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: &'a ty::ParameterEnvironment<'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 infcx = bccx.tcx.borrowck_fake_infer_ctxt(body.id());
195 let mut clcx = CheckLoanCtxt {
197 dfcx_loans: dfcx_loans,
198 move_data: move_data,
199 all_loans: all_loans,
200 param_env: &infcx.parameter_environment
202 euv::ExprUseVisitor::new(&mut clcx, &infcx).consume_body(body);
206 enum UseError<'tcx> {
208 UseWhileBorrowed(/*loan*/Rc<LoanPath<'tcx>>, /*loan*/Span)
211 fn compatible_borrow_kinds(borrow_kind1: ty::BorrowKind,
212 borrow_kind2: ty::BorrowKind)
214 borrow_kind1 == ty::ImmBorrow && borrow_kind2 == ty::ImmBorrow
217 impl<'a, 'tcx> CheckLoanCtxt<'a, 'tcx> {
218 pub fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.bccx.tcx }
220 pub fn each_issued_loan<F>(&self, node: ast::NodeId, mut op: F) -> bool where
221 F: FnMut(&Loan<'tcx>) -> bool,
223 //! Iterates over each loan that has been issued
224 //! on entrance to `node`, regardless of whether it is
225 //! actually *in scope* at that point. Sometimes loans
226 //! are issued for future scopes and thus they may have been
227 //! *issued* but not yet be in effect.
229 self.dfcx_loans.each_bit_on_entry(node, |loan_index| {
230 let loan = &self.all_loans[loan_index];
235 pub fn each_in_scope_loan<F>(&self, scope: region::CodeExtent<'tcx>, mut op: F) -> bool where
236 F: FnMut(&Loan<'tcx>) -> bool,
238 //! Like `each_issued_loan()`, but only considers loans that are
239 //! currently in scope.
241 let tcx = self.tcx();
242 self.each_issued_loan(scope.node_id(), |loan| {
243 if tcx.region_maps().is_subscope_of(scope, loan.kill_scope) {
251 fn each_in_scope_loan_affecting_path<F>(&self,
252 scope: region::CodeExtent<'tcx>,
253 loan_path: &LoanPath<'tcx>,
256 F: FnMut(&Loan<'tcx>) -> bool,
258 //! Iterates through all of the in-scope loans affecting `loan_path`,
259 //! calling `op`, and ceasing iteration if `false` is returned.
261 // First, we check for a loan restricting the path P being used. This
262 // accounts for borrows of P but also borrows of subpaths, like P.a.b.
263 // Consider the following example:
265 // let x = &mut a.b.c; // Restricts a, a.b, and a.b.c
266 // let y = a; // Conflicts with restriction
268 let loan_path = owned_ptr_base_path(loan_path);
269 let cont = self.each_in_scope_loan(scope, |loan| {
271 for restr_path in &loan.restricted_paths {
272 if **restr_path == *loan_path {
286 // Next, we must check for *loans* (not restrictions) on the path P or
287 // any base path. This rejects examples like the following:
292 // Limiting this search to *loans* and not *restrictions* means that
293 // examples like the following continue to work:
298 let mut loan_path = loan_path;
300 match loan_path.kind {
301 LpVar(_) | LpUpvar(_) => {
304 LpDowncast(ref lp_base, _) |
305 LpExtend(ref lp_base, ..) => {
306 loan_path = &lp_base;
310 let cont = self.each_in_scope_loan(scope, |loan| {
311 if *loan.loan_path == *loan_path {
326 pub fn loans_generated_by(&self, node: ast::NodeId) -> Vec<usize> {
327 //! Returns a vector of the loans that are generated as
330 let mut result = Vec::new();
331 self.dfcx_loans.each_gen_bit(node, |loan_index| {
332 result.push(loan_index);
338 pub fn check_for_conflicting_loans(&self, node: ast::NodeId) {
339 //! Checks to see whether any of the loans that are issued
340 //! on entrance to `node` conflict with loans that have already been
341 //! issued when we enter `node` (for example, we do not
342 //! permit two `&mut` borrows of the same variable).
344 //! (Note that some loans can be *issued* without necessarily
345 //! taking effect yet.)
347 debug!("check_for_conflicting_loans(node={:?})", node);
349 let new_loan_indices = self.loans_generated_by(node);
350 debug!("new_loan_indices = {:?}", new_loan_indices);
352 for &new_loan_index in &new_loan_indices {
353 self.each_issued_loan(node, |issued_loan| {
354 let new_loan = &self.all_loans[new_loan_index];
355 // Only report an error for the first issued loan that conflicts
356 // to avoid O(n^2) errors.
