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: ({:?}, {:?})",
690 l @ (ProjectionKind::Index
691 | ProjectionKind::Subslice
692 | ProjectionKind::Deref
693 | ProjectionKind::Field(..)),
694 r @ (ProjectionKind::Index
695 | ProjectionKind::Subslice
696 | ProjectionKind::Deref
697 | ProjectionKind::Field(..)),
699 "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
707 "we captured two identical projections: capture1 = {:?}, capture2 = {:?}",
714 "For closure={:?}, min_captures after sorting={:#?}",
715 closure_def_id, root_var_min_capture_list
717 typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
720 /// Perform the migration analysis for RFC 2229, and emit lint
721 /// `disjoint_capture_drop_reorder` if needed.
722 fn perform_2229_migration_anaysis(
724 closure_def_id: DefId,
725 body_id: hir::BodyId,
726 capture_clause: hir::CaptureBy,
729 let (need_migrations, reasons) = self.compute_2229_migrations(
733 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
736 if !need_migrations.is_empty() {
737 let (migration_string, migrated_variables_concat) =
738 migration_suggestion_for_2229(self.tcx, &need_migrations);
740 let local_def_id = closure_def_id.expect_local();
741 let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(local_def_id);
742 let closure_span = self.tcx.hir().span(closure_hir_id);
743 let closure_head_span = self.tcx.sess.source_map().guess_head_span(closure_span);
744 self.tcx.struct_span_lint_hir(
745 lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
749 let mut diagnostics_builder = lint.build(
750 &reasons.migration_message(),
752 for NeededMigration { var_hir_id, diagnostics_info } in &need_migrations {
753 // Labels all the usage of the captured variable and why they are responsible
754 // for migration being needed
755 for lint_note in diagnostics_info.iter() {
756 match &lint_note.captures_info {
757 UpvarMigrationInfo::CapturingPrecise { source_expr: Some(capture_expr_id), var_name: captured_name } => {
758 let cause_span = self.tcx.hir().span(*capture_expr_id);
759 diagnostics_builder.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
760 self.tcx.hir().name(*var_hir_id),
764 UpvarMigrationInfo::CapturingNothing { use_span } => {
765 diagnostics_builder.span_label(*use_span, format!("in Rust 2018, this causes the closure to capture `{}`, but in Rust 2021, it has no effect",
766 self.tcx.hir().name(*var_hir_id),
773 // Add a label pointing to where a captured variable affected by drop order
775 if lint_note.reason.drop_order {
776 let drop_location_span = drop_location_span(self.tcx, &closure_hir_id);
778 match &lint_note.captures_info {
779 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
780 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",
781 self.tcx.hir().name(*var_hir_id),
785 UpvarMigrationInfo::CapturingNothing { use_span: _ } => {
786 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",
787 v = self.tcx.hir().name(*var_hir_id),
793 // Add a label explaining why a closure no longer implements a trait
794 for &missing_trait in &lint_note.reason.auto_traits {
795 // not capturing something anymore cannot cause a trait to fail to be implemented:
796 match &lint_note.captures_info {
797 UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
798 let var_name = self.tcx.hir().name(*var_hir_id);
799 diagnostics_builder.span_label(closure_head_span, format!("\
800 in Rust 2018, this closure implements {missing_trait} \
801 as `{var_name}` implements {missing_trait}, but in Rust 2021, \
802 this closure will no longer implement {missing_trait} \
803 because `{var_name}` is not fully captured \
804 and `{captured_name}` does not implement {missing_trait}"));
807 // Cannot happen: if we don't capture a variable, we impl strictly more traits
808 UpvarMigrationInfo::CapturingNothing { use_span } => span_bug!(*use_span, "missing trait from not capturing something"),
813 diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
815 let diagnostic_msg = format!(
816 "add a dummy let to cause {} to be fully captured",
817 migrated_variables_concat
820 let mut closure_body_span = {
821 // If the body was entirely expanded from a macro
822 // invocation, i.e. the body is not contained inside the
823 // closure span, then we walk up the expansion until we
824 // find the span before the expansion.
825 let s = self.tcx.hir().span(body_id.hir_id);
826 s.find_ancestor_inside(closure_span).unwrap_or(s)
829 if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
830 if s.starts_with('$') {
831 // Looks like a macro fragment. Try to find the real block.
832 if let Some(hir::Node::Expr(&hir::Expr {
833 kind: hir::ExprKind::Block(block, ..), ..
834 })) = self.tcx.hir().find(body_id.hir_id) {
835 // If the body is a block (with `{..}`), we use the span of that block.
836 // E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
837 // Since we know it's a block, we know we can insert the `let _ = ..` without
838 // breaking the macro syntax.
839 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
840 closure_body_span = block.span;
846 let mut lines = s.lines();
847 let line1 = lines.next().unwrap_or_default();
849 if line1.trim_end() == "{" {
850 // This is a multi-line closure with just a `{` on the first line,
851 // so we put the `let` on its own line.
852 // We take the indentation from the next non-empty line.
853 let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
854 let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
855 diagnostics_builder.span_suggestion(
856 closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
858 format!("\n{}{};", indent, migration_string),
859 Applicability::MachineApplicable,
861 } else if line1.starts_with('{') {
862 // This is a closure with its body wrapped in
863 // braces, but with more than just the opening
864 // brace on the first line. We put the `let`
865 // directly after the `{`.
866 diagnostics_builder.span_suggestion(
867 closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
869 format!(" {};", migration_string),
870 Applicability::MachineApplicable,
873 // This is a closure without braces around the body.
874 // We add braces to add the `let` before the body.
875 diagnostics_builder.multipart_suggestion(
878 (closure_body_span.shrink_to_lo(), format!("{{ {}; ", migration_string)),
879 (closure_body_span.shrink_to_hi(), " }".to_string()),
881 Applicability::MachineApplicable
885 diagnostics_builder.span_suggestion(
889 Applicability::HasPlaceholders
893 diagnostics_builder.emit();
899 /// Combines all the reasons for 2229 migrations
900 fn compute_2229_migrations_reasons(
902 auto_trait_reasons: FxHashSet<&'static str>,
904 ) -> MigrationWarningReason {
905 let mut reasons = MigrationWarningReason::default();
907 reasons.auto_traits.extend(auto_trait_reasons);
908 reasons.drop_order = drop_order;
913 /// Figures out the list of root variables (and their types) that aren't completely
914 /// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
915 /// differ between the root variable and the captured paths.
