1 //! ### Inferring borrow kinds for upvars
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:
9 //! ty::ImmBorrow -> ty::UniqueImmBorrow -> ty::MutBorrow
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
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.)
35 use crate::expr_use_visitor as euv;
36 use rustc_data_structures::fx::FxIndexMap;
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};
45 use rustc_span::{MultiSpan, Span, Symbol};
47 /// Describe the relationship between the paths of two places
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 {
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);
62 // it's our job to process these.
63 assert!(self.deferred_call_resolutions.borrow().is_empty());
67 struct InferBorrowKindVisitor<'a, 'tcx> {
68 fcx: &'a FnCtxt<'a, 'tcx>,
71 impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
72 type Map = intravisit::ErasedMap<'tcx>;
74 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
75 NestedVisitorMap::None
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);
85 intravisit::walk_expr(self, expr);
89 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
90 /// Analysis starting point.
93 closure_hir_id: hir::HirId,
96 capture_clause: hir::CaptureBy,
98 debug!("analyze_closure(id={:?}, body.id={:?})", closure_hir_id, body.id());
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)),
106 // #51714: skip analysis when we have already encountered type errors
112 "type of closure expr {:?} is not a closure {:?}",
119 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
120 self.closure_kind(closure_substs).is_none().then_some(closure_substs)
125 let local_def_id = closure_def_id.expect_local();
127 let mut capture_information: FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>> =
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);
134 debug!("seed place {:?}", place);
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,
144 capture_information.insert(place, info);
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 {
156 current_closure_kind: ty::ClosureKind::LATTICE_BOTTOM,
157 current_origin: None,
160 euv::ExprUseVisitor::new(
165 &self.typeck_results.borrow(),
170 "For closure={:?}, capture_information={:#?}",
171 closure_def_id, delegate.capture_information
173 self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
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);
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 {
187 // FIXME(project-rfc-2229#31): Once the changes to support reborrowing are
188 // made, make sure we are selecting and restricting
189 // the origin correctly.
190 (origin.0, Place { projections: vec![], ..origin.1 })
195 .closure_kind_origins_mut()
196 .insert(closure_hir_id, origin);
200 self.compute_min_captures(closure_def_id, delegate);
201 self.log_closure_min_capture_info(closure_def_id, span);
203 self.min_captures_to_closure_captures_bridge(closure_def_id);
205 // Now that we've analyzed the closure, we know how each
206 // variable is borrowed, and we know what traits the closure
207 // implements (Fn vs FnMut etc). We now have some updates to do
208 // with that information.
210 // Note that no closure type C may have an upvar of type C
211 // (though it may reference itself via a trait object). This
212 // results from the desugaring of closures to a struct like
213 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
214 // C, then the type would have infinite size (and the
215 // inference algorithm will reject it).
217 // Equate the type variables for the upvars with the actual types.
218 let final_upvar_tys = self.final_upvar_tys(closure_def_id);
220 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
221 closure_hir_id, substs, final_upvar_tys
224 // Build a tuple (U0..Un) of the final upvar types U0..Un
225 // and unify the upvar tupe type in the closure with it:
226 let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
227 self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
229 // If we are also inferred the closure kind here,
230 // process any deferred resolutions.
231 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
232 for deferred_call_resolution in deferred_call_resolutions {
233 deferred_call_resolution.resolve(self);
237 // Returns a list of `Ty`s for each upvar.
238 fn final_upvar_tys(&self, closure_id: DefId) -> Vec<Ty<'tcx>> {
239 // Presently an unboxed closure type cannot "escape" out of a
240 // function, so we will only encounter ones that originated in the
241 // local crate or were inlined into it along with some function.
242 // This may change if abstract return types of some sort are
248 .closure_min_captures_flattened(closure_id)
249 .map(|captured_place| {
250 let upvar_ty = captured_place.place.ty();
251 let capture = captured_place.info.capture_kind;
254 "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
255 captured_place.place, upvar_ty, capture, captured_place.mutability,
259 ty::UpvarCapture::ByValue(_) => upvar_ty,
260 ty::UpvarCapture::ByRef(borrow) => tcx.mk_ref(
262 ty::TypeAndMut { ty: upvar_ty, mutbl: borrow.kind.to_mutbl_lossy() },
269 /// Bridge for closure analysis
270 /// ----------------------------
272 /// For closure with DefId `c`, the bridge converts structures required for supporting RFC 2229,
273 /// to structures currently used in the compiler for handling closure captures.