357 self.report_error_if_loans_conflict(issued_loan, new_loan)
361 for (i, &x) in new_loan_indices.iter().enumerate() {
362 let old_loan = &self.all_loans[x];
363 for &y in &new_loan_indices[(i+1) ..] {
364 let new_loan = &self.all_loans[y];
365 self.report_error_if_loans_conflict(old_loan, new_loan);
370 pub fn report_error_if_loans_conflict(&self,
371 old_loan: &Loan<'tcx>,
372 new_loan: &Loan<'tcx>)
374 //! Checks whether `old_loan` and `new_loan` can safely be issued
377 debug!("report_error_if_loans_conflict(old_loan={:?}, new_loan={:?})",
381 // Should only be called for loans that are in scope at the same time.
382 assert!(self.tcx().region_maps().scopes_intersect(old_loan.kill_scope,
383 new_loan.kill_scope));
385 self.report_error_if_loan_conflicts_with_restriction(
386 old_loan, new_loan, old_loan, new_loan) &&
387 self.report_error_if_loan_conflicts_with_restriction(
388 new_loan, old_loan, old_loan, new_loan)
391 pub fn report_error_if_loan_conflicts_with_restriction(&self,
394 old_loan: &Loan<'tcx>,
395 new_loan: &Loan<'tcx>)
397 //! Checks whether the restrictions introduced by `loan1` would
398 //! prohibit `loan2`. Returns false if an error is reported.
400 debug!("report_error_if_loan_conflicts_with_restriction(\
401 loan1={:?}, loan2={:?})",
405 if compatible_borrow_kinds(loan1.kind, loan2.kind) {
409 let loan2_base_path = owned_ptr_base_path_rc(&loan2.loan_path);
410 for restr_path in &loan1.restricted_paths {
411 if *restr_path != loan2_base_path { continue; }
413 // If new_loan is something like `x.a`, and old_loan is something like `x.b`, we would
414 // normally generate a rather confusing message (in this case, for multiple mutable
417 // error: cannot borrow `x.b` as mutable more than once at a time
418 // note: previous borrow of `x.a` occurs here; the mutable borrow prevents
419 // subsequent moves, borrows, or modification of `x.a` until the borrow ends
421 // What we want to do instead is get the 'common ancestor' of the two borrow paths and
422 // use that for most of the message instead, giving is something like this:
424 // error: cannot borrow `x` as mutable more than once at a time
425 // note: previous borrow of `x` occurs here (through borrowing `x.a`); the mutable
426 // borrow prevents subsequent moves, borrows, or modification of `x` until the
429 let common = new_loan.loan_path.common(&old_loan.loan_path);
430 let (nl, ol, new_loan_msg, old_loan_msg) = {
431 if new_loan.loan_path.has_fork(&old_loan.loan_path) && common.is_some() {
432 let nl = self.bccx.loan_path_to_string(&common.unwrap());
434 let new_loan_msg = format!(" (via `{}`)",
435 self.bccx.loan_path_to_string(
436 &new_loan.loan_path));
437 let old_loan_msg = format!(" (via `{}`)",
438 self.bccx.loan_path_to_string(
439 &old_loan.loan_path));
440 (nl, ol, new_loan_msg, old_loan_msg)
442 (self.bccx.loan_path_to_string(&new_loan.loan_path),
443 self.bccx.loan_path_to_string(&old_loan.loan_path),
449 let ol_pronoun = if new_loan.loan_path == old_loan.loan_path {
455 // We want to assemble all the relevant locations for the error.
457 // 1. Where did the new loan occur.
458 // - if due to closure creation, where was the variable used in closure?
459 // 2. Where did old loan occur.
460 // 3. Where does old loan expire.