917 /// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
918 /// if migration is needed for traits for the provided var_hir_id, otherwise returns None
919 fn compute_2229_migrations_for_trait(
921 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
922 var_hir_id: hir::HirId,
923 closure_clause: hir::CaptureBy,
924 ) -> Option<FxHashMap<UpvarMigrationInfo, FxHashSet<&'static str>>> {
925 let auto_traits_def_id = vec![
926 self.tcx.lang_items().clone_trait(),
927 self.tcx.lang_items().sync_trait(),
928 self.tcx.get_diagnostic_item(sym::Send),
929 self.tcx.lang_items().unpin_trait(),
930 self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
931 self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
933 const AUTO_TRAITS: [&str; 6] =
934 ["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
936 let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
938 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
940 let ty = match closure_clause {
941 hir::CaptureBy::Value => ty, // For move closure the capture kind should be by value
942 hir::CaptureBy::Ref => {
943 // For non move closure the capture kind is the max capture kind of all captures
944 // according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
945 let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
946 for capture in root_var_min_capture_list.iter() {
947 max_capture_info = determine_capture_info(max_capture_info, capture.info);
950 apply_capture_kind_on_capture_ty(self.tcx, ty, max_capture_info.capture_kind)
954 let mut obligations_should_hold = Vec::new();
955 // Checks if a root variable implements any of the auto traits
956 for check_trait in auto_traits_def_id.iter() {
957 obligations_should_hold.push(
961 .type_implements_trait(
964 self.tcx.mk_substs_trait(ty, &[]),
967 .must_apply_modulo_regions()
973 let mut problematic_captures = FxHashMap::default();
974 // Check whether captured fields also implement the trait
975 for capture in root_var_min_capture_list.iter() {
976 let ty = apply_capture_kind_on_capture_ty(
979 capture.info.capture_kind,
982 // Checks if a capture implements any of the auto traits
983 let mut obligations_holds_for_capture = Vec::new();
984 for check_trait in auto_traits_def_id.iter() {
985 obligations_holds_for_capture.push(
989 .type_implements_trait(
992 self.tcx.mk_substs_trait(ty, &[]),
995 .must_apply_modulo_regions()
1001 let mut capture_problems = FxHashSet::default();
1003 // Checks if for any of the auto traits, one or more trait is implemented
1004 // by the root variable but not by the capture
1005 for (idx, _) in obligations_should_hold.iter().enumerate() {
1006 if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
1007 capture_problems.insert(AUTO_TRAITS[idx]);
1011 if !capture_problems.is_empty() {
1012 problematic_captures.insert(
1013 UpvarMigrationInfo::CapturingPrecise {
1014 source_expr: capture.info.path_expr_id,
1015 var_name: capture.to_string(self.tcx),
1021 if !problematic_captures.is_empty() {
1022 return Some(problematic_captures);
1027 /// Figures out the list of root variables (and their types) that aren't completely
1028 /// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
1029 /// some path starting at that root variable **might** be affected.
1031 /// The output list would include a root variable if:
1032 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1033 /// enabled, **and**
1034 /// - It wasn't completely captured by the closure, **and**
1035 /// - One of the paths starting at this root variable, that is not captured needs Drop.
1037 /// This function only returns a HashSet of CapturesInfo for significant drops. If there
1038 /// are no significant drops than None is returned
1039 #[instrument(level = "debug", skip(self))]
1040 fn compute_2229_migrations_for_drop(
1042 closure_def_id: DefId,
1044 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1045 closure_clause: hir::CaptureBy,
1046 var_hir_id: hir::HirId,
1047 ) -> Option<FxHashSet<UpvarMigrationInfo>> {
1048 let ty = self.infcx.resolve_vars_if_possible(self.node_ty(var_hir_id));
1050 if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local())) {
1051 debug!("does not have significant drop");
1055 let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
1056 // The upvar is mentioned within the closure but no path starting from it is
1057 // used. This occurs when you have (e.g.)
1060 // let x = move || {
1064 debug!("no path starting from it is used");
1067 match closure_clause {
1068 // Only migrate if closure is a move closure
1069 hir::CaptureBy::Value => {
1070 let mut diagnostics_info = FxHashSet::default();
1071 let upvars = self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
1072 let upvar = upvars[&var_hir_id];
1073 diagnostics_info.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
1074 return Some(diagnostics_info);
1076 hir::CaptureBy::Ref => {}
1081 debug!(?root_var_min_capture_list);
1083 let mut projections_list = Vec::new();
1084 let mut diagnostics_info = FxHashSet::default();
1086 for captured_place in root_var_min_capture_list.iter() {
1087 match captured_place.info.capture_kind {
1088 // Only care about captures that are moved into the closure
1089 ty::UpvarCapture::ByValue(..) => {
1090 projections_list.push(captured_place.place.projections.as_slice());
1091 diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
1092 source_expr: captured_place.info.path_expr_id,
1093 var_name: captured_place.to_string(self.tcx),
1096 ty::UpvarCapture::ByRef(..) => {}
1100 debug!(?projections_list);
1101 debug!(?diagnostics_info);
1103 let is_moved = !projections_list.is_empty();
1106 let is_not_completely_captured =
1107 root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
1108 debug!(?is_not_completely_captured);
1111 && is_not_completely_captured
1112 && self.has_significant_drop_outside_of_captures(
1119 return Some(diagnostics_info);
1125 /// Figures out the list of root variables (and their types) that aren't completely
1126 /// captured by the closure when `capture_disjoint_fields` is enabled and either drop
1127 /// order of some path starting at that root variable **might** be affected or auto-traits
1128 /// differ between the root variable and the captured paths.
