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)]
90 enum UpvarMigrationInfo {
91 /// We previously captured all of `x`, but now we capture some sub-path.
92 CapturingPrecise { source_expr: Option<hir::HirId>, var_name: String },
94 // where the variable appears in the closure (but is not captured)
99 /// Reasons that we might issue a migration warning.
100 #[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
101 struct MigrationWarningReason {
102 /// When we used to capture `x` in its entirety, we implemented the auto-trait(s)
103 /// in this vec, but now we don't.
104 auto_traits: Vec<&'static str>,
106 /// When we used to capture `x` in its entirety, we would execute some destructors
107 /// at a different time.
111 impl MigrationWarningReason {
112 fn migration_message(&self) -> String {
113 let base = "changes to closure capture in Rust 2021 will affect";
114 if !self.auto_traits.is_empty() && self.drop_order {
115 format!("{} drop order and which traits the closure implements", base)
116 } else if self.drop_order {
117 format!("{} drop order", base)
119 format!("{} which traits the closure implements", base)
124 /// Intermediate format to store information needed to generate a note in the migration lint.
125 struct MigrationLintNote {
126 captures_info: UpvarMigrationInfo,
128 /// reasons why migration is needed for this capture
129 reason: MigrationWarningReason,
132 /// Intermediate format to store the hir id of the root variable and a HashSet containing
133 /// information on why the root variable should be fully captured
134 struct NeededMigration {
135 var_hir_id: hir::HirId,
136 diagnostics_info: Vec<MigrationLintNote>,
139 struct InferBorrowKindVisitor<'a, 'tcx> {
140 fcx: &'a FnCtxt<'a, 'tcx>,
143 impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
144 type Map = intravisit::ErasedMap<'tcx>;
146 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
147 NestedVisitorMap::None
150 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
152 hir::ExprKind::Closure(cc, _, body_id, _, _) => {
153 let body = self.fcx.tcx.hir().body(body_id);
154 self.visit_body(body);
155 self.fcx.analyze_closure(expr.hir_id, expr.span, body_id, body, cc);
157 hir::ExprKind::ConstBlock(anon_const) => {
158 let body = self.fcx.tcx.hir().body(anon_const.body);
159 self.visit_body(body);
164 intravisit::walk_expr(self, expr);
168 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
169 /// Analysis starting point.
170 #[instrument(skip(self, body), level = "debug")]
173 closure_hir_id: hir::HirId,
175 body_id: hir::BodyId,
176 body: &'tcx hir::Body<'tcx>,
177 capture_clause: hir::CaptureBy,
179 // Extract the type of the closure.
180 let ty = self.node_ty(closure_hir_id);
181 let (closure_def_id, substs) = match *ty.kind() {
182 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
183 ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
185 // #51714: skip analysis when we have already encountered type errors
191 "type of closure expr {:?} is not a closure {:?}",
198 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
199 self.closure_kind(closure_substs).is_none().then_some(closure_substs)
204 let local_def_id = closure_def_id.expect_local();
206 let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
207 assert_eq!(body_owner_def_id.to_def_id(), closure_def_id);
208 let mut delegate = InferBorrowKind {
212 capture_information: Default::default(),
213 fake_reads: Default::default(),
215 euv::ExprUseVisitor::new(
220 &self.typeck_results.borrow(),
225 "For closure={:?}, capture_information={:#?}",
226 closure_def_id, delegate.capture_information
229 self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
231 let (capture_information, closure_kind, origin) = self
232 .process_collected_capture_information(capture_clause, delegate.capture_information);
234 self.compute_min_captures(closure_def_id, capture_information);
236 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
238 if should_do_rust_2021_incompatible_closure_captures_analysis(self.tcx, closure_hir_id) {
239 self.perform_2229_migration_anaysis(closure_def_id, body_id, capture_clause, span);
242 let after_feature_tys = self.final_upvar_tys(closure_def_id);
244 // We now fake capture information for all variables that are mentioned within the closure
245 // We do this after handling migrations so that min_captures computes before
246 if !enable_precise_capture(self.tcx, span) {
247 let mut capture_information: InferredCaptureInformation<'tcx> = Default::default();
249 if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
250 for var_hir_id in upvars.keys() {
251 let place = self.place_for_root_variable(local_def_id, *var_hir_id);
253 debug!("seed place {:?}", place);
255 let upvar_id = ty::UpvarId::new(*var_hir_id, local_def_id);
257 self.init_capture_kind_for_place(&place, capture_clause, upvar_id, span);
258 let fake_info = ty::CaptureInfo {
259 capture_kind_expr_id: None,
264 capture_information.insert(place, fake_info);
268 // This will update the min captures based on this new fake information.
269 self.compute_min_captures(closure_def_id, capture_information);
272 let before_feature_tys = self.final_upvar_tys(closure_def_id);
274 if let Some(closure_substs) = infer_kind {
275 // Unify the (as yet unbound) type variable in the closure
276 // substs with the kind we inferred.
277 let closure_kind_ty = closure_substs.as_closure().kind_ty();
278 self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
280 // If we have an origin, store it.
281 if let Some(origin) = origin {
282 let origin = if enable_precise_capture(self.tcx, span) {
285 (origin.0, Place { projections: vec![], ..origin.1 })
290 .closure_kind_origins_mut()
291 .insert(closure_hir_id, origin);
295 self.log_closure_min_capture_info(closure_def_id, span);
297 // Now that we've analyzed the closure, we know how each
298 // variable is borrowed, and we know what traits the closure
299 // implements (Fn vs FnMut etc). We now have some updates to do
300 // with that information.
302 // Note that no closure type C may have an upvar of type C
303 // (though it may reference itself via a trait object). This
304 // results from the desugaring of closures to a struct like
305 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
306 // C, then the type would have infinite size (and the
307 // inference algorithm will reject it).
309 // Equate the type variables for the upvars with the actual types.
310 let final_upvar_tys = self.final_upvar_tys(closure_def_id);
312 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
313 closure_hir_id, substs, final_upvar_tys
316 // Build a tuple (U0..Un) of the final upvar types U0..Un
317 // and unify the upvar tupe type in the closure with it:
318 let final_tupled_upvars_type = self.tcx.mk_tup(final_upvar_tys.iter());
319 self.demand_suptype(span, substs.tupled_upvars_ty(), final_tupled_upvars_type);
321 let fake_reads = delegate
324 .map(|(place, cause, hir_id)| (place, cause, hir_id))
326 self.typeck_results.borrow_mut().closure_fake_reads.insert(closure_def_id, fake_reads);
328 if self.tcx.sess.opts.debugging_opts.profile_closures {
329 self.typeck_results.borrow_mut().closure_size_eval.insert(
331 ClosureSizeProfileData {
332 before_feature_tys: self.tcx.mk_tup(before_feature_tys.into_iter()),
333 after_feature_tys: self.tcx.mk_tup(after_feature_tys.into_iter()),
338 // If we are also inferred the closure kind here,
339 // process any deferred resolutions.
340 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
341 for deferred_call_resolution in deferred_call_resolutions {
342 deferred_call_resolution.resolve(self);
346 // Returns a list of `Ty`s for each upvar.
347 fn final_upvar_tys(&self, closure_id: DefId) -> Vec<Ty<'tcx>> {
348 // Presently an unboxed closure type cannot "escape" out of a
349 // function, so we will only encounter ones that originated in the
350 // local crate or were inlined into it along with some function.
351 // This may change if abstract return types of some sort are
355 .closure_min_captures_flattened(closure_id)
356 .map(|captured_place| {
357 let upvar_ty = captured_place.place.ty();
358 let capture = captured_place.info.capture_kind;
361 "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
362 captured_place.place, upvar_ty, capture, captured_place.mutability,
365 apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture)
370 /// Adjusts the closure capture information to ensure that the operations aren't unsafe,
371 /// and that the path can be captured with required capture kind (depending on use in closure,
372 /// move closure etc.)
