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 self.visit_block(body);
188 debug!("analyzing closure `{}` with fn body id `{}`", id, body.id);
190 let mut euv = euv::ExprUseVisitor::new(self, self.fcx.infcx());
191 euv.walk_fn(decl, body);
193 // If we had not yet settled on a closure kind for this closure,
194 // then we should have by now. Process and remove any deferred resolutions.
196 // Interesting fact: all calls to this closure must come
197 // *after* its definition. Initially, I thought that some
198 // kind of fixed-point iteration would be required, due to the
199 // possibility of twisted examples like this one:
202 // let mut closure0 = None;
203 // let vec = vec!(1, 2, 3);
207 // let closure1 = || {
208 // match closure0.take() {
210 // return c(); // (*) call to `closure0` before it is defined
218 // closure0 = || vec;
222 // However, this turns out to be wrong. Examples like this
223 // fail to compile because the type of the variable `c` above
224 // is an inference variable. And in fact since closure types
225 // cannot be written, there is no way to make this example
226 // work without a boxed closure. This implies that we can't
227 // have two closures that recursively call one another without
228 // some form of boxing (and hence explicit writing of a
229 // closure kind) involved. Huzzah. -nmatsakis
230 let closure_def_id = ast_util::local_def(id);
231 if self.closures_with_inferred_kinds.contains(&id) {
232 let mut deferred_call_resolutions =
233 self.fcx.remove_deferred_call_resolutions(closure_def_id);
234 for deferred_call_resolution in &mut deferred_call_resolutions {
235 deferred_call_resolution.resolve(self.fcx);
240 fn adjust_upvar_borrow_kind_for_consume(&self,
242 mode: euv::ConsumeMode)
244 debug!("adjust_upvar_borrow_kind_for_consume(cmt={:?}, mode={:?})",
247 // we only care about moves
249 euv::Copy => { return; }
253 // watch out for a move of the deref of a borrowed pointer;
254 // for that to be legal, the upvar would have to be borrowed
256 let guarantor = cmt.guarantor();
257 debug!("adjust_upvar_borrow_kind_for_consume: guarantor={:?}",
259 match guarantor.cat {
260 mc::cat_deref(_, _, mc::BorrowedPtr(..)) |
261 mc::cat_deref(_, _, mc::Implicit(..)) => {
263 mc::NoteUpvarRef(upvar_id) => {
264 debug!("adjust_upvar_borrow_kind_for_consume: \
265 setting upvar_id={:?} to by value",
268 // to move out of an upvar, this must be a FnOnce closure
269 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
271 let upvar_capture_map = &mut self.fcx
275 upvar_capture_map.insert(upvar_id, ty::UpvarCapture::ByValue);
277 mc::NoteClosureEnv(upvar_id) => {
278 // we get just a closureenv ref if this is a
279 // `move` closure, or if the upvar has already
280 // been inferred to by-value. In any case, we
281 // must still adjust the kind of the closure
282 // to be a FnOnce closure to permit moves out
283 // of the environment.
284 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
294 /// Indicates that `cmt` is being directly mutated (e.g., assigned
295 /// to). If cmt contains any by-ref upvars, this implies that
296 /// those upvars must be borrowed using an `&mut` borrow.
297 fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: mc::cmt<'tcx>) {
298 debug!("adjust_upvar_borrow_kind_for_mut(cmt={:?})",
301 match cmt.cat.clone() {
302 mc::cat_deref(base, _, mc::Unique) |
303 mc::cat_interior(base, _) |
304 mc::cat_downcast(base, _) => {
305 // Interior or owned data is mutable if base is
306 // mutable, so iterate to the base.
307 self.adjust_upvar_borrow_kind_for_mut(base);
310 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
311 mc::cat_deref(base, _, mc::Implicit(..)) => {
312 if !self.try_adjust_upvar_deref(&cmt.note, ty::MutBorrow) {
313 // assignment to deref of an `&mut`
314 // borrowed pointer implies that the
315 // pointer itself must be unique, but not
316 // necessarily *mutable*
317 self.adjust_upvar_borrow_kind_for_unique(base);
321 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
322 mc::cat_static_item |
325 mc::cat_upvar(..) => {
331 fn adjust_upvar_borrow_kind_for_unique(&self, cmt: mc::cmt<'tcx>) {
332 debug!("adjust_upvar_borrow_kind_for_unique(cmt={:?})",
335 match cmt.cat.clone() {
336 mc::cat_deref(base, _, mc::Unique) |
337 mc::cat_interior(base, _) |
338 mc::cat_downcast(base, _) => {
339 // Interior or owned data is unique if base is
341 self.adjust_upvar_borrow_kind_for_unique(base);
344 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
345 mc::cat_deref(base, _, mc::Implicit(..)) => {
346 if !self.try_adjust_upvar_deref(&cmt.note, ty::UniqueImmBorrow) {
347 // for a borrowed pointer to be unique, its
348 // base must be unique
349 self.adjust_upvar_borrow_kind_for_unique(base);
353 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
354 mc::cat_static_item |
357 mc::cat_upvar(..) => {
362 fn try_adjust_upvar_deref(&self,
364 borrow_kind: ty::BorrowKind)
367 assert!(match borrow_kind {
368 ty::MutBorrow => true,
369 ty::UniqueImmBorrow => true,
371 // imm borrows never require adjusting any kinds, so we don't wind up here
372 ty::ImmBorrow => false,
376 mc::NoteUpvarRef(upvar_id) => {
377 // if this is an implicit deref of an
378 // upvar, then we need to modify the
379 // borrow_kind of the upvar to make sure it
380 // is inferred to mutable if necessary
382 let upvar_capture_map = &mut self.fcx.inh.tables.borrow_mut().upvar_capture_map;
383 let ub = upvar_capture_map.get_mut(&upvar_id).unwrap();
384 self.adjust_upvar_borrow_kind(upvar_id, ub, borrow_kind);
387 // also need to be in an FnMut closure since this is not an ImmBorrow
388 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
392 mc::NoteClosureEnv(upvar_id) => {
393 // this kind of deref occurs in a `move` closure, or
394 // for a by-value upvar; in either case, to mutate an
395 // upvar, we need to be an FnMut closure
396 self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
406 /// We infer the borrow_kind with which to borrow upvars in a stack closure. The borrow_kind
407 /// basically follows a lattice of `imm < unique-imm < mut`, moving from left to right as needed
408 /// (but never right to left). Here the argument `mutbl` is the borrow_kind that is required by
409 /// some particular use.
