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};
50 use syntax::codemap::Span;
51 use syntax::visit::{self, Visitor};
52 use util::ppaux::Repr;
54 ///////////////////////////////////////////////////////////////////////////
55 // PUBLIC ENTRY POINTS
57 pub fn closure_analyze_fn(fcx: &FnCtxt,
61 let mut seed = SeedBorrowKind::new(fcx);
62 seed.visit_block(body);
64 let mut adjust = AdjustBorrowKind::new(fcx);
65 adjust.analyze_fn(decl, body);
68 ///////////////////////////////////////////////////////////////////////////
71 struct SeedBorrowKind<'a,'tcx:'a> {
72 fcx: &'a FnCtxt<'a,'tcx>,
75 impl<'a, 'tcx, 'v> Visitor<'v> for SeedBorrowKind<'a, 'tcx> {
76 fn visit_expr(&mut self, expr: &ast::Expr) {
78 ast::ExprClosure(cc, _, _, ref body) => {
79 self.check_closure(expr, cc, &**body);
85 visit::walk_expr(self, expr);
88 fn visit_fn(&mut self,
89 fn_kind: visit::FnKind<'v>,
90 decl: &'v ast::FnDecl,
91 block: &'v ast::Block,
96 visit::FkItemFn(..) | visit::FkMethod(..) => {
97 // ignore nested fn items
100 visit::walk_fn(self, fn_kind, decl, block, span);
106 impl<'a,'tcx> SeedBorrowKind<'a,'tcx> {
107 fn new(fcx: &'a FnCtxt<'a,'tcx>) -> SeedBorrowKind<'a,'tcx> {
108 SeedBorrowKind { fcx: fcx }
111 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
115 fn infcx(&self) -> &'a InferCtxt<'a,'tcx> {
119 fn check_closure(&mut self,
121 capture_clause: ast::CaptureClause,
124 match capture_clause {
125 ast::CaptureByValue => {}
127 ty::with_freevars(self.tcx(), expr.id, |freevars| {
128 for freevar in freevars.iter() {
129 let var_node_id = freevar.def.local_node_id();
130 let upvar_id = ty::UpvarId { var_id: var_node_id,
131 closure_expr_id: expr.id };
132 debug!("seed upvar_id {:?}", upvar_id);
133 let origin = UpvarRegion(upvar_id, expr.span);
134 let freevar_region = self.infcx().next_region_var(origin);
135 let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow,
136 region: freevar_region };
137 self.fcx.inh.upvar_borrow_map.borrow_mut().insert(upvar_id,
146 ///////////////////////////////////////////////////////////////////////////
147 // ADJUST BORROW KIND
149 struct AdjustBorrowKind<'a,'tcx:'a> {
150 fcx: &'a FnCtxt<'a,'tcx>
153 impl<'a,'tcx> AdjustBorrowKind<'a,'tcx>{
154 fn new(fcx: &'a FnCtxt<'a,'tcx>) -> AdjustBorrowKind<'a,'tcx> {
155 AdjustBorrowKind { fcx: fcx }
158 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
162 fn analyze_fn(&mut self, decl: &ast::FnDecl, body: &ast::Block) {
164 * Analysis starting point.
167 self.visit_block(body);
169 debug!("analyzing fn body with id {}", body.id);
171 let mut euv = euv::ExprUseVisitor::new(self, self.fcx);
172 euv.walk_fn(decl, body);
175 /// Indicates that `cmt` is being directly mutated (e.g., assigned
176 /// to). If cmt contains any by-ref upvars, this implies that
177 /// those upvars must be borrowed using an `&mut` borow.
178 fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: mc::cmt<'tcx>) {
179 debug!("adjust_upvar_borrow_kind_for_mut(cmt={})",
180 cmt.repr(self.tcx()));
182 match cmt.cat.clone() {
183 mc::cat_deref(base, _, mc::Unique) |
184 mc::cat_interior(base, _) |
185 mc::cat_downcast(base, _) => {
186 // Interior or owned data is mutable if base is
187 // mutable, so iterate to the base.
