1 // Copyright 2012-2013 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 // Phase 2 of check: we walk down the tree and check that:
15 // 1. assignments are always made to mutable locations;
16 // 2. loans made in overlapping scopes do not conflict
17 // 3. assignments do not affect things loaned out as immutable
18 // 4. moves do not affect things loaned out in any way
19 use self::UseError::*;
22 use borrowck::InteriorKind::{InteriorElement, InteriorField};
23 use rustc::middle::expr_use_visitor as euv;
24 use rustc::middle::expr_use_visitor::MutateMode;
25 use rustc::middle::mem_categorization as mc;
26 use rustc::middle::mem_categorization::Categorization;
27 use rustc::middle::region;
28 use rustc::ty::{self, TyCtxt};
35 // FIXME (#16118): These functions are intended to allow the borrow checker to
36 // be less precise in its handling of Box while still allowing moves out of a
37 // Box. They should be removed when Unique is removed from LoanPath.
39 fn owned_ptr_base_path<'a, 'tcx>(loan_path: &'a LoanPath<'tcx>) -> &'a LoanPath<'tcx> {
40 //! Returns the base of the leftmost dereference of an Unique in
41 //! `loan_path`. If there is no dereference of an Unique in `loan_path`,
42 //! then it just returns `loan_path` itself.
44 return match helper(loan_path) {
45 Some(new_loan_path) => new_loan_path,
46 None => loan_path.clone()
49 fn helper<'a, 'tcx>(loan_path: &'a LoanPath<'tcx>) -> Option<&'a LoanPath<'tcx>> {
50 match loan_path.kind {
51 LpVar(_) | LpUpvar(_) => None,
52 LpExtend(ref lp_base, _, LpDeref(mc::Unique)) => {
53 match helper(&lp_base) {
55 None => Some(&lp_base)
58 LpDowncast(ref lp_base, _) |
59 LpExtend(ref lp_base, ..) => helper(&lp_base)
64 fn owned_ptr_base_path_rc<'tcx>(loan_path: &Rc<LoanPath<'tcx>>) -> Rc<LoanPath<'tcx>> {
65 //! The equivalent of `owned_ptr_base_path` for an &Rc<LoanPath> rather than
68 return match helper(loan_path) {
69 Some(new_loan_path) => new_loan_path,
70 None => loan_path.clone()
73 fn helper<'tcx>(loan_path: &Rc<LoanPath<'tcx>>) -> Option<Rc<LoanPath<'tcx>>> {
74 match loan_path.kind {
75 LpVar(_) | LpUpvar(_) => None,
76 LpExtend(ref lp_base, _, LpDeref(mc::Unique)) => {
77 match helper(lp_base) {
79 None => Some(lp_base.clone())
82 LpDowncast(ref lp_base, _) |
83 LpExtend(ref lp_base, ..) => helper(lp_base)
88 struct CheckLoanCtxt<'a, 'tcx: 'a> {
89 bccx: &'a BorrowckCtxt<'a, 'tcx>,
90 dfcx_loans: &'a LoanDataFlow<'a, 'tcx>,
91 move_data: &'a move_data::FlowedMoveData<'a, 'tcx>,
92 all_loans: &'a [Loan<'tcx>],
93 param_env: ty::ParamEnv<'tcx>,
96 impl<'a, 'tcx> euv::Delegate<'tcx> for CheckLoanCtxt<'a, 'tcx> {
98 consume_id: ast::NodeId,
101 mode: euv::ConsumeMode) {
102 debug!("consume(consume_id={}, cmt={:?}, mode={:?})",
103 consume_id, cmt, mode);
105 self.consume_common(consume_id, consume_span, cmt, mode);
108 fn matched_pat(&mut self,
109 _matched_pat: &hir::Pat,
111 _mode: euv::MatchMode) { }
113 fn consume_pat(&mut self,
114 consume_pat: &hir::Pat,
116 mode: euv::ConsumeMode) {
117 debug!("consume_pat(consume_pat={:?}, cmt={:?}, mode={:?})",
122 self.consume_common(consume_pat.id, consume_pat.span, cmt, mode);
126 borrow_id: ast::NodeId,
129 loan_region: ty::Region<'tcx>,
131 loan_cause: euv::LoanCause)
133 debug!("borrow(borrow_id={}, cmt={:?}, loan_region={:?}, \
134 bk={:?}, loan_cause={:?})",
