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::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, 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 tuple 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.
452 /// struct Point { x: i32, y: i32 }
454 /// let s = String::from("s"); // hir_id_s
455 /// let mut p = Point { x: 2, y: -2 }; // his_id_p
457 /// println!("{s:?}"); // L1
459 /// println!("{}" , p.y); // L3
460 /// println!("{p:?}"); // L4
464 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
465 /// the lines L1..5 respectively.
467 /// InferBorrowKind results in a structure like this:
469 /// ```ignore (illustrative)
471 /// Place(base: hir_id_s, projections: [], ....) -> {
472 /// capture_kind_expr: hir_id_L5,
473 /// path_expr_id: hir_id_L5,
474 /// capture_kind: ByValue
476 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
477 /// capture_kind_expr: hir_id_L2,
478 /// path_expr_id: hir_id_L2,
479 /// capture_kind: ByValue
481 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
482 /// capture_kind_expr: hir_id_L3,
483 /// path_expr_id: hir_id_L3,
484 /// capture_kind: ByValue
486 /// Place(base: hir_id_p, projections: [], ...) -> {
487 /// capture_kind_expr: hir_id_L4,
488 /// path_expr_id: hir_id_L4,
489 /// capture_kind: ByValue
493 /// After the min capture analysis, we get:
494 /// ```ignore (illustrative)
497 /// Place(base: hir_id_s, projections: [], ....) -> {
498 /// capture_kind_expr: hir_id_L5,
499 /// path_expr_id: hir_id_L5,
500 /// capture_kind: ByValue
504 /// Place(base: hir_id_p, projections: [], ...) -> {
505 /// capture_kind_expr: hir_id_L2,
506 /// path_expr_id: hir_id_L4,
507 /// capture_kind: ByValue
511 fn compute_min_captures(
513 closure_def_id: DefId,
514 capture_information: InferredCaptureInformation<'tcx>,
517 if capture_information.is_empty() {
521 let mut typeck_results = self.typeck_results.borrow_mut();
523 let mut root_var_min_capture_list =
524 typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
526 for (mut place, capture_info) in capture_information.into_iter() {
527 let var_hir_id = match place.base {
528 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
529 base => bug!("Expected upvar, found={:?}", base),
532 let Some(min_cap_list) = root_var_min_capture_list.get_mut(&var_hir_id) else {
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);
544 // Go through each entry in the current list of min_captures
545 // - if ancestor is found, update it's capture kind to account for current place's
546 // capture information.
548 // - if descendant is found, remove it from the list, and update the current place's
549 // capture information to account for the descendant's capture kind.
551 // We can never be in a case where the list contains both an ancestor and a descendant
552 // Also there can only be ancestor but in case of descendants there might be
555 let mut descendant_found = false;
556 let mut updated_capture_info = capture_info;
557 min_cap_list.retain(|possible_descendant| {
558 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
559 // current place is ancestor of possible_descendant
560 PlaceAncestryRelation::Ancestor => {
561 descendant_found = true;
563 let mut possible_descendant = possible_descendant.clone();
564 let backup_path_expr_id = updated_capture_info.path_expr_id;
566 // Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
567 // possible change in capture mode.
568 truncate_place_to_len_and_update_capture_kind(
569 &mut possible_descendant.place,
570 &mut possible_descendant.info.capture_kind,
571 place.projections.len(),
574 updated_capture_info =
575 determine_capture_info(updated_capture_info, possible_descendant.info);
577 // we need to keep the ancestor's `path_expr_id`
578 updated_capture_info.path_expr_id = backup_path_expr_id;
586 let mut ancestor_found = false;
587 if !descendant_found {
588 for possible_ancestor in min_cap_list.iter_mut() {
589 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
590 PlaceAncestryRelation::SamePlace => {
591 ancestor_found = true;
592 possible_ancestor.info = determine_capture_info(
593 possible_ancestor.info,
594 updated_capture_info,
597 // Only one related place will be in the list.
600 // current place is descendant of possible_ancestor
601 PlaceAncestryRelation::Descendant => {
602 ancestor_found = true;
603 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
605 // Truncate the descendant (current place) to be same as the ancestor to handle any
606 // possible change in capture mode.
607 truncate_place_to_len_and_update_capture_kind(
609 &mut updated_capture_info.capture_kind,
610 possible_ancestor.place.projections.len(),
613 possible_ancestor.info = determine_capture_info(
614 possible_ancestor.info,
615 updated_capture_info,
618 // we need to keep the ancestor's `path_expr_id`
619 possible_ancestor.info.path_expr_id = backup_path_expr_id;
621 // Only one related place will be in the list.
