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::middle::expr_use_visitor as euv;
36 use crate::middle::mem_categorization as mc;
37 use crate::middle::mem_categorization::Categorization;
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::UpvarRegion;
43 use rustc::ty::{self, Ty, TyCtxt, UpvarSubsts};
47 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
48 pub fn closure_analyze(&self, body: &'gcx hir::Body) {
49 InferBorrowKindVisitor { fcx: self }.visit_body(body);
51 // it's our job to process these.
52 assert!(self.deferred_call_resolutions.borrow().is_empty());
56 struct InferBorrowKindVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
57 fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
60 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for InferBorrowKindVisitor<'a, 'gcx, 'tcx> {
61 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
62 NestedVisitorMap::None
65 fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
66 if let hir::ExprKind::Closure(cc, _, body_id, _, _) = expr.node {
67 let body = self.fcx.tcx.hir().body(body_id);
68 self.visit_body(body);
70 .analyze_closure(expr.hir_id, expr.span, body, cc);
73 intravisit::walk_expr(self, expr);
77 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
80 closure_hir_id: hir::HirId,
83 capture_clause: hir::CaptureClause,
86 * Analysis starting point.
90 "analyze_closure(id={:?}, body.id={:?})",
95 // Extract the type of the closure.
96 let ty = self.node_ty(closure_hir_id);
97 let (closure_def_id, substs) = match ty.sty {
98 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs)),
99 ty::Generator(def_id, substs, _) => (def_id, UpvarSubsts::Generator(substs)),
101 // #51714: skip analysis when we have already encountered type errors
107 "type of closure expr {:?} is not a closure {:?}",
114 let infer_kind = if let UpvarSubsts::Closure(closure_substs) = substs {
115 if self.closure_kind(closure_def_id, closure_substs).is_none() {
124 if let Some(upvars) = self.tcx.upvars(closure_def_id) {
125 let mut upvar_list: Vec<ty::UpvarId> = Vec::with_capacity(upvars.len());
126 for upvar in upvars.iter() {
127 let upvar_id = ty::UpvarId {
128 var_path: ty::UpvarPath {
129 hir_id: upvar.var_id,
131 closure_expr_id: LocalDefId::from_def_id(closure_def_id),
133 debug!("seed upvar_id {:?}", upvar_id);
134 // Adding the upvar Id to the list of Upvars, which will be added
135 // to the map for the closure at the end of the for loop.
136 upvar_list.push(upvar_id);
138 let capture_kind = match capture_clause {
139 hir::CaptureByValue => ty::UpvarCapture::ByValue,
140 hir::CaptureByRef => {
141 let origin = UpvarRegion(upvar_id, span);
142 let upvar_region = self.next_region_var(origin);
143 let upvar_borrow = ty::UpvarBorrow {
145 region: upvar_region,
147 ty::UpvarCapture::ByRef(upvar_borrow)
154 .insert(upvar_id, capture_kind);
156 // Add the vector of upvars to the map keyed with the closure id.
157 // This gives us an easier access to them without having to call
158 // tcx.upvars again..
159 if !upvar_list.is_empty() {
163 .insert(closure_def_id, upvar_list);
167 let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
168 let region_scope_tree = &self.tcx.region_scope_tree(body_owner_def_id);
169 let mut delegate = InferBorrowKind {
171 closure_def_id: closure_def_id,
172 current_closure_kind: ty::ClosureKind::LATTICE_BOTTOM,
173 current_origin: None,
174 adjust_upvar_captures: ty::UpvarCaptureMap::default(),
176 euv::ExprUseVisitor::with_infer(
181 &self.tables.borrow(),
185 if let Some(closure_substs) = infer_kind {
186 // Unify the (as yet unbound) type variable in the closure
187 // substs with the kind we inferred.
188 let inferred_kind = delegate.current_closure_kind;
189 let closure_kind_ty = closure_substs.closure_kind_ty(closure_def_id, self.tcx);
190 self.demand_eqtype(span, inferred_kind.to_ty(self.tcx), closure_kind_ty);
192 // If we have an origin, store it.
193 if let Some(origin) = delegate.current_origin {
196 .closure_kind_origins_mut()
197 .insert(closure_hir_id, origin);
204 .extend(delegate.adjust_upvar_captures);
206 // Now that we've analyzed the closure, we know how each
207 // variable is borrowed, and we know what traits the closure
208 // implements (Fn vs FnMut etc). We now have some updates to do
209 // with that information.