1130 /// The output list would include a root variable if:
1131 /// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
1132 /// enabled, **and**
1133 /// - It wasn't completely captured by the closure, **and**
1134 /// - One of the paths starting at this root variable, that is not captured needs Drop **or**
1135 /// - One of the paths captured does not implement all the auto-traits its root variable
1138 /// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
1139 /// containing the reason why root variables whose HirId is contained in the vector should
1141 #[instrument(level = "debug", skip(self))]
1142 fn compute_2229_migrations(
1144 closure_def_id: DefId,
1146 closure_clause: hir::CaptureBy,
1147 min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
1148 ) -> (Vec<NeededMigration>, MigrationWarningReason) {
1149 let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
1150 return (Vec::new(), MigrationWarningReason::default());
1153 let mut need_migrations = Vec::new();
1154 let mut auto_trait_migration_reasons = FxHashSet::default();
1155 let mut drop_migration_needed = false;
1157 // Perform auto-trait analysis
1158 for (&var_hir_id, _) in upvars.iter() {
1159 let mut diagnostics_info = Vec::new();
1161 let auto_trait_diagnostic = if let Some(diagnostics_info) =
1162 self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
1166 FxHashMap::default()
1169 let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
1170 .compute_2229_migrations_for_drop(
1177 drop_migration_needed = true;
1180 FxHashSet::default()
1183 // Combine all the captures responsible for needing migrations into one HashSet
1184 let mut capture_diagnostic = drop_reorder_diagnostic.clone();
1185 for key in auto_trait_diagnostic.keys() {
1186 capture_diagnostic.insert(key.clone());
1189 let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
1190 capture_diagnostic.sort();
1191 for captures_info in capture_diagnostic {
1192 // Get the auto trait reasons of why migration is needed because of that capture, if there are any
1193 let capture_trait_reasons =
1194 if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
1197 FxHashSet::default()
1200 // Check if migration is needed because of drop reorder as a result of that capture
1201 let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
1203 // Combine all the reasons of why the root variable should be captured as a result of
1204 // auto trait implementation issues
1205 auto_trait_migration_reasons.extend(capture_trait_reasons.clone());
1207 diagnostics_info.push(MigrationLintNote {
1209 reason: self.compute_2229_migrations_reasons(
1210 capture_trait_reasons,
1211 capture_drop_reorder_reason,
1216 if !diagnostics_info.is_empty() {
1217 need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
1222 self.compute_2229_migrations_reasons(
1223 auto_trait_migration_reasons,
1224 drop_migration_needed,
1229 /// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
1230 /// of a root variable and a list of captured paths starting at this root variable (expressed
1231 /// using list of `Projection` slices), it returns true if there is a path that is not
1232 /// captured starting at this root variable that implements Drop.
1234 /// The way this function works is at a given call it looks at type `base_path_ty` of some base
1235 /// path say P and then list of projection slices which represent the different captures moved
1236 /// into the closure starting off of P.
1238 /// This will make more sense with an example:
1241 /// #![feature(capture_disjoint_fields)]
1243 /// struct FancyInteger(i32); // This implements Drop
1245 /// struct Point { x: FancyInteger, y: FancyInteger }
1248 /// struct Wrapper { p: Point, c: Color }
1250 /// fn f(w: Wrapper) {
1252 /// // Closure captures w.p.x and w.c by move.
1259 /// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
1260 /// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
1261 /// therefore Drop ordering would change and we want this function to return true.
1263 /// Call stack to figure out if we need to migrate for `w` would look as follows:
1265 /// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
1268 /// - Ty(place): Type of place
1269 /// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
1272 /// (Ty(w), [ &[p, x], &[c] ])
1274 /// ----------------------------
1277 /// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
1280 /// (Ty(w.p), [ &[x] ]) false
1283 /// -------------------------------
1286 /// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
1289 /// false NeedsSignificantDrop(Ty(w.p.y))
1295 /// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
1296 /// This implies that the `w.c` is completely captured by the closure.
1297 /// Since drop for this path will be called when the closure is
1298 /// dropped we don't need to migrate for it.
1300 /// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
1301 /// path wasn't captured by the closure. Also note that even
1302 /// though we didn't capture this path, the function visits it,
1303 /// which is kind of the point of this function. We then return
1304 /// if the type of `w.p.y` implements Drop, which in this case is
1307 /// Consider another example:
1311 /// impl Drop for X {}
1314 /// impl Drop for Y {}
1318 /// let c = || move(y.0);
1322 /// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
1323 /// return true, because even though all paths starting at `y` are captured, `y` itself
1324 /// implements Drop which will be affected since `y` isn't completely captured.
1325 fn has_significant_drop_outside_of_captures(
1327 closure_def_id: DefId,
1329 base_path_ty: Ty<'tcx>,
1330 captured_by_move_projs: Vec<&[Projection<'tcx>]>,
1332 let needs_drop = |ty: Ty<'tcx>| {
1333 ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id.expect_local()))
1336 let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
1337 let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
1338 let ty_params = self.tcx.mk_substs_trait(base_path_ty, &[]);
1340 .type_implements_trait(
1344 self.tcx.param_env(closure_def_id.expect_local()),
1346 .must_apply_modulo_regions()
1349 let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
1351 // If there is a case where no projection is applied on top of current place
1352 // then there must be exactly one capture corresponding to such a case. Note that this
1353 // represents the case of the path being completely captured by the variable.
1355 // eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
1356 // capture `a.b.c`, because that voilates min capture.
1357 let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
1359 assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
1361 if is_completely_captured {
1362 // The place is captured entirely, so doesn't matter if needs dtor, it will be drop
1363 // when the closure is dropped.
1367 if captured_by_move_projs.is_empty() {
1368 return needs_drop(base_path_ty);
1371 if is_drop_defined_for_ty {
1372 // If drop is implemented for this type then we need it to be fully captured,
1373 // and we know it is not completely captured because of the previous checks.
1375 // Note that this is a bug in the user code that will be reported by the
1376 // borrow checker, since we can't move out of drop types.
1378 // The bug exists in the user's code pre-migration, and we don't migrate here.
1382 match base_path_ty.kind() {
1384 // - `captured_by_move_projs` is not empty. Therefore we can call
1385 // `captured_by_move_projs.first().unwrap()` safely.
1386 // - All entries in `captured_by_move_projs` have atleast one projection.
