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::fx::{FxHashMap, FxHashSet};
53 use rustc_index::vec::Idx;
54 use rustc_target::abi::VariantIdx;
58 /// Describe the relationship between the paths of two places
60 /// - `foo` is ancestor of `foo.bar.baz`
61 /// - `foo.bar.baz` is an descendant of `foo.bar`
62 /// - `foo.bar` and `foo.baz` are divergent
63 enum PlaceAncestryRelation {
70 /// Intermediate format to store a captured `Place` and associated `ty::CaptureInfo`
71 /// during capture analysis. Information in this map feeds into the minimum capture
73 type InferredCaptureInformation<'tcx> = Vec<(Place<'tcx>, ty::CaptureInfo)>;
75 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
76 pub fn closure_analyze(&self, body: &'tcx hir::Body<'tcx>) {
77 InferBorrowKindVisitor { fcx: self }.visit_body(body);
79 // it's our job to process these.
80 assert!(self.deferred_call_resolutions.borrow().is_empty());
84 /// Intermediate format to store the hir_id pointing to the use that resulted in the
85 /// corresponding place being captured and a String which contains the captured value's
87 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
88 enum UpvarMigrationInfo {
89 /// We previously captured all of `x`, but now we capture some sub-path.
90 CapturingPrecise { source_expr: Option<hir::HirId>, var_name: String },
92 // where the variable appears in the closure (but is not captured)
97 /// Reasons that we might issue a migration warning.
98 #[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
99 struct MigrationWarningReason {
100 /// When we used to capture `x` in its entirety, we implemented the auto-trait(s)
101 /// in this vec, but now we don't.
102 auto_traits: Vec<&'static str>,
104 /// When we used to capture `x` in its entirety, we would execute some destructors
105 /// at a different time.
109 impl MigrationWarningReason {
110 fn migration_message(&self) -> String {
111 let base = "changes to closure capture in Rust 2021 will affect";
112 if !self.auto_traits.is_empty() && self.drop_order {
113 format!("{} drop order and which traits the closure implements", base)
114 } else if self.drop_order {
115 format!("{} drop order", base)
117 format!("{} which traits the closure implements", base)
122 /// Intermediate format to store information needed to generate a note in the migration lint.
123 struct MigrationLintNote {
124 captures_info: UpvarMigrationInfo,
126 /// reasons why migration is needed for this capture
127 reason: MigrationWarningReason,
130 /// Intermediate format to store the hir id of the root variable and a HashSet containing
131 /// information on why the root variable should be fully captured
132 struct NeededMigration {
133 var_hir_id: hir::HirId,
134 diagnostics_info: Vec<MigrationLintNote>,
137 struct InferBorrowKindVisitor<'a, 'tcx> {
138 fcx: &'a FnCtxt<'a, 'tcx>,
141 impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
142 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
144 hir::ExprKind::Closure(&hir::Closure { capture_clause, body: body_id, .. }) => {
145 let body = self.fcx.tcx.hir().body(body_id);
146 self.visit_body(body);
147 self.fcx.analyze_closure(expr.hir_id, expr.span, body_id, body, capture_clause);
149 hir::ExprKind::ConstBlock(anon_const) => {
150 let body = self.fcx.tcx.hir().body(anon_const.body);
151 self.visit_body(body);
156 intravisit::walk_expr(self, expr);
160 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
161 /// Analysis starting point.
162 #[instrument(skip(self, body), level = "debug")]
165 closure_hir_id: hir::HirId,
167 body_id: hir::BodyId,
168 body: &'tcx hir::Body<'tcx>,
169 capture_clause: hir::CaptureBy,
171 // Extract the type of the closure.
172 let ty = self.node_ty(closure_hir_id);
173 let (closure_def_id, substs) = match *ty.kind() {
174 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
175 ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
177 // #51714: skip analysis when we have already encountered type errors
183 "type of closure expr {:?} is not a closure {:?}",
190 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
191 self.closure_kind(closure_substs).is_none().then_some(closure_substs)
196 let local_def_id = closure_def_id.expect_local();
198 let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
199 assert_eq!(body_owner_def_id.to_def_id(), closure_def_id);
200 let mut delegate = InferBorrowKind {
202 closure_def_id: local_def_id,
203 capture_information: Default::default(),
204 fake_reads: Default::default(),
206 euv::ExprUseVisitor::new(
211 &self.typeck_results.borrow(),
216 "For closure={:?}, capture_information={:#?}",
217 closure_def_id, delegate.capture_information
220 self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
222 let (capture_information, closure_kind, origin) = self
223 .process_collected_capture_information(capture_clause, delegate.capture_information);
225 self.compute_min_captures(closure_def_id, capture_information, span);
227 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
229 if should_do_rust_2021_incompatible_closure_captures_analysis(self.tcx, closure_hir_id) {
230 self.perform_2229_migration_anaysis(closure_def_id, body_id, capture_clause, span);
233 let after_feature_tys = self.final_upvar_tys(closure_def_id);
235 // We now fake capture information for all variables that are mentioned within the closure
236 // We do this after handling migrations so that min_captures computes before
237 if !enable_precise_capture(self.tcx, span) {
238 let mut capture_information: InferredCaptureInformation<'tcx> = Default::default();
240 if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
241 for var_hir_id in upvars.keys() {
242 let place = self.place_for_root_variable(local_def_id, *var_hir_id);
244 debug!("seed place {:?}", place);
246 let capture_kind = self.init_capture_kind_for_place(&place, capture_clause);
247 let fake_info = ty::CaptureInfo {
248 capture_kind_expr_id: None,
253 capture_information.push((place, fake_info));
257 // This will update the min captures based on this new fake information.
258 self.compute_min_captures(closure_def_id, capture_information, span);
261 let before_feature_tys = self.final_upvar_tys(closure_def_id);
263 if let Some(closure_substs) = infer_kind {
264 // Unify the (as yet unbound) type variable in the closure
265 // substs with the kind we inferred.
266 let closure_kind_ty = closure_substs.as_closure().kind_ty();
267 self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
269 // If we have an origin, store it.
270 if let Some(origin) = origin {
271 let origin = if enable_precise_capture(self.tcx, span) {
274 (origin.0, Place { projections: vec![], ..origin.1 })
279 .closure_kind_origins_mut()
280 .insert(closure_hir_id, origin);
284 self.log_closure_min_capture_info(closure_def_id, span);
286 // Now that we've analyzed the closure, we know how each
287 // variable is borrowed, and we know what traits the closure
288 // implements (Fn vs FnMut etc). We now have some updates to do
289 // with that information.
291 // Note that no closure type C may have an upvar of type C
292 // (though it may reference itself via a trait object). This
293 // results from the desugaring of closures to a struct like
294 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
295 // C, then the type would have infinite size (and the
296 // inference algorithm will reject it).
298 // Equate the type variables for the upvars with the actual types.
