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_errors::Applicability;
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, Projection, ProjectionKind};
43 use rustc_middle::mir::FakeReadCause;
44 use rustc_middle::ty::{
45 self, ClosureSizeProfileData, Ty, TyCtxt, TypeckResults, UpvarCapture, UpvarSubsts,
47 use rustc_session::lint;
49 use rustc_span::{BytePos, MultiSpan, Pos, Span, Symbol};
50 use rustc_trait_selection::infer::InferCtxtExt;
52 use rustc_data_structures::stable_map::FxHashMap;
53 use rustc_data_structures::stable_set::FxHashSet;
54 use rustc_index::vec::Idx;
55 use rustc_target::abi::VariantIdx;
59 /// Describe the relationship between the paths of two places
61 /// - `foo` is ancestor of `foo.bar.baz`
62 /// - `foo.bar.baz` is an descendant of `foo.bar`
63 /// - `foo.bar` and `foo.baz` are divergent
64 enum PlaceAncestryRelation {
71 /// Intermediate format to store a captured `Place` and associated `ty::CaptureInfo`
72 /// during capture analysis. Information in this map feeds into the minimum capture
74 type InferredCaptureInformation<'tcx> = Vec<(Place<'tcx>, ty::CaptureInfo)>;
76 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
77 pub fn closure_analyze(&self, body: &'tcx hir::Body<'tcx>) {
78 InferBorrowKindVisitor { fcx: self }.visit_body(body);
80 // it's our job to process these.
81 assert!(self.deferred_call_resolutions.borrow().is_empty());
85 /// Intermediate format to store the hir_id pointing to the use that resulted in the
86 /// corresponding place being captured and a String which contains the captured value's
88 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
89 enum UpvarMigrationInfo {
90 /// We previously captured all of `x`, but now we capture some sub-path.
91 CapturingPrecise { source_expr: Option<hir::HirId>, var_name: String },
93 // where the variable appears in the closure (but is not captured)
98 /// Reasons that we might issue a migration warning.
99 #[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
100 struct MigrationWarningReason {
101 /// When we used to capture `x` in its entirety, we implemented the auto-trait(s)
102 /// in this vec, but now we don't.
103 auto_traits: Vec<&'static str>,
105 /// When we used to capture `x` in its entirety, we would execute some destructors
106 /// at a different time.
110 impl MigrationWarningReason {
111 fn migration_message(&self) -> String {
112 let base = "changes to closure capture in Rust 2021 will affect";
113 if !self.auto_traits.is_empty() && self.drop_order {
114 format!("{} drop order and which traits the closure implements", base)
115 } else if self.drop_order {
116 format!("{} drop order", base)
118 format!("{} which traits the closure implements", base)
123 /// Intermediate format to store information needed to generate a note in the migration lint.
124 struct MigrationLintNote {
125 captures_info: UpvarMigrationInfo,
127 /// reasons why migration is needed for this capture
128 reason: MigrationWarningReason,
131 /// Intermediate format to store the hir id of the root variable and a HashSet containing
132 /// information on why the root variable should be fully captured
133 struct NeededMigration {
134 var_hir_id: hir::HirId,
135 diagnostics_info: Vec<MigrationLintNote>,
138 struct InferBorrowKindVisitor<'a, 'tcx> {
139 fcx: &'a FnCtxt<'a, 'tcx>,
142 impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
143 type Map = intravisit::ErasedMap<'tcx>;
145 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
146 NestedVisitorMap::None
149 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
151 hir::ExprKind::Closure(cc, _, body_id, _, _) => {
152 let body = self.fcx.tcx.hir().body(body_id);
153 self.visit_body(body);
154 self.fcx.analyze_closure(expr.hir_id, expr.span, body_id, body, cc);
156 hir::ExprKind::ConstBlock(anon_const) => {
157 let body = self.fcx.tcx.hir().body(anon_const.body);
158 self.visit_body(body);
163 intravisit::walk_expr(self, expr);
167 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
168 /// Analysis starting point.
169 #[instrument(skip(self, body), level = "debug")]
172 closure_hir_id: hir::HirId,
174 body_id: hir::BodyId,
175 body: &'tcx hir::Body<'tcx>,
176 capture_clause: hir::CaptureBy,
178 // Extract the type of the closure.
179 let ty = self.node_ty(closure_hir_id);
180 let (closure_def_id, substs) = match *ty.kind() {
181 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
182 ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
184 // #51714: skip analysis when we have already encountered type errors
190 "type of closure expr {:?} is not a closure {:?}",
197 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
198 self.closure_kind(closure_substs).is_none().then_some(closure_substs)
203 let local_def_id = closure_def_id.expect_local();
205 let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
206 assert_eq!(body_owner_def_id.to_def_id(), closure_def_id);
207 let mut delegate = InferBorrowKind {
209 closure_def_id: local_def_id,
210 capture_information: Default::default(),
211 fake_reads: Default::default(),
213 euv::ExprUseVisitor::new(
218 &self.typeck_results.borrow(),
223 "For closure={:?}, capture_information={:#?}",
224 closure_def_id, delegate.capture_information
227 self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
229 let (capture_information, closure_kind, origin) = self
230 .process_collected_capture_information(capture_clause, delegate.capture_information);
232 self.compute_min_captures(closure_def_id, capture_information, span);
234 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
236 if should_do_rust_2021_incompatible_closure_captures_analysis(self.tcx, closure_hir_id) {
237 self.perform_2229_migration_anaysis(closure_def_id, body_id, capture_clause, span);
240 let after_feature_tys = self.final_upvar_tys(closure_def_id);
242 // We now fake capture information for all variables that are mentioned within the closure
243 // We do this after handling migrations so that min_captures computes before
244 if !enable_precise_capture(self.tcx, span) {
245 let mut capture_information: InferredCaptureInformation<'tcx> = Default::default();
247 if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
248 for var_hir_id in upvars.keys() {
249 let place = self.place_for_root_variable(local_def_id, *var_hir_id);
251 debug!("seed place {:?}", place);
253 let capture_kind = self.init_capture_kind_for_place(&place, capture_clause);
254 let fake_info = ty::CaptureInfo {
255 capture_kind_expr_id: None,
260 capture_information.push((place, fake_info));
264 // This will update the min captures based on this new fake information.
265 self.compute_min_captures(closure_def_id, capture_information, span);
268 let before_feature_tys = self.final_upvar_tys(closure_def_id);
270 if let Some(closure_substs) = infer_kind {
271 // Unify the (as yet unbound) type variable in the closure
272 // substs with the kind we inferred.
273 let closure_kind_ty = closure_substs.as_closure().kind_ty();
274 self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
276 // If we have an origin, store it.
277 if let Some(origin) = origin {
278 let origin = if enable_precise_capture(self.tcx, span) {
281 (origin.0, Place { projections: vec![], ..origin.1 })
286 .closure_kind_origins_mut()
287 .insert(closure_hir_id, origin);
291 self.log_closure_min_capture_info(closure_def_id, span);
293 // Now that we've analyzed the closure, we know how each
294 // variable is borrowed, and we know what traits the closure
295 // implements (Fn vs FnMut etc). We now have some updates to do
296 // with that information.
298 // Note that no closure type C may have an upvar of type C
299 // (though it may reference itself via a trait object). This
300 // results from the desugaring of closures to a struct like
301 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
302 // C, then the type would have infinite size (and the
303 // inference algorithm will reject it).