410 fn adjust_upvar_borrow_kind(&self,
411 upvar_id: ty::UpvarId,
412 upvar_capture: &mut ty::UpvarCapture,
413 kind: ty::BorrowKind) {
414 debug!("adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
415 upvar_id, upvar_capture, kind);
417 match *upvar_capture {
418 ty::UpvarCapture::ByValue => {
419 // Upvar is already by-value, the strongest criteria.
421 ty::UpvarCapture::ByRef(ref mut upvar_borrow) => {
422 match (upvar_borrow.kind, kind) {
424 (ty::ImmBorrow, ty::UniqueImmBorrow) |
425 (ty::ImmBorrow, ty::MutBorrow) |
426 (ty::UniqueImmBorrow, ty::MutBorrow) => {
427 upvar_borrow.kind = kind;
430 (ty::ImmBorrow, ty::ImmBorrow) |
431 (ty::UniqueImmBorrow, ty::ImmBorrow) |
432 (ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
433 (ty::MutBorrow, _) => {
440 fn adjust_closure_kind(&self,
441 closure_id: ast::NodeId,
442 new_kind: ty::ClosureKind) {
443 debug!("adjust_closure_kind(closure_id={}, new_kind={:?})",
444 closure_id, new_kind);
446 if !self.closures_with_inferred_kinds.contains(&closure_id) {
450 let closure_def_id = ast_util::local_def(closure_id);
451 let closure_kinds = &mut self.fcx.inh.tables.borrow_mut().closure_kinds;
452 let existing_kind = *closure_kinds.get(&closure_def_id).unwrap();
454 debug!("adjust_closure_kind: closure_id={}, existing_kind={:?}, new_kind={:?}",
455 closure_id, existing_kind, new_kind);
457 match (existing_kind, new_kind) {
458 (ty::FnClosureKind, ty::FnClosureKind) |
459 (ty::FnMutClosureKind, ty::FnClosureKind) |
460 (ty::FnMutClosureKind, ty::FnMutClosureKind) |
461 (ty::FnOnceClosureKind, _) => {
465 (ty::FnClosureKind, ty::FnMutClosureKind) |
466 (ty::FnClosureKind, ty::FnOnceClosureKind) |
467 (ty::FnMutClosureKind, ty::FnOnceClosureKind) => {
468 // new kind is stronger than the old kind
469 closure_kinds.insert(closure_def_id, new_kind);
475 impl<'a, 'tcx, 'v> Visitor<'v> for AdjustBorrowKind<'a, 'tcx> {
476 fn visit_fn(&mut self,
477 fn_kind: visit::FnKind<'v>,
478 decl: &'v ast::FnDecl,
479 body: &'v ast::Block,
484 visit::FkItemFn(..) | visit::FkMethod(..) => {
485 // ignore nested fn items
487 visit::FkFnBlock => {
488 self.analyze_closure(id, decl, body);
489 visit::walk_fn(self, fn_kind, decl, body, span);
495 impl<'a,'tcx> euv::Delegate<'tcx> for AdjustBorrowKind<'a,'tcx> {
496 fn consume(&mut self,
497 _consume_id: ast::NodeId,
500 mode: euv::ConsumeMode)
502 debug!("consume(cmt={:?},mode={:?})", cmt, mode);
503 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
506 fn matched_pat(&mut self,
507 _matched_pat: &ast::Pat,
509 _mode: euv::MatchMode)
512 fn consume_pat(&mut self,
513 _consume_pat: &ast::Pat,
515 mode: euv::ConsumeMode)
517 debug!("consume_pat(cmt={:?},mode={:?})", cmt, mode);
518 self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
522 borrow_id: ast::NodeId,
525 _loan_region: ty::Region,
527 _loan_cause: euv::LoanCause)
529 debug!("borrow(borrow_id={}, cmt={:?}, bk={:?})",
534 ty::UniqueImmBorrow => {
535 self.adjust_upvar_borrow_kind_for_unique(cmt);
538 self.adjust_upvar_borrow_kind_for_mut(cmt);
543 fn decl_without_init(&mut self,
549 _assignment_id: ast::NodeId,
550 _assignment_span: Span,
551 assignee_cmt: mc::cmt<'tcx>,
552 _mode: euv::MutateMode)
554 debug!("mutate(assignee_cmt={:?})",
557 self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);