1387 // Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
1389 // We don't capture derefs in case of move captures, which would have be applied to
1390 // access any further paths.
1391 ty::Adt(def, _) if def.is_box() => unreachable!(),
1392 ty::Ref(..) => unreachable!(),
1393 ty::RawPtr(..) => unreachable!(),
1395 ty::Adt(def, substs) => {
1396 // Multi-varaint enums are captured in entirety,
1397 // which would've been handled in the case of single empty slice in `captured_by_move_projs`.
1398 assert_eq!(def.variants.len(), 1);
1400 // Only Field projections can be applied to a non-box Adt.
1402 captured_by_move_projs.iter().all(|projs| matches!(
1403 projs.first().unwrap().kind,
1404 ProjectionKind::Field(..)
1407 def.variants.get(VariantIdx::new(0)).unwrap().fields.iter().enumerate().any(
1409 let paths_using_field = captured_by_move_projs
1411 .filter_map(|projs| {
1412 if let ProjectionKind::Field(field_idx, _) =
1413 projs.first().unwrap().kind
1415 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1422 let after_field_ty = field.ty(self.tcx, substs);
1423 self.has_significant_drop_outside_of_captures(
1434 // Only Field projections can be applied to a tuple.
1436 captured_by_move_projs.iter().all(|projs| matches!(
1437 projs.first().unwrap().kind,
1438 ProjectionKind::Field(..)
1442 base_path_ty.tuple_fields().enumerate().any(|(i, element_ty)| {
1443 let paths_using_field = captured_by_move_projs
1445 .filter_map(|projs| {
1446 if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
1448 if (field_idx as usize) == i { Some(&projs[1..]) } else { None }
1455 self.has_significant_drop_outside_of_captures(
1464 // Anything else would be completely captured and therefore handled already.
1465 _ => unreachable!(),
1469 fn init_capture_kind_for_place(
1471 place: &Place<'tcx>,
1472 capture_clause: hir::CaptureBy,
1473 upvar_id: ty::UpvarId,
1475 ) -> ty::UpvarCapture<'tcx> {
1476 match capture_clause {
1477 // In case of a move closure if the data is accessed through a reference we
1478 // want to capture by ref to allow precise capture using reborrows.
1480 // If the data will be moved out of this place, then the place will be truncated
1481 // at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
1483 hir::CaptureBy::Value if !place.deref_tys().any(ty::TyS::is_ref) => {
1484 ty::UpvarCapture::ByValue(None)
1486 hir::CaptureBy::Value | hir::CaptureBy::Ref => {
1487 let origin = UpvarRegion(upvar_id, closure_span);
1488 let upvar_region = self.next_region_var(origin);
1489 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
1490 ty::UpvarCapture::ByRef(upvar_borrow)
1495 fn place_for_root_variable(
1497 closure_def_id: LocalDefId,
1498 var_hir_id: hir::HirId,
1500 let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
1503 base_ty: self.node_ty(var_hir_id),
1504 base: PlaceBase::Upvar(upvar_id),
1505 projections: Default::default(),
1509 fn should_log_capture_analysis(&self, closure_def_id: DefId) -> bool {
1510 self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
1513 fn log_capture_analysis_first_pass(
1515 closure_def_id: rustc_hir::def_id::DefId,
1516 capture_information: &FxIndexMap<Place<'tcx>, ty::CaptureInfo<'tcx>>,
1519 if self.should_log_capture_analysis(closure_def_id) {
1521 self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
1522 for (place, capture_info) in capture_information {
1523 let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
1524 let output_str = format!("Capturing {}", capture_str);
1527 capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
1528 diag.span_note(span, &output_str);
1534 fn log_closure_min_capture_info(&self, closure_def_id: DefId, closure_span: Span) {
1535 if self.should_log_capture_analysis(closure_def_id) {
1536 if let Some(min_captures) =
1537 self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
1540 self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
1542 for (_, min_captures_for_var) in min_captures {
1543 for capture in min_captures_for_var {
1544 let place = &capture.place;
1545 let capture_info = &capture.info;
1548 construct_capture_info_string(self.tcx, place, capture_info);
1549 let output_str = format!("Min Capture {}", capture_str);
1551 if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
1552 let path_span = capture_info
1554 .map_or(closure_span, |e| self.tcx.hir().span(e));
1555 let capture_kind_span = capture_info
1556 .capture_kind_expr_id
1557 .map_or(closure_span, |e| self.tcx.hir().span(e));
1559 let mut multi_span: MultiSpan =
1560 MultiSpan::from_spans(vec![path_span, capture_kind_span]);
1562 let capture_kind_label =
1563 construct_capture_kind_reason_string(self.tcx, place, capture_info);
1564 let path_label = construct_path_string(self.tcx, place);
1566 multi_span.push_span_label(path_span, path_label);
1567 multi_span.push_span_label(capture_kind_span, capture_kind_label);
1569 diag.span_note(multi_span, &output_str);
1571 let span = capture_info
1573 .map_or(closure_span, |e| self.tcx.hir().span(e));
1575 diag.span_note(span, &output_str);
1584 /// A captured place is mutable if
1585 /// 1. Projections don't include a Deref of an immut-borrow, **and**
1586 /// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
1587 fn determine_capture_mutability(
1589 typeck_results: &'a TypeckResults<'tcx>,
1590 place: &Place<'tcx>,
1591 ) -> hir::Mutability {
1592 let var_hir_id = match place.base {
1593 PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
1594 _ => unreachable!(),
1597 let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
1599 let mut is_mutbl = match bm {
1600 ty::BindByValue(mutability) => mutability,
1601 ty::BindByReference(_) => hir::Mutability::Not,
1604 for pointer_ty in place.deref_tys() {
1605 match pointer_ty.kind() {
1606 // We don't capture derefs of raw ptrs
1607 ty::RawPtr(_) => unreachable!(),
1609 // Derefencing a mut-ref allows us to mut the Place if we don't deref
1610 // an immut-ref after on top of this.
1611 ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
1613 // The place isn't mutable once we dereference an immutable reference.