305 // Equate the type variables for the upvars with the actual types.
306 let final_upvar_tys = self.final_upvar_tys(closure_def_id);
308 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
309 closure_hir_id, substs, final_upvar_tys
312 // Build a tuple (U0..Un) of the final upvar types U0..Un
313 // and unify the upvar tupe type in the closure with it:
314 let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
315 self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
317 let fake_reads = delegate
320 .map(|(place, cause, hir_id)| (place, cause, hir_id))
322 self.typeck_results.borrow_mut().closure_fake_reads.insert(closure_def_id, fake_reads);
324 if self.tcx.sess.opts.debugging_opts.profile_closures {
325 self.typeck_results.borrow_mut().closure_size_eval.insert(
327 ClosureSizeProfileData {
328 before_feature_tys: self.tcx.mk_tup(before_feature_tys.into_iter()),
329 after_feature_tys: self.tcx.mk_tup(after_feature_tys.into_iter()),
334 // If we are also inferred the closure kind here,
335 // process any deferred resolutions.
336 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
337 for deferred_call_resolution in deferred_call_resolutions {
338 deferred_call_resolution.resolve(self);
342 // Returns a list of `Ty`s for each upvar.
343 fn final_upvar_tys(&self, closure_id: DefId) -> Vec<Ty<'tcx>> {
344 // Presently an unboxed closure type cannot "escape" out of a
345 // function, so we will only encounter ones that originated in the
346 // local crate or were inlined into it along with some function.
347 // This may change if abstract return types of some sort are
351 .closure_min_captures_flattened(closure_id)
352 .map(|captured_place| {
353 let upvar_ty = captured_place.place.ty();
354 let capture = captured_place.info.capture_kind;
357 "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
358 captured_place.place, upvar_ty, capture, captured_place.mutability,
361 apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture, captured_place.region)
366 /// Adjusts the closure capture information to ensure that the operations aren't unsafe,
367 /// and that the path can be captured with required capture kind (depending on use in closure,
368 /// move closure etc.)
370 /// Returns the set of of adjusted information along with the inferred closure kind and span
371 /// associated with the closure kind inference.
373 /// Note that we *always* infer a minimal kind, even if
374 /// we don't always *use* that in the final result (i.e., sometimes
375 /// we've taken the closure kind from the expectations instead, and
376 /// for generators we don't even implement the closure traits
379 /// If we inferred that the closure needs to be FnMut/FnOnce, last element of the returned tuple
380 /// contains a `Some()` with the `Place` that caused us to do so.
381 fn process_collected_capture_information(
383 capture_clause: hir::CaptureBy,
384 capture_information: InferredCaptureInformation<'tcx>,
385 ) -> (InferredCaptureInformation<'tcx>, ty::ClosureKind, Option<(Span, Place<'tcx>)>) {
386 let mut closure_kind = ty::ClosureKind::LATTICE_BOTTOM;
387 let mut origin: Option<(Span, Place<'tcx>)> = None;
389 let processed = capture_information
391 .map(|(place, mut capture_info)| {
392 // Apply rules for safety before inferring closure kind
393 let (place, capture_kind) =
394 restrict_capture_precision(place, capture_info.capture_kind);
396 let (place, capture_kind) = truncate_capture_for_optimization(place, capture_kind);
398 let usage_span = if let Some(usage_expr) = capture_info.path_expr_id {
399 self.tcx.hir().span(usage_expr)
404 let updated = match capture_kind {
405 ty::UpvarCapture::ByValue => match closure_kind {
406 ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
407 (ty::ClosureKind::FnOnce, Some((usage_span, place.clone())))
409 // If closure is already FnOnce, don't update
410 ty::ClosureKind::FnOnce => (closure_kind, origin.take()),
413 ty::UpvarCapture::ByRef(
414 ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
417 ty::ClosureKind::Fn => {
418 (ty::ClosureKind::FnMut, Some((usage_span, place.clone())))
420 // Don't update the origin
421 ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce => {
422 (closure_kind, origin.take())
427 _ => (closure_kind, origin.take()),
430 closure_kind = updated.0;
433 let (place, capture_kind) = match capture_clause {
434 hir::CaptureBy::Value => adjust_for_move_closure(place, capture_kind),
435 hir::CaptureBy::Ref => adjust_for_non_move_closure(place, capture_kind),
438 // This restriction needs to be applied after we have handled adjustments for `move`
439 // closures. We want to make sure any adjustment that might make us move the place into
440 // the closure gets handled.
441 let (place, capture_kind) =
442 restrict_precision_for_drop_types(self, place, capture_kind, usage_span);
444 capture_info.capture_kind = capture_kind;
445 (place, capture_info)
449 (processed, closure_kind, origin)
452 /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
453 /// Places (and corresponding capture kind) that we need to keep track of to support all
454 /// the required captured paths.
457 /// Note: If this function is called multiple times for the same closure, it will update
458 /// the existing min_capture map that is stored in TypeckResults.
462 /// struct Point { x: i32, y: i32 }
464 /// let s: String; // hir_id_s
465 /// let mut p: Point; // his_id_p
467 /// println!("{}", s); // L1
469 /// println!("{}" , p.y) // L3
470 /// println!("{}", p) // L4
474 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
475 /// the lines L1..5 respectively.
477 /// InferBorrowKind results in a structure like this:
481 /// Place(base: hir_id_s, projections: [], ....) -> {
482 /// capture_kind_expr: hir_id_L5,
483 /// path_expr_id: hir_id_L5,
484 /// capture_kind: ByValue
486 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
487 /// capture_kind_expr: hir_id_L2,
488 /// path_expr_id: hir_id_L2,
489 /// capture_kind: ByValue
491 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
492 /// capture_kind_expr: hir_id_L3,
493 /// path_expr_id: hir_id_L3,
494 /// capture_kind: ByValue
496 /// Place(base: hir_id_p, projections: [], ...) -> {
497 /// capture_kind_expr: hir_id_L4,
498 /// path_expr_id: hir_id_L4,
499 /// capture_kind: ByValue
503 /// After the min capture analysis, we get:
507 /// Place(base: hir_id_s, projections: [], ....) -> {
508 /// capture_kind_expr: hir_id_L5,
509 /// path_expr_id: hir_id_L5,
510 /// capture_kind: ByValue
514 /// Place(base: hir_id_p, projections: [], ...) -> {
515 /// capture_kind_expr: hir_id_L2,
516 /// path_expr_id: hir_id_L4,
517 /// capture_kind: ByValue
521 fn compute_min_captures(
523 closure_def_id: DefId,
524 capture_information: InferredCaptureInformation<'tcx>,
527 if capture_information.is_empty() {
531 let mut typeck_results = self.typeck_results.borrow_mut();
533 let mut root_var_min_capture_list =
534 typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
536 for (mut place, capture_info) in capture_information.into_iter() {
537 let var_hir_id = match place.base {
538 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
539 base => bug!("Expected upvar, found={:?}", base),
542 let min_cap_list = match root_var_min_capture_list.get_mut(&var_hir_id) {
544 let mutability = self.determine_capture_mutability(&typeck_results, &place);
545 let min_cap_list = vec![ty::CapturedPlace {
551 root_var_min_capture_list.insert(var_hir_id, min_cap_list);
554 Some(min_cap_list) => min_cap_list,
557 // Go through each entry in the current list of min_captures
558 // - if ancestor is found, update it's capture kind to account for current place's
559 // capture information.
