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:
8 //! ```ignore (not-rust)
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, MultiSpan};
38 use rustc_hir::def_id::LocalDefId;
39 use rustc_hir::intravisit::{self, Visitor};
40 use rustc_infer::infer::UpvarRegion;
41 use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection, ProjectionKind};
42 use rustc_middle::mir::FakeReadCause;
43 use rustc_middle::ty::{
44 self, ClosureSizeProfileData, Ty, TyCtxt, TypeckResults, UpvarCapture, UpvarSubsts,
46 use rustc_session::lint;
48 use rustc_span::{BytePos, Pos, Span, Symbol};
49 use rustc_trait_selection::infer::InferCtxtExt;
51 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
52 use rustc_index::vec::Idx;
53 use rustc_target::abi::VariantIdx;
57 /// Describe the relationship between the paths of two places
59 /// - `foo` is ancestor of `foo.bar.baz`
60 /// - `foo.bar.baz` is an descendant of `foo.bar`
61 /// - `foo.bar` and `foo.baz` are divergent
62 enum PlaceAncestryRelation {
69 /// Intermediate format to store a captured `Place` and associated `ty::CaptureInfo`
70 /// during capture analysis. Information in this map feeds into the minimum capture
72 type InferredCaptureInformation<'tcx> = Vec<(Place<'tcx>, ty::CaptureInfo)>;
74 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
75 pub fn closure_analyze(&self, body: &'tcx hir::Body<'tcx>) {
76 InferBorrowKindVisitor { fcx: self }.visit_body(body);
78 // it's our job to process these.
79 assert!(self.deferred_call_resolutions.borrow().is_empty());
83 /// Intermediate format to store the hir_id pointing to the use that resulted in the
84 /// corresponding place being captured and a String which contains the captured value's
86 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
87 enum UpvarMigrationInfo {
88 /// We previously captured all of `x`, but now we capture some sub-path.
89 CapturingPrecise { source_expr: Option<hir::HirId>, var_name: String },
91 // where the variable appears in the closure (but is not captured)
96 /// Reasons that we might issue a migration warning.
97 #[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
98 struct MigrationWarningReason {
99 /// When we used to capture `x` in its entirety, we implemented the auto-trait(s)
100 /// in this vec, but now we don't.
101 auto_traits: Vec<&'static str>,
103 /// When we used to capture `x` in its entirety, we would execute some destructors
104 /// at a different time.
108 impl MigrationWarningReason {
109 fn migration_message(&self) -> String {
110 let base = "changes to closure capture in Rust 2021 will affect";
111 if !self.auto_traits.is_empty() && self.drop_order {
112 format!("{} drop order and which traits the closure implements", base)
113 } else if self.drop_order {
114 format!("{} drop order", base)
116 format!("{} which traits the closure implements", base)
121 /// Intermediate format to store information needed to generate a note in the migration lint.
122 struct MigrationLintNote {
123 captures_info: UpvarMigrationInfo,
125 /// reasons why migration is needed for this capture
126 reason: MigrationWarningReason,
129 /// Intermediate format to store the hir id of the root variable and a HashSet containing
130 /// information on why the root variable should be fully captured
131 struct NeededMigration {
132 var_hir_id: hir::HirId,
133 diagnostics_info: Vec<MigrationLintNote>,
136 struct InferBorrowKindVisitor<'a, 'tcx> {
137 fcx: &'a FnCtxt<'a, 'tcx>,
140 impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
141 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
143 hir::ExprKind::Closure(&hir::Closure { capture_clause, body: body_id, .. }) => {
144 let body = self.fcx.tcx.hir().body(body_id);
145 self.visit_body(body);
146 self.fcx.analyze_closure(expr.hir_id, expr.span, body_id, body, capture_clause);
148 hir::ExprKind::ConstBlock(anon_const) => {
149 let body = self.fcx.tcx.hir().body(anon_const.body);
150 self.visit_body(body);
155 intravisit::walk_expr(self, expr);
159 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
160 /// Analysis starting point.
161 #[instrument(skip(self, body), level = "debug")]
164 closure_hir_id: hir::HirId,
166 body_id: hir::BodyId,
167 body: &'tcx hir::Body<'tcx>,
168 capture_clause: hir::CaptureBy,
170 // Extract the type of the closure.
171 let ty = self.node_ty(closure_hir_id);
172 let (closure_def_id, substs) = match *ty.kind() {
173 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
174 ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
176 // #51714: skip analysis when we have already encountered type errors
182 "type of closure expr {:?} is not a closure {:?}",
188 let closure_def_id = closure_def_id.expect_local();
190 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
191 self.closure_kind(closure_substs).is_none().then_some(closure_substs)
196 assert_eq!(self.tcx.hir().body_owner_def_id(body.id()), closure_def_id);
197 let mut delegate = InferBorrowKind {
200 capture_information: Default::default(),
201 fake_reads: Default::default(),
203 euv::ExprUseVisitor::new(
208 &self.typeck_results.borrow(),
213 "For closure={:?}, capture_information={:#?}",
214 closure_def_id, delegate.capture_information
217 self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
219 let (capture_information, closure_kind, origin) = self
220 .process_collected_capture_information(capture_clause, delegate.capture_information);
222 self.compute_min_captures(closure_def_id, capture_information, span);
224 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(closure_def_id);
226 if should_do_rust_2021_incompatible_closure_captures_analysis(self.tcx, closure_hir_id) {
227 self.perform_2229_migration_anaysis(closure_def_id, body_id, capture_clause, span);
230 let after_feature_tys = self.final_upvar_tys(closure_def_id);
232 // We now fake capture information for all variables that are mentioned within the closure
233 // We do this after handling migrations so that min_captures computes before
234 if !enable_precise_capture(self.tcx, span) {
235 let mut capture_information: InferredCaptureInformation<'tcx> = Default::default();
237 if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
238 for var_hir_id in upvars.keys() {
239 let place = self.place_for_root_variable(closure_def_id, *var_hir_id);
241 debug!("seed place {:?}", place);
243 let capture_kind = self.init_capture_kind_for_place(&place, capture_clause);
244 let fake_info = ty::CaptureInfo {
245 capture_kind_expr_id: None,
250 capture_information.push((place, fake_info));
254 // This will update the min captures based on this new fake information.
255 self.compute_min_captures(closure_def_id, capture_information, span);
258 let before_feature_tys = self.final_upvar_tys(closure_def_id);
260 if let Some(closure_substs) = infer_kind {
261 // Unify the (as yet unbound) type variable in the closure
262 // substs with the kind we inferred.
263 let closure_kind_ty = closure_substs.as_closure().kind_ty();
264 self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
266 // If we have an origin, store it.
267 if let Some(origin) = origin {
268 let origin = if enable_precise_capture(self.tcx, span) {
271 (origin.0, Place { projections: vec![], ..origin.1 })
276 .closure_kind_origins_mut()
277 .insert(closure_hir_id, origin);
281 self.log_closure_min_capture_info(closure_def_id, span);
283 // Now that we've analyzed the closure, we know how each
284 // variable is borrowed, and we know what traits the closure
285 // implements (Fn vs FnMut etc). We now have some updates to do
286 // with that information.
288 // Note that no closure type C may have an upvar of type C
289 // (though it may reference itself via a trait object). This
290 // results from the desugaring of closures to a struct like
291 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
292 // C, then the type would have infinite size (and the
293 // inference algorithm will reject it).
