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 //! This file actually contains two passes related to regions. The first
12 //! pass builds up the `scope_map`, which describes the parent links in
13 //! the region hierarchy. The second pass infers which types must be
14 //! region parameterized.
16 //! Most of the documentation on regions can be found in
17 //! `middle/infer/region_inference/README.md`
19 use hir::map as hir_map;
20 use util::nodemap::{FxHashMap, NodeMap, NodeSet};
29 use ty::maps::Providers;
32 use hir::def_id::DefId;
33 use hir::intravisit::{self, Visitor, NestedVisitorMap};
34 use hir::{Block, Arm, Pat, PatKind, Stmt, Expr, Local};
35 use mir::transform::MirSource;
37 /// CodeExtent represents a statically-describable extent that can be
38 /// used to bound the lifetime/region for values.
40 /// `Misc(node_id)`: Any AST node that has any extent at all has the
41 /// `Misc(node_id)` extent. Other variants represent special cases not
42 /// immediately derivable from the abstract syntax tree structure.
44 /// `DestructionScope(node_id)` represents the extent of destructors
45 /// implicitly-attached to `node_id` that run immediately after the
46 /// expression for `node_id` itself. Not every AST node carries a
47 /// `DestructionScope`, but those that are `terminating_scopes` do;
48 /// see discussion with `RegionMaps`.
50 /// `Remainder(BlockRemainder { block, statement_index })` represents
51 /// the extent of user code running immediately after the initializer
52 /// expression for the indexed statement, until the end of the block.
54 /// So: the following code can be broken down into the extents beneath:
56 /// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y) } ) ;
61 /// +---------+ (R10.)
63 /// +----------+ (M8.)
64 /// +----------------------+ (R7.)
66 /// +----------+ (M5.)
67 /// +-----------------------------------+ (M4.)
68 /// +--------------------------------------------------+ (M3.)
70 /// +-----------------------------------------------------------+ (M1.)
72 /// (M1.): Misc extent of the whole `let a = ...;` statement.
73 /// (M2.): Misc extent of the `f()` expression.
74 /// (M3.): Misc extent of the `f().g(..)` expression.
75 /// (M4.): Misc extent of the block labelled `'b:`.
76 /// (M5.): Misc extent of the `let x = d();` statement
77 /// (D6.): DestructionScope for temporaries created during M5.
78 /// (R7.): Remainder extent for block `'b:`, stmt 0 (let x = ...).
79 /// (M8.): Misc Extent of the `let y = d();` statement.
80 /// (D9.): DestructionScope for temporaries created during M8.
81 /// (R10.): Remainder extent for block `'b:`, stmt 1 (let y = ...).
82 /// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
83 /// (D12.): DestructionScope for temporaries created during M1 (e.g. f()).
85 /// Note that while the above picture shows the destruction scopes
86 /// as following their corresponding misc extents, in the internal
87 /// data structures of the compiler the destruction scopes are
88 /// represented as enclosing parents. This is sound because we use the
89 /// enclosing parent relationship just to ensure that referenced
90 /// values live long enough; phrased another way, the starting point
91 /// of each range is not really the important thing in the above
92 /// picture, but rather the ending point.
94 /// FIXME (pnkfelix): This currently derives `PartialOrd` and `Ord` to
95 /// placate the same deriving in `ty::FreeRegion`, but we may want to
96 /// actually attach a more meaningful ordering to scopes than the one
97 /// generated via deriving here.
98 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, RustcEncodable, RustcDecodable)]
102 // extent of the call-site for a function or closure (outlives
103 // the parameters as well as the body).
104 CallSiteScope(hir::BodyId),
106 // extent of parameters passed to a function or closure (they
108 ParameterScope(hir::BodyId),
110 // extent of destructors for temporaries of node-id
111 DestructionScope(ast::NodeId),
113 // extent of code following a `let id = expr;` binding in a block
114 Remainder(BlockRemainder)
117 /// Represents a subscope of `block` for a binding that is introduced
118 /// by `block.stmts[first_statement_index]`. Such subscopes represent
119 /// a suffix of the block. Note that each subscope does not include
120 /// the initializer expression, if any, for the statement indexed by
121 /// `first_statement_index`.