135 borrow_id, cmt, loan_region,
138 if let Some(lp) = opt_loan_path(&cmt) {
139 let moved_value_use_kind = match loan_cause {
140 euv::ClosureCapture(_) => MovedInCapture,
143 self.check_if_path_is_moved(borrow_id, borrow_span, moved_value_use_kind, &lp);
146 self.check_for_conflicting_loans(borrow_id);
150 assignment_id: ast::NodeId,
151 assignment_span: Span,
152 assignee_cmt: mc::cmt<'tcx>,
153 mode: euv::MutateMode)
155 debug!("mutate(assignment_id={}, assignee_cmt={:?})",
156 assignment_id, assignee_cmt);
158 if let Some(lp) = opt_loan_path(&assignee_cmt) {
160 MutateMode::Init | MutateMode::JustWrite => {
161 // In a case like `path = 1`, then path does not
162 // have to be *FULLY* initialized, but we still
163 // must be careful lest it contains derefs of
165 self.check_if_assigned_path_is_moved(assignee_cmt.id,
170 MutateMode::WriteAndRead => {
171 // In a case like `path += 1`, then path must be
172 // fully initialized, since we will read it before
174 self.check_if_path_is_moved(assignee_cmt.id,
181 self.check_assignment(assignment_id, assignment_span, assignee_cmt);
184 fn decl_without_init(&mut self, _id: ast::NodeId, _span: Span) { }
187 pub fn check_loans<'a, 'b, 'c, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
188 dfcx_loans: &LoanDataFlow<'b, 'tcx>,
189 move_data: &move_data::FlowedMoveData<'c, 'tcx>,
190 all_loans: &[Loan<'tcx>],
192 debug!("check_loans(body id={})", body.value.id);
194 let def_id = bccx.tcx.hir.body_owner_def_id(body.id());
195 let infcx = bccx.tcx.borrowck_fake_infer_ctxt(body.id());
196 let param_env = bccx.tcx.param_env(def_id);
197 let mut clcx = CheckLoanCtxt {
199 dfcx_loans: dfcx_loans,
200 move_data: move_data,
201 all_loans: all_loans,
204 euv::ExprUseVisitor::new(&mut clcx, &bccx.region_maps, &infcx, param_env).consume_body(body);
208 enum UseError<'tcx> {
210 UseWhileBorrowed(/*loan*/Rc<LoanPath<'tcx>>, /*loan*/Span)
213 fn compatible_borrow_kinds(borrow_kind1: ty::BorrowKind,
214 borrow_kind2: ty::BorrowKind)
216 borrow_kind1 == ty::ImmBorrow && borrow_kind2 == ty::ImmBorrow
219 impl<'a, 'tcx> CheckLoanCtxt<'a, 'tcx> {
220 pub fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.bccx.tcx }
222 pub fn each_issued_loan<F>(&self, node: ast::NodeId, mut op: F) -> bool where
223 F: FnMut(&Loan<'tcx>) -> bool,
225 //! Iterates over each loan that has been issued
226 //! on entrance to `node`, regardless of whether it is
227 //! actually *in scope* at that point. Sometimes loans
228 //! are issued for future scopes and thus they may have been
229 //! *issued* but not yet be in effect.
231 self.dfcx_loans.each_bit_on_entry(node, |loan_index| {
232 let loan = &self.all_loans[loan_index];
237 pub fn each_in_scope_loan<F>(&self, scope: region::CodeExtent, mut op: F) -> bool where
238 F: FnMut(&Loan<'tcx>) -> bool,
240 //! Like `each_issued_loan()`, but only considers loans that are
241 //! currently in scope.
243 self.each_issued_loan(scope.node_id(), |loan| {
244 if self.bccx.region_maps.is_subscope_of(scope, loan.kill_scope) {
252 fn each_in_scope_loan_affecting_path<F>(&self,
253 scope: region::CodeExtent,
254 loan_path: &LoanPath<'tcx>,
257 F: FnMut(&Loan<'tcx>) -> bool,
259 //! Iterates through all of the in-scope loans affecting `loan_path`,
260 //! calling `op`, and ceasing iteration if `false` is returned.
