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 crate::mem_categorization
as mc
;
37 use crate::mem_categorization
::PlaceBase
;
39 use rustc_data_structures
::fx
::FxIndexMap
;
41 use rustc_hir
::def_id
::DefId
;
42 use rustc_hir
::def_id
::LocalDefId
;
43 use rustc_hir
::intravisit
::{self, NestedVisitorMap, Visitor}
;
44 use rustc_infer
::infer
::UpvarRegion
;
45 use rustc_middle
::ty
::{self, Ty, TyCtxt, UpvarSubsts}
;
48 impl<'a
, 'tcx
> FnCtxt
<'a
, 'tcx
> {
49 pub fn closure_analyze(&self, body
: &'tcx hir
::Body
<'tcx
>) {
50 InferBorrowKindVisitor { fcx: self }
.visit_body(body
);
52 // it's our job to process these.
53 assert
!(self.deferred_call_resolutions
.borrow().is_empty());
57 struct InferBorrowKindVisitor
<'a
, 'tcx
> {
58 fcx
: &'a FnCtxt
<'a
, 'tcx
>,
61 impl<'a
, 'tcx
> Visitor
<'tcx
> for InferBorrowKindVisitor
<'a
, 'tcx
> {
62 type Map
= intravisit
::ErasedMap
<'tcx
>;
64 fn nested_visit_map(&mut self) -> NestedVisitorMap
<Self::Map
> {
65 NestedVisitorMap
::None
68 fn visit_expr(&mut self, expr
: &'tcx hir
::Expr
<'tcx
>) {
69 if let hir
::ExprKind
::Closure(cc
, _
, body_id
, _
, _
) = expr
.kind
{
70 let body
= self.fcx
.tcx
.hir().body(body_id
);
71 self.visit_body(body
);
72 self.fcx
.analyze_closure(expr
.hir_id
, expr
.span
, body
, cc
);
75 intravisit
::walk_expr(self, expr
);
79 impl<'a
, 'tcx
> FnCtxt
<'a
, 'tcx
> {
80 /// Analysis starting point.
83 closure_hir_id
: hir
::HirId
,
86 capture_clause
: hir
::CaptureBy
,
88 debug
!("analyze_closure(id={:?}, body.id={:?})", closure_hir_id
, body
.id());
90 // Extract the type of the closure.
91 let ty
= self.node_ty(closure_hir_id
);
92 let (closure_def_id
, substs
) = match ty
.kind
{
93 ty
::Closure(def_id
, substs
) => (def_id
, UpvarSubsts
::Closure(substs
)),
94 ty
::Generator(def_id
, substs
, _
) => (def_id
, UpvarSubsts
::Generator(substs
)),
96 // #51714: skip analysis when we have already encountered type errors
102 "type of closure expr {:?} is not a closure {:?}",
109 let infer_kind
= if let UpvarSubsts
::Closure(closure_substs
) = substs
{
110 self.closure_kind(closure_substs
).is_none().then_some(closure_substs
)
115 if let Some(upvars
) = self.tcx
.upvars(closure_def_id
) {
116 let mut upvar_list
: FxIndexMap
<hir
::HirId
, ty
::UpvarId
> =
117 FxIndexMap
::with_capacity_and_hasher(upvars
.len(), Default
::default());
118 for (&var_hir_id
, _
) in upvars
.iter() {
119 let upvar_id
= ty
::UpvarId
{
120 var_path
: ty
::UpvarPath { hir_id: var_hir_id }
,
121 closure_expr_id
: closure_def_id
.expect_local(),
123 debug
!("seed upvar_id {:?}", upvar_id
);
124 // Adding the upvar Id to the list of Upvars, which will be added
125 // to the map for the closure at the end of the for loop.
126 upvar_list
.insert(var_hir_id
, upvar_id
);
128 let capture_kind
= match capture_clause
{
129 hir
::CaptureBy
::Value
=> ty
::UpvarCapture
::ByValue
,
130 hir
::CaptureBy
::Ref
=> {
131 let origin
= UpvarRegion(upvar_id
, span
);
132 let upvar_region
= self.next_region_var(origin
);
134 ty
::UpvarBorrow { kind: ty::ImmBorrow, region: upvar_region }
;
135 ty
::UpvarCapture
::ByRef(upvar_borrow
)
139 self.tables
.borrow_mut().upvar_capture_map
.insert(upvar_id
, capture_kind
);
141 // Add the vector of upvars to the map keyed with the closure id.
