1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! ### Inferring borrow kinds for upvars
13 //! Whenever there is a closure expression, we need to determine how each
14 //! upvar is used. We do this by initially assigning each upvar an
15 //! immutable "borrow kind" (see `ty::BorrowKind` for details) and then
16 //! "escalating" the kind as needed. The borrow kind proceeds according to
17 //! the following lattice:
19 //! ty::ImmBorrow -> ty::UniqueImmBorrow -> ty::MutBorrow
21 //! So, for example, if we see an assignment `x = 5` to an upvar `x`, we
22 //! will promote its borrow kind to mutable borrow. If we see an `&mut x`
23 //! we'll do the same. Naturally, this applies not just to the upvar, but
24 //! to everything owned by `x`, so the result is the same for something
25 //! like `x.f = 5` and so on (presuming `x` is not a borrowed pointer to a
26 //! struct). These adjustments are performed in
27 //! `adjust_upvar_borrow_kind()` (you can trace backwards through the code
30 //! The fact that we are inferring borrow kinds as we go results in a
31 //! semi-hacky interaction with mem-categorization. In particular,
32 //! mem-categorization will query the current borrow kind as it
33 //! categorizes, and we'll return the *current* value, but this may get
34 //! adjusted later. Therefore, in this module, we generally ignore the
35 //! borrow kind (and derived mutabilities) that are returned from
36 //! mem-categorization, since they may be inaccurate. (Another option
37 //! would be to use a unification scheme, where instead of returning a
38 //! concrete borrow kind like `ty::ImmBorrow`, we return a
39 //! `ty::InferBorrow(upvar_id)` or something like that, but this would
40 //! then mean that all later passes would have to check for these figments
41 //! and report an error, and it just seems like more mess in the end.)
45 use middle::expr_use_visitor as euv;
46 use middle::mem_categorization as mc;
47 use middle::ty::{self};
48 use middle::infer::{InferCtxt, UpvarRegion};
49 use std::collections::HashSet;
52 use syntax::codemap::Span;
53 use syntax::visit::{self, Visitor};
55 ///////////////////////////////////////////////////////////////////////////
56 // PUBLIC ENTRY POINTS
58 pub fn closure_analyze_fn(fcx: &FnCtxt,
63 let mut seed = SeedBorrowKind::new(fcx);
64 seed.visit_block(body);
65 let closures_with_inferred_kinds = seed.closures_with_inferred_kinds;
67 let mut adjust = AdjustBorrowKind::new(fcx, &closures_with_inferred_kinds);
68 adjust.visit_block(body);
70 // it's our job to process these.
71 assert!(fcx.inh.deferred_call_resolutions.borrow().is_empty());
74 ///////////////////////////////////////////////////////////////////////////
77 struct SeedBorrowKind<'a,'tcx:'a> {
78 fcx: &'a FnCtxt<'a,'tcx>,
79 closures_with_inferred_kinds: HashSet<ast::NodeId>,
82 impl<'a, 'tcx, 'v> Visitor<'v> for SeedBorrowKind<'a, 'tcx> {
83 fn visit_expr(&mut self, expr: &ast::Expr) {
85 ast::ExprClosure(cc, _, ref body) => {
86 self.check_closure(expr, cc, &**body);
92 visit::walk_expr(self, expr);
95 fn visit_fn(&mut self,
96 fn_kind: visit::FnKind<'v>,
97 decl: &'v ast::FnDecl,
98 block: &'v ast::Block,
103 visit::FkItemFn(..) | visit::FkMethod(..) => {
104 // ignore nested fn items
106 visit::FkFnBlock => {
107 visit::walk_fn(self, fn_kind, decl, block, span);
113 impl<'a,'tcx> SeedBorrowKind<'a,'tcx> {
114 fn new(fcx: &'a FnCtxt<'a,'tcx>) -> SeedBorrowKind<'a,'tcx> {
115 SeedBorrowKind { fcx: fcx, closures_with_inferred_kinds: HashSet::new() }
118 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
122 fn infcx(&self) -> &'a InferCtxt<'a,'tcx> {
126 fn check_closure(&mut self,
128 capture_clause: ast::CaptureClause,
131 let closure_def_id = ast_util::local_def(expr.id);
132 if !self.fcx.inh.tables.borrow().closure_kinds.contains_key(&closure_def_id) {
133 self.closures_with_inferred_kinds.insert(expr.id);
134 self.fcx.inh.tables.borrow_mut().closure_kinds
135 .insert(closure_def_id, ty::FnClosureKind);
136 debug!("check_closure: adding closure_id={:?} to closures_with_inferred_kinds",
140 self.tcx().with_freevars(expr.id, |freevars| {