262 // First, we check for a loan restricting the path P being used. This
263 // accounts for borrows of P but also borrows of subpaths, like P.a.b.
264 // Consider the following example:
266 // let x = &mut a.b.c; // Restricts a, a.b, and a.b.c
267 // let y = a; // Conflicts with restriction
269 let loan_path = owned_ptr_base_path(loan_path);
270 let cont = self.each_in_scope_loan(scope, |loan| {
272 for restr_path in &loan.restricted_paths {
273 if **restr_path == *loan_path {
287 // Next, we must check for *loans* (not restrictions) on the path P or
288 // any base path. This rejects examples like the following:
293 // Limiting this search to *loans* and not *restrictions* means that
294 // examples like the following continue to work:
299 let mut loan_path = loan_path;
301 match loan_path.kind {
302 LpVar(_) | LpUpvar(_) => {
305 LpDowncast(ref lp_base, _) |
306 LpExtend(ref lp_base, ..) => {
307 loan_path = &lp_base;
311 let cont = self.each_in_scope_loan(scope, |loan| {
312 if *loan.loan_path == *loan_path {
327 pub fn loans_generated_by(&self, node: ast::NodeId) -> Vec<usize> {
328 //! Returns a vector of the loans that are generated as
331 let mut result = Vec::new();
332 self.dfcx_loans.each_gen_bit(node, |loan_index| {
333 result.push(loan_index);
339 pub fn check_for_conflicting_loans(&self, node: ast::NodeId) {
340 //! Checks to see whether any of the loans that are issued
341 //! on entrance to `node` conflict with loans that have already been
342 //! issued when we enter `node` (for example, we do not
343 //! permit two `&mut` borrows of the same variable).
345 //! (Note that some loans can be *issued* without necessarily
346 //! taking effect yet.)
348 debug!("check_for_conflicting_loans(node={:?})", node);
350 let new_loan_indices = self.loans_generated_by(node);
351 debug!("new_loan_indices = {:?}", new_loan_indices);
353 for &new_loan_index in &new_loan_indices {
354 self.each_issued_loan(node, |issued_loan| {
355 let new_loan = &self.all_loans[new_loan_index];
356 // Only report an error for the first issued loan that conflicts
357 // to avoid O(n^2) errors.
358 self.report_error_if_loans_conflict(issued_loan, new_loan)
362 for (i, &x) in new_loan_indices.iter().enumerate() {
363 let old_loan = &self.all_loans[x];
364 for &y in &new_loan_indices[(i+1) ..] {
365 let new_loan = &self.all_loans[y];
366 self.report_error_if_loans_conflict(old_loan, new_loan);
371 pub fn report_error_if_loans_conflict(&self,
372 old_loan: &Loan<'tcx>,
373 new_loan: &Loan<'tcx>)
375 //! Checks whether `old_loan` and `new_loan` can safely be issued
378 debug!("report_error_if_loans_conflict(old_loan={:?}, new_loan={:?})",
382 // Should only be called for loans that are in scope at the same time.
383 assert!(self.bccx.region_maps.scopes_intersect(old_loan.kill_scope,
384 new_loan.kill_scope));
386 self.report_error_if_loan_conflicts_with_restriction(
387 old_loan, new_loan, old_loan, new_loan) &&
388 self.report_error_if_loan_conflicts_with_restriction(
389 new_loan, old_loan, old_loan, new_loan)
392 pub fn report_error_if_loan_conflicts_with_restriction(&self,
395 old_loan: &Loan<'tcx>,
396 new_loan: &Loan<'tcx>)
398 //! Checks whether the restrictions introduced by `loan1` would
399 //! prohibit `loan2`. Returns false if an error is reported.