374 /// Returns the set of of adjusted information along with the inferred closure kind and span
375 /// associated with the closure kind inference.
377 /// Note that we *always* infer a minimal kind, even if
378 /// we don't always *use* that in the final result (i.e., sometimes
379 /// we've taken the closure kind from the expectations instead, and
380 /// for generators we don't even implement the closure traits
383 /// If we inferred that the closure needs to be FnMut/FnOnce, last element of the returned tuple
384 /// contains a `Some()` with the `Place` that caused us to do so.
385 fn process_collected_capture_information(
387 capture_clause: hir::CaptureBy,
388 capture_information: InferredCaptureInformation<'tcx>,
389 ) -> (InferredCaptureInformation<'tcx>, ty::ClosureKind, Option<(Span, Place<'tcx>)>) {
390 let mut processed: InferredCaptureInformation<'tcx> = Default::default();
392 let mut closure_kind = ty::ClosureKind::LATTICE_BOTTOM;
393 let mut origin: Option<(Span, Place<'tcx>)> = None;
395 for (place, mut capture_info) in capture_information {
396 // Apply rules for safety before inferring closure kind
397 let (place, capture_kind) =
398 restrict_capture_precision(place, capture_info.capture_kind);
399 capture_info.capture_kind = capture_kind;
401 let (place, capture_kind) =
402 truncate_capture_for_optimization(place, capture_info.capture_kind);
403 capture_info.capture_kind = capture_kind;
405 let usage_span = if let Some(usage_expr) = capture_info.path_expr_id {
406 self.tcx.hir().span(usage_expr)
411 let updated = match capture_info.capture_kind {
412 ty::UpvarCapture::ByValue(..) => match closure_kind {
413 ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
414 (ty::ClosureKind::FnOnce, Some((usage_span, place.clone())))
416 // If closure is already FnOnce, don't update
417 ty::ClosureKind::FnOnce => (closure_kind, origin),
420 ty::UpvarCapture::ByRef(ty::UpvarBorrow {
421 kind: ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
425 ty::ClosureKind::Fn => {
426 (ty::ClosureKind::FnMut, Some((usage_span, place.clone())))
428 // Don't update the origin
429 ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce => (closure_kind, origin),
433 _ => (closure_kind, origin),
436 closure_kind = updated.0;
439 let (place, capture_kind) = match capture_clause {
440 hir::CaptureBy::Value => adjust_for_move_closure(place, capture_info.capture_kind),
441 hir::CaptureBy::Ref => {
442 adjust_for_non_move_closure(place, capture_info.capture_kind)
446 // This restriction needs to be applied after we have handled adjustments for `move`
447 // closures. We want to make sure any adjustment that might make us move the place into
448 // the closure gets handled.
449 let (place, capture_kind) =
450 restrict_precision_for_drop_types(self, place, capture_kind, usage_span);
452 capture_info.capture_kind = capture_kind;
454 let capture_info = if let Some(existing) = processed.get(&place) {
455 determine_capture_info(*existing, capture_info)
459 processed.insert(place, capture_info);
462 (processed, closure_kind, origin)
465 /// Analyzes the information collected by `InferBorrowKind` to compute the min number of
466 /// Places (and corresponding capture kind) that we need to keep track of to support all
467 /// the required captured paths.
470 /// Note: If this function is called multiple times for the same closure, it will update
471 /// the existing min_capture map that is stored in TypeckResults.
475 /// struct Point { x: i32, y: i32 }
477 /// let s: String; // hir_id_s
478 /// let mut p: Point; // his_id_p
480 /// println!("{}", s); // L1
482 /// println!("{}" , p.y) // L3
483 /// println!("{}", p) // L4
487 /// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
488 /// the lines L1..5 respectively.
490 /// InferBorrowKind results in a structure like this:
494 /// Place(base: hir_id_s, projections: [], ....) -> {
495 /// capture_kind_expr: hir_id_L5,
496 /// path_expr_id: hir_id_L5,
497 /// capture_kind: ByValue
499 /// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
500 /// capture_kind_expr: hir_id_L2,
501 /// path_expr_id: hir_id_L2,
502 /// capture_kind: ByValue
504 /// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
505 /// capture_kind_expr: hir_id_L3,
506 /// path_expr_id: hir_id_L3,
507 /// capture_kind: ByValue
509 /// Place(base: hir_id_p, projections: [], ...) -> {
510 /// capture_kind_expr: hir_id_L4,
511 /// path_expr_id: hir_id_L4,
512 /// capture_kind: ByValue
516 /// After the min capture analysis, we get:
520 /// Place(base: hir_id_s, projections: [], ....) -> {
521 /// capture_kind_expr: hir_id_L5,
522 /// path_expr_id: hir_id_L5,
523 /// capture_kind: ByValue
527 /// Place(base: hir_id_p, projections: [], ...) -> {
528 /// capture_kind_expr: hir_id_L2,
529 /// path_expr_id: hir_id_L4,
530 /// capture_kind: ByValue
534 fn compute_min_captures(
536 closure_def_id: DefId,
537 capture_information: InferredCaptureInformation<'tcx>,
539 if capture_information.is_empty() {
543 let mut typeck_results = self.typeck_results.borrow_mut();
545 let mut root_var_min_capture_list =
546 typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
548 for (mut place, capture_info) in capture_information.into_iter() {
549 let var_hir_id = match place.base {
550 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
551 base => bug!("Expected upvar, found={:?}", base),
554 let min_cap_list = match root_var_min_capture_list.get_mut(&var_hir_id) {
556 let mutability = self.determine_capture_mutability(&typeck_results, &place);
558 vec![ty::CapturedPlace { place, info: capture_info, mutability }];
559 root_var_min_capture_list.insert(var_hir_id, min_cap_list);
562 Some(min_cap_list) => min_cap_list,
565 // Go through each entry in the current list of min_captures
566 // - if ancestor is found, update it's capture kind to account for current place's
567 // capture information.
569 // - if descendant is found, remove it from the list, and update the current place's
570 // capture information to account for the descendants's capture kind.
572 // We can never be in a case where the list contains both an ancestor and a descendant
573 // Also there can only be ancestor but in case of descendants there might be
576 let mut descendant_found = false;
577 let mut updated_capture_info = capture_info;
578 min_cap_list.retain(|possible_descendant| {
579 match determine_place_ancestry_relation(&place, &possible_descendant.place) {
580 // current place is ancestor of possible_descendant
581 PlaceAncestryRelation::Ancestor => {
582 descendant_found = true;
584 let mut possible_descendant = possible_descendant.clone();
585 let backup_path_expr_id = updated_capture_info.path_expr_id;
587 // Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
588 // possible change in capture mode.
589 truncate_place_to_len_and_update_capture_kind(
590 &mut possible_descendant.place,
591 &mut possible_descendant.info.capture_kind,
592 place.projections.len(),
595 updated_capture_info =
596 determine_capture_info(updated_capture_info, possible_descendant.info);
598 // we need to keep the ancestor's `path_expr_id`
599 updated_capture_info.path_expr_id = backup_path_expr_id;
607 let mut ancestor_found = false;
608 if !descendant_found {
609 for possible_ancestor in min_cap_list.iter_mut() {
610 match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
611 // current place is descendant of possible_ancestor
612 PlaceAncestryRelation::Descendant | PlaceAncestryRelation::SamePlace => {
613 ancestor_found = true;
614 let backup_path_expr_id = possible_ancestor.info.path_expr_id;
616 // Truncate the descendant (current place) to be same as the ancestor to handle any
617 // possible change in capture mode.
618 truncate_place_to_len_and_update_capture_kind(
620 &mut updated_capture_info.capture_kind,
621 possible_ancestor.place.projections.len(),
624 possible_ancestor.info = determine_capture_info(
625 possible_ancestor.info,
626 updated_capture_info,
629 // we need to keep the ancestor's `path_expr_id`
630 possible_ancestor.info.path_expr_id = backup_path_expr_id;
632 // Only one ancestor of the current place will be in the list.