275 /// For example the following structure will be converted:
277 /// closure_min_captures
278 /// foo -> [ {foo.x, ImmBorrow}, {foo.y, MutBorrow} ]
279 /// bar -> [ {bar.z, ByValue}, {bar.q, MutBorrow} ]
283 /// 1. closure_captures
284 /// foo -> UpvarId(foo, c), bar -> UpvarId(bar, c)
286 /// 2. upvar_capture_map
287 /// UpvarId(foo,c) -> MutBorrow, UpvarId(bar, c) -> ByValue
288 fn min_captures_to_closure_captures_bridge(&self, closure_def_id: DefId) {
289 let mut closure_captures: FxIndexMap<hir::HirId, ty::UpvarId> = Default::default();
290 let mut upvar_capture_map = ty::UpvarCaptureMap::default();
292 if let Some(min_captures) =
293 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
295 for (var_hir_id, min_list) in min_captures.iter() {
296 for captured_place in min_list {
297 let place = &captured_place.place;
298 let capture_info = captured_place.info;
300 let upvar_id = match place.base {
301 PlaceBase::Upvar(upvar_id) => upvar_id,
302 base => bug!("Expected upvar, found={:?}", base),
305 assert_eq!(upvar_id.var_path.hir_id, *var_hir_id);
306 assert_eq!(upvar_id.closure_expr_id, closure_def_id.expect_local());
308 closure_captures.insert(*var_hir_id, upvar_id);
310 let new_capture_kind =
311 if let Some(capture_kind) = upvar_capture_map.get(&upvar_id) {
312 // upvar_capture_map only stores the UpvarCapture (CaptureKind),
313 // so we create a fake capture info with no expression.
314 let fake_capture_info = ty::CaptureInfo {
315 capture_kind_expr_id: None,
317 capture_kind: *capture_kind,
319 determine_capture_info(fake_capture_info, capture_info).capture_kind
321 capture_info.capture_kind
323 upvar_capture_map.insert(upvar_id, new_capture_kind);
327 debug!("For closure_def_id={:?}, closure_captures={:#?}", closure_def_id, closure_captures);
329 "For closure_def_id={:?}, upvar_capture_map={:#?}",
330 closure_def_id, upvar_capture_map
333 if !closure_captures.is_empty() {
337 .insert(closure_def_id, closure_captures);
339 self.typeck_results.borrow_mut().upvar_capture_map.extend(upvar_capture_map);
343 /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
344 /// Places (and corresponding capture kind) that we need to keep track of to support all
345 /// the required captured paths.
349 /// struct Point { x: i32, y: i32 }
351 /// let s: String; // hir_id_s
352 /// let mut p: Point; // his_id_p
354 /// println!("{}", s); // L1
356 /// println!("{}" , p.y) // L3
357 /// println!("{}", p) // L4
361 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
362 /// the lines L1..5 respectively.
