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 // ----------------------------------------------------------------------
14 // The borrow check proceeds in two phases. In phase one, we gather the full
15 // set of loans that are required at any point. These are sorted according to
16 // their associated scopes. In phase two, checking loans, we will then make
17 // sure that all of these loans are honored.
20 use borrowck::move_data::MoveData;
21 use rustc::infer::InferCtxt;
22 use rustc::middle::expr_use_visitor as euv;
23 use rustc::middle::mem_categorization as mc;
24 use rustc::middle::mem_categorization::Categorization;
25 use rustc::middle::region;
26 use rustc::ty::{self, TyCtxt};
32 use self::restrictions::RestrictionResult;
39 pub fn gather_loans_in_fn<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
41 -> (Vec<Loan<'tcx>>, move_data::MoveData<'tcx>) {
42 let def_id = bccx.tcx.hir.body_owner_def_id(body);
43 let infcx = bccx.tcx.borrowck_fake_infer_ctxt(body);
44 let param_env = bccx.tcx.param_env(def_id);
45 let mut glcx = GatherLoanCtxt {
48 all_loans: Vec::new(),
49 item_ub: region::CodeExtent::Misc(body.node_id),
50 move_data: MoveData::new(),
51 move_error_collector: move_error::MoveErrorCollector::new(),
54 let body = glcx.bccx.tcx.hir.body(body);
55 euv::ExprUseVisitor::new(&mut glcx, &bccx.region_maps, &infcx, param_env).consume_body(body);
57 glcx.report_potential_errors();
58 let GatherLoanCtxt { all_loans, move_data, .. } = glcx;
59 (all_loans, move_data)
62 struct GatherLoanCtxt<'a, 'tcx: 'a> {
63 bccx: &'a BorrowckCtxt<'a, 'tcx>,
64 infcx: &'a InferCtxt<'a, 'tcx, 'tcx>,
65 move_data: move_data::MoveData<'tcx>,
66 move_error_collector: move_error::MoveErrorCollector<'tcx>,
67 all_loans: Vec<Loan<'tcx>>,
68 /// `item_ub` is used as an upper-bound on the lifetime whenever we
69 /// ask for the scope of an expression categorized as an upvar.
70 item_ub: region::CodeExtent,
73 impl<'a, 'tcx> euv::Delegate<'tcx> for GatherLoanCtxt<'a, 'tcx> {
75 consume_id: ast::NodeId,
78 mode: euv::ConsumeMode) {
79 debug!("consume(consume_id={}, cmt={:?}, mode={:?})",
80 consume_id, cmt, mode);
83 euv::Move(move_reason) => {
84 gather_moves::gather_move_from_expr(
85 self.bccx, &self.move_data, &mut self.move_error_collector,
86 consume_id, cmt, move_reason);
92 fn matched_pat(&mut self,
93 matched_pat: &hir::Pat,
95 mode: euv::MatchMode) {
96 debug!("matched_pat(matched_pat={:?}, cmt={:?}, mode={:?})",
101 if let Categorization::Downcast(..) = cmt.cat {
102 gather_moves::gather_match_variant(
103 self.bccx, &self.move_data, &mut self.move_error_collector,
104 matched_pat, cmt, mode);
108 fn consume_pat(&mut self,
109 consume_pat: &hir::Pat,
111 mode: euv::ConsumeMode) {
112 debug!("consume_pat(consume_pat={:?}, cmt={:?}, mode={:?})",
118 euv::Copy => { return; }
122 gather_moves::gather_move_from_pat(
123 self.bccx, &self.move_data, &mut self.move_error_collector,
128 borrow_id: ast::NodeId,
131 loan_region: ty::Region<'tcx>,
133 loan_cause: euv::LoanCause)
135 debug!("borrow(borrow_id={}, cmt={:?}, loan_region={:?}, \
136 bk={:?}, loan_cause={:?})",
137 borrow_id, cmt, loan_region,
140 self.guarantee_valid(borrow_id,
149 assignment_id: ast::NodeId,
150 assignment_span: Span,
151 assignee_cmt: mc::cmt<'tcx>,
152 mode: euv::MutateMode)
154 self.guarantee_assignment_valid(assignment_id,
160 fn decl_without_init(&mut self, id: ast::NodeId, _span: Span) {
161 let ty = self.infcx.tables.borrow().node_id_to_type(id);
162 gather_moves::gather_decl(self.bccx, &self.move_data, id, ty);
166 /// Implements the A-* rules in README.md.
167 fn check_aliasability<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
169 loan_cause: AliasableViolationKind,
171 req_kind: ty::BorrowKind)
174 let aliasability = cmt.freely_aliasable();
175 debug!("check_aliasability aliasability={:?} req_kind={:?}",
176 aliasability, req_kind);
178 match (aliasability, req_kind) {
179 (mc::Aliasability::NonAliasable, _) => {
180 /* Uniquely accessible path -- OK for `&` and `&mut` */
183 (mc::Aliasability::FreelyAliasable(mc::AliasableStatic), ty::ImmBorrow) => {
184 // Borrow of an immutable static item.