211 // Note that no closure type C may have an upvar of type C
212 // (though it may reference itself via a trait object). This
213 // results from the desugaring of closures to a struct like
214 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
215 // C, then the type would have infinite size (and the
216 // inference algorithm will reject it).
218 // Equate the type variables for the upvars with the actual types.
219 let final_upvar_tys = self.final_upvar_tys(closure_hir_id);
221 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
222 closure_hir_id, substs, final_upvar_tys
224 for (upvar_ty, final_upvar_ty) in substs
225 .upvar_tys(closure_def_id, self.tcx)
226 .zip(final_upvar_tys)
228 self.demand_suptype(span, upvar_ty, final_upvar_ty);
231 // If we are also inferred the closure kind here,
232 // process any deferred resolutions.
233 let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
234 for deferred_call_resolution in deferred_call_resolutions {
235 deferred_call_resolution.resolve(self);
239 // Returns a list of `ClosureUpvar`s for each upvar.
240 fn final_upvar_tys(&self, closure_id: hir::HirId) -> Vec<Ty<'tcx>> {
241 // Presently an unboxed closure type cannot "escape" out of a
242 // function, so we will only encounter ones that originated in the
243 // local crate or were inlined into it along with some function.
244 // This may change if abstract return types of some sort are
247 let closure_def_id = tcx.hir().local_def_id_from_hir_id(closure_id);
249 tcx.upvars(closure_def_id).iter().flat_map(|upvars| {
253 let upvar_ty = self.node_ty(upvar.var_id);
254 let upvar_id = ty::UpvarId {
255 var_path: ty::UpvarPath { hir_id: upvar.var_id },
256 closure_expr_id: LocalDefId::from_def_id(closure_def_id),
258 let capture = self.tables.borrow().upvar_capture(upvar_id);
261 "var_id={:?} upvar_ty={:?} capture={:?}",
262 upvar.var_id, upvar_ty, capture
266 ty::UpvarCapture::ByValue => upvar_ty,
267 ty::UpvarCapture::ByRef(borrow) => tcx.mk_ref(
271 mutbl: borrow.kind.to_mutbl_lossy(),
281 struct InferBorrowKind<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
282 fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
284 // The def-id of the closure whose kind and upvar accesses are being inferred.
285 closure_def_id: DefId,
287 // The kind that we have inferred that the current closure
288 // requires. Note that we *always* infer a minimal kind, even if
289 // we don't always *use* that in the final result (i.e., sometimes
290 // we've taken the closure kind from the expectations instead, and
291 // for generators we don't even implement the closure traits
293 current_closure_kind: ty::ClosureKind,
295 // If we modified `current_closure_kind`, this field contains a `Some()` with the
296 // variable access that caused us to do so.
297 current_origin: Option<(Span, ast::Name)>,
299 // For each upvar that we access, we track the minimal kind of
300 // access we need (ref, ref mut, move, etc).
301 adjust_upvar_captures: ty::UpvarCaptureMap<'tcx>,
304 impl<'a, 'gcx, 'tcx> InferBorrowKind<'a, 'gcx, 'tcx> {
305 fn adjust_upvar_borrow_kind_for_consume(
307 cmt: &mc::cmt_<'tcx>,
308 mode: euv::ConsumeMode,
311 "adjust_upvar_borrow_kind_for_consume(cmt={:?}, mode={:?})",
315 // we only care about moves
323 let tcx = self.fcx.tcx;
325 // watch out for a move of the deref of a borrowed pointer;
326 // for that to be legal, the upvar would have to be borrowed
328 let guarantor = cmt.guarantor();
330 "adjust_upvar_borrow_kind_for_consume: guarantor={:?}",
334 "adjust_upvar_borrow_kind_for_consume: guarantor.cat={:?}",
337 if let Categorization::Deref(_, mc::BorrowedPtr(..)) = guarantor.cat {
339 "adjust_upvar_borrow_kind_for_consume: found deref with note {:?}",
342 match guarantor.note {
343 mc::NoteUpvarRef(upvar_id) => {
345 "adjust_upvar_borrow_kind_for_consume: \
346 setting upvar_id={:?} to by value",
350 // to move out of an upvar, this must be a FnOnce closure
351 self.adjust_closure_kind(
352 upvar_id.closure_expr_id,
353 ty::ClosureKind::FnOnce,
355 var_name(tcx, upvar_id.var_path.hir_id),
358 self.adjust_upvar_captures
359 .insert(upvar_id, ty::UpvarCapture::ByValue);
361 mc::NoteClosureEnv(upvar_id) => {
362 // we get just a closureenv ref if this is a
363 // `move` closure, or if the upvar has already
364 // been inferred to by-value. In any case, we
365 // must still adjust the kind of the closure
366 // to be a FnOnce closure to permit moves out
367 // of the environment.