640 // Only need to insert when we don't have an ancestor in the existing min capture list
642 let mutability = self.determine_capture_mutability(&typeck_results, &place);
644 ty::CapturedPlace { place, info: updated_capture_info, mutability };
645 min_cap_list.push(captured_place);
650 "For closure={:?}, min_captures before sorting={:?}",
651 closure_def_id, root_var_min_capture_list
654 // Now that we have the minimized list of captures, sort the captures by field id.
655 // This causes the closure to capture the upvars in the same order as the fields are
656 // declared which is also the drop order. Thus, in situations where we capture all the
657 // fields of some type, the obserable drop order will remain the same as it previously
658 // was even though we're dropping each capture individually.
659 // See https://github.com/rust-lang/project-rfc-2229/issues/42 and
660 // `src/test/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
661 for (_, captures) in &mut root_var_min_capture_list {
662 captures.sort_by(|capture1, capture2| {
663 for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
664 // We do not need to look at the `Projection.ty` fields here because at each
665 // step of the iteration, the projections will either be the same and therefore
666 // the types must be as well or the current projection will be different and
667 // we will return the result of comparing the field indexes.
668 match (p1.kind, p2.kind) {
669 // Paths are the same, continue to next loop.
670 (ProjectionKind::Deref, ProjectionKind::Deref) => {}
671 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
674 // Fields are different, compare them.
675 (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
679 // We should have either a pair of `Deref`s or a pair of `Field`s.
680 // Anything else is a bug.
682 l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
683 r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
685 "ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
692 (ProjectionKind::Index
693 | ProjectionKind::Subslice
694 | ProjectionKind::Deref
695 | ProjectionKind::Field(..)),
698 (ProjectionKind::Index
699 | ProjectionKind::Subslice
700 | ProjectionKind::Deref
701 | ProjectionKind::Field(..)),
703 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
711 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
718 "For closure={:?}, min_captures after sorting={:#?}",
719 closure_def_id, root_var_min_capture_list
721 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
724 /// Perform the migration analysis for RFC 2229, and emit lint
725 /// `disjoint_capture_drop_reorder` if needed.
726 fn perform_2229_migration_anaysis(
728 closure_def_id: DefId,
729 body_id: hir::BodyId,
730 capture_clause: hir::CaptureBy,
733 let (need_migrations, reasons) = self.compute_2229_migrations(
737 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
740 if !need_migrations.is_empty() {
741 let (migration_string, migrated_variables_concat) =
742 migration_suggestion_for_2229(self.tcx, &need_migrations);
744 let local_def_id = closure_def_id.expect_local();
745 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
746 let closure_span = self.tcx.hir().span(closure_hir_id);
747 let closure_head_span = self.tcx.sess.source_map().guess_head_span(closure_span);
748 self.tcx.struct_span_lint_hir(
749 lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
753 let mut diagnostics_builder = lint.build(
754 &reasons.migration_message(),
756 for NeededMigration { var_hir_id, diagnostics_info } in &need_migrations {
757 // Labels all the usage of the captured variable and why they are responsible
758 // for migration being needed
759 for lint_note in diagnostics_info.iter() {
760 match &lint_note.captures_info {
761 UpvarMigrationInfo::CapturingPrecise { source_expr: Some(capture_expr_id), var_name: captured_name } => {
762 let cause_span = self.tcx.hir().span(*capture_expr_id);
763 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
764 self.tcx.hir().name(*var_hir_id),
768 UpvarMigrationInfo::CapturingNothing { use_span } => {
769 diagnostics_builder.span_label(*use_span, format!("in Rust 2018, this causes the closure to capture `{}`, but in Rust 2021, it has no effect",
770 self.tcx.hir().name(*var_hir_id),
777 // Add a label pointing to where a captured variable affected by drop order
779 if lint_note.reason.drop_order {
780 let drop_location_span = drop_location_span(self.tcx, &closure_hir_id);
782 match &lint_note.captures_info {
783 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
784 diagnostics_builder.span_label(drop_location_span, format!("in Rust 2018, `{}` is dropped here, but in Rust 2021, only `{}` will be dropped here as part of the closure",
785 self.tcx.hir().name(*var_hir_id),
789 UpvarMigrationInfo::CapturingNothing { use_span: _ } => {
790 diagnostics_builder.span_label(drop_location_span, format!("in Rust 2018, `{v}` is dropped here along with the closure, but in Rust 2021 `{v}` is not part of the closure",
791 v = self.tcx.hir().name(*var_hir_id),
797 // Add a label explaining why a closure no longer implements a trait
798 for &missing_trait in &lint_note.reason.auto_traits {
799 // not capturing something anymore cannot cause a trait to fail to be implemented:
800 match &lint_note.captures_info {
801 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
802 let var_name = self.tcx.hir().name(*var_hir_id);
803 diagnostics_builder.span_label(closure_head_span, format!("\
804 in Rust 2018, this closure implements {missing_trait} \
805 as `{var_name}` implements {missing_trait}, but in Rust 2021, \
806 this closure will no longer implement {missing_trait} \
807 because `{var_name}` is not fully captured \
808 and `{captured_name}` does not implement {missing_trait}"));
811 // Cannot happen: if we don't capture a variable, we impl strictly more traits
812 UpvarMigrationInfo::CapturingNothing { use_span } => span_bug!(*use_span, "missing trait from not capturing something"),
817 diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
819 let diagnostic_msg = format!(
820 "add a dummy let to cause {} to be fully captured",
821 migrated_variables_concat
824 let mut closure_body_span = {
825 // If the body was entirely expanded from a macro
826 // invocation, i.e. the body is not contained inside the
827 // closure span, then we walk up the expansion until we
828 // find the span before the expansion.
829 let s = self.tcx.hir().span(body_id.hir_id);
830 s.find_ancestor_inside(closure_span).unwrap_or(s)
833 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
834 if s.starts_with('$') {
835 // Looks like a macro fragment. Try to find the real block.
836 if let Some(hir::Node::Expr(&hir::Expr {
837 kind: hir::ExprKind::Block(block, ..), ..
838 })) = self.tcx.hir().find(body_id.hir_id) {
839 // If the body is a block (with `{..}`), we use the span of that block.
840 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
841 // Since we know it's a block, we know we can insert the `let _ = ..` without
842 // breaking the macro syntax.
843 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
844 closure_body_span = block.span;
850 let mut lines = s.lines();
851 let line1 = lines.next().unwrap_or_default();
853 if line1.trim_end() == "{" {
854 // This is a multi-line closure with just a `{` on the first line,
855 // so we put the `let` on its own line.
856 // We take the indentation from the next non-empty line.
857 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
858 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
859 diagnostics_builder.span_suggestion(
860 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
862 format!("\n{}{};", indent, migration_string),
863 Applicability::MachineApplicable,
865 } else if line1.starts_with('{') {
866 // This is a closure with its body wrapped in
867 // braces, but with more than just the opening
868 // brace on the first line. We put the `let`
869 // directly after the `{`.
870 diagnostics_builder.span_suggestion(
871 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
873 format!(" {};", migration_string),
874 Applicability::MachineApplicable,
877 // This is a closure without braces around the body.
878 // We add braces to add the `let` before the body.