364 /// InferBorrowKind results in a structure like this:
368 /// Place(base: hir_id_s, projections: [], ....) -> {
369 /// capture_kind_expr: hir_id_L5,
370 /// path_expr_id: hir_id_L5,
371 /// capture_kind: ByValue
373 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
374 /// capture_kind_expr: hir_id_L2,
375 /// path_expr_id: hir_id_L2,
376 /// capture_kind: ByValue
378 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
379 /// capture_kind_expr: hir_id_L3,
380 /// path_expr_id: hir_id_L3,
381 /// capture_kind: ByValue
383 /// Place(base: hir_id_p, projections: [], ...) -> {
384 /// capture_kind_expr: hir_id_L4,
385 /// path_expr_id: hir_id_L4,
386 /// capture_kind: ByValue
390 /// After the min capture analysis, we get:
394 /// Place(base: hir_id_s, projections: [], ....) -> {
395 /// capture_kind_expr: hir_id_L5,
396 /// path_expr_id: hir_id_L5,
397 /// capture_kind: ByValue
401 /// Place(base: hir_id_p, projections: [], ...) -> {
402 /// capture_kind_expr: hir_id_L2,
403 /// path_expr_id: hir_id_L4,
404 /// capture_kind: ByValue
408 fn compute_min_captures(
410 closure_def_id: DefId,
411 inferred_info: InferBorrowKind<'_, 'tcx>,
413 let mut root_var_min_capture_list: ty::RootVariableMinCaptureList<'_> = Default::default();
415 for (place, capture_info) in inferred_info.capture_information.into_iter() {
416 let var_hir_id = match place.base {
417 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
418 base => bug!("Expected upvar, found={:?}", base),
421 let place = restrict_capture_precision(place, capture_info.capture_kind);
423 let min_cap_list = match root_var_min_capture_list.get_mut(&var_hir_id) {
425 let mutability = self.determine_capture_mutability(&place);
427 vec![ty::CapturedPlace { place, info: capture_info, mutability }];
428 root_var_min_capture_list.insert(var_hir_id, min_cap_list);
431 Some(min_cap_list) => min_cap_list,
434 // Go through each entry in the current list of min_captures
435 // - if ancestor is found, update it's capture kind to account for current place's
436 // capture information.
438 // - if descendant is found, remove it from the list, and update the current place's
439 // capture information to account for the descendants's capture kind.
441 // We can never be in a case where the list contains both an ancestor and a descendant
442 // Also there can only be ancestor but in case of descendants there might be
445 let mut descendant_found = false;
446 let mut updated_capture_info = capture_info;
447 min_cap_list.retain(|possible_descendant| {
448 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
449 // current place is ancestor of possible_descendant
450 PlaceAncestryRelation::Ancestor => {
451 descendant_found = true;
452 let backup_path_expr_id = updated_capture_info.path_expr_id;
454 updated_capture_info =
455 determine_capture_info(updated_capture_info, possible_descendant.info);
457 // we need to keep the ancestor's `path_expr_id`
458 updated_capture_info.path_expr_id = backup_path_expr_id;
466 let mut ancestor_found = false;
467 if !descendant_found {
468 for possible_ancestor in min_cap_list.iter_mut() {
469 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
470 // current place is descendant of possible_ancestor
471 PlaceAncestryRelation::Descendant => {
472 ancestor_found = true;
473 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
474 possible_ancestor.info =
475 determine_capture_info(possible_ancestor.info, capture_info);
477 // we need to keep the ancestor's `path_expr_id`
478 possible_ancestor.info.path_expr_id = backup_path_expr_id;
480 // Only one ancestor of the current place will be in the list.
488 // Only need to insert when we don't have an ancestor in the existing min capture list
490 let mutability = self.determine_capture_mutability(&place);
492 ty::CapturedPlace { place, info: updated_capture_info, mutability };
493 min_cap_list.push(captured_place);
497 debug!("For closure={:?}, min_captures={:#?}", closure_def_id, root_var_min_capture_list);
499 if !root_var_min_capture_list.is_empty() {
502 .closure_min_captures
503 .insert(closure_def_id, root_var_min_capture_list);
507 fn init_capture_kind(
509 capture_clause: hir::CaptureBy,
510 upvar_id: ty::UpvarId,
512 ) -> ty::UpvarCapture<'tcx> {
513 match capture_clause {
514 hir::CaptureBy::Value => ty::UpvarCapture::ByValue(None),
515 hir::CaptureBy::Ref => {