295 // Equate the type variables for the upvars with the actual types.
296 let final_upvar_tys = self.final_upvar_tys(closure_def_id);
298 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
299 closure_hir_id, substs, final_upvar_tys
302 // Build a tuple (U0..Un) of the final upvar types U0..Un
303 // and unify the upvar tuple type in the closure with it:
304 let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
305 self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
307 let fake_reads = delegate
310 .map(|(place, cause, hir_id)| (place, cause, hir_id))
312 self.typeck_results.borrow_mut().closure_fake_reads.insert(closure_def_id, fake_reads);
314 if self.tcx.sess.opts.unstable_opts.profile_closures {
315 self.typeck_results.borrow_mut().closure_size_eval.insert(
317 ClosureSizeProfileData {
318 before_feature_tys: self.tcx.mk_tup(before_feature_tys.into_iter()),
319 after_feature_tys: self.tcx.mk_tup(after_feature_tys.into_iter()),
324 // If we are also inferred the closure kind here,
325 // process any deferred resolutions.
326 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
327 for deferred_call_resolution in deferred_call_resolutions {
328 deferred_call_resolution.resolve(self);
332 // Returns a list of `Ty`s for each upvar.
333 fn final_upvar_tys(&self, closure_id: LocalDefId) -> Vec<Ty<'tcx>> {
336 .closure_min_captures_flattened(closure_id)
337 .map(|captured_place| {
338 let upvar_ty = captured_place.place.ty();
339 let capture = captured_place.info.capture_kind;
342 "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
343 captured_place.place, upvar_ty, capture, captured_place.mutability,
346 apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture, captured_place.region)
351 /// Adjusts the closure capture information to ensure that the operations aren't unsafe,
352 /// and that the path can be captured with required capture kind (depending on use in closure,
353 /// move closure etc.)
355 /// Returns the set of of adjusted information along with the inferred closure kind and span
356 /// associated with the closure kind inference.
358 /// Note that we *always* infer a minimal kind, even if
359 /// we don't always *use* that in the final result (i.e., sometimes
360 /// we've taken the closure kind from the expectations instead, and
361 /// for generators we don't even implement the closure traits
364 /// If we inferred that the closure needs to be FnMut/FnOnce, last element of the returned tuple
365 /// contains a `Some()` with the `Place` that caused us to do so.
366 fn process_collected_capture_information(
368 capture_clause: hir::CaptureBy,
369 capture_information: InferredCaptureInformation<'tcx>,
370 ) -> (InferredCaptureInformation<'tcx>, ty::ClosureKind, Option<(Span, Place<'tcx>)>) {
371 let mut closure_kind = ty::ClosureKind::LATTICE_BOTTOM;
372 let mut origin: Option<(Span, Place<'tcx>)> = None;
374 let processed = capture_information
376 .map(|(place, mut capture_info)| {
377 // Apply rules for safety before inferring closure kind
378 let (place, capture_kind) =
379 restrict_capture_precision(place, capture_info.capture_kind);
381 let (place, capture_kind) = truncate_capture_for_optimization(place, capture_kind);
383 let usage_span = if let Some(usage_expr) = capture_info.path_expr_id {
384 self.tcx.hir().span(usage_expr)
389 let updated = match capture_kind {
390 ty::UpvarCapture::ByValue => match closure_kind {
391 ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
392 (ty::ClosureKind::FnOnce, Some((usage_span, place.clone())))
394 // If closure is already FnOnce, don't update
395 ty::ClosureKind::FnOnce => (closure_kind, origin.take()),
398 ty::UpvarCapture::ByRef(
399 ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
402 ty::ClosureKind::Fn => {
403 (ty::ClosureKind::FnMut, Some((usage_span, place.clone())))
405 // Don't update the origin
406 ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce => {
407 (closure_kind, origin.take())
412 _ => (closure_kind, origin.take()),
415 closure_kind = updated.0;
418 let (place, capture_kind) = match capture_clause {
419 hir::CaptureBy::Value => adjust_for_move_closure(place, capture_kind),
420 hir::CaptureBy::Ref => adjust_for_non_move_closure(place, capture_kind),
423 // This restriction needs to be applied after we have handled adjustments for `move`
424 // closures. We want to make sure any adjustment that might make us move the place into
425 // the closure gets handled.
426 let (place, capture_kind) =
427 restrict_precision_for_drop_types(self, place, capture_kind, usage_span);
429 capture_info.capture_kind = capture_kind;
430 (place, capture_info)
434 (processed, closure_kind, origin)
437 /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
438 /// Places (and corresponding capture kind) that we need to keep track of to support all
439 /// the required captured paths.
442 /// Note: If this function is called multiple times for the same closure, it will update
443 /// the existing min_capture map that is stored in TypeckResults.
448 /// struct Point { x: i32, y: i32 }
450 /// let s = String::from("s"); // hir_id_s
451 /// let mut p = Point { x: 2, y: -2 }; // his_id_p
453 /// println!("{s:?}"); // L1
455 /// println!("{}" , p.y); // L3
456 /// println!("{p:?}"); // L4
460 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
461 /// the lines L1..5 respectively.
463 /// InferBorrowKind results in a structure like this:
465 /// ```ignore (illustrative)
467 /// Place(base: hir_id_s, projections: [], ....) -> {
468 /// capture_kind_expr: hir_id_L5,
469 /// path_expr_id: hir_id_L5,
470 /// capture_kind: ByValue
472 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
473 /// capture_kind_expr: hir_id_L2,
474 /// path_expr_id: hir_id_L2,
475 /// capture_kind: ByValue
477 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
478 /// capture_kind_expr: hir_id_L3,
479 /// path_expr_id: hir_id_L3,
480 /// capture_kind: ByValue
482 /// Place(base: hir_id_p, projections: [], ...) -> {
483 /// capture_kind_expr: hir_id_L4,
484 /// path_expr_id: hir_id_L4,
485 /// capture_kind: ByValue
490 /// After the min capture analysis, we get:
491 /// ```ignore (illustrative)
494 /// Place(base: hir_id_s, projections: [], ....) -> {
495 /// capture_kind_expr: hir_id_L5,
496 /// path_expr_id: hir_id_L5,
497 /// capture_kind: ByValue
501 /// Place(base: hir_id_p, projections: [], ...) -> {
502 /// capture_kind_expr: hir_id_L2,
503 /// path_expr_id: hir_id_L4,
504 /// capture_kind: ByValue
509 fn compute_min_captures(
511 closure_def_id: LocalDefId,
512 capture_information: InferredCaptureInformation<'tcx>,
515 if capture_information.is_empty() {
519 let mut typeck_results = self.typeck_results.borrow_mut();
521 let mut root_var_min_capture_list =
522 typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
524 for (mut place, capture_info) in capture_information.into_iter() {
525 let var_hir_id = match place.base {
526 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
527 base => bug!("Expected upvar, found={:?}", base),
530 let Some(min_cap_list) = root_var_min_capture_list.get_mut(&var_hir_id) else {
531 let mutability = self.determine_capture_mutability(&typeck_results, &place);
532 let min_cap_list = vec![ty::CapturedPlace {
538 root_var_min_capture_list.insert(var_hir_id, min_cap_list);
542 // Go through each entry in the current list of min_captures
543 // - if ancestor is found, update it's capture kind to account for current place's
544 // capture information.
546 // - if descendant is found, remove it from the list, and update the current place's
547 // capture information to account for the descendant's capture kind.