879 diagnostics_builder.multipart_suggestion(
882 (closure_body_span.shrink_to_lo(), format!("{{ {}; ", migration_string)),
883 (closure_body_span.shrink_to_hi(), " }".to_string()),
885 Applicability::MachineApplicable
889 diagnostics_builder.span_suggestion(
893 Applicability::HasPlaceholders
897 diagnostics_builder.emit();
903 /// Combines all the reasons for 2229 migrations
904 fn compute_2229_migrations_reasons(
906 auto_trait_reasons: FxHashSet<&'static str>,
908 ) -> MigrationWarningReason {
909 let mut reasons = MigrationWarningReason::default();
911 for auto_trait in auto_trait_reasons {
912 reasons.auto_traits.push(auto_trait);
915 reasons.drop_order = drop_order;
920 /// Figures out the list of root variables (and their types) that aren't completely
921 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
922 /// differ between the root variable and the captured paths.
924 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
925 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
926 fn compute_2229_migrations_for_trait(
928 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
929 var_hir_id: hir::HirId,
930 closure_clause: hir::CaptureBy,
931 ) -> Option<FxHashMap<UpvarMigrationInfo, FxHashSet<&'static str>>> {
932 let auto_traits_def_id = vec![
933 self.tcx.lang_items().clone_trait(),
934 self.tcx.lang_items().sync_trait(),
935 self.tcx.get_diagnostic_item(sym::Send),
936 self.tcx.lang_items().unpin_trait(),
937 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
938 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
940 const AUTO_TRAITS: [&str; 6] =
941 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
943 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
945 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
947 let ty = match closure_clause {
948 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
949 hir::CaptureBy::Ref => {
950 // For non move closure the capture kind is the max capture kind of all captures
951 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
952 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
953 for capture in root_var_min_capture_list.iter() {
954 max_capture_info = determine_capture_info(max_capture_info, capture.info);
957 apply_capture_kind_on_capture_ty(self.tcx, ty, max_capture_info.capture_kind)
961 let mut obligations_should_hold = Vec::new();
962 // Checks if a root variable implements any of the auto traits
963 for check_trait in auto_traits_def_id.iter() {
964 obligations_should_hold.push(
968 .type_implements_trait(
971 self.tcx.mk_substs_trait(ty, &[]),
974 .must_apply_modulo_regions()
980 let mut problematic_captures = FxHashMap::default();
981 // Check whether captured fields also implement the trait
982 for capture in root_var_min_capture_list.iter() {
983 let ty = apply_capture_kind_on_capture_ty(
986 capture.info.capture_kind,
989 // Checks if a capture implements any of the auto traits
990 let mut obligations_holds_for_capture = Vec::new();
991 for check_trait in auto_traits_def_id.iter() {
992 obligations_holds_for_capture.push(
996 .type_implements_trait(
999 self.tcx.mk_substs_trait(ty, &[]),
1002 .must_apply_modulo_regions()
1008 let mut capture_problems = FxHashSet::default();
1010 // Checks if for any of the auto traits, one or more trait is implemented
1011 // by the root variable but not by the capture
1012 for (idx, _) in obligations_should_hold.iter().enumerate() {
1013 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
1014 capture_problems.insert(AUTO_TRAITS[idx]);
1018 if !capture_problems.is_empty() {
1019 problematic_captures.insert(
1020 UpvarMigrationInfo::CapturingPrecise {
1021 source_expr: capture.info.path_expr_id,
1022 var_name: capture.to_string(self.tcx),
1028 if !problematic_captures.is_empty() {
1029 return Some(problematic_captures);
1034 /// Figures out the list of root variables (and their types) that aren't completely
1035 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
1036 /// some path starting at that root variable **might** be affected.
1038 /// The output list would include a root variable if:
1039 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1040 /// enabled, **and**
1041 /// - It wasn't completely captured by the closure, **and**
1042 /// - One of the paths starting at this root variable, that is not captured needs Drop.
1044 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
1045 /// are no significant drops than None is returned
1046 #[instrument(level = "debug", skip(self))]
1047 fn compute_2229_migrations_for_drop(
1049 closure_def_id: DefId,
1051 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1052 closure_clause: hir::CaptureBy,
1053 var_hir_id: hir::HirId,
1054 ) -> Option<FxHashSet<UpvarMigrationInfo>> {
1055 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
1057 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local())) {
1058 debug!("does not have significant drop");
1062 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1063 // The upvar is mentioned within the closure but no path starting from it is
1064 // used. This occurs when you have (e.g.)
1067 // let x = move || {
1071 debug!("no path starting from it is used");
1074 match closure_clause {
1075 // Only migrate if closure is a move closure
1076 hir::CaptureBy::Value => {
1077 let mut diagnostics_info = FxHashSet::default();
1078 let upvars = self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
1079 let upvar = upvars[&var_hir_id];
1080 diagnostics_info.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
1081 return Some(diagnostics_info);
1083 hir::CaptureBy::Ref => {}
1088 debug!(?root_var_min_capture_list);
1090 let mut projections_list = Vec::new();
1091 let mut diagnostics_info = FxHashSet::default();
1093 for captured_place in root_var_min_capture_list.iter() {
1094 match captured_place.info.capture_kind {
1095 // Only care about captures that are moved into the closure
1096 ty::UpvarCapture::ByValue(..) => {
1097 projections_list.push(captured_place.place.projections.as_slice());
1098 diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
1099 source_expr: captured_place.info.path_expr_id,
1100 var_name: captured_place.to_string(self.tcx),
1103 ty::UpvarCapture::ByRef(..) => {}
1107 debug!(?projections_list);
1108 debug!(?diagnostics_info);
1110 let is_moved = !projections_list.is_empty();
1113 let is_not_completely_captured =
1114 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1115 debug!(?is_not_completely_captured);
1118 && is_not_completely_captured
1119 && self.has_significant_drop_outside_of_captures(
1126 return Some(diagnostics_info);
1132 /// Figures out the list of root variables (and their types) that aren't completely
1133 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1134 /// order of some path starting at that root variable **might** be affected or auto-traits
1135 /// differ between the root variable and the captured paths.
1137 /// The output list would include a root variable if:
1138 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1139 /// enabled, **and**
1140 /// - It wasn't completely captured by the closure, **and**
1141 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1142 /// - One of the paths captured does not implement all the auto-traits its root variable
1145 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1146 /// containing the reason why root variables whose HirId is contained in the vector should
1148 #[instrument(level = "debug", skip(self))]
1149 fn compute_2229_migrations(
1151 closure_def_id: DefId,
1153 closure_clause: hir::CaptureBy,
1154 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1155 ) -> (Vec<NeededMigration>, MigrationWarningReason) {
1156 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1157 return (Vec::new(), MigrationWarningReason::default());
1160 let mut need_migrations = Vec::new();
1161 let mut auto_trait_migration_reasons = FxHashSet::default();
1162 let mut drop_migration_needed = false;
1164 // Perform auto-trait analysis
1165 for (&var_hir_id, _) in upvars.iter() {
1166 let mut diagnostics_info = Vec::new();
1168 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1169 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1173 FxHashMap::default()
1176 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1177 .compute_2229_migrations_for_drop(
1184 drop_migration_needed = true;
1187 FxHashSet::default()
1190 // Combine all the captures responsible for needing migrations into one HashSet
1191 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1192 for key in auto_trait_diagnostic.keys() {
1193 capture_diagnostic.insert(key.clone());
1196 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1197 capture_diagnostic.sort();
1198 for captures_info in capture_diagnostic {
1199 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1200 let capture_trait_reasons =
1201 if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
1204 FxHashSet::default()
1207 // Check if migration is needed because of drop reorder as a result of that capture
1208 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
1210 // Combine all the reasons of why the root variable should be captured as a result of
1211 // auto trait implementation issues
1212 auto_trait_migration_reasons.extend(capture_trait_reasons.clone());
1214 diagnostics_info.push(MigrationLintNote {
1216 reason: self.compute_2229_migrations_reasons(
1217 capture_trait_reasons,
1218 capture_drop_reorder_reason,
1223 if !diagnostics_info.is_empty() {
1224 need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
1229 self.compute_2229_migrations_reasons(
1230 auto_trait_migration_reasons,
1231 drop_migration_needed,
1236 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1237 /// of a root variable and a list of captured paths starting at this root variable (expressed
1238 /// using list of `Projection` slices), it returns true if there is a path that is not
1239 /// captured starting at this root variable that implements Drop.