561 // - if descendant is found, remove it from the list, and update the current place's
562 // capture information to account for the descendants's capture kind.
564 // We can never be in a case where the list contains both an ancestor and a descendant
565 // Also there can only be ancestor but in case of descendants there might be
568 let mut descendant_found = false;
569 let mut updated_capture_info = capture_info;
570 min_cap_list.retain(|possible_descendant| {
571 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
572 // current place is ancestor of possible_descendant
573 PlaceAncestryRelation::Ancestor => {
574 descendant_found = true;
576 let mut possible_descendant = possible_descendant.clone();
577 let backup_path_expr_id = updated_capture_info.path_expr_id;
579 // Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
580 // possible change in capture mode.
581 truncate_place_to_len_and_update_capture_kind(
582 &mut possible_descendant.place,
583 &mut possible_descendant.info.capture_kind,
584 place.projections.len(),
587 updated_capture_info =
588 determine_capture_info(updated_capture_info, possible_descendant.info);
590 // we need to keep the ancestor's `path_expr_id`
591 updated_capture_info.path_expr_id = backup_path_expr_id;
599 let mut ancestor_found = false;
600 if !descendant_found {
601 for possible_ancestor in min_cap_list.iter_mut() {
602 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
603 PlaceAncestryRelation::SamePlace => {
604 ancestor_found = true;
605 possible_ancestor.info = determine_capture_info(
606 possible_ancestor.info,
607 updated_capture_info,
610 // Only one related place will be in the list.
613 // current place is descendant of possible_ancestor
614 PlaceAncestryRelation::Descendant => {
615 ancestor_found = true;
616 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
618 // Truncate the descendant (current place) to be same as the ancestor to handle any
619 // possible change in capture mode.
620 truncate_place_to_len_and_update_capture_kind(
622 &mut updated_capture_info.capture_kind,
623 possible_ancestor.place.projections.len(),
626 possible_ancestor.info = determine_capture_info(
627 possible_ancestor.info,
628 updated_capture_info,
631 // we need to keep the ancestor's `path_expr_id`
632 possible_ancestor.info.path_expr_id = backup_path_expr_id;
634 // Only one related place will be in the list.
642 // Only need to insert when we don't have an ancestor in the existing min capture list
644 let mutability = self.determine_capture_mutability(&typeck_results, &place);
645 let captured_place = ty::CapturedPlace {
647 info: updated_capture_info,
651 min_cap_list.push(captured_place);
655 // For each capture that is determined to be captured by ref, add region info.
656 for (_, captures) in &mut root_var_min_capture_list {
657 for capture in captures {
658 match capture.info.capture_kind {
659 ty::UpvarCapture::ByRef(_) => {
660 let PlaceBase::Upvar(upvar_id) = capture.place.base else { bug!("expected upvar") };
661 let origin = UpvarRegion(upvar_id, closure_span);
662 let upvar_region = self.next_region_var(origin);
663 capture.region = Some(upvar_region);
671 "For closure={:?}, min_captures before sorting={:?}",
672 closure_def_id, root_var_min_capture_list
675 // Now that we have the minimized list of captures, sort the captures by field id.
676 // This causes the closure to capture the upvars in the same order as the fields are
677 // declared which is also the drop order. Thus, in situations where we capture all the
678 // fields of some type, the obserable drop order will remain the same as it previously
679 // was even though we're dropping each capture individually.
680 // See https://github.com/rust-lang/project-rfc-2229/issues/42 and
681 // `src/test/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
682 for (_, captures) in &mut root_var_min_capture_list {
683 captures.sort_by(|capture1, capture2| {
684 for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
685 // We do not need to look at the `Projection.ty` fields here because at each
686 // step of the iteration, the projections will either be the same and therefore
687 // the types must be as well or the current projection will be different and
688 // we will return the result of comparing the field indexes.
689 match (p1.kind, p2.kind) {
690 // Paths are the same, continue to next loop.
691 (ProjectionKind::Deref, ProjectionKind::Deref) => {}
692 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
695 // Fields are different, compare them.
696 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
700 // We should have either a pair of `Deref`s or a pair of `Field`s.
701 // Anything else is a bug.
703 l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
704 r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
706 "ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
711 l @ (ProjectionKind::Index
712 | ProjectionKind::Subslice
713 | ProjectionKind::Deref
714 | ProjectionKind::Field(..)),
715 r @ (ProjectionKind::Index
716 | ProjectionKind::Subslice
717 | ProjectionKind::Deref
718 | ProjectionKind::Field(..)),
720 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
728 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
735 "For closure={:?}, min_captures after sorting={:#?}",
736 closure_def_id, root_var_min_capture_list
738 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
741 /// Perform the migration analysis for RFC 2229, and emit lint
742 /// `disjoint_capture_drop_reorder` if needed.
743 fn perform_2229_migration_anaysis(
745 closure_def_id: DefId,
746 body_id: hir::BodyId,
747 capture_clause: hir::CaptureBy,
750 let (need_migrations, reasons) = self.compute_2229_migrations(
754 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
757 if !need_migrations.is_empty() {
758 let (migration_string, migrated_variables_concat) =
759 migration_suggestion_for_2229(self.tcx, &need_migrations);
761 let local_def_id = closure_def_id.expect_local();
762 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
763 let closure_span = self.tcx.hir().span(closure_hir_id);
764 let closure_head_span = self.tcx.sess.source_map().guess_head_span(closure_span);
765 self.tcx.struct_span_lint_hir(
766 lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
770 let mut diagnostics_builder = lint.build(
771 &reasons.migration_message(),
773 for NeededMigration { var_hir_id, diagnostics_info } in &need_migrations {
774 // Labels all the usage of the captured variable and why they are responsible
775 // for migration being needed
776 for lint_note in diagnostics_info.iter() {
777 match &lint_note.captures_info {
778 UpvarMigrationInfo::CapturingPrecise { source_expr: Some(capture_expr_id), var_name: captured_name } => {
779 let cause_span = self.tcx.hir().span(*capture_expr_id);
780 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
781 self.tcx.hir().name(*var_hir_id),
785 UpvarMigrationInfo::CapturingNothing { use_span } => {
786 diagnostics_builder.span_label(*use_span, format!("in Rust 2018, this causes the closure to capture `{}`, but in Rust 2021, it has no effect",
787 self.tcx.hir().name(*var_hir_id),
794 // Add a label pointing to where a captured variable affected by drop order
796 if lint_note.reason.drop_order {
797 let drop_location_span = drop_location_span(self.tcx, &closure_hir_id);
799 match &lint_note.captures_info {
800 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
801 diagnostics_builder.span_label(drop_location_span, format!("in Rust 2018, `{}` is dropped here, but in Rust 2021, only `{}` will be dropped here as part of the closure",
802 self.tcx.hir().name(*var_hir_id),
806 UpvarMigrationInfo::CapturingNothing { use_span: _ } => {
807 diagnostics_builder.span_label(drop_location_span, format!("in Rust 2018, `{v}` is dropped here along with the closure, but in Rust 2021 `{v}` is not part of the closure",
808 v = self.tcx.hir().name(*var_hir_id),
814 // Add a label explaining why a closure no longer implements a trait
815 for &missing_trait in &lint_note.reason.auto_traits {
816 // not capturing something anymore cannot cause a trait to fail to be implemented:
817 match &lint_note.captures_info {
818 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
819 let var_name = self.tcx.hir().name(*var_hir_id);
820 diagnostics_builder.span_label(closure_head_span, format!("\
821 in Rust 2018, this closure implements {missing_trait} \
822 as `{var_name}` implements {missing_trait}, but in Rust 2021, \
823 this closure will no longer implement {missing_trait} \
824 because `{var_name}` is not fully captured \
825 and `{captured_name}` does not implement {missing_trait}"));
828 // Cannot happen: if we don't capture a variable, we impl strictly more traits
829 UpvarMigrationInfo::CapturingNothing { use_span } => span_bug!(*use_span, "missing trait from not capturing something"),
834 diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
836 let diagnostic_msg = format!(
837 "add a dummy let to cause {} to be fully captured",
838 migrated_variables_concat
841 let mut closure_body_span = {
842 // If the body was entirely expanded from a macro
843 // invocation, i.e. the body is not contained inside the
844 // closure span, then we walk up the expansion until we
845 // find the span before the expansion.