549 // We can never be in a case where the list contains both an ancestor and a descendant
550 // Also there can only be ancestor but in case of descendants there might be
553 let mut descendant_found = false;
554 let mut updated_capture_info = capture_info;
555 min_cap_list.retain(|possible_descendant| {
556 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
557 // current place is ancestor of possible_descendant
558 PlaceAncestryRelation::Ancestor => {
559 descendant_found = true;
561 let mut possible_descendant = possible_descendant.clone();
562 let backup_path_expr_id = updated_capture_info.path_expr_id;
564 // Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
565 // possible change in capture mode.
566 truncate_place_to_len_and_update_capture_kind(
567 &mut possible_descendant.place,
568 &mut possible_descendant.info.capture_kind,
569 place.projections.len(),
572 updated_capture_info =
573 determine_capture_info(updated_capture_info, possible_descendant.info);
575 // we need to keep the ancestor's `path_expr_id`
576 updated_capture_info.path_expr_id = backup_path_expr_id;
584 let mut ancestor_found = false;
585 if !descendant_found {
586 for possible_ancestor in min_cap_list.iter_mut() {
587 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
588 PlaceAncestryRelation::SamePlace => {
589 ancestor_found = true;
590 possible_ancestor.info = determine_capture_info(
591 possible_ancestor.info,
592 updated_capture_info,
595 // Only one related place will be in the list.
598 // current place is descendant of possible_ancestor
599 PlaceAncestryRelation::Descendant => {
600 ancestor_found = true;
601 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
603 // Truncate the descendant (current place) to be same as the ancestor to handle any
604 // possible change in capture mode.
605 truncate_place_to_len_and_update_capture_kind(
607 &mut updated_capture_info.capture_kind,
608 possible_ancestor.place.projections.len(),
611 possible_ancestor.info = determine_capture_info(
612 possible_ancestor.info,
613 updated_capture_info,
616 // we need to keep the ancestor's `path_expr_id`
617 possible_ancestor.info.path_expr_id = backup_path_expr_id;
619 // Only one related place will be in the list.
627 // Only need to insert when we don't have an ancestor in the existing min capture list
629 let mutability = self.determine_capture_mutability(&typeck_results, &place);
630 let captured_place = ty::CapturedPlace {
632 info: updated_capture_info,
636 min_cap_list.push(captured_place);
640 // For each capture that is determined to be captured by ref, add region info.
641 for (_, captures) in &mut root_var_min_capture_list {
642 for capture in captures {
643 match capture.info.capture_kind {
644 ty::UpvarCapture::ByRef(_) => {
645 let PlaceBase::Upvar(upvar_id) = capture.place.base else { bug!("expected upvar") };
646 let origin = UpvarRegion(upvar_id, closure_span);
647 let upvar_region = self.next_region_var(origin);
648 capture.region = Some(upvar_region);
656 "For closure={:?}, min_captures before sorting={:?}",
657 closure_def_id, root_var_min_capture_list
660 // Now that we have the minimized list of captures, sort the captures by field id.
661 // This causes the closure to capture the upvars in the same order as the fields are
662 // declared which is also the drop order. Thus, in situations where we capture all the
663 // fields of some type, the observable drop order will remain the same as it previously
664 // was even though we're dropping each capture individually.
665 // See https://github.com/rust-lang/project-rfc-2229/issues/42 and
666 // `src/test/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
667 for (_, captures) in &mut root_var_min_capture_list {
668 captures.sort_by(|capture1, capture2| {
669 for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
670 // We do not need to look at the `Projection.ty` fields here because at each
671 // step of the iteration, the projections will either be the same and therefore
672 // the types must be as well or the current projection will be different and
673 // we will return the result of comparing the field indexes.
674 match (p1.kind, p2.kind) {
675 // Paths are the same, continue to next loop.
676 (ProjectionKind::Deref, ProjectionKind::Deref) => {}
677 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
680 // Fields are different, compare them.
681 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
685 // We should have either a pair of `Deref`s or a pair of `Field`s.
686 // Anything else is a bug.
688 l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
689 r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
691 "ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
696 l @ (ProjectionKind::Index
697 | ProjectionKind::Subslice
698 | ProjectionKind::Deref
699 | ProjectionKind::Field(..)),
700 r @ (ProjectionKind::Index
701 | ProjectionKind::Subslice
702 | ProjectionKind::Deref
703 | ProjectionKind::Field(..)),
705 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
713 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
720 "For closure={:?}, min_captures after sorting={:#?}",
721 closure_def_id, root_var_min_capture_list
723 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
726 /// Perform the migration analysis for RFC 2229, and emit lint
727 /// `disjoint_capture_drop_reorder` if needed.
728 fn perform_2229_migration_anaysis(
730 closure_def_id: LocalDefId,
731 body_id: hir::BodyId,
732 capture_clause: hir::CaptureBy,
735 let (need_migrations, reasons) = self.compute_2229_migrations(
739 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
742 if !need_migrations.is_empty() {
743 let (migration_string, migrated_variables_concat) =
744 migration_suggestion_for_2229(self.tcx, &need_migrations);
746 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(closure_def_id);
747 let closure_head_span = self.tcx.def_span(closure_def_id);
748 self.tcx.struct_span_lint_hir(
749 lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
753 let mut diagnostics_builder = lint.build(
754 &reasons.migration_message(),
756 for NeededMigration { var_hir_id, diagnostics_info } in &need_migrations {
757 // Labels all the usage of the captured variable and why they are responsible
758 // for migration being needed
759 for lint_note in diagnostics_info.iter() {
760 match &lint_note.captures_info {
761 UpvarMigrationInfo::CapturingPrecise { source_expr: Some(capture_expr_id), var_name: captured_name } => {
762 let cause_span = self.tcx.hir().span(*capture_expr_id);
763 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
764 self.tcx.hir().name(*var_hir_id),
768 UpvarMigrationInfo::CapturingNothing { use_span } => {
769 diagnostics_builder.span_label(*use_span, format!("in Rust 2018, this causes the closure to capture `{}`, but in Rust 2021, it has no effect",
770 self.tcx.hir().name(*var_hir_id),
777 // Add a label pointing to where a captured variable affected by drop order
779 if lint_note.reason.drop_order {
780 let drop_location_span = drop_location_span(self.tcx, closure_hir_id);
782 match &lint_note.captures_info {
783 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
784 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",
785 self.tcx.hir().name(*var_hir_id),
789 UpvarMigrationInfo::CapturingNothing { use_span: _ } => {
790 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",
791 v = self.tcx.hir().name(*var_hir_id),
797 // Add a label explaining why a closure no longer implements a trait
798 for &missing_trait in &lint_note.reason.auto_traits {
799 // not capturing something anymore cannot cause a trait to fail to be implemented:
800 match &lint_note.captures_info {
801 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
802 let var_name = self.tcx.hir().name(*var_hir_id);
803 diagnostics_builder.span_label(closure_head_span, format!("\
804 in Rust 2018, this closure implements {missing_trait} \
805 as `{var_name}` implements {missing_trait}, but in Rust 2021, \
806 this closure will no longer implement {missing_trait} \
807 because `{var_name}` is not fully captured \
808 and `{captured_name}` does not implement {missing_trait}"));
811 // Cannot happen: if we don't capture a variable, we impl strictly more traits
812 UpvarMigrationInfo::CapturingNothing { use_span } => span_bug!(*use_span, "missing trait from not capturing something"),
817 diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
819 let diagnostic_msg = format!(
820 "add a dummy let to cause {} to be fully captured",
821 migrated_variables_concat
824 let closure_span = self.tcx.hir().span_with_body(closure_hir_id);
825 let mut closure_body_span = {
826 // If the body was entirely expanded from a macro
827 // invocation, i.e. the body is not contained inside the
828 // closure span, then we walk up the expansion until we
829 // find the span before the expansion.
