1 //! ### Inferring borrow kinds for upvars
3 //! Whenever there is a closure expression, we need to determine how each
4 //! upvar is used. We do this by initially assigning each upvar an
5 //! immutable "borrow kind" (see `ty::BorrowKind` for details) and then
6 //! "escalating" the kind as needed. The borrow kind proceeds according to
7 //! the following lattice:
9 //! ty::ImmBorrow -> ty::UniqueImmBorrow -> ty::MutBorrow
11 //! So, for example, if we see an assignment `x = 5` to an upvar `x`, we
12 //! will promote its borrow kind to mutable borrow. If we see an `&mut x`
13 //! we'll do the same. Naturally, this applies not just to the upvar, but
14 //! to everything owned by `x`, so the result is the same for something
15 //! like `x.f = 5` and so on (presuming `x` is not a borrowed pointer to a
16 //! struct). These adjustments are performed in
17 //! `adjust_upvar_borrow_kind()` (you can trace backwards through the code
20 //! The fact that we are inferring borrow kinds as we go results in a
21 //! semi-hacky interaction with mem-categorization. In particular,
22 //! mem-categorization will query the current borrow kind as it
23 //! categorizes, and we'll return the *current* value, but this may get
24 //! adjusted later. Therefore, in this module, we generally ignore the
25 //! borrow kind (and derived mutabilities) that are returned from
26 //! mem-categorization, since they may be inaccurate. (Another option
27 //! would be to use a unification scheme, where instead of returning a
28 //! concrete borrow kind like `ty::ImmBorrow`, we return a
29 //! `ty::InferBorrow(upvar_id)` or something like that, but this would
30 //! then mean that all later passes would have to check for these figments
31 //! and report an error, and it just seems like more mess in the end.)
35 use crate::expr_use_visitor as euv;
36 use rustc_data_structures::fx::FxIndexMap;
37 use rustc_errors::Applicability;
39 use rustc_hir::def_id::DefId;
40 use rustc_hir::def_id::LocalDefId;
41 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
42 use rustc_infer::infer::UpvarRegion;
43 use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection, ProjectionKind};
44 use rustc_middle::mir::FakeReadCause;
45 use rustc_middle::ty::{
46 self, ClosureSizeProfileData, Ty, TyCtxt, TypeckResults, UpvarCapture, UpvarSubsts,
48 use rustc_session::lint;
50 use rustc_span::{BytePos, MultiSpan, Pos, Span, Symbol};
51 use rustc_trait_selection::infer::InferCtxtExt;
53 use rustc_data_structures::stable_map::FxHashMap;
54 use rustc_data_structures::stable_set::FxHashSet;
55 use rustc_index::vec::Idx;
56 use rustc_target::abi::VariantIdx;
60 /// Describe the relationship between the paths of two places
62 /// - `foo` is ancestor of `foo.bar.baz`
63 /// - `foo.bar.baz` is an descendant of `foo.bar`
64 /// - `foo.bar` and `foo.baz` are divergent
65 enum PlaceAncestryRelation {
72 /// Intermediate format to store a captured `Place` and associated `ty::CaptureInfo`
73 /// during capture analysis. Information in this map feeds into the minimum capture
75 type InferredCaptureInformation<'tcx> = FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>;
77 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
78 pub fn closure_analyze(&self, body: &'tcx hir::Body<'tcx>) {
79 InferBorrowKindVisitor { fcx: self }.visit_body(body);
81 // it's our job to process these.
82 assert!(self.deferred_call_resolutions.borrow().is_empty());
86 /// Intermediate format to store the hir_id pointing to the use that resulted in the
87 /// corresponding place being captured and a String which contains the captured value's
89 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
91 CapturingLess { source_expr: Option<hir::HirId>, var_name: String },
94 /// Intermediate format to store information needed to generate migration lint. The tuple
95 /// contains the hir_id pointing to the use that resulted in the
96 /// corresponding place being captured, a String which contains the captured value's
97 /// name (i.e: a.b.c) and a String which contains the reason why migration is needed for that
99 type MigrationNeededForCapture = (Option<hir::HirId>, String, String);
101 /// Intermediate format to store the hir id of the root variable and a HashSet containing
102 /// information on why the root variable should be fully captured
103 type MigrationDiagnosticInfo = (hir::HirId, Vec<MigrationNeededForCapture>);
105 struct InferBorrowKindVisitor<'a, 'tcx> {
106 fcx: &'a FnCtxt<'a, 'tcx>,
109 impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
110 type Map = intravisit::ErasedMap<'tcx>;
112 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
113 NestedVisitorMap::None
116 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
117 if let hir::ExprKind::Closure(cc, _, body_id, _, _) = expr.kind {
118 let body = self.fcx.tcx.hir().body(body_id);
119 self.visit_body(body);
120 self.fcx.analyze_closure(expr.hir_id, expr.span, body_id, body, cc);
123 intravisit::walk_expr(self, expr);
127 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
128 /// Analysis starting point.
129 #[instrument(skip(self, body), level = "debug")]
132 closure_hir_id: hir::HirId,
134 body_id: hir::BodyId,
135 body: &'tcx hir::Body<'tcx>,
136 capture_clause: hir::CaptureBy,
138 // Extract the type of the closure.
139 let ty = self.node_ty(closure_hir_id);
140 let (closure_def_id, substs) = match *ty.kind() {
141 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
142 ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
144 // #51714: skip analysis when we have already encountered type errors
150 "type of closure expr {:?} is not a closure {:?}",
157 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
158 self.closure_kind(closure_substs).is_none().then_some(closure_substs)
163 let local_def_id = closure_def_id.expect_local();
165 let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
166 assert_eq!(body_owner_def_id.to_def_id(), closure_def_id);
167 let mut delegate = InferBorrowKind {
171 capture_information: Default::default(),
172 fake_reads: Default::default(),
174 euv::ExprUseVisitor::new(
179 &self.typeck_results.borrow(),
184 "For closure={:?}, capture_information={:#?}",
185 closure_def_id, delegate.capture_information
188 self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
190 let (capture_information, closure_kind, origin) = self
191 .process_collected_capture_information(capture_clause, delegate.capture_information);
193 self.compute_min_captures(closure_def_id, capture_information);
195 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
197 if should_do_rust_2021_incompatible_closure_captures_analysis(self.tcx, closure_hir_id) {
198 self.perform_2229_migration_anaysis(closure_def_id, body_id, capture_clause, span);
201 let after_feature_tys = self.final_upvar_tys(closure_def_id);
203 // We now fake capture information for all variables that are mentioned within the closure
204 // We do this after handling migrations so that min_captures computes before
205 if !enable_precise_capture(self.tcx, span) {
206 let mut capture_information: InferredCaptureInformation<'tcx> = Default::default();
208 if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
209 for var_hir_id in upvars.keys() {
210 let place = self.place_for_root_variable(local_def_id, *var_hir_id);
212 debug!("seed place {:?}", place);
214 let upvar_id = ty::UpvarId::new(*var_hir_id, local_def_id);
216 self.init_capture_kind_for_place(&place, capture_clause, upvar_id, span);
217 let fake_info = ty::CaptureInfo {
218 capture_kind_expr_id: None,
223 capture_information.insert(place, fake_info);
227 // This will update the min captures based on this new fake information.
228 self.compute_min_captures(closure_def_id, capture_information);
231 let before_feature_tys = self.final_upvar_tys(closure_def_id);
233 if let Some(closure_substs) = infer_kind {
234 // Unify the (as yet unbound) type variable in the closure
235 // substs with the kind we inferred.
236 let closure_kind_ty = closure_substs.as_closure().kind_ty();
237 self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
239 // If we have an origin, store it.
240 if let Some(origin) = origin {
241 let origin = if enable_precise_capture(self.tcx, span) {
244 (origin.0, Place { projections: vec![], ..origin.1 })
249 .closure_kind_origins_mut()
250 .insert(closure_hir_id, origin);
254 self.log_closure_min_capture_info(closure_def_id, span);
256 // Now that we've analyzed the closure, we know how each
257 // variable is borrowed, and we know what traits the closure
258 // implements (Fn vs FnMut etc). We now have some updates to do
259 // with that information.