142 // This gives us an easier access to them without having to call
143 // tcx.upvars again..
144 if !upvar_list
.is_empty() {
145 self.tables
.borrow_mut().upvar_list
.insert(closure_def_id
, upvar_list
);
149 let body_owner_def_id
= self.tcx
.hir().body_owner_def_id(body
.id()).to_def_id();
150 assert_eq
!(body_owner_def_id
, closure_def_id
);
151 let mut delegate
= InferBorrowKind
{
154 current_closure_kind
: ty
::ClosureKind
::LATTICE_BOTTOM
,
155 current_origin
: None
,
156 adjust_upvar_captures
: ty
::UpvarCaptureMap
::default(),
158 euv
::ExprUseVisitor
::new(
163 &self.tables
.borrow(),
167 if let Some(closure_substs
) = infer_kind
{
168 // Unify the (as yet unbound) type variable in the closure
169 // substs with the kind we inferred.
170 let inferred_kind
= delegate
.current_closure_kind
;
171 let closure_kind_ty
= closure_substs
.as_closure().kind_ty();
172 self.demand_eqtype(span
, inferred_kind
.to_ty(self.tcx
), closure_kind_ty
);
174 // If we have an origin, store it.
175 if let Some(origin
) = delegate
.current_origin
{
176 self.tables
.borrow_mut().closure_kind_origins_mut().insert(closure_hir_id
, origin
);
180 self.tables
.borrow_mut().upvar_capture_map
.extend(delegate
.adjust_upvar_captures
);
182 // Now that we've analyzed the closure, we know how each
183 // variable is borrowed, and we know what traits the closure
184 // implements (Fn vs FnMut etc). We now have some updates to do
185 // with that information.
187 // Note that no closure type C may have an upvar of type C
188 // (though it may reference itself via a trait object). This
189 // results from the desugaring of closures to a struct like
190 // `Foo<..., UV0...UVn>`. If one of those upvars referenced
191 // C, then the type would have infinite size (and the
192 // inference algorithm will reject it).
194 // Equate the type variables for the upvars with the actual types.
195 let final_upvar_tys
= self.final_upvar_tys(closure_hir_id
);
197 "analyze_closure: id={:?} substs={:?} final_upvar_tys={:?}",
198 closure_hir_id
, substs
, final_upvar_tys
200 for (upvar_ty
, final_upvar_ty
) in substs
.upvar_tys().zip(final_upvar_tys
) {
201 self.demand_suptype(span
, upvar_ty
, final_upvar_ty
);
204 // If we are also inferred the closure kind here,
205 // process any deferred resolutions.
206 let deferred_call_resolutions
= self.remove_deferred_call_resolutions(closure_def_id
);
207 for deferred_call_resolution
in deferred_call_resolutions
{
208 deferred_call_resolution
.resolve(self);
212 // Returns a list of `Ty`s for each upvar.
213 fn final_upvar_tys(&self, closure_id
: hir
::HirId
) -> Vec
<Ty
<'tcx
>> {
214 // Presently an unboxed closure type cannot "escape" out of a
215 // function, so we will only encounter ones that originated in the
216 // local crate or were inlined into it along with some function.
217 // This may change if abstract return types of some sort are
220 let closure_def_id
= tcx
.hir().local_def_id(closure_id
);
222 tcx
.upvars(closure_def_id
)
225 upvars
.iter().map(|(&var_hir_id
, _
)| {
226 let upvar_ty
= self.node_ty(var_hir_id
);
227 let upvar_id
= ty
::UpvarId
{
228 var_path
: ty
::UpvarPath { hir_id: var_hir_id }
,
229 closure_expr_id
: closure_def_id
.expect_local(),
231 let capture
= self.tables
.borrow().upvar_capture(upvar_id
);
233 debug
!("var_id={:?} upvar_ty={:?} capture={:?}", var_hir_id
, upvar_ty
, capture
);
236 ty
::UpvarCapture
::ByValue
=> upvar_ty
,
237 ty
::UpvarCapture
::ByRef(borrow
) => tcx
.mk_ref(
239 ty
::TypeAndMut { ty: upvar_ty, mutbl: borrow.kind.to_mutbl_lossy() }
,
248 struct InferBorrowKind
<'a
, 'tcx
> {
249 fcx
: &'a FnCtxt
<'a
, 'tcx
>,
251 // The def-id of the closure whose kind and upvar accesses are being inferred.