629 // Only need to insert when we don't have an ancestor in the existing min capture list
631 let mutability = self.determine_capture_mutability(&typeck_results, &place);
632 let captured_place = ty::CapturedPlace {
634 info: updated_capture_info,
638 min_cap_list.push(captured_place);
642 // For each capture that is determined to be captured by ref, add region info.
643 for (_, captures) in &mut root_var_min_capture_list {
644 for capture in captures {
645 match capture.info.capture_kind {
646 ty::UpvarCapture::ByRef(_) => {
647 let PlaceBase::Upvar(upvar_id) = capture.place.base else { bug!("expected upvar") };
648 let origin = UpvarRegion(upvar_id, closure_span);
649 let upvar_region = self.next_region_var(origin);
650 capture.region = Some(upvar_region);
658 "For closure={:?}, min_captures before sorting={:?}",
659 closure_def_id, root_var_min_capture_list
662 // Now that we have the minimized list of captures, sort the captures by field id.
663 // This causes the closure to capture the upvars in the same order as the fields are
664 // declared which is also the drop order. Thus, in situations where we capture all the
665 // fields of some type, the observable drop order will remain the same as it previously
666 // was even though we're dropping each capture individually.
667 // See https://github.com/rust-lang/project-rfc-2229/issues/42 and
668 // `src/test/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
669 for (_, captures) in &mut root_var_min_capture_list {
670 captures.sort_by(|capture1, capture2| {
671 for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
672 // We do not need to look at the `Projection.ty` fields here because at each
673 // step of the iteration, the projections will either be the same and therefore
674 // the types must be as well or the current projection will be different and
675 // we will return the result of comparing the field indexes.
676 match (p1.kind, p2.kind) {
677 // Paths are the same, continue to next loop.
678 (ProjectionKind::Deref, ProjectionKind::Deref) => {}
679 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
682 // Fields are different, compare them.
683 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
687 // We should have either a pair of `Deref`s or a pair of `Field`s.
688 // Anything else is a bug.
690 l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
691 r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
693 "ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
698 l @ (ProjectionKind::Index
699 | ProjectionKind::Subslice
700 | ProjectionKind::Deref
701 | ProjectionKind::Field(..)),
702 r @ (ProjectionKind::Index
703 | ProjectionKind::Subslice
704 | ProjectionKind::Deref
705 | ProjectionKind::Field(..)),
707 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
715 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
722 "For closure={:?}, min_captures after sorting={:#?}",
723 closure_def_id, root_var_min_capture_list
725 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
728 /// Perform the migration analysis for RFC 2229, and emit lint
729 /// `disjoint_capture_drop_reorder` if needed.
730 fn perform_2229_migration_anaysis(
732 closure_def_id: DefId,
733 body_id: hir::BodyId,
734 capture_clause: hir::CaptureBy,
737 let (need_migrations, reasons) = self.compute_2229_migrations(
741 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
744 if !need_migrations.is_empty() {
745 let (migration_string, migrated_variables_concat) =
746 migration_suggestion_for_2229(self.tcx, &need_migrations);
748 let local_def_id = closure_def_id.expect_local();
749 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
750 let closure_span = self.tcx.hir().span(closure_hir_id);
751 let closure_head_span = self.tcx.sess.source_map().guess_head_span(closure_span);
752 self.tcx.struct_span_lint_hir(
753 lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
757 let mut diagnostics_builder = lint.build(
758 &reasons.migration_message(),
760 for NeededMigration { var_hir_id, diagnostics_info } in &need_migrations {
761 // Labels all the usage of the captured variable and why they are responsible
762 // for migration being needed
763 for lint_note in diagnostics_info.iter() {
764 match &lint_note.captures_info {
765 UpvarMigrationInfo::CapturingPrecise { source_expr: Some(capture_expr_id), var_name: captured_name } => {
766 let cause_span = self.tcx.hir().span(*capture_expr_id);
767 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
768 self.tcx.hir().name(*var_hir_id),
772 UpvarMigrationInfo::CapturingNothing { use_span } => {
773 diagnostics_builder.span_label(*use_span, format!("in Rust 2018, this causes the closure to capture `{}`, but in Rust 2021, it has no effect",
774 self.tcx.hir().name(*var_hir_id),
781 // Add a label pointing to where a captured variable affected by drop order
783 if lint_note.reason.drop_order {
784 let drop_location_span = drop_location_span(self.tcx, closure_hir_id);
786 match &lint_note.captures_info {
787 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
788 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",
789 self.tcx.hir().name(*var_hir_id),
793 UpvarMigrationInfo::CapturingNothing { use_span: _ } => {
794 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",
795 v = self.tcx.hir().name(*var_hir_id),
801 // Add a label explaining why a closure no longer implements a trait
802 for &missing_trait in &lint_note.reason.auto_traits {
803 // not capturing something anymore cannot cause a trait to fail to be implemented:
804 match &lint_note.captures_info {
805 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
806 let var_name = self.tcx.hir().name(*var_hir_id);
807 diagnostics_builder.span_label(closure_head_span, format!("\
808 in Rust 2018, this closure implements {missing_trait} \
809 as `{var_name}` implements {missing_trait}, but in Rust 2021, \
810 this closure will no longer implement {missing_trait} \
811 because `{var_name}` is not fully captured \
812 and `{captured_name}` does not implement {missing_trait}"));
815 // Cannot happen: if we don't capture a variable, we impl strictly more traits
816 UpvarMigrationInfo::CapturingNothing { use_span } => span_bug!(*use_span, "missing trait from not capturing something"),
821 diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
823 let diagnostic_msg = format!(
824 "add a dummy let to cause {} to be fully captured",
825 migrated_variables_concat
828 let mut closure_body_span = {
829 // If the body was entirely expanded from a macro
830 // invocation, i.e. the body is not contained inside the
831 // closure span, then we walk up the expansion until we
832 // find the span before the expansion.