1614 ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
1616 // Dereferencing a box doesn't change mutability
1617 ty::Adt(def, ..) if def.is_box() => {}
1619 unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
1627 /// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
1628 /// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
1629 fn restrict_repr_packed_field_ref_capture<'tcx>(
1631 param_env: ty::ParamEnv<'tcx>,
1632 place: &Place<'tcx>,
1633 mut curr_borrow_kind: ty::UpvarCapture<'tcx>,
1634 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1635 let pos = place.projections.iter().enumerate().position(|(i, p)| {
1636 let ty = place.ty_before_projection(i);
1638 // Return true for fields of packed structs, unless those fields have alignment 1.
1640 ProjectionKind::Field(..) => match ty.kind() {
1641 ty::Adt(def, _) if def.repr.packed() => {
1642 match tcx.layout_of(param_env.and(p.ty)) {
1643 Ok(layout) if layout.align.abi.bytes() == 1 => {
1644 // if the alignment is 1, the type can't be further
1647 "restrict_repr_packed_field_ref_capture: ({:?}) - align = 1",
1653 debug!("restrict_repr_packed_field_ref_capture: ({:?}) - true", place);
1665 let mut place = place.clone();
1667 if let Some(pos) = pos {
1668 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
1671 (place, curr_borrow_kind)
1674 /// Returns a Ty that applies the specified capture kind on the provided capture Ty
1675 fn apply_capture_kind_on_capture_ty<'tcx>(
1678 capture_kind: UpvarCapture<'tcx>,
1680 match capture_kind {
1681 ty::UpvarCapture::ByValue(_) => ty,
1682 ty::UpvarCapture::ByRef(borrow) => tcx
1683 .mk_ref(borrow.region, ty::TypeAndMut { ty: ty, mutbl: borrow.kind.to_mutbl_lossy() }),
1687 /// Returns the Span of where the value with the provided HirId would be dropped
1688 fn drop_location_span<'tcx>(tcx: TyCtxt<'tcx>, hir_id: &hir::HirId) -> Span {
1689 let owner_id = tcx.hir().get_enclosing_scope(*hir_id).unwrap();
1691 let owner_node = tcx.hir().get(owner_id);
1692 let owner_span = match owner_node {
1693 hir::Node::Item(item) => match item.kind {
1694 hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
1696 bug!("Drop location span error: need to handle more ItemKind {:?}", item.kind);
1699 hir::Node::Block(block) => tcx.hir().span(block.hir_id),
1701 bug!("Drop location span error: need to handle more Node {:?}", owner_node);
1704 tcx.sess.source_map().end_point(owner_span)
1707 struct InferBorrowKind<'a, 'tcx> {
1708 fcx: &'a FnCtxt<'a, 'tcx>,
1710 // The def-id of the closure whose kind and upvar accesses are being inferred.
1711 closure_def_id: DefId,
1715 /// For each Place that is captured by the closure, we track the minimal kind of
1716 /// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
1718 /// Consider closure where s.str1 is captured via an ImmutableBorrow and
1719 /// s.str2 via a MutableBorrow
1722 /// struct SomeStruct { str1: String, str2: String }
1724 /// // Assume that the HirId for the variable definition is `V1`
1725 /// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") }
1727 /// let fix_s = |new_s2| {
1728 /// // Assume that the HirId for the expression `s.str1` is `E1`
1729 /// println!("Updating SomeStruct with str1=", s.str1);
1730 /// // Assume that the HirId for the expression `*s.str2` is `E2`
1731 /// s.str2 = new_s2;
1735 /// For closure `fix_s`, (at a high level) the map contains
1738 /// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
1739 /// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
1741 capture_information: InferredCaptureInformation<'tcx>,
1742 fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
1745 impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
1746 #[instrument(skip(self), level = "debug")]
1747 fn adjust_upvar_borrow_kind_for_consume(
1749 place_with_id: &PlaceWithHirId<'tcx>,
1750 diag_expr_id: hir::HirId,
1752 let tcx = self.fcx.tcx;
1753 let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else {
1759 let usage_span = tcx.hir().span(diag_expr_id);
1761 let capture_info = ty::CaptureInfo {
1762 capture_kind_expr_id: Some(diag_expr_id),
1763 path_expr_id: Some(diag_expr_id),
1764 capture_kind: ty::UpvarCapture::ByValue(Some(usage_span)),
1767 let curr_info = self.capture_information[&place_with_id.place];
1768 let updated_info = determine_capture_info(curr_info, capture_info);
1770 self.capture_information[&place_with_id.place] = updated_info;
1773 /// Indicates that `place_with_id` is being directly mutated (e.g., assigned
1774 /// to). If the place is based on a by-ref upvar, this implies that
1775 /// the upvar must be borrowed using an `&mut` borrow.
1776 #[instrument(skip(self), level = "debug")]
1777 fn adjust_upvar_borrow_kind_for_mut(
1779 place_with_id: &PlaceWithHirId<'tcx>,
1780 diag_expr_id: hir::HirId,
1782 if let PlaceBase::Upvar(_) = place_with_id.place.base {
1783 // Raw pointers don't inherit mutability
1784 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1787 self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::MutBorrow);
1791 #[instrument(skip(self), level = "debug")]
1792 fn adjust_upvar_borrow_kind_for_unique(
1794 place_with_id: &PlaceWithHirId<'tcx>,
1795 diag_expr_id: hir::HirId,
1797 if let PlaceBase::Upvar(_) = place_with_id.place.base {
1798 if place_with_id.place.deref_tys().any(ty::TyS::is_unsafe_ptr) {
1799 // Raw pointers don't inherit mutability.
1802 // for a borrowed pointer to be unique, its base must be unique
1803 self.adjust_upvar_deref(place_with_id, diag_expr_id, ty::UniqueImmBorrow);
1807 fn adjust_upvar_deref(
1809 place_with_id: &PlaceWithHirId<'tcx>,
1810 diag_expr_id: hir::HirId,
1811 borrow_kind: ty::BorrowKind,
1813 assert!(match borrow_kind {
1814 ty::MutBorrow => true,
1815 ty::UniqueImmBorrow => true,
1817 // imm borrows never require adjusting any kinds, so we don't wind up here
1818 ty::ImmBorrow => false,
1821 // if this is an implicit deref of an
1822 // upvar, then we need to modify the
1823 // borrow_kind of the upvar to make sure it
1824 // is inferred to mutable if necessary
1825 self.adjust_upvar_borrow_kind(place_with_id, diag_expr_id, borrow_kind);
1828 /// We infer the borrow_kind with which to borrow upvars in a stack closure.