252 closure_def_id
: DefId
,
254 // The kind that we have inferred that the current closure
255 // requires. Note that we *always* infer a minimal kind, even if
256 // we don't always *use* that in the final result (i.e., sometimes
257 // we've taken the closure kind from the expectations instead, and
258 // for generators we don't even implement the closure traits
260 current_closure_kind
: ty
::ClosureKind
,
262 // If we modified `current_closure_kind`, this field contains a `Some()` with the
263 // variable access that caused us to do so.
264 current_origin
: Option
<(Span
, ast
::Name
)>,
266 // For each upvar that we access, we track the minimal kind of
267 // access we need (ref, ref mut, move, etc).
268 adjust_upvar_captures
: ty
::UpvarCaptureMap
<'tcx
>,
271 impl<'a
, 'tcx
> InferBorrowKind
<'a
, 'tcx
> {
272 fn adjust_upvar_borrow_kind_for_consume(
274 place
: &mc
::Place
<'tcx
>,
275 mode
: euv
::ConsumeMode
,
277 debug
!("adjust_upvar_borrow_kind_for_consume(place={:?}, mode={:?})", place
, mode
);
279 // we only care about moves
287 let tcx
= self.fcx
.tcx
;
288 let upvar_id
= if let PlaceBase
::Upvar(upvar_id
) = place
.base
{
294 debug
!("adjust_upvar_borrow_kind_for_consume: upvar={:?}", upvar_id
);
296 // To move out of an upvar, this must be a FnOnce closure
297 self.adjust_closure_kind(
298 upvar_id
.closure_expr_id
,
299 ty
::ClosureKind
::FnOnce
,
301 var_name(tcx
, upvar_id
.var_path
.hir_id
),
304 self.adjust_upvar_captures
.insert(upvar_id
, ty
::UpvarCapture
::ByValue
);
307 /// Indicates that `place` is being directly mutated (e.g., assigned
308 /// to). If the place is based on a by-ref upvar, this implies that
309 /// the upvar must be borrowed using an `&mut` borrow.
310 fn adjust_upvar_borrow_kind_for_mut(&mut self, place
: &mc
::Place
<'tcx
>) {
311 debug
!("adjust_upvar_borrow_kind_for_mut(place={:?})", place
);
313 if let PlaceBase
::Upvar(upvar_id
) = place
.base
{
314 let mut borrow_kind
= ty
::MutBorrow
;
315 for pointer_ty
in place
.deref_tys() {
316 match pointer_ty
.kind
{
317 // Raw pointers don't inherit mutability.
318 ty
::RawPtr(_
) => return,
319 // assignment to deref of an `&mut`
320 // borrowed pointer implies that the
321 // pointer itself must be unique, but not
322 // necessarily *mutable*
323 ty
::Ref(.., hir
::Mutability
::Mut
) => borrow_kind
= ty
::UniqueImmBorrow
,
327 self.adjust_upvar_deref(upvar_id
, place
.span
, borrow_kind
);
331 fn adjust_upvar_borrow_kind_for_unique(&mut self, place
: &mc
::Place
<'tcx
>) {
332 debug
!("adjust_upvar_borrow_kind_for_unique(place={:?})", place
);
334 if let PlaceBase
::Upvar(upvar_id
) = place
.base
{
335 if place
.deref_tys().any(ty
::TyS
::is_unsafe_ptr
) {
336 // Raw pointers don't inherit mutability.
339 // for a borrowed pointer to be unique, its base must be unique
340 self.adjust_upvar_deref(upvar_id
, place
.span
, ty
::UniqueImmBorrow
);
344 fn adjust_upvar_deref(
346 upvar_id
: ty
::UpvarId
,
348 borrow_kind
: ty
::BorrowKind
,
350 assert
!(match borrow_kind
{
351 ty
::MutBorrow
=> true,
352 ty
::UniqueImmBorrow
=> true,
354 // imm borrows never require adjusting any kinds, so we don't wind up here
355 ty
::ImmBorrow
=> false,
358 let tcx
= self.fcx
.tcx
;
360 // if this is an implicit deref of an
361 // upvar, then we need to modify the
362 // borrow_kind of the upvar to make sure it
363 // is inferred to mutable if necessary
364 self.adjust_upvar_borrow_kind(upvar_id
, borrow_kind
);
366 // also need to be in an FnMut closure since this is not an ImmBorrow
367 self.adjust_closure_kind(
368 upvar_id
.closure_expr_id
,
369 ty
::ClosureKind
::FnMut
,
371 var_name(tcx
, upvar_id
.var_path
.hir_id
),
375 /// We infer the borrow_kind with which to borrow upvars in a stack closure.