830 let s = self.tcx.hir().span_with_body(body_id.hir_id);
831 s.find_ancestor_inside(closure_span).unwrap_or(s)
834 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
835 if s.starts_with('$') {
836 // Looks like a macro fragment. Try to find the real block.
837 if let Some(hir::Node::Expr(&hir::Expr {
838 kind: hir::ExprKind::Block(block, ..), ..
839 })) = self.tcx.hir().find(body_id.hir_id) {
840 // If the body is a block (with `{..}`), we use the span of that block.
841 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
842 // Since we know it's a block, we know we can insert the `let _ = ..` without
843 // breaking the macro syntax.
844 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
845 closure_body_span = block.span;
851 let mut lines = s.lines();
852 let line1 = lines.next().unwrap_or_default();
854 if line1.trim_end() == "{" {
855 // This is a multi-line closure with just a `{` on the first line,
856 // so we put the `let` on its own line.
857 // We take the indentation from the next non-empty line.
858 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
859 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
860 diagnostics_builder.span_suggestion(
861 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
863 format!("\n{indent}{migration_string};"),
864 Applicability::MachineApplicable,
866 } else if line1.starts_with('{') {
867 // This is a closure with its body wrapped in
868 // braces, but with more than just the opening
869 // brace on the first line. We put the `let`
870 // directly after the `{`.
871 diagnostics_builder.span_suggestion(
872 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
874 format!(" {migration_string};"),
875 Applicability::MachineApplicable,
878 // This is a closure without braces around the body.
879 // We add braces to add the `let` before the body.
880 diagnostics_builder.multipart_suggestion(
883 (closure_body_span.shrink_to_lo(), format!("{{ {migration_string}; ")),
884 (closure_body_span.shrink_to_hi(), " }".to_string()),
886 Applicability::MachineApplicable
890 diagnostics_builder.span_suggestion(
894 Applicability::HasPlaceholders
898 diagnostics_builder.emit();
904 /// Combines all the reasons for 2229 migrations
905 fn compute_2229_migrations_reasons(
907 auto_trait_reasons: FxHashSet<&'static str>,
909 ) -> MigrationWarningReason {
910 let mut reasons = MigrationWarningReason::default();
912 reasons.auto_traits.extend(auto_trait_reasons);
913 reasons.drop_order = drop_order;
915 // `auto_trait_reasons` are in hashset order, so sort them to put the
916 // diagnostics we emit later in a cross-platform-consistent order.
917 reasons.auto_traits.sort_unstable();
922 /// Figures out the list of root variables (and their types) that aren't completely
923 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
924 /// differ between the root variable and the captured paths.
926 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
927 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
928 fn compute_2229_migrations_for_trait(
930 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
931 var_hir_id: hir::HirId,
932 closure_clause: hir::CaptureBy,
933 ) -> Option<FxHashMap<UpvarMigrationInfo, FxHashSet<&'static str>>> {
934 let auto_traits_def_id = vec![
935 self.tcx.lang_items().clone_trait(),
936 self.tcx.lang_items().sync_trait(),
937 self.tcx.get_diagnostic_item(sym::Send),
938 self.tcx.lang_items().unpin_trait(),
939 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
940 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
942 const AUTO_TRAITS: [&str; 6] =
943 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
945 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
947 let ty = self.resolve_vars_if_possible(self.node_ty(var_hir_id));
949 let ty = match closure_clause {
950 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
951 hir::CaptureBy::Ref => {
952 // For non move closure the capture kind is the max capture kind of all captures
953 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
954 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
955 for capture in root_var_min_capture_list.iter() {
956 max_capture_info = determine_capture_info(max_capture_info, capture.info);
959 apply_capture_kind_on_capture_ty(
962 max_capture_info.capture_kind,
963 Some(self.tcx.lifetimes.re_erased),
968 let mut obligations_should_hold = Vec::new();
969 // Checks if a root variable implements any of the auto traits
970 for check_trait in auto_traits_def_id.iter() {
971 obligations_should_hold.push(
975 .type_implements_trait(
978 self.tcx.mk_substs_trait(ty, &[]),
981 .must_apply_modulo_regions()
987 let mut problematic_captures = FxHashMap::default();
988 // Check whether captured fields also implement the trait
989 for capture in root_var_min_capture_list.iter() {
990 let ty = apply_capture_kind_on_capture_ty(
993 capture.info.capture_kind,
994 Some(self.tcx.lifetimes.re_erased),
997 // Checks if a capture implements any of the auto traits
998 let mut obligations_holds_for_capture = Vec::new();
999 for check_trait in auto_traits_def_id.iter() {
1000 obligations_holds_for_capture.push(
1002 .map(|check_trait| {
1004 .type_implements_trait(
1007 self.tcx.mk_substs_trait(ty, &[]),
1010 .must_apply_modulo_regions()
1016 let mut capture_problems = FxHashSet::default();
1018 // Checks if for any of the auto traits, one or more trait is implemented
1019 // by the root variable but not by the capture
1020 for (idx, _) in obligations_should_hold.iter().enumerate() {
1021 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
1022 capture_problems.insert(AUTO_TRAITS[idx]);
1026 if !capture_problems.is_empty() {
1027 problematic_captures.insert(
1028 UpvarMigrationInfo::CapturingPrecise {
1029 source_expr: capture.info.path_expr_id,
1030 var_name: capture.to_string(self.tcx),
1036 if !problematic_captures.is_empty() {
1037 return Some(problematic_captures);
1042 /// Figures out the list of root variables (and their types) that aren't completely
1043 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
1044 /// some path starting at that root variable **might** be affected.
1046 /// The output list would include a root variable if:
1047 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1048 /// enabled, **and**
1049 /// - It wasn't completely captured by the closure, **and**
1050 /// - One of the paths starting at this root variable, that is not captured needs Drop.
1052 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
1053 /// are no significant drops than None is returned
1054 #[instrument(level = "debug", skip(self))]
1055 fn compute_2229_migrations_for_drop(
1057 closure_def_id: LocalDefId,
1059 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1060 closure_clause: hir::CaptureBy,
1061 var_hir_id: hir::HirId,
1062 ) -> Option<FxHashSet<UpvarMigrationInfo>> {
1063 let ty = self.resolve_vars_if_possible(self.node_ty(var_hir_id));
1065 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id)) {
1066 debug!("does not have significant drop");
1070 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1071 // The upvar is mentioned within the closure but no path starting from it is
1072 // used. This occurs when you have (e.g.)