1241 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1242 /// path say P and then list of projection slices which represent the different captures moved
1243 /// into the closure starting off of P.
1245 /// This will make more sense with an example:
1248 /// #![feature(capture_disjoint_fields)]
1250 /// struct FancyInteger(i32); // This implements Drop
1252 /// struct Point { x: FancyInteger, y: FancyInteger }
1255 /// struct Wrapper { p: Point, c: Color }
1257 /// fn f(w: Wrapper) {
1259 /// // Closure captures w.p.x and w.c by move.
1266 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1267 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1268 /// therefore Drop ordering would change and we want this function to return true.
1270 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1272 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1275 /// - Ty(place): Type of place
1276 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1279 /// (Ty(w), [ &[p, x], &[c] ])
1281 /// ----------------------------
1284 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1287 /// (Ty(w.p), [ &[x] ]) false
1290 /// -------------------------------
1293 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1296 /// false NeedsSignificantDrop(Ty(w.p.y))
1302 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1303 /// This implies that the `w.c` is completely captured by the closure.
1304 /// Since drop for this path will be called when the closure is
1305 /// dropped we don't need to migrate for it.
1307 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1308 /// path wasn't captured by the closure. Also note that even
1309 /// though we didn't capture this path, the function visits it,
1310 /// which is kind of the point of this function. We then return
1311 /// if the type of `w.p.y` implements Drop, which in this case is
1314 /// Consider another example:
1318 /// impl Drop for X {}
1321 /// impl Drop for Y {}
1325 /// let c = || move(y.0);
1329 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1330 /// return true, because even though all paths starting at `y` are captured, `y` itself
1331 /// implements Drop which will be affected since `y` isn't completely captured.
1332 fn has_significant_drop_outside_of_captures(
1334 closure_def_id: DefId,
1336 base_path_ty: Ty<'tcx>,
1337 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1339 let needs_drop = |ty: Ty<'tcx>| {
1340 ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local()))
1343 let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
1344 let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
1345 let ty_params = self.tcx.mk_substs_trait(base_path_ty, &[]);
1347 .type_implements_trait(
1351 self.tcx.param_env(closure_def_id.expect_local()),
1353 .must_apply_modulo_regions()
1356 let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
1358 // If there is a case where no projection is applied on top of current place
1359 // then there must be exactly one capture corresponding to such a case. Note that this
1360 // represents the case of the path being completely captured by the variable.
1362 // eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
1363 // capture `a.b.c`, because that voilates min capture.
1364 let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
1366 assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
1368 if is_completely_captured {
1369 // The place is captured entirely, so doesn't matter if needs dtor, it will be drop
1370 // when the closure is dropped.
1374 if captured_by_move_projs.is_empty() {
1375 return needs_drop(base_path_ty);
1378 if is_drop_defined_for_ty {
1379 // If drop is implemented for this type then we need it to be fully captured,
1380 // and we know it is not completely captured because of the previous checks.
1382 // Note that this is a bug in the user code that will be reported by the
1383 // borrow checker, since we can't move out of drop types.
1385 // The bug exists in the user's code pre-migration, and we don't migrate here.
1389 match base_path_ty.kind() {
1391 // - `captured_by_move_projs` is not empty. Therefore we can call
1392 // `captured_by_move_projs.first().unwrap()` safely.
1393 // - All entries in `captured_by_move_projs` have atleast one projection.
1394 // Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
1396 // We don't capture derefs in case of move captures, which would have be applied to
1397 // access any further paths.
1398 ty::Adt(def, _) if def.is_box() => unreachable!(),
1399 ty::Ref(..) => unreachable!(),
1400 ty::RawPtr(..) => unreachable!(),
1402 ty::Adt(def, substs) => {
1403 // Multi-varaint enums are captured in entirety,
1404 // which would've been handled in the case of single empty slice in `captured_by_move_projs`.
1405 assert_eq!(def.variants.len(), 1);
1407 // Only Field projections can be applied to a non-box Adt.
1409 captured_by_move_projs.iter().all(|projs| matches!(
1410 projs.first().unwrap().kind,
1411 ProjectionKind::Field(..)
1414 def.variants.get(VariantIdx::new(0)).unwrap().fields.iter().enumerate().any(
1416 let paths_using_field = captured_by_move_projs
1418 .filter_map(|projs| {
1419 if let ProjectionKind::Field(field_idx, _) =
1420 projs.first().unwrap().kind
1422 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1429 let after_field_ty = field.ty(self.tcx, substs);
1430 self.has_significant_drop_outside_of_captures(
1441 // Only Field projections can be applied to a tuple.
1443 captured_by_move_projs.iter().all(|projs| matches!(
1444 projs.first().unwrap().kind,
1445 ProjectionKind::Field(..)
1449 base_path_ty.tuple_fields().enumerate().any(|(i, element_ty)| {
1450 let paths_using_field = captured_by_move_projs
1452 .filter_map(|projs| {
1453 if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
1455 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1462 self.has_significant_drop_outside_of_captures(
1471 // Anything else would be completely captured and therefore handled already.
1472 _ => unreachable!(),
1476 fn init_capture_kind_for_place(
1478 place: &Place<'tcx>,
1479 capture_clause: hir::CaptureBy,
1480 upvar_id: ty::UpvarId,
1482 ) -> ty::UpvarCapture<'tcx> {
1483 match capture_clause {
1484 // In case of a move closure if the data is accessed through a reference we
1485 // want to capture by ref to allow precise capture using reborrows.
1487 // If the data will be moved out of this place, then the place will be truncated
1488 // at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
1490 hir::CaptureBy::Value if !place.deref_tys().any(ty::TyS::is_ref) => {
1491 ty::UpvarCapture::ByValue(None)
1493 hir::CaptureBy::Value | hir::CaptureBy::Ref => {
1494 let origin = UpvarRegion(upvar_id, closure_span);
1495 let upvar_region = self.next_region_var(origin);
1496 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
1497 ty::UpvarCapture::ByRef(upvar_borrow)
1502 fn place_for_root_variable(
1504 closure_def_id: LocalDefId,
1505 var_hir_id: hir::HirId,
1507 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
1510 base_ty: self.node_ty(var_hir_id),
1511 base: PlaceBase::Upvar(upvar_id),
1512 projections: Default::default(),
1516 fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
1517 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
1520 fn log_capture_analysis_first_pass(
1522 closure_def_id: rustc_hir::def_id::DefId,
1523 capture_information: &FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>,
1526 if self.should_log_capture_analysis(closure_def_id) {
1528 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
1529 for (place, capture_info) in capture_information {
1530 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
1531 let output_str = format!("Capturing {}", capture_str);
1534 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
1535 diag.span_note(span, &output_str);
1541 fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
1542 if self.should_log_capture_analysis(closure_def_id) {
1543 if let Some(min_captures) =
1544 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
1547 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
1549 for (_, min_captures_for_var) in min_captures {
1550 for capture in min_captures_for_var {
1551 let place = &capture.place;
1552 let capture_info = &capture.info;
1555 construct_capture_info_string(self.tcx, place, capture_info);
1556 let output_str = format!("Min Capture {}", capture_str);
1558 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
1559 let path_span = capture_info
1561 .map_or(closure_span, |e| self.tcx.hir().span(e));
1562 let capture_kind_span = capture_info
1563 .capture_kind_expr_id
1564 .map_or(closure_span, |e| self.tcx.hir().span(e));
1566 let mut multi_span: MultiSpan =
1567 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
1569 let capture_kind_label =
1570 construct_capture_kind_reason_string(self.tcx, place, capture_info);
1571 let path_label = construct_path_string(self.tcx, place);
1573 multi_span.push_span_label(path_span, path_label);
1574 multi_span.push_span_label(capture_kind_span, capture_kind_label);
1576 diag.span_note(multi_span, &output_str);
1578 let span = capture_info
1580 .map_or(closure_span, |e| self.tcx.hir().span(e));
1582 diag.span_note(span, &output_str);
1591 /// A captured place is mutable if
1592 /// 1. Projections don't include a Deref of an immut-borrow, **and**
1593 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
1594 fn determine_capture_mutability(
1596 typeck_results: &'a TypeckResults<'tcx>,
1597 place: &Place<'tcx>,
1598 ) -> hir::Mutability {
1599 let var_hir_id = match place.base {
1600 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
1601 _ => unreachable!(),
1604 let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
1606 let mut is_mutbl = match bm {
1607 ty::BindByValue(mutability) => mutability,
1608 ty::BindByReference(_) => hir::Mutability::Not,
1611 for pointer_ty in place.deref_tys() {
1612 match pointer_ty.kind() {
1613 // We don't capture derefs of raw ptrs
1614 ty::RawPtr(_) => unreachable!(),
1616 // Derefencing a mut-ref allows us to mut the Place if we don't deref
1617 // an immut-ref after on top of this.
