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, 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 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
145 hir::ExprKind::Closure(cc, _, body_id, _, _) => {
146 let body = self.fcx.tcx.hir().body(body_id);
147 self.visit_body(body);
148 self.fcx.analyze_closure(expr.hir_id, expr.span, body_id, body, cc);
150 hir::ExprKind::ConstBlock(anon_const) => {
151 let body = self.fcx.tcx.hir().body(anon_const.body);
152 self.visit_body(body);
157 intravisit::walk_expr(self, expr);
161 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
162 /// Analysis starting point.
163 #[instrument(skip(self, body), level = "debug")]
166 closure_hir_id: hir::HirId,
168 body_id: hir::BodyId,
169 body: &'tcx hir::Body<'tcx>,
170 capture_clause: hir::CaptureBy,
172 // Extract the type of the closure.
173 let ty = self.node_ty(closure_hir_id);
174 let (closure_def_id, substs) = match *ty.kind() {
175 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
176 ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
178 // #51714: skip analysis when we have already encountered type errors
184 "type of closure expr {:?} is not a closure {:?}",
191 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
192 self.closure_kind(closure_substs).is_none().then_some(closure_substs)
197 let local_def_id = closure_def_id.expect_local();
199 let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
200 assert_eq!(body_owner_def_id.to_def_id(), closure_def_id);
201 let mut delegate = InferBorrowKind {
203 closure_def_id: local_def_id,
204 capture_information: Default::default(),
205 fake_reads: Default::default(),
207 euv::ExprUseVisitor::new(
212 &self.typeck_results.borrow(),
217 "For closure={:?}, capture_information={:#?}",
218 closure_def_id, delegate.capture_information
221 self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
223 let (capture_information, closure_kind, origin) = self
224 .process_collected_capture_information(capture_clause, delegate.capture_information);
226 self.compute_min_captures(closure_def_id, capture_information, span);
228 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
230 if should_do_rust_2021_incompatible_closure_captures_analysis(self.tcx, closure_hir_id) {
231 self.perform_2229_migration_anaysis(closure_def_id, body_id, capture_clause, span);
234 let after_feature_tys = self.final_upvar_tys(closure_def_id);
236 // We now fake capture information for all variables that are mentioned within the closure
237 // We do this after handling migrations so that min_captures computes before
238 if !enable_precise_capture(self.tcx, span) {
239 let mut capture_information: InferredCaptureInformation<'tcx> = Default::default();
241 if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
242 for var_hir_id in upvars.keys() {
243 let place = self.place_for_root_variable(local_def_id, *var_hir_id);
245 debug!("seed place {:?}", place);
247 let capture_kind = self.init_capture_kind_for_place(&place, capture_clause);
248 let fake_info = ty::CaptureInfo {
249 capture_kind_expr_id: None,
254 capture_information.push((place, fake_info));
258 // This will update the min captures based on this new fake information.
259 self.compute_min_captures(closure_def_id, capture_information, span);
262 let before_feature_tys = self.final_upvar_tys(closure_def_id);
264 if let Some(closure_substs) = infer_kind {
265 // Unify the (as yet unbound) type variable in the closure
266 // substs with the kind we inferred.
267 let closure_kind_ty = closure_substs.as_closure().kind_ty();
268 self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
270 // If we have an origin, store it.
271 if let Some(origin) = origin {
272 let origin = if enable_precise_capture(self.tcx, span) {
275 (origin.0, Place { projections: vec![], ..origin.1 })
280 .closure_kind_origins_mut()
281 .insert(closure_hir_id, origin);
285 self.log_closure_min_capture_info(closure_def_id, span);
287 // Now that we've analyzed the closure, we know how each
288 // variable is borrowed, and we know what traits the closure
289 // implements (Fn vs FnMut etc). We now have some updates to do
290 // with that information.
292 // Note that no closure type C may have an upvar of type C
293 // (though it may reference itself via a trait object). This
294 // results from the desugaring of closures to a struct like
295 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
296 // C, then the type would have infinite size (and the
297 // inference algorithm will reject it).
299 // Equate the type variables for the upvars with the actual types.
300 let final_upvar_tys = self.final_upvar_tys(closure_def_id);
302 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
303 closure_hir_id, substs, final_upvar_tys
306 // Build a tuple (U0..Un) of the final upvar types U0..Un
307 // and unify the upvar tupe type in the closure with it:
308 let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
309 self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
311 let fake_reads = delegate
314 .map(|(place, cause, hir_id)| (place, cause, hir_id))
316 self.typeck_results.borrow_mut().closure_fake_reads.insert(closure_def_id, fake_reads);
318 if self.tcx.sess.opts.debugging_opts.profile_closures {
319 self.typeck_results.borrow_mut().closure_size_eval.insert(
321 ClosureSizeProfileData {
322 before_feature_tys: self.tcx.mk_tup(before_feature_tys.into_iter()),
323 after_feature_tys: self.tcx.mk_tup(after_feature_tys.into_iter()),
328 // If we are also inferred the closure kind here,
329 // process any deferred resolutions.
330 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
331 for deferred_call_resolution in deferred_call_resolutions {
332 deferred_call_resolution.resolve(self);
336 // Returns a list of `Ty`s for each upvar.
337 fn final_upvar_tys(&self, closure_id: DefId) -> Vec<Ty<'tcx>> {
340 .closure_min_captures_flattened(closure_id)
341 .map(|captured_place| {
342 let upvar_ty = captured_place.place.ty();
343 let capture = captured_place.info.capture_kind;
346 "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
347 captured_place.place, upvar_ty, capture, captured_place.mutability,
350 apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture, captured_place.region)
355 /// Adjusts the closure capture information to ensure that the operations aren't unsafe,
356 /// and that the path can be captured with required capture kind (depending on use in closure,
357 /// move closure etc.)
359 /// Returns the set of of adjusted information along with the inferred closure kind and span
360 /// associated with the closure kind inference.
362 /// Note that we *always* infer a minimal kind, even if
363 /// we don't always *use* that in the final result (i.e., sometimes
364 /// we've taken the closure kind from the expectations instead, and
365 /// for generators we don't even implement the closure traits
368 /// If we inferred that the closure needs to be FnMut/FnOnce, last element of the returned tuple
369 /// contains a `Some()` with the `Place` that caused us to do so.