261 // Note that no closure type C may have an upvar of type C
262 // (though it may reference itself via a trait object). This
263 // results from the desugaring of closures to a struct like
264 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
265 // C, then the type would have infinite size (and the
266 // inference algorithm will reject it).
268 // Equate the type variables for the upvars with the actual types.
269 let final_upvar_tys = self.final_upvar_tys(closure_def_id);
271 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
272 closure_hir_id, substs, final_upvar_tys
275 // Build a tuple (U0..Un) of the final upvar types U0..Un
276 // and unify the upvar tupe type in the closure with it:
277 let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
278 self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
280 let fake_reads = delegate
283 .map(|(place, cause, hir_id)| (place, cause, hir_id))
285 self.typeck_results.borrow_mut().closure_fake_reads.insert(closure_def_id, fake_reads);
287 if self.tcx.sess.opts.debugging_opts.profile_closures {
288 self.typeck_results.borrow_mut().closure_size_eval.insert(
290 ClosureSizeProfileData {
291 before_feature_tys: self.tcx.mk_tup(before_feature_tys.into_iter()),
292 after_feature_tys: self.tcx.mk_tup(after_feature_tys.into_iter()),
297 // If we are also inferred the closure kind here,
298 // process any deferred resolutions.
299 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
300 for deferred_call_resolution in deferred_call_resolutions {
301 deferred_call_resolution.resolve(self);
305 // Returns a list of `Ty`s for each upvar.
306 fn final_upvar_tys(&self, closure_id: DefId) -> Vec<Ty<'tcx>> {
307 // Presently an unboxed closure type cannot "escape" out of a
308 // function, so we will only encounter ones that originated in the
309 // local crate or were inlined into it along with some function.
310 // This may change if abstract return types of some sort are
314 .closure_min_captures_flattened(closure_id)
315 .map(|captured_place| {
316 let upvar_ty = captured_place.place.ty();
317 let capture = captured_place.info.capture_kind;
320 "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
321 captured_place.place, upvar_ty, capture, captured_place.mutability,
324 apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture)
329 /// Adjusts the closure capture information to ensure that the operations aren't unsafe,
330 /// and that the path can be captured with required capture kind (depending on use in closure,
331 /// move closure etc.)
333 /// Returns the set of of adjusted information along with the inferred closure kind and span
334 /// associated with the closure kind inference.
336 /// Note that we *always* infer a minimal kind, even if
337 /// we don't always *use* that in the final result (i.e., sometimes
338 /// we've taken the closure kind from the expectations instead, and
339 /// for generators we don't even implement the closure traits
342 /// If we inferred that the closure needs to be FnMut/FnOnce, last element of the returned tuple
343 /// contains a `Some()` with the `Place` that caused us to do so.
344 fn process_collected_capture_information(
346 capture_clause: hir::CaptureBy,
347 capture_information: InferredCaptureInformation<'tcx>,
348 ) -> (InferredCaptureInformation<'tcx>, ty::ClosureKind, Option<(Span, Place<'tcx>)>) {
349 let mut processed: InferredCaptureInformation<'tcx> = Default::default();
351 let mut closure_kind = ty::ClosureKind::LATTICE_BOTTOM;
352 let mut origin: Option<(Span, Place<'tcx>)> = None;
354 for (place, mut capture_info) in capture_information {
355 // Apply rules for safety before inferring closure kind
356 let (place, capture_kind) =
357 restrict_capture_precision(place, capture_info.capture_kind);
358 capture_info.capture_kind = capture_kind;
360 let (place, capture_kind) =
361 truncate_capture_for_optimization(place, capture_info.capture_kind);
362 capture_info.capture_kind = capture_kind;
364 let usage_span = if let Some(usage_expr) = capture_info.path_expr_id {
365 self.tcx.hir().span(usage_expr)
370 let updated = match capture_info.capture_kind {
371 ty::UpvarCapture::ByValue(..) => match closure_kind {
372 ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
373 (ty::ClosureKind::FnOnce, Some((usage_span, place.clone())))
375 // If closure is already FnOnce, don't update
376 ty::ClosureKind::FnOnce => (closure_kind, origin),
379 ty::UpvarCapture::ByRef(ty::UpvarBorrow {
380 kind: ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
384 ty::ClosureKind::Fn => {
385 (ty::ClosureKind::FnMut, Some((usage_span, place.clone())))
387 // Don't update the origin
388 ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce => (closure_kind, origin),
392 _ => (closure_kind, origin),
395 closure_kind = updated.0;
398 let (place, capture_kind) = match capture_clause {
399 hir::CaptureBy::Value => adjust_for_move_closure(place, capture_info.capture_kind),
400 hir::CaptureBy::Ref => {
401 adjust_for_non_move_closure(place, capture_info.capture_kind)
405 // This restriction needs to be applied after we have handled adjustments for `move`
406 // closures. We want to make sure any adjustment that might make us move the place into
407 // the closure gets handled.
408 let (place, capture_kind) =
409 restrict_precision_for_drop_types(self, place, capture_kind, usage_span);
411 capture_info.capture_kind = capture_kind;
413 let capture_info = if let Some(existing) = processed.get(&place) {
414 determine_capture_info(*existing, capture_info)
418 processed.insert(place, capture_info);
421 (processed, closure_kind, origin)
424 /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
425 /// Places (and corresponding capture kind) that we need to keep track of to support all
426 /// the required captured paths.
429 /// Note: If this function is called multiple times for the same closure, it will update
430 /// the existing min_capture map that is stored in TypeckResults.
434 /// struct Point { x: i32, y: i32 }
436 /// let s: String; // hir_id_s
437 /// let mut p: Point; // his_id_p
439 /// println!("{}", s); // L1
441 /// println!("{}" , p.y) // L3
442 /// println!("{}", p) // L4
446 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
447 /// the lines L1..5 respectively.
449 /// InferBorrowKind results in a structure like this:
453 /// Place(base: hir_id_s, projections: [], ....) -> {
454 /// capture_kind_expr: hir_id_L5,
455 /// path_expr_id: hir_id_L5,
456 /// capture_kind: ByValue
458 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
459 /// capture_kind_expr: hir_id_L2,
460 /// path_expr_id: hir_id_L2,
461 /// capture_kind: ByValue
463 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
464 /// capture_kind_expr: hir_id_L3,
465 /// path_expr_id: hir_id_L3,
466 /// capture_kind: ByValue
468 /// Place(base: hir_id_p, projections: [], ...) -> {
469 /// capture_kind_expr: hir_id_L4,
470 /// path_expr_id: hir_id_L4,
471 /// capture_kind: ByValue
475 /// After the min capture analysis, we get:
479 /// Place(base: hir_id_s, projections: [], ....) -> {
480 /// capture_kind_expr: hir_id_L5,
481 /// path_expr_id: hir_id_L5,
482 /// capture_kind: ByValue
486 /// Place(base: hir_id_p, projections: [], ...) -> {
487 /// capture_kind_expr: hir_id_L2,
488 /// path_expr_id: hir_id_L4,
489 /// capture_kind: ByValue
493 fn compute_min_captures(
495 closure_def_id: DefId,
496 capture_information: InferredCaptureInformation<'tcx>,
498 if capture_information.is_empty() {
502 let mut typeck_results = self.typeck_results.borrow_mut();
504 let mut root_var_min_capture_list =
505 typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
507 for (mut place, capture_info) in capture_information.into_iter() {
508 let var_hir_id = match place.base {
509 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
510 base => bug!("Expected upvar, found={:?}", base),
513 let min_cap_list = match root_var_min_capture_list.get_mut(&var_hir_id) {
515 let mutability = self.determine_capture_mutability(&typeck_results, &place);
517 vec![ty::CapturedPlace { place, info: capture_info, mutability }];
518 root_var_min_capture_list.insert(var_hir_id, min_cap_list);
521 Some(min_cap_list) => min_cap_list,
524 // Go through each entry in the current list of min_captures
525 // - if ancestor is found, update it's capture kind to account for current place's
526 // capture information.