833 let s = self.tcx.hir().span(body_id.hir_id);
834 s.find_ancestor_inside(closure_span).unwrap_or(s)
837 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
838 if s.starts_with('$') {
839 // Looks like a macro fragment. Try to find the real block.
840 if let Some(hir::Node::Expr(&hir::Expr {
841 kind: hir::ExprKind::Block(block, ..), ..
842 })) = self.tcx.hir().find(body_id.hir_id) {
843 // If the body is a block (with `{..}`), we use the span of that block.
844 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
845 // Since we know it's a block, we know we can insert the `let _ = ..` without
846 // breaking the macro syntax.
847 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
848 closure_body_span = block.span;
854 let mut lines = s.lines();
855 let line1 = lines.next().unwrap_or_default();
857 if line1.trim_end() == "{" {
858 // This is a multi-line closure with just a `{` on the first line,
859 // so we put the `let` on its own line.
860 // We take the indentation from the next non-empty line.
861 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
862 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
863 diagnostics_builder.span_suggestion(
864 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
866 format!("\n{indent}{migration_string};"),
867 Applicability::MachineApplicable,
869 } else if line1.starts_with('{') {
870 // This is a closure with its body wrapped in
871 // braces, but with more than just the opening
872 // brace on the first line. We put the `let`
873 // directly after the `{`.
874 diagnostics_builder.span_suggestion(
875 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
877 format!(" {migration_string};"),
878 Applicability::MachineApplicable,
881 // This is a closure without braces around the body.
882 // We add braces to add the `let` before the body.
883 diagnostics_builder.multipart_suggestion(
886 (closure_body_span.shrink_to_lo(), format!("{{ {migration_string}; ")),
887 (closure_body_span.shrink_to_hi(), " }".to_string()),
889 Applicability::MachineApplicable
893 diagnostics_builder.span_suggestion(
897 Applicability::HasPlaceholders
901 diagnostics_builder.emit();
907 /// Combines all the reasons for 2229 migrations
908 fn compute_2229_migrations_reasons(
910 auto_trait_reasons: FxHashSet<&'static str>,
912 ) -> MigrationWarningReason {
913 let mut reasons = MigrationWarningReason::default();
915 reasons.auto_traits.extend(auto_trait_reasons);
916 reasons.drop_order = drop_order;
921 /// Figures out the list of root variables (and their types) that aren't completely
922 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
923 /// differ between the root variable and the captured paths.