1829 /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
1830 /// moving from left to right as needed (but never right to left).
1831 /// Here the argument `mutbl` is the borrow_kind that is required by
1832 /// some particular use.
1833 #[instrument(skip(self), level = "debug")]
1834 fn adjust_upvar_borrow_kind(
1836 place_with_id: &PlaceWithHirId<'tcx>,
1837 diag_expr_id: hir::HirId,
1838 kind: ty::BorrowKind,
1840 let curr_capture_info = self.capture_information[&place_with_id.place];
1842 debug!(?curr_capture_info);
1844 if let ty::UpvarCapture::ByValue(_) = curr_capture_info.capture_kind {
1845 // It's already captured by value, we don't need to do anything here
1847 } else if let ty::UpvarCapture::ByRef(curr_upvar_borrow) = curr_capture_info.capture_kind {
1848 // Use the same region as the current capture information
1849 // Doesn't matter since only one of the UpvarBorrow will be used.
1850 let new_upvar_borrow = ty::UpvarBorrow { kind, region: curr_upvar_borrow.region };
1852 let capture_info = ty::CaptureInfo {
1853 capture_kind_expr_id: Some(diag_expr_id),
1854 path_expr_id: Some(diag_expr_id),
1855 capture_kind: ty::UpvarCapture::ByRef(new_upvar_borrow),
1857 let updated_info = determine_capture_info(curr_capture_info, capture_info);
1858 self.capture_information[&place_with_id.place] = updated_info;
1862 #[instrument(skip(self, diag_expr_id), level = "debug")]
1863 fn init_capture_info_for_place(
1865 place_with_id: &PlaceWithHirId<'tcx>,
1866 diag_expr_id: hir::HirId,
1868 if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
1869 assert_eq!(self.closure_def_id.expect_local(), upvar_id.closure_expr_id);
1871 // Initialize to ImmBorrow
1872 // We will escalate the CaptureKind based on any uses we see or in `process_collected_capture_information`.
1873 let origin = UpvarRegion(upvar_id, self.closure_span);
1874 let upvar_region = self.fcx.next_region_var(origin);
1875 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region };
1876 let capture_kind = ty::UpvarCapture::ByRef(upvar_borrow);
1878 let expr_id = Some(diag_expr_id);
1879 let capture_info = ty::CaptureInfo {
1880 capture_kind_expr_id: expr_id,
1881 path_expr_id: expr_id,
1885 debug!("Capturing new place {:?}, capture_info={:?}", place_with_id, capture_info);
1887 self.capture_information.insert(place_with_id.place.clone(), capture_info);
1889 debug!("Not upvar");
1894 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
1895 fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId) {
1896 if let PlaceBase::Upvar(_) = place.base {
1897 // We need to restrict Fake Read precision to avoid fake reading unsafe code,
1898 // such as deref of a raw pointer.
1899 let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::UpvarBorrow {
1900 kind: ty::BorrowKind::ImmBorrow,
1901 region: &ty::ReErased,
1904 let (place, _) = restrict_capture_precision(place, dummy_capture_kind);
1906 let (place, _) = restrict_repr_packed_field_ref_capture(
1912 self.fake_reads.push((place, cause, diag_expr_id));
1916 #[instrument(skip(self), level = "debug")]
1917 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1918 if !self.capture_information.contains_key(&place_with_id.place) {
1919 self.init_capture_info_for_place(place_with_id, diag_expr_id);
1922 self.adjust_upvar_borrow_kind_for_consume(place_with_id, diag_expr_id);
1925 #[instrument(skip(self), level = "debug")]
1928 place_with_id: &PlaceWithHirId<'tcx>,
1929 diag_expr_id: hir::HirId,
1932 // The region here will get discarded/ignored
1933 let dummy_capture_kind =
1934 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind: bk, region: &ty::ReErased });
1936 // We only want repr packed restriction to be applied to reading references into a packed
1937 // struct, and not when the data is being moved. Therefore we call this method here instead
1938 // of in `restrict_capture_precision`.
1939 let (place, updated_kind) = restrict_repr_packed_field_ref_capture(
1942 &place_with_id.place,
1946 let place_with_id = PlaceWithHirId { place, ..*place_with_id };
1948 if !self.capture_information.contains_key(&place_with_id.place) {
1949 self.init_capture_info_for_place(&place_with_id, diag_expr_id);
1952 match updated_kind {
1953 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind, .. }) => match kind {
1955 ty::UniqueImmBorrow => {
1956 self.adjust_upvar_borrow_kind_for_unique(&place_with_id, diag_expr_id);
1959 self.adjust_upvar_borrow_kind_for_mut(&place_with_id, diag_expr_id);
1963 // Just truncating the place will never cause capture kind to be updated to ByValue
1964 ty::UpvarCapture::ByValue(..) => unreachable!(),
1968 #[instrument(skip(self), level = "debug")]
1969 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
1970 self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
1974 /// Rust doesn't permit moving fields out of a type that implements drop
1975 fn restrict_precision_for_drop_types<'a, 'tcx>(
1976 fcx: &'a FnCtxt<'a, 'tcx>,
1977 mut place: Place<'tcx>,
1978 mut curr_mode: ty::UpvarCapture<'tcx>,
1980 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
1981 let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty(), span);
1983 if let (false, UpvarCapture::ByValue(..)) = (is_copy_type, curr_mode) {
1984 for i in 0..place.projections.len() {
1985 match place.ty_before_projection(i).kind() {
1986 ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
1987 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
1998 /// Truncate `place` so that an `unsafe` block isn't required to capture it.
1999 /// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
2000 /// them completely.