846 let s = self.tcx.hir().span(body_id.hir_id);
847 s.find_ancestor_inside(closure_span).unwrap_or(s)
850 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
851 if s.starts_with('$') {
852 // Looks like a macro fragment. Try to find the real block.
853 if let Some(hir::Node::Expr(&hir::Expr {
854 kind: hir::ExprKind::Block(block, ..), ..
855 })) = self.tcx.hir().find(body_id.hir_id) {
856 // If the body is a block (with `{..}`), we use the span of that block.
857 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
858 // Since we know it's a block, we know we can insert the `let _ = ..` without
859 // breaking the macro syntax.
860 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
861 closure_body_span = block.span;
867 let mut lines = s.lines();
868 let line1 = lines.next().unwrap_or_default();
870 if line1.trim_end() == "{" {
871 // This is a multi-line closure with just a `{` on the first line,
872 // so we put the `let` on its own line.
873 // We take the indentation from the next non-empty line.
874 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
875 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
876 diagnostics_builder.span_suggestion(
877 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
879 format!("\n{}{};", indent, migration_string),
880 Applicability::MachineApplicable,
882 } else if line1.starts_with('{') {
883 // This is a closure with its body wrapped in
884 // braces, but with more than just the opening
885 // brace on the first line. We put the `let`
886 // directly after the `{`.
887 diagnostics_builder.span_suggestion(
888 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
890 format!(" {};", migration_string),
891 Applicability::MachineApplicable,
894 // This is a closure without braces around the body.
895 // We add braces to add the `let` before the body.
896 diagnostics_builder.multipart_suggestion(
899 (closure_body_span.shrink_to_lo(), format!("{{ {}; ", migration_string)),
900 (closure_body_span.shrink_to_hi(), " }".to_string()),
902 Applicability::MachineApplicable
906 diagnostics_builder.span_suggestion(
910 Applicability::HasPlaceholders
914 diagnostics_builder.emit();
920 /// Combines all the reasons for 2229 migrations
921 fn compute_2229_migrations_reasons(
923 auto_trait_reasons: FxHashSet<&'static str>,
925 ) -> MigrationWarningReason {
926 let mut reasons = MigrationWarningReason::default();
928 reasons.auto_traits.extend(auto_trait_reasons);
929 reasons.drop_order = drop_order;
934 /// Figures out the list of root variables (and their types) that aren't completely
935 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
936 /// differ between the root variable and the captured paths.
938 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
939 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
940 fn compute_2229_migrations_for_trait(
942 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
943 var_hir_id: hir::HirId,
944 closure_clause: hir::CaptureBy,
945 ) -> Option<FxHashMap<UpvarMigrationInfo, FxHashSet<&'static str>>> {
946 let auto_traits_def_id = vec![
947 self.tcx.lang_items().clone_trait(),
948 self.tcx.lang_items().sync_trait(),
949 self.tcx.get_diagnostic_item(sym::Send),
950 self.tcx.lang_items().unpin_trait(),
951 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
952 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
954 const AUTO_TRAITS: [&str; 6] =
955 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
957 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
959 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
961 let ty = match closure_clause {
962 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
963 hir::CaptureBy::Ref => {
964 // For non move closure the capture kind is the max capture kind of all captures
965 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
966 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
967 for capture in root_var_min_capture_list.iter() {
968 max_capture_info = determine_capture_info(max_capture_info, capture.info);
971 apply_capture_kind_on_capture_ty(
974 max_capture_info.capture_kind,
980 let mut obligations_should_hold = Vec::new();
981 // Checks if a root variable implements any of the auto traits
982 for check_trait in auto_traits_def_id.iter() {
983 obligations_should_hold.push(
987 .type_implements_trait(
990 self.tcx.mk_substs_trait(ty, &[]),
993 .must_apply_modulo_regions()
999 let mut problematic_captures = FxHashMap::default();
1000 // Check whether captured fields also implement the trait
1001 for capture in root_var_min_capture_list.iter() {
1002 let ty = apply_capture_kind_on_capture_ty(
1005 capture.info.capture_kind,
1006 Some(&ty::ReErased),
1009 // Checks if a capture implements any of the auto traits
1010 let mut obligations_holds_for_capture = Vec::new();
1011 for check_trait in auto_traits_def_id.iter() {
1012 obligations_holds_for_capture.push(
1014 .map(|check_trait| {
1016 .type_implements_trait(
1019 self.tcx.mk_substs_trait(ty, &[]),
1022 .must_apply_modulo_regions()
1028 let mut capture_problems = FxHashSet::default();
1030 // Checks if for any of the auto traits, one or more trait is implemented
1031 // by the root variable but not by the capture
1032 for (idx, _) in obligations_should_hold.iter().enumerate() {
1033 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
1034 capture_problems.insert(AUTO_TRAITS[idx]);
1038 if !capture_problems.is_empty() {
1039 problematic_captures.insert(
1040 UpvarMigrationInfo::CapturingPrecise {
1041 source_expr: capture.info.path_expr_id,
1042 var_name: capture.to_string(self.tcx),
1048 if !problematic_captures.is_empty() {
1049 return Some(problematic_captures);
1054 /// Figures out the list of root variables (and their types) that aren't completely
1055 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
1056 /// some path starting at that root variable **might** be affected.
1058 /// The output list would include a root variable if:
1059 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1060 /// enabled, **and**
1061 /// - It wasn't completely captured by the closure, **and**
1062 /// - One of the paths starting at this root variable, that is not captured needs Drop.
1064 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
1065 /// are no significant drops than None is returned
1066 #[instrument(level = "debug", skip(self))]
1067 fn compute_2229_migrations_for_drop(
1069 closure_def_id: DefId,
1071 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1072 closure_clause: hir::CaptureBy,
1073 var_hir_id: hir::HirId,
1074 ) -> Option<FxHashSet<UpvarMigrationInfo>> {
1075 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
1077 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local())) {
1078 debug!("does not have significant drop");
1082 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1083 // The upvar is mentioned within the closure but no path starting from it is
1084 // used. This occurs when you have (e.g.)