516 let origin = UpvarRegion(upvar_id, closure_span);
517 let upvar_region = self.next_region_var(origin);
518 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
519 ty::UpvarCapture::ByRef(upvar_borrow)
524 fn place_for_root_variable(
526 closure_def_id: LocalDefId,
527 var_hir_id: hir::HirId,
529 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
532 base_ty: self.node_ty(var_hir_id),
533 base: PlaceBase::Upvar(upvar_id),
534 projections: Default::default(),
538 fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
539 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
542 fn log_capture_analysis_first_pass(
544 closure_def_id: rustc_hir::def_id::DefId,
545 capture_information: &FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>,
548 if self.should_log_capture_analysis(closure_def_id) {
550 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
551 for (place, capture_info) in capture_information {
552 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
553 let output_str = format!("Capturing {}", capture_str);
556 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
557 diag.span_note(span, &output_str);
563 fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
564 if self.should_log_capture_analysis(closure_def_id) {
565 if let Some(min_captures) =
566 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
569 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
571 for (_, min_captures_for_var) in min_captures {
572 for capture in min_captures_for_var {
573 let place = &capture.place;
574 let capture_info = &capture.info;
577 construct_capture_info_string(self.tcx, place, capture_info);
578 let output_str = format!("Min Capture {}", capture_str);
580 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
581 let path_span = capture_info
583 .map_or(closure_span, |e| self.tcx.hir().span(e));
584 let capture_kind_span = capture_info
585 .capture_kind_expr_id
586 .map_or(closure_span, |e| self.tcx.hir().span(e));
588 let mut multi_span: MultiSpan =
589 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
591 let capture_kind_label =
592 construct_capture_kind_reason_string(self.tcx, place, capture_info);
593 let path_label = construct_path_string(self.tcx, place);
595 multi_span.push_span_label(path_span, path_label);
596 multi_span.push_span_label(capture_kind_span, capture_kind_label);
598 diag.span_note(multi_span, &output_str);
600 let span = capture_info
602 .map_or(closure_span, |e| self.tcx.hir().span(e));
604 diag.span_note(span, &output_str);
613 /// A captured place is mutable if
614 /// 1. Projections don't include a Deref of an immut-borrow, **and**
615 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
616 fn determine_capture_mutability(&self, place: &Place<'tcx>) -> hir::Mutability {
617 let var_hir_id = match place.base {
618 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
627 .expect("missing binding mode");
629 let mut is_mutbl = match bm {
630 ty::BindByValue(mutability) => mutability,
631 ty::BindByReference(_) => hir::Mutability::Not,
634 for pointer_ty in place.deref_tys() {
635 match pointer_ty.kind() {
636 // We don't capture derefs of raw ptrs
637 ty::RawPtr(_) => unreachable!(),
639 // Derefencing a mut-ref allows us to mut the Place if we don't deref
640 // an immut-ref after on top of this.
641 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
643 // The place isn't mutable once we dereference a immutable reference.
644 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
646 // Dereferencing a box doesn't change mutability
647 ty::Adt(def, ..) if def.is_box() => {}
649 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
657 struct InferBorrowKind<'a, 'tcx> {
658 fcx: &'a FnCtxt<'a, 'tcx>,
660 // The def-id of the closure whose kind and upvar accesses are being inferred.
661 closure_def_id: DefId,
665 capture_clause: hir::CaptureBy,
667 // The kind that we have inferred that the current closure
668 // requires. Note that we *always* infer a minimal kind, even if
669 // we don't always *use* that in the final result (i.e., sometimes
670 // we've taken the closure kind from the expectations instead, and
671 // for generators we don't even implement the closure traits
673 current_closure_kind: ty::ClosureKind,
675 // If we modified `current_closure_kind`, this field contains a `Some()` with the
676 // variable access that caused us to do so.
