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::middle::expr_use_visitor as euv;
22 use rustc::middle::infer;
23 use rustc::middle::mem_categorization as mc;
24 use rustc::middle::mem_categorization::Categorization;
25 use rustc::middle::region;
26 use rustc::middle::ty;
29 use syntax::codemap::Span;
30 use syntax::ast::NodeId;
32 use rustc_front::hir::{Expr, FnDecl, Block, Pat};
33 use rustc_front::intravisit;
34 use rustc_front::intravisit::Visitor;
41 pub fn gather_loans_in_fn<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
46 move_data::MoveData<'tcx>) {
47 let mut glcx = GatherLoanCtxt {
49 all_loans: Vec::new(),
50 item_ub: bccx.tcx.region_maps.node_extent(body.id),
51 move_data: MoveData::new(),
52 move_error_collector: move_error::MoveErrorCollector::new(),
55 let param_env = ty::ParameterEnvironment::for_item(bccx.tcx, fn_id);
56 let infcx = infer::new_infer_ctxt(bccx.tcx, &bccx.tcx.tables, Some(param_env), false);
58 let mut euv = euv::ExprUseVisitor::new(&mut glcx, &infcx);
59 euv.walk_fn(decl, body);
62 glcx.report_potential_errors();
63 let GatherLoanCtxt { all_loans, move_data, .. } = glcx;
64 (all_loans, move_data)
67 struct GatherLoanCtxt<'a, 'tcx: 'a> {
68 bccx: &'a BorrowckCtxt<'a, 'tcx>,
69 move_data: move_data::MoveData<'tcx>,
70 move_error_collector: move_error::MoveErrorCollector<'tcx>,
71 all_loans: Vec<Loan<'tcx>>,
72 /// `item_ub` is used as an upper-bound on the lifetime whenever we
73 /// ask for the scope of an expression categorized as an upvar.
74 item_ub: region::CodeExtent,
77 impl<'a, 'tcx> euv::Delegate<'tcx> for GatherLoanCtxt<'a, 'tcx> {
79 consume_id: ast::NodeId,
82 mode: euv::ConsumeMode) {
83 debug!("consume(consume_id={}, cmt={:?}, mode={:?})",
84 consume_id, cmt, mode);
87 euv::Move(move_reason) => {
88 gather_moves::gather_move_from_expr(
89 self.bccx, &self.move_data, &mut self.move_error_collector,
90 consume_id, cmt, move_reason);
96 fn matched_pat(&mut self,
97 matched_pat: &hir::Pat,
99 mode: euv::MatchMode) {
100 debug!("matched_pat(matched_pat={:?}, cmt={:?}, mode={:?})",
105 if let Categorization::Downcast(..) = cmt.cat {
106 gather_moves::gather_match_variant(
107 self.bccx, &self.move_data, &mut self.move_error_collector,
108 matched_pat, cmt, mode);
112 fn consume_pat(&mut self,
113 consume_pat: &hir::Pat,
115 mode: euv::ConsumeMode) {
116 debug!("consume_pat(consume_pat={:?}, cmt={:?}, mode={:?})",
122 euv::Copy => { return; }
126 gather_moves::gather_move_from_pat(
127 self.bccx, &self.move_data, &mut self.move_error_collector,
132 borrow_id: ast::NodeId,
135 loan_region: ty::Region,
137 loan_cause: euv::LoanCause)
139 debug!("borrow(borrow_id={}, cmt={:?}, loan_region={:?}, \
140 bk={:?}, loan_cause={:?})",
141 borrow_id, cmt, loan_region,
144 self.guarantee_valid(borrow_id,
153 assignment_id: ast::NodeId,
154 assignment_span: Span,
155 assignee_cmt: mc::cmt<'tcx>,
156 mode: euv::MutateMode)
158 self.guarantee_assignment_valid(assignment_id,
164 fn decl_without_init(&mut self, id: ast::NodeId, span: Span) {
165 gather_moves::gather_decl(self.bccx, &self.move_data, id, span, id);
169 /// Implements the A-* rules in README.md.