925 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
926 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
927 fn compute_2229_migrations_for_trait(
929 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
930 var_hir_id: hir::HirId,
931 closure_clause: hir::CaptureBy,
932 ) -> Option<FxHashMap<UpvarMigrationInfo, FxHashSet<&'static str>>> {
933 let auto_traits_def_id = vec![
934 self.tcx.lang_items().clone_trait(),
935 self.tcx.lang_items().sync_trait(),
936 self.tcx.get_diagnostic_item(sym::Send),
937 self.tcx.lang_items().unpin_trait(),
938 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
939 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
941 const AUTO_TRAITS: [&str; 6] =
942 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
944 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
946 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
948 let ty = match closure_clause {
949 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
950 hir::CaptureBy::Ref => {
951 // For non move closure the capture kind is the max capture kind of all captures
952 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
953 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
954 for capture in root_var_min_capture_list.iter() {
955 max_capture_info = determine_capture_info(max_capture_info, capture.info);
958 apply_capture_kind_on_capture_ty(
961 max_capture_info.capture_kind,
962 Some(self.tcx.lifetimes.re_erased),
967 let mut obligations_should_hold = Vec::new();
968 // Checks if a root variable implements any of the auto traits
969 for check_trait in auto_traits_def_id.iter() {
970 obligations_should_hold.push(
974 .type_implements_trait(
977 self.tcx.mk_substs_trait(ty, &[]),
980 .must_apply_modulo_regions()
986 let mut problematic_captures = FxHashMap::default();
987 // Check whether captured fields also implement the trait
988 for capture in root_var_min_capture_list.iter() {
989 let ty = apply_capture_kind_on_capture_ty(
992 capture.info.capture_kind,
993 Some(self.tcx.lifetimes.re_erased),
996 // Checks if a capture implements any of the auto traits
997 let mut obligations_holds_for_capture = Vec::new();
998 for check_trait in auto_traits_def_id.iter() {
999 obligations_holds_for_capture.push(
1001 .map(|check_trait| {
1003 .type_implements_trait(
1006 self.tcx.mk_substs_trait(ty, &[]),
1009 .must_apply_modulo_regions()
1015 let mut capture_problems = FxHashSet::default();
1017 // Checks if for any of the auto traits, one or more trait is implemented
1018 // by the root variable but not by the capture
1019 for (idx, _) in obligations_should_hold.iter().enumerate() {
1020 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
1021 capture_problems.insert(AUTO_TRAITS[idx]);
1025 if !capture_problems.is_empty() {
1026 problematic_captures.insert(
1027 UpvarMigrationInfo::CapturingPrecise {
1028 source_expr: capture.info.path_expr_id,
1029 var_name: capture.to_string(self.tcx),
1035 if !problematic_captures.is_empty() {
1036 return Some(problematic_captures);
1041 /// Figures out the list of root variables (and their types) that aren't completely
1042 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
1043 /// some path starting at that root variable **might** be affected.
1045 /// The output list would include a root variable if:
1046 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1047 /// enabled, **and**
1048 /// - It wasn't completely captured by the closure, **and**
1049 /// - One of the paths starting at this root variable, that is not captured needs Drop.
1051 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
1052 /// are no significant drops than None is returned
1053 #[instrument(level = "debug", skip(self))]
1054 fn compute_2229_migrations_for_drop(
1056 closure_def_id: DefId,
1058 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1059 closure_clause: hir::CaptureBy,
1060 var_hir_id: hir::HirId,
1061 ) -> Option<FxHashSet<UpvarMigrationInfo>> {
1062 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
1064 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local())) {
1065 debug!("does not have significant drop");
1069 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1070 // The upvar is mentioned within the closure but no path starting from it is
1071 // used. This occurs when you have (e.g.)
1074 // let x = move || {
1078 debug!("no path starting from it is used");
1081 match closure_clause {
1082 // Only migrate if closure is a move closure
1083 hir::CaptureBy::Value => {
1084 let mut diagnostics_info = FxHashSet::default();
1085 let upvars = self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
1086 let upvar = upvars[&var_hir_id];
1087 diagnostics_info.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
1088 return Some(diagnostics_info);
1090 hir::CaptureBy::Ref => {}
1095 debug!(?root_var_min_capture_list);
1097 let mut projections_list = Vec::new();
1098 let mut diagnostics_info = FxHashSet::default();
1100 for captured_place in root_var_min_capture_list.iter() {
1101 match captured_place.info.capture_kind {
1102 // Only care about captures that are moved into the closure
1103 ty::UpvarCapture::ByValue => {
1104 projections_list.push(captured_place.place.projections.as_slice());
1105 diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
1106 source_expr: captured_place.info.path_expr_id,
1107 var_name: captured_place.to_string(self.tcx),
1110 ty::UpvarCapture::ByRef(..) => {}
1114 debug!(?projections_list);
1115 debug!(?diagnostics_info);
1117 let is_moved = !projections_list.is_empty();
1120 let is_not_completely_captured =
1121 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1122 debug!(?is_not_completely_captured);
1125 && is_not_completely_captured
1126 && self.has_significant_drop_outside_of_captures(
1133 return Some(diagnostics_info);
1139 /// Figures out the list of root variables (and their types) that aren't completely
1140 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1141 /// order of some path starting at that root variable **might** be affected or auto-traits
1142 /// differ between the root variable and the captured paths.