299 let final_upvar_tys = self.final_upvar_tys(closure_def_id);
301 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
302 closure_hir_id, substs, final_upvar_tys
305 // Build a tuple (U0..Un) of the final upvar types U0..Un
306 // and unify the upvar tuple type in the closure with it:
307 let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
308 self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
310 let fake_reads = delegate
313 .map(|(place, cause, hir_id)| (place, cause, hir_id))
315 self.typeck_results.borrow_mut().closure_fake_reads.insert(closure_def_id, fake_reads);
317 if self.tcx.sess.opts.unstable_opts.profile_closures {
318 self.typeck_results.borrow_mut().closure_size_eval.insert(
320 ClosureSizeProfileData {
321 before_feature_tys: self.tcx.mk_tup(before_feature_tys.into_iter()),
322 after_feature_tys: self.tcx.mk_tup(after_feature_tys.into_iter()),
327 // If we are also inferred the closure kind here,
328 // process any deferred resolutions.
329 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
330 for deferred_call_resolution in deferred_call_resolutions {
331 deferred_call_resolution.resolve(self);
335 // Returns a list of `Ty`s for each upvar.
336 fn final_upvar_tys(&self, closure_id: DefId) -> Vec<Ty<'tcx>> {
339 .closure_min_captures_flattened(closure_id)
340 .map(|captured_place| {
341 let upvar_ty = captured_place.place.ty();
342 let capture = captured_place.info.capture_kind;
345 "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
346 captured_place.place, upvar_ty, capture, captured_place.mutability,
349 apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture, captured_place.region)
354 /// Adjusts the closure capture information to ensure that the operations aren't unsafe,
355 /// and that the path can be captured with required capture kind (depending on use in closure,
356 /// move closure etc.)
358 /// Returns the set of of adjusted information along with the inferred closure kind and span
359 /// associated with the closure kind inference.
361 /// Note that we *always* infer a minimal kind, even if
362 /// we don't always *use* that in the final result (i.e., sometimes
363 /// we've taken the closure kind from the expectations instead, and
364 /// for generators we don't even implement the closure traits
367 /// If we inferred that the closure needs to be FnMut/FnOnce, last element of the returned tuple
368 /// contains a `Some()` with the `Place` that caused us to do so.
369 fn process_collected_capture_information(
371 capture_clause: hir::CaptureBy,
372 capture_information: InferredCaptureInformation<'tcx>,
373 ) -> (InferredCaptureInformation<'tcx>, ty::ClosureKind, Option<(Span, Place<'tcx>)>) {
374 let mut closure_kind = ty::ClosureKind::LATTICE_BOTTOM;
375 let mut origin: Option<(Span, Place<'tcx>)> = None;
377 let processed = capture_information
379 .map(|(place, mut capture_info)| {
380 // Apply rules for safety before inferring closure kind
381 let (place, capture_kind) =
382 restrict_capture_precision(place, capture_info.capture_kind);
384 let (place, capture_kind) = truncate_capture_for_optimization(place, capture_kind);
386 let usage_span = if let Some(usage_expr) = capture_info.path_expr_id {
387 self.tcx.hir().span(usage_expr)
392 let updated = match capture_kind {
393 ty::UpvarCapture::ByValue => match closure_kind {
394 ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
395 (ty::ClosureKind::FnOnce, Some((usage_span, place.clone())))
397 // If closure is already FnOnce, don't update
398 ty::ClosureKind::FnOnce => (closure_kind, origin.take()),
401 ty::UpvarCapture::ByRef(
402 ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
405 ty::ClosureKind::Fn => {
406 (ty::ClosureKind::FnMut, Some((usage_span, place.clone())))
408 // Don't update the origin
409 ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce => {
410 (closure_kind, origin.take())
415 _ => (closure_kind, origin.take()),
418 closure_kind = updated.0;
421 let (place, capture_kind) = match capture_clause {
422 hir::CaptureBy::Value => adjust_for_move_closure(place, capture_kind),
423 hir::CaptureBy::Ref => adjust_for_non_move_closure(place, capture_kind),
426 // This restriction needs to be applied after we have handled adjustments for `move`
427 // closures. We want to make sure any adjustment that might make us move the place into
428 // the closure gets handled.
429 let (place, capture_kind) =
430 restrict_precision_for_drop_types(self, place, capture_kind, usage_span);
432 capture_info.capture_kind = capture_kind;
433 (place, capture_info)
437 (processed, closure_kind, origin)
440 /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
441 /// Places (and corresponding capture kind) that we need to keep track of to support all
442 /// the required captured paths.
445 /// Note: If this function is called multiple times for the same closure, it will update
446 /// the existing min_capture map that is stored in TypeckResults.
451 /// struct Point { x: i32, y: i32 }
453 /// let s = String::from("s"); // hir_id_s
454 /// let mut p = Point { x: 2, y: -2 }; // his_id_p
456 /// println!("{s:?}"); // L1
458 /// println!("{}" , p.y); // L3
459 /// println!("{p:?}"); // L4
463 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
464 /// the lines L1..5 respectively.
466 /// InferBorrowKind results in a structure like this:
468 /// ```ignore (illustrative)
470 /// Place(base: hir_id_s, projections: [], ....) -> {
471 /// capture_kind_expr: hir_id_L5,
472 /// path_expr_id: hir_id_L5,
473 /// capture_kind: ByValue
475 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
476 /// capture_kind_expr: hir_id_L2,
477 /// path_expr_id: hir_id_L2,
478 /// capture_kind: ByValue
480 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
481 /// capture_kind_expr: hir_id_L3,
482 /// path_expr_id: hir_id_L3,
483 /// capture_kind: ByValue
485 /// Place(base: hir_id_p, projections: [], ...) -> {
486 /// capture_kind_expr: hir_id_L4,
487 /// path_expr_id: hir_id_L4,
488 /// capture_kind: ByValue
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
512 fn compute_min_captures(
514 closure_def_id: DefId,
515 capture_information: InferredCaptureInformation<'tcx>,
518 if capture_information.is_empty() {
522 let mut typeck_results = self.typeck_results.borrow_mut();
524 let mut root_var_min_capture_list =
525 typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
527 for (mut place, capture_info) in capture_information.into_iter() {
528 let var_hir_id = match place.base {
529 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
530 base => bug!("Expected upvar, found={:?}", base),
533 let Some(min_cap_list) = root_var_min_capture_list.get_mut(&var_hir_id) else {
534 let mutability = self.determine_capture_mutability(&typeck_results, &place);
535 let min_cap_list = vec![ty::CapturedPlace {
541 root_var_min_capture_list.insert(var_hir_id, min_cap_list);
545 // Go through each entry in the current list of min_captures
546 // - if ancestor is found, update it's capture kind to account for current place's
547 // capture information.
549 // - if descendant is found, remove it from the list, and update the current place's
550 // capture information to account for the descendant's capture kind.