170 fn check_aliasability<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
172 loan_cause: AliasableViolationKind,
174 req_kind: ty::BorrowKind)
177 let aliasability = cmt.freely_aliasable(bccx.tcx);
178 debug!("check_aliasability aliasability={:?} req_kind={:?}",
179 aliasability, req_kind);
181 match (aliasability, req_kind) {
182 (mc::Aliasability::NonAliasable, _) => {
183 /* Uniquely accessible path -- OK for `&` and `&mut` */
186 (mc::Aliasability::FreelyAliasable(mc::AliasableStatic), ty::ImmBorrow) => {
187 // Borrow of an immutable static item.
190 (mc::Aliasability::FreelyAliasable(mc::AliasableStaticMut), _) => {
191 // Even touching a static mut is considered unsafe. We assume the
192 // user knows what they're doing in these cases.
195 (mc::Aliasability::ImmutableUnique(_), ty::MutBorrow) => {
196 bccx.report_aliasability_violation(
199 mc::AliasableReason::UnaliasableImmutable);
202 (mc::Aliasability::FreelyAliasable(alias_cause), ty::UniqueImmBorrow) |
203 (mc::Aliasability::FreelyAliasable(alias_cause), ty::MutBorrow) => {
204 bccx.report_aliasability_violation(
216 /// Implements the M-* rules in README.md.
217 fn check_mutability<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
219 cause: AliasableViolationKind,
221 req_kind: ty::BorrowKind)
223 debug!("check_mutability(cause={:?} cmt={:?} req_kind={:?}",
224 cause, cmt, req_kind);
226 ty::UniqueImmBorrow | ty::ImmBorrow => {
228 // I am intentionally leaving this here to help
229 // refactoring if, in the future, we should add new
230 // kinds of mutability.
231 mc::McImmutable | mc::McDeclared | mc::McInherited => {
232 // both imm and mut data can be lent as imm;
233 // for mutable data, this is a freeze
240 // Only mutable data can be lent as mutable.
241 if !cmt.mutbl.is_mutable() {
242 Err(bccx.report(BckError { span: borrow_span,
253 impl<'a, 'tcx> GatherLoanCtxt<'a, 'tcx> {
254 pub fn tcx(&self) -> &'a ty::ctxt<'tcx> { self.bccx.tcx }
256 /// Guarantees that `cmt` is assignable, or reports an error.
257 fn guarantee_assignment_valid(&mut self,
258 assignment_id: ast::NodeId,
259 assignment_span: Span,
261 mode: euv::MutateMode) {
263 let opt_lp = opt_loan_path(&cmt);
264 debug!("guarantee_assignment_valid(assignment_id={}, cmt={:?}) opt_lp={:?}",
265 assignment_id, cmt, opt_lp);
267 if let Categorization::Local(..) = cmt.cat {
268 // Only re-assignments to locals require it to be
269 // mutable - this is checked in check_loans.
271 // Check that we don't allow assignments to non-mutable data.
272 if check_mutability(self.bccx, assignment_span, MutabilityViolation,
273 cmt.clone(), ty::MutBorrow).is_err() {
274 return; // reported an error, no sense in reporting more.
278 // Check that we don't allow assignments to aliasable data
279 if check_aliasability(self.bccx, assignment_span, MutabilityViolation,
280 cmt.clone(), ty::MutBorrow).is_err() {
281 return; // reported an error, no sense in reporting more.
286 if let Categorization::Local(..) = cmt.cat {
287 // Only re-assignments to locals require it to be
288 // mutable - this is checked in check_loans.
290 self.mark_loan_path_as_mutated(&lp);
292 gather_moves::gather_assignment(self.bccx, &self.move_data,
293 assignment_id, assignment_span,
297 // This can occur with e.g. `*foo() = 5`. In such
298 // cases, there is no need to check for conflicts
299 // with moves etc, just ignore.