1144 /// The output list would include a root variable if:
1145 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1146 /// enabled, **and**
1147 /// - It wasn't completely captured by the closure, **and**
1148 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1149 /// - One of the paths captured does not implement all the auto-traits its root variable
1152 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1153 /// containing the reason why root variables whose HirId is contained in the vector should
1155 #[instrument(level = "debug", skip(self))]
1156 fn compute_2229_migrations(
1158 closure_def_id: DefId,
1160 closure_clause: hir::CaptureBy,
1161 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1162 ) -> (Vec<NeededMigration>, MigrationWarningReason) {
1163 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1164 return (Vec::new(), MigrationWarningReason::default());
1167 let mut need_migrations = Vec::new();
1168 let mut auto_trait_migration_reasons = FxHashSet::default();
1169 let mut drop_migration_needed = false;
1171 // Perform auto-trait analysis
1172 for (&var_hir_id, _) in upvars.iter() {
1173 let mut diagnostics_info = Vec::new();
1175 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1176 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1180 FxHashMap::default()
1183 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1184 .compute_2229_migrations_for_drop(
1191 drop_migration_needed = true;
1194 FxHashSet::default()
1197 // Combine all the captures responsible for needing migrations into one HashSet
1198 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1199 for key in auto_trait_diagnostic.keys() {
1200 capture_diagnostic.insert(key.clone());
1203 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1204 capture_diagnostic.sort();
1205 for captures_info in capture_diagnostic {
1206 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1207 let capture_trait_reasons =
1208 if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
1211 FxHashSet::default()
1214 // Check if migration is needed because of drop reorder as a result of that capture
1215 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
1217 // Combine all the reasons of why the root variable should be captured as a result of
1218 // auto trait implementation issues
1219 auto_trait_migration_reasons.extend(capture_trait_reasons.clone());
1221 diagnostics_info.push(MigrationLintNote {
1223 reason: self.compute_2229_migrations_reasons(
1224 capture_trait_reasons,
1225 capture_drop_reorder_reason,
1230 if !diagnostics_info.is_empty() {
1231 need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
1236 self.compute_2229_migrations_reasons(
1237 auto_trait_migration_reasons,
1238 drop_migration_needed,
1243 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1244 /// of a root variable and a list of captured paths starting at this root variable (expressed
1245 /// using list of `Projection` slices), it returns true if there is a path that is not
1246 /// captured starting at this root variable that implements Drop.
1248 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1249 /// path say P and then list of projection slices which represent the different captures moved
1250 /// into the closure starting off of P.
1252 /// This will make more sense with an example:
1255 /// #![feature(capture_disjoint_fields)]
1257 /// struct FancyInteger(i32); // This implements Drop
1259 /// struct Point { x: FancyInteger, y: FancyInteger }
1262 /// struct Wrapper { p: Point, c: Color }
1264 /// fn f(w: Wrapper) {
1266 /// // Closure captures w.p.x and w.c by move.
1273 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1274 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1275 /// therefore Drop ordering would change and we want this function to return true.
1277 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1279 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1282 /// - Ty(place): Type of place
1283 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1285 /// ```ignore (illustrative)
1286 /// (Ty(w), [ &[p, x], &[c] ])
1288 /// // ----------------------------
1291 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1294 /// (Ty(w.p), [ &[x] ]) false
1297 /// // -------------------------------
1300 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1303 /// false NeedsSignificantDrop(Ty(w.p.y))
1309 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1310 /// This implies that the `w.c` is completely captured by the closure.
1311 /// Since drop for this path will be called when the closure is
1312 /// dropped we don't need to migrate for it.
1314 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1315 /// path wasn't captured by the closure. Also note that even
1316 /// though we didn't capture this path, the function visits it,
1317 /// which is kind of the point of this function. We then return
1318 /// if the type of `w.p.y` implements Drop, which in this case is
1321 /// Consider another example:
1323 /// ```ignore (pseudo-rust)
1325 /// impl Drop for X {}
1328 /// impl Drop for Y {}
1332 /// let c = || move(y.0);
1336 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1337 /// return true, because even though all paths starting at `y` are captured, `y` itself
1338 /// implements Drop which will be affected since `y` isn't completely captured.
1339 fn has_significant_drop_outside_of_captures(
1341 closure_def_id: DefId,
1343 base_path_ty: Ty<'tcx>,
1344 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1346 let needs_drop = |ty: Ty<'tcx>| {
1347 ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local()))
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.expect_local()),
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: DefId) -> bool {
1517 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
1520 fn log_capture_analysis_first_pass(
1522 closure_def_id: rustc_hir::def_id::DefId,
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: DefId, 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),
1709 bug!("Drop location span error: need to handle more Node {:?}", owner_node);
1712 tcx.sess.source_map().end_point(owner_span)
1715 struct InferBorrowKind<'a, 'tcx> {
1716 fcx: &'a FnCtxt<'a, 'tcx>,
1718 // The def-id of the closure whose kind and upvar accesses are being inferred.