141 for freevar in freevars {
142 let var_node_id = freevar.def.local_node_id();
143 let upvar_id = ty::UpvarId { var_id: var_node_id,
144 closure_expr_id: expr.id };
145 debug!("seed upvar_id {:?}", upvar_id);
147 let capture_kind = match capture_clause {
148 ast::CaptureByValue => {
149 ty::UpvarCapture::ByValue
151 ast::CaptureByRef => {
152 let origin = UpvarRegion(upvar_id, expr.span);
153 let freevar_region = self.infcx().next_region_var(origin);
154 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow,
155 region: freevar_region };
156 ty::UpvarCapture::ByRef(upvar_borrow)
160 self.fcx.inh.tables.borrow_mut().upvar_capture_map.insert(upvar_id, capture_kind);
166 ///////////////////////////////////////////////////////////////////////////
167 // ADJUST BORROW KIND
169 struct AdjustBorrowKind<'a,'tcx:'a> {
170 fcx: &'a FnCtxt<'a,'tcx>,
171 closures_with_inferred_kinds: &'a HashSet<ast::NodeId>,
174 impl<'a,'tcx> AdjustBorrowKind<'a,'tcx> {
175 fn new(fcx: &'a FnCtxt<'a,'tcx>,
176 closures_with_inferred_kinds: &'a HashSet<ast::NodeId>)
177 -> AdjustBorrowKind<'a,'tcx> {
178 AdjustBorrowKind { fcx: fcx, closures_with_inferred_kinds: closures_with_inferred_kinds }
181 fn analyze_closure(&mut self, id: ast::NodeId, decl: &ast::FnDecl, body: &ast::Block) {
183 * Analysis starting point.
186 debug!("analyze_closure(id={:?}, body.id={:?})", id, body.id);
189 let mut euv = euv::ExprUseVisitor::new(self, self.fcx.infcx());
190 euv.walk_fn(decl, body);
192 // If we had not yet settled on a closure kind for this closure,
193 // then we should have by now. Process and remove any deferred resolutions.
195 // Interesting fact: all calls to this closure must come
196 // *after* its definition. Initially, I thought that some
197 // kind of fixed-point iteration would be required, due to the
198 // possibility of twisted examples like this one:
201 // let mut closure0 = None;
202 // let vec = vec!(1, 2, 3);
206 // let closure1 = || {
207 // match closure0.take() {
209 // return c(); // (*) call to `closure0` before it is defined
217 // closure0 = || vec;
221 // However, this turns out to be wrong. Examples like this
222 // fail to compile because the type of the variable `c` above
223 // is an inference variable. And in fact since closure types
224 // cannot be written, there is no way to make this example
225 // work without a boxed closure. This implies that we can't
226 // have two closures that recursively call one another without
227 // some form of boxing (and hence explicit writing of a
228 // closure kind) involved. Huzzah. -nmatsakis
229 let closure_def_id = ast_util::local_def(id);
230 if self.closures_with_inferred_kinds.contains(&id) {
231 let mut deferred_call_resolutions =
232 self.fcx.remove_deferred_call_resolutions(closure_def_id);
233 for deferred_call_resolution in &mut deferred_call_resolutions {
234 deferred_call_resolution.resolve(self.fcx);
239 fn adjust_upvar_borrow_kind_for_consume(&self,
241 mode: euv::ConsumeMode)
243 debug!("adjust_upvar_borrow_kind_for_consume(cmt={:?}, mode={:?})",
246 // we only care about moves
248 euv::Copy => { return; }
252 // watch out for a move of the deref of a borrowed pointer;
253 // for that to be legal, the upvar would have to be borrowed
255 let guarantor = cmt.guarantor();
256 debug!("adjust_upvar_borrow_kind_for_consume: guarantor={:?}",
258 match guarantor.cat {
259 mc::cat_deref(_, _, mc::BorrowedPtr(..)) |
260 mc::cat_deref(_, _, mc::Implicit(..)) => {
262 mc::NoteUpvarRef(upvar_id) => {
263 debug!("adjust_upvar_borrow_kind_for_consume: \
264 setting upvar_id={:?} to by value",
267 // to move out of an upvar, this must be a FnOnce closure
268 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
270 let upvar_capture_map = &mut self.fcx
274 upvar_capture_map.insert(upvar_id, ty::UpvarCapture::ByValue);
276 mc::NoteClosureEnv(upvar_id) => {
277 // we get just a closureenv ref if this is a
278 // `move` closure, or if the upvar has already
279 // been inferred to by-value. In any case, we
280 // must still adjust the kind of the closure
281 // to be a FnOnce closure to permit moves out
282 // of the environment.