370 fn process_collected_capture_information(
372 capture_clause: hir::CaptureBy,
373 capture_information: InferredCaptureInformation<'tcx>,
374 ) -> (InferredCaptureInformation<'tcx>, ty::ClosureKind, Option<(Span, Place<'tcx>)>) {
375 let mut closure_kind = ty::ClosureKind::LATTICE_BOTTOM;
376 let mut origin: Option<(Span, Place<'tcx>)> = None;
378 let processed = capture_information
380 .map(|(place, mut capture_info)| {
381 // Apply rules for safety before inferring closure kind
382 let (place, capture_kind) =
383 restrict_capture_precision(place, capture_info.capture_kind);
385 let (place, capture_kind) = truncate_capture_for_optimization(place, capture_kind);
387 let usage_span = if let Some(usage_expr) = capture_info.path_expr_id {
388 self.tcx.hir().span(usage_expr)
393 let updated = match capture_kind {
394 ty::UpvarCapture::ByValue => match closure_kind {
395 ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
396 (ty::ClosureKind::FnOnce, Some((usage_span, place.clone())))
398 // If closure is already FnOnce, don't update
399 ty::ClosureKind::FnOnce => (closure_kind, origin.take()),
402 ty::UpvarCapture::ByRef(
403 ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
406 ty::ClosureKind::Fn => {
407 (ty::ClosureKind::FnMut, Some((usage_span, place.clone())))
409 // Don't update the origin
410 ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce => {
411 (closure_kind, origin.take())
416 _ => (closure_kind, origin.take()),
419 closure_kind = updated.0;
422 let (place, capture_kind) = match capture_clause {
423 hir::CaptureBy::Value => adjust_for_move_closure(place, capture_kind),
424 hir::CaptureBy::Ref => adjust_for_non_move_closure(place, capture_kind),
427 // This restriction needs to be applied after we have handled adjustments for `move`
428 // closures. We want to make sure any adjustment that might make us move the place into
429 // the closure gets handled.
430 let (place, capture_kind) =
431 restrict_precision_for_drop_types(self, place, capture_kind, usage_span);
433 capture_info.capture_kind = capture_kind;
434 (place, capture_info)
438 (processed, closure_kind, origin)
441 /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
442 /// Places (and corresponding capture kind) that we need to keep track of to support all
443 /// the required captured paths.
446 /// Note: If this function is called multiple times for the same closure, it will update
447 /// the existing min_capture map that is stored in TypeckResults.
451 /// struct Point { x: i32, y: i32 }
453 /// let s: String; // hir_id_s
454 /// let mut p: Point; // his_id_p
456 /// println!("{}", s); // L1
458 /// println!("{}" , p.y) // L3
459 /// println!("{}", p) // L4
463 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
464 /// the lines L1..5 respectively.
466 /// InferBorrowKind results in a structure like this:
470 /// Place(base: hir_id_s, projections: [], ....) -> {
471 /// capture_kind_expr: hir_id_L5,
472 /// path_expr_id: hir_id_L5,
473 /// capture_kind: ByValue
475 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
476 /// capture_kind_expr: hir_id_L2,
477 /// path_expr_id: hir_id_L2,
478 /// capture_kind: ByValue
480 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
481 /// capture_kind_expr: hir_id_L3,
482 /// path_expr_id: hir_id_L3,
483 /// capture_kind: ByValue
485 /// Place(base: hir_id_p, projections: [], ...) -> {
486 /// capture_kind_expr: hir_id_L4,
487 /// path_expr_id: hir_id_L4,
488 /// capture_kind: ByValue
492 /// After the min capture analysis, we get:
496 /// Place(base: hir_id_s, projections: [], ....) -> {
497 /// capture_kind_expr: hir_id_L5,
498 /// path_expr_id: hir_id_L5,
499 /// capture_kind: ByValue
503 /// Place(base: hir_id_p, projections: [], ...) -> {
504 /// capture_kind_expr: hir_id_L2,
505 /// path_expr_id: hir_id_L4,
506 /// capture_kind: ByValue
510 fn compute_min_captures(
512 closure_def_id: DefId,
513 capture_information: InferredCaptureInformation<'tcx>,
516 if capture_information.is_empty() {
520 let mut typeck_results = self.typeck_results.borrow_mut();
522 let mut root_var_min_capture_list =
523 typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
525 for (mut place, capture_info) in capture_information.into_iter() {
526 let var_hir_id = match place.base {
527 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
528 base => bug!("Expected upvar, found={:?}", base),
531 let min_cap_list = match root_var_min_capture_list.get_mut(&var_hir_id) {
533 let mutability = self.determine_capture_mutability(&typeck_results, &place);
534 let min_cap_list = vec![ty::CapturedPlace {
540 root_var_min_capture_list.insert(var_hir_id, min_cap_list);
543 Some(min_cap_list) => min_cap_list,
546 // Go through each entry in the current list of min_captures
547 // - if ancestor is found, update it's capture kind to account for current place's
548 // capture information.
550 // - if descendant is found, remove it from the list, and update the current place's
551 // capture information to account for the descendants's capture kind.
553 // We can never be in a case where the list contains both an ancestor and a descendant
554 // Also there can only be ancestor but in case of descendants there might be
557 let mut descendant_found = false;
558 let mut updated_capture_info = capture_info;
559 min_cap_list.retain(|possible_descendant| {
560 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
561 // current place is ancestor of possible_descendant
562 PlaceAncestryRelation::Ancestor => {
563 descendant_found = true;
565 let mut possible_descendant = possible_descendant.clone();
566 let backup_path_expr_id = updated_capture_info.path_expr_id;
568 // Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
569 // possible change in capture mode.
570 truncate_place_to_len_and_update_capture_kind(
571 &mut possible_descendant.place,
572 &mut possible_descendant.info.capture_kind,
573 place.projections.len(),
576 updated_capture_info =
577 determine_capture_info(updated_capture_info, possible_descendant.info);
579 // we need to keep the ancestor's `path_expr_id`
580 updated_capture_info.path_expr_id = backup_path_expr_id;
588 let mut ancestor_found = false;
589 if !descendant_found {
590 for possible_ancestor in min_cap_list.iter_mut() {
591 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
592 PlaceAncestryRelation::SamePlace => {
593 ancestor_found = true;
594 possible_ancestor.info = determine_capture_info(
595 possible_ancestor.info,
596 updated_capture_info,
599 // Only one related place will be in the list.
602 // current place is descendant of possible_ancestor
603 PlaceAncestryRelation::Descendant => {
604 ancestor_found = true;
605 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
607 // Truncate the descendant (current place) to be same as the ancestor to handle any
608 // possible change in capture mode.
609 truncate_place_to_len_and_update_capture_kind(
611 &mut updated_capture_info.capture_kind,
612 possible_ancestor.place.projections.len(),
615 possible_ancestor.info = determine_capture_info(
616 possible_ancestor.info,
617 updated_capture_info,
620 // we need to keep the ancestor's `path_expr_id`
621 possible_ancestor.info.path_expr_id = backup_path_expr_id;
623 // Only one related place will be in the list.
631 // Only need to insert when we don't have an ancestor in the existing min capture list
633 let mutability = self.determine_capture_mutability(&typeck_results, &place);
634 let captured_place = ty::CapturedPlace {
636 info: updated_capture_info,
640 min_cap_list.push(captured_place);
644 // For each capture that is determined to be captured by ref, add region info.