1719 closure_def_id: LocalDefId,
1721 /// For each Place that is captured by the closure, we track the minimal kind of
1722 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1724 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1725 /// s.str2 via a MutableBorrow
1728 /// struct SomeStruct { str1: String, str2: String };
1730 /// // Assume that the HirId for the variable definition is `V1`
1731 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") };
1733 /// let fix_s = |new_s2| {
1734 /// // Assume that the HirId for the expression `s.str1` is `E1`
1735 /// println!("Updating SomeStruct with str1={0}", s.str1);
1736 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1737 /// s.str2 = new_s2;
1741 /// For closure `fix_s`, (at a high level) the map contains
1743 /// ```ignore (illustrative)
1744 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1745 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1747 capture_information: InferredCaptureInformation<'tcx>,
1748 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1751 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1752 fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId) {
1753 let PlaceBase::Upvar(_) = place.base else { return };
1755 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1756 // such as deref of a raw pointer.
1757 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1759 let (place, _) = restrict_capture_precision(place, dummy_capture_kind);
1761 let (place, _) = restrict_repr_packed_field_ref_capture(
1767 self.fake_reads.push((place, cause, diag_expr_id));
1770 #[instrument(skip(self), level = "debug")]
1771 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1772 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1773 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1775 self.capture_information.push((
1776 place_with_id.place.clone(),
1778 capture_kind_expr_id: Some(diag_expr_id),
1779 path_expr_id: Some(diag_expr_id),
1780 capture_kind: ty::UpvarCapture::ByValue,
1785 #[instrument(skip(self), level = "debug")]
1788 place_with_id: &PlaceWithHirId<'tcx>,
1789 diag_expr_id: hir::HirId,
1792 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1793 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1795 // The region here will get discarded/ignored
1796 let capture_kind = ty::UpvarCapture::ByRef(bk);
1798 // We only want repr packed restriction to be applied to reading references into a packed
1799 // struct, and not when the data is being moved. Therefore we call this method here instead
1800 // of in `restrict_capture_precision`.
1801 let (place, mut capture_kind) = restrict_repr_packed_field_ref_capture(
1804 place_with_id.place.clone(),
1808 // Raw pointers don't inherit mutability
1809 if place_with_id.place.deref_tys().any(Ty::is_unsafe_ptr) {
1810 capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1813 self.capture_information.push((
1816 capture_kind_expr_id: Some(diag_expr_id),
1817 path_expr_id: Some(diag_expr_id),
1823 #[instrument(skip(self), level = "debug")]
1824 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1825 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1829 /// Rust doesn't permit moving fields out of a type that implements drop
1830 fn restrict_precision_for_drop_types<'a, 'tcx>(
1831 fcx: &'a FnCtxt<'a, 'tcx>,
1832 mut place: Place<'tcx>,
1833 mut curr_mode: ty::UpvarCapture,
1835 ) -> (Place<'tcx>, ty::UpvarCapture) {
1836 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1838 if let (false, UpvarCapture::ByValue) = (is_copy_type, curr_mode) {
1839 for i in 0..place.projections.len() {
1840 match place.ty_before_projection(i).kind() {
1841 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1842 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1853 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
1854 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
1855 /// them completely.
1856 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
1857 fn restrict_precision_for_unsafe<'tcx>(
1858 mut place: Place<'tcx>,
1859 mut curr_mode: ty::UpvarCapture,
1860 ) -> (Place<'tcx>, ty::UpvarCapture) {
1861 if place.base_ty.is_unsafe_ptr() {
1862 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1865 if place.base_ty.is_union() {
1866 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1869 for (i, proj) in place.projections.iter().enumerate() {
1870 if proj.ty.is_unsafe_ptr() {
1871 // Don't apply any projections on top of an unsafe ptr.
1872 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1876 if proj.ty.is_union() {
1877 // Don't capture precise fields of a union.
1878 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1886 /// Truncate projections so that following rules are obeyed by the captured `place`:
1887 /// - No Index projections are captured, since arrays are captured completely.
1888 /// - No unsafe block is required to capture `place`
1889 /// Returns the truncated place and updated capture mode.
1890 fn restrict_capture_precision<'tcx>(
1892 curr_mode: ty::UpvarCapture,
1893 ) -> (Place<'tcx>, ty::UpvarCapture) {
1894 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
1896 if place.projections.is_empty() {
1897 // Nothing to do here
1898 return (place, curr_mode);
1901 for (i, proj) in place.projections.iter().enumerate() {
1903 ProjectionKind::Index => {
1904 // Arrays are completely captured, so we drop Index projections
1905 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1906 return (place, curr_mode);
1908 ProjectionKind::Deref => {}
1909 ProjectionKind::Field(..) => {} // ignore
1910 ProjectionKind::Subslice => {} // We never capture this
1917 /// Truncate deref of any reference.