187 (mc::Aliasability::FreelyAliasable(mc::AliasableStaticMut), _) => {
188 // Even touching a static mut is considered unsafe. We assume the
189 // user knows what they're doing in these cases.
192 (mc::Aliasability::FreelyAliasable(alias_cause), ty::UniqueImmBorrow) |
193 (mc::Aliasability::FreelyAliasable(alias_cause), ty::MutBorrow) => {
194 bccx.report_aliasability_violation(
207 /// Implements the M-* rules in README.md.
208 fn check_mutability<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
210 cause: AliasableViolationKind,
212 req_kind: ty::BorrowKind)
214 debug!("check_mutability(cause={:?} cmt={:?} req_kind={:?}",
215 cause, cmt, req_kind);
217 ty::UniqueImmBorrow | ty::ImmBorrow => {
219 // I am intentionally leaving this here to help
220 // refactoring if, in the future, we should add new
221 // kinds of mutability.
222 mc::McImmutable | mc::McDeclared | mc::McInherited => {
223 // both imm and mut data can be lent as imm;
224 // for mutable data, this is a freeze
231 // Only mutable data can be lent as mutable.
232 if !cmt.mutbl.is_mutable() {
233 Err(bccx.report(BckError { span: borrow_span,
244 impl<'a, 'tcx> GatherLoanCtxt<'a, 'tcx> {
245 pub fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.bccx.tcx }
247 /// Guarantees that `cmt` is assignable, or reports an error.
248 fn guarantee_assignment_valid(&mut self,
249 assignment_id: ast::NodeId,
250 assignment_span: Span,
252 mode: euv::MutateMode) {
254 let opt_lp = opt_loan_path(&cmt);
255 debug!("guarantee_assignment_valid(assignment_id={}, cmt={:?}) opt_lp={:?}",
256 assignment_id, cmt, opt_lp);
258 if let Categorization::Local(..) = cmt.cat {
259 // Only re-assignments to locals require it to be
260 // mutable - this is checked in check_loans.
262 // Check that we don't allow assignments to non-mutable data.
263 if check_mutability(self.bccx, assignment_span, MutabilityViolation,
264 cmt.clone(), ty::MutBorrow).is_err() {
265 return; // reported an error, no sense in reporting more.
269 // Check that we don't allow assignments to aliasable data
270 if check_aliasability(self.bccx, assignment_span, MutabilityViolation,
271 cmt.clone(), ty::MutBorrow).is_err() {
272 return; // reported an error, no sense in reporting more.
277 if let Categorization::Local(..) = cmt.cat {
278 // Only re-assignments to locals require it to be
279 // mutable - this is checked in check_loans.
281 self.mark_loan_path_as_mutated(&lp);
283 gather_moves::gather_assignment(self.bccx, &self.move_data,
284 assignment_id, assignment_span,
288 // This can occur with e.g. `*foo() = 5`. In such
289 // cases, there is no need to check for conflicts
290 // with moves etc, just ignore.
295 /// Guarantees that `addr_of(cmt)` will be valid for the duration of `static_scope_r`, or
296 /// reports an error. This may entail taking out loans, which will be added to the
298 fn guarantee_valid(&mut self,
299 borrow_id: ast::NodeId,
302 req_kind: ty::BorrowKind,
303 loan_region: ty::Region<'tcx>,
304 cause: euv::LoanCause) {
305 debug!("guarantee_valid(borrow_id={}, cmt={:?}, \
306 req_mutbl={:?}, loan_region={:?})",
312 // a loan for the empty region can never be dereferenced, so
314 if *loan_region == ty::ReEmpty {
318 // Check that the lifetime of the borrow does not exceed
319 // the lifetime of the data being borrowed.
320 if lifetime::guarantee_lifetime(self.bccx, self.item_ub,
321 borrow_span, cause, cmt.clone(), loan_region,
323 return; // reported an error, no sense in reporting more.
326 // Check that we don't allow mutable borrows of non-mutable data.
327 if check_mutability(self.bccx, borrow_span, BorrowViolation(cause),
328 cmt.clone(), req_kind).is_err() {
329 return; // reported an error, no sense in reporting more.
332 // Check that we don't allow mutable borrows of aliasable data.
333 if check_aliasability(self.bccx, borrow_span, BorrowViolation(cause),
334 cmt.clone(), req_kind).is_err() {
335 return; // reported an error, no sense in reporting more.
338 // Compute the restrictions that are required to enforce the
340 let restr = restrictions::compute_restrictions(
341 self.bccx, borrow_span, cause,
342 cmt.clone(), loan_region);
344 debug!("guarantee_valid(): restrictions={:?}", restr);
346 // Create the loan record (if needed).