1087 // let x = move || {
1091 debug!("no path starting from it is used");
1094 match closure_clause {
1095 // Only migrate if closure is a move closure
1096 hir::CaptureBy::Value => {
1097 let mut diagnostics_info = FxHashSet::default();
1098 let upvars = self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
1099 let upvar = upvars[&var_hir_id];
1100 diagnostics_info.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
1101 return Some(diagnostics_info);
1103 hir::CaptureBy::Ref => {}
1108 debug!(?root_var_min_capture_list);
1110 let mut projections_list = Vec::new();
1111 let mut diagnostics_info = FxHashSet::default();
1113 for captured_place in root_var_min_capture_list.iter() {
1114 match captured_place.info.capture_kind {
1115 // Only care about captures that are moved into the closure
1116 ty::UpvarCapture::ByValue => {
1117 projections_list.push(captured_place.place.projections.as_slice());
1118 diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
1119 source_expr: captured_place.info.path_expr_id,
1120 var_name: captured_place.to_string(self.tcx),
1123 ty::UpvarCapture::ByRef(..) => {}
1127 debug!(?projections_list);
1128 debug!(?diagnostics_info);
1130 let is_moved = !projections_list.is_empty();
1133 let is_not_completely_captured =
1134 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1135 debug!(?is_not_completely_captured);
1138 && is_not_completely_captured
1139 && self.has_significant_drop_outside_of_captures(
1146 return Some(diagnostics_info);
1152 /// Figures out the list of root variables (and their types) that aren't completely
1153 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1154 /// order of some path starting at that root variable **might** be affected or auto-traits
1155 /// differ between the root variable and the captured paths.
1157 /// The output list would include a root variable if:
1158 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1159 /// enabled, **and**
1160 /// - It wasn't completely captured by the closure, **and**
1161 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1162 /// - One of the paths captured does not implement all the auto-traits its root variable
1165 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1166 /// containing the reason why root variables whose HirId is contained in the vector should
1168 #[instrument(level = "debug", skip(self))]
1169 fn compute_2229_migrations(
1171 closure_def_id: DefId,
1173 closure_clause: hir::CaptureBy,
1174 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1175 ) -> (Vec<NeededMigration>, MigrationWarningReason) {
1176 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1177 return (Vec::new(), MigrationWarningReason::default());
1180 let mut need_migrations = Vec::new();
1181 let mut auto_trait_migration_reasons = FxHashSet::default();
1182 let mut drop_migration_needed = false;
1184 // Perform auto-trait analysis
1185 for (&var_hir_id, _) in upvars.iter() {
1186 let mut diagnostics_info = Vec::new();
1188 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1189 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1193 FxHashMap::default()
1196 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1197 .compute_2229_migrations_for_drop(
1204 drop_migration_needed = true;
1207 FxHashSet::default()
1210 // Combine all the captures responsible for needing migrations into one HashSet
1211 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1212 for key in auto_trait_diagnostic.keys() {
1213 capture_diagnostic.insert(key.clone());
1216 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1217 capture_diagnostic.sort();
1218 for captures_info in capture_diagnostic {
1219 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1220 let capture_trait_reasons =
1221 if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
1224 FxHashSet::default()
1227 // Check if migration is needed because of drop reorder as a result of that capture
1228 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
1230 // Combine all the reasons of why the root variable should be captured as a result of
1231 // auto trait implementation issues
1232 auto_trait_migration_reasons.extend(capture_trait_reasons.clone());
1234 diagnostics_info.push(MigrationLintNote {
1236 reason: self.compute_2229_migrations_reasons(
1237 capture_trait_reasons,
1238 capture_drop_reorder_reason,
1243 if !diagnostics_info.is_empty() {
1244 need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
1249 self.compute_2229_migrations_reasons(
1250 auto_trait_migration_reasons,
1251 drop_migration_needed,
1256 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1257 /// of a root variable and a list of captured paths starting at this root variable (expressed
1258 /// using list of `Projection` slices), it returns true if there is a path that is not
1259 /// captured starting at this root variable that implements Drop.
1261 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1262 /// path say P and then list of projection slices which represent the different captures moved
1263 /// into the closure starting off of P.
1265 /// This will make more sense with an example:
1268 /// #![feature(capture_disjoint_fields)]
1270 /// struct FancyInteger(i32); // This implements Drop
1272 /// struct Point { x: FancyInteger, y: FancyInteger }
1275 /// struct Wrapper { p: Point, c: Color }
1277 /// fn f(w: Wrapper) {
1279 /// // Closure captures w.p.x and w.c by move.
1286 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1287 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1288 /// therefore Drop ordering would change and we want this function to return true.
1290 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1292 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1295 /// - Ty(place): Type of place
1296 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1299 /// (Ty(w), [ &[p, x], &[c] ])
1301 /// ----------------------------
1304 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1307 /// (Ty(w.p), [ &[x] ]) false
1310 /// -------------------------------
1313 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1316 /// false NeedsSignificantDrop(Ty(w.p.y))
1322 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1323 /// This implies that the `w.c` is completely captured by the closure.
1324 /// Since drop for this path will be called when the closure is
1325 /// dropped we don't need to migrate for it.
1327 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1328 /// path wasn't captured by the closure. Also note that even
1329 /// though we didn't capture this path, the function visits it,
1330 /// which is kind of the point of this function. We then return
1331 /// if the type of `w.p.y` implements Drop, which in this case is
1334 /// Consider another example:
1338 /// impl Drop for X {}
1341 /// impl Drop for Y {}
1345 /// let c = || move(y.0);
1349 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1350 /// return true, because even though all paths starting at `y` are captured, `y` itself
1351 /// implements Drop which will be affected since `y` isn't completely captured.
1352 fn has_significant_drop_outside_of_captures(
1354 closure_def_id: DefId,
1356 base_path_ty: Ty<'tcx>,
1357 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1359 let needs_drop = |ty: Ty<'tcx>| {
1360 ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local()))
1363 let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
1364 let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
1365 let ty_params = self.tcx.mk_substs_trait(base_path_ty, &[]);
1367 .type_implements_trait(
1371 self.tcx.param_env(closure_def_id.expect_local()),
1373 .must_apply_modulo_regions()
1376 let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
1378 // If there is a case where no projection is applied on top of current place
1379 // then there must be exactly one capture corresponding to such a case. Note that this
1380 // represents the case of the path being completely captured by the variable.
1382 // eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
1383 // capture `a.b.c`, because that voilates min capture.
1384 let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
1386 assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
1388 if is_completely_captured {
1389 // The place is captured entirely, so doesn't matter if needs dtor, it will be drop
1390 // when the closure is dropped.
1394 if captured_by_move_projs.is_empty() {
1395 return needs_drop(base_path_ty);
1398 if is_drop_defined_for_ty {
1399 // If drop is implemented for this type then we need it to be fully captured,
1400 // and we know it is not completely captured because of the previous checks.
1402 // Note that this is a bug in the user code that will be reported by the
1403 // borrow checker, since we can't move out of drop types.
1405 // The bug exists in the user's code pre-migration, and we don't migrate here.
1409 match base_path_ty.kind() {
1411 // - `captured_by_move_projs` is not empty. Therefore we can call
1412 // `captured_by_move_projs.first().unwrap()` safely.
1413 // - All entries in `captured_by_move_projs` have atleast one projection.