1918 fn adjust_for_move_closure<'tcx>(
1919 mut place: Place<'tcx>,
1920 mut kind: ty::UpvarCapture,
1921 ) -> (Place<'tcx>, ty::UpvarCapture) {
1922 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1924 if let Some(idx) = first_deref {
1925 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1928 (place, ty::UpvarCapture::ByValue)
1931 /// Adjust closure capture just that if taking ownership of data, only move data
1932 /// from enclosing stack frame.
1933 fn adjust_for_non_move_closure<'tcx>(
1934 mut place: Place<'tcx>,
1935 mut kind: ty::UpvarCapture,
1936 ) -> (Place<'tcx>, ty::UpvarCapture) {
1937 let contains_deref =
1938 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1941 ty::UpvarCapture::ByValue => {
1942 if let Some(idx) = contains_deref {
1943 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1947 ty::UpvarCapture::ByRef(..) => {}
1953 fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1954 let variable_name = match place.base {
1955 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
1956 _ => bug!("Capture_information should only contain upvars"),
1959 let mut projections_str = String::new();
1960 for (i, item) in place.projections.iter().enumerate() {
1961 let proj = match item.kind {
1962 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
1963 ProjectionKind::Deref => String::from("Deref"),
1964 ProjectionKind::Index => String::from("Index"),
1965 ProjectionKind::Subslice => String::from("Subslice"),
1968 projections_str.push(',');
1970 projections_str.push_str(proj.as_str());
1973 format!("{variable_name}[{projections_str}]")
1976 fn construct_capture_kind_reason_string<'tcx>(
1978 place: &Place<'tcx>,
1979 capture_info: &ty::CaptureInfo,
1981 let place_str = construct_place_string(tcx, place);
1983 let capture_kind_str = match capture_info.capture_kind {
1984 ty::UpvarCapture::ByValue => "ByValue".into(),
1985 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
1988 format!("{place_str} captured as {capture_kind_str} here")
1991 fn construct_path_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1992 let place_str = construct_place_string(tcx, place);
1994 format!("{place_str} used here")
1997 fn construct_capture_info_string<'tcx>(
1999 place: &Place<'tcx>,
2000 capture_info: &ty::CaptureInfo,
2002 let place_str = construct_place_string(tcx, place);
2004 let capture_kind_str = match capture_info.capture_kind {
2005 ty::UpvarCapture::ByValue => "ByValue".into(),
2006 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
2008 format!("{place_str} -> {capture_kind_str}")
2011 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2012 tcx.hir().name(var_hir_id)
2015 #[instrument(level = "debug", skip(tcx))]
2016 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2018 closure_id: hir::HirId,
2021 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2023 !matches!(level, lint::Level::Allow)
2026 /// Return a two string tuple (s1, s2)
2027 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2028 /// - s2: Comma separated names of the variables being migrated.
2029 fn migration_suggestion_for_2229(
2031 need_migrations: &Vec<NeededMigration>,
2032 ) -> (String, String) {
2033 let need_migrations_variables = need_migrations
2035 .map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
2036 .collect::<Vec<_>>();
2038 let migration_ref_concat =
2039 need_migrations_variables.iter().map(|v| format!("&{v}")).collect::<Vec<_>>().join(", ");
2041 let migration_string = if 1 == need_migrations.len() {
2042 format!("let _ = {migration_ref_concat}")
2044 format!("let _ = ({migration_ref_concat})")
2047 let migrated_variables_concat =
2048 need_migrations_variables.iter().map(|v| format!("`{v}`")).collect::<Vec<_>>().join(", ");
2050 (migration_string, migrated_variables_concat)
2053 /// Helper function to determine if we need to escalate CaptureKind from
2054 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2055 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2057 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2058 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2060 /// It is the caller's duty to figure out which path_expr_id to use.
2062 /// If both the CaptureKind and Expression are considered to be equivalent,
2063 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to prioritize
2064 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2065 /// in the closure. This can be achieved simply by calling
2066 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2067 /// expressions that occur earlier in the closure body than the current expression are processed before.
2068 /// Consider the following example
2070 /// struct Point { x: i32, y: i32 }
2071 /// let mut p = Point { x: 10, y: 10 };
2079 /// p.x += 10; // E2
2083 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2084 /// and both have an expression associated, however for diagnostics we prefer reporting
2085 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2086 /// would've already handled `E1`, and have an existing capture_information for it.