1075 // let x = move || {
1079 debug!("no path starting from it is used");
1082 match closure_clause {
1083 // Only migrate if closure is a move closure
1084 hir::CaptureBy::Value => {
1085 let mut diagnostics_info = FxHashSet::default();
1086 let upvars = self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
1087 let upvar = upvars[&var_hir_id];
1088 diagnostics_info.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
1089 return Some(diagnostics_info);
1091 hir::CaptureBy::Ref => {}
1096 debug!(?root_var_min_capture_list);
1098 let mut projections_list = Vec::new();
1099 let mut diagnostics_info = FxHashSet::default();
1101 for captured_place in root_var_min_capture_list.iter() {
1102 match captured_place.info.capture_kind {
1103 // Only care about captures that are moved into the closure
1104 ty::UpvarCapture::ByValue => {
1105 projections_list.push(captured_place.place.projections.as_slice());
1106 diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
1107 source_expr: captured_place.info.path_expr_id,
1108 var_name: captured_place.to_string(self.tcx),
1111 ty::UpvarCapture::ByRef(..) => {}
1115 debug!(?projections_list);
1116 debug!(?diagnostics_info);
1118 let is_moved = !projections_list.is_empty();
1121 let is_not_completely_captured =
1122 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1123 debug!(?is_not_completely_captured);
1126 && is_not_completely_captured
1127 && self.has_significant_drop_outside_of_captures(
1134 return Some(diagnostics_info);
1140 /// Figures out the list of root variables (and their types) that aren't completely
1141 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1142 /// order of some path starting at that root variable **might** be affected or auto-traits
1143 /// differ between the root variable and the captured paths.
1145 /// The output list would include a root variable if:
1146 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1147 /// enabled, **and**
1148 /// - It wasn't completely captured by the closure, **and**
1149 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1150 /// - One of the paths captured does not implement all the auto-traits its root variable
1153 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1154 /// containing the reason why root variables whose HirId is contained in the vector should
1156 #[instrument(level = "debug", skip(self))]
1157 fn compute_2229_migrations(
1159 closure_def_id: LocalDefId,
1161 closure_clause: hir::CaptureBy,
1162 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1163 ) -> (Vec<NeededMigration>, MigrationWarningReason) {
1164 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1165 return (Vec::new(), MigrationWarningReason::default());
1168 let mut need_migrations = Vec::new();
1169 let mut auto_trait_migration_reasons = FxHashSet::default();
1170 let mut drop_migration_needed = false;
1172 // Perform auto-trait analysis
1173 for (&var_hir_id, _) in upvars.iter() {
1174 let mut diagnostics_info = Vec::new();
1176 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1177 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1181 FxHashMap::default()
1184 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1185 .compute_2229_migrations_for_drop(
1192 drop_migration_needed = true;
1195 FxHashSet::default()
1198 // Combine all the captures responsible for needing migrations into one HashSet
1199 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1200 for key in auto_trait_diagnostic.keys() {
1201 capture_diagnostic.insert(key.clone());
1204 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1205 capture_diagnostic.sort();
1206 for captures_info in capture_diagnostic {
1207 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1208 let capture_trait_reasons =
1209 if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
1212 FxHashSet::default()
1215 // Check if migration is needed because of drop reorder as a result of that capture
1216 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
1218 // Combine all the reasons of why the root variable should be captured as a result of
1219 // auto trait implementation issues
1220 auto_trait_migration_reasons.extend(capture_trait_reasons.iter().copied());
1222 diagnostics_info.push(MigrationLintNote {
1224 reason: self.compute_2229_migrations_reasons(
1225 capture_trait_reasons,
1226 capture_drop_reorder_reason,
1231 if !diagnostics_info.is_empty() {
1232 need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
1237 self.compute_2229_migrations_reasons(
1238 auto_trait_migration_reasons,
1239 drop_migration_needed,
1244 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1245 /// of a root variable and a list of captured paths starting at this root variable (expressed
1246 /// using list of `Projection` slices), it returns true if there is a path that is not
1247 /// captured starting at this root variable that implements Drop.
1249 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1250 /// path say P and then list of projection slices which represent the different captures moved
1251 /// into the closure starting off of P.
1253 /// This will make more sense with an example:
1256 /// #![feature(capture_disjoint_fields)]
1258 /// struct FancyInteger(i32); // This implements Drop
1260 /// struct Point { x: FancyInteger, y: FancyInteger }
1263 /// struct Wrapper { p: Point, c: Color }
1265 /// fn f(w: Wrapper) {
1267 /// // Closure captures w.p.x and w.c by move.
1274 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1275 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1276 /// therefore Drop ordering would change and we want this function to return true.
1278 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1280 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1283 /// - Ty(place): Type of place
1284 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1286 /// ```ignore (illustrative)
1287 /// (Ty(w), [ &[p, x], &[c] ])
1289 /// // ----------------------------
1292 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1295 /// (Ty(w.p), [ &[x] ]) false
1298 /// // -------------------------------
1301 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1304 /// false NeedsSignificantDrop(Ty(w.p.y))
1310 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1311 /// This implies that the `w.c` is completely captured by the closure.
1312 /// Since drop for this path will be called when the closure is
1313 /// dropped we don't need to migrate for it.
1315 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1316 /// path wasn't captured by the closure. Also note that even
1317 /// though we didn't capture this path, the function visits it,
1318 /// which is kind of the point of this function. We then return
1319 /// if the type of `w.p.y` implements Drop, which in this case is
1322 /// Consider another example:
1324 /// ```ignore (pseudo-rust)
1326 /// impl Drop for X {}
1329 /// impl Drop for Y {}
1333 /// let c = || move(y.0);
1337 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1338 /// return true, because even though all paths starting at `y` are captured, `y` itself
1339 /// implements Drop which will be affected since `y` isn't completely captured.
1340 fn has_significant_drop_outside_of_captures(
1342 closure_def_id: LocalDefId,
1344 base_path_ty: Ty<'tcx>,
1345 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1348 |ty: Ty<'tcx>| ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id));
1350 let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
1351 let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
1352 let ty_params = self.tcx.mk_substs_trait(base_path_ty, &[]);
1354 .type_implements_trait(
1358 self.tcx.param_env(closure_def_id),
1360 .must_apply_modulo_regions()
1363 let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
1365 // If there is a case where no projection is applied on top of current place
1366 // then there must be exactly one capture corresponding to such a case. Note that this
1367 // represents the case of the path being completely captured by the variable.
1369 // eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
1370 // capture `a.b.c`, because that violates min capture.
1371 let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
1373 assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
1375 if is_completely_captured {
1376 // The place is captured entirely, so doesn't matter if needs dtor, it will be drop
1377 // when the closure is dropped.
1381 if captured_by_move_projs.is_empty() {
1382 return needs_drop(base_path_ty);
1385 if is_drop_defined_for_ty {
1386 // If drop is implemented for this type then we need it to be fully captured,
1387 // and we know it is not completely captured because of the previous checks.
1389 // Note that this is a bug in the user code that will be reported by the
1390 // borrow checker, since we can't move out of drop types.
1392 // The bug exists in the user's code pre-migration, and we don't migrate here.
1396 match base_path_ty.kind() {
1398 // - `captured_by_move_projs` is not empty. Therefore we can call
1399 // `captured_by_move_projs.first().unwrap()` safely.
1400 // - All entries in `captured_by_move_projs` have at least one projection.
1401 // Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
1403 // We don't capture derefs in case of move captures, which would have be applied to
1404 // access any further paths.
1405 ty::Adt(def, _) if def.is_box() => unreachable!(),
1406 ty::Ref(..) => unreachable!(),
1407 ty::RawPtr(..) => unreachable!(),
1409 ty::Adt(def, substs) => {
1410 // Multi-variant enums are captured in entirety,
1411 // which would've been handled in the case of single empty slice in `captured_by_move_projs`.