401 debug!("report_error_if_loan_conflicts_with_restriction(\
402 loan1={:?}, loan2={:?})",
406 if compatible_borrow_kinds(loan1.kind, loan2.kind) {
410 let loan2_base_path = owned_ptr_base_path_rc(&loan2.loan_path);
411 for restr_path in &loan1.restricted_paths {
412 if *restr_path != loan2_base_path { continue; }
414 // If new_loan is something like `x.a`, and old_loan is something like `x.b`, we would
415 // normally generate a rather confusing message (in this case, for multiple mutable
418 // error: cannot borrow `x.b` as mutable more than once at a time
419 // note: previous borrow of `x.a` occurs here; the mutable borrow prevents
420 // subsequent moves, borrows, or modification of `x.a` until the borrow ends
422 // What we want to do instead is get the 'common ancestor' of the two borrow paths and
423 // use that for most of the message instead, giving is something like this:
425 // error: cannot borrow `x` as mutable more than once at a time
426 // note: previous borrow of `x` occurs here (through borrowing `x.a`); the mutable
427 // borrow prevents subsequent moves, borrows, or modification of `x` until the
430 let common = new_loan.loan_path.common(&old_loan.loan_path);
431 let (nl, ol, new_loan_msg, old_loan_msg) = {
432 if new_loan.loan_path.has_fork(&old_loan.loan_path) && common.is_some() {
433 let nl = self.bccx.loan_path_to_string(&common.unwrap());
435 let new_loan_msg = format!(" (via `{}`)",
436 self.bccx.loan_path_to_string(
437 &new_loan.loan_path));
438 let old_loan_msg = format!(" (via `{}`)",
439 self.bccx.loan_path_to_string(
440 &old_loan.loan_path));
441 (nl, ol, new_loan_msg, old_loan_msg)
443 (self.bccx.loan_path_to_string(&new_loan.loan_path),
444 self.bccx.loan_path_to_string(&old_loan.loan_path),
450 let ol_pronoun = if new_loan.loan_path == old_loan.loan_path {
456 // We want to assemble all the relevant locations for the error.
458 // 1. Where did the new loan occur.
459 // - if due to closure creation, where was the variable used in closure?
460 // 2. Where did old loan occur.
461 // 3. Where does old loan expire.
463 let previous_end_span =
464 self.tcx().hir.span(old_loan.kill_scope.node_id()).end_point();
466 let mut err = match (new_loan.kind, old_loan.kind) {
467 (ty::MutBorrow, ty::MutBorrow) => {
468 let mut err = struct_span_err!(self.bccx, new_loan.span, E0499,
469 "cannot borrow `{}`{} as mutable \
470 more than once at a time",
474 format!("first mutable borrow occurs here{}", old_loan_msg));
477 format!("second mutable borrow occurs here{}", new_loan_msg));
480 "first borrow ends here");
484 (ty::UniqueImmBorrow, ty::UniqueImmBorrow) => {
485 let mut err = struct_span_err!(self.bccx, new_loan.span, E0524,
486 "two closures require unique access to `{}` \
491 "first closure is constructed here");
494 "second closure is constructed here");
497 "borrow from first closure ends here");
501 (ty::UniqueImmBorrow, _) => {
502 let mut err = struct_span_err!(self.bccx, new_loan.span, E0500,
503 "closure requires unique access to `{}` \
504 but {} is already borrowed{}",
505 nl, ol_pronoun, old_loan_msg);
508 format!("closure construction occurs here{}", new_loan_msg));
511 format!("borrow occurs here{}", old_loan_msg));
518 (_, ty::UniqueImmBorrow) => {
519 let mut err = struct_span_err!(self.bccx, new_loan.span, E0501,
520 "cannot borrow `{}`{} as {} because \
521 previous closure requires unique access",
522 nl, new_loan_msg, new_loan.kind.to_user_str());
525 format!("borrow occurs here{}", new_loan_msg));
528 format!("closure construction occurs here{}", old_loan_msg));
531 "borrow from closure ends here");
536 let mut err = struct_span_err!(self.bccx, new_loan.span, E0502,
537 "cannot borrow `{}`{} as {} because \
538 {} is also borrowed as {}{}",
541 new_loan.kind.to_user_str(),
543 old_loan.kind.to_user_str(),
547 format!("{} borrow occurs here{}",
548 new_loan.kind.to_user_str(),
552 format!("{} borrow occurs here{}",
553 old_loan.kind.to_user_str(),
557 format!("{} borrow ends here",
558 old_loan.kind.to_user_str()));
563 match new_loan.cause {
564 euv::ClosureCapture(span) => {
567 format!("borrow occurs due to use of `{}` in closure", nl));
572 match old_loan.cause {
573 euv::ClosureCapture(span) => {
576 format!("previous borrow occurs due to use of `{}` in closure",
589 fn consume_common(&self,
593 mode: euv::ConsumeMode) {
594 if let Some(lp) = opt_loan_path(&cmt) {
595 let moved_value_use_kind = match mode {
597 self.check_for_copy_of_frozen_path(id, span, &lp);
601 match self.move_data.kind_of_move_of_path(id, &lp) {
603 // Sometimes moves don't have a move kind;
604 // this either means that the original move
605 // was from something illegal to move,
606 // or was moved from referent of an unsafe
607 // pointer or something like that.