188 self.adjust_upvar_borrow_kind_for_mut(base);
191 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
192 mc::cat_deref(base, _, mc::Implicit(..)) => {
193 if let mc::NoteUpvarRef(upvar_id) = cmt.note {
194 // if this is an implicit deref of an
195 // upvar, then we need to modify the
196 // borrow_kind of the upvar to make sure it
197 // is inferred to mutable if necessary
198 let mut upvar_borrow_map = self.fcx.inh.upvar_borrow_map.borrow_mut();
199 let ub = &mut upvar_borrow_map[upvar_id];
200 self.adjust_upvar_borrow_kind(upvar_id, ub, ty::MutBorrow);
202 // assignment to deref of an `&mut`
203 // borrowed pointer implies that the
204 // pointer itself must be unique, but not
205 // necessarily *mutable*
206 self.adjust_upvar_borrow_kind_for_unique(base);
210 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
211 mc::cat_static_item |
214 mc::cat_upvar(..) => {
220 fn adjust_upvar_borrow_kind_for_unique(&self, cmt: mc::cmt<'tcx>) {
221 debug!("adjust_upvar_borrow_kind_for_unique(cmt={})",
222 cmt.repr(self.tcx()));
224 match cmt.cat.clone() {
225 mc::cat_deref(base, _, mc::Unique) |
226 mc::cat_interior(base, _) |
227 mc::cat_downcast(base, _) => {
228 // Interior or owned data is unique if base is
230 self.adjust_upvar_borrow_kind_for_unique(base);
233 mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
234 mc::cat_deref(base, _, mc::Implicit(..)) => {
235 if let mc::NoteUpvarRef(upvar_id) = cmt.note {
236 // if this is an implicit deref of an
237 // upvar, then we need to modify the
238 // borrow_kind of the upvar to make sure it
239 // is inferred to unique if necessary
240 let mut ub = self.fcx.inh.upvar_borrow_map.borrow_mut();
241 let ub = &mut ub[upvar_id];
242 self.adjust_upvar_borrow_kind(upvar_id, ub, ty::UniqueImmBorrow);
244 // for a borrowed pointer to be unique, its
245 // base must be unique
246 self.adjust_upvar_borrow_kind_for_unique(base);
250 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
251 mc::cat_static_item |
254 mc::cat_upvar(..) => {
259 /// We infer the borrow_kind with which to borrow upvars in a stack closure. The borrow_kind
260 /// basically follows a lattice of `imm < unique-imm < mut`, moving from left to right as needed
261 /// (but never right to left). Here the argument `mutbl` is the borrow_kind that is required by
262 /// some particular use.
263 fn adjust_upvar_borrow_kind(&self,
264 upvar_id: ty::UpvarId,
265 upvar_borrow: &mut ty::UpvarBorrow,
266 kind: ty::BorrowKind) {
267 debug!("adjust_upvar_borrow_kind: id={:?} kind=({:?} -> {:?})",
268 upvar_id, upvar_borrow.kind, kind);
270 match (upvar_borrow.kind, kind) {
272 (ty::ImmBorrow, ty::UniqueImmBorrow) |
273 (ty::ImmBorrow, ty::MutBorrow) |
274 (ty::UniqueImmBorrow, ty::MutBorrow) => {
275 upvar_borrow.kind = kind;
278 (ty::ImmBorrow, ty::ImmBorrow) |
279 (ty::UniqueImmBorrow, ty::ImmBorrow) |
280 (ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
281 (ty::MutBorrow, _) => {
287 impl<'a, 'tcx, 'v> Visitor<'v> for AdjustBorrowKind<'a, 'tcx> {
288 fn visit_fn(&mut self,
289 fn_kind: visit::FnKind<'v>,
290 decl: &'v ast::FnDecl,
291 body: &'v ast::Block,
296 visit::FkItemFn(..) | visit::FkMethod(..) => {
297 // ignore nested fn items
299 visit::FkFnBlock => {
300 self.analyze_fn(decl, body);
301 visit::walk_fn(self, fn_kind, decl, body, span);
307 impl<'a,'tcx> euv::Delegate<'tcx> for AdjustBorrowKind<'a,'tcx> {
308 fn consume(&mut self,
309 _consume_id: ast::NodeId,
312 _mode: euv::ConsumeMode)
315 fn matched_pat(&mut self,
316 _matched_pat: &ast::Pat,
318 _mode: euv::MatchMode)
321 fn consume_pat(&mut self,
322 _consume_pat: &ast::Pat,
324 _mode: euv::ConsumeMode)
328 borrow_id: ast::NodeId,
331 _loan_region: ty::Region,
333 _loan_cause: euv::LoanCause)
335 debug!("borrow(borrow_id={}, cmt={}, bk={:?})",
336 borrow_id, cmt.repr(self.tcx()), bk);
340 ty::UniqueImmBorrow => {
341 self.adjust_upvar_borrow_kind_for_unique(cmt);
344 self.adjust_upvar_borrow_kind_for_mut(cmt);
349 fn decl_without_init(&mut self,
355 _assignment_id: ast::NodeId,
356 _assignment_span: Span,
357 assignee_cmt: mc::cmt<'tcx>,
358 _mode: euv::MutateMode)
360 debug!("mutate(assignee_cmt={})",
361 assignee_cmt.repr(self.tcx()));
363 self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);