1618 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
1620 // The place isn't mutable once we dereference an immutable reference.
1621 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
1623 // Dereferencing a box doesn't change mutability
1624 ty::Adt(def, ..) if def.is_box() => {}
1626 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
1634 /// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
1635 /// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
1636 fn restrict_repr_packed_field_ref_capture<'tcx>(
1638 param_env: ty::ParamEnv<'tcx>,
1639 place: &Place<'tcx>,
1640 mut curr_borrow_kind: ty::UpvarCapture<'tcx>,
1641 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1642 let pos = place.projections.iter().enumerate().position(|(i, p)| {
1643 let ty = place.ty_before_projection(i);
1645 // Return true for fields of packed structs, unless those fields have alignment 1.
1647 ProjectionKind::Field(..) => match ty.kind() {
1648 ty::Adt(def, _) if def.repr.packed() => {
1649 match tcx.layout_of(param_env.and(p.ty)) {
1650 Ok(layout) if layout.align.abi.bytes() == 1 => {
1651 // if the alignment is 1, the type can't be further
1654 "restrict_repr_packed_field_ref_capture: ({:?}) - align = 1",
1660 debug!("restrict_repr_packed_field_ref_capture: ({:?}) - true", place);
1672 let mut place = place.clone();
1674 if let Some(pos) = pos {
1675 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
1678 (place, curr_borrow_kind)
1681 /// Returns a Ty that applies the specified capture kind on the provided capture Ty
1682 fn apply_capture_kind_on_capture_ty(
1685 capture_kind: UpvarCapture<'tcx>,
1687 match capture_kind {
1688 ty::UpvarCapture::ByValue(_) => ty,
1689 ty::UpvarCapture::ByRef(borrow) => tcx
1690 .mk_ref(borrow.region, ty::TypeAndMut { ty: ty, mutbl: borrow.kind.to_mutbl_lossy() }),
1694 /// Returns the Span of where the value with the provided HirId would be dropped
1695 fn drop_location_span(tcx: TyCtxt<'tcx>, hir_id: &hir::HirId) -> Span {
1696 let owner_id = tcx.hir().get_enclosing_scope(*hir_id).unwrap();
1698 let owner_node = tcx.hir().get(owner_id);
1699 let owner_span = match owner_node {
1700 hir::Node::Item(item) => match item.kind {
1701 hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
1703 bug!("Drop location span error: need to handle more ItemKind {:?}", item.kind);
1706 hir::Node::Block(block) => tcx.hir().span(block.hir_id),
1708 bug!("Drop location span error: need to handle more Node {:?}", owner_node);
1711 tcx.sess.source_map().end_point(owner_span)
1714 struct InferBorrowKind<'a, 'tcx> {
1715 fcx: &'a FnCtxt<'a, 'tcx>,
1717 // The def-id of the closure whose kind and upvar accesses are being inferred.
1718 closure_def_id: DefId,
1722 /// For each Place that is captured by the closure, we track the minimal kind of
1723 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1725 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1726 /// s.str2 via a MutableBorrow
1729 /// struct SomeStruct { str1: String, str2: String }
1731 /// // Assume that the HirId for the variable definition is `V1`
1732 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
1734 /// let fix_s = |new_s2| {
1735 /// // Assume that the HirId for the expression `s.str1` is `E1`
1736 /// println!("Updating SomeStruct with str1=", s.str1);
1737 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1738 /// s.str2 = new_s2;
1742 /// For closure `fix_s`, (at a high level) the map contains
1745 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1746 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1748 capture_information: InferredCaptureInformation<'tcx>,
1749 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1752 impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
1753 #[instrument(skip(self), level = "debug")]
1754 fn adjust_upvar_borrow_kind_for_consume(
1756 place_with_id: &PlaceWithHirId<'tcx>,
1757 diag_expr_id: hir::HirId,
1759 let tcx = self.fcx.tcx;
1760 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else {
1766 let usage_span = tcx.hir().span(diag_expr_id);
1768 let capture_info = ty::CaptureInfo {
1769 capture_kind_expr_id: Some(diag_expr_id),
1770 path_expr_id: Some(diag_expr_id),
1771 capture_kind: ty::UpvarCapture::ByValue(Some(usage_span)),
1774 let curr_info = self.capture_information[&place_with_id.place];
1775 let updated_info = determine_capture_info(curr_info, capture_info);
1777 self.capture_information[&place_with_id.place] = updated_info;
1780 /// Indicates that `place_with_id` is being directly mutated (e.g., assigned
1781 /// to). If the place is based on a by-ref upvar, this implies that
1782 /// the upvar must be borrowed using an `&mut` borrow.
1783 #[instrument(skip(self), level = "debug")]
1784 fn adjust_upvar_borrow_kind_for_mut(
1786 place_with_id: &PlaceWithHirId<'tcx>,
1787 diag_expr_id: hir::HirId,
1789 if let PlaceBase::Upvar(_) = place_with_id.place.base {
1790 // Raw pointers don't inherit mutability
1791 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1794 self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::MutBorrow);
1798 #[instrument(skip(self), level = "debug")]
1799 fn adjust_upvar_borrow_kind_for_unique(
1801 place_with_id: &PlaceWithHirId<'tcx>,
1802 diag_expr_id: hir::HirId,
1804 if let PlaceBase::Upvar(_) = place_with_id.place.base {
1805 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1806 // Raw pointers don't inherit mutability.
1809 // for a borrowed pointer to be unique, its base must be unique
1810 self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::UniqueImmBorrow);
1814 fn adjust_upvar_deref(
1816 place_with_id: &PlaceWithHirId<'tcx>,
1817 diag_expr_id: hir::HirId,
1818 borrow_kind: ty::BorrowKind,
1820 assert!(match borrow_kind {
1821 ty::MutBorrow => true,
1822 ty::UniqueImmBorrow => true,
1824 // imm borrows never require adjusting any kinds, so we don't wind up here
1825 ty::ImmBorrow => false,
1828 // if this is an implicit deref of an
1829 // upvar, then we need to modify the
1830 // borrow_kind of the upvar to make sure it
1831 // is inferred to mutable if necessary
1832 self.adjust_upvar_borrow_kind(place_with_id, diag_expr_id, borrow_kind);
1835 /// We infer the borrow_kind with which to borrow upvars in a stack closure.
1836 /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
1837 /// moving from left to right as needed (but never right to left).
1838 /// Here the argument `mutbl` is the borrow_kind that is required by
1839 /// some particular use.