304 /// Guarantees that `addr_of(cmt)` will be valid for the duration of `static_scope_r`, or
305 /// reports an error. This may entail taking out loans, which will be added to the
307 fn guarantee_valid(&mut self,
308 borrow_id: ast::NodeId,
311 req_kind: ty::BorrowKind,
312 loan_region: ty::Region,
313 cause: euv::LoanCause) {
314 debug!("guarantee_valid(borrow_id={}, cmt={:?}, \
315 req_mutbl={:?}, loan_region={:?})",
321 // a loan for the empty region can never be dereferenced, so
323 if loan_region == ty::ReEmpty {
327 // Check that the lifetime of the borrow does not exceed
328 // the lifetime of the data being borrowed.
329 if lifetime::guarantee_lifetime(self.bccx, self.item_ub,
330 borrow_span, cause, cmt.clone(), loan_region,
332 return; // reported an error, no sense in reporting more.
335 // Check that we don't allow mutable borrows of non-mutable data.
336 if check_mutability(self.bccx, borrow_span, BorrowViolation(cause),
337 cmt.clone(), req_kind).is_err() {
338 return; // reported an error, no sense in reporting more.
341 // Check that we don't allow mutable borrows of aliasable data.
342 if check_aliasability(self.bccx, borrow_span, BorrowViolation(cause),
343 cmt.clone(), req_kind).is_err() {
344 return; // reported an error, no sense in reporting more.
347 // Compute the restrictions that are required to enforce the
349 let restr = restrictions::compute_restrictions(
350 self.bccx, borrow_span, cause,
351 cmt.clone(), loan_region);
353 debug!("guarantee_valid(): restrictions={:?}", restr);
355 // Create the loan record (if needed).
356 let loan = match restr {
357 restrictions::Safe => {
358 // No restrictions---no loan record necessary
362 restrictions::SafeIf(loan_path, restricted_paths) => {
363 let loan_scope = match loan_region {
364 ty::ReScope(scope) => scope,
366 ty::ReFree(ref fr) => fr.scope,
368 ty::ReStatic => self.item_ub,
371 ty::ReLateBound(..) |
372 ty::ReEarlyBound(..) |
374 ty::ReSkolemized(..) => {
375 self.tcx().sess.span_bug(
377 &format!("invalid borrow lifetime: {:?}",
381 debug!("loan_scope = {:?}", loan_scope);
383 let borrow_scope = self.tcx().region_maps.node_extent(borrow_id);
384 let gen_scope = self.compute_gen_scope(borrow_scope, loan_scope);
385 debug!("gen_scope = {:?}", gen_scope);
387 let kill_scope = self.compute_kill_scope(loan_scope, &*loan_path);
388 debug!("kill_scope = {:?}", kill_scope);
390 if req_kind == ty::MutBorrow {
391 self.mark_loan_path_as_mutated(&*loan_path);
395 index: self.all_loans.len(),
396 loan_path: loan_path,
398 gen_scope: gen_scope,
399 kill_scope: kill_scope,
401 restricted_paths: restricted_paths,
407 debug!("guarantee_valid(borrow_id={}), loan={:?}",
410 // let loan_path = loan.loan_path;
411 // let loan_gen_scope = loan.gen_scope;
412 // let loan_kill_scope = loan.kill_scope;
413 self.all_loans.push(loan);
415 // if loan_gen_scope != borrow_id {
416 // FIXME(#6268) Nested method calls
418 // Typically, the scope of the loan includes the point at
419 // which the loan is originated. This
420 // This is a subtle case. See the test case
421 // <compile-fail/borrowck-bad-nested-calls-free.rs>
422 // to see what we are guarding against.
424 //let restr = restrictions::compute_restrictions(
425 // self.bccx, borrow_span, cmt, RESTR_EMPTY);
427 // let all_loans = &mut *self.all_loans; // FIXME(#5074)
429 // index: all_loans.len(),
430 // loan_path: loan_path,
432 // mutbl: ConstMutability,
433 // gen_scope: borrow_id,
434 // kill_scope: kill_scope,
435 // span: borrow_span,
436 // restrictions: restrictions
441 pub fn mark_loan_path_as_mutated(&self, loan_path: &LoanPath) {
442 //! For mutable loans of content whose mutability derives
443 //! from a local variable, mark the mutability decl as necessary.