376 /// The borrow_kind basically follows a lattice of `imm < unique-imm < mut`,
377 /// moving from left to right as needed (but never right to left).
378 /// Here the argument `mutbl` is the borrow_kind that is required by
379 /// some particular use.
380 fn adjust_upvar_borrow_kind(&mut self, upvar_id
: ty
::UpvarId
, kind
: ty
::BorrowKind
) {
381 let upvar_capture
= self
382 .adjust_upvar_captures
385 .unwrap_or_else(|| self.fcx
.tables
.borrow().upvar_capture(upvar_id
));
387 "adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
388 upvar_id
, upvar_capture
, kind
391 match upvar_capture
{
392 ty
::UpvarCapture
::ByValue
=> {
393 // Upvar is already by-value, the strongest criteria.
395 ty
::UpvarCapture
::ByRef(mut upvar_borrow
) => {
396 match (upvar_borrow
.kind
, kind
) {
398 (ty
::ImmBorrow
, ty
::UniqueImmBorrow
| ty
::MutBorrow
)
399 | (ty
::UniqueImmBorrow
, ty
::MutBorrow
) => {
400 upvar_borrow
.kind
= kind
;
401 self.adjust_upvar_captures
402 .insert(upvar_id
, ty
::UpvarCapture
::ByRef(upvar_borrow
));
405 (ty
::ImmBorrow
, ty
::ImmBorrow
)
406 | (ty
::UniqueImmBorrow
, ty
::ImmBorrow
| ty
::UniqueImmBorrow
)
407 | (ty
::MutBorrow
, _
) => {}
413 fn adjust_closure_kind(
415 closure_id
: LocalDefId
,
416 new_kind
: ty
::ClosureKind
,
421 "adjust_closure_kind(closure_id={:?}, new_kind={:?}, upvar_span={:?}, var_name={})",
422 closure_id
, new_kind
, upvar_span
, var_name
425 // Is this the closure whose kind is currently being inferred?
426 if closure_id
.to_def_id() != self.closure_def_id
{
427 debug
!("adjust_closure_kind: not current closure");
431 // closures start out as `Fn`.
432 let existing_kind
= self.current_closure_kind
;
435 "adjust_closure_kind: closure_id={:?}, existing_kind={:?}, new_kind={:?}",
436 closure_id
, existing_kind
, new_kind
439 match (existing_kind
, new_kind
) {
440 (ty
::ClosureKind
::Fn
, ty
::ClosureKind
::Fn
)
441 | (ty
::ClosureKind
::FnMut
, ty
::ClosureKind
::Fn
| ty
::ClosureKind
::FnMut
)
442 | (ty
::ClosureKind
::FnOnce
, _
) => {
446 (ty
::ClosureKind
::Fn
, ty
::ClosureKind
::FnMut
| ty
::ClosureKind
::FnOnce
)
447 | (ty
::ClosureKind
::FnMut
, ty
::ClosureKind
::FnOnce
) => {
448 // new kind is stronger than the old kind
449 self.current_closure_kind
= new_kind
;
450 self.current_origin
= Some((upvar_span
, var_name
));
456 impl<'a
, 'tcx
> euv
::Delegate
<'tcx
> for InferBorrowKind
<'a
, 'tcx
> {
457 fn consume(&mut self, place
: &mc
::Place
<'tcx
>, mode
: euv
::ConsumeMode
) {
458 debug
!("consume(place={:?},mode={:?})", place
, mode
);
459 self.adjust_upvar_borrow_kind_for_consume(place
, mode
);
462 fn borrow(&mut self, place
: &mc
::Place
<'tcx
>, bk
: ty
::BorrowKind
) {
463 debug
!("borrow(place={:?}, bk={:?})", place
, bk
);
467 ty
::UniqueImmBorrow
=> {
468 self.adjust_upvar_borrow_kind_for_unique(place
);
471 self.adjust_upvar_borrow_kind_for_mut(place
);
476 fn mutate(&mut self, assignee_place
: &mc
::Place
<'tcx
>) {
477 debug
!("mutate(assignee_place={:?})", assignee_place
);
479 self.adjust_upvar_borrow_kind_for_mut(assignee_place
);
483 fn var_name(tcx
: TyCtxt
<'_
>, var_hir_id
: hir
::HirId
) -> ast
::Name
{
484 tcx
.hir().name(var_hir_id
)