368 self.adjust_closure_kind(
369 upvar_id.closure_expr_id,
370 ty::ClosureKind::FnOnce,
372 var_name(tcx, upvar_id.var_path.hir_id),
375 mc::NoteIndex | mc::NoteNone => {}
380 /// Indicates that `cmt` is being directly mutated (e.g., assigned
381 /// to). If cmt contains any by-ref upvars, this implies that
382 /// those upvars must be borrowed using an `&mut` borrow.
383 fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: &mc::cmt_<'tcx>) {
384 debug!("adjust_upvar_borrow_kind_for_mut(cmt={:?})", cmt);
386 match cmt.cat.clone() {
387 Categorization::Deref(base, mc::Unique)
388 | Categorization::Interior(base, _)
389 | Categorization::Downcast(base, _) => {
390 // Interior or owned data is mutable if base is
391 // mutable, so iterate to the base.
392 self.adjust_upvar_borrow_kind_for_mut(&base);
395 Categorization::Deref(base, mc::BorrowedPtr(..)) => {
396 if !self.try_adjust_upvar_deref(cmt, ty::MutBorrow) {
397 // assignment to deref of an `&mut`
398 // borrowed pointer implies that the
399 // pointer itself must be unique, but not
400 // necessarily *mutable*
401 self.adjust_upvar_borrow_kind_for_unique(&base);
405 Categorization::Deref(_, mc::UnsafePtr(..))
406 | Categorization::StaticItem
407 | Categorization::ThreadLocal(..)
408 | Categorization::Rvalue(..)
409 | Categorization::Local(_)
410 | Categorization::Upvar(..) => {
416 fn adjust_upvar_borrow_kind_for_unique(&mut self, cmt: &mc::cmt_<'tcx>) {
417 debug!("adjust_upvar_borrow_kind_for_unique(cmt={:?})", cmt);
419 match cmt.cat.clone() {
420 Categorization::Deref(base, mc::Unique)
421 | Categorization::Interior(base, _)
422 | Categorization::Downcast(base, _) => {
423 // Interior or owned data is unique if base is
425 self.adjust_upvar_borrow_kind_for_unique(&base);
428 Categorization::Deref(base, mc::BorrowedPtr(..)) => {
429 if !self.try_adjust_upvar_deref(cmt, ty::UniqueImmBorrow) {
430 // for a borrowed pointer to be unique, its
431 // base must be unique
432 self.adjust_upvar_borrow_kind_for_unique(&base);
436 Categorization::Deref(_, mc::UnsafePtr(..))
437 | Categorization::StaticItem
438 | Categorization::ThreadLocal(..)
439 | Categorization::Rvalue(..)
440 | Categorization::Local(_)
441 | Categorization::Upvar(..) => {}
445 fn try_adjust_upvar_deref(
447 cmt: &mc::cmt_<'tcx>,
448 borrow_kind: ty::BorrowKind,
450 assert!(match borrow_kind {
451 ty::MutBorrow => true,
452 ty::UniqueImmBorrow => true,
454 // imm borrows never require adjusting any kinds, so we don't wind up here
455 ty::ImmBorrow => false,
458 let tcx = self.fcx.tcx;
461 mc::NoteUpvarRef(upvar_id) => {
462 // if this is an implicit deref of an
463 // upvar, then we need to modify the
464 // borrow_kind of the upvar to make sure it
465 // is inferred to mutable if necessary
466 self.adjust_upvar_borrow_kind(upvar_id, borrow_kind);
468 // also need to be in an FnMut closure since this is not an ImmBorrow
469 self.adjust_closure_kind(
470 upvar_id.closure_expr_id,
471 ty::ClosureKind::FnMut,
473 var_name(tcx, upvar_id.var_path.hir_id),
478 mc::NoteClosureEnv(upvar_id) => {
479 // this kind of deref occurs in a `move` closure, or
480 // for a by-value upvar; in either case, to mutate an
481 // upvar, we need to be an FnMut closure
482 self.adjust_closure_kind(
483 upvar_id.closure_expr_id,
484 ty::ClosureKind::FnMut,
486 var_name(tcx, upvar_id.var_path.hir_id),
491 mc::NoteIndex | mc::NoteNone => false,
495 /// We infer the borrow_kind with which to borrow upvars in a stack closure.