552 // We can never be in a case where the list contains both an ancestor and a descendant
553 // Also there can only be ancestor but in case of descendants there might be
556 let mut descendant_found = false;
557 let mut updated_capture_info = capture_info;
558 min_cap_list.retain(|possible_descendant| {
559 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
560 // current place is ancestor of possible_descendant
561 PlaceAncestryRelation::Ancestor => {
562 descendant_found = true;
564 let mut possible_descendant = possible_descendant.clone();
565 let backup_path_expr_id = updated_capture_info.path_expr_id;
567 // Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
568 // possible change in capture mode.
569 truncate_place_to_len_and_update_capture_kind(
570 &mut possible_descendant.place,
571 &mut possible_descendant.info.capture_kind,
572 place.projections.len(),
575 updated_capture_info =
576 determine_capture_info(updated_capture_info, possible_descendant.info);
578 // we need to keep the ancestor's `path_expr_id`
579 updated_capture_info.path_expr_id = backup_path_expr_id;
587 let mut ancestor_found = false;
588 if !descendant_found {
589 for possible_ancestor in min_cap_list.iter_mut() {
590 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
591 PlaceAncestryRelation::SamePlace => {
592 ancestor_found = true;
593 possible_ancestor.info = determine_capture_info(
594 possible_ancestor.info,
595 updated_capture_info,
598 // Only one related place will be in the list.
601 // current place is descendant of possible_ancestor
602 PlaceAncestryRelation::Descendant => {
603 ancestor_found = true;
604 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
606 // Truncate the descendant (current place) to be same as the ancestor to handle any
607 // possible change in capture mode.
608 truncate_place_to_len_and_update_capture_kind(
610 &mut updated_capture_info.capture_kind,
611 possible_ancestor.place.projections.len(),
614 possible_ancestor.info = determine_capture_info(
615 possible_ancestor.info,
616 updated_capture_info,
619 // we need to keep the ancestor's `path_expr_id`
620 possible_ancestor.info.path_expr_id = backup_path_expr_id;
622 // Only one related place will be in the list.
630 // Only need to insert when we don't have an ancestor in the existing min capture list
632 let mutability = self.determine_capture_mutability(&typeck_results, &place);
633 let captured_place = ty::CapturedPlace {
635 info: updated_capture_info,
639 min_cap_list.push(captured_place);
643 // For each capture that is determined to be captured by ref, add region info.
644 for (_, captures) in &mut root_var_min_capture_list {
645 for capture in captures {
646 match capture.info.capture_kind {
647 ty::UpvarCapture::ByRef(_) => {
648 let PlaceBase::Upvar(upvar_id) = capture.place.base else { bug!("expected upvar") };
649 let origin = UpvarRegion(upvar_id, closure_span);
650 let upvar_region = self.next_region_var(origin);
651 capture.region = Some(upvar_region);
659 "For closure={:?}, min_captures before sorting={:?}",
660 closure_def_id, root_var_min_capture_list
663 // Now that we have the minimized list of captures, sort the captures by field id.
664 // This causes the closure to capture the upvars in the same order as the fields are
665 // declared which is also the drop order. Thus, in situations where we capture all the
666 // fields of some type, the observable drop order will remain the same as it previously
667 // was even though we're dropping each capture individually.
668 // See https://github.com/rust-lang/project-rfc-2229/issues/42 and
669 // `src/test/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
670 for (_, captures) in &mut root_var_min_capture_list {
671 captures.sort_by(|capture1, capture2| {
672 for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
673 // We do not need to look at the `Projection.ty` fields here because at each
674 // step of the iteration, the projections will either be the same and therefore
675 // the types must be as well or the current projection will be different and
676 // we will return the result of comparing the field indexes.
677 match (p1.kind, p2.kind) {
678 // Paths are the same, continue to next loop.
679 (ProjectionKind::Deref, ProjectionKind::Deref) => {}
680 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
683 // Fields are different, compare them.
684 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
688 // We should have either a pair of `Deref`s or a pair of `Field`s.
689 // Anything else is a bug.
691 l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
692 r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
694 "ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
699 l @ (ProjectionKind::Index
700 | ProjectionKind::Subslice
701 | ProjectionKind::Deref
702 | ProjectionKind::Field(..)),
703 r @ (ProjectionKind::Index
704 | ProjectionKind::Subslice
705 | ProjectionKind::Deref
706 | ProjectionKind::Field(..)),
708 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
716 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
723 "For closure={:?}, min_captures after sorting={:#?}",
724 closure_def_id, root_var_min_capture_list
726 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
729 /// Perform the migration analysis for RFC 2229, and emit lint
730 /// `disjoint_capture_drop_reorder` if needed.
731 fn perform_2229_migration_anaysis(
733 closure_def_id: DefId,
734 body_id: hir::BodyId,
735 capture_clause: hir::CaptureBy,
738 let (need_migrations, reasons) = self.compute_2229_migrations(
742 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
745 if !need_migrations.is_empty() {
746 let (migration_string, migrated_variables_concat) =
747 migration_suggestion_for_2229(self.tcx, &need_migrations);
750 self.tcx.hir().local_def_id_to_hir_id(closure_def_id.expect_local());
751 let closure_head_span = self.tcx.def_span(closure_def_id);
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 closure_span = self.tcx.hir().span_with_body(closure_hir_id);
829 let mut closure_body_span = {
830 // If the body was entirely expanded from a macro
831 // invocation, i.e. the body is not contained inside the
832 // closure span, then we walk up the expansion until we
833 // find the span before the expansion.
834 let s = self.tcx.hir().span_with_body(body_id.hir_id);
835 s.find_ancestor_inside(closure_span).unwrap_or(s)
838 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
839 if s.starts_with('$') {
840 // Looks like a macro fragment. Try to find the real block.
841 if let Some(hir::Node::Expr(&hir::Expr {
842 kind: hir::ExprKind::Block(block, ..), ..
843 })) = self.tcx.hir().find(body_id.hir_id) {
844 // If the body is a block (with `{..}`), we use the span of that block.
845 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
846 // Since we know it's a block, we know we can insert the `let _ = ..` without
847 // breaking the macro syntax.
848 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
849 closure_body_span = block.span;
855 let mut lines = s.lines();
856 let line1 = lines.next().unwrap_or_default();
858 if line1.trim_end() == "{" {
859 // This is a multi-line closure with just a `{` on the first line,
860 // so we put the `let` on its own line.
861 // We take the indentation from the next non-empty line.
862 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
863 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
864 diagnostics_builder.span_suggestion(
865 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
867 format!("\n{indent}{migration_string};"),
868 Applicability::MachineApplicable,
870 } else if line1.starts_with('{') {
871 // This is a closure with its body wrapped in
872 // braces, but with more than just the opening
873 // brace on the first line. We put the `let`
874 // directly after the `{`.
875 diagnostics_builder.span_suggestion(
876 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
878 format!(" {migration_string};"),
879 Applicability::MachineApplicable,
882 // This is a closure without braces around the body.
883 // We add braces to add the `let` before the body.