645 for (_, captures) in &mut root_var_min_capture_list {
646 for capture in captures {
647 match capture.info.capture_kind {
648 ty::UpvarCapture::ByRef(_) => {
649 let PlaceBase::Upvar(upvar_id) = capture.place.base else { bug!("expected upvar") };
650 let origin = UpvarRegion(upvar_id, closure_span);
651 let upvar_region = self.next_region_var(origin);
652 capture.region = Some(upvar_region);
660 "For closure={:?}, min_captures before sorting={:?}",
661 closure_def_id, root_var_min_capture_list
664 // Now that we have the minimized list of captures, sort the captures by field id.
665 // This causes the closure to capture the upvars in the same order as the fields are
666 // declared which is also the drop order. Thus, in situations where we capture all the
667 // fields of some type, the obserable drop order will remain the same as it previously
668 // was even though we're dropping each capture individually.
669 // See https://github.com/rust-lang/project-rfc-2229/issues/42 and
670 // `src/test/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
671 for (_, captures) in &mut root_var_min_capture_list {
672 captures.sort_by(|capture1, capture2| {
673 for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
674 // We do not need to look at the `Projection.ty` fields here because at each
675 // step of the iteration, the projections will either be the same and therefore
676 // the types must be as well or the current projection will be different and
677 // we will return the result of comparing the field indexes.
678 match (p1.kind, p2.kind) {
679 // Paths are the same, continue to next loop.
680 (ProjectionKind::Deref, ProjectionKind::Deref) => {}
681 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
684 // Fields are different, compare them.
685 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
689 // We should have either a pair of `Deref`s or a pair of `Field`s.
690 // Anything else is a bug.
692 l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
693 r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
695 "ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
700 l @ (ProjectionKind::Index
701 | ProjectionKind::Subslice
702 | ProjectionKind::Deref
703 | ProjectionKind::Field(..)),
704 r @ (ProjectionKind::Index
705 | ProjectionKind::Subslice
706 | ProjectionKind::Deref
707 | ProjectionKind::Field(..)),
709 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
717 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
724 "For closure={:?}, min_captures after sorting={:#?}",
725 closure_def_id, root_var_min_capture_list
727 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
730 /// Perform the migration analysis for RFC 2229, and emit lint
731 /// `disjoint_capture_drop_reorder` if needed.
732 fn perform_2229_migration_anaysis(
734 closure_def_id: DefId,
735 body_id: hir::BodyId,
736 capture_clause: hir::CaptureBy,
739 let (need_migrations, reasons) = self.compute_2229_migrations(
743 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
746 if !need_migrations.is_empty() {
747 let (migration_string, migrated_variables_concat) =
748 migration_suggestion_for_2229(self.tcx, &need_migrations);
750 let local_def_id = closure_def_id.expect_local();
751 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
752 let closure_span = self.tcx.hir().span(closure_hir_id);
753 let closure_head_span = self.tcx.sess.source_map().guess_head_span(closure_span);
754 self.tcx.struct_span_lint_hir(
755 lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
759 let mut diagnostics_builder = lint.build(
760 &reasons.migration_message(),
762 for NeededMigration { var_hir_id, diagnostics_info } in &need_migrations {
763 // Labels all the usage of the captured variable and why they are responsible
764 // for migration being needed
765 for lint_note in diagnostics_info.iter() {
766 match &lint_note.captures_info {
767 UpvarMigrationInfo::CapturingPrecise { source_expr: Some(capture_expr_id), var_name: captured_name } => {
768 let cause_span = self.tcx.hir().span(*capture_expr_id);
769 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
770 self.tcx.hir().name(*var_hir_id),
774 UpvarMigrationInfo::CapturingNothing { use_span } => {
775 diagnostics_builder.span_label(*use_span, format!("in Rust 2018, this causes the closure to capture `{}`, but in Rust 2021, it has no effect",
776 self.tcx.hir().name(*var_hir_id),
783 // Add a label pointing to where a captured variable affected by drop order
785 if lint_note.reason.drop_order {
786 let drop_location_span = drop_location_span(self.tcx, &closure_hir_id);
788 match &lint_note.captures_info {
789 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
790 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",
791 self.tcx.hir().name(*var_hir_id),
795 UpvarMigrationInfo::CapturingNothing { use_span: _ } => {
796 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",
797 v = self.tcx.hir().name(*var_hir_id),
803 // Add a label explaining why a closure no longer implements a trait
804 for &missing_trait in &lint_note.reason.auto_traits {
805 // not capturing something anymore cannot cause a trait to fail to be implemented:
806 match &lint_note.captures_info {
807 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
808 let var_name = self.tcx.hir().name(*var_hir_id);
809 diagnostics_builder.span_label(closure_head_span, format!("\
810 in Rust 2018, this closure implements {missing_trait} \
811 as `{var_name}` implements {missing_trait}, but in Rust 2021, \
812 this closure will no longer implement {missing_trait} \
813 because `{var_name}` is not fully captured \
814 and `{captured_name}` does not implement {missing_trait}"));
817 // Cannot happen: if we don't capture a variable, we impl strictly more traits
818 UpvarMigrationInfo::CapturingNothing { use_span } => span_bug!(*use_span, "missing trait from not capturing something"),
823 diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
825 let diagnostic_msg = format!(
826 "add a dummy let to cause {} to be fully captured",
827 migrated_variables_concat
830 let mut closure_body_span = {
831 // If the body was entirely expanded from a macro
832 // invocation, i.e. the body is not contained inside the
833 // closure span, then we walk up the expansion until we
834 // find the span before the expansion.
835 let s = self.tcx.hir().span(body_id.hir_id);
836 s.find_ancestor_inside(closure_span).unwrap_or(s)
839 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
840 if s.starts_with('$') {
841 // Looks like a macro fragment. Try to find the real block.
842 if let Some(hir::Node::Expr(&hir::Expr {
843 kind: hir::ExprKind::Block(block, ..), ..
844 })) = self.tcx.hir().find(body_id.hir_id) {
845 // If the body is a block (with `{..}`), we use the span of that block.
846 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
847 // Since we know it's a block, we know we can insert the `let _ = ..` without
848 // breaking the macro syntax.
849 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
850 closure_body_span = block.span;
856 let mut lines = s.lines();
857 let line1 = lines.next().unwrap_or_default();
859 if line1.trim_end() == "{" {
860 // This is a multi-line closure with just a `{` on the first line,
861 // so we put the `let` on its own line.
862 // We take the indentation from the next non-empty line.
863 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
864 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
865 diagnostics_builder.span_suggestion(
866 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
868 format!("\n{}{};", indent, migration_string),
869 Applicability::MachineApplicable,
871 } else if line1.starts_with('{') {
872 // This is a closure with its body wrapped in
873 // braces, but with more than just the opening
874 // brace on the first line. We put the `let`
875 // directly after the `{`.