462 let previous_end_span =
463 self.tcx().hir.span(old_loan.kill_scope.node_id()).end_point();
465 let mut err = match (new_loan.kind, old_loan.kind) {
466 (ty::MutBorrow, ty::MutBorrow) => {
467 let mut err = struct_span_err!(self.bccx, new_loan.span, E0499,
468 "cannot borrow `{}`{} as mutable \
469 more than once at a time",
473 &format!("first mutable borrow occurs here{}", old_loan_msg));
476 &format!("second mutable borrow occurs here{}", new_loan_msg));
479 &format!("first borrow ends here"));
483 (ty::UniqueImmBorrow, ty::UniqueImmBorrow) => {
484 let mut err = struct_span_err!(self.bccx, new_loan.span, E0524,
485 "two closures require unique access to `{}` \
490 &format!("first closure is constructed here"));
493 &format!("second closure is constructed here"));
496 &format!("borrow from first closure ends here"));
500 (ty::UniqueImmBorrow, _) => {
501 let mut err = struct_span_err!(self.bccx, new_loan.span, E0500,
502 "closure requires unique access to `{}` \
503 but {} is already borrowed{}",
504 nl, ol_pronoun, old_loan_msg);
507 &format!("closure construction occurs here{}", new_loan_msg));
510 &format!("borrow occurs here{}", old_loan_msg));
513 &format!("borrow ends here"));
517 (_, ty::UniqueImmBorrow) => {
518 let mut err = struct_span_err!(self.bccx, new_loan.span, E0501,
519 "cannot borrow `{}`{} as {} because \
520 previous closure requires unique access",
521 nl, new_loan_msg, new_loan.kind.to_user_str());
524 &format!("borrow occurs here{}", new_loan_msg));
527 &format!("closure construction occurs here{}", old_loan_msg));
530 &format!("borrow from closure ends here"));
535 let mut err = struct_span_err!(self.bccx, new_loan.span, E0502,
536 "cannot borrow `{}`{} as {} because \
537 {} is also borrowed as {}{}",
540 new_loan.kind.to_user_str(),
542 old_loan.kind.to_user_str(),
546 &format!("{} borrow occurs here{}",
547 new_loan.kind.to_user_str(),
551 &format!("{} borrow occurs here{}",
552 old_loan.kind.to_user_str(),
556 &format!("{} borrow ends here",
557 old_loan.kind.to_user_str()));
562 match new_loan.cause {
563 euv::ClosureCapture(span) => {
566 &format!("borrow occurs due to use of `{}` in closure", nl));
571 match old_loan.cause {
572 euv::ClosureCapture(span) => {
575 &format!("previous borrow occurs due to use of `{}` in closure",
588 fn consume_common(&self,
592 mode: euv::ConsumeMode) {
593 if let Some(lp) = opt_loan_path(&cmt) {
594 let moved_value_use_kind = match mode {
596 self.check_for_copy_of_frozen_path(id, span, &lp);
600 match self.move_data.kind_of_move_of_path(id, &lp) {
602 // Sometimes moves don't have a move kind;
603 // this either means that the original move
604 // was from something illegal to move,
605 // or was moved from referent of an unsafe
606 // pointer or something like that.
610 self.check_for_move_of_borrowed_path(id, span,
612 if move_kind == move_data::Captured {
622 self.check_if_path_is_moved(id, span, moved_value_use_kind, &lp);
626 fn check_for_copy_of_frozen_path(&self,
629 copy_path: &LoanPath<'tcx>) {
630 match self.analyze_restrictions_on_use(id, copy_path, ty::ImmBorrow) {
632 UseWhileBorrowed(loan_path, loan_span) => {
633 struct_span_err!(self.bccx, span, E0503,
634 "cannot use `{}` because it was mutably borrowed",
635 &self.bccx.loan_path_to_string(copy_path))
636 .span_label(loan_span,
637 &format!("borrow of `{}` occurs here",
638 &self.bccx.loan_path_to_string(&loan_path))
641 &format!("use of borrowed `{}`",
642 &self.bccx.loan_path_to_string(&loan_path)))
648 fn check_for_move_of_borrowed_path(&self,
651 move_path: &LoanPath<'tcx>,
652 move_kind: move_data::MoveKind) {
653 // We want to detect if there are any loans at all, so we search for
654 // any loans incompatible with MutBorrrow, since all other kinds of
655 // loans are incompatible with that.
656 match self.analyze_restrictions_on_use(id, move_path, ty::MutBorrow) {
658 UseWhileBorrowed(loan_path, loan_span) => {
659 let mut err = match move_kind {
660 move_data::Captured => {
661 let mut err = struct_span_err!(self.bccx, span, E0504,
662 "cannot move `{}` into closure because it is borrowed",
663 &self.bccx.loan_path_to_string(move_path));
666 &format!("borrow of `{}` occurs here",
667 &self.bccx.loan_path_to_string(&loan_path))
671 &format!("move into closure occurs here")
675 move_data::Declared |
676 move_data::MoveExpr |
677 move_data::MovePat => {
678 let mut err = struct_span_err!(self.bccx, span, E0505,
679 "cannot move out of `{}` because it is borrowed",
680 &self.bccx.loan_path_to_string(move_path));
683 &format!("borrow of `{}` occurs here",
684 &self.bccx.loan_path_to_string(&loan_path))
688 &format!("move out of `{}` occurs here",
689 &self.bccx.loan_path_to_string(move_path))
700 pub fn analyze_restrictions_on_use(&self,
701 expr_id: ast::NodeId,
702 use_path: &LoanPath<'tcx>,
703 borrow_kind: ty::BorrowKind)
705 debug!("analyze_restrictions_on_use(expr_id={}, use_path={:?})",
706 self.tcx().hir.node_to_string(expr_id),
711 self.each_in_scope_loan_affecting_path(
712 self.tcx().node_extent(expr_id), use_path, |loan| {
713 if !compatible_borrow_kinds(loan.kind, borrow_kind) {
714 ret = UseWhileBorrowed(loan.loan_path.clone(), loan.span);
724 /// Reports an error if `expr` (which should be a path)
725 /// is using a moved/uninitialized value
726 fn check_if_path_is_moved(&self,
729 use_kind: MovedValueUseKind,
730 lp: &Rc<LoanPath<'tcx>>) {
731 debug!("check_if_path_is_moved(id={}, use_kind={:?}, lp={:?})",
734 // FIXME (22079): if you find yourself tempted to cut and paste
735 // the body below and then specializing the error reporting,
736 // consider refactoring this instead!