528 // - if descendant is found, remove it from the list, and update the current place's
529 // capture information to account for the descendants's capture kind.
531 // We can never be in a case where the list contains both an ancestor and a descendant
532 // Also there can only be ancestor but in case of descendants there might be
535 let mut descendant_found = false;
536 let mut updated_capture_info = capture_info;
537 min_cap_list.retain(|possible_descendant| {
538 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
539 // current place is ancestor of possible_descendant
540 PlaceAncestryRelation::Ancestor => {
541 descendant_found = true;
543 let mut possible_descendant = possible_descendant.clone();
544 let backup_path_expr_id = updated_capture_info.path_expr_id;
546 // Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
547 // possible change in capture mode.
548 truncate_place_to_len_and_update_capture_kind(
549 &mut possible_descendant.place,
550 &mut possible_descendant.info.capture_kind,
551 place.projections.len(),
554 updated_capture_info =
555 determine_capture_info(updated_capture_info, possible_descendant.info);
557 // we need to keep the ancestor's `path_expr_id`
558 updated_capture_info.path_expr_id = backup_path_expr_id;
566 let mut ancestor_found = false;
567 if !descendant_found {
568 for possible_ancestor in min_cap_list.iter_mut() {
569 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
570 // current place is descendant of possible_ancestor
571 PlaceAncestryRelation::Descendant | PlaceAncestryRelation::SamePlace => {
572 ancestor_found = true;
573 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
575 // Truncate the descendant (current place) to be same as the ancestor to handle any
576 // possible change in capture mode.
577 truncate_place_to_len_and_update_capture_kind(
579 &mut updated_capture_info.capture_kind,
580 possible_ancestor.place.projections.len(),
583 possible_ancestor.info = determine_capture_info(
584 possible_ancestor.info,
585 updated_capture_info,
588 // we need to keep the ancestor's `path_expr_id`
589 possible_ancestor.info.path_expr_id = backup_path_expr_id;
591 // Only one ancestor of the current place will be in the list.
599 // Only need to insert when we don't have an ancestor in the existing min capture list
601 let mutability = self.determine_capture_mutability(&typeck_results, &place);
603 ty::CapturedPlace { place, info: updated_capture_info, mutability };
604 min_cap_list.push(captured_place);
609 "For closure={:?}, min_captures before sorting={:?}",
610 closure_def_id, root_var_min_capture_list
613 // Now that we have the minimized list of captures, sort the captures by field id.
614 // This causes the closure to capture the upvars in the same order as the fields are
615 // declared which is also the drop order. Thus, in situations where we capture all the
616 // fields of some type, the obserable drop order will remain the same as it previously
617 // was even though we're dropping each capture individually.
618 // See https://github.com/rust-lang/project-rfc-2229/issues/42 and
619 // `src/test/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
620 for (_, captures) in &mut root_var_min_capture_list {
621 captures.sort_by(|capture1, capture2| {
622 for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
623 // We do not need to look at the `Projection.ty` fields here because at each
624 // step of the iteration, the projections will either be the same and therefore
625 // the types must be as well or the current projection will be different and
626 // we will return the result of comparing the field indexes.
627 match (p1.kind, p2.kind) {
628 // Paths are the same, continue to next loop.
629 (ProjectionKind::Deref, ProjectionKind::Deref) => {}
630 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
633 // Fields are different, compare them.
634 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
638 // We should have either a pair of `Deref`s or a pair of `Field`s.
639 // Anything else is a bug.
641 l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
642 r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
644 "ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
651 (ProjectionKind::Index
652 | ProjectionKind::Subslice
653 | ProjectionKind::Deref
654 | ProjectionKind::Field(..)),
657 (ProjectionKind::Index
658 | ProjectionKind::Subslice
659 | ProjectionKind::Deref
660 | ProjectionKind::Field(..)),
662 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
670 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
677 "For closure={:?}, min_captures after sorting={:#?}",
678 closure_def_id, root_var_min_capture_list
680 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
683 /// Perform the migration analysis for RFC 2229, and emit lint
684 /// `disjoint_capture_drop_reorder` if needed.
685 fn perform_2229_migration_anaysis(
687 closure_def_id: DefId,
688 body_id: hir::BodyId,
689 capture_clause: hir::CaptureBy,
692 let (need_migrations, reasons) = self.compute_2229_migrations(
696 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
699 if !need_migrations.is_empty() {
700 let (migration_string, migrated_variables_concat) =
701 migration_suggestion_for_2229(self.tcx, &need_migrations);
703 let local_def_id = closure_def_id.expect_local();
704 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
705 let closure_span = self.tcx.hir().span(closure_hir_id);
706 let closure_head_span = self.tcx.sess.source_map().guess_head_span(closure_span);
707 self.tcx.struct_span_lint_hir(
708 lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
712 let mut diagnostics_builder = lint.build(
714 "changes to closure capture in Rust 2021 will affect {}",
719 for (var_hir_id, diagnostics_info) in need_migrations.iter() {
720 // Labels all the usage of the captured variable and why they are responsible
721 // for migration being needed
722 for (captured_hir_id, captured_name, reasons) in diagnostics_info.iter() {
723 if let Some(captured_hir_id) = captured_hir_id {
724 let cause_span = self.tcx.hir().span(*captured_hir_id);
725 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
726 self.tcx.hir().name(*var_hir_id),
731 // Add a label pointing to where a captured variable affected by drop order
733 if reasons.contains("drop order") {
734 let drop_location_span = drop_location_span(self.tcx, &closure_hir_id);
736 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",
737 self.tcx.hir().name(*var_hir_id),
742 // Add a label explaining why a closure no longer implements a trait
743 if reasons.contains("trait implementation") {
744 let missing_trait = &reasons[..reasons.find("trait implementation").unwrap() - 1];
746 diagnostics_builder.span_label(closure_head_span, format!("in Rust 2018, this closure implements {} as `{}` implements {}, but in Rust 2021, this closure will no longer implement {} as `{}` does not implement {}",
748 self.tcx.hir().name(*var_hir_id),
757 diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
759 let diagnostic_msg = format!(
760 "add a dummy let to cause {} to be fully captured",
761 migrated_variables_concat
764 let mut closure_body_span = {
765 // If the body was entirely expanded from a macro
766 // invocation, i.e. the body is not contained inside the
767 // closure span, then we walk up the expansion until we
768 // find the span before the expansion.
769 let s = self.tcx.hir().span(body_id.hir_id);
770 s.find_ancestor_inside(closure_span).unwrap_or(s)
773 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
774 if s.starts_with('$') {
775 // Looks like a macro fragment. Try to find the real block.
776 if let Some(hir::Node::Expr(&hir::Expr {
777 kind: hir::ExprKind::Block(block, ..), ..
778 })) = self.tcx.hir().find(body_id.hir_id) {
779 // If the body is a block (with `{..}`), we use the span of that block.
780 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
781 // Since we know it's a block, we know we can insert the `let _ = ..` without
782 // breaking the macro syntax.
783 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
784 closure_body_span = block.span;
790 let mut lines = s.lines();
791 let line1 = lines.next().unwrap_or_default();
793 if line1.trim_end() == "{" {
794 // This is a multi-line closure with just a `{` on the first line,
795 // so we put the `let` on its own line.
796 // We take the indentation from the next non-empty line.
797 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
798 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
799 diagnostics_builder.span_suggestion(
800 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
802 format!("\n{}{};", indent, migration_string),
803 Applicability::MachineApplicable,
805 } else if line1.starts_with('{') {
806 // This is a closure with its body wrapped in
807 // braces, but with more than just the opening
808 // brace on the first line. We put the `let`
809 // directly after the `{`.
810 diagnostics_builder.span_suggestion(
811 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
813 format!(" {};", migration_string),
814 Applicability::MachineApplicable,
817 // This is a closure without braces around the body.