496 /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
497 /// moving from left to right as needed (but never right to left).
498 /// Here the argument `mutbl` is the borrow_kind that is required by
499 /// some particular use.
500 fn adjust_upvar_borrow_kind(&mut self, upvar_id: ty::UpvarId, kind: ty::BorrowKind) {
501 let upvar_capture = self
502 .adjust_upvar_captures
505 .unwrap_or_else(|| self.fcx.tables.borrow().upvar_capture(upvar_id));
507 "adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
508 upvar_id, upvar_capture, kind
511 match upvar_capture {
512 ty::UpvarCapture::ByValue => {
513 // Upvar is already by-value, the strongest criteria.
515 ty::UpvarCapture::ByRef(mut upvar_borrow) => {
516 match (upvar_borrow.kind, kind) {
518 (ty::ImmBorrow, ty::UniqueImmBorrow)
519 | (ty::ImmBorrow, ty::MutBorrow)
520 | (ty::UniqueImmBorrow, ty::MutBorrow) => {
521 upvar_borrow.kind = kind;
522 self.adjust_upvar_captures
523 .insert(upvar_id, ty::UpvarCapture::ByRef(upvar_borrow));
526 (ty::ImmBorrow, ty::ImmBorrow)
527 | (ty::UniqueImmBorrow, ty::ImmBorrow)
528 | (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
529 | (ty::MutBorrow, _) => {}
535 fn adjust_closure_kind(
537 closure_id: LocalDefId,
538 new_kind: ty::ClosureKind,
543 "adjust_closure_kind(closure_id={:?}, new_kind={:?}, upvar_span={:?}, var_name={})",
544 closure_id, new_kind, upvar_span, var_name
547 // Is this the closure whose kind is currently being inferred?
548 if closure_id.to_def_id() != self.closure_def_id {
549 debug!("adjust_closure_kind: not current closure");
553 // closures start out as `Fn`.
554 let existing_kind = self.current_closure_kind;
557 "adjust_closure_kind: closure_id={:?}, existing_kind={:?}, new_kind={:?}",
558 closure_id, existing_kind, new_kind
561 match (existing_kind, new_kind) {
562 (ty::ClosureKind::Fn, ty::ClosureKind::Fn)
563 | (ty::ClosureKind::FnMut, ty::ClosureKind::Fn)
564 | (ty::ClosureKind::FnMut, ty::ClosureKind::FnMut)
565 | (ty::ClosureKind::FnOnce, _) => {
569 (ty::ClosureKind::Fn, ty::ClosureKind::FnMut)
570 | (ty::ClosureKind::Fn, ty::ClosureKind::FnOnce)
571 | (ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => {
572 // new kind is stronger than the old kind
573 self.current_closure_kind = new_kind;
574 self.current_origin = Some((upvar_span, var_name));
580 impl<'a, 'gcx, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'gcx, 'tcx> {
583 _consume_id: hir::HirId,
585 cmt: &mc::cmt_<'tcx>,
586 mode: euv::ConsumeMode,
588 debug!("consume(cmt={:?},mode={:?})", cmt, mode);
589 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
594 _matched_pat: &hir::Pat,
595 _cmt: &mc::cmt_<'tcx>,
596 _mode: euv::MatchMode,
602 _consume_pat: &hir::Pat,
603 cmt: &mc::cmt_<'tcx>,
604 mode: euv::ConsumeMode,
606 debug!("consume_pat(cmt={:?},mode={:?})", cmt, mode);
607 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
612 borrow_id: hir::HirId,
614 cmt: &mc::cmt_<'tcx>,
615 _loan_region: ty::Region<'tcx>,
617 _loan_cause: euv::LoanCause,
620 "borrow(borrow_id={}, cmt={:?}, bk={:?})",
626 ty::UniqueImmBorrow => {
627 self.adjust_upvar_borrow_kind_for_unique(cmt);
630 self.adjust_upvar_borrow_kind_for_mut(cmt);
635 fn decl_without_init(&mut self, _id: hir::HirId, _span: Span) {}
639 _assignment_id: hir::HirId,
640 _assignment_span: Span,
641 assignee_cmt: &mc::cmt_<'tcx>,
642 _mode: euv::MutateMode,
644 debug!("mutate(assignee_cmt={:?})", assignee_cmt);
646 self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);
650 fn var_name(tcx: TyCtxt<'_, '_, '_>, var_hir_id: hir::HirId) -> ast::Name {
651 tcx.hir().name_by_hir_id(var_hir_id)