445 match loan_path.kind {
447 LpUpvar(ty::UpvarId{ var_id: local_id, closure_expr_id: _ }) => {
448 self.tcx().used_mut_nodes.borrow_mut().insert(local_id);
450 LpDowncast(ref base, _) |
451 LpExtend(ref base, mc::McInherited, _) |
452 LpExtend(ref base, mc::McDeclared, _) => {
453 self.mark_loan_path_as_mutated(&**base);
455 LpExtend(_, mc::McImmutable, _) => {
461 pub fn compute_gen_scope(&self,
462 borrow_scope: region::CodeExtent,
463 loan_scope: region::CodeExtent)
464 -> region::CodeExtent {
465 //! Determine when to introduce the loan. Typically the loan
466 //! is introduced at the point of the borrow, but in some cases,
467 //! notably method arguments, the loan may be introduced only
468 //! later, once it comes into scope.
470 if self.bccx.tcx.region_maps.is_subscope_of(borrow_scope, loan_scope) {
477 pub fn compute_kill_scope(&self, loan_scope: region::CodeExtent, lp: &LoanPath<'tcx>)
478 -> region::CodeExtent {
479 //! Determine when the loan restrictions go out of scope.
480 //! This is either when the lifetime expires or when the
481 //! local variable which roots the loan-path goes out of scope,
482 //! whichever happens faster.
484 //! It may seem surprising that we might have a loan region
485 //! larger than the variable which roots the loan-path; this can
486 //! come about when variables of `&mut` type are re-borrowed,
487 //! as in this example:
489 //! fn counter<'a>(v: &'a mut Foo) -> &'a mut uint {
493 //! In this case, the reference (`'a`) outlives the
494 //! variable `v` that hosts it. Note that this doesn't come up
495 //! with immutable `&` pointers, because borrows of such pointers
496 //! do not require restrictions and hence do not cause a loan.
498 let lexical_scope = lp.kill_scope(self.bccx.tcx);
499 let rm = &self.bccx.tcx.region_maps;
500 if rm.is_subscope_of(lexical_scope, loan_scope) {
503 assert!(self.bccx.tcx.region_maps.is_subscope_of(loan_scope, lexical_scope));
508 pub fn report_potential_errors(&self) {
509 self.move_error_collector.report_potential_errors(self.bccx);
513 /// Context used while gathering loans on static initializers
515 /// This visitor walks static initializer's expressions and makes
516 /// sure the loans being taken are sound.
517 struct StaticInitializerCtxt<'a, 'tcx: 'a> {
518 bccx: &'a BorrowckCtxt<'a, 'tcx>,
521 impl<'a, 'tcx, 'v> Visitor<'v> for StaticInitializerCtxt<'a, 'tcx> {
522 fn visit_expr(&mut self, ex: &Expr) {
523 if let hir::ExprAddrOf(mutbl, ref base) = ex.node {
524 let infcx = infer::new_infer_ctxt(self.bccx.tcx, &self.bccx.tcx.tables, None, false);
525 let mc = mc::MemCategorizationContext::new(&infcx);
526 let base_cmt = mc.cat_expr(&**base).unwrap();
527 let borrow_kind = ty::BorrowKind::from_mutbl(mutbl);
528 // Check that we don't allow borrows of unsafe static items.
529 if check_aliasability(self.bccx, ex.span,
530 BorrowViolation(euv::AddrOf),
531 base_cmt, borrow_kind).is_err() {
532 return; // reported an error, no sense in reporting more.
536 intravisit::walk_expr(self, ex);
540 pub fn gather_loans_in_static_initializer(bccx: &mut BorrowckCtxt, expr: &hir::Expr) {
542 debug!("gather_loans_in_static_initializer(expr={:?})", expr);
544 let mut sicx = StaticInitializerCtxt {
548 sicx.visit_expr(expr);