818 // We add braces to add the `let` before the body.
819 diagnostics_builder.multipart_suggestion(
822 (closure_body_span.shrink_to_lo(), format!("{{ {}; ", migration_string)),
823 (closure_body_span.shrink_to_hi(), " }".to_string()),
825 Applicability::MachineApplicable
829 diagnostics_builder.span_suggestion(
833 Applicability::HasPlaceholders
837 diagnostics_builder.emit();
843 /// Combines all the reasons for 2229 migrations
844 fn compute_2229_migrations_reasons(
846 auto_trait_reasons: FxHashSet<&str>,
849 let mut reasons = String::new();
851 if !auto_trait_reasons.is_empty() {
853 "{} trait implementation for closure",
854 auto_trait_reasons.clone().into_iter().collect::<Vec<&str>>().join(", ")
858 if !auto_trait_reasons.is_empty() && drop_reason {
859 reasons = format!("{} and ", reasons);
863 reasons = format!("{}drop order", reasons);
869 /// Figures out the list of root variables (and their types) that aren't completely
870 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
871 /// differ between the root variable and the captured paths.
873 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
874 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
875 fn compute_2229_migrations_for_trait(
877 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
878 var_hir_id: hir::HirId,
879 closure_clause: hir::CaptureBy,
880 ) -> Option<FxHashMap<CapturesInfo, FxHashSet<&str>>> {
881 let auto_traits_def_id = vec![
882 self.tcx.lang_items().clone_trait(),
883 self.tcx.lang_items().sync_trait(),
884 self.tcx.get_diagnostic_item(sym::Send),
885 self.tcx.lang_items().unpin_trait(),
886 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
887 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
889 const AUTO_TRAITS: [&str; 6] =
890 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
892 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
894 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
896 let ty = match closure_clause {
897 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
898 hir::CaptureBy::Ref => {
899 // For non move closure the capture kind is the max capture kind of all captures
900 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
901 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
902 for capture in root_var_min_capture_list.iter() {
903 max_capture_info = determine_capture_info(max_capture_info, capture.info);
906 apply_capture_kind_on_capture_ty(self.tcx, ty, max_capture_info.capture_kind)
910 let mut obligations_should_hold = Vec::new();
911 // Checks if a root variable implements any of the auto traits
912 for check_trait in auto_traits_def_id.iter() {
913 obligations_should_hold.push(
917 .type_implements_trait(
920 self.tcx.mk_substs_trait(ty, &[]),
923 .must_apply_modulo_regions()
929 let mut problematic_captures = FxHashMap::default();
930 // Check whether captured fields also implement the trait
931 for capture in root_var_min_capture_list.iter() {
932 let ty = apply_capture_kind_on_capture_ty(
935 capture.info.capture_kind,
938 // Checks if a capture implements any of the auto traits
939 let mut obligations_holds_for_capture = Vec::new();
940 for check_trait in auto_traits_def_id.iter() {
941 obligations_holds_for_capture.push(
945 .type_implements_trait(
948 self.tcx.mk_substs_trait(ty, &[]),
951 .must_apply_modulo_regions()
957 let mut capture_problems = FxHashSet::default();
959 // Checks if for any of the auto traits, one or more trait is implemented
960 // by the root variable but not by the capture
961 for (idx, _) in obligations_should_hold.iter().enumerate() {
962 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
963 capture_problems.insert(AUTO_TRAITS[idx]);
967 if !capture_problems.is_empty() {
968 problematic_captures.insert(
969 CapturesInfo::CapturingLess {
970 source_expr: capture.info.path_expr_id,
971 var_name: capture.to_string(self.tcx),
977 if !problematic_captures.is_empty() {
978 return Some(problematic_captures);
983 /// Figures out the list of root variables (and their types) that aren't completely
984 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
985 /// some path starting at that root variable **might** be affected.
987 /// The output list would include a root variable if:
988 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
990 /// - It wasn't completely captured by the closure, **and**
991 /// - One of the paths starting at this root variable, that is not captured needs Drop.
993 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
994 /// are no significant drops than None is returned
995 #[instrument(level = "debug", skip(self))]
996 fn compute_2229_migrations_for_drop(
998 closure_def_id: DefId,
1000 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1001 closure_clause: hir::CaptureBy,
1002 var_hir_id: hir::HirId,
1003 ) -> Option<FxHashSet<CapturesInfo>> {
1004 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
1006 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local())) {
1007 debug!("does not have significant drop");
1011 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1012 // The upvar is mentioned within the closure but no path starting from it is
1013 // used. This occurs when you have (e.g.)
1016 // let x = move || {
1020 debug!("no path starting from it is used");
1023 match closure_clause {
1024 // Only migrate if closure is a move closure
1025 hir::CaptureBy::Value => return Some(FxHashSet::default()),
1026 hir::CaptureBy::Ref => {}
1031 debug!(?root_var_min_capture_list);
1033 let mut projections_list = Vec::new();
1034 let mut diagnostics_info = FxHashSet::default();
1036 for captured_place in root_var_min_capture_list.iter() {
1037 match captured_place.info.capture_kind {
1038 // Only care about captures that are moved into the closure
1039 ty::UpvarCapture::ByValue(..) => {
1040 projections_list.push(captured_place.place.projections.as_slice());
1041 diagnostics_info.insert(CapturesInfo::CapturingLess {
1042 source_expr: captured_place.info.path_expr_id,
1043 var_name: captured_place.to_string(self.tcx),
1046 ty::UpvarCapture::ByRef(..) => {}
1050 debug!(?projections_list);
1051 debug!(?diagnostics_info);
1053 let is_moved = !projections_list.is_empty();
1056 let is_not_completely_captured =
1057 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1058 debug!(?is_not_completely_captured);
1061 && is_not_completely_captured
1062 && self.has_significant_drop_outside_of_captures(
1069 return Some(diagnostics_info);
1075 /// Figures out the list of root variables (and their types) that aren't completely
1076 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1077 /// order of some path starting at that root variable **might** be affected or auto-traits
1078 /// differ between the root variable and the captured paths.
1080 /// The output list would include a root variable if:
1081 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1082 /// enabled, **and**
1083 /// - It wasn't completely captured by the closure, **and**
1084 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1085 /// - One of the paths captured does not implement all the auto-traits its root variable
1088 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1089 /// containing the reason why root variables whose HirId is contained in the vector should
1091 #[instrument(level = "debug", skip(self))]
1092 fn compute_2229_migrations(
1094 closure_def_id: DefId,
1096 closure_clause: hir::CaptureBy,
1097 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1098 ) -> (Vec<MigrationDiagnosticInfo>, String) {
1099 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1100 return (Vec::new(), String::new());
1103 let mut need_migrations = Vec::new();
1104 let mut auto_trait_migration_reasons = FxHashSet::default();
1105 let mut drop_migration_needed = false;
1107 // Perform auto-trait analysis
1108 for (&var_hir_id, _) in upvars.iter() {
1109 let mut responsible_captured_hir_ids = Vec::new();
1111 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1112 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1116 FxHashMap::default()
1119 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1120 .compute_2229_migrations_for_drop(
1127 drop_migration_needed = true;
1130 FxHashSet::default()
1133 // Combine all the captures responsible for needing migrations into one HashSet
1134 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1135 for key in auto_trait_diagnostic.keys() {
1136 capture_diagnostic.insert(key.clone());
1139 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1140 capture_diagnostic.sort();
1141 for captured_info in capture_diagnostic.iter() {
1142 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1143 let capture_trait_reasons =
1144 if let Some(reasons) = auto_trait_diagnostic.get(captured_info) {
1147 FxHashSet::default()
1150 // Check if migration is needed because of drop reorder as a result of that capture
1151 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(captured_info);
1153 // Combine all the reasons of why the root variable should be captured as a result of
1154 // auto trait implementation issues
1155 auto_trait_migration_reasons.extend(capture_trait_reasons.clone());
1157 match captured_info {
1158 CapturesInfo::CapturingLess { source_expr, var_name } => {
1159 responsible_captured_hir_ids.push((
1162 self.compute_2229_migrations_reasons(
1163 capture_trait_reasons,
1164 capture_drop_reorder_reason,
1171 if !capture_diagnostic.is_empty() {
1172 need_migrations.push((var_hir_id, responsible_captured_hir_ids));
1177 self.compute_2229_migrations_reasons(
1178 auto_trait_migration_reasons,
1179 drop_migration_needed,
1184 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1185 /// of a root variable and a list of captured paths starting at this root variable (expressed
1186 /// using list of `Projection` slices), it returns true if there is a path that is not
1187 /// captured starting at this root variable that implements Drop.