738 let base_lp = owned_ptr_base_path_rc(lp);
739 self.move_data.each_move_of(id, &base_lp, |the_move, moved_lp| {
740 self.bccx.report_use_of_moved_value(
751 /// Reports an error if assigning to `lp` will use a
752 /// moved/uninitialized value. Mainly this is concerned with
753 /// detecting derefs of uninitialized pointers.
759 /// a = 10; // ok, even though a is uninitialized
761 /// struct Point { x: u32, y: u32 }
763 /// p.x = 22; // ok, even though `p` is uninitialized
765 /// let p: Box<Point>;
766 /// (*p).x = 22; // not ok, p is uninitialized, can't deref
768 fn check_if_assigned_path_is_moved(&self,
771 use_kind: MovedValueUseKind,
772 lp: &Rc<LoanPath<'tcx>>)
775 LpVar(_) | LpUpvar(_) => {
776 // assigning to `x` does not require that `x` is initialized
778 LpDowncast(ref lp_base, _) => {
779 // assigning to `(P->Variant).f` is ok if assigning to `P` is ok
780 self.check_if_assigned_path_is_moved(id, span,
783 LpExtend(ref lp_base, _, LpInterior(_, InteriorField(_))) => {
784 match lp_base.to_type().sty {
785 ty::TyAdt(def, _) if def.has_dtor(self.tcx()) => {
786 // In the case where the owner implements drop, then
787 // the path must be initialized to prevent a case of
788 // partial reinitialization
790 // FIXME (22079): could refactor via hypothetical
791 // generalized check_if_path_is_moved
792 let loan_path = owned_ptr_base_path_rc(lp_base);
793 self.move_data.each_move_of(id, &loan_path, |_, _| {
795 .report_partial_reinitialization_of_uninitialized_structure(
805 // assigning to `P.f` is ok if assigning to `P` is ok
806 self.check_if_assigned_path_is_moved(id, span,
809 LpExtend(ref lp_base, _, LpInterior(_, InteriorElement(..))) |
810 LpExtend(ref lp_base, _, LpDeref(_)) => {
811 // assigning to `P[i]` requires `P` is initialized
812 // assigning to `(*P)` requires `P` is initialized
813 self.check_if_path_is_moved(id, span, use_kind, lp_base);
818 fn check_assignment(&self,
819 assignment_id: ast::NodeId,
820 assignment_span: Span,
821 assignee_cmt: mc::cmt<'tcx>) {
822 debug!("check_assignment(assignee_cmt={:?})", assignee_cmt);
824 // Check that we don't invalidate any outstanding loans
825 if let Some(loan_path) = opt_loan_path(&assignee_cmt) {
826 let scope = self.tcx().node_extent(assignment_id);
827 self.each_in_scope_loan_affecting_path(scope, &loan_path, |loan| {
828 self.report_illegal_mutation(assignment_span, &loan_path, loan);
833 // Check for reassignments to (immutable) local variables. This
834 // needs to be done here instead of in check_loans because we
835 // depend on move data.
836 if let Categorization::Local(local_id) = assignee_cmt.cat {
837 let lp = opt_loan_path(&assignee_cmt).unwrap();
838 self.move_data.each_assignment_of(assignment_id, &lp, |assign| {
839 if assignee_cmt.mutbl.is_mutable() {
840 self.tcx().used_mut_nodes.borrow_mut().insert(local_id);
842 self.bccx.report_reassigned_immutable_variable(
853 pub fn report_illegal_mutation(&self,
855 loan_path: &LoanPath<'tcx>,
857 struct_span_err!(self.bccx, span, E0506,
858 "cannot assign to `{}` because it is borrowed",
859 self.bccx.loan_path_to_string(loan_path))
860 .span_label(loan.span,
861 &format!("borrow of `{}` occurs here",
862 self.bccx.loan_path_to_string(loan_path)))
864 &format!("assignment to borrowed `{}` occurs here",
865 self.bccx.loan_path_to_string(loan_path)))