884 diagnostics_builder.multipart_suggestion(
887 (closure_body_span.shrink_to_lo(), format!("{{ {migration_string}; ")),
888 (closure_body_span.shrink_to_hi(), " }".to_string()),
890 Applicability::MachineApplicable
894 diagnostics_builder.span_suggestion(
898 Applicability::HasPlaceholders
902 diagnostics_builder.emit();
908 /// Combines all the reasons for 2229 migrations
909 fn compute_2229_migrations_reasons(
911 auto_trait_reasons: FxHashSet<&'static str>,
913 ) -> MigrationWarningReason {
914 let mut reasons = MigrationWarningReason::default();
916 reasons.auto_traits.extend(auto_trait_reasons);
917 reasons.drop_order = drop_order;
919 // `auto_trait_reasons` are in hashset order, so sort them to put the
920 // diagnostics we emit later in a cross-platform-consistent order.
921 reasons.auto_traits.sort_unstable();
926 /// Figures out the list of root variables (and their types) that aren't completely
927 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
928 /// differ between the root variable and the captured paths.
930 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
931 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
932 fn compute_2229_migrations_for_trait(
934 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
935 var_hir_id: hir::HirId,
936 closure_clause: hir::CaptureBy,
937 ) -> Option<FxHashMap<UpvarMigrationInfo, FxHashSet<&'static str>>> {
938 let auto_traits_def_id = vec![
939 self.tcx.lang_items().clone_trait(),
940 self.tcx.lang_items().sync_trait(),
941 self.tcx.get_diagnostic_item(sym::Send),
942 self.tcx.lang_items().unpin_trait(),
943 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
944 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
946 const AUTO_TRAITS: [&str; 6] =
947 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
949 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
951 let ty = self.resolve_vars_if_possible(self.node_ty(var_hir_id));
953 let ty = match closure_clause {
954 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
955 hir::CaptureBy::Ref => {
956 // For non move closure the capture kind is the max capture kind of all captures
957 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
958 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
959 for capture in root_var_min_capture_list.iter() {
960 max_capture_info = determine_capture_info(max_capture_info, capture.info);
963 apply_capture_kind_on_capture_ty(
966 max_capture_info.capture_kind,
967 Some(self.tcx.lifetimes.re_erased),
972 let mut obligations_should_hold = Vec::new();
973 // Checks if a root variable implements any of the auto traits
974 for check_trait in auto_traits_def_id.iter() {
975 obligations_should_hold.push(
979 .type_implements_trait(
982 self.tcx.mk_substs_trait(ty, &[]),
985 .must_apply_modulo_regions()
991 let mut problematic_captures = FxHashMap::default();
992 // Check whether captured fields also implement the trait
993 for capture in root_var_min_capture_list.iter() {
994 let ty = apply_capture_kind_on_capture_ty(
997 capture.info.capture_kind,
998 Some(self.tcx.lifetimes.re_erased),
1001 // Checks if a capture implements any of the auto traits
1002 let mut obligations_holds_for_capture = Vec::new();
1003 for check_trait in auto_traits_def_id.iter() {
1004 obligations_holds_for_capture.push(
1006 .map(|check_trait| {
1008 .type_implements_trait(
1011 self.tcx.mk_substs_trait(ty, &[]),
1014 .must_apply_modulo_regions()
1020 let mut capture_problems = FxHashSet::default();
1022 // Checks if for any of the auto traits, one or more trait is implemented
1023 // by the root variable but not by the capture
1024 for (idx, _) in obligations_should_hold.iter().enumerate() {
1025 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
1026 capture_problems.insert(AUTO_TRAITS[idx]);
1030 if !capture_problems.is_empty() {
1031 problematic_captures.insert(
1032 UpvarMigrationInfo::CapturingPrecise {
1033 source_expr: capture.info.path_expr_id,
1034 var_name: capture.to_string(self.tcx),
1040 if !problematic_captures.is_empty() {
1041 return Some(problematic_captures);
1046 /// Figures out the list of root variables (and their types) that aren't completely
1047 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
1048 /// some path starting at that root variable **might** be affected.
1050 /// The output list would include a root variable if:
1051 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1052 /// enabled, **and**
1053 /// - It wasn't completely captured by the closure, **and**
1054 /// - One of the paths starting at this root variable, that is not captured needs Drop.
1056 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
1057 /// are no significant drops than None is returned
1058 #[instrument(level = "debug", skip(self))]
1059 fn compute_2229_migrations_for_drop(
1061 closure_def_id: DefId,
1063 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1064 closure_clause: hir::CaptureBy,
1065 var_hir_id: hir::HirId,
1066 ) -> Option<FxHashSet<UpvarMigrationInfo>> {
1067 let ty = self.resolve_vars_if_possible(self.node_ty(var_hir_id));
1069 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local())) {
1070 debug!("does not have significant drop");
1074 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1075 // The upvar is mentioned within the closure but no path starting from it is
1076 // used. This occurs when you have (e.g.)
1079 // let x = move || {
1083 debug!("no path starting from it is used");
1086 match closure_clause {
1087 // Only migrate if closure is a move closure
1088 hir::CaptureBy::Value => {
1089 let mut diagnostics_info = FxHashSet::default();
1090 let upvars = self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
1091 let upvar = upvars[&var_hir_id];
1092 diagnostics_info.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
1093 return Some(diagnostics_info);
1095 hir::CaptureBy::Ref => {}
1100 debug!(?root_var_min_capture_list);
1102 let mut projections_list = Vec::new();
1103 let mut diagnostics_info = FxHashSet::default();
1105 for captured_place in root_var_min_capture_list.iter() {
1106 match captured_place.info.capture_kind {
1107 // Only care about captures that are moved into the closure
1108 ty::UpvarCapture::ByValue => {
1109 projections_list.push(captured_place.place.projections.as_slice());
1110 diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
1111 source_expr: captured_place.info.path_expr_id,
1112 var_name: captured_place.to_string(self.tcx),
1115 ty::UpvarCapture::ByRef(..) => {}
1119 debug!(?projections_list);
1120 debug!(?diagnostics_info);
1122 let is_moved = !projections_list.is_empty();
1125 let is_not_completely_captured =
1126 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1127 debug!(?is_not_completely_captured);
1130 && is_not_completely_captured
1131 && self.has_significant_drop_outside_of_captures(
1138 return Some(diagnostics_info);
1144 /// Figures out the list of root variables (and their types) that aren't completely
1145 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1146 /// order of some path starting at that root variable **might** be affected or auto-traits
1147 /// differ between the root variable and the captured paths.