1189 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1190 /// path say P and then list of projection slices which represent the different captures moved
1191 /// into the closure starting off of P.
1193 /// This will make more sense with an example:
1196 /// #![feature(capture_disjoint_fields)]
1198 /// struct FancyInteger(i32); // This implements Drop
1200 /// struct Point { x: FancyInteger, y: FancyInteger }
1203 /// struct Wrapper { p: Point, c: Color }
1205 /// fn f(w: Wrapper) {
1207 /// // Closure captures w.p.x and w.c by move.
1214 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1215 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1216 /// therefore Drop ordering would change and we want this function to return true.
1218 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1220 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1223 /// - Ty(place): Type of place
1224 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1227 /// (Ty(w), [ &[p, x], &[c] ])
1229 /// ----------------------------
1232 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1235 /// (Ty(w.p), [ &[x] ]) false
1238 /// -------------------------------
1241 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1244 /// false NeedsSignificantDrop(Ty(w.p.y))
1250 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1251 /// This implies that the `w.c` is completely captured by the closure.
1252 /// Since drop for this path will be called when the closure is
1253 /// dropped we don't need to migrate for it.
1255 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1256 /// path wasn't captured by the closure. Also note that even
1257 /// though we didn't capture this path, the function visits it,
1258 /// which is kind of the point of this function. We then return
1259 /// if the type of `w.p.y` implements Drop, which in this case is
1262 /// Consider another example:
1266 /// impl Drop for X {}
1269 /// impl Drop for Y {}
1273 /// let c = || move(y.0);
1277 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1278 /// return true, because even though all paths starting at `y` are captured, `y` itself
1279 /// implements Drop which will be affected since `y` isn't completely captured.
1280 fn has_significant_drop_outside_of_captures(
1282 closure_def_id: DefId,
1284 base_path_ty: Ty<'tcx>,
1285 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1287 let needs_drop = |ty: Ty<'tcx>| {
1288 ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local()))
1291 let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
1292 let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
1293 let ty_params = self.tcx.mk_substs_trait(base_path_ty, &[]);
1295 .type_implements_trait(
1299 self.tcx.param_env(closure_def_id.expect_local()),
1301 .must_apply_modulo_regions()
1304 let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
1306 // If there is a case where no projection is applied on top of current place
1307 // then there must be exactly one capture corresponding to such a case. Note that this
1308 // represents the case of the path being completely captured by the variable.
1310 // eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
1311 // capture `a.b.c`, because that voilates min capture.
1312 let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
1314 assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
1316 if is_completely_captured {
1317 // The place is captured entirely, so doesn't matter if needs dtor, it will be drop
1318 // when the closure is dropped.
1322 if captured_by_move_projs.is_empty() {
1323 return needs_drop(base_path_ty);
1326 if is_drop_defined_for_ty {
1327 // If drop is implemented for this type then we need it to be fully captured,
1328 // and we know it is not completely captured because of the previous checks.
1330 // Note that this is a bug in the user code that will be reported by the
1331 // borrow checker, since we can't move out of drop types.
1333 // The bug exists in the user's code pre-migration, and we don't migrate here.
1337 match base_path_ty.kind() {
1339 // - `captured_by_move_projs` is not empty. Therefore we can call
1340 // `captured_by_move_projs.first().unwrap()` safely.
1341 // - All entries in `captured_by_move_projs` have atleast one projection.
1342 // Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
1344 // We don't capture derefs in case of move captures, which would have be applied to
1345 // access any further paths.
1346 ty::Adt(def, _) if def.is_box() => unreachable!(),
1347 ty::Ref(..) => unreachable!(),
1348 ty::RawPtr(..) => unreachable!(),
1350 ty::Adt(def, substs) => {
1351 // Multi-varaint enums are captured in entirety,
1352 // which would've been handled in the case of single empty slice in `captured_by_move_projs`.
1353 assert_eq!(def.variants.len(), 1);
1355 // Only Field projections can be applied to a non-box Adt.
1357 captured_by_move_projs.iter().all(|projs| matches!(
1358 projs.first().unwrap().kind,
1359 ProjectionKind::Field(..)
1362 def.variants.get(VariantIdx::new(0)).unwrap().fields.iter().enumerate().any(
1364 let paths_using_field = captured_by_move_projs
1366 .filter_map(|projs| {
1367 if let ProjectionKind::Field(field_idx, _) =
1368 projs.first().unwrap().kind
1370 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1377 let after_field_ty = field.ty(self.tcx, substs);
1378 self.has_significant_drop_outside_of_captures(
1389 // Only Field projections can be applied to a tuple.
1391 captured_by_move_projs.iter().all(|projs| matches!(
1392 projs.first().unwrap().kind,
1393 ProjectionKind::Field(..)
1397 base_path_ty.tuple_fields().enumerate().any(|(i, element_ty)| {
1398 let paths_using_field = captured_by_move_projs
1400 .filter_map(|projs| {
1401 if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
1403 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1410 self.has_significant_drop_outside_of_captures(
1419 // Anything else would be completely captured and therefore handled already.
1420 _ => unreachable!(),
1424 fn init_capture_kind_for_place(
1426 place: &Place<'tcx>,
1427 capture_clause: hir::CaptureBy,
1428 upvar_id: ty::UpvarId,
1430 ) -> ty::UpvarCapture<'tcx> {
1431 match capture_clause {
1432 // In case of a move closure if the data is accessed through a reference we
1433 // want to capture by ref to allow precise capture using reborrows.
1435 // If the data will be moved out of this place, then the place will be truncated
1436 // at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
1438 hir::CaptureBy::Value if !place.deref_tys().any(ty::TyS::is_ref) => {
1439 ty::UpvarCapture::ByValue(None)
1441 hir::CaptureBy::Value | hir::CaptureBy::Ref => {
1442 let origin = UpvarRegion(upvar_id, closure_span);
1443 let upvar_region = self.next_region_var(origin);
1444 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
1445 ty::UpvarCapture::ByRef(upvar_borrow)
1450 fn place_for_root_variable(
1452 closure_def_id: LocalDefId,
1453 var_hir_id: hir::HirId,
1455 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
1458 base_ty: self.node_ty(var_hir_id),
1459 base: PlaceBase::Upvar(upvar_id),
1460 projections: Default::default(),
1464 fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
1465 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
1468 fn log_capture_analysis_first_pass(
1470 closure_def_id: rustc_hir::def_id::DefId,
1471 capture_information: &FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>,
1474 if self.should_log_capture_analysis(closure_def_id) {
1476 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
1477 for (place, capture_info) in capture_information {
1478 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
1479 let output_str = format!("Capturing {}", capture_str);
1482 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
1483 diag.span_note(span, &output_str);
1489 fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
1490 if self.should_log_capture_analysis(closure_def_id) {
1491 if let Some(min_captures) =
1492 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
1495 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
1497 for (_, min_captures_for_var) in min_captures {
1498 for capture in min_captures_for_var {
1499 let place = &capture.place;
1500 let capture_info = &capture.info;
1503 construct_capture_info_string(self.tcx, place, capture_info);
1504 let output_str = format!("Min Capture {}", capture_str);
1506 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
1507 let path_span = capture_info
1509 .map_or(closure_span, |e| self.tcx.hir().span(e));
1510 let capture_kind_span = capture_info
1511 .capture_kind_expr_id
1512 .map_or(closure_span, |e| self.tcx.hir().span(e));
1514 let mut multi_span: MultiSpan =
1515 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
1517 let capture_kind_label =
1518 construct_capture_kind_reason_string(self.tcx, place, capture_info);
1519 let path_label = construct_path_string(self.tcx, place);
1521 multi_span.push_span_label(path_span, path_label);
1522 multi_span.push_span_label(capture_kind_span, capture_kind_label);
1524 diag.span_note(multi_span, &output_str);
1526 let span = capture_info
1528 .map_or(closure_span, |e| self.tcx.hir().span(e));
1530 diag.span_note(span, &output_str);
1539 /// A captured place is mutable if
1540 /// 1. Projections don't include a Deref of an immut-borrow, **and**
1541 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
1542 fn determine_capture_mutability(
1544 typeck_results: &'a TypeckResults<'tcx>,
1545 place: &Place<'tcx>,
1546 ) -> hir::Mutability {
1547 let var_hir_id = match place.base {
1548 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
1549 _ => unreachable!(),
1552 let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
1554 let mut is_mutbl = match bm {
1555 ty::BindByValue(mutability) => mutability,
1556 ty::BindByReference(_) => hir::Mutability::Not,
1559 for pointer_ty in place.deref_tys() {
1560 match pointer_ty.kind() {
1561 // We don't capture derefs of raw ptrs
1562 ty::RawPtr(_) => unreachable!(),
1564 // Derefencing a mut-ref allows us to mut the Place if we don't deref
1565 // an immut-ref after on top of this.