677 current_origin: Option<(Span, Place<'tcx>)>,
679 /// For each Place that is captured by the closure, we track the minimal kind of
680 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
682 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
683 /// s.str2 via a MutableBorrow
686 /// struct SomeStruct { str1: String, str2: String }
688 /// // Assume that the HirId for the variable definition is `V1`
689 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
691 /// let fix_s = |new_s2| {
692 /// // Assume that the HirId for the expression `s.str1` is `E1`
693 /// println!("Updating SomeStruct with str1=", s.str1);
694 /// // Assume that the HirId for the expression `*s.str2` is `E2`
699 /// For closure `fix_s`, (at a high level) the map contains
701 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
702 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
703 capture_information: FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>,
706 impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
707 fn adjust_upvar_borrow_kind_for_consume(
709 place_with_id: &PlaceWithHirId<'tcx>,
710 diag_expr_id: hir::HirId,
711 mode: euv::ConsumeMode,
714 "adjust_upvar_borrow_kind_for_consume(place_with_id={:?}, diag_expr_id={:?}, mode={:?})",
715 place_with_id, diag_expr_id, mode
718 // we only care about moves
726 let tcx = self.fcx.tcx;
727 let upvar_id = if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
733 debug!("adjust_upvar_borrow_kind_for_consume: upvar={:?}", upvar_id);
735 let usage_span = tcx.hir().span(diag_expr_id);
737 // To move out of an upvar, this must be a FnOnce closure
738 self.adjust_closure_kind(
739 upvar_id.closure_expr_id,
740 ty::ClosureKind::FnOnce,
742 place_with_id.place.clone(),
745 let capture_info = ty::CaptureInfo {
746 capture_kind_expr_id: Some(diag_expr_id),
747 path_expr_id: Some(diag_expr_id),
748 capture_kind: ty::UpvarCapture::ByValue(Some(usage_span)),
751 let curr_info = self.capture_information[&place_with_id.place];
752 let updated_info = determine_capture_info(curr_info, capture_info);
754 self.capture_information[&place_with_id.place] = updated_info;
757 /// Indicates that `place_with_id` is being directly mutated (e.g., assigned
758 /// to). If the place is based on a by-ref upvar, this implies that
759 /// the upvar must be borrowed using an `&mut` borrow.
760 fn adjust_upvar_borrow_kind_for_mut(
762 place_with_id: &PlaceWithHirId<'tcx>,
763 diag_expr_id: hir::HirId,
766 "adjust_upvar_borrow_kind_for_mut(place_with_id={:?}, diag_expr_id={:?})",
767 place_with_id, diag_expr_id
770 if let PlaceBase::Upvar(_) = place_with_id.place.base {
771 let mut borrow_kind = ty::MutBorrow;
772 for pointer_ty in place_with_id.place.deref_tys() {
773 match pointer_ty.kind() {
774 // Raw pointers don't inherit mutability.
775 ty::RawPtr(_) => return,
776 // assignment to deref of an `&mut`
777 // borrowed pointer implies that the
778 // pointer itself must be unique, but not
779 // necessarily *mutable*
780 ty::Ref(.., hir::Mutability::Mut) => borrow_kind = ty::UniqueImmBorrow,
784 self.adjust_upvar_deref(place_with_id, diag_expr_id, borrow_kind);
788 fn adjust_upvar_borrow_kind_for_unique(
790 place_with_id: &PlaceWithHirId<'tcx>,
791 diag_expr_id: hir::HirId,
794 "adjust_upvar_borrow_kind_for_unique(place_with_id={:?}, diag_expr_id={:?})",
795 place_with_id, diag_expr_id
798 if let PlaceBase::Upvar(_) = place_with_id.place.base {
799 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
800 // Raw pointers don't inherit mutability.
803 // for a borrowed pointer to be unique, its base must be unique
804 self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::UniqueImmBorrow);
808 fn adjust_upvar_deref(
810 place_with_id: &PlaceWithHirId<'tcx>,
811 diag_expr_id: hir::HirId,
812 borrow_kind: ty::BorrowKind,
814 assert!(match borrow_kind {
815 ty::MutBorrow => true,
816 ty::UniqueImmBorrow => true,
818 // imm borrows never require adjusting any kinds, so we don't wind up here
819 ty::ImmBorrow => false,
822 let tcx = self.fcx.tcx;
824 // if this is an implicit deref of an
825 // upvar, then we need to modify the
826 // borrow_kind of the upvar to make sure it
827 // is inferred to mutable if necessary
828 self.adjust_upvar_borrow_kind(place_with_id, diag_expr_id, borrow_kind);
830 if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
831 self.adjust_closure_kind(
832 upvar_id.closure_expr_id,
833 ty::ClosureKind::FnMut,
834 tcx.hir().span(diag_expr_id),
835 place_with_id.place.clone(),
840 /// We infer the borrow_kind with which to borrow upvars in a stack closure.
