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.insert(closure_def_id, ty::FnClosureKind);
135 debug!("check_closure: adding closure_id={:?} to closures_with_inferred_kinds",
139 self.tcx().with_freevars(expr.id, |freevars| {
140 for freevar in freevars {
141 let var_node_id = freevar.def.local_node_id();
142 let upvar_id = ty::UpvarId { var_id: var_node_id,
143 closure_expr_id: expr.id };
144 debug!("seed upvar_id {:?}", upvar_id);
146 let capture_kind = match capture_clause {
147 ast::CaptureByValue => {
148 ty::UpvarCapture::ByValue
150 ast::CaptureByRef => {
151 let origin = UpvarRegion(upvar_id, expr.span);
152 let freevar_region = self.infcx().next_region_var(origin);
153 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow,
154 region: freevar_region };
155 ty::UpvarCapture::ByRef(upvar_borrow)
159 self.fcx.inh.tables.borrow_mut().upvar_capture_map.insert(upvar_id, capture_kind);
165 ///////////////////////////////////////////////////////////////////////////
166 // ADJUST BORROW KIND
168 struct AdjustBorrowKind<'a,'tcx:'a> {
169 fcx: &'a FnCtxt<'a,'tcx>,
170 closures_with_inferred_kinds: &'a HashSet<ast::NodeId>,
173 impl<'a,'tcx> AdjustBorrowKind<'a,'tcx> {
174 fn new(fcx: &'a FnCtxt<'a,'tcx>,
175 closures_with_inferred_kinds: &'a HashSet<ast::NodeId>)
176 -> AdjustBorrowKind<'a,'tcx> {
177 AdjustBorrowKind { fcx: fcx, closures_with_inferred_kinds: closures_with_inferred_kinds }
180 fn analyze_closure(&mut self, id: ast::NodeId, decl: &ast::FnDecl, body: &ast::Block) {
182 * Analysis starting point.
185 self.visit_block(body);
187 debug!("analyzing closure `{}` with fn 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.inh.tables.borrow_mut().upvar_capture_map;
271 upvar_capture_map.insert(upvar_id, ty::UpvarCapture::ByValue);
273 mc::NoteClosureEnv(upvar_id) => {
274 // we get just a closureenv ref if this is a
275 // `move` closure, or if the upvar has already
276 // been inferred to by-value. In any case, we
277 // must still adjust the kind of the closure
278 // to be a FnOnce closure to permit moves out
279 // of the environment.
280 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
290 /// Indicates that `cmt` is being directly mutated (e.g., assigned
291 /// to). If cmt contains any by-ref upvars, this implies that
292 /// those upvars must be borrowed using an `&mut` borrow.
293 fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: mc::cmt<'tcx>) {
294 debug!("adjust_upvar_borrow_kind_for_mut(cmt={:?})",
297 match cmt.cat.clone() {
298 mc::cat_deref(base, _, mc::Unique) |
299 mc::cat_interior(base, _) |
300 mc::cat_downcast(base, _) => {
301 // Interior or owned data is mutable if base is
302 // mutable, so iterate to the base.
303 self.adjust_upvar_borrow_kind_for_mut(base);
306 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
307 mc::cat_deref(base, _, mc::Implicit(..)) => {
308 if !self.try_adjust_upvar_deref(&cmt.note, ty::MutBorrow) {
309 // assignment to deref of an `&mut`
310 // borrowed pointer implies that the
311 // pointer itself must be unique, but not
312 // necessarily *mutable*
313 self.adjust_upvar_borrow_kind_for_unique(base);
317 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
318 mc::cat_static_item |
321 mc::cat_upvar(..) => {
327 fn adjust_upvar_borrow_kind_for_unique(&self, cmt: mc::cmt<'tcx>) {
328 debug!("adjust_upvar_borrow_kind_for_unique(cmt={:?})",
331 match cmt.cat.clone() {
332 mc::cat_deref(base, _, mc::Unique) |
333 mc::cat_interior(base, _) |
334 mc::cat_downcast(base, _) => {
335 // Interior or owned data is unique if base is
337 self.adjust_upvar_borrow_kind_for_unique(base);
340 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
341 mc::cat_deref(base, _, mc::Implicit(..)) => {
342 if !self.try_adjust_upvar_deref(&cmt.note, ty::UniqueImmBorrow) {
343 // for a borrowed pointer to be unique, its
344 // base must be unique
345 self.adjust_upvar_borrow_kind_for_unique(base);
349 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
350 mc::cat_static_item |
353 mc::cat_upvar(..) => {
358 fn try_adjust_upvar_deref(&self,
360 borrow_kind: ty::BorrowKind)
363 assert!(match borrow_kind {
364 ty::MutBorrow => true,
365 ty::UniqueImmBorrow => true,
367 // imm borrows never require adjusting any kinds, so we don't wind up here
368 ty::ImmBorrow => false,
372 mc::NoteUpvarRef(upvar_id) => {
373 // if this is an implicit deref of an
374 // upvar, then we need to modify the
375 // borrow_kind of the upvar to make sure it
376 // is inferred to mutable if necessary
378 let upvar_capture_map = &mut self.fcx.inh.tables.borrow_mut().upvar_capture_map;
379 let ub = upvar_capture_map.get_mut(&upvar_id).unwrap();
380 self.adjust_upvar_borrow_kind(upvar_id, ub, borrow_kind);
383 // also need to be in an FnMut closure since this is not an ImmBorrow
384 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
388 mc::NoteClosureEnv(upvar_id) => {
389 // this kind of deref occurs in a `move` closure, or
390 // for a by-value upvar; in either case, to mutate an
391 // upvar, we need to be an FnMut closure
392 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
402 /// We infer the borrow_kind with which to borrow upvars in a stack closure. The borrow_kind
403 /// basically follows a lattice of `imm < unique-imm < mut`, moving from left to right as needed
404 /// (but never right to left). Here the argument `mutbl` is the borrow_kind that is required by
405 /// some particular use.