1566 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
1568 // The place isn't mutable once we dereference an immutable reference.
1569 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
1571 // Dereferencing a box doesn't change mutability
1572 ty::Adt(def, ..) if def.is_box() => {}
1574 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
1582 /// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
1583 /// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
1584 fn restrict_repr_packed_field_ref_capture<'tcx>(
1586 param_env: ty::ParamEnv<'tcx>,
1587 place: &Place<'tcx>,
1588 mut curr_borrow_kind: ty::UpvarCapture<'tcx>,
1589 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1590 let pos = place.projections.iter().enumerate().position(|(i, p)| {
1591 let ty = place.ty_before_projection(i);
1593 // Return true for fields of packed structs, unless those fields have alignment 1.
1595 ProjectionKind::Field(..) => match ty.kind() {
1596 ty::Adt(def, _) if def.repr.packed() => {
1597 match tcx.layout_of(param_env.and(p.ty)) {
1598 Ok(layout) if layout.align.abi.bytes() == 1 => {
1599 // if the alignment is 1, the type can't be further
1602 "restrict_repr_packed_field_ref_capture: ({:?}) - align = 1",
1608 debug!("restrict_repr_packed_field_ref_capture: ({:?}) - true", place);
1620 let mut place = place.clone();
1622 if let Some(pos) = pos {
1623 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
1626 (place, curr_borrow_kind)
1629 /// Returns a Ty that applies the specified capture kind on the provided capture Ty
1630 fn apply_capture_kind_on_capture_ty(
1633 capture_kind: UpvarCapture<'tcx>,
1635 match capture_kind {
1636 ty::UpvarCapture::ByValue(_) => ty,
1637 ty::UpvarCapture::ByRef(borrow) => tcx
1638 .mk_ref(borrow.region, ty::TypeAndMut { ty: ty, mutbl: borrow.kind.to_mutbl_lossy() }),
1642 /// Returns the Span of where the value with the provided HirId would be dropped
1643 fn drop_location_span(tcx: TyCtxt<'tcx>, hir_id: &hir::HirId) -> Span {
1644 let owner_id = tcx.hir().get_enclosing_scope(*hir_id).unwrap();
1646 let owner_node = tcx.hir().get(owner_id);
1647 let owner_span = match owner_node {
1648 hir::Node::Item(item) => match item.kind {
1649 hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
1651 bug!("Drop location span error: need to handle more ItemKind {:?}", item.kind);
1654 hir::Node::Block(block) => tcx.hir().span(block.hir_id),
1656 bug!("Drop location span error: need to handle more Node {:?}", owner_node);
1659 tcx.sess.source_map().end_point(owner_span)
1662 struct InferBorrowKind<'a, 'tcx> {
1663 fcx: &'a FnCtxt<'a, 'tcx>,
1665 // The def-id of the closure whose kind and upvar accesses are being inferred.
1666 closure_def_id: DefId,
1670 /// For each Place that is captured by the closure, we track the minimal kind of
1671 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1673 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1674 /// s.str2 via a MutableBorrow
1677 /// struct SomeStruct { str1: String, str2: String }
1679 /// // Assume that the HirId for the variable definition is `V1`
1680 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
1682 /// let fix_s = |new_s2| {
1683 /// // Assume that the HirId for the expression `s.str1` is `E1`
1684 /// println!("Updating SomeStruct with str1=", s.str1);
1685 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1686 /// s.str2 = new_s2;
1690 /// For closure `fix_s`, (at a high level) the map contains
1693 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1694 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1696 capture_information: InferredCaptureInformation<'tcx>,
1697 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1700 impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
1701 #[instrument(skip(self), level = "debug")]
1702 fn adjust_upvar_borrow_kind_for_consume(
1704 place_with_id: &PlaceWithHirId<'tcx>,
1705 diag_expr_id: hir::HirId,
1707 let tcx = self.fcx.tcx;
1708 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else {
1714 let usage_span = tcx.hir().span(diag_expr_id);
1716 let capture_info = ty::CaptureInfo {
1717 capture_kind_expr_id: Some(diag_expr_id),
1718 path_expr_id: Some(diag_expr_id),
1719 capture_kind: ty::UpvarCapture::ByValue(Some(usage_span)),
1722 let curr_info = self.capture_information[&place_with_id.place];
1723 let updated_info = determine_capture_info(curr_info, capture_info);
1725 self.capture_information[&place_with_id.place] = updated_info;
1728 /// Indicates that `place_with_id` is being directly mutated (e.g., assigned
1729 /// to). If the place is based on a by-ref upvar, this implies that
1730 /// the upvar must be borrowed using an `&mut` borrow.
1731 #[instrument(skip(self), level = "debug")]
1732 fn adjust_upvar_borrow_kind_for_mut(
1734 place_with_id: &PlaceWithHirId<'tcx>,
1735 diag_expr_id: hir::HirId,
1737 if let PlaceBase::Upvar(_) = place_with_id.place.base {
1738 // Raw pointers don't inherit mutability
1739 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1742 self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::MutBorrow);
1746 #[instrument(skip(self), level = "debug")]
1747 fn adjust_upvar_borrow_kind_for_unique(
1749 place_with_id: &PlaceWithHirId<'tcx>,
1750 diag_expr_id: hir::HirId,
1752 if let PlaceBase::Upvar(_) = place_with_id.place.base {
1753 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1754 // Raw pointers don't inherit mutability.
1757 // for a borrowed pointer to be unique, its base must be unique
1758 self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::UniqueImmBorrow);
1762 fn adjust_upvar_deref(
1764 place_with_id: &PlaceWithHirId<'tcx>,
1765 diag_expr_id: hir::HirId,
1766 borrow_kind: ty::BorrowKind,
1768 assert!(match borrow_kind {
1769 ty::MutBorrow => true,
1770 ty::UniqueImmBorrow => true,
1772 // imm borrows never require adjusting any kinds, so we don't wind up here
1773 ty::ImmBorrow => false,
1776 // if this is an implicit deref of an
1777 // upvar, then we need to modify the
1778 // borrow_kind of the upvar to make sure it
1779 // is inferred to mutable if necessary
1780 self.adjust_upvar_borrow_kind(place_with_id, diag_expr_id, borrow_kind);
1783 /// We infer the borrow_kind with which to borrow upvars in a stack closure.
1784 /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
1785 /// moving from left to right as needed (but never right to left).
1786 /// Here the argument `mutbl` is the borrow_kind that is required by
1787 /// some particular use.