1840 #[instrument(skip(self), level = "debug")]
1841 fn adjust_upvar_borrow_kind(
1843 place_with_id: &PlaceWithHirId<'tcx>,
1844 diag_expr_id: hir::HirId,
1845 kind: ty::BorrowKind,
1847 let curr_capture_info = self.capture_information[&place_with_id.place];
1849 debug!(?curr_capture_info);
1851 if let ty::UpvarCapture::ByValue(_) = curr_capture_info.capture_kind {
1852 // It's already captured by value, we don't need to do anything here
1854 } else if let ty::UpvarCapture::ByRef(curr_upvar_borrow) = curr_capture_info.capture_kind {
1855 // Use the same region as the current capture information
1856 // Doesn't matter since only one of the UpvarBorrow will be used.
1857 let new_upvar_borrow = ty::UpvarBorrow { kind, region: curr_upvar_borrow.region };
1859 let capture_info = ty::CaptureInfo {
1860 capture_kind_expr_id: Some(diag_expr_id),
1861 path_expr_id: Some(diag_expr_id),
1862 capture_kind: ty::UpvarCapture::ByRef(new_upvar_borrow),
1864 let updated_info = determine_capture_info(curr_capture_info, capture_info);
1865 self.capture_information[&place_with_id.place] = updated_info;
1869 #[instrument(skip(self, diag_expr_id), level = "debug")]
1870 fn init_capture_info_for_place(
1872 place_with_id: &PlaceWithHirId<'tcx>,
1873 diag_expr_id: hir::HirId,
1875 if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
1876 assert_eq!(self.closure_def_id.expect_local(), upvar_id.closure_expr_id);
1878 // Initialize to ImmBorrow
1879 // We will escalate the CaptureKind based on any uses we see or in `process_collected_capture_information`.
1880 let origin = UpvarRegion(upvar_id, self.closure_span);
1881 let upvar_region = self.fcx.next_region_var(origin);
1882 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
1883 let capture_kind = ty::UpvarCapture::ByRef(upvar_borrow);
1885 let expr_id = Some(diag_expr_id);
1886 let capture_info = ty::CaptureInfo {
1887 capture_kind_expr_id: expr_id,
1888 path_expr_id: expr_id,
1892 debug!("Capturing new place {:?}, capture_info={:?}", place_with_id, capture_info);
1894 self.capture_information.insert(place_with_id.place.clone(), capture_info);
1896 debug!("Not upvar");
1901 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1902 fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId) {
1903 if let PlaceBase::Upvar(_) = place.base {
1904 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1905 // such as deref of a raw pointer.
1906 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::UpvarBorrow {
1907 kind: ty::BorrowKind::ImmBorrow,
1908 region: &ty::ReErased,
1911 let (place, _) = restrict_capture_precision(place, dummy_capture_kind);
1913 let (place, _) = restrict_repr_packed_field_ref_capture(
1919 self.fake_reads.push((place, cause, diag_expr_id));
1923 #[instrument(skip(self), level = "debug")]
1924 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1925 if !self.capture_information.contains_key(&place_with_id.place) {
1926 self.init_capture_info_for_place(place_with_id, diag_expr_id);
1929 self.adjust_upvar_borrow_kind_for_consume(place_with_id, diag_expr_id);
1932 #[instrument(skip(self), level = "debug")]
1935 place_with_id: &PlaceWithHirId<'tcx>,
1936 diag_expr_id: hir::HirId,
1939 // The region here will get discarded/ignored
1940 let dummy_capture_kind =
1941 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind: bk, region: &ty::ReErased });
1943 // We only want repr packed restriction to be applied to reading references into a packed
1944 // struct, and not when the data is being moved. Therefore we call this method here instead
1945 // of in `restrict_capture_precision`.
1946 let (place, updated_kind) = restrict_repr_packed_field_ref_capture(
1949 &place_with_id.place,
1953 let place_with_id = PlaceWithHirId { place, ..*place_with_id };
1955 if !self.capture_information.contains_key(&place_with_id.place) {
1956 self.init_capture_info_for_place(&place_with_id, diag_expr_id);
1959 match updated_kind {
1960 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind, .. }) => match kind {
1962 ty::UniqueImmBorrow => {
1963 self.adjust_upvar_borrow_kind_for_unique(&place_with_id, diag_expr_id);
1966 self.adjust_upvar_borrow_kind_for_mut(&place_with_id, diag_expr_id);
1970 // Just truncating the place will never cause capture kind to be updated to ByValue
1971 ty::UpvarCapture::ByValue(..) => unreachable!(),
1975 #[instrument(skip(self), level = "debug")]
1976 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1977 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1981 /// Rust doesn't permit moving fields out of a type that implements drop
1982 fn restrict_precision_for_drop_types<'a, 'tcx>(
1983 fcx: &'a FnCtxt<'a, 'tcx>,
1984 mut place: Place<'tcx>,
1985 mut curr_mode: ty::UpvarCapture<'tcx>,
1987 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1988 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1990 if let (false, UpvarCapture::ByValue(..)) = (is_copy_type, curr_mode) {
1991 for i in 0..place.projections.len() {
1992 match place.ty_before_projection(i).kind() {
1993 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1994 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
2005 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
2006 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
2007 /// them completely.
2008 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
2009 fn restrict_precision_for_unsafe(
2010 mut place: Place<'tcx>,
2011 mut curr_mode: ty::UpvarCapture<'tcx>,
2012 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2013 if place.base_ty.is_unsafe_ptr() {
2014 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
2017 if place.base_ty.is_union() {
2018 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
2021 for (i, proj) in place.projections.iter().enumerate() {
2022 if proj.ty.is_unsafe_ptr() {
2023 // Don't apply any projections on top of an unsafe ptr.
2024 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
2028 if proj.ty.is_union() {
2029 // Don't capture preicse fields of a union.
2030 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
2038 /// Truncate projections so that following rules are obeyed by the captured `place`:
2039 /// - No Index projections are captured, since arrays are captured completely.
2040 /// - No unsafe block is required to capture `place`
2041 /// Returns the truncated place and updated cature mode.
2042 fn restrict_capture_precision<'tcx>(
2044 curr_mode: ty::UpvarCapture<'tcx>,
2045 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2046 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
2048 if place.projections.is_empty() {
2049 // Nothing to do here
2050 return (place, curr_mode);
2053 for (i, proj) in place.projections.iter().enumerate() {
2055 ProjectionKind::Index => {
2056 // Arrays are completely captured, so we drop Index projections
2057 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
2058 return (place, curr_mode);
2060 ProjectionKind::Deref => {}
2061 ProjectionKind::Field(..) => {} // ignore
2062 ProjectionKind::Subslice => {} // We never capture this
2069 /// Truncate deref of any reference.
2070 fn adjust_for_move_closure<'tcx>(
2071 mut place: Place<'tcx>,
2072 mut kind: ty::UpvarCapture<'tcx>,
2073 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2074 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
2076 if let Some(idx) = first_deref {
2077 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
2080 // AMAN: I think we don't need the span inside the ByValue anymore
2081 // we have more detailed span in CaptureInfo
2082 (place, ty::UpvarCapture::ByValue(None))
2085 /// Adjust closure capture just that if taking ownership of data, only move data
2086 /// from enclosing stack frame.