1149 /// The output list would include a root variable if:
1150 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1151 /// enabled, **and**
1152 /// - It wasn't completely captured by the closure, **and**
1153 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1154 /// - One of the paths captured does not implement all the auto-traits its root variable
1157 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1158 /// containing the reason why root variables whose HirId is contained in the vector should
1160 #[instrument(level = "debug", skip(self))]
1161 fn compute_2229_migrations(
1163 closure_def_id: DefId,
1165 closure_clause: hir::CaptureBy,
1166 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1167 ) -> (Vec<NeededMigration>, MigrationWarningReason) {
1168 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1169 return (Vec::new(), MigrationWarningReason::default());
1172 let mut need_migrations = Vec::new();
1173 let mut auto_trait_migration_reasons = FxHashSet::default();
1174 let mut drop_migration_needed = false;
1176 // Perform auto-trait analysis
1177 for (&var_hir_id, _) in upvars.iter() {
1178 let mut diagnostics_info = Vec::new();
1180 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1181 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1185 FxHashMap::default()
1188 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1189 .compute_2229_migrations_for_drop(
1196 drop_migration_needed = true;
1199 FxHashSet::default()
1202 // Combine all the captures responsible for needing migrations into one HashSet
1203 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1204 for key in auto_trait_diagnostic.keys() {
1205 capture_diagnostic.insert(key.clone());
1208 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1209 capture_diagnostic.sort();
1210 for captures_info in capture_diagnostic {
1211 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1212 let capture_trait_reasons =
1213 if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
1216 FxHashSet::default()
1219 // Check if migration is needed because of drop reorder as a result of that capture
1220 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
1222 // Combine all the reasons of why the root variable should be captured as a result of
1223 // auto trait implementation issues
1224 auto_trait_migration_reasons.extend(capture_trait_reasons.clone());
1226 diagnostics_info.push(MigrationLintNote {
1228 reason: self.compute_2229_migrations_reasons(
1229 capture_trait_reasons,
1230 capture_drop_reorder_reason,
1235 if !diagnostics_info.is_empty() {
1236 need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
1241 self.compute_2229_migrations_reasons(
1242 auto_trait_migration_reasons,
1243 drop_migration_needed,
1248 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1249 /// of a root variable and a list of captured paths starting at this root variable (expressed
1250 /// using list of `Projection` slices), it returns true if there is a path that is not
1251 /// captured starting at this root variable that implements Drop.
1253 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1254 /// path say P and then list of projection slices which represent the different captures moved
1255 /// into the closure starting off of P.
1257 /// This will make more sense with an example:
1260 /// #![feature(capture_disjoint_fields)]
1262 /// struct FancyInteger(i32); // This implements Drop
1264 /// struct Point { x: FancyInteger, y: FancyInteger }
1267 /// struct Wrapper { p: Point, c: Color }
1269 /// fn f(w: Wrapper) {
1271 /// // Closure captures w.p.x and w.c by move.
1278 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1279 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1280 /// therefore Drop ordering would change and we want this function to return true.
1282 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1284 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1287 /// - Ty(place): Type of place
1288 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1290 /// ```ignore (illustrative)
1291 /// (Ty(w), [ &[p, x], &[c] ])
1293 /// // ----------------------------
1296 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1299 /// (Ty(w.p), [ &[x] ]) false
1302 /// // -------------------------------
1305 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1308 /// false NeedsSignificantDrop(Ty(w.p.y))
1314 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1315 /// This implies that the `w.c` is completely captured by the closure.
1316 /// Since drop for this path will be called when the closure is
1317 /// dropped we don't need to migrate for it.
1319 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1320 /// path wasn't captured by the closure. Also note that even
1321 /// though we didn't capture this path, the function visits it,
1322 /// which is kind of the point of this function. We then return
1323 /// if the type of `w.p.y` implements Drop, which in this case is
1326 /// Consider another example:
1328 /// ```ignore (pseudo-rust)
1330 /// impl Drop for X {}
1333 /// impl Drop for Y {}
1337 /// let c = || move(y.0);
1341 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1342 /// return true, because even though all paths starting at `y` are captured, `y` itself
1343 /// implements Drop which will be affected since `y` isn't completely captured.
1344 fn has_significant_drop_outside_of_captures(
1346 closure_def_id: DefId,
1348 base_path_ty: Ty<'tcx>,
1349 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1351 let needs_drop = |ty: Ty<'tcx>| {
1352 ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local()))
1355 let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
1356 let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
1357 let ty_params = self.tcx.mk_substs_trait(base_path_ty, &[]);
1359 .type_implements_trait(
1363 self.tcx.param_env(closure_def_id.expect_local()),
1365 .must_apply_modulo_regions()
1368 let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
1370 // If there is a case where no projection is applied on top of current place
1371 // then there must be exactly one capture corresponding to such a case. Note that this
1372 // represents the case of the path being completely captured by the variable.
1374 // eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
1375 // capture `a.b.c`, because that violates min capture.
1376 let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
1378 assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
1380 if is_completely_captured {
1381 // The place is captured entirely, so doesn't matter if needs dtor, it will be drop
1382 // when the closure is dropped.
1386 if captured_by_move_projs.is_empty() {
1387 return needs_drop(base_path_ty);
1390 if is_drop_defined_for_ty {
1391 // If drop is implemented for this type then we need it to be fully captured,
1392 // and we know it is not completely captured because of the previous checks.
1394 // Note that this is a bug in the user code that will be reported by the
1395 // borrow checker, since we can't move out of drop types.
1397 // The bug exists in the user's code pre-migration, and we don't migrate here.
1401 match base_path_ty.kind() {
1403 // - `captured_by_move_projs` is not empty. Therefore we can call
1404 // `captured_by_move_projs.first().unwrap()` safely.
1405 // - All entries in `captured_by_move_projs` have at least one projection.
1406 // Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
1408 // We don't capture derefs in case of move captures, which would have be applied to
1409 // access any further paths.
1410 ty::Adt(def, _) if def.is_box() => unreachable!(),
1411 ty::Ref(..) => unreachable!(),
1412 ty::RawPtr(..) => unreachable!(),
1414 ty::Adt(def, substs) => {
1415 // Multi-variant enums are captured in entirety,
1416 // which would've been handled in the case of single empty slice in `captured_by_move_projs`.
1417 assert_eq!(def.variants().len(), 1);
1419 // Only Field projections can be applied to a non-box Adt.
1421 captured_by_move_projs.iter().all(|projs| matches!(
1422 projs.first().unwrap().kind,
1423 ProjectionKind::Field(..)
1426 def.variants().get(VariantIdx::new(0)).unwrap().fields.iter().enumerate().any(
1428 let paths_using_field = captured_by_move_projs
1430 .filter_map(|projs| {
1431 if let ProjectionKind::Field(field_idx, _) =
1432 projs.first().unwrap().kind
1434 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1441 let after_field_ty = field.ty(self.tcx, substs);
1442 self.has_significant_drop_outside_of_captures(
1452 ty::Tuple(fields) => {
1453 // Only Field projections can be applied to a tuple.
1455 captured_by_move_projs.iter().all(|projs| matches!(
1456 projs.first().unwrap().kind,
1457 ProjectionKind::Field(..)
1461 fields.iter().enumerate().any(|(i, element_ty)| {
1462 let paths_using_field = captured_by_move_projs
1464 .filter_map(|projs| {
1465 if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
1467 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1474 self.has_significant_drop_outside_of_captures(
1483 // Anything else would be completely captured and therefore handled already.