1788 #[instrument(skip(self), level = "debug")]
1789 fn adjust_upvar_borrow_kind(
1791 place_with_id: &PlaceWithHirId<'tcx>,
1792 diag_expr_id: hir::HirId,
1793 kind: ty::BorrowKind,
1795 let curr_capture_info = self.capture_information[&place_with_id.place];
1797 debug!(?curr_capture_info);
1799 if let ty::UpvarCapture::ByValue(_) = curr_capture_info.capture_kind {
1800 // It's already captured by value, we don't need to do anything here
1802 } else if let ty::UpvarCapture::ByRef(curr_upvar_borrow) = curr_capture_info.capture_kind {
1803 // Use the same region as the current capture information
1804 // Doesn't matter since only one of the UpvarBorrow will be used.
1805 let new_upvar_borrow = ty::UpvarBorrow { kind, region: curr_upvar_borrow.region };
1807 let capture_info = ty::CaptureInfo {
1808 capture_kind_expr_id: Some(diag_expr_id),
1809 path_expr_id: Some(diag_expr_id),
1810 capture_kind: ty::UpvarCapture::ByRef(new_upvar_borrow),
1812 let updated_info = determine_capture_info(curr_capture_info, capture_info);
1813 self.capture_information[&place_with_id.place] = updated_info;
1817 #[instrument(skip(self, diag_expr_id), level = "debug")]
1818 fn init_capture_info_for_place(
1820 place_with_id: &PlaceWithHirId<'tcx>,
1821 diag_expr_id: hir::HirId,
1823 if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
1824 assert_eq!(self.closure_def_id.expect_local(), upvar_id.closure_expr_id);
1826 // Initialize to ImmBorrow
1827 // We will escalate the CaptureKind based on any uses we see or in `process_collected_capture_information`.
1828 let origin = UpvarRegion(upvar_id, self.closure_span);
1829 let upvar_region = self.fcx.next_region_var(origin);
1830 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
1831 let capture_kind = ty::UpvarCapture::ByRef(upvar_borrow);
1833 let expr_id = Some(diag_expr_id);
1834 let capture_info = ty::CaptureInfo {
1835 capture_kind_expr_id: expr_id,
1836 path_expr_id: expr_id,
1840 debug!("Capturing new place {:?}, capture_info={:?}", place_with_id, capture_info);
1842 self.capture_information.insert(place_with_id.place.clone(), capture_info);
1844 debug!("Not upvar");
1849 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1850 fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId) {
1851 if let PlaceBase::Upvar(_) = place.base {
1852 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1853 // such as deref of a raw pointer.
1854 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::UpvarBorrow {
1855 kind: ty::BorrowKind::ImmBorrow,
1856 region: &ty::ReErased,
1859 let (place, _) = restrict_capture_precision(place, dummy_capture_kind);
1861 let (place, _) = restrict_repr_packed_field_ref_capture(
1867 self.fake_reads.push((place, cause, diag_expr_id));
1871 #[instrument(skip(self), level = "debug")]
1872 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1873 if !self.capture_information.contains_key(&place_with_id.place) {
1874 self.init_capture_info_for_place(place_with_id, diag_expr_id);
1877 self.adjust_upvar_borrow_kind_for_consume(place_with_id, diag_expr_id);
1880 #[instrument(skip(self), level = "debug")]
1883 place_with_id: &PlaceWithHirId<'tcx>,
1884 diag_expr_id: hir::HirId,
1887 // The region here will get discarded/ignored
1888 let dummy_capture_kind =
1889 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind: bk, region: &ty::ReErased });
1891 // We only want repr packed restriction to be applied to reading references into a packed
1892 // struct, and not when the data is being moved. Therefore we call this method here instead
1893 // of in `restrict_capture_precision`.
1894 let (place, updated_kind) = restrict_repr_packed_field_ref_capture(
1897 &place_with_id.place,
1901 let place_with_id = PlaceWithHirId { place, ..*place_with_id };
1903 if !self.capture_information.contains_key(&place_with_id.place) {
1904 self.init_capture_info_for_place(&place_with_id, diag_expr_id);
1907 match updated_kind {
1908 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind, .. }) => match kind {
1910 ty::UniqueImmBorrow => {
1911 self.adjust_upvar_borrow_kind_for_unique(&place_with_id, diag_expr_id);
1914 self.adjust_upvar_borrow_kind_for_mut(&place_with_id, diag_expr_id);
1918 // Just truncating the place will never cause capture kind to be updated to ByValue
1919 ty::UpvarCapture::ByValue(..) => unreachable!(),
1923 #[instrument(skip(self), level = "debug")]
1924 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1925 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1929 /// Rust doesn't permit moving fields out of a type that implements drop
1930 fn restrict_precision_for_drop_types<'a, 'tcx>(
1931 fcx: &'a FnCtxt<'a, 'tcx>,
1932 mut place: Place<'tcx>,
1933 mut curr_mode: ty::UpvarCapture<'tcx>,
1935 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1936 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1938 if let (false, UpvarCapture::ByValue(..)) = (is_copy_type, curr_mode) {
1939 for i in 0..place.projections.len() {
1940 match place.ty_before_projection(i).kind() {
1941 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1942 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1953 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
1954 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
1955 /// them completely.
1956 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
1957 fn restrict_precision_for_unsafe(
1958 mut place: Place<'tcx>,
1959 mut curr_mode: ty::UpvarCapture<'tcx>,
1960 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1961 if place.base_ty.is_unsafe_ptr() {
1962 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1965 if place.base_ty.is_union() {
1966 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
1969 for (i, proj) in place.projections.iter().enumerate() {
1970 if proj.ty.is_unsafe_ptr() {
1971 // Don't apply any projections on top of an unsafe ptr.
1972 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1976 if proj.ty.is_union() {
1977 // Don't capture preicse fields of a union.
1978 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
1986 /// Truncate projections so that following rules are obeyed by the captured `place`:
1987 /// - No Index projections are captured, since arrays are captured completely.
1988 /// - No unsafe block is required to capture `place`
1989 /// Returns the truncated place and updated cature mode.
1990 fn restrict_capture_precision<'tcx>(
1992 curr_mode: ty::UpvarCapture<'tcx>,
1993 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1994 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
1996 if place.projections.is_empty() {
1997 // Nothing to do here
1998 return (place, curr_mode);
2001 for (i, proj) in place.projections.iter().enumerate() {
2003 ProjectionKind::Index => {
2004 // Arrays are completely captured, so we drop Index projections
2005 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
2006 return (place, curr_mode);
2008 ProjectionKind::Deref => {}
2009 ProjectionKind::Field(..) => {} // ignore
2010 ProjectionKind::Subslice => {} // We never capture this
2017 /// Truncate deref of any reference.
2018 fn adjust_for_move_closure<'tcx>(
2019 mut place: Place<'tcx>,
2020 mut kind: ty::UpvarCapture<'tcx>,
2021 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2022 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
2024 if let Some(idx) = first_deref {
2025 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
2028 // AMAN: I think we don't need the span inside the ByValue anymore
2029 // we have more detailed span in CaptureInfo
2030 (place, ty::UpvarCapture::ByValue(None))
2033 /// Adjust closure capture just that if taking ownership of data, only move data
2034 /// from enclosing stack frame.