347 let loan = match restr {
348 RestrictionResult::Safe => {
349 // No restrictions---no loan record necessary
353 RestrictionResult::SafeIf(loan_path, restricted_paths) => {
354 let loan_scope = match *loan_region {
355 ty::ReScope(scope) => scope,
357 ty::ReEarlyBound(ref br) => {
358 self.bccx.region_maps.early_free_extent(self.tcx(), br)
361 ty::ReFree(ref fr) => {
362 self.bccx.region_maps.free_extent(self.tcx(), fr)
365 ty::ReStatic => self.item_ub,
368 ty::ReLateBound(..) |
370 ty::ReSkolemized(..) |
374 "invalid borrow lifetime: {:?}",
378 debug!("loan_scope = {:?}", loan_scope);
380 let borrow_scope = region::CodeExtent::Misc(borrow_id);
381 let gen_scope = self.compute_gen_scope(borrow_scope, loan_scope);
382 debug!("gen_scope = {:?}", gen_scope);
384 let kill_scope = self.compute_kill_scope(loan_scope, &loan_path);
385 debug!("kill_scope = {:?}", kill_scope);
387 if req_kind == ty::MutBorrow {
388 self.mark_loan_path_as_mutated(&loan_path);
392 index: self.all_loans.len(),
393 loan_path: loan_path,
395 gen_scope: gen_scope,
396 kill_scope: kill_scope,
398 restricted_paths: restricted_paths,
404 debug!("guarantee_valid(borrow_id={}), loan={:?}",
407 // let loan_path = loan.loan_path;
408 // let loan_gen_scope = loan.gen_scope;
409 // let loan_kill_scope = loan.kill_scope;
410 self.all_loans.push(loan);
412 // if loan_gen_scope != borrow_id {
413 // FIXME(#6268) Nested method calls
415 // Typically, the scope of the loan includes the point at
416 // which the loan is originated. This
417 // This is a subtle case. See the test case
418 // <compile-fail/borrowck-bad-nested-calls-free.rs>
419 // to see what we are guarding against.
421 //let restr = restrictions::compute_restrictions(
422 // self.bccx, borrow_span, cmt, RESTR_EMPTY);
424 // let all_loans = &mut *self.all_loans; // FIXME(#5074)
426 // index: all_loans.len(),
427 // loan_path: loan_path,
429 // mutbl: ConstMutability,
430 // gen_scope: borrow_id,
431 // kill_scope: kill_scope,
432 // span: borrow_span,
433 // restrictions: restrictions
438 pub fn mark_loan_path_as_mutated(&self, loan_path: &LoanPath) {
439 //! For mutable loans of content whose mutability derives
440 //! from a local variable, mark the mutability decl as necessary.
442 match loan_path.kind {
444 LpUpvar(ty::UpvarId{ var_id: local_id, closure_expr_id: _ }) => {
445 self.tcx().used_mut_nodes.borrow_mut().insert(local_id);
447 LpDowncast(ref base, _) |
448 LpExtend(ref base, mc::McInherited, _) |
449 LpExtend(ref base, mc::McDeclared, _) => {
450 self.mark_loan_path_as_mutated(&base);
452 LpExtend(_, mc::McImmutable, _) => {
458 pub fn compute_gen_scope(&self,
459 borrow_scope: region::CodeExtent,
460 loan_scope: region::CodeExtent)
461 -> region::CodeExtent {
462 //! Determine when to introduce the loan. Typically the loan
463 //! is introduced at the point of the borrow, but in some cases,
464 //! notably method arguments, the loan may be introduced only
465 //! later, once it comes into scope.
467 if self.bccx.region_maps.is_subscope_of(borrow_scope, loan_scope) {
474 pub fn compute_kill_scope(&self, loan_scope: region::CodeExtent, lp: &LoanPath<'tcx>)
475 -> region::CodeExtent {
476 //! Determine when the loan restrictions go out of scope.
477 //! This is either when the lifetime expires or when the
478 //! local variable which roots the loan-path goes out of scope,
479 //! whichever happens faster.
481 //! It may seem surprising that we might have a loan region
482 //! larger than the variable which roots the loan-path; this can
483 //! come about when variables of `&mut` type are re-borrowed,
484 //! as in this example:
486 //! struct Foo { counter: u32 }
488 //! fn counter<'a>(v: &'a mut Foo) -> &'a mut u32 {
492 //! In this case, the reference (`'a`) outlives the
493 //! variable `v` that hosts it. Note that this doesn't come up
494 //! with immutable `&` pointers, because borrows of such pointers
495 //! do not require restrictions and hence do not cause a loan.
497 let lexical_scope = lp.kill_scope(self.bccx);
498 if self.bccx.region_maps.is_subscope_of(lexical_scope, loan_scope) {
501 assert!(self.bccx.region_maps.is_subscope_of(loan_scope, lexical_scope));
506 pub fn report_potential_errors(&self) {
507 self.move_error_collector.report_potential_errors(self.bccx);