2001 /// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
2002 fn restrict_precision_for_unsafe<'tcx>(
2003 mut place: Place<'tcx>,
2004 mut curr_mode: ty::UpvarCapture<'tcx>,
2005 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2006 if place.base_ty.is_unsafe_ptr() {
2007 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
2010 if place.base_ty.is_union() {
2011 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
2014 for (i, proj) in place.projections.iter().enumerate() {
2015 if proj.ty.is_unsafe_ptr() {
2016 // Don't apply any projections on top of an unsafe ptr.
2017 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
2021 if proj.ty.is_union() {
2022 // Don't capture preicse fields of a union.
2023 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
2031 /// Truncate projections so that following rules are obeyed by the captured `place`:
2032 /// - No Index projections are captured, since arrays are captured completely.
2033 /// - No unsafe block is required to capture `place`
2034 /// Returns the truncated place and updated cature mode.
2035 fn restrict_capture_precision<'tcx>(
2037 curr_mode: ty::UpvarCapture<'tcx>,
2038 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2039 let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
2041 if place.projections.is_empty() {
2042 // Nothing to do here
2043 return (place, curr_mode);
2046 for (i, proj) in place.projections.iter().enumerate() {
2048 ProjectionKind::Index => {
2049 // Arrays are completely captured, so we drop Index projections
2050 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
2051 return (place, curr_mode);
2053 ProjectionKind::Deref => {}
2054 ProjectionKind::Field(..) => {} // ignore
2055 ProjectionKind::Subslice => {} // We never capture this
2062 /// Truncate deref of any reference.
2063 fn adjust_for_move_closure<'tcx>(
2064 mut place: Place<'tcx>,
2065 mut kind: ty::UpvarCapture<'tcx>,
2066 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2067 let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
2069 if let Some(idx) = first_deref {
2070 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
2073 // AMAN: I think we don't need the span inside the ByValue anymore
2074 // we have more detailed span in CaptureInfo
2075 (place, ty::UpvarCapture::ByValue(None))
2078 /// Adjust closure capture just that if taking ownership of data, only move data
2079 /// from enclosing stack frame.
2080 fn adjust_for_non_move_closure<'tcx>(
2081 mut place: Place<'tcx>,
2082 mut kind: ty::UpvarCapture<'tcx>,
2083 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2084 let contains_deref =
2085 place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
2088 ty::UpvarCapture::ByValue(..) => {
2089 if let Some(idx) = contains_deref {
2090 truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
2094 ty::UpvarCapture::ByRef(..) => {}
2100 fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2101 let variable_name = match place.base {
2102 PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
2103 _ => bug!("Capture_information should only contain upvars"),
2106 let mut projections_str = String::new();
2107 for (i, item) in place.projections.iter().enumerate() {
2108 let proj = match item.kind {
2109 ProjectionKind::Field(a, b) => format!("({:?}, {:?})", a, b),
2110 ProjectionKind::Deref => String::from("Deref"),
2111 ProjectionKind::Index => String::from("Index"),
2112 ProjectionKind::Subslice => String::from("Subslice"),
2115 projections_str.push(',');
2117 projections_str.push_str(proj.as_str());
2120 format!("{}[{}]", variable_name, projections_str)
2123 fn construct_capture_kind_reason_string<'tcx>(
2125 place: &Place<'tcx>,
2126 capture_info: &ty::CaptureInfo<'tcx>,
2128 let place_str = construct_place_string(tcx, place);
2130 let capture_kind_str = match capture_info.capture_kind {
2131 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
2132 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
2135 format!("{} captured as {} here", place_str, capture_kind_str)
2138 fn construct_path_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
2139 let place_str = construct_place_string(tcx, place);
2141 format!("{} used here", place_str)
2144 fn construct_capture_info_string<'tcx>(
2146 place: &Place<'tcx>,
2147 capture_info: &ty::CaptureInfo<'tcx>,
2149 let place_str = construct_place_string(tcx, place);
2151 let capture_kind_str = match capture_info.capture_kind {
2152 ty::UpvarCapture::ByValue(_) => "ByValue".into(),
2153 ty::UpvarCapture::ByRef(borrow) => format!("{:?}", borrow.kind),
2155 format!("{} -> {}", place_str, capture_kind_str)
2158 fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
2159 tcx.hir().name(var_hir_id)
2162 #[instrument(level = "debug", skip(tcx))]
2163 fn should_do_rust_2021_incompatible_closure_captures_analysis(
2165 closure_id: hir::HirId,
2168 tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
2170 !matches!(level, lint::Level::Allow)
2173 /// Return a two string tuple (s1, s2)
2174 /// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
2175 /// - s2: Comma separated names of the variables being migrated.
2176 fn migration_suggestion_for_2229(
2178 need_migrations: &Vec<NeededMigration>,
2179 ) -> (String, String) {
2180 let need_migrations_variables = need_migrations
2182 .map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
2183 .collect::<Vec<_>>();
2185 let migration_ref_concat =
2186 need_migrations_variables.iter().map(|v| format!("&{}", v)).collect::<Vec<_>>().join(", ");
2188 let migration_string = if 1 == need_migrations.len() {
2189 format!("let _ = {}", migration_ref_concat)
2191 format!("let _ = ({})", migration_ref_concat)
2194 let migrated_variables_concat =
2195 need_migrations_variables.iter().map(|v| format!("`{}`", v)).collect::<Vec<_>>().join(", ");
2197 (migration_string, migrated_variables_concat)
2200 /// Helper function to determine if we need to escalate CaptureKind from
2201 /// CaptureInfo A to B and returns the escalated CaptureInfo.
2202 /// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
2204 /// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
2205 /// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
2207 /// It is the caller's duty to figure out which path_expr_id to use.
2209 /// If both the CaptureKind and Expression are considered to be equivalent,
2210 /// then `CaptureInfo` A is preferred. This can be useful in cases where we want to priortize
2211 /// expressions reported back to the user as part of diagnostics based on which appears earlier
2212 /// in the closure. This can be achieved simply by calling
2213 /// `determine_capture_info(existing_info, current_info)`. This works out because the
2214 /// expressions that occur earlier in the closure body than the current expression are processed before.