876 diagnostics_builder.span_suggestion(
877 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
879 format!(" {};", migration_string),
880 Applicability::MachineApplicable,
883 // This is a closure without braces around the body.
884 // We add braces to add the `let` before the body.
885 diagnostics_builder.multipart_suggestion(
888 (closure_body_span.shrink_to_lo(), format!("{{ {}; ", migration_string)),
889 (closure_body_span.shrink_to_hi(), " }".to_string()),
891 Applicability::MachineApplicable
895 diagnostics_builder.span_suggestion(
899 Applicability::HasPlaceholders
903 diagnostics_builder.emit();
909 /// Combines all the reasons for 2229 migrations
910 fn compute_2229_migrations_reasons(
912 auto_trait_reasons: FxHashSet<&'static str>,
914 ) -> MigrationWarningReason {
915 let mut reasons = MigrationWarningReason::default();
917 reasons.auto_traits.extend(auto_trait_reasons);
918 reasons.drop_order = drop_order;
923 /// Figures out the list of root variables (and their types) that aren't completely
924 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
925 /// differ between the root variable and the captured paths.
927 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
928 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
929 fn compute_2229_migrations_for_trait(
931 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
932 var_hir_id: hir::HirId,
933 closure_clause: hir::CaptureBy,
934 ) -> Option<FxHashMap<UpvarMigrationInfo, FxHashSet<&'static str>>> {
935 let auto_traits_def_id = vec![
936 self.tcx.lang_items().clone_trait(),
937 self.tcx.lang_items().sync_trait(),
938 self.tcx.get_diagnostic_item(sym::Send),
939 self.tcx.lang_items().unpin_trait(),
940 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
941 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
943 const AUTO_TRAITS: [&str; 6] =
944 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
946 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
948 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
950 let ty = match closure_clause {
951 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
952 hir::CaptureBy::Ref => {
953 // For non move closure the capture kind is the max capture kind of all captures
954 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
955 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
956 for capture in root_var_min_capture_list.iter() {
957 max_capture_info = determine_capture_info(max_capture_info, capture.info);
960 apply_capture_kind_on_capture_ty(
963 max_capture_info.capture_kind,
969 let mut obligations_should_hold = Vec::new();
970 // Checks if a root variable implements any of the auto traits
971 for check_trait in auto_traits_def_id.iter() {
972 obligations_should_hold.push(
976 .type_implements_trait(
979 self.tcx.mk_substs_trait(ty, &[]),
982 .must_apply_modulo_regions()
988 let mut problematic_captures = FxHashMap::default();
989 // Check whether captured fields also implement the trait
990 for capture in root_var_min_capture_list.iter() {
991 let ty = apply_capture_kind_on_capture_ty(
994 capture.info.capture_kind,
998 // Checks if a capture implements any of the auto traits
999 let mut obligations_holds_for_capture = Vec::new();
1000 for check_trait in auto_traits_def_id.iter() {
1001 obligations_holds_for_capture.push(
1003 .map(|check_trait| {
1005 .type_implements_trait(
1008 self.tcx.mk_substs_trait(ty, &[]),
1011 .must_apply_modulo_regions()
1017 let mut capture_problems = FxHashSet::default();
1019 // Checks if for any of the auto traits, one or more trait is implemented
1020 // by the root variable but not by the capture
1021 for (idx, _) in obligations_should_hold.iter().enumerate() {
1022 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
1023 capture_problems.insert(AUTO_TRAITS[idx]);
1027 if !capture_problems.is_empty() {
1028 problematic_captures.insert(
1029 UpvarMigrationInfo::CapturingPrecise {
1030 source_expr: capture.info.path_expr_id,
1031 var_name: capture.to_string(self.tcx),
1037 if !problematic_captures.is_empty() {
1038 return Some(problematic_captures);
1043 /// Figures out the list of root variables (and their types) that aren't completely
1044 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
1045 /// some path starting at that root variable **might** be affected.
1047 /// The output list would include a root variable if:
1048 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1049 /// enabled, **and**
1050 /// - It wasn't completely captured by the closure, **and**
1051 /// - One of the paths starting at this root variable, that is not captured needs Drop.
1053 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
1054 /// are no significant drops than None is returned
1055 #[instrument(level = "debug", skip(self))]
1056 fn compute_2229_migrations_for_drop(
1058 closure_def_id: DefId,
1060 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1061 closure_clause: hir::CaptureBy,
1062 var_hir_id: hir::HirId,
1063 ) -> Option<FxHashSet<UpvarMigrationInfo>> {
1064 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
1066 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local())) {
1067 debug!("does not have significant drop");
1071 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1072 // The upvar is mentioned within the closure but no path starting from it is
1073 // used. This occurs when you have (e.g.)
1076 // let x = move || {
1080 debug!("no path starting from it is used");
1083 match closure_clause {
1084 // Only migrate if closure is a move closure
1085 hir::CaptureBy::Value => {
1086 let mut diagnostics_info = FxHashSet::default();
1087 let upvars = self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
1088 let upvar = upvars[&var_hir_id];
1089 diagnostics_info.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
1090 return Some(diagnostics_info);
1092 hir::CaptureBy::Ref => {}
1097 debug!(?root_var_min_capture_list);
1099 let mut projections_list = Vec::new();
1100 let mut diagnostics_info = FxHashSet::default();
1102 for captured_place in root_var_min_capture_list.iter() {
1103 match captured_place.info.capture_kind {
1104 // Only care about captures that are moved into the closure
1105 ty::UpvarCapture::ByValue => {
1106 projections_list.push(captured_place.place.projections.as_slice());
1107 diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
1108 source_expr: captured_place.info.path_expr_id,
1109 var_name: captured_place.to_string(self.tcx),
1112 ty::UpvarCapture::ByRef(..) => {}
1116 debug!(?projections_list);
1117 debug!(?diagnostics_info);
1119 let is_moved = !projections_list.is_empty();
1122 let is_not_completely_captured =
1123 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1124 debug!(?is_not_completely_captured);
1127 && is_not_completely_captured
1128 && self.has_significant_drop_outside_of_captures(
1135 return Some(diagnostics_info);
1141 /// Figures out the list of root variables (and their types) that aren't completely
1142 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1143 /// order of some path starting at that root variable **might** be affected or auto-traits
1144 /// differ between the root variable and the captured paths.