283 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
293 /// Indicates that `cmt` is being directly mutated (e.g., assigned
294 /// to). If cmt contains any by-ref upvars, this implies that
295 /// those upvars must be borrowed using an `&mut` borrow.
296 fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: mc::cmt<'tcx>) {
297 debug!("adjust_upvar_borrow_kind_for_mut(cmt={:?})",
300 match cmt.cat.clone() {
301 mc::cat_deref(base, _, mc::Unique) |
302 mc::cat_interior(base, _) |
303 mc::cat_downcast(base, _) => {
304 // Interior or owned data is mutable if base is
305 // mutable, so iterate to the base.
306 self.adjust_upvar_borrow_kind_for_mut(base);
309 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
310 mc::cat_deref(base, _, mc::Implicit(..)) => {
311 if !self.try_adjust_upvar_deref(&cmt.note, ty::MutBorrow) {
312 // assignment to deref of an `&mut`
313 // borrowed pointer implies that the
314 // pointer itself must be unique, but not
315 // necessarily *mutable*
316 self.adjust_upvar_borrow_kind_for_unique(base);
320 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
321 mc::cat_static_item |
324 mc::cat_upvar(..) => {
330 fn adjust_upvar_borrow_kind_for_unique(&self, cmt: mc::cmt<'tcx>) {
331 debug!("adjust_upvar_borrow_kind_for_unique(cmt={:?})",
334 match cmt.cat.clone() {
335 mc::cat_deref(base, _, mc::Unique) |
336 mc::cat_interior(base, _) |
337 mc::cat_downcast(base, _) => {
338 // Interior or owned data is unique if base is
340 self.adjust_upvar_borrow_kind_for_unique(base);
343 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
344 mc::cat_deref(base, _, mc::Implicit(..)) => {
345 if !self.try_adjust_upvar_deref(&cmt.note, ty::UniqueImmBorrow) {
346 // for a borrowed pointer to be unique, its
347 // base must be unique
348 self.adjust_upvar_borrow_kind_for_unique(base);
352 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
353 mc::cat_static_item |
356 mc::cat_upvar(..) => {
361 fn try_adjust_upvar_deref(&self,
363 borrow_kind: ty::BorrowKind)
366 assert!(match borrow_kind {
367 ty::MutBorrow => true,
368 ty::UniqueImmBorrow => true,
370 // imm borrows never require adjusting any kinds, so we don't wind up here
371 ty::ImmBorrow => false,
375 mc::NoteUpvarRef(upvar_id) => {
376 // if this is an implicit deref of an
377 // upvar, then we need to modify the
378 // borrow_kind of the upvar to make sure it
379 // is inferred to mutable if necessary
381 let upvar_capture_map = &mut self.fcx.inh.tables.borrow_mut().upvar_capture_map;
382 let ub = upvar_capture_map.get_mut(&upvar_id).unwrap();
383 self.adjust_upvar_borrow_kind(upvar_id, ub, borrow_kind);
386 // also need to be in an FnMut closure since this is not an ImmBorrow
387 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
391 mc::NoteClosureEnv(upvar_id) => {
392 // this kind of deref occurs in a `move` closure, or
393 // for a by-value upvar; in either case, to mutate an
394 // upvar, we need to be an FnMut closure
395 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
405 /// We infer the borrow_kind with which to borrow upvars in a stack closure. The borrow_kind
406 /// basically follows a lattice of `imm < unique-imm < mut`, moving from left to right as needed
407 /// (but never right to left). Here the argument `mutbl` is the borrow_kind that is required by
408 /// some particular use.