123 /// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
125 /// * the subscope with `first_statement_index == 0` is scope of both
126 /// `a` and `b`; it does not include EXPR_1, but does include
127 /// everything after that first `let`. (If you want a scope that
128 /// includes EXPR_1 as well, then do not use `CodeExtent::Remainder`,
129 /// but instead another `CodeExtent` that encompasses the whole block,
130 /// e.g. `CodeExtent::Misc`.
132 /// * the subscope with `first_statement_index == 1` is scope of `c`,
133 /// and thus does not include EXPR_2, but covers the `...`.
134 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
135 RustcDecodable, Debug, Copy)]
136 pub struct BlockRemainder {
137 pub block: ast::NodeId,
138 pub first_statement_index: u32,
142 /// Returns a node id associated with this scope.
144 /// NB: likely to be replaced as API is refined; e.g. pnkfelix
145 /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
146 pub fn node_id(&self) -> ast::NodeId {
148 CodeExtent::Misc(node_id) => node_id,
150 // These cases all return rough approximations to the
151 // precise extent denoted by `self`.
152 CodeExtent::Remainder(br) => br.block,
153 CodeExtent::DestructionScope(node_id) => node_id,
154 CodeExtent::CallSiteScope(body_id) |
155 CodeExtent::ParameterScope(body_id) => body_id.node_id,
159 /// Returns the span of this CodeExtent. Note that in general the
160 /// returned span may not correspond to the span of any node id in
162 pub fn span(&self, hir_map: &hir_map::Map) -> Option<Span> {
163 match hir_map.find(self.node_id()) {
164 Some(hir_map::NodeBlock(ref blk)) => {
166 CodeExtent::CallSiteScope(_) |
167 CodeExtent::ParameterScope(_) |
168 CodeExtent::Misc(_) |
169 CodeExtent::DestructionScope(_) => Some(blk.span),
171 CodeExtent::Remainder(r) => {
172 assert_eq!(r.block, blk.id);
173 // Want span for extent starting after the
174 // indexed statement and ending at end of
175 // `blk`; reuse span of `blk` and shift `lo`
176 // forward to end of indexed statement.
178 // (This is the special case aluded to in the
179 // doc-comment for this method)
180 let stmt_span = blk.stmts[r.first_statement_index as usize].span;
181 Some(Span { lo: stmt_span.hi, hi: blk.span.hi, ctxt: stmt_span.ctxt })
185 Some(hir_map::NodeExpr(ref expr)) => Some(expr.span),
186 Some(hir_map::NodeStmt(ref stmt)) => Some(stmt.span),
187 Some(hir_map::NodeItem(ref item)) => Some(item.span),
188 Some(_) | None => None,
193 /// The region maps encode information about region relationships.
194 pub struct RegionMaps {
195 /// If not empty, this body is the root of this region hierarchy.
196 root_body: Option<hir::BodyId>,
198 /// The parent of the root body owner, if the latter is an
199 /// an associated const or method, as impls/traits can also
200 /// have lifetime parameters free in this body.
201 root_parent: Option<ast::NodeId>,
203 /// `scope_map` maps from a scope id to the enclosing scope id;
204 /// this is usually corresponding to the lexical nesting, though
205 /// in the case of closures the parent scope is the innermost
206 /// conditional expression or repeating block. (Note that the
207 /// enclosing scope id for the block associated with a closure is
208 /// the closure itself.)
209 scope_map: FxHashMap<CodeExtent, CodeExtent>,
211 /// `var_map` maps from a variable or binding id to the block in
212 /// which that variable is declared.
213 var_map: NodeMap<CodeExtent>,
215 /// maps from a node-id to the associated destruction scope (if any)
216 destruction_scopes: NodeMap<CodeExtent>,
218 /// `rvalue_scopes` includes entries for those expressions whose cleanup scope is
219 /// larger than the default. The map goes from the expression id
220 /// to the cleanup scope id. For rvalues not present in this
221 /// table, the appropriate cleanup scope is the innermost
222 /// enclosing statement, conditional expression, or repeating
223 /// block (see `terminating_scopes`).