1146 /// The output list would include a root variable if:
1147 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1148 /// enabled, **and**
1149 /// - It wasn't completely captured by the closure, **and**
1150 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1151 /// - One of the paths captured does not implement all the auto-traits its root variable
1154 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1155 /// containing the reason why root variables whose HirId is contained in the vector should
1157 #[instrument(level = "debug", skip(self))]
1158 fn compute_2229_migrations(
1160 closure_def_id: DefId,
1162 closure_clause: hir::CaptureBy,
1163 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1164 ) -> (Vec<NeededMigration>, MigrationWarningReason) {
1165 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1166 return (Vec::new(), MigrationWarningReason::default());
1169 let mut need_migrations = Vec::new();
1170 let mut auto_trait_migration_reasons = FxHashSet::default();
1171 let mut drop_migration_needed = false;
1173 // Perform auto-trait analysis
1174 for (&var_hir_id, _) in upvars.iter() {
1175 let mut diagnostics_info = Vec::new();
1177 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1178 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1182 FxHashMap::default()
1185 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1186 .compute_2229_migrations_for_drop(
1193 drop_migration_needed = true;
1196 FxHashSet::default()
1199 // Combine all the captures responsible for needing migrations into one HashSet
1200 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1201 for key in auto_trait_diagnostic.keys() {
1202 capture_diagnostic.insert(key.clone());
1205 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1206 capture_diagnostic.sort();
1207 for captures_info in capture_diagnostic {
1208 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1209 let capture_trait_reasons =
1210 if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
1213 FxHashSet::default()
1216 // Check if migration is needed because of drop reorder as a result of that capture
1217 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
1219 // Combine all the reasons of why the root variable should be captured as a result of
1220 // auto trait implementation issues
1221 auto_trait_migration_reasons.extend(capture_trait_reasons.clone());
1223 diagnostics_info.push(MigrationLintNote {
1225 reason: self.compute_2229_migrations_reasons(
1226 capture_trait_reasons,
1227 capture_drop_reorder_reason,
1232 if !diagnostics_info.is_empty() {
1233 need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
1238 self.compute_2229_migrations_reasons(
1239 auto_trait_migration_reasons,
1240 drop_migration_needed,
1245 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1246 /// of a root variable and a list of captured paths starting at this root variable (expressed
1247 /// using list of `Projection` slices), it returns true if there is a path that is not
1248 /// captured starting at this root variable that implements Drop.
1250 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1251 /// path say P and then list of projection slices which represent the different captures moved
1252 /// into the closure starting off of P.
1254 /// This will make more sense with an example:
1257 /// #![feature(capture_disjoint_fields)]
1259 /// struct FancyInteger(i32); // This implements Drop
1261 /// struct Point { x: FancyInteger, y: FancyInteger }
1264 /// struct Wrapper { p: Point, c: Color }
1266 /// fn f(w: Wrapper) {
1268 /// // Closure captures w.p.x and w.c by move.
1275 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1276 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1277 /// therefore Drop ordering would change and we want this function to return true.
1279 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1281 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1284 /// - Ty(place): Type of place
1285 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1288 /// (Ty(w), [ &[p, x], &[c] ])
1290 /// ----------------------------
1293 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1296 /// (Ty(w.p), [ &[x] ]) false
1299 /// -------------------------------
1302 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1305 /// false NeedsSignificantDrop(Ty(w.p.y))
1311 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1312 /// This implies that the `w.c` is completely captured by the closure.
1313 /// Since drop for this path will be called when the closure is
1314 /// dropped we don't need to migrate for it.
1316 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1317 /// path wasn't captured by the closure. Also note that even
1318 /// though we didn't capture this path, the function visits it,
1319 /// which is kind of the point of this function. We then return
1320 /// if the type of `w.p.y` implements Drop, which in this case is
1323 /// Consider another example:
1327 /// impl Drop for X {}
1330 /// impl Drop for Y {}
1334 /// let c = || move(y.0);
1338 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1339 /// return true, because even though all paths starting at `y` are captured, `y` itself
1340 /// implements Drop which will be affected since `y` isn't completely captured.
1341 fn has_significant_drop_outside_of_captures(
1343 closure_def_id: DefId,
1345 base_path_ty: Ty<'tcx>,
1346 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1348 let needs_drop = |ty: Ty<'tcx>| {
1349 ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local()))
1352 let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
1353 let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
1354 let ty_params = self.tcx.mk_substs_trait(base_path_ty, &[]);
1356 .type_implements_trait(
1360 self.tcx.param_env(closure_def_id.expect_local()),
1362 .must_apply_modulo_regions()
1365 let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
1367 // If there is a case where no projection is applied on top of current place
1368 // then there must be exactly one capture corresponding to such a case. Note that this
1369 // represents the case of the path being completely captured by the variable.
1371 // eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
1372 // capture `a.b.c`, because that voilates min capture.
1373 let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
1375 assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
1377 if is_completely_captured {
1378 // The place is captured entirely, so doesn't matter if needs dtor, it will be drop
1379 // when the closure is dropped.
1383 if captured_by_move_projs.is_empty() {
1384 return needs_drop(base_path_ty);
1387 if is_drop_defined_for_ty {
1388 // If drop is implemented for this type then we need it to be fully captured,
1389 // and we know it is not completely captured because of the previous checks.
1391 // Note that this is a bug in the user code that will be reported by the
1392 // borrow checker, since we can't move out of drop types.
1394 // The bug exists in the user's code pre-migration, and we don't migrate here.
1398 match base_path_ty.kind() {
1400 // - `captured_by_move_projs` is not empty. Therefore we can call
1401 // `captured_by_move_projs.first().unwrap()` safely.
1402 // - All entries in `captured_by_move_projs` have atleast one projection.
1403 // Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
1405 // We don't capture derefs in case of move captures, which would have be applied to
1406 // access any further paths.
1407 ty::Adt(def, _) if def.is_box() => unreachable!(),
1408 ty::Ref(..) => unreachable!(),
1409 ty::RawPtr(..) => unreachable!(),
1411 ty::Adt(def, substs) => {
1412 // Multi-varaint enums are captured in entirety,
1413 // which would've been handled in the case of single empty slice in `captured_by_move_projs`.
1414 assert_eq!(def.variants.len(), 1);
1416 // Only Field projections can be applied to a non-box Adt.
1418 captured_by_move_projs.iter().all(|projs| matches!(
1419 projs.first().unwrap().kind,
1420 ProjectionKind::Field(..)
1423 def.variants.get(VariantIdx::new(0)).unwrap().fields.iter().enumerate().any(
1425 let paths_using_field = captured_by_move_projs
1427 .filter_map(|projs| {
1428 if let ProjectionKind::Field(field_idx, _) =
1429 projs.first().unwrap().kind
1431 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1438 let after_field_ty = field.ty(self.tcx, substs);
1439 self.has_significant_drop_outside_of_captures(
1450 // Only Field projections can be applied to a tuple.
1452 captured_by_move_projs.iter().all(|projs| matches!(
1453 projs.first().unwrap().kind,
1454 ProjectionKind::Field(..)
1458 base_path_ty.tuple_fields().enumerate().any(|(i, element_ty)| {
1459 let paths_using_field = captured_by_move_projs
1461 .filter_map(|projs| {
1462 if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
1464 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1471 self.has_significant_drop_outside_of_captures(
1480 // Anything else would be completely captured and therefore handled already.