1484 _ => unreachable!(),
1488 fn init_capture_kind_for_place(
1490 place: &Place<'tcx>,
1491 capture_clause: hir::CaptureBy,
1492 ) -> ty::UpvarCapture {
1493 match capture_clause {
1494 // In case of a move closure if the data is accessed through a reference we
1495 // want to capture by ref to allow precise capture using reborrows.
1497 // If the data will be moved out of this place, then the place will be truncated
1498 // at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
1500 hir::CaptureBy::Value if !place.deref_tys().any(Ty::is_ref) => {
1501 ty::UpvarCapture::ByValue
1503 hir::CaptureBy::Value | hir::CaptureBy::Ref => ty::UpvarCapture::ByRef(ty::ImmBorrow),
1507 fn place_for_root_variable(
1509 closure_def_id: LocalDefId,
1510 var_hir_id: hir::HirId,
1512 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
1515 base_ty: self.node_ty(var_hir_id),
1516 base: PlaceBase::Upvar(upvar_id),
1517 projections: Default::default(),
1521 fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
1522 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
1525 fn log_capture_analysis_first_pass(
1527 closure_def_id: rustc_hir::def_id::DefId,
1528 capture_information: &InferredCaptureInformation<'tcx>,
1531 if self.should_log_capture_analysis(closure_def_id) {
1533 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
1534 for (place, capture_info) in capture_information {
1535 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
1536 let output_str = format!("Capturing {capture_str}");
1539 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
1540 diag.span_note(span, &output_str);
1546 fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
1547 if self.should_log_capture_analysis(closure_def_id) {
1548 if let Some(min_captures) =
1549 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
1552 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
1554 for (_, min_captures_for_var) in min_captures {
1555 for capture in min_captures_for_var {
1556 let place = &capture.place;
1557 let capture_info = &capture.info;
1560 construct_capture_info_string(self.tcx, place, capture_info);
1561 let output_str = format!("Min Capture {capture_str}");
1563 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
1564 let path_span = capture_info
1566 .map_or(closure_span, |e| self.tcx.hir().span(e));
1567 let capture_kind_span = capture_info
1568 .capture_kind_expr_id
1569 .map_or(closure_span, |e| self.tcx.hir().span(e));
1571 let mut multi_span: MultiSpan =
1572 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
1574 let capture_kind_label =
1575 construct_capture_kind_reason_string(self.tcx, place, capture_info);
1576 let path_label = construct_path_string(self.tcx, place);
1578 multi_span.push_span_label(path_span, path_label);
1579 multi_span.push_span_label(capture_kind_span, capture_kind_label);
1581 diag.span_note(multi_span, &output_str);
1583 let span = capture_info
1585 .map_or(closure_span, |e| self.tcx.hir().span(e));
1587 diag.span_note(span, &output_str);
1596 /// A captured place is mutable if
1597 /// 1. Projections don't include a Deref of an immut-borrow, **and**
1598 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
1599 fn determine_capture_mutability(
1601 typeck_results: &'a TypeckResults<'tcx>,
1602 place: &Place<'tcx>,
1603 ) -> hir::Mutability {
1604 let var_hir_id = match place.base {
1605 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
1606 _ => unreachable!(),
1609 let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
1611 let mut is_mutbl = match bm {
1612 ty::BindByValue(mutability) => mutability,
1613 ty::BindByReference(_) => hir::Mutability::Not,
1616 for pointer_ty in place.deref_tys() {
1617 match pointer_ty.kind() {
1618 // We don't capture derefs of raw ptrs
1619 ty::RawPtr(_) => unreachable!(),
1621 // Dereferencing a mut-ref allows us to mut the Place if we don't deref
1622 // an immut-ref after on top of this.
1623 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
1625 // The place isn't mutable once we dereference an immutable reference.
1626 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
1628 // Dereferencing a box doesn't change mutability
1629 ty::Adt(def, ..) if def.is_box() => {}
1631 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
1639 /// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
1640 /// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
1641 fn restrict_repr_packed_field_ref_capture<'tcx>(
1643 param_env: ty::ParamEnv<'tcx>,
1644 mut place: Place<'tcx>,
1645 mut curr_borrow_kind: ty::UpvarCapture,
1646 ) -> (Place<'tcx>, ty::UpvarCapture) {
1647 let pos = place.projections.iter().enumerate().position(|(i, p)| {
1648 let ty = place.ty_before_projection(i);
1650 // Return true for fields of packed structs, unless those fields have alignment 1.
1652 ProjectionKind::Field(..) => match ty.kind() {
1653 ty::Adt(def, _) if def.repr().packed() => {
1654 // We erase regions here because they cannot be hashed
1655 match tcx.layout_of(param_env.and(tcx.erase_regions(p.ty))) {
1656 Ok(layout) if layout.align.abi.bytes() == 1 => {
1657 // if the alignment is 1, the type can't be further
1660 "restrict_repr_packed_field_ref_capture: ({:?}) - align = 1",
1666 debug!("restrict_repr_packed_field_ref_capture: ({:?}) - true", place);
1678 if let Some(pos) = pos {
1679 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
1682 (place, curr_borrow_kind)
1685 /// Returns a Ty that applies the specified capture kind on the provided capture Ty
1686 fn apply_capture_kind_on_capture_ty<'tcx>(
1689 capture_kind: UpvarCapture,
1690 region: Option<ty::Region<'tcx>>,
1692 match capture_kind {
1693 ty::UpvarCapture::ByValue => ty,
1694 ty::UpvarCapture::ByRef(kind) => {
1695 tcx.mk_ref(region.unwrap(), ty::TypeAndMut { ty: ty, mutbl: kind.to_mutbl_lossy() })
1700 /// Returns the Span of where the value with the provided HirId would be dropped
1701 fn drop_location_span<'tcx>(tcx: TyCtxt<'tcx>, hir_id: hir::HirId) -> Span {
1702 let owner_id = tcx.hir().get_enclosing_scope(hir_id).unwrap();
1704 let owner_node = tcx.hir().get(owner_id);
1705 let owner_span = match owner_node {
1706 hir::Node::Item(item) => match item.kind {
1707 hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
1709 bug!("Drop location span error: need to handle more ItemKind '{:?}'", item.kind);
1712 hir::Node::Block(block) => tcx.hir().span(block.hir_id),
1713 hir::Node::TraitItem(item) => tcx.hir().span(item.hir_id()),
1714 hir::Node::ImplItem(item) => tcx.hir().span(item.hir_id()),
1716 bug!("Drop location span error: need to handle more Node '{:?}'", owner_node);
1719 tcx.sess.source_map().end_point(owner_span)
1722 struct InferBorrowKind<'a, 'tcx> {
1723 fcx: &'a FnCtxt<'a, 'tcx>,
1725 // The def-id of the closure whose kind and upvar accesses are being inferred.