224 rvalue_scopes: NodeMap<CodeExtent>,
226 /// Encodes the hierarchy of fn bodies. Every fn body (including
227 /// closures) forms its own distinct region hierarchy, rooted in
228 /// the block that is the fn body. This map points from the id of
229 /// that root block to the id of the root block for the enclosing
230 /// fn, if any. Thus the map structures the fn bodies into a
231 /// hierarchy based on their lexical mapping. This is used to
232 /// handle the relationships between regions in a fn and in a
233 /// closure defined by that fn. See the "Modeling closures"
234 /// section of the README in infer::region_inference for
236 fn_tree: NodeMap<ast::NodeId>,
239 #[derive(Debug, Copy, Clone)]
241 /// the root of the current region tree. This is typically the id
242 /// of the innermost fn body. Each fn forms its own disjoint tree
243 /// in the region hierarchy. These fn bodies are themselves
244 /// arranged into a tree. See the "Modeling closures" section of
245 /// the README in infer::region_inference for more
247 root_id: Option<ast::NodeId>,
249 /// the scope that contains any new variables declared
250 var_parent: Option<CodeExtent>,
252 /// region parent of expressions etc
253 parent: Option<CodeExtent>,
256 struct RegionResolutionVisitor<'a, 'tcx: 'a> {
257 tcx: TyCtxt<'a, 'tcx, 'tcx>,
260 region_maps: RegionMaps,
264 /// `terminating_scopes` is a set containing the ids of each
265 /// statement, or conditional/repeating expression. These scopes
266 /// are calling "terminating scopes" because, when attempting to
267 /// find the scope of a temporary, by default we search up the
268 /// enclosing scopes until we encounter the terminating scope. A
269 /// conditional/repeating expression is one which is not
270 /// guaranteed to execute exactly once upon entering the parent
271 /// scope. This could be because the expression only executes
272 /// conditionally, such as the expression `b` in `a && b`, or
273 /// because the expression may execute many times, such as a loop
274 /// body. The reason that we distinguish such expressions is that,
275 /// upon exiting the parent scope, we cannot statically know how
276 /// many times the expression executed, and thus if the expression
277 /// creates temporaries we cannot know statically how many such
278 /// temporaries we would have to cleanup. Therefore we ensure that
279 /// the temporaries never outlast the conditional/repeating
280 /// expression, preventing the need for dynamic checks and/or
281 /// arbitrary amounts of stack space. Terminating scopes end
282 /// up being contained in a DestructionScope that contains the
283 /// destructor's execution.
284 terminating_scopes: NodeSet,
288 impl<'tcx> RegionMaps {
289 pub fn new() -> Self {
293 scope_map: FxHashMap(),
294 destruction_scopes: FxHashMap(),
296 rvalue_scopes: NodeMap(),
301 pub fn record_code_extent(&mut self,
303 parent: Option<CodeExtent>) {
304 debug!("{:?}.parent = {:?}", child, parent);
306 if let Some(p) = parent {
307 let prev = self.scope_map.insert(child, p);
308 assert!(prev.is_none());
311 // record the destruction scopes for later so we can query them
312 if let CodeExtent::DestructionScope(n) = child {
313 self.destruction_scopes.insert(n, child);
317 pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(CodeExtent, CodeExtent) {
318 for (&child, &parent) in &self.scope_map {
323 pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&ast::NodeId, CodeExtent) {
324 for (child, &parent) in self.var_map.iter() {
329 pub fn opt_destruction_extent(&self, n: ast::NodeId) -> Option<CodeExtent> {
330 self.destruction_scopes.get(&n).cloned()
333 /// Records that `sub_fn` is defined within `sup_fn`. These ids
334 /// should be the id of the block that is the fn body, which is
335 /// also the root of the region hierarchy for that fn.
336 fn record_fn_parent(&mut self, sub_fn: ast::NodeId, sup_fn: ast::NodeId) {
337 debug!("record_fn_parent(sub_fn={:?}, sup_fn={:?})", sub_fn, sup_fn);
338 assert!(sub_fn != sup_fn);
339 let previous = self.fn_tree.insert(sub_fn, sup_fn);
340 assert!(previous.is_none());
343 fn fn_is_enclosed_by(&self, mut sub_fn: ast::NodeId, sup_fn: ast::NodeId) -> bool {
345 if sub_fn == sup_fn { return true; }
346 match self.fn_tree.get(&sub_fn) {
347 Some(&s) => { sub_fn = s; }
348 None => { return false; }
353 fn record_var_scope(&mut self, var: ast::NodeId, lifetime: CodeExtent) {
354 debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
355 assert!(var != lifetime.node_id());
356 self.var_map.insert(var, lifetime);
359 fn record_rvalue_scope(&mut self, var: ast::NodeId, lifetime: CodeExtent) {
360 debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
361 assert!(var != lifetime.node_id());
362 self.rvalue_scopes.insert(var, lifetime);
365 pub fn opt_encl_scope(&self, id: CodeExtent) -> Option<CodeExtent> {
366 //! Returns the narrowest scope that encloses `id`, if any.