1414 // Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
1416 // We don't capture derefs in case of move captures, which would have be applied to
1417 // access any further paths.
1418 ty::Adt(def, _) if def.is_box() => unreachable!(),
1419 ty::Ref(..) => unreachable!(),
1420 ty::RawPtr(..) => unreachable!(),
1422 ty::Adt(def, substs) => {
1423 // Multi-varaint enums are captured in entirety,
1424 // which would've been handled in the case of single empty slice in `captured_by_move_projs`.
1425 assert_eq!(def.variants.len(), 1);
1427 // Only Field projections can be applied to a non-box Adt.
1429 captured_by_move_projs.iter().all(|projs| matches!(
1430 projs.first().unwrap().kind,
1431 ProjectionKind::Field(..)
1434 def.variants.get(VariantIdx::new(0)).unwrap().fields.iter().enumerate().any(
1436 let paths_using_field = captured_by_move_projs
1438 .filter_map(|projs| {
1439 if let ProjectionKind::Field(field_idx, _) =
1440 projs.first().unwrap().kind
1442 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1449 let after_field_ty = field.ty(self.tcx, substs);
1450 self.has_significant_drop_outside_of_captures(
1461 // Only Field projections can be applied to a tuple.
1463 captured_by_move_projs.iter().all(|projs| matches!(
1464 projs.first().unwrap().kind,
1465 ProjectionKind::Field(..)
1469 base_path_ty.tuple_fields().enumerate().any(|(i, element_ty)| {
1470 let paths_using_field = captured_by_move_projs
1472 .filter_map(|projs| {
1473 if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
1475 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1482 self.has_significant_drop_outside_of_captures(
1491 // Anything else would be completely captured and therefore handled already.
1492 _ => unreachable!(),
1496 fn init_capture_kind_for_place(
1498 place: &Place<'tcx>,
1499 capture_clause: hir::CaptureBy,
1500 ) -> ty::UpvarCapture {
1501 match capture_clause {
1502 // In case of a move closure if the data is accessed through a reference we
1503 // want to capture by ref to allow precise capture using reborrows.
1505 // If the data will be moved out of this place, then the place will be truncated
1506 // at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
1508 hir::CaptureBy::Value if !place.deref_tys().any(ty::TyS::is_ref) => {
1509 ty::UpvarCapture::ByValue
1511 hir::CaptureBy::Value | hir::CaptureBy::Ref => ty::UpvarCapture::ByRef(ty::ImmBorrow),
1515 fn place_for_root_variable(
1517 closure_def_id: LocalDefId,
1518 var_hir_id: hir::HirId,
1520 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
1523 base_ty: self.node_ty(var_hir_id),
1524 base: PlaceBase::Upvar(upvar_id),
1525 projections: Default::default(),
1529 fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
1530 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
1533 fn log_capture_analysis_first_pass(
1535 closure_def_id: rustc_hir::def_id::DefId,
1536 capture_information: &InferredCaptureInformation<'tcx>,
1539 if self.should_log_capture_analysis(closure_def_id) {
1541 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
1542 for (place, capture_info) in capture_information {
1543 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
1544 let output_str = format!("Capturing {}", capture_str);
1547 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
1548 diag.span_note(span, &output_str);
1554 fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
1555 if self.should_log_capture_analysis(closure_def_id) {
1556 if let Some(min_captures) =
1557 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
1560 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
1562 for (_, min_captures_for_var) in min_captures {
1563 for capture in min_captures_for_var {
1564 let place = &capture.place;
1565 let capture_info = &capture.info;
1568 construct_capture_info_string(self.tcx, place, capture_info);
1569 let output_str = format!("Min Capture {}", capture_str);
1571 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
1572 let path_span = capture_info
1574 .map_or(closure_span, |e| self.tcx.hir().span(e));
1575 let capture_kind_span = capture_info
1576 .capture_kind_expr_id
1577 .map_or(closure_span, |e| self.tcx.hir().span(e));
1579 let mut multi_span: MultiSpan =
1580 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
1582 let capture_kind_label =
1583 construct_capture_kind_reason_string(self.tcx, place, capture_info);
1584 let path_label = construct_path_string(self.tcx, place);
1586 multi_span.push_span_label(path_span, path_label);
1587 multi_span.push_span_label(capture_kind_span, capture_kind_label);
1589 diag.span_note(multi_span, &output_str);
1591 let span = capture_info
1593 .map_or(closure_span, |e| self.tcx.hir().span(e));
1595 diag.span_note(span, &output_str);
1604 /// A captured place is mutable if
1605 /// 1. Projections don't include a Deref of an immut-borrow, **and**
1606 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
1607 fn determine_capture_mutability(
1609 typeck_results: &'a TypeckResults<'tcx>,
1610 place: &Place<'tcx>,
1611 ) -> hir::Mutability {
1612 let var_hir_id = match place.base {
1613 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
1614 _ => unreachable!(),
1617 let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
1619 let mut is_mutbl = match bm {
1620 ty::BindByValue(mutability) => mutability,
1621 ty::BindByReference(_) => hir::Mutability::Not,
1624 for pointer_ty in place.deref_tys() {
1625 match pointer_ty.kind() {
1626 // We don't capture derefs of raw ptrs
1627 ty::RawPtr(_) => unreachable!(),
1629 // Derefencing a mut-ref allows us to mut the Place if we don't deref
1630 // an immut-ref after on top of this.
1631 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
1633 // The place isn't mutable once we dereference an immutable reference.
1634 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
1636 // Dereferencing a box doesn't change mutability
1637 ty::Adt(def, ..) if def.is_box() => {}
1639 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
1647 /// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
1648 /// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
1649 fn restrict_repr_packed_field_ref_capture<'tcx>(
1651 param_env: ty::ParamEnv<'tcx>,
1652 mut place: Place<'tcx>,
1653 mut curr_borrow_kind: ty::UpvarCapture,
1654 ) -> (Place<'tcx>, ty::UpvarCapture) {
1655 let pos = place.projections.iter().enumerate().position(|(i, p)| {
1656 let ty = place.ty_before_projection(i);
1658 // Return true for fields of packed structs, unless those fields have alignment 1.
1660 ProjectionKind::Field(..) => match ty.kind() {
1661 ty::Adt(def, _) if def.repr.packed() => {
1662 match tcx.layout_of(param_env.and(p.ty)) {
1663 Ok(layout) if layout.align.abi.bytes() == 1 => {
1664 // if the alignment is 1, the type can't be further
1667 "restrict_repr_packed_field_ref_capture: ({:?}) - align = 1",
1673 debug!("restrict_repr_packed_field_ref_capture: ({:?}) - true", place);
1685 if let Some(pos) = pos {
1686 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
1689 (place, curr_borrow_kind)
1692 /// Returns a Ty that applies the specified capture kind on the provided capture Ty
1693 fn apply_capture_kind_on_capture_ty<'tcx>(
1696 capture_kind: UpvarCapture,
1697 region: Option<ty::Region<'tcx>>,
1699 match capture_kind {
1700 ty::UpvarCapture::ByValue => ty,
1701 ty::UpvarCapture::ByRef(kind) => {
1702 tcx.mk_ref(region.unwrap(), ty::TypeAndMut { ty: ty, mutbl: kind.to_mutbl_lossy() })
1707 /// Returns the Span of where the value with the provided HirId would be dropped
1708 fn drop_location_span<'tcx>(tcx: TyCtxt<'tcx>, hir_id: &hir::HirId) -> Span {
1709 let owner_id = tcx.hir().get_enclosing_scope(*hir_id).unwrap();
1711 let owner_node = tcx.hir().get(owner_id);
1712 let owner_span = match owner_node {
1713 hir::Node::Item(item) => match item.kind {
1714 hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
1716 bug!("Drop location span error: need to handle more ItemKind {:?}", item.kind);
1719 hir::Node::Block(block) => tcx.hir().span(block.hir_id),
1721 bug!("Drop location span error: need to handle more Node {:?}", owner_node);
1724 tcx.sess.source_map().end_point(owner_span)
1727 struct InferBorrowKind<'a, 'tcx> {
1728 fcx: &'a FnCtxt<'a, 'tcx>,
1730 // The def-id of the closure whose kind and upvar accesses are being inferred.