2215 /// Consider the following example
2217 /// struct Point { x: i32, y: i32 }
2218 /// let mut p: Point { x: 10, y: 10 };
2226 /// p.x += 10; // E2
2230 /// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
2231 /// and both have an expression associated, however for diagnostics we prefer reporting
2232 /// `E1` since it appears earlier in the closure body. When `E2` is being processed we
2233 /// would've already handled `E1`, and have an existing capture_information for it.
2234 /// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
2235 /// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
2236 fn determine_capture_info<'tcx>(
2237 capture_info_a: ty::CaptureInfo<'tcx>,
2238 capture_info_b: ty::CaptureInfo<'tcx>,
2239 ) -> ty::CaptureInfo<'tcx> {
2240 // If the capture kind is equivalent then, we don't need to escalate and can compare the
2242 let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2243 (ty::UpvarCapture::ByValue(_), ty::UpvarCapture::ByValue(_)) => {
2244 // We don't need to worry about the spans being ignored here.
2246 // The expr_id in capture_info corresponds to the span that is stored within
2247 // ByValue(span) and therefore it gets handled with priortizing based on
2248 // expressions below.
2251 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2252 ref_a.kind == ref_b.kind
2254 (ty::UpvarCapture::ByValue(_), _) | (ty::UpvarCapture::ByRef(_), _) => false,
2257 if eq_capture_kind {
2258 match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
2259 (Some(_), _) | (None, None) => capture_info_a,
2260 (None, Some(_)) => capture_info_b,
2263 // We select the CaptureKind which ranks higher based the following priority order:
2264 // ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
2265 match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
2266 (ty::UpvarCapture::ByValue(_), _) => capture_info_a,
2267 (_, ty::UpvarCapture::ByValue(_)) => capture_info_b,
2268 (ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
2269 match (ref_a.kind, ref_b.kind) {
2271 (ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
2272 | (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
2275 (ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
2276 | (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
2278 (ty::ImmBorrow, ty::ImmBorrow)
2279 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
2280 | (ty::MutBorrow, ty::MutBorrow) => {
2281 bug!("Expected unequal capture kinds");
2289 /// Truncates `place` to have up to `len` projections.
2290 /// `curr_mode` is the current required capture kind for the place.
2291 /// Returns the truncated `place` and the updated required capture kind.
2293 /// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
2294 /// contained `Deref` of `&mut`.
2295 fn truncate_place_to_len_and_update_capture_kind<'tcx>(
2296 place: &mut Place<'tcx>,
2297 curr_mode: &mut ty::UpvarCapture<'tcx>,
2300 let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
2302 // If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
2304 // Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
2305 // we don't need to worry about that case here.
2307 ty::UpvarCapture::ByRef(ty::UpvarBorrow { kind: ty::BorrowKind::MutBorrow, region }) => {
2308 for i in len..place.projections.len() {
2309 if place.projections[i].kind == ProjectionKind::Deref
2310 && is_mut_ref(place.ty_before_projection(i))
2312 *curr_mode = ty::UpvarCapture::ByRef(ty::UpvarBorrow {
2313 kind: ty::BorrowKind::UniqueImmBorrow,
2321 ty::UpvarCapture::ByRef(..) => {}
2322 ty::UpvarCapture::ByValue(..) => {}
2325 place.projections.truncate(len);
2328 /// Determines the Ancestry relationship of Place A relative to Place B
2330 /// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
2331 /// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
2332 /// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
2333 fn determine_place_ancestry_relation<'tcx>(
2334 place_a: &Place<'tcx>,
2335 place_b: &Place<'tcx>,
2336 ) -> PlaceAncestryRelation {
2337 // If Place A and Place B, don't start off from the same root variable, they are divergent.
2338 if place_a.base != place_b.base {
2339 return PlaceAncestryRelation::Divergent;
2342 // Assume of length of projections_a = n
2343 let projections_a = &place_a.projections;
2345 // Assume of length of projections_b = m
2346 let projections_b = &place_b.projections;
2348 let same_initial_projections =
2349 iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
2351 if same_initial_projections {
2352 use std::cmp::Ordering;
2354 // First min(n, m) projections are the same
2355 // Select Ancestor/Descendant
2356 match projections_b.len().cmp(&projections_a.len()) {
2357 Ordering::Greater => PlaceAncestryRelation::Ancestor,
2358 Ordering::Equal => PlaceAncestryRelation::SamePlace,
2359 Ordering::Less => PlaceAncestryRelation::Descendant,
2362 PlaceAncestryRelation::Divergent
2366 /// Reduces the precision of the captured place when the precision doesn't yeild any benefit from
2367 /// borrow checking prespective, allowing us to save us on the size of the capture.
2370 /// Fields that are read through a shared reference will always be read via a shared ref or a copy,
2371 /// and therefore capturing precise paths yields no benefit. This optimization truncates the
2372 /// rightmost deref of the capture if the deref is applied to a shared ref.
2374 /// Reason we only drop the last deref is because of the following edge case:
2377 /// struct MyStruct<'a> {
2383 /// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
2384 /// let c = || drop(&*m.a.field_of_a);
2385 /// // Here we really do want to capture `*m.a` because that outlives `'static`
2387 /// // If we capture `m`, then the closure no longer outlives `'static'
2388 /// // it is constrained to `'a`
2391 fn truncate_capture_for_optimization<'tcx>(
2392 mut place: Place<'tcx>,
2393 mut curr_mode: ty::UpvarCapture<'tcx>,
2394 ) -> (Place<'tcx>, ty::UpvarCapture<'tcx>) {
2395 let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
2397 // Find the right-most deref (if any). All the projections that come after this
2398 // are fields or other "in-place pointer adjustments"; these refer therefore to
2399 // data owned by whatever pointer is being dereferenced here.
2400 let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
2403 // If that pointer is a shared reference, then we don't need those fields.
2404 Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
2405 truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
2407 None | Some(_) => {}
2413 /// Precise capture is enabled if the feature gate `capture_disjoint_fields` is enabled or if
2414 /// user is using Rust Edition 2021 or higher.
2416 /// `span` is the span of the closure.
2417 fn enable_precise_capture(tcx: TyCtxt<'_>, span: Span) -> bool {
2418 // We use span here to ensure that if the closure was generated by a macro with a different
2420 tcx.features().capture_disjoint_fields || span.rust_2021()