1412 assert_eq!(def.variants().len(), 1);
1414 // Only Field projections can be applied to a non-box Adt.
1416 captured_by_move_projs.iter().all(|projs| matches!(
1417 projs.first().unwrap().kind,
1418 ProjectionKind::Field(..)
1421 def.variants().get(VariantIdx::new(0)).unwrap().fields.iter().enumerate().any(
1423 let paths_using_field = captured_by_move_projs
1425 .filter_map(|projs| {
1426 if let ProjectionKind::Field(field_idx, _) =
1427 projs.first().unwrap().kind
1429 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1436 let after_field_ty = field.ty(self.tcx, substs);
1437 self.has_significant_drop_outside_of_captures(
1447 ty::Tuple(fields) => {
1448 // Only Field projections can be applied to a tuple.
1450 captured_by_move_projs.iter().all(|projs| matches!(
1451 projs.first().unwrap().kind,
1452 ProjectionKind::Field(..)
1456 fields.iter().enumerate().any(|(i, element_ty)| {
1457 let paths_using_field = captured_by_move_projs
1459 .filter_map(|projs| {
1460 if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
1462 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1469 self.has_significant_drop_outside_of_captures(
1478 // Anything else would be completely captured and therefore handled already.
1479 _ => unreachable!(),
1483 fn init_capture_kind_for_place(
1485 place: &Place<'tcx>,
1486 capture_clause: hir::CaptureBy,
1487 ) -> ty::UpvarCapture {
1488 match capture_clause {
1489 // In case of a move closure if the data is accessed through a reference we
1490 // want to capture by ref to allow precise capture using reborrows.
1492 // If the data will be moved out of this place, then the place will be truncated
1493 // at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
1495 hir::CaptureBy::Value if !place.deref_tys().any(Ty::is_ref) => {
1496 ty::UpvarCapture::ByValue
1498 hir::CaptureBy::Value | hir::CaptureBy::Ref => ty::UpvarCapture::ByRef(ty::ImmBorrow),
1502 fn place_for_root_variable(
1504 closure_def_id: LocalDefId,
1505 var_hir_id: hir::HirId,
1507 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
1510 base_ty: self.node_ty(var_hir_id),
1511 base: PlaceBase::Upvar(upvar_id),
1512 projections: Default::default(),
1516 fn should_log_capture_analysis(&self, closure_def_id: LocalDefId) -> bool {
1517 self.tcx.has_attr(closure_def_id.to_def_id(), sym::rustc_capture_analysis)
1520 fn log_capture_analysis_first_pass(
1522 closure_def_id: LocalDefId,
1523 capture_information: &InferredCaptureInformation<'tcx>,
1526 if self.should_log_capture_analysis(closure_def_id) {
1528 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
1529 for (place, capture_info) in capture_information {
1530 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
1531 let output_str = format!("Capturing {capture_str}");
1534 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
1535 diag.span_note(span, &output_str);
1541 fn log_closure_min_capture_info(&self, closure_def_id: LocalDefId, closure_span: Span) {
1542 if self.should_log_capture_analysis(closure_def_id) {
1543 if let Some(min_captures) =
1544 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
1547 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
1549 for (_, min_captures_for_var) in min_captures {
1550 for capture in min_captures_for_var {
1551 let place = &capture.place;
1552 let capture_info = &capture.info;
1555 construct_capture_info_string(self.tcx, place, capture_info);
1556 let output_str = format!("Min Capture {capture_str}");
1558 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
1559 let path_span = capture_info
1561 .map_or(closure_span, |e| self.tcx.hir().span(e));
1562 let capture_kind_span = capture_info
1563 .capture_kind_expr_id
1564 .map_or(closure_span, |e| self.tcx.hir().span(e));
1566 let mut multi_span: MultiSpan =
1567 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
1569 let capture_kind_label =
1570 construct_capture_kind_reason_string(self.tcx, place, capture_info);
1571 let path_label = construct_path_string(self.tcx, place);
1573 multi_span.push_span_label(path_span, path_label);
1574 multi_span.push_span_label(capture_kind_span, capture_kind_label);
1576 diag.span_note(multi_span, &output_str);
1578 let span = capture_info
1580 .map_or(closure_span, |e| self.tcx.hir().span(e));
1582 diag.span_note(span, &output_str);
1591 /// A captured place is mutable if
1592 /// 1. Projections don't include a Deref of an immut-borrow, **and**
1593 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
1594 fn determine_capture_mutability(
1596 typeck_results: &'a TypeckResults<'tcx>,
1597 place: &Place<'tcx>,
1598 ) -> hir::Mutability {
1599 let var_hir_id = match place.base {
1600 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
1601 _ => unreachable!(),
1604 let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
1606 let mut is_mutbl = match bm {
1607 ty::BindByValue(mutability) => mutability,
1608 ty::BindByReference(_) => hir::Mutability::Not,
1611 for pointer_ty in place.deref_tys() {
1612 match pointer_ty.kind() {
1613 // We don't capture derefs of raw ptrs
1614 ty::RawPtr(_) => unreachable!(),
1616 // Dereferencing a mut-ref allows us to mut the Place if we don't deref
1617 // an immut-ref after on top of this.
1618 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
1620 // The place isn't mutable once we dereference an immutable reference.
1621 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
1623 // Dereferencing a box doesn't change mutability
1624 ty::Adt(def, ..) if def.is_box() => {}
1626 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
1634 /// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
1635 /// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
1636 fn restrict_repr_packed_field_ref_capture<'tcx>(
1638 param_env: ty::ParamEnv<'tcx>,
1639 mut place: Place<'tcx>,
1640 mut curr_borrow_kind: ty::UpvarCapture,
1641 ) -> (Place<'tcx>, ty::UpvarCapture) {
1642 let pos = place.projections.iter().enumerate().position(|(i, p)| {
1643 let ty = place.ty_before_projection(i);
1645 // Return true for fields of packed structs, unless those fields have alignment 1.
1647 ProjectionKind::Field(..) => match ty.kind() {
1648 ty::Adt(def, _) if def.repr().packed() => {
1649 // We erase regions here because they cannot be hashed
1650 match tcx.layout_of(param_env.and(tcx.erase_regions(p.ty))) {
1651 Ok(layout) if layout.align.abi.bytes() == 1 => {
1652 // if the alignment is 1, the type can't be further
1655 "restrict_repr_packed_field_ref_capture: ({:?}) - align = 1",
1661 debug!("restrict_repr_packed_field_ref_capture: ({:?}) - true", place);
1673 if let Some(pos) = pos {
1674 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
1677 (place, curr_borrow_kind)
1680 /// Returns a Ty that applies the specified capture kind on the provided capture Ty
1681 fn apply_capture_kind_on_capture_ty<'tcx>(
1684 capture_kind: UpvarCapture,
1685 region: Option<ty::Region<'tcx>>,
1687 match capture_kind {
1688 ty::UpvarCapture::ByValue => ty,
1689 ty::UpvarCapture::ByRef(kind) => {
1690 tcx.mk_ref(region.unwrap(), ty::TypeAndMut { ty: ty, mutbl: kind.to_mutbl_lossy() })
1695 /// Returns the Span of where the value with the provided HirId would be dropped
1696 fn drop_location_span<'tcx>(tcx: TyCtxt<'tcx>, hir_id: hir::HirId) -> Span {
1697 let owner_id = tcx.hir().get_enclosing_scope(hir_id).unwrap();
1699 let owner_node = tcx.hir().get(owner_id);
1700 let owner_span = match owner_node {
1701 hir::Node::Item(item) => match item.kind {
1702 hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
1704 bug!("Drop location span error: need to handle more ItemKind '{:?}'", item.kind);
1707 hir::Node::Block(block) => tcx.hir().span(block.hir_id),
1708 hir::Node::TraitItem(item) => tcx.hir().span(item.hir_id()),
1709 hir::Node::ImplItem(item) => tcx.hir().span(item.hir_id()),
1711 bug!("Drop location span error: need to handle more Node '{:?}'", owner_node);
1714 tcx.sess.source_map().end_point(owner_span)
1717 struct InferBorrowKind<'a, 'tcx> {
1718 fcx: &'a FnCtxt<'a, 'tcx>,
1720 // The def-id of the closure whose kind and upvar accesses are being inferred.