1731 closure_def_id: LocalDefId,
1733 /// For each Place that is captured by the closure, we track the minimal kind of
1734 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1736 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1737 /// s.str2 via a MutableBorrow
1740 /// struct SomeStruct { str1: String, str2: String }
1742 /// // Assume that the HirId for the variable definition is `V1`
1743 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
1745 /// let fix_s = |new_s2| {
1746 /// // Assume that the HirId for the expression `s.str1` is `E1`
1747 /// println!("Updating SomeStruct with str1=", s.str1);
1748 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1749 /// s.str2 = new_s2;
1753 /// For closure `fix_s`, (at a high level) the map contains
1756 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1757 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1759 capture_information: InferredCaptureInformation<'tcx>,
1760 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1763 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1764 fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId) {
1765 let PlaceBase::Upvar(_) = place.base else { return };
1767 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1768 // such as deref of a raw pointer.
1769 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1771 let (place, _) = restrict_capture_precision(place, dummy_capture_kind);
1773 let (place, _) = restrict_repr_packed_field_ref_capture(
1779 self.fake_reads.push((place, cause, diag_expr_id));
1782 #[instrument(skip(self), level = "debug")]
1783 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1784 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1785 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1787 self.capture_information.push((
1788 place_with_id.place.clone(),
1790 capture_kind_expr_id: Some(diag_expr_id),
1791 path_expr_id: Some(diag_expr_id),
1792 capture_kind: ty::UpvarCapture::ByValue,
1797 #[instrument(skip(self), level = "debug")]
1800 place_with_id: &PlaceWithHirId<'tcx>,
1801 diag_expr_id: hir::HirId,
1804 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1805 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1807 // The region here will get discarded/ignored
1808 let capture_kind = ty::UpvarCapture::ByRef(bk);
1810 // We only want repr packed restriction to be applied to reading references into a packed
1811 // struct, and not when the data is being moved. Therefore we call this method here instead
1812 // of in `restrict_capture_precision`.
1813 let (place, mut capture_kind) = restrict_repr_packed_field_ref_capture(
1816 place_with_id.place.clone(),
1820 // Raw pointers don't inherit mutability
1821 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1822 capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1825 self.capture_information.push((
1828 capture_kind_expr_id: Some(diag_expr_id),
1829 path_expr_id: Some(diag_expr_id),
1835 #[instrument(skip(self), level = "debug")]
1836 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1837 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1841 /// Rust doesn't permit moving fields out of a type that implements drop
1842 fn restrict_precision_for_drop_types<'a, 'tcx>(
1843 fcx: &'a FnCtxt<'a, 'tcx>,
1844 mut place: Place<'tcx>,
1845 mut curr_mode: ty::UpvarCapture,
1847 ) -> (Place<'tcx>, ty::UpvarCapture) {
1848 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1850 if let (false, UpvarCapture::ByValue) = (is_copy_type, curr_mode) {
1851 for i in 0..place.projections.len() {
1852 match place.ty_before_projection(i).kind() {
1853 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1854 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1865 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
1866 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
1867 /// them completely.
1868 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
1869 fn restrict_precision_for_unsafe<'tcx>(
1870 mut place: Place<'tcx>,
1871 mut curr_mode: ty::UpvarCapture,
1872 ) -> (Place<'tcx>, ty::UpvarCapture) {
1873 if place.base_ty.is_unsafe_ptr() {
1874 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1877 if place.base_ty.is_union() {
1878 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1881 for (i, proj) in place.projections.iter().enumerate() {
1882 if proj.ty.is_unsafe_ptr() {
1883 // Don't apply any projections on top of an unsafe ptr.
1884 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1888 if proj.ty.is_union() {
1889 // Don't capture preicse fields of a union.
1890 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1898 /// Truncate projections so that following rules are obeyed by the captured `place`:
1899 /// - No Index projections are captured, since arrays are captured completely.
1900 /// - No unsafe block is required to capture `place`
1901 /// Returns the truncated place and updated cature mode.
1902 fn restrict_capture_precision<'tcx>(
1904 curr_mode: ty::UpvarCapture,
1905 ) -> (Place<'tcx>, ty::UpvarCapture) {
1906 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
1908 if place.projections.is_empty() {
1909 // Nothing to do here
1910 return (place, curr_mode);
1913 for (i, proj) in place.projections.iter().enumerate() {
1915 ProjectionKind::Index => {
1916 // Arrays are completely captured, so we drop Index projections
1917 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1918 return (place, curr_mode);
1920 ProjectionKind::Deref => {}
1921 ProjectionKind::Field(..) => {} // ignore
1922 ProjectionKind::Subslice => {} // We never capture this
1929 /// Truncate deref of any reference.
1930 fn adjust_for_move_closure<'tcx>(
1931 mut place: Place<'tcx>,
1932 mut kind: ty::UpvarCapture,
1933 ) -> (Place<'tcx>, ty::UpvarCapture) {
1934 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1936 if let Some(idx) = first_deref {
1937 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1940 (place, ty::UpvarCapture::ByValue)
1943 /// Adjust closure capture just that if taking ownership of data, only move data
1944 /// from enclosing stack frame.
1945 fn adjust_for_non_move_closure<'tcx>(
1946 mut place: Place<'tcx>,
1947 mut kind: ty::UpvarCapture,
1948 ) -> (Place<'tcx>, ty::UpvarCapture) {
1949 let contains_deref =
1950 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1953 ty::UpvarCapture::ByValue => {
1954 if let Some(idx) = contains_deref {
1955 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1959 ty::UpvarCapture::ByRef(..) => {}
1965 fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1966 let variable_name = match place.base {
1967 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
1968 _ => bug!("Capture_information should only contain upvars"),
1971 let mut projections_str = String::new();
1972 for (i, item) in place.projections.iter().enumerate() {
1973 let proj = match item.kind {
1974 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
1975 ProjectionKind::Deref => String::from("Deref"),
1976 ProjectionKind::Index => String::from("Index"),
1977 ProjectionKind::Subslice => String::from("Subslice"),
1980 projections_str.push(',');
1982 projections_str.push_str(proj.as_str());
1985 format!("{}[{}]", variable_name, projections_str)
1988 fn construct_capture_kind_reason_string<'tcx>(
1990 place: &Place<'tcx>,
1991 capture_info: &ty::CaptureInfo,
1993 let place_str = construct_place_string(tcx, place);
1995 let capture_kind_str = match capture_info.capture_kind {
1996 ty::UpvarCapture::ByValue => "ByValue".into(),
1997 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
2000 format!("{} captured as {} here", place_str, capture_kind_str)
2003 fn construct_path_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2004 let place_str = construct_place_string(tcx, place);
2006 format!("{} used here", place_str)
2009 fn construct_capture_info_string<'tcx>(
2011 place: &Place<'tcx>,
2012 capture_info: &ty::CaptureInfo,
2014 let place_str = construct_place_string(tcx, place);
2016 let capture_kind_str = match capture_info.capture_kind {
2017 ty::UpvarCapture::ByValue => "ByValue".into(),
2018 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
2020 format!("{} -> {}", place_str, capture_kind_str)
2023 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2024 tcx.hir().name(var_hir_id)
2027 #[instrument(level = "debug", skip(tcx))]
2028 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2030 closure_id: hir::HirId,
2033 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2035 !matches!(level, lint::Level::Allow)
2038 /// Return a two string tuple (s1, s2)
2039 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2040 /// - s2: Comma separated names of the variables being migrated.