1726 closure_def_id: LocalDefId,
1728 /// For each Place that is captured by the closure, we track the minimal kind of
1729 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1731 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1732 /// s.str2 via a MutableBorrow
1735 /// struct SomeStruct { str1: String, str2: String };
1737 /// // Assume that the HirId for the variable definition is `V1`
1738 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") };
1740 /// let fix_s = |new_s2| {
1741 /// // Assume that the HirId for the expression `s.str1` is `E1`
1742 /// println!("Updating SomeStruct with str1={0}", s.str1);
1743 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1744 /// s.str2 = new_s2;
1748 /// For closure `fix_s`, (at a high level) the map contains
1750 /// ```ignore (illustrative)
1751 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1752 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1754 capture_information: InferredCaptureInformation<'tcx>,
1755 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1758 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1761 place: &PlaceWithHirId<'tcx>,
1762 cause: FakeReadCause,
1763 diag_expr_id: hir::HirId,
1765 let PlaceBase::Upvar(_) = place.place.base else { return };
1767 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1768 // such as deref of a raw pointer.
1769 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1771 let (place, _) = restrict_capture_precision(place.place.clone(), dummy_capture_kind);
1773 let (place, _) = restrict_repr_packed_field_ref_capture(
1779 self.fake_reads.push((place, cause, diag_expr_id));
1782 #[instrument(skip(self), level = "debug")]
1783 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1784 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1785 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1787 self.capture_information.push((
1788 place_with_id.place.clone(),
1790 capture_kind_expr_id: Some(diag_expr_id),
1791 path_expr_id: Some(diag_expr_id),
1792 capture_kind: ty::UpvarCapture::ByValue,
1797 #[instrument(skip(self), level = "debug")]
1800 place_with_id: &PlaceWithHirId<'tcx>,
1801 diag_expr_id: hir::HirId,
1804 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
1805 assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
1807 // The region here will get discarded/ignored
1808 let capture_kind = ty::UpvarCapture::ByRef(bk);
1810 // We only want repr packed restriction to be applied to reading references into a packed
1811 // struct, and not when the data is being moved. Therefore we call this method here instead
1812 // of in `restrict_capture_precision`.
1813 let (place, mut capture_kind) = restrict_repr_packed_field_ref_capture(
1816 place_with_id.place.clone(),
1820 // Raw pointers don't inherit mutability
1821 if place_with_id.place.deref_tys().any(Ty::is_unsafe_ptr) {
1822 capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
1825 self.capture_information.push((
1828 capture_kind_expr_id: Some(diag_expr_id),
1829 path_expr_id: Some(diag_expr_id),
1835 #[instrument(skip(self), level = "debug")]
1836 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1837 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1841 /// Rust doesn't permit moving fields out of a type that implements drop
1842 fn restrict_precision_for_drop_types<'a, 'tcx>(
1843 fcx: &'a FnCtxt<'a, 'tcx>,
1844 mut place: Place<'tcx>,
1845 mut curr_mode: ty::UpvarCapture,
1847 ) -> (Place<'tcx>, ty::UpvarCapture) {
1848 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1850 if let (false, UpvarCapture::ByValue) = (is_copy_type, curr_mode) {
1851 for i in 0..place.projections.len() {
1852 match place.ty_before_projection(i).kind() {
1853 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1854 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1865 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
1866 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
1867 /// them completely.
1868 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
1869 fn restrict_precision_for_unsafe<'tcx>(
1870 mut place: Place<'tcx>,
1871 mut curr_mode: ty::UpvarCapture,
1872 ) -> (Place<'tcx>, ty::UpvarCapture) {
1873 if place.base_ty.is_unsafe_ptr() {
1874 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1877 if place.base_ty.is_union() {
1878 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1881 for (i, proj) in place.projections.iter().enumerate() {
1882 if proj.ty.is_unsafe_ptr() {
1883 // Don't apply any projections on top of an unsafe ptr.
1884 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1888 if proj.ty.is_union() {
1889 // Don't capture precise fields of a union.
1890 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1898 /// Truncate projections so that following rules are obeyed by the captured `place`:
1899 /// - No Index projections are captured, since arrays are captured completely.
1900 /// - No unsafe block is required to capture `place`
1901 /// Returns the truncated place and updated capture mode.
1902 fn restrict_capture_precision<'tcx>(
1904 curr_mode: ty::UpvarCapture,
1905 ) -> (Place<'tcx>, ty::UpvarCapture) {
1906 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
1908 if place.projections.is_empty() {
1909 // Nothing to do here
1910 return (place, curr_mode);
1913 for (i, proj) in place.projections.iter().enumerate() {
1915 ProjectionKind::Index => {
1916 // Arrays are completely captured, so we drop Index projections
1917 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1918 return (place, curr_mode);
1920 ProjectionKind::Deref => {}
1921 ProjectionKind::Field(..) => {} // ignore
1922 ProjectionKind::Subslice => {} // We never capture this
1929 /// Truncate deref of any reference.
1930 fn adjust_for_move_closure<'tcx>(
1931 mut place: Place<'tcx>,
1932 mut kind: ty::UpvarCapture,
1933 ) -> (Place<'tcx>, ty::UpvarCapture) {
1934 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1936 if let Some(idx) = first_deref {
1937 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1940 (place, ty::UpvarCapture::ByValue)
1943 /// Adjust closure capture just that if taking ownership of data, only move data
1944 /// from enclosing stack frame.
1945 fn adjust_for_non_move_closure<'tcx>(
1946 mut place: Place<'tcx>,
1947 mut kind: ty::UpvarCapture,
1948 ) -> (Place<'tcx>, ty::UpvarCapture) {
1949 let contains_deref =
1950 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
1953 ty::UpvarCapture::ByValue => {
1954 if let Some(idx) = contains_deref {
1955 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
1959 ty::UpvarCapture::ByRef(..) => {}
1965 fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
1966 let variable_name = match place.base {
1967 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
1968 _ => bug!("Capture_information should only contain upvars"),
1971 let mut projections_str = String::new();
1972 for (i, item) in place.projections.iter().enumerate() {
1973 let proj = match item.kind {
1974 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
1975 ProjectionKind::Deref => String::from("Deref"),
1976 ProjectionKind::Index => String::from("Index"),
1977 ProjectionKind::Subslice => String::from("Subslice"),
1980 projections_str.push(',');
1982 projections_str.push_str(proj.as_str());
1985 format!("{variable_name}[{projections_str}]")
1988 fn construct_capture_kind_reason_string<'tcx>(
1990 place: &Place<'tcx>,
1991 capture_info: &ty::CaptureInfo,
1993 let place_str = construct_place_string(tcx, place);
1995 let capture_kind_str = match capture_info.capture_kind {
1996 ty::UpvarCapture::ByValue => "ByValue".into(),
1997 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
2000 format!("{place_str} captured as {capture_kind_str} here")
2003 fn construct_path_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2004 let place_str = construct_place_string(tcx, place);
2006 format!("{place_str} used here")
2009 fn construct_capture_info_string<'tcx>(
2011 place: &Place<'tcx>,
2012 capture_info: &ty::CaptureInfo,
2014 let place_str = construct_place_string(tcx, place);
2016 let capture_kind_str = match capture_info.capture_kind {
2017 ty::UpvarCapture::ByValue => "ByValue".into(),
2018 ty::UpvarCapture::ByRef(kind) => format!("{:?}", kind),
2020 format!("{place_str} -> {capture_kind_str}")
2023 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2024 tcx.hir().name(var_hir_id)
2027 #[instrument(level = "debug", skip(tcx))]
2028 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2030 closure_id: hir::HirId,
2033 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2035 !matches!(level, lint::Level::Allow)
2038 /// Return a two string tuple (s1, s2)
2039 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2040 /// - s2: Comma separated names of the variables being migrated.