1481 _ => unreachable!(),
1485 fn init_capture_kind_for_place(
1487 place: &Place<'tcx>,
1488 capture_clause: hir::CaptureBy,
1489 ) -> ty::UpvarCapture {
1490 match capture_clause {
1491 // In case of a move closure if the data is accessed through a reference we
1492 // want to capture by ref to allow precise capture using reborrows.
1494 // If the data will be moved out of this place, then the place will be truncated
1495 // at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
1497 hir::CaptureBy::Value if !place.deref_tys().any(ty::TyS::is_ref) => {
1498 ty::UpvarCapture::ByValue
1500 hir::CaptureBy::Value | hir::CaptureBy::Ref => ty::UpvarCapture::ByRef(ty::ImmBorrow),
1504 fn place_for_root_variable(
1506 closure_def_id: LocalDefId,
1507 var_hir_id: hir::HirId,
1509 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
1512 base_ty: self.node_ty(var_hir_id),
1513 base: PlaceBase::Upvar(upvar_id),
1514 projections: Default::default(),
1518 fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
1519 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
1522 fn log_capture_analysis_first_pass(
1524 closure_def_id: rustc_hir::def_id::DefId,
1525 capture_information: &InferredCaptureInformation<'tcx>,
1528 if self.should_log_capture_analysis(closure_def_id) {
1530 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
1531 for (place, capture_info) in capture_information {
1532 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
1533 let output_str = format!("Capturing {}", capture_str);
1536 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
1537 diag.span_note(span, &output_str);
1543 fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
1544 if self.should_log_capture_analysis(closure_def_id) {
1545 if let Some(min_captures) =
1546 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
1549 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
1551 for (_, min_captures_for_var) in min_captures {
1552 for capture in min_captures_for_var {
1553 let place = &capture.place;
1554 let capture_info = &capture.info;
1557 construct_capture_info_string(self.tcx, place, capture_info);
1558 let output_str = format!("Min Capture {}", capture_str);
1560 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
1561 let path_span = capture_info
1563 .map_or(closure_span, |e| self.tcx.hir().span(e));
1564 let capture_kind_span = capture_info
1565 .capture_kind_expr_id
1566 .map_or(closure_span, |e| self.tcx.hir().span(e));
1568 let mut multi_span: MultiSpan =
1569 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
1571 let capture_kind_label =
1572 construct_capture_kind_reason_string(self.tcx, place, capture_info);
1573 let path_label = construct_path_string(self.tcx, place);
1575 multi_span.push_span_label(path_span, path_label);
1576 multi_span.push_span_label(capture_kind_span, capture_kind_label);
1578 diag.span_note(multi_span, &output_str);
1580 let span = capture_info
1582 .map_or(closure_span, |e| self.tcx.hir().span(e));
1584 diag.span_note(span, &output_str);
1593 /// A captured place is mutable if
1594 /// 1. Projections don't include a Deref of an immut-borrow, **and**
1595 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
1596 fn determine_capture_mutability(
1598 typeck_results: &'a TypeckResults<'tcx>,
1599 place: &Place<'tcx>,
1600 ) -> hir::Mutability {
1601 let var_hir_id = match place.base {
1602 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
1603 _ => unreachable!(),
1606 let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
1608 let mut is_mutbl = match bm {
1609 ty::BindByValue(mutability) => mutability,
1610 ty::BindByReference(_) => hir::Mutability::Not,
1613 for pointer_ty in place.deref_tys() {
1614 match pointer_ty.kind() {
1615 // We don't capture derefs of raw ptrs
1616 ty::RawPtr(_) => unreachable!(),
1618 // Derefencing a mut-ref allows us to mut the Place if we don't deref
1619 // an immut-ref after on top of this.
1620 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
1622 // The place isn't mutable once we dereference an immutable reference.
1623 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
1625 // Dereferencing a box doesn't change mutability
1626 ty::Adt(def, ..) if def.is_box() => {}
1628 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
1636 /// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
1637 /// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
1638 fn restrict_repr_packed_field_ref_capture<'tcx>(
1640 param_env: ty::ParamEnv<'tcx>,
1641 mut place: Place<'tcx>,
1642 mut curr_borrow_kind: ty::UpvarCapture,
1643 ) -> (Place<'tcx>, ty::UpvarCapture) {
1644 let pos = place.projections.iter().enumerate().position(|(i, p)| {
1645 let ty = place.ty_before_projection(i);
1647 // Return true for fields of packed structs, unless those fields have alignment 1.
1649 ProjectionKind::Field(..) => match ty.kind() {
1650 ty::Adt(def, _) if def.repr.packed() => {
1651 match tcx.layout_of(param_env.and(p.ty)) {
1652 Ok(layout) if layout.align.abi.bytes() == 1 => {
1653 // if the alignment is 1, the type can't be further
1656 "restrict_repr_packed_field_ref_capture: ({:?}) - align = 1",
1662 debug!("restrict_repr_packed_field_ref_capture: ({:?}) - true", place);
1674 if let Some(pos) = pos {
1675 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
1678 (place, curr_borrow_kind)
1681 /// Returns a Ty that applies the specified capture kind on the provided capture Ty
1682 fn apply_capture_kind_on_capture_ty<'tcx>(
1685 capture_kind: UpvarCapture,
1686 region: Option<ty::Region<'tcx>>,
1688 match capture_kind {
1689 ty::UpvarCapture::ByValue => ty,
1690 ty::UpvarCapture::ByRef(kind) => {
1691 tcx.mk_ref(region.unwrap(), ty::TypeAndMut { ty: ty, mutbl: kind.to_mutbl_lossy() })
1696 /// Returns the Span of where the value with the provided HirId would be dropped
1697 fn drop_location_span<'tcx>(tcx: TyCtxt<'tcx>, hir_id: &hir::HirId) -> Span {
1698 let owner_id = tcx.hir().get_enclosing_scope(*hir_id).unwrap();
1700 let owner_node = tcx.hir().get(owner_id);
1701 let owner_span = match owner_node {
1702 hir::Node::Item(item) => match item.kind {
1703 hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
1705 bug!("Drop location span error: need to handle more ItemKind {:?}", item.kind);
1708 hir::Node::Block(block) => tcx.hir().span(block.hir_id),
1710 bug!("Drop location span error: need to handle more Node {:?}", owner_node);
1713 tcx.sess.source_map().end_point(owner_span)
1716 struct InferBorrowKind<'a, 'tcx> {
1717 fcx: &'a FnCtxt<'a, 'tcx>,
1719 // The def-id of the closure whose kind and upvar accesses are being inferred.