2087 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2088 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2089 fn determine_capture_info(
2090 capture_info_a: ty::CaptureInfo,
2091 capture_info_b: ty::CaptureInfo,
2092 ) -> ty::CaptureInfo {
2093 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2095 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2096 (ty::UpvarCapture::ByValue, ty::UpvarCapture::ByValue) => true,
2097 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => ref_a == ref_b,
2098 (ty::UpvarCapture::ByValue, _) | (ty::UpvarCapture::ByRef(_), _) => false,
2101 if eq_capture_kind {
2102 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2103 (Some(_), _) | (None, None) => capture_info_a,
2104 (None, Some(_)) => capture_info_b,
2107 // We select the CaptureKind which ranks higher based the following priority order:
2108 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2109 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2110 (ty::UpvarCapture::ByValue, _) => capture_info_a,
2111 (_, ty::UpvarCapture::ByValue) => capture_info_b,
2112 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2113 match (ref_a, ref_b) {
2115 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2116 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2119 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2120 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2122 (ty::ImmBorrow, ty::ImmBorrow)
2123 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2124 | (ty::MutBorrow, ty::MutBorrow) => {
2125 bug!("Expected unequal capture kinds");
2133 /// Truncates `place` to have up to `len` projections.
2134 /// `curr_mode` is the current required capture kind for the place.
2135 /// Returns the truncated `place` and the updated required capture kind.
2137 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2138 /// contained `Deref` of `&mut`.
2139 fn truncate_place_to_len_and_update_capture_kind<'tcx>(
2140 place: &mut Place<'tcx>,
2141 curr_mode: &mut ty::UpvarCapture,
2144 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2146 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2148 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2149 // we don't need to worry about that case here.
2151 ty::UpvarCapture::ByRef(ty::BorrowKind::MutBorrow) => {
2152 for i in len..place.projections.len() {
2153 if place.projections[i].kind == ProjectionKind::Deref
2154 && is_mut_ref(place.ty_before_projection(i))
2156 *curr_mode = ty::UpvarCapture::ByRef(ty::BorrowKind::UniqueImmBorrow);
2162 ty::UpvarCapture::ByRef(..) => {}
2163 ty::UpvarCapture::ByValue => {}
2166 place.projections.truncate(len);
2169 /// Determines the Ancestry relationship of Place A relative to Place B
2171 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2172 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2173 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2174 fn determine_place_ancestry_relation<'tcx>(
2175 place_a: &Place<'tcx>,
2176 place_b: &Place<'tcx>,
2177 ) -> PlaceAncestryRelation {
2178 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2179 if place_a.base != place_b.base {
2180 return PlaceAncestryRelation::Divergent;
2183 // Assume of length of projections_a = n
2184 let projections_a = &place_a.projections;
2186 // Assume of length of projections_b = m
2187 let projections_b = &place_b.projections;
2189 let same_initial_projections =
2190 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2192 if same_initial_projections {
2193 use std::cmp::Ordering;
2195 // First min(n, m) projections are the same
2196 // Select Ancestor/Descendant
2197 match projections_b.len().cmp(&projections_a.len()) {
2198 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2199 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2200 Ordering::Less => PlaceAncestryRelation::Descendant,
2203 PlaceAncestryRelation::Divergent
2207 /// Reduces the precision of the captured place when the precision doesn't yield any benefit from
2208 /// borrow checking perspective, allowing us to save us on the size of the capture.
2211 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2212 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2213 /// rightmost deref of the capture if the deref is applied to a shared ref.
2215 /// Reason we only drop the last deref is because of the following edge case:
2218 /// # struct A { field_of_a: Box<i32> }
2220 /// # struct C<'a>(&'a i32);
2221 /// struct MyStruct<'a> {
2227 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2228 /// || drop(&*m.a.field_of_a)
2229 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2231 /// // If we capture `m`, then the closure no longer outlives `'static'
2232 /// // it is constrained to `'a`
2235 fn truncate_capture_for_optimization<'tcx>(
2236 mut place: Place<'tcx>,
2237 mut curr_mode: ty::UpvarCapture,
2238 ) -> (Place<'tcx>, ty::UpvarCapture) {
2239 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2241 // Find the right-most deref (if any). All the projections that come after this
2242 // are fields or other "in-place pointer adjustments"; these refer therefore to
2243 // data owned by whatever pointer is being dereferenced here.
2244 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2247 // If that pointer is a shared reference, then we don't need those fields.
2248 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2249 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2251 None | Some(_) => {}
2257 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2258 /// user is using Rust Edition 2021 or higher.
2260 /// `span` is the span of the closure.
2261 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2262 // We use span here to ensure that if the closure was generated by a macro with a different
2264 tcx.features().capture_disjoint_fields || span.rust_2021()