1721 closure_def_id: LocalDefId,
1723 /// For each Place that is captured by the closure, we track the minimal kind of
1724 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1726 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1727 /// s.str2 via a MutableBorrow
1730 /// struct SomeStruct { str1: String, str2: String };
1732 /// // Assume that the HirId for the variable definition is `V1`
1733 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") };
1735 /// let fix_s = |new_s2| {
1736 /// // Assume that the HirId for the expression `s.str1` is `E1`
1737 /// println!("Updating SomeStruct with str1={0}", s.str1);
1738 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1739 /// s.str2 = new_s2;
1743 /// For closure `fix_s`, (at a high level) the map contains
1745 /// ```ignore (illustrative)
1746 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1747 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1749 capture_information: InferredCaptureInformation<'tcx>,
1750 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1753 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1756 place: &PlaceWithHirId<'tcx>,
1757 cause: FakeReadCause,
1758 diag_expr_id: hir::HirId,
1760 let PlaceBase::Upvar(_) = place.place.base else { return };
1762 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1763 // such as deref of a raw pointer.
1764 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1766 let (place, _) = restrict_capture_precision(place.place.clone(), dummy_capture_kind);
1768 let (place, _) = restrict_repr_packed_field_ref_capture(
1774 self.fake_reads.push((place, cause, diag_expr_id));
1777 #[instrument(skip(self), level = "debug")]
1778 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1779 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1780 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1782 self.capture_information.push((
1783 place_with_id.place.clone(),
1785 capture_kind_expr_id: Some(diag_expr_id),
1786 path_expr_id: Some(diag_expr_id),
1787 capture_kind: ty::UpvarCapture::ByValue,
1792 #[instrument(skip(self), level = "debug")]
1795 place_with_id: &PlaceWithHirId<'tcx>,
1796 diag_expr_id: hir::HirId,
1799 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1800 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1802 // The region here will get discarded/ignored
1803 let capture_kind = ty::UpvarCapture::ByRef(bk);
1805 // We only want repr packed restriction to be applied to reading references into a packed
1806 // struct, and not when the data is being moved. Therefore we call this method here instead
1807 // of in `restrict_capture_precision`.
1808 let (place, mut capture_kind) = restrict_repr_packed_field_ref_capture(
1811 place_with_id.place.clone(),
1815 // Raw pointers don't inherit mutability
1816 if place_with_id.place.deref_tys().any(Ty::is_unsafe_ptr) {
1817 capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1820 self.capture_information.push((
1823 capture_kind_expr_id: Some(diag_expr_id),
1824 path_expr_id: Some(diag_expr_id),
1830 #[instrument(skip(self), level = "debug")]
1831 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1832 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1836 /// Rust doesn't permit moving fields out of a type that implements drop
1837 fn restrict_precision_for_drop_types<'a, 'tcx>(
1838 fcx: &'a FnCtxt<'a, 'tcx>,
1839 mut place: Place<'tcx>,
1840 mut curr_mode: ty::UpvarCapture,
1842 ) -> (Place<'tcx>, ty::UpvarCapture) {
1843 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1845 if let (false, UpvarCapture::ByValue) = (is_copy_type, curr_mode) {
1846 for i in 0..place.projections.len() {
1847 match place.ty_before_projection(i).kind() {
1848 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1849 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1860 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
1861 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
1862 /// them completely.
1863 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
1864 fn restrict_precision_for_unsafe<'tcx>(
1865 mut place: Place<'tcx>,
1866 mut curr_mode: ty::UpvarCapture,
1867 ) -> (Place<'tcx>, ty::UpvarCapture) {
1868 if place.base_ty.is_unsafe_ptr() {
1869 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1872 if place.base_ty.is_union() {
1873 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1876 for (i, proj) in place.projections.iter().enumerate() {
1877 if proj.ty.is_unsafe_ptr() {
1878 // Don't apply any projections on top of an unsafe ptr.
1879 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1883 if proj.ty.is_union() {
1884 // Don't capture precise fields of a union.
1885 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1893 /// Truncate projections so that following rules are obeyed by the captured `place`:
1894 /// - No Index projections are captured, since arrays are captured completely.
1895 /// - No unsafe block is required to capture `place`
1896 /// Returns the truncated place and updated capture mode.
1897 fn restrict_capture_precision<'tcx>(
1899 curr_mode: ty::UpvarCapture,
1900 ) -> (Place<'tcx>, ty::UpvarCapture) {
1901 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
1903 if place.projections.is_empty() {
1904 // Nothing to do here
1905 return (place, curr_mode);
1908 for (i, proj) in place.projections.iter().enumerate() {
1910 ProjectionKind::Index => {
1911 // Arrays are completely captured, so we drop Index projections
1912 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1913 return (place, curr_mode);
1915 ProjectionKind::Deref => {}
1916 ProjectionKind::Field(..) => {} // ignore
1917 ProjectionKind::Subslice => {} // We never capture this
1924 /// Truncate deref of any reference.
1925 fn adjust_for_move_closure<'tcx>(
1926 mut place: Place<'tcx>,
1927 mut kind: ty::UpvarCapture,
1928 ) -> (Place<'tcx>, ty::UpvarCapture) {
1929 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1931 if let Some(idx) = first_deref {
1932 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1935 (place, ty::UpvarCapture::ByValue)
1938 /// Adjust closure capture just that if taking ownership of data, only move data
1939 /// from enclosing stack frame.
1940 fn adjust_for_non_move_closure<'tcx>(
1941 mut place: Place<'tcx>,
1942 mut kind: ty::UpvarCapture,
1943 ) -> (Place<'tcx>, ty::UpvarCapture) {
1944 let contains_deref =
1945 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1948 ty::UpvarCapture::ByValue => {
1949 if let Some(idx) = contains_deref {
1950 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1954 ty::UpvarCapture::ByRef(..) => {}
1960 fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1961 let variable_name = match place.base {
1962 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
1963 _ => bug!("Capture_information should only contain upvars"),
1966 let mut projections_str = String::new();
1967 for (i, item) in place.projections.iter().enumerate() {
1968 let proj = match item.kind {
1969 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
1970 ProjectionKind::Deref => String::from("Deref"),
1971 ProjectionKind::Index => String::from("Index"),
1972 ProjectionKind::Subslice => String::from("Subslice"),
1975 projections_str.push(',');
1977 projections_str.push_str(proj.as_str());
1980 format!("{variable_name}[{projections_str}]")
1983 fn construct_capture_kind_reason_string<'tcx>(
1985 place: &Place<'tcx>,
1986 capture_info: &ty::CaptureInfo,
1988 let place_str = construct_place_string(tcx, place);
1990 let capture_kind_str = match capture_info.capture_kind {
1991 ty::UpvarCapture::ByValue => "ByValue".into(),
1992 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
1995 format!("{place_str} captured as {capture_kind_str} here")
1998 fn construct_path_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1999 let place_str = construct_place_string(tcx, place);
2001 format!("{place_str} used here")
2004 fn construct_capture_info_string<'tcx>(
2006 place: &Place<'tcx>,
2007 capture_info: &ty::CaptureInfo,
2009 let place_str = construct_place_string(tcx, place);
2011 let capture_kind_str = match capture_info.capture_kind {
2012 ty::UpvarCapture::ByValue => "ByValue".into(),
2013 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
2015 format!("{place_str} -> {capture_kind_str}")
2018 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2019 tcx.hir().name(var_hir_id)
2022 #[instrument(level = "debug", skip(tcx))]
2023 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2025 closure_id: hir::HirId,
2028 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2030 !matches!(level, lint::Level::Allow)
2033 /// Return a two string tuple (s1, s2)
2034 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2035 /// - s2: Comma separated names of the variables being migrated.