611 self.check_for_move_of_borrowed_path(id, span,
613 if move_kind == move_data::Captured {
623 self.check_if_path_is_moved(id, span, moved_value_use_kind, &lp);
627 fn check_for_copy_of_frozen_path(&self,
630 copy_path: &LoanPath<'tcx>) {
631 match self.analyze_restrictions_on_use(id, copy_path, ty::ImmBorrow) {
633 UseWhileBorrowed(loan_path, loan_span) => {
634 struct_span_err!(self.bccx, span, E0503,
635 "cannot use `{}` because it was mutably borrowed",
636 &self.bccx.loan_path_to_string(copy_path))
637 .span_label(loan_span,
638 format!("borrow of `{}` occurs here",
639 &self.bccx.loan_path_to_string(&loan_path))
642 format!("use of borrowed `{}`",
643 &self.bccx.loan_path_to_string(&loan_path)))
649 fn check_for_move_of_borrowed_path(&self,
652 move_path: &LoanPath<'tcx>,
653 move_kind: move_data::MoveKind) {
654 // We want to detect if there are any loans at all, so we search for
655 // any loans incompatible with MutBorrrow, since all other kinds of
656 // loans are incompatible with that.
657 match self.analyze_restrictions_on_use(id, move_path, ty::MutBorrow) {
659 UseWhileBorrowed(loan_path, loan_span) => {
660 let mut err = match move_kind {
661 move_data::Captured => {
662 let mut err = struct_span_err!(self.bccx, span, E0504,
663 "cannot move `{}` into closure because it is borrowed",
664 &self.bccx.loan_path_to_string(move_path));
667 format!("borrow of `{}` occurs here",
668 &self.bccx.loan_path_to_string(&loan_path))
672 "move into closure occurs here"
676 move_data::Declared |
677 move_data::MoveExpr |
678 move_data::MovePat => {
679 let mut err = struct_span_err!(self.bccx, span, E0505,
680 "cannot move out of `{}` because it is borrowed",
681 &self.bccx.loan_path_to_string(move_path));
684 format!("borrow of `{}` occurs here",
685 &self.bccx.loan_path_to_string(&loan_path))
689 format!("move out of `{}` occurs here",
690 &self.bccx.loan_path_to_string(move_path))
701 pub fn analyze_restrictions_on_use(&self,
702 expr_id: ast::NodeId,
703 use_path: &LoanPath<'tcx>,
704 borrow_kind: ty::BorrowKind)
706 debug!("analyze_restrictions_on_use(expr_id={}, use_path={:?})",
707 self.tcx().hir.node_to_string(expr_id),
712 self.each_in_scope_loan_affecting_path(
713 region::CodeExtent::Misc(expr_id), use_path, |loan| {
714 if !compatible_borrow_kinds(loan.kind, borrow_kind) {
715 ret = UseWhileBorrowed(loan.loan_path.clone(), loan.span);
725 /// Reports an error if `expr` (which should be a path)
726 /// is using a moved/uninitialized value
727 fn check_if_path_is_moved(&self,
730 use_kind: MovedValueUseKind,
731 lp: &Rc<LoanPath<'tcx>>) {
732 debug!("check_if_path_is_moved(id={}, use_kind={:?}, lp={:?})",
735 // FIXME (22079): if you find yourself tempted to cut and paste
736 // the body below and then specializing the error reporting,
737 // consider refactoring this instead!