841 /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
842 /// moving from left to right as needed (but never right to left).
843 /// Here the argument `mutbl` is the borrow_kind that is required by
844 /// some particular use.
845 fn adjust_upvar_borrow_kind(
847 place_with_id: &PlaceWithHirId<'tcx>,
848 diag_expr_id: hir::HirId,
849 kind: ty::BorrowKind,
851 let curr_capture_info = self.capture_information[&place_with_id.place];
854 "adjust_upvar_borrow_kind(place={:?}, diag_expr_id={:?}, capture_info={:?}, kind={:?})",
855 place_with_id, diag_expr_id, curr_capture_info, kind
858 if let ty::UpvarCapture::ByValue(_) = curr_capture_info.capture_kind {
859 // It's already captured by value, we don't need to do anything here
861 } else if let ty::UpvarCapture::ByRef(curr_upvar_borrow) = curr_capture_info.capture_kind {
862 // Use the same region as the current capture information
863 // Doesn't matter since only one of the UpvarBorrow will be used.
864 let new_upvar_borrow = ty::UpvarBorrow { kind, region: curr_upvar_borrow.region };
866 let capture_info = ty::CaptureInfo {
867 capture_kind_expr_id: Some(diag_expr_id),
868 path_expr_id: Some(diag_expr_id),
869 capture_kind: ty::UpvarCapture::ByRef(new_upvar_borrow),
871 let updated_info = determine_capture_info(curr_capture_info, capture_info);
872 self.capture_information[&place_with_id.place] = updated_info;
876 fn adjust_closure_kind(
878 closure_id: LocalDefId,
879 new_kind: ty::ClosureKind,
884 "adjust_closure_kind(closure_id={:?}, new_kind={:?}, upvar_span={:?}, place={:?})",
885 closure_id, new_kind, upvar_span, place
888 // Is this the closure whose kind is currently being inferred?
889 if closure_id.to_def_id() != self.closure_def_id {
890 debug!("adjust_closure_kind: not current closure");
894 // closures start out as `Fn`.
895 let existing_kind = self.current_closure_kind;
898 "adjust_closure_kind: closure_id={:?}, existing_kind={:?}, new_kind={:?}",
899 closure_id, existing_kind, new_kind
902 match (existing_kind, new_kind) {
903 (ty::ClosureKind::Fn, ty::ClosureKind::Fn)
904 | (ty::ClosureKind::FnMut, ty::ClosureKind::Fn | ty::ClosureKind::FnMut)
905 | (ty::ClosureKind::FnOnce, _) => {
909 (ty::ClosureKind::Fn, ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce)
910 | (ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => {
911 // new kind is stronger than the old kind
912 self.current_closure_kind = new_kind;
913 self.current_origin = Some((upvar_span, place));
918 fn init_capture_info_for_place(
920 place_with_id: &PlaceWithHirId<'tcx>,
921 diag_expr_id: hir::HirId,
923 if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
924 assert_eq!(self.closure_def_id.expect_local(), upvar_id.closure_expr_id);
927 self.fcx.init_capture_kind(self.capture_clause, upvar_id, self.closure_span);
929 let expr_id = Some(diag_expr_id);
930 let capture_info = ty::CaptureInfo {
931 capture_kind_expr_id: expr_id,
932 path_expr_id: expr_id,
936 debug!("Capturing new place {:?}, capture_info={:?}", place_with_id, capture_info);
938 self.capture_information.insert(place_with_id.place.clone(), capture_info);
940 debug!("Not upvar: {:?}", place_with_id);
945 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
948 place_with_id: &PlaceWithHirId<'tcx>,
949 diag_expr_id: hir::HirId,
950 mode: euv::ConsumeMode,
953 "consume(place_with_id={:?}, diag_expr_id={:?}, mode={:?})",
954 place_with_id, diag_expr_id, mode
956 if !self.capture_information.contains_key(&place_with_id.place) {
957 self.init_capture_info_for_place(place_with_id, diag_expr_id);
960 self.adjust_upvar_borrow_kind_for_consume(place_with_id, diag_expr_id, mode);
965 place_with_id: &PlaceWithHirId<'tcx>,
966 diag_expr_id: hir::HirId,
970 "borrow(place_with_id={:?}, diag_expr_id={:?}, bk={:?})",
971 place_with_id, diag_expr_id, bk
974 if !self.capture_information.contains_key(&place_with_id.place) {
975 self.init_capture_info_for_place(place_with_id, diag_expr_id);
980 ty::UniqueImmBorrow => {
981 self.adjust_upvar_borrow_kind_for_unique(&place_with_id, diag_expr_id);
984 self.adjust_upvar_borrow_kind_for_mut(&place_with_id, diag_expr_id);
989 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
990 debug!("mutate(assignee_place={:?}, diag_expr_id={:?})", assignee_place, diag_expr_id);
992 if !self.capture_information.contains_key(&assignee_place.place) {
993 self.init_capture_info_for_place(assignee_place, diag_expr_id);
996 self.adjust_upvar_borrow_kind_for_mut(assignee_place, diag_expr_id);
1000 /// Truncate projections so that following rules are obeyed by the captured `place`:
1002 /// - No Derefs in move closure, this will result in value behind a reference getting moved.