2041 fn migration_suggestion_for_2229(
2043 need_migrations: &[NeededMigration],
2044 ) -> (String, String) {
2045 let need_migrations_variables = need_migrations
2047 .map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
2048 .collect::<Vec<_>>();
2050 let migration_ref_concat =
2051 need_migrations_variables.iter().map(|v| format!("&{v}")).collect::<Vec<_>>().join(", ");
2053 let migration_string = if 1 == need_migrations.len() {
2054 format!("let _ = {migration_ref_concat}")
2056 format!("let _ = ({migration_ref_concat})")
2059 let migrated_variables_concat =
2060 need_migrations_variables.iter().map(|v| format!("`{v}`")).collect::<Vec<_>>().join(", ");
2062 (migration_string, migrated_variables_concat)
2065 /// Helper function to determine if we need to escalate CaptureKind from
2066 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2067 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2069 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2070 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2072 /// It is the caller's duty to figure out which path_expr_id to use.
2074 /// If both the CaptureKind and Expression are considered to be equivalent,
2075 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to prioritize
2076 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2077 /// in the closure. This can be achieved simply by calling
2078 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2079 /// expressions that occur earlier in the closure body than the current expression are processed before.
2080 /// Consider the following example
2082 /// struct Point { x: i32, y: i32 }
2083 /// let mut p = Point { x: 10, y: 10 };
2091 /// p.x += 10; // E2
2095 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2096 /// and both have an expression associated, however for diagnostics we prefer reporting
2097 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2098 /// would've already handled `E1`, and have an existing capture_information for it.
2099 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2100 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2101 fn determine_capture_info(
2102 capture_info_a: ty::CaptureInfo,
2103 capture_info_b: ty::CaptureInfo,
2104 ) -> ty::CaptureInfo {
2105 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2107 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2108 (ty::UpvarCapture::ByValue, ty::UpvarCapture::ByValue) => true,
2109 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => ref_a == ref_b,
2110 (ty::UpvarCapture::ByValue, _) | (ty::UpvarCapture::ByRef(_), _) => false,
2113 if eq_capture_kind {
2114 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2115 (Some(_), _) | (None, None) => capture_info_a,
2116 (None, Some(_)) => capture_info_b,
2119 // We select the CaptureKind which ranks higher based the following priority order:
2120 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2121 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2122 (ty::UpvarCapture::ByValue, _) => capture_info_a,
2123 (_, ty::UpvarCapture::ByValue) => capture_info_b,
2124 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2125 match (ref_a, ref_b) {
2127 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2128 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2131 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2132 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2134 (ty::ImmBorrow, ty::ImmBorrow)
2135 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2136 | (ty::MutBorrow, ty::MutBorrow) => {
2137 bug!("Expected unequal capture kinds");
2145 /// Truncates `place` to have up to `len` projections.
2146 /// `curr_mode` is the current required capture kind for the place.
2147 /// Returns the truncated `place` and the updated required capture kind.
2149 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2150 /// contained `Deref` of `&mut`.
2151 fn truncate_place_to_len_and_update_capture_kind<'tcx>(
2152 place: &mut Place<'tcx>,
2153 curr_mode: &mut ty::UpvarCapture,
2156 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2158 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2160 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2161 // we don't need to worry about that case here.
2163 ty::UpvarCapture::ByRef(ty::BorrowKind::MutBorrow) => {
2164 for i in len..place.projections.len() {
2165 if place.projections[i].kind == ProjectionKind::Deref
2166 && is_mut_ref(place.ty_before_projection(i))
2168 *curr_mode = ty::UpvarCapture::ByRef(ty::BorrowKind::UniqueImmBorrow);
2174 ty::UpvarCapture::ByRef(..) => {}
2175 ty::UpvarCapture::ByValue => {}
2178 place.projections.truncate(len);
2181 /// Determines the Ancestry relationship of Place A relative to Place B
2183 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2184 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2185 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2186 fn determine_place_ancestry_relation<'tcx>(
2187 place_a: &Place<'tcx>,
2188 place_b: &Place<'tcx>,
2189 ) -> PlaceAncestryRelation {
2190 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2191 if place_a.base != place_b.base {
2192 return PlaceAncestryRelation::Divergent;
2195 // Assume of length of projections_a = n
2196 let projections_a = &place_a.projections;
2198 // Assume of length of projections_b = m
2199 let projections_b = &place_b.projections;
2201 let same_initial_projections =
2202 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2204 if same_initial_projections {
2205 use std::cmp::Ordering;
2207 // First min(n, m) projections are the same
2208 // Select Ancestor/Descendant
2209 match projections_b.len().cmp(&projections_a.len()) {
2210 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2211 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2212 Ordering::Less => PlaceAncestryRelation::Descendant,
2215 PlaceAncestryRelation::Divergent
2219 /// Reduces the precision of the captured place when the precision doesn't yield any benefit from
2220 /// borrow checking perspective, allowing us to save us on the size of the capture.
2223 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2224 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2225 /// rightmost deref of the capture if the deref is applied to a shared ref.
2227 /// Reason we only drop the last deref is because of the following edge case:
2230 /// # struct A { field_of_a: Box<i32> }
2232 /// # struct C<'a>(&'a i32);
2233 /// struct MyStruct<'a> {
2239 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2240 /// || drop(&*m.a.field_of_a)
2241 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2243 /// // If we capture `m`, then the closure no longer outlives `'static'
2244 /// // it is constrained to `'a`
2247 fn truncate_capture_for_optimization<'tcx>(
2248 mut place: Place<'tcx>,
2249 mut curr_mode: ty::UpvarCapture,
2250 ) -> (Place<'tcx>, ty::UpvarCapture) {
2251 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2253 // Find the right-most deref (if any). All the projections that come after this
2254 // are fields or other "in-place pointer adjustments"; these refer therefore to
2255 // data owned by whatever pointer is being dereferenced here.
2256 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2259 // If that pointer is a shared reference, then we don't need those fields.
2260 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2261 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2263 None | Some(_) => {}
2269 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2270 /// user is using Rust Edition 2021 or higher.
2272 /// `span` is the span of the closure.
2273 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2274 // We use span here to ensure that if the closure was generated by a macro with a different
2276 tcx.features().capture_disjoint_fields || span.rust_2021()