2035 fn adjust_for_non_move_closure<'tcx>(
2036 mut place: Place<'tcx>,
2037 mut kind: ty::UpvarCapture<'tcx>,
2038 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2039 let contains_deref =
2040 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
2043 ty::UpvarCapture::ByValue(..) => {
2044 if let Some(idx) = contains_deref {
2045 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
2049 ty::UpvarCapture::ByRef(..) => {}
2055 fn construct_place_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2056 let variable_name = match place.base {
2057 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
2058 _ => bug!("Capture_information should only contain upvars"),
2061 let mut projections_str = String::new();
2062 for (i, item) in place.projections.iter().enumerate() {
2063 let proj = match item.kind {
2064 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
2065 ProjectionKind::Deref => String::from("Deref"),
2066 ProjectionKind::Index => String::from("Index"),
2067 ProjectionKind::Subslice => String::from("Subslice"),
2070 projections_str.push(',');
2072 projections_str.push_str(proj.as_str());
2075 format!("{}[{}]", variable_name, projections_str)
2078 fn construct_capture_kind_reason_string(
2080 place: &Place<'tcx>,
2081 capture_info: &ty::CaptureInfo<'tcx>,
2083 let place_str = construct_place_string(tcx, place);
2085 let capture_kind_str = match capture_info.capture_kind {
2086 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
2087 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
2090 format!("{} captured as {} here", place_str, capture_kind_str)
2093 fn construct_path_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2094 let place_str = construct_place_string(tcx, place);
2096 format!("{} used here", place_str)
2099 fn construct_capture_info_string(
2101 place: &Place<'tcx>,
2102 capture_info: &ty::CaptureInfo<'tcx>,
2104 let place_str = construct_place_string(tcx, place);
2106 let capture_kind_str = match capture_info.capture_kind {
2107 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
2108 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
2110 format!("{} -> {}", place_str, capture_kind_str)
2113 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2114 tcx.hir().name(var_hir_id)
2117 #[instrument(level = "debug", skip(tcx))]
2118 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2120 closure_id: hir::HirId,
2123 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2125 !matches!(level, lint::Level::Allow)
2128 /// Return a two string tuple (s1, s2)
2129 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2130 /// - s2: Comma separated names of the variables being migrated.
2131 fn migration_suggestion_for_2229(
2133 need_migrations: &Vec<MigrationDiagnosticInfo>,
2134 ) -> (String, String) {
2135 let need_migrations_variables =
2136 need_migrations.iter().map(|(v, _)| var_name(tcx, *v)).collect::<Vec<_>>();
2138 let migration_ref_concat =
2139 need_migrations_variables.iter().map(|v| format!("&{}", v)).collect::<Vec<_>>().join(", ");
2141 let migration_string = if 1 == need_migrations.len() {
2142 format!("let _ = {}", migration_ref_concat)
2144 format!("let _ = ({})", migration_ref_concat)
2147 let migrated_variables_concat =
2148 need_migrations_variables.iter().map(|v| format!("`{}`", v)).collect::<Vec<_>>().join(", ");
2150 (migration_string, migrated_variables_concat)
2153 /// Helper function to determine if we need to escalate CaptureKind from
2154 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2155 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2157 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2158 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2160 /// It is the caller's duty to figure out which path_expr_id to use.
2162 /// If both the CaptureKind and Expression are considered to be equivalent,
2163 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to priortize
2164 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2165 /// in the closure. This can be achieved simply by calling
2166 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2167 /// expressions that occur earlier in the closure body than the current expression are processed before.
2168 /// Consider the following example
2170 /// struct Point { x: i32, y: i32 }
2171 /// let mut p: Point { x: 10, y: 10 };
2179 /// p.x += 10; // E2
2183 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2184 /// and both have an expression associated, however for diagnostics we prefer reporting
2185 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2186 /// would've already handled `E1`, and have an existing capture_information for it.
2187 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2188 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2189 fn determine_capture_info(
2190 capture_info_a: ty::CaptureInfo<'tcx>,
2191 capture_info_b: ty::CaptureInfo<'tcx>,
2192 ) -> ty::CaptureInfo<'tcx> {
2193 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2195 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2196 (ty::UpvarCapture::ByValue(_), ty::UpvarCapture::ByValue(_)) => {
2197 // We don't need to worry about the spans being ignored here.
2199 // The expr_id in capture_info corresponds to the span that is stored within
2200 // ByValue(span) and therefore it gets handled with priortizing based on
2201 // expressions below.
2204 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2205 ref_a.kind == ref_b.kind
2207 (ty::UpvarCapture::ByValue(_), _) | (ty::UpvarCapture::ByRef(_), _) => false,
2210 if eq_capture_kind {
2211 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2212 (Some(_), _) | (None, None) => capture_info_a,
2213 (None, Some(_)) => capture_info_b,
2216 // We select the CaptureKind which ranks higher based the following priority order:
2217 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2218 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2219 (ty::UpvarCapture::ByValue(_), _) => capture_info_a,
2220 (_, ty::UpvarCapture::ByValue(_)) => capture_info_b,
2221 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2222 match (ref_a.kind, ref_b.kind) {
2224 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2225 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2228 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2229 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2231 (ty::ImmBorrow, ty::ImmBorrow)
2232 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2233 | (ty::MutBorrow, ty::MutBorrow) => {
2234 bug!("Expected unequal capture kinds");
2242 /// Truncates `place` to have up to `len` projections.
2243 /// `curr_mode` is the current required capture kind for the place.
2244 /// Returns the truncated `place` and the updated required capture kind.
2246 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2247 /// contained `Deref` of `&mut`.
2248 fn truncate_place_to_len_and_update_capture_kind(
2249 place: &mut Place<'tcx>,
2250 curr_mode: &mut ty::UpvarCapture<'tcx>,
2253 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2255 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2257 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2258 // we don't need to worry about that case here.
2260 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind: ty::BorrowKind::MutBorrow, region }) => {
2261 for i in len..place.projections.len() {
2262 if place.projections[i].kind == ProjectionKind::Deref
2263 && is_mut_ref(place.ty_before_projection(i))
2265 *curr_mode = ty::UpvarCapture::ByRef(ty::UpvarBorrow {
2266 kind: ty::BorrowKind::UniqueImmBorrow,
2274 ty::UpvarCapture::ByRef(..) => {}
2275 ty::UpvarCapture::ByValue(..) => {}
2278 place.projections.truncate(len);
2281 /// Determines the Ancestry relationship of Place A relative to Place B
2283 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2284 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2285 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2286 fn determine_place_ancestry_relation(
2287 place_a: &Place<'tcx>,
2288 place_b: &Place<'tcx>,
2289 ) -> PlaceAncestryRelation {
2290 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2291 if place_a.base != place_b.base {
2292 return PlaceAncestryRelation::Divergent;
2295 // Assume of length of projections_a = n
2296 let projections_a = &place_a.projections;
2298 // Assume of length of projections_b = m
2299 let projections_b = &place_b.projections;
2301 let same_initial_projections =
2302 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2304 if same_initial_projections {
2305 use std::cmp::Ordering;
2307 // First min(n, m) projections are the same
2308 // Select Ancestor/Descendant
2309 match projections_b.len().cmp(&projections_a.len()) {
2310 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2311 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2312 Ordering::Less => PlaceAncestryRelation::Descendant,
2315 PlaceAncestryRelation::Divergent
2319 /// Reduces the precision of the captured place when the precision doesn't yeild any benefit from
2320 /// borrow checking prespective, allowing us to save us on the size of the capture.
2323 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2324 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2325 /// rightmost deref of the capture if the deref is applied to a shared ref.
2327 /// Reason we only drop the last deref is because of the following edge case:
2330 /// struct MyStruct<'a> {
2336 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2337 /// let c = || drop(&*m.a.field_of_a);
2338 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2340 /// // If we capture `m`, then the closure no longer outlives `'static'
2341 /// // it is constrained to `'a`
2344 fn truncate_capture_for_optimization<'tcx>(
2345 mut place: Place<'tcx>,
2346 mut curr_mode: ty::UpvarCapture<'tcx>,
2347 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2348 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2350 // Find the right-most deref (if any). All the projections that come after this
2351 // are fields or other "in-place pointer adjustments"; these refer therefore to
2352 // data owned by whatever pointer is being dereferenced here.
2353 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2356 // If that pointer is a shared reference, then we don't need those fields.
2357 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2358 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2360 None | Some(_) => {}
2366 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2367 /// user is using Rust Edition 2021 or higher.
2369 /// `span` is the span of the closure.
2370 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2371 // We use span here to ensure that if the closure was generated by a macro with a different
2373 tcx.features().capture_disjoint_fields || span.rust_2021()