1003 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
1004 /// them completely.
1005 /// - No Index projections are captured, since arrays are captured completely.
1006 fn restrict_capture_precision<'tcx>(
1007 mut place: Place<'tcx>,
1008 capture_kind: ty::UpvarCapture<'tcx>,
1010 if place.projections.is_empty() {
1011 // Nothing to do here
1015 if place.base_ty.is_unsafe_ptr() {
1016 place.projections.truncate(0);
1020 let mut truncated_length = usize::MAX;
1021 let mut first_deref_projection = usize::MAX;
1023 for (i, proj) in place.projections.iter().enumerate() {
1024 if proj.ty.is_unsafe_ptr() {
1025 // Don't apply any projections on top of an unsafe ptr
1026 truncated_length = truncated_length.min(i + 1);
1030 ProjectionKind::Index => {
1031 // Arrays are completely captured, so we drop Index projections
1032 truncated_length = truncated_length.min(i);
1035 ProjectionKind::Deref => {
1036 // We only drop Derefs in case of move closures
1037 // There might be an index projection or raw ptr ahead, so we don't stop here.
1038 first_deref_projection = first_deref_projection.min(i);
1040 ProjectionKind::Field(..) => {} // ignore
1041 ProjectionKind::Subslice => {} // We never capture this
1048 .min(truncated_length)
1049 // In case of capture `ByValue` we want to not capture derefs
1050 .min(match capture_kind {
1051 ty::UpvarCapture::ByValue(..) => first_deref_projection,
1052 ty::UpvarCapture::ByRef(..) => usize::MAX,
1055 place.projections.truncate(length);
1060 fn construct_place_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1061 let variable_name = match place.base {
1062 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
1063 _ => bug!("Capture_information should only contain upvars"),
1066 let mut projections_str = String::new();
1067 for (i, item) in place.projections.iter().enumerate() {
1068 let proj = match item.kind {
1069 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
1070 ProjectionKind::Deref => String::from("Deref"),
1071 ProjectionKind::Index => String::from("Index"),
1072 ProjectionKind::Subslice => String::from("Subslice"),
1075 projections_str.push_str(",");
1077 projections_str.push_str(proj.as_str());
1080 format!("{}[{}]", variable_name, projections_str)
1083 fn construct_capture_kind_reason_string(
1085 place: &Place<'tcx>,
1086 capture_info: &ty::CaptureInfo<'tcx>,
1088 let place_str = construct_place_string(tcx, &place);
1090 let capture_kind_str = match capture_info.capture_kind {
1091 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
1092 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
1095 format!("{} captured as {} here", place_str, capture_kind_str)
1098 fn construct_path_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1099 let place_str = construct_place_string(tcx, &place);
1101 format!("{} used here", place_str)
1104 fn construct_capture_info_string(
1106 place: &Place<'tcx>,
1107 capture_info: &ty::CaptureInfo<'tcx>,
1109 let place_str = construct_place_string(tcx, &place);
1111 let capture_kind_str = match capture_info.capture_kind {
1112 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
1113 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
1115 format!("{} -> {}", place_str, capture_kind_str)
1118 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
1119 tcx.hir().name(var_hir_id)
1122 /// Helper function to determine if we need to escalate CaptureKind from
1123 /// CaptureInfo A to B and returns the escalated CaptureInfo.