406 fn adjust_upvar_borrow_kind(&self,
407 upvar_id: ty::UpvarId,
408 upvar_capture: &mut ty::UpvarCapture,
409 kind: ty::BorrowKind) {
410 debug!("adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
411 upvar_id, upvar_capture, kind);
413 match *upvar_capture {
414 ty::UpvarCapture::ByValue => {
415 // Upvar is already by-value, the strongest criteria.
417 ty::UpvarCapture::ByRef(ref mut upvar_borrow) => {
418 match (upvar_borrow.kind, kind) {
420 (ty::ImmBorrow, ty::UniqueImmBorrow) |
421 (ty::ImmBorrow, ty::MutBorrow) |
422 (ty::UniqueImmBorrow, ty::MutBorrow) => {
423 upvar_borrow.kind = kind;
426 (ty::ImmBorrow, ty::ImmBorrow) |
427 (ty::UniqueImmBorrow, ty::ImmBorrow) |
428 (ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
429 (ty::MutBorrow, _) => {
436 fn adjust_closure_kind(&self,
437 closure_id: ast::NodeId,
438 new_kind: ty::ClosureKind) {
439 debug!("adjust_closure_kind(closure_id={}, new_kind={:?})",
440 closure_id, new_kind);
442 if !self.closures_with_inferred_kinds.contains(&closure_id) {
446 let closure_def_id = ast_util::local_def(closure_id);
447 let closure_kinds = &mut self.fcx.inh.tables.borrow_mut().closure_kinds;
448 let existing_kind = *closure_kinds.get(&closure_def_id).unwrap();
450 debug!("adjust_closure_kind: closure_id={}, existing_kind={:?}, new_kind={:?}",
451 closure_id, existing_kind, new_kind);
453 match (existing_kind, new_kind) {
454 (ty::FnClosureKind, ty::FnClosureKind) |
455 (ty::FnMutClosureKind, ty::FnClosureKind) |
456 (ty::FnMutClosureKind, ty::FnMutClosureKind) |
457 (ty::FnOnceClosureKind, _) => {
461 (ty::FnClosureKind, ty::FnMutClosureKind) |
462 (ty::FnClosureKind, ty::FnOnceClosureKind) |
463 (ty::FnMutClosureKind, ty::FnOnceClosureKind) => {
464 // new kind is stronger than the old kind
465 closure_kinds.insert(closure_def_id, new_kind);
471 impl<'a, 'tcx, 'v> Visitor<'v> for AdjustBorrowKind<'a, 'tcx> {
472 fn visit_fn(&mut self,
473 fn_kind: visit::FnKind<'v>,
474 decl: &'v ast::FnDecl,
475 body: &'v ast::Block,
480 visit::FkItemFn(..) | visit::FkMethod(..) => {
481 // ignore nested fn items
483 visit::FkFnBlock => {
484 self.analyze_closure(id, decl, body);
485 visit::walk_fn(self, fn_kind, decl, body, span);
491 impl<'a,'tcx> euv::Delegate<'tcx> for AdjustBorrowKind<'a,'tcx> {
492 fn consume(&mut self,
493 _consume_id: ast::NodeId,
496 mode: euv::ConsumeMode)
498 debug!("consume(cmt={:?},mode={:?})", cmt, mode);
499 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
502 fn matched_pat(&mut self,
503 _matched_pat: &ast::Pat,
505 _mode: euv::MatchMode)
508 fn consume_pat(&mut self,
509 _consume_pat: &ast::Pat,
511 mode: euv::ConsumeMode)
513 debug!("consume_pat(cmt={:?},mode={:?})", cmt, mode);
514 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
518 borrow_id: ast::NodeId,
521 _loan_region: ty::Region,
523 _loan_cause: euv::LoanCause)
525 debug!("borrow(borrow_id={}, cmt={:?}, bk={:?})",
530 ty::UniqueImmBorrow => {
531 self.adjust_upvar_borrow_kind_for_unique(cmt);
534 self.adjust_upvar_borrow_kind_for_mut(cmt);
539 fn decl_without_init(&mut self,
545 _assignment_id: ast::NodeId,
546 _assignment_span: Span,
547 assignee_cmt: mc::cmt<'tcx>,
548 _mode: euv::MutateMode)
550 debug!("mutate(assignee_cmt={:?})",
553 self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);