739 let base_lp = owned_ptr_base_path_rc(lp);
740 self.move_data.each_move_of(id, &base_lp, |the_move, moved_lp| {
741 self.bccx.report_use_of_moved_value(
752 /// Reports an error if assigning to `lp` will use a
753 /// moved/uninitialized value. Mainly this is concerned with
754 /// detecting derefs of uninitialized pointers.
760 /// a = 10; // ok, even though a is uninitialized
762 /// struct Point { x: u32, y: u32 }
764 /// p.x = 22; // ok, even though `p` is uninitialized
766 /// let p: Box<Point>;
767 /// (*p).x = 22; // not ok, p is uninitialized, can't deref
769 fn check_if_assigned_path_is_moved(&self,
772 use_kind: MovedValueUseKind,
773 lp: &Rc<LoanPath<'tcx>>)
776 LpVar(_) | LpUpvar(_) => {
777 // assigning to `x` does not require that `x` is initialized
779 LpDowncast(ref lp_base, _) => {
780 // assigning to `(P->Variant).f` is ok if assigning to `P` is ok
781 self.check_if_assigned_path_is_moved(id, span,
784 LpExtend(ref lp_base, _, LpInterior(_, InteriorField(_))) => {
785 match lp_base.to_type().sty {
786 ty::TyAdt(def, _) if def.has_dtor(self.tcx()) => {
787 // In the case where the owner implements drop, then
788 // the path must be initialized to prevent a case of
789 // partial reinitialization
791 // FIXME (22079): could refactor via hypothetical
792 // generalized check_if_path_is_moved
793 let loan_path = owned_ptr_base_path_rc(lp_base);
794 self.move_data.each_move_of(id, &loan_path, |_, _| {
796 .report_partial_reinitialization_of_uninitialized_structure(
806 // assigning to `P.f` is ok if assigning to `P` is ok
807 self.check_if_assigned_path_is_moved(id, span,
810 LpExtend(ref lp_base, _, LpInterior(_, InteriorElement)) |
811 LpExtend(ref lp_base, _, LpDeref(_)) => {
812 // assigning to `P[i]` requires `P` is initialized
813 // assigning to `(*P)` requires `P` is initialized
814 self.check_if_path_is_moved(id, span, use_kind, lp_base);
819 fn check_assignment(&self,
820 assignment_id: ast::NodeId,
821 assignment_span: Span,
822 assignee_cmt: mc::cmt<'tcx>) {
823 debug!("check_assignment(assignee_cmt={:?})", assignee_cmt);
825 // Check that we don't invalidate any outstanding loans
826 if let Some(loan_path) = opt_loan_path(&assignee_cmt) {
827 let scope = region::CodeExtent::Misc(assignment_id);
828 self.each_in_scope_loan_affecting_path(scope, &loan_path, |loan| {
829 self.report_illegal_mutation(assignment_span, &loan_path, loan);
834 // Check for reassignments to (immutable) local variables. This
835 // needs to be done here instead of in check_loans because we
836 // depend on move data.
837 if let Categorization::Local(local_id) = assignee_cmt.cat {
838 let lp = opt_loan_path(&assignee_cmt).unwrap();
839 self.move_data.each_assignment_of(assignment_id, &lp, |assign| {
840 if assignee_cmt.mutbl.is_mutable() {
841 self.tcx().used_mut_nodes.borrow_mut().insert(local_id);
843 self.bccx.report_reassigned_immutable_variable(
854 pub fn report_illegal_mutation(&self,
856 loan_path: &LoanPath<'tcx>,
858 struct_span_err!(self.bccx, span, E0506,
859 "cannot assign to `{}` because it is borrowed",
860 self.bccx.loan_path_to_string(loan_path))
861 .span_label(loan.span,
862 format!("borrow of `{}` occurs here",
863 self.bccx.loan_path_to_string(loan_path)))
865 format!("assignment to borrowed `{}` occurs here",
866 self.bccx.loan_path_to_string(loan_path)))