2041 fn migration_suggestion_for_2229(
2043 need_migrations: &Vec<NeededMigration>,
2044 ) -> (String, String) {
2045 let need_migrations_variables = need_migrations
2047 .map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
2048 .collect::<Vec<_>>();
2050 let migration_ref_concat =
2051 need_migrations_variables.iter().map(|v| format!("&{}", v)).collect::<Vec<_>>().join(", ");
2053 let migration_string = if 1 == need_migrations.len() {
2054 format!("let _ = {}", migration_ref_concat)
2056 format!("let _ = ({})", migration_ref_concat)
2059 let migrated_variables_concat =
2060 need_migrations_variables.iter().map(|v| format!("`{}`", v)).collect::<Vec<_>>().join(", ");
2062 (migration_string, migrated_variables_concat)
2065 /// Helper function to determine if we need to escalate CaptureKind from
2066 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2067 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2069 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2070 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2072 /// It is the caller's duty to figure out which path_expr_id to use.
2074 /// If both the CaptureKind and Expression are considered to be equivalent,
2075 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to priortize
2076 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2077 /// in the closure. This can be achieved simply by calling
2078 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2079 /// expressions that occur earlier in the closure body than the current expression are processed before.
2080 /// Consider the following example
2082 /// struct Point { x: i32, y: i32 }
2083 /// let mut p: Point { x: 10, y: 10 };
2091 /// p.x += 10; // E2
2095 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2096 /// and both have an expression associated, however for diagnostics we prefer reporting
2097 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2098 /// would've already handled `E1`, and have an existing capture_information for it.
2099 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2100 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2101 fn determine_capture_info(
2102 capture_info_a: ty::CaptureInfo,
2103 capture_info_b: ty::CaptureInfo,
2104 ) -> ty::CaptureInfo {
2105 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2107 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2108 (ty::UpvarCapture::ByValue, ty::UpvarCapture::ByValue) => true,
2109 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => ref_a == ref_b,
2110 (ty::UpvarCapture::ByValue, _) | (ty::UpvarCapture::ByRef(_), _) => false,
2113 if eq_capture_kind {
2114 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2115 (Some(_), _) | (None, None) => capture_info_a,
2116 (None, Some(_)) => capture_info_b,
2119 // We select the CaptureKind which ranks higher based the following priority order:
2120 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2121 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2122 (ty::UpvarCapture::ByValue, _) => capture_info_a,
2123 (_, ty::UpvarCapture::ByValue) => capture_info_b,
2124 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2125 match (ref_a, ref_b) {
2127 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2128 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2131 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2132 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2134 (ty::ImmBorrow, ty::ImmBorrow)
2135 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2136 | (ty::MutBorrow, ty::MutBorrow) => {
2137 bug!("Expected unequal capture kinds");
2145 /// Truncates `place` to have up to `len` projections.
2146 /// `curr_mode` is the current required capture kind for the place.
2147 /// Returns the truncated `place` and the updated required capture kind.
2149 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2150 /// contained `Deref` of `&mut`.
2151 fn truncate_place_to_len_and_update_capture_kind<'tcx>(
2152 place: &mut Place<'tcx>,
2153 curr_mode: &mut ty::UpvarCapture,
2156 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2158 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2160 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2161 // we don't need to worry about that case here.
2163 ty::UpvarCapture::ByRef(ty::BorrowKind::MutBorrow) => {
2164 for i in len..place.projections.len() {
2165 if place.projections[i].kind == ProjectionKind::Deref
2166 && is_mut_ref(place.ty_before_projection(i))
2168 *curr_mode = ty::UpvarCapture::ByRef(ty::BorrowKind::UniqueImmBorrow);
2174 ty::UpvarCapture::ByRef(..) => {}
2175 ty::UpvarCapture::ByValue => {}
2178 place.projections.truncate(len);
2181 /// Determines the Ancestry relationship of Place A relative to Place B
2183 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2184 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2185 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2186 fn determine_place_ancestry_relation<'tcx>(
2187 place_a: &Place<'tcx>,
2188 place_b: &Place<'tcx>,
2189 ) -> PlaceAncestryRelation {
2190 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2191 if place_a.base != place_b.base {
2192 return PlaceAncestryRelation::Divergent;
2195 // Assume of length of projections_a = n
2196 let projections_a = &place_a.projections;
2198 // Assume of length of projections_b = m
2199 let projections_b = &place_b.projections;
2201 let same_initial_projections =
2202 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2204 if same_initial_projections {
2205 use std::cmp::Ordering;
2207 // First min(n, m) projections are the same
2208 // Select Ancestor/Descendant
2209 match projections_b.len().cmp(&projections_a.len()) {
2210 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2211 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2212 Ordering::Less => PlaceAncestryRelation::Descendant,
2215 PlaceAncestryRelation::Divergent
2219 /// Reduces the precision of the captured place when the precision doesn't yeild any benefit from
2220 /// borrow checking prespective, allowing us to save us on the size of the capture.
2223 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2224 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2225 /// rightmost deref of the capture if the deref is applied to a shared ref.
2227 /// Reason we only drop the last deref is because of the following edge case:
2230 /// struct MyStruct<'a> {
2236 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2237 /// let c = || drop(&*m.a.field_of_a);
2238 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2240 /// // If we capture `m`, then the closure no longer outlives `'static'
2241 /// // it is constrained to `'a`
2244 fn truncate_capture_for_optimization<'tcx>(
2245 mut place: Place<'tcx>,
2246 mut curr_mode: ty::UpvarCapture,
2247 ) -> (Place<'tcx>, ty::UpvarCapture) {
2248 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2250 // Find the right-most deref (if any). All the projections that come after this
2251 // are fields or other "in-place pointer adjustments"; these refer therefore to
2252 // data owned by whatever pointer is being dereferenced here.
2253 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2256 // If that pointer is a shared reference, then we don't need those fields.
2257 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2258 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2260 None | Some(_) => {}
2266 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2267 /// user is using Rust Edition 2021 or higher.
2269 /// `span` is the span of the closure.
2270 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2271 // We use span here to ensure that if the closure was generated by a macro with a different
2273 tcx.features().capture_disjoint_fields || span.rust_2021()