2036 fn migration_suggestion_for_2229(
2038 need_migrations: &[NeededMigration],
2039 ) -> (String, String) {
2040 let need_migrations_variables = need_migrations
2042 .map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
2043 .collect::<Vec<_>>();
2045 let migration_ref_concat =
2046 need_migrations_variables.iter().map(|v| format!("&{v}")).collect::<Vec<_>>().join(", ");
2048 let migration_string = if 1 == need_migrations.len() {
2049 format!("let _ = {migration_ref_concat}")
2051 format!("let _ = ({migration_ref_concat})")
2054 let migrated_variables_concat =
2055 need_migrations_variables.iter().map(|v| format!("`{v}`")).collect::<Vec<_>>().join(", ");
2057 (migration_string, migrated_variables_concat)
2060 /// Helper function to determine if we need to escalate CaptureKind from
2061 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2062 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2064 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2065 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2067 /// It is the caller's duty to figure out which path_expr_id to use.
2069 /// If both the CaptureKind and Expression are considered to be equivalent,
2070 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to prioritize
2071 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2072 /// in the closure. This can be achieved simply by calling
2073 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2074 /// expressions that occur earlier in the closure body than the current expression are processed before.
2075 /// Consider the following example
2077 /// struct Point { x: i32, y: i32 }
2078 /// let mut p = Point { x: 10, y: 10 };
2086 /// p.x += 10; // E2
2090 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2091 /// and both have an expression associated, however for diagnostics we prefer reporting
2092 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2093 /// would've already handled `E1`, and have an existing capture_information for it.
2094 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2095 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2096 fn determine_capture_info(
2097 capture_info_a: ty::CaptureInfo,
2098 capture_info_b: ty::CaptureInfo,
2099 ) -> ty::CaptureInfo {
2100 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2102 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2103 (ty::UpvarCapture::ByValue, ty::UpvarCapture::ByValue) => true,
2104 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => ref_a == ref_b,
2105 (ty::UpvarCapture::ByValue, _) | (ty::UpvarCapture::ByRef(_), _) => false,
2108 if eq_capture_kind {
2109 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2110 (Some(_), _) | (None, None) => capture_info_a,
2111 (None, Some(_)) => capture_info_b,
2114 // We select the CaptureKind which ranks higher based the following priority order:
2115 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2116 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2117 (ty::UpvarCapture::ByValue, _) => capture_info_a,
2118 (_, ty::UpvarCapture::ByValue) => capture_info_b,
2119 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2120 match (ref_a, ref_b) {
2122 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2123 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2126 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2127 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2129 (ty::ImmBorrow, ty::ImmBorrow)
2130 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2131 | (ty::MutBorrow, ty::MutBorrow) => {
2132 bug!("Expected unequal capture kinds");
2140 /// Truncates `place` to have up to `len` projections.
2141 /// `curr_mode` is the current required capture kind for the place.
2142 /// Returns the truncated `place` and the updated required capture kind.
2144 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2145 /// contained `Deref` of `&mut`.
2146 fn truncate_place_to_len_and_update_capture_kind<'tcx>(
2147 place: &mut Place<'tcx>,
2148 curr_mode: &mut ty::UpvarCapture,
2151 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2153 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2155 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2156 // we don't need to worry about that case here.
2158 ty::UpvarCapture::ByRef(ty::BorrowKind::MutBorrow) => {
2159 for i in len..place.projections.len() {
2160 if place.projections[i].kind == ProjectionKind::Deref
2161 && is_mut_ref(place.ty_before_projection(i))
2163 *curr_mode = ty::UpvarCapture::ByRef(ty::BorrowKind::UniqueImmBorrow);
2169 ty::UpvarCapture::ByRef(..) => {}
2170 ty::UpvarCapture::ByValue => {}
2173 place.projections.truncate(len);
2176 /// Determines the Ancestry relationship of Place A relative to Place B
2178 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2179 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2180 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2181 fn determine_place_ancestry_relation<'tcx>(
2182 place_a: &Place<'tcx>,
2183 place_b: &Place<'tcx>,
2184 ) -> PlaceAncestryRelation {
2185 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2186 if place_a.base != place_b.base {
2187 return PlaceAncestryRelation::Divergent;
2190 // Assume of length of projections_a = n
2191 let projections_a = &place_a.projections;
2193 // Assume of length of projections_b = m
2194 let projections_b = &place_b.projections;
2196 let same_initial_projections =
2197 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2199 if same_initial_projections {
2200 use std::cmp::Ordering;
2202 // First min(n, m) projections are the same
2203 // Select Ancestor/Descendant
2204 match projections_b.len().cmp(&projections_a.len()) {
2205 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2206 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2207 Ordering::Less => PlaceAncestryRelation::Descendant,
2210 PlaceAncestryRelation::Divergent
2214 /// Reduces the precision of the captured place when the precision doesn't yield any benefit from
2215 /// borrow checking perspective, allowing us to save us on the size of the capture.
2218 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2219 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2220 /// rightmost deref of the capture if the deref is applied to a shared ref.
2222 /// Reason we only drop the last deref is because of the following edge case:
2225 /// # struct A { field_of_a: Box<i32> }
2227 /// # struct C<'a>(&'a i32);
2228 /// struct MyStruct<'a> {
2234 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2235 /// || drop(&*m.a.field_of_a)
2236 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2238 /// // If we capture `m`, then the closure no longer outlives `'static'
2239 /// // it is constrained to `'a`
2242 fn truncate_capture_for_optimization<'tcx>(
2243 mut place: Place<'tcx>,
2244 mut curr_mode: ty::UpvarCapture,
2245 ) -> (Place<'tcx>, ty::UpvarCapture) {
2246 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2248 // Find the right-most deref (if any). All the projections that come after this
2249 // are fields or other "in-place pointer adjustments"; these refer therefore to
2250 // data owned by whatever pointer is being dereferenced here.
2251 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2254 // If that pointer is a shared reference, then we don't need those fields.
2255 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2256 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2258 None | Some(_) => {}
2264 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2265 /// user is using Rust Edition 2021 or higher.
2267 /// `span` is the span of the closure.
2268 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2269 // We use span here to ensure that if the closure was generated by a macro with a different
2271 tcx.features().capture_disjoint_fields || span.rust_2021()