1720 closure_def_id: LocalDefId,
1722 /// For each Place that is captured by the closure, we track the minimal kind of
1723 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1725 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1726 /// s.str2 via a MutableBorrow
1729 /// struct SomeStruct { str1: String, str2: String }
1731 /// // Assume that the HirId for the variable definition is `V1`
1732 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
1734 /// let fix_s = |new_s2| {
1735 /// // Assume that the HirId for the expression `s.str1` is `E1`
1736 /// println!("Updating SomeStruct with str1=", s.str1);
1737 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1738 /// s.str2 = new_s2;
1742 /// For closure `fix_s`, (at a high level) the map contains
1745 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1746 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1748 capture_information: InferredCaptureInformation<'tcx>,
1749 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1752 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1753 fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId) {
1754 let PlaceBase::Upvar(_) = place.base else { return };
1756 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1757 // such as deref of a raw pointer.
1758 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1760 let (place, _) = restrict_capture_precision(place, dummy_capture_kind);
1762 let (place, _) = restrict_repr_packed_field_ref_capture(
1768 self.fake_reads.push((place, cause, diag_expr_id));
1771 #[instrument(skip(self), level = "debug")]
1772 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1773 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1774 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1776 self.capture_information.push((
1777 place_with_id.place.clone(),
1779 capture_kind_expr_id: Some(diag_expr_id),
1780 path_expr_id: Some(diag_expr_id),
1781 capture_kind: ty::UpvarCapture::ByValue,
1786 #[instrument(skip(self), level = "debug")]
1789 place_with_id: &PlaceWithHirId<'tcx>,
1790 diag_expr_id: hir::HirId,
1793 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1794 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1796 // The region here will get discarded/ignored
1797 let capture_kind = ty::UpvarCapture::ByRef(bk);
1799 // We only want repr packed restriction to be applied to reading references into a packed
1800 // struct, and not when the data is being moved. Therefore we call this method here instead
1801 // of in `restrict_capture_precision`.
1802 let (place, mut capture_kind) = restrict_repr_packed_field_ref_capture(
1805 place_with_id.place.clone(),
1809 // Raw pointers don't inherit mutability
1810 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1811 capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1814 self.capture_information.push((
1817 capture_kind_expr_id: Some(diag_expr_id),
1818 path_expr_id: Some(diag_expr_id),
1824 #[instrument(skip(self), level = "debug")]
1825 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1826 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1830 /// Rust doesn't permit moving fields out of a type that implements drop
1831 fn restrict_precision_for_drop_types<'a, 'tcx>(
1832 fcx: &'a FnCtxt<'a, 'tcx>,
1833 mut place: Place<'tcx>,
1834 mut curr_mode: ty::UpvarCapture,
1836 ) -> (Place<'tcx>, ty::UpvarCapture) {
1837 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1839 if let (false, UpvarCapture::ByValue) = (is_copy_type, curr_mode) {
1840 for i in 0..place.projections.len() {
1841 match place.ty_before_projection(i).kind() {
1842 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1843 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1854 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
1855 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
1856 /// them completely.
1857 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
1858 fn restrict_precision_for_unsafe<'tcx>(
1859 mut place: Place<'tcx>,
1860 mut curr_mode: ty::UpvarCapture,
1861 ) -> (Place<'tcx>, ty::UpvarCapture) {
1862 if place.base_ty.is_unsafe_ptr() {
1863 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1866 if place.base_ty.is_union() {
1867 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1870 for (i, proj) in place.projections.iter().enumerate() {
1871 if proj.ty.is_unsafe_ptr() {
1872 // Don't apply any projections on top of an unsafe ptr.
1873 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1877 if proj.ty.is_union() {
1878 // Don't capture preicse fields of a union.
1879 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1887 /// Truncate projections so that following rules are obeyed by the captured `place`:
1888 /// - No Index projections are captured, since arrays are captured completely.
1889 /// - No unsafe block is required to capture `place`
1890 /// Returns the truncated place and updated cature mode.
1891 fn restrict_capture_precision<'tcx>(
1893 curr_mode: ty::UpvarCapture,
1894 ) -> (Place<'tcx>, ty::UpvarCapture) {
1895 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
1897 if place.projections.is_empty() {
1898 // Nothing to do here
1899 return (place, curr_mode);
1902 for (i, proj) in place.projections.iter().enumerate() {
1904 ProjectionKind::Index => {
1905 // Arrays are completely captured, so we drop Index projections
1906 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1907 return (place, curr_mode);
1909 ProjectionKind::Deref => {}
1910 ProjectionKind::Field(..) => {} // ignore
1911 ProjectionKind::Subslice => {} // We never capture this
1918 /// Truncate deref of any reference.
1919 fn adjust_for_move_closure<'tcx>(
1920 mut place: Place<'tcx>,
1921 mut kind: ty::UpvarCapture,
1922 ) -> (Place<'tcx>, ty::UpvarCapture) {
1923 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1925 if let Some(idx) = first_deref {
1926 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1929 (place, ty::UpvarCapture::ByValue)
1932 /// Adjust closure capture just that if taking ownership of data, only move data
1933 /// from enclosing stack frame.
1934 fn adjust_for_non_move_closure<'tcx>(
1935 mut place: Place<'tcx>,
1936 mut kind: ty::UpvarCapture,
1937 ) -> (Place<'tcx>, ty::UpvarCapture) {
1938 let contains_deref =
1939 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1942 ty::UpvarCapture::ByValue => {
1943 if let Some(idx) = contains_deref {
1944 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1948 ty::UpvarCapture::ByRef(..) => {}
1954 fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1955 let variable_name = match place.base {
1956 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
1957 _ => bug!("Capture_information should only contain upvars"),
1960 let mut projections_str = String::new();
1961 for (i, item) in place.projections.iter().enumerate() {
1962 let proj = match item.kind {
1963 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
1964 ProjectionKind::Deref => String::from("Deref"),
1965 ProjectionKind::Index => String::from("Index"),
1966 ProjectionKind::Subslice => String::from("Subslice"),
1969 projections_str.push(',');
1971 projections_str.push_str(proj.as_str());
1974 format!("{}[{}]", variable_name, projections_str)
1977 fn construct_capture_kind_reason_string<'tcx>(
1979 place: &Place<'tcx>,
1980 capture_info: &ty::CaptureInfo,
1982 let place_str = construct_place_string(tcx, place);
1984 let capture_kind_str = match capture_info.capture_kind {
1985 ty::UpvarCapture::ByValue => "ByValue".into(),
1986 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
1989 format!("{} captured as {} here", place_str, capture_kind_str)
1992 fn construct_path_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1993 let place_str = construct_place_string(tcx, place);
1995 format!("{} used here", place_str)
1998 fn construct_capture_info_string<'tcx>(
2000 place: &Place<'tcx>,
2001 capture_info: &ty::CaptureInfo,
2003 let place_str = construct_place_string(tcx, place);
2005 let capture_kind_str = match capture_info.capture_kind {
2006 ty::UpvarCapture::ByValue => "ByValue".into(),
2007 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
2009 format!("{} -> {}", place_str, capture_kind_str)
2012 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2013 tcx.hir().name(var_hir_id)
2016 #[instrument(level = "debug", skip(tcx))]
2017 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2019 closure_id: hir::HirId,
2022 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2024 !matches!(level, lint::Level::Allow)
2027 /// Return a two string tuple (s1, s2)
2028 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2029 /// - s2: Comma separated names of the variables being migrated.