2087 fn adjust_for_non_move_closure<'tcx>(
2088 mut place: Place<'tcx>,
2089 mut kind: ty::UpvarCapture<'tcx>,
2090 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2091 let contains_deref =
2092 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
2095 ty::UpvarCapture::ByValue(..) => {
2096 if let Some(idx) = contains_deref {
2097 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
2101 ty::UpvarCapture::ByRef(..) => {}
2107 fn construct_place_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2108 let variable_name = match place.base {
2109 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
2110 _ => bug!("Capture_information should only contain upvars"),
2113 let mut projections_str = String::new();
2114 for (i, item) in place.projections.iter().enumerate() {
2115 let proj = match item.kind {
2116 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
2117 ProjectionKind::Deref => String::from("Deref"),
2118 ProjectionKind::Index => String::from("Index"),
2119 ProjectionKind::Subslice => String::from("Subslice"),
2122 projections_str.push(',');
2124 projections_str.push_str(proj.as_str());
2127 format!("{}[{}]", variable_name, projections_str)
2130 fn construct_capture_kind_reason_string(
2132 place: &Place<'tcx>,
2133 capture_info: &ty::CaptureInfo<'tcx>,
2135 let place_str = construct_place_string(tcx, place);
2137 let capture_kind_str = match capture_info.capture_kind {
2138 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
2139 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
2142 format!("{} captured as {} here", place_str, capture_kind_str)
2145 fn construct_path_string(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2146 let place_str = construct_place_string(tcx, place);
2148 format!("{} used here", place_str)
2151 fn construct_capture_info_string(
2153 place: &Place<'tcx>,
2154 capture_info: &ty::CaptureInfo<'tcx>,
2156 let place_str = construct_place_string(tcx, place);
2158 let capture_kind_str = match capture_info.capture_kind {
2159 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
2160 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
2162 format!("{} -> {}", place_str, capture_kind_str)
2165 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2166 tcx.hir().name(var_hir_id)
2169 #[instrument(level = "debug", skip(tcx))]
2170 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2172 closure_id: hir::HirId,
2175 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2177 !matches!(level, lint::Level::Allow)
2180 /// Return a two string tuple (s1, s2)
2181 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2182 /// - s2: Comma separated names of the variables being migrated.
2183 fn migration_suggestion_for_2229(
2185 need_migrations: &Vec<NeededMigration>,
2186 ) -> (String, String) {
2187 let need_migrations_variables = need_migrations
2189 .map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
2190 .collect::<Vec<_>>();
2192 let migration_ref_concat =
2193 need_migrations_variables.iter().map(|v| format!("&{}", v)).collect::<Vec<_>>().join(", ");
2195 let migration_string = if 1 == need_migrations.len() {
2196 format!("let _ = {}", migration_ref_concat)
2198 format!("let _ = ({})", migration_ref_concat)
2201 let migrated_variables_concat =
2202 need_migrations_variables.iter().map(|v| format!("`{}`", v)).collect::<Vec<_>>().join(", ");
2204 (migration_string, migrated_variables_concat)
2207 /// Helper function to determine if we need to escalate CaptureKind from
2208 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2209 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2211 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2212 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2214 /// It is the caller's duty to figure out which path_expr_id to use.
2216 /// If both the CaptureKind and Expression are considered to be equivalent,
2217 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to priortize
2218 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2219 /// in the closure. This can be achieved simply by calling
2220 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2221 /// expressions that occur earlier in the closure body than the current expression are processed before.
2222 /// Consider the following example
2224 /// struct Point { x: i32, y: i32 }
2225 /// let mut p: Point { x: 10, y: 10 };
2233 /// p.x += 10; // E2
2237 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2238 /// and both have an expression associated, however for diagnostics we prefer reporting
2239 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2240 /// would've already handled `E1`, and have an existing capture_information for it.
2241 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2242 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2243 fn determine_capture_info(
2244 capture_info_a: ty::CaptureInfo<'tcx>,
2245 capture_info_b: ty::CaptureInfo<'tcx>,
2246 ) -> ty::CaptureInfo<'tcx> {
2247 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2249 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2250 (ty::UpvarCapture::ByValue(_), ty::UpvarCapture::ByValue(_)) => {
2251 // We don't need to worry about the spans being ignored here.
2253 // The expr_id in capture_info corresponds to the span that is stored within
2254 // ByValue(span) and therefore it gets handled with priortizing based on
2255 // expressions below.
2258 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2259 ref_a.kind == ref_b.kind
2261 (ty::UpvarCapture::ByValue(_), _) | (ty::UpvarCapture::ByRef(_), _) => false,
2264 if eq_capture_kind {
2265 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2266 (Some(_), _) | (None, None) => capture_info_a,
2267 (None, Some(_)) => capture_info_b,
2270 // We select the CaptureKind which ranks higher based the following priority order:
2271 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2272 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2273 (ty::UpvarCapture::ByValue(_), _) => capture_info_a,
2274 (_, ty::UpvarCapture::ByValue(_)) => capture_info_b,
2275 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2276 match (ref_a.kind, ref_b.kind) {
2278 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2279 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2282 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2283 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2285 (ty::ImmBorrow, ty::ImmBorrow)
2286 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2287 | (ty::MutBorrow, ty::MutBorrow) => {
2288 bug!("Expected unequal capture kinds");
2296 /// Truncates `place` to have up to `len` projections.
2297 /// `curr_mode` is the current required capture kind for the place.
2298 /// Returns the truncated `place` and the updated required capture kind.
2300 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2301 /// contained `Deref` of `&mut`.
2302 fn truncate_place_to_len_and_update_capture_kind(
2303 place: &mut Place<'tcx>,
2304 curr_mode: &mut ty::UpvarCapture<'tcx>,
2307 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2309 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2311 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2312 // we don't need to worry about that case here.
2314 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind: ty::BorrowKind::MutBorrow, region }) => {
2315 for i in len..place.projections.len() {
2316 if place.projections[i].kind == ProjectionKind::Deref
2317 && is_mut_ref(place.ty_before_projection(i))
2319 *curr_mode = ty::UpvarCapture::ByRef(ty::UpvarBorrow {
2320 kind: ty::BorrowKind::UniqueImmBorrow,
2328 ty::UpvarCapture::ByRef(..) => {}
2329 ty::UpvarCapture::ByValue(..) => {}
2332 place.projections.truncate(len);
2335 /// Determines the Ancestry relationship of Place A relative to Place B
2337 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2338 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2339 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2340 fn determine_place_ancestry_relation(
2341 place_a: &Place<'tcx>,
2342 place_b: &Place<'tcx>,
2343 ) -> PlaceAncestryRelation {
2344 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2345 if place_a.base != place_b.base {
2346 return PlaceAncestryRelation::Divergent;
2349 // Assume of length of projections_a = n
2350 let projections_a = &place_a.projections;
2352 // Assume of length of projections_b = m
2353 let projections_b = &place_b.projections;
2355 let same_initial_projections =
2356 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2358 if same_initial_projections {
2359 use std::cmp::Ordering;
2361 // First min(n, m) projections are the same
2362 // Select Ancestor/Descendant
2363 match projections_b.len().cmp(&projections_a.len()) {
2364 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2365 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2366 Ordering::Less => PlaceAncestryRelation::Descendant,
2369 PlaceAncestryRelation::Divergent
2373 /// Reduces the precision of the captured place when the precision doesn't yeild any benefit from
2374 /// borrow checking prespective, allowing us to save us on the size of the capture.
2377 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2378 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2379 /// rightmost deref of the capture if the deref is applied to a shared ref.
2381 /// Reason we only drop the last deref is because of the following edge case:
2384 /// struct MyStruct<'a> {
2390 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2391 /// let c = || drop(&*m.a.field_of_a);
2392 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2394 /// // If we capture `m`, then the closure no longer outlives `'static'
2395 /// // it is constrained to `'a`
2398 fn truncate_capture_for_optimization<'tcx>(
2399 mut place: Place<'tcx>,
2400 mut curr_mode: ty::UpvarCapture<'tcx>,
2401 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2402 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2404 // Find the right-most deref (if any). All the projections that come after this
2405 // are fields or other "in-place pointer adjustments"; these refer therefore to
2406 // data owned by whatever pointer is being dereferenced here.
2407 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2410 // If that pointer is a shared reference, then we don't need those fields.
2411 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2412 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2414 None | Some(_) => {}
2420 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2421 /// user is using Rust Edition 2021 or higher.
2423 /// `span` is the span of the closure.
2424 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2425 // We use span here to ensure that if the closure was generated by a macro with a different
2427 tcx.features().capture_disjoint_fields || span.rust_2021()