable_name, projections_str)
 984 }
 985
 986 fn construct_capture_kind_reason_string(
 987     tcx: TyCtxt<'_>,
 988     place: &Place<'tcx>,
 989     capture_info: &ty::CaptureInfo<'tcx>,
 990 ) -> String {
 991     let place_str = construct_place_string(tcx, &place);
 992
 993     let capture_kind_str = match capture_info.capture_kind {
 994         ty::UpvarCapture::ByValue(_) => "ByValue".into(),
 995         ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
 996     };
 997
 998     format!("{} captured as {} here", place_str, capture_kind_str)
 999 }
1000
1001 fn construct_path_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1002     let place_str = construct_place_string(tcx, &place);
1003
1004     format!("{} used here", place_str)
1005 }
1006
1007 fn construct_capture_info_string(
1008     tcx: TyCtxt<'_>,
1009     place: &Place<'tcx>,
1010     capture_info: &ty::CaptureInfo<'tcx>,
1011 ) -> String {
1012     let place_str = construct_place_string(tcx, &place);
1013
1014     let capture_kind_str = match capture_info.capture_kind {
1015         ty::UpvarCapture::ByValue(_) => "ByValue".into(),
1016         ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
1017     };
1018     format!("{} -> {}", place_str, capture_kind_str)
1019 }
1020
1021 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
1022     tcx.hir().name(var_hir_id)
1023 }
1024
1025 /// Helper function to determine if we need to escalate CaptureKind from
1026 /// CaptureInfo A to B and returns the escalated CaptureInfo.
1027 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
1028 ///
1029 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
1030 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
1031 ///
1032 /// It is the caller's duty to figure out which path_expr_id to use.
1033 ///
1034 /// If both the CaptureKind and Expression are considered to be equivalent,
1035 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to priortize
1036 /// expressions reported back to the user as part of diagnostics based on which appears earlier
1037 /// in the closure. This can be acheived simply by calling
1038 /// `determine_capture_info(existing_info, current_info)`. This works out because the
1039 /// expressions that occur earlier in the closure body than the current expression are processed before.
1040 /// Consider the following example
1041 /// ```rust,no_run
1042 /// struct Point { x: i32, y: i32 }
1043 /// let mut p: Point { x: 10, y: 10 };
1044 ///
1045 /// let c = || {
1046 ///     p.x     += 10;
1047 /// // ^ E1 ^
1048 ///     // ...
1049 ///     // More code
1050 ///     // ...
1051 ///     p.x += 10; // E2
1052 /// // ^ E2 ^
1053 /// };
1054 /// ```
1055 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
1056 /// and both have an expression associated, however for diagnostics we prefer reporting
1057 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
1058 /// would've already handled `E1`, and have an existing capture_information for it.
1059 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
1060 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
1061 fn determine_capture_info(
1062     capture_info_a: ty::CaptureInfo<'tcx>,
1063     capture_info_b: ty::CaptureInfo<'tcx>,
1064 ) -> ty::CaptureInfo<'tcx> {
1065     // If the capture kind is equivalent then, we don't need to escalate and can compare the
1066     // expressions.
1067     let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
1068         (ty::UpvarCapture::ByValue(_), ty::UpvarCapture::ByValue(_)) => {
1069             // We don't need to worry about the spans being ignored here.
1070             //
1071             // The expr_id in capture_info corresponds to the span that is stored within
1072             // ByValue(span) and therefore it gets handled with priortizing based on
1073             // expressions below.
1074             true
1075         }
1076         (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
1077             ref_a.kind == ref_b.kind
1078         }
1079         (ty::UpvarCapture::ByValue(_), _) | (ty::UpvarCapture::ByRef(_), _) => false,
1080     };
1081
1082     if eq_capture_kind {
1083         match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
1084             (Some(_), _) | (None, None) => capture_info_a,
1085             (None, Some(_)) => capture_info_b,
1086         }
1087     } else {
1088         // We select the CaptureKind which ranks higher based the following priority order:
1089         // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
1090         match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
1091             (ty::UpvarCapture::ByValue(_), _) => capture_info_a,
1092             (_, ty::UpvarCapture::ByValue(_)) => capture_info_b,
1093             (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
1094                 match (ref_a.kind, ref_b.kind) {
1095                     // Take LHS:
1096                     (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
1097                     | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
1098
1099                     // Take RHS:
1100                     (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
1101                     | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
1102
1103                     (ty::ImmBorrow, ty::ImmBorrow)
1104                     | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
1105                     | (ty::MutBorrow, ty::MutBorrow) => {
1106                         bug!("Expected unequal capture kinds");
1107                     }
1108                 }
1109             }
1110         }
1111     }
1112 }
1113
1114 /// Determines the Ancestry relationship of Place A relative to Place B
1115 ///
1116 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
1117 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
1118 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
1119 fn determine_place_ancestry_relation(
1120     place_a: &Place<'tcx>,
1121     place_b: &Place<'tcx>,
1122 ) -> PlaceAncestryRelation {
1123     // If Place A and Place B, don't start off from the same root variable, they are divergent.
1124     if place_a.base != place_b.base {
1125         return PlaceAncestryRelation::Divergent;
1126     }
1127
1128     // Assume of length of projections_a = n
1129     let projections_a = &place_a.projections;
1130
1131     // Assume of length of projections_b = m
1132     let projections_b = &place_b.projections;
1133
1134     let mut same_initial_projections = true;
1135
1136     for (proj_a, proj_b) in projections_a.iter().zip(projections_b.iter()) {
1137         if proj_a != proj_b {
1138             same_initial_projections = false;
1139             break;
1140         }
1141     }
1142
1143     if same_initial_projections {
1144         // First min(n, m) projections are the same
1145         // Select Ancestor/Descendant
1146         if projections_b.len() >= projections_a.len() {
1147             PlaceAncestryRelation::Ancestor
1148         } else {
1149             PlaceAncestryRelation::Descendant
1150         }
1151     } else {
1152         PlaceAncestryRelation::Divergent
1153     }
1154 }