2030 fn migration_suggestion_for_2229(
2032 need_migrations: &Vec<NeededMigration>,
2033 ) -> (String, String) {
2034 let need_migrations_variables = need_migrations
2036 .map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
2037 .collect::<Vec<_>>();
2039 let migration_ref_concat =
2040 need_migrations_variables.iter().map(|v| format!("&{}", v)).collect::<Vec<_>>().join(", ");
2042 let migration_string = if 1 == need_migrations.len() {
2043 format!("let _ = {}", migration_ref_concat)
2045 format!("let _ = ({})", migration_ref_concat)
2048 let migrated_variables_concat =
2049 need_migrations_variables.iter().map(|v| format!("`{}`", v)).collect::<Vec<_>>().join(", ");
2051 (migration_string, migrated_variables_concat)
2054 /// Helper function to determine if we need to escalate CaptureKind from
2055 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2056 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2058 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2059 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2061 /// It is the caller's duty to figure out which path_expr_id to use.
2063 /// If both the CaptureKind and Expression are considered to be equivalent,
2064 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to priortize
2065 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2066 /// in the closure. This can be achieved simply by calling
2067 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2068 /// expressions that occur earlier in the closure body than the current expression are processed before.
2069 /// Consider the following example
2071 /// struct Point { x: i32, y: i32 }
2072 /// let mut p: Point { x: 10, y: 10 };
2080 /// p.x += 10; // E2
2084 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2085 /// and both have an expression associated, however for diagnostics we prefer reporting
2086 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2087 /// would've already handled `E1`, and have an existing capture_information for it.
2088 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2089 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2090 fn determine_capture_info(
2091 capture_info_a: ty::CaptureInfo,
2092 capture_info_b: ty::CaptureInfo,
2093 ) -> ty::CaptureInfo {
2094 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2096 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2097 (ty::UpvarCapture::ByValue, ty::UpvarCapture::ByValue) => true,
2098 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => ref_a == ref_b,
2099 (ty::UpvarCapture::ByValue, _) | (ty::UpvarCapture::ByRef(_), _) => false,
2102 if eq_capture_kind {
2103 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2104 (Some(_), _) | (None, None) => capture_info_a,
2105 (None, Some(_)) => capture_info_b,
2108 // We select the CaptureKind which ranks higher based the following priority order:
2109 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2110 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2111 (ty::UpvarCapture::ByValue, _) => capture_info_a,
2112 (_, ty::UpvarCapture::ByValue) => capture_info_b,
2113 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2114 match (ref_a, ref_b) {
2116 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2117 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2120 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2121 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2123 (ty::ImmBorrow, ty::ImmBorrow)
2124 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2125 | (ty::MutBorrow, ty::MutBorrow) => {
2126 bug!("Expected unequal capture kinds");
2134 /// Truncates `place` to have up to `len` projections.
2135 /// `curr_mode` is the current required capture kind for the place.
2136 /// Returns the truncated `place` and the updated required capture kind.
2138 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2139 /// contained `Deref` of `&mut`.
2140 fn truncate_place_to_len_and_update_capture_kind<'tcx>(
2141 place: &mut Place<'tcx>,
2142 curr_mode: &mut ty::UpvarCapture,
2145 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2147 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2149 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2150 // we don't need to worry about that case here.
2152 ty::UpvarCapture::ByRef(ty::BorrowKind::MutBorrow) => {
2153 for i in len..place.projections.len() {
2154 if place.projections[i].kind == ProjectionKind::Deref
2155 && is_mut_ref(place.ty_before_projection(i))
2157 *curr_mode = ty::UpvarCapture::ByRef(ty::BorrowKind::UniqueImmBorrow);
2163 ty::UpvarCapture::ByRef(..) => {}
2164 ty::UpvarCapture::ByValue => {}
2167 place.projections.truncate(len);
2170 /// Determines the Ancestry relationship of Place A relative to Place B
2172 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2173 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2174 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2175 fn determine_place_ancestry_relation<'tcx>(
2176 place_a: &Place<'tcx>,
2177 place_b: &Place<'tcx>,
2178 ) -> PlaceAncestryRelation {
2179 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2180 if place_a.base != place_b.base {
2181 return PlaceAncestryRelation::Divergent;
2184 // Assume of length of projections_a = n
2185 let projections_a = &place_a.projections;
2187 // Assume of length of projections_b = m
2188 let projections_b = &place_b.projections;
2190 let same_initial_projections =
2191 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2193 if same_initial_projections {
2194 use std::cmp::Ordering;
2196 // First min(n, m) projections are the same
2197 // Select Ancestor/Descendant
2198 match projections_b.len().cmp(&projections_a.len()) {
2199 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2200 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2201 Ordering::Less => PlaceAncestryRelation::Descendant,
2204 PlaceAncestryRelation::Divergent
2208 /// Reduces the precision of the captured place when the precision doesn't yeild any benefit from
2209 /// borrow checking prespective, allowing us to save us on the size of the capture.
2212 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2213 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2214 /// rightmost deref of the capture if the deref is applied to a shared ref.
2216 /// Reason we only drop the last deref is because of the following edge case:
2219 /// struct MyStruct<'a> {
2225 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2226 /// let c = || drop(&*m.a.field_of_a);
2227 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2229 /// // If we capture `m`, then the closure no longer outlives `'static'
2230 /// // it is constrained to `'a`
2233 fn truncate_capture_for_optimization<'tcx>(
2234 mut place: Place<'tcx>,
2235 mut curr_mode: ty::UpvarCapture,
2236 ) -> (Place<'tcx>, ty::UpvarCapture) {
2237 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2239 // Find the right-most deref (if any). All the projections that come after this
2240 // are fields or other "in-place pointer adjustments"; these refer therefore to
2241 // data owned by whatever pointer is being dereferenced here.
2242 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2245 // If that pointer is a shared reference, then we don't need those fields.
2246 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2247 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2249 None | Some(_) => {}
2255 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2256 /// user is using Rust Edition 2021 or higher.
2258 /// `span` is the span of the closure.
2259 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2260 // We use span here to ensure that if the closure was generated by a macro with a different
2262 tcx.features().capture_disjoint_fields || span.rust_2021()