409 fn adjust_upvar_borrow_kind(&self,
410 upvar_id: ty::UpvarId,
411 upvar_capture: &mut ty::UpvarCapture,
412 kind: ty::BorrowKind) {
413 debug!("adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
414 upvar_id, upvar_capture, kind);
416 match *upvar_capture {
417 ty::UpvarCapture::ByValue => {
418 // Upvar is already by-value, the strongest criteria.
420 ty::UpvarCapture::ByRef(ref mut upvar_borrow) => {
421 match (upvar_borrow.kind, kind) {
423 (ty::ImmBorrow, ty::UniqueImmBorrow) |
424 (ty::ImmBorrow, ty::MutBorrow) |
425 (ty::UniqueImmBorrow, ty::MutBorrow) => {
426 upvar_borrow.kind = kind;
429 (ty::ImmBorrow, ty::ImmBorrow) |
430 (ty::UniqueImmBorrow, ty::ImmBorrow) |
431 (ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
432 (ty::MutBorrow, _) => {
439 fn adjust_closure_kind(&self,
440 closure_id: ast::NodeId,
441 new_kind: ty::ClosureKind) {
442 debug!("adjust_closure_kind(closure_id={}, new_kind={:?})",
443 closure_id, new_kind);
445 if !self.closures_with_inferred_kinds.contains(&closure_id) {
449 let closure_def_id = ast_util::local_def(closure_id);
450 let closure_kinds = &mut self.fcx.inh.tables.borrow_mut().closure_kinds;
451 let existing_kind = *closure_kinds.get(&closure_def_id).unwrap();
453 debug!("adjust_closure_kind: closure_id={}, existing_kind={:?}, new_kind={:?}",
454 closure_id, existing_kind, new_kind);
456 match (existing_kind, new_kind) {
457 (ty::FnClosureKind, ty::FnClosureKind) |
458 (ty::FnMutClosureKind, ty::FnClosureKind) |
459 (ty::FnMutClosureKind, ty::FnMutClosureKind) |
460 (ty::FnOnceClosureKind, _) => {
464 (ty::FnClosureKind, ty::FnMutClosureKind) |
465 (ty::FnClosureKind, ty::FnOnceClosureKind) |
466 (ty::FnMutClosureKind, ty::FnOnceClosureKind) => {
467 // new kind is stronger than the old kind
468 closure_kinds.insert(closure_def_id, new_kind);
474 impl<'a, 'tcx, 'v> Visitor<'v> for AdjustBorrowKind<'a, 'tcx> {
475 fn visit_fn(&mut self,
476 fn_kind: visit::FnKind<'v>,
477 decl: &'v ast::FnDecl,
478 body: &'v ast::Block,
483 visit::FkItemFn(..) | visit::FkMethod(..) => {
484 // ignore nested fn items
486 visit::FkFnBlock => {
487 visit::walk_fn(self, fn_kind, decl, body, span);
488 self.analyze_closure(id, span, decl, body);
494 impl<'a,'tcx> euv::Delegate<'tcx> for AdjustBorrowKind<'a,'tcx> {
495 fn consume(&mut self,
496 _consume_id: ast::NodeId,
499 mode: euv::ConsumeMode)
501 debug!("consume(cmt={:?},mode={:?})", cmt, mode);
502 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
505 fn matched_pat(&mut self,
506 _matched_pat: &ast::Pat,
508 _mode: euv::MatchMode)
511 fn consume_pat(&mut self,
512 _consume_pat: &ast::Pat,
514 mode: euv::ConsumeMode)
516 debug!("consume_pat(cmt={:?},mode={:?})", cmt, mode);
517 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
521 borrow_id: ast::NodeId,
524 _loan_region: ty::Region,
526 _loan_cause: euv::LoanCause)
528 debug!("borrow(borrow_id={}, cmt={:?}, bk={:?})",
533 ty::UniqueImmBorrow => {
534 self.adjust_upvar_borrow_kind_for_unique(cmt);
537 self.adjust_upvar_borrow_kind_for_mut(cmt);
542 fn decl_without_init(&mut self,
548 _assignment_id: ast::NodeId,
549 _assignment_span: Span,
550 assignee_cmt: mc::cmt<'tcx>,
551 _mode: euv::MutateMode)
553 debug!("mutate(assignee_cmt={:?})",
556 self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);