1124 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
1126 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
1127 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
1129 /// It is the caller's duty to figure out which path_expr_id to use.
1131 /// If both the CaptureKind and Expression are considered to be equivalent,
1132 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to priortize
1133 /// expressions reported back to the user as part of diagnostics based on which appears earlier
1134 /// in the closure. This can be acheived simply by calling
1135 /// `determine_capture_info(existing_info, current_info)`. This works out because the
1136 /// expressions that occur earlier in the closure body than the current expression are processed before.
1137 /// Consider the following example
1139 /// struct Point { x: i32, y: i32 }
1140 /// let mut p: Point { x: 10, y: 10 };
1148 /// p.x += 10; // E2
1152 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
1153 /// and both have an expression associated, however for diagnostics we prefer reporting
1154 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
1155 /// would've already handled `E1`, and have an existing capture_information for it.
1156 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
1157 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
1158 fn determine_capture_info(
1159 capture_info_a: ty::CaptureInfo<'tcx>,
1160 capture_info_b: ty::CaptureInfo<'tcx>,
1161 ) -> ty::CaptureInfo<'tcx> {
1162 // If the capture kind is equivalent then, we don't need to escalate and can compare the
1164 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
1165 (ty::UpvarCapture::ByValue(_), ty::UpvarCapture::ByValue(_)) => {
1166 // We don't need to worry about the spans being ignored here.
1168 // The expr_id in capture_info corresponds to the span that is stored within
1169 // ByValue(span) and therefore it gets handled with priortizing based on
1170 // expressions below.
1173 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
1174 ref_a.kind == ref_b.kind
1176 (ty::UpvarCapture::ByValue(_), _) | (ty::UpvarCapture::ByRef(_), _) => false,
1179 if eq_capture_kind {
1180 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
1181 (Some(_), _) | (None, None) => capture_info_a,
1182 (None, Some(_)) => capture_info_b,
1185 // We select the CaptureKind which ranks higher based the following priority order:
1186 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
1187 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
1188 (ty::UpvarCapture::ByValue(_), _) => capture_info_a,
1189 (_, ty::UpvarCapture::ByValue(_)) => capture_info_b,
1190 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
1191 match (ref_a.kind, ref_b.kind) {
1193 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
1194 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
1197 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
1198 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
1200 (ty::ImmBorrow, ty::ImmBorrow)
1201 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
1202 | (ty::MutBorrow, ty::MutBorrow) => {
1203 bug!("Expected unequal capture kinds");
1211 /// Determines the Ancestry relationship of Place A relative to Place B
1213 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
1214 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
1215 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
1216 fn determine_place_ancestry_relation(
1217 place_a: &Place<'tcx>,
1218 place_b: &Place<'tcx>,
1219 ) -> PlaceAncestryRelation {
1220 // If Place A and Place B, don't start off from the same root variable, they are divergent.
1221 if place_a.base != place_b.base {
1222 return PlaceAncestryRelation::Divergent;
1225 // Assume of length of projections_a = n
1226 let projections_a = &place_a.projections;
1228 // Assume of length of projections_b = m
1229 let projections_b = &place_b.projections;
1231 let mut same_initial_projections = true;
1233 for (proj_a, proj_b) in projections_a.iter().zip(projections_b.iter()) {
1234 if proj_a != proj_b {
1235 same_initial_projections = false;
1240 if same_initial_projections {
1241 // First min(n, m) projections are the same
1242 // Select Ancestor/Descendant
1243 if projections_b.len() >= projections_a.len() {
1244 PlaceAncestryRelation::Ancestor
1246 PlaceAncestryRelation::Descendant
1249 PlaceAncestryRelation::Divergent