367 self.scope_map.get(&id).cloned()
370 #[allow(dead_code)] // used in cfg
371 pub fn encl_scope(&self, id: CodeExtent) -> CodeExtent {
372 //! Returns the narrowest scope that encloses `id`, if any.
373 self.opt_encl_scope(id).unwrap()
376 /// Returns the lifetime of the local variable `var_id`
377 pub fn var_scope(&self, var_id: ast::NodeId) -> CodeExtent {
378 match self.var_map.get(&var_id) {
380 None => { bug!("no enclosing scope for id {:?}", var_id); }
384 pub fn temporary_scope(&self, expr_id: ast::NodeId) -> Option<CodeExtent> {
385 //! Returns the scope when temp created by expr_id will be cleaned up
387 // check for a designated rvalue scope
388 if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
389 debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
393 // else, locate the innermost terminating scope
394 // if there's one. Static items, for instance, won't
395 // have an enclosing scope, hence no scope will be
397 let mut id = CodeExtent::Misc(expr_id);
399 while let Some(&p) = self.scope_map.get(&id) {
401 CodeExtent::DestructionScope(..) => {
402 debug!("temporary_scope({:?}) = {:?} [enclosing]",
410 debug!("temporary_scope({:?}) = None", expr_id);
414 pub fn var_region(&self, id: ast::NodeId) -> ty::RegionKind {
415 //! Returns the lifetime of the variable `id`.
417 let scope = ty::ReScope(self.var_scope(id));
418 debug!("var_region({:?}) = {:?}", id, scope);
422 pub fn scopes_intersect(&self, scope1: CodeExtent, scope2: CodeExtent)
424 self.is_subscope_of(scope1, scope2) ||
425 self.is_subscope_of(scope2, scope1)
428 /// Returns true if `subscope` is equal to or is lexically nested inside `superscope` and false
430 pub fn is_subscope_of(&self,
431 subscope: CodeExtent,
432 superscope: CodeExtent)
434 let mut s = subscope;
435 debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
436 while superscope != s {
437 match self.opt_encl_scope(s) {
439 debug!("is_subscope_of({:?}, {:?}, s={:?})=false",
440 subscope, superscope, s);
443 Some(scope) => s = scope
447 debug!("is_subscope_of({:?}, {:?})=true",
448 subscope, superscope);
453 /// Finds the nearest common ancestor (if any) of two scopes. That is, finds the smallest
454 /// scope which is greater than or equal to both `scope_a` and `scope_b`.
455 pub fn nearest_common_ancestor(&self,
459 if scope_a == scope_b { return scope_a; }
461 /// [1] The initial values for `a_buf` and `b_buf` are not used.
462 /// The `ancestors_of` function will return some prefix that
463 /// is re-initialized with new values (or else fallback to a
464 /// heap-allocated vector).
465 let mut a_buf: [CodeExtent; 32] = [scope_a /* [1] */; 32];
466 let mut a_vec: Vec<CodeExtent> = vec![];
467 let mut b_buf: [CodeExtent; 32] = [scope_b /* [1] */; 32];
468 let mut b_vec: Vec<CodeExtent> = vec![];
469 let scope_map = &self.scope_map;
470 let a_ancestors = ancestors_of(scope_map, scope_a, &mut a_buf, &mut a_vec);
471 let b_ancestors = ancestors_of(scope_map, scope_b, &mut b_buf, &mut b_vec);
472 let mut a_index = a_ancestors.len() - 1;
473 let mut b_index = b_ancestors.len() - 1;
475 // Here, [ab]_ancestors is a vector going from narrow to broad.
476 // The end of each vector will be the item where the scope is
477 // defined; if there are any common ancestors, then the tails of
478 // the vector will be the same. So basically we want to walk
479 // backwards from the tail of each vector and find the first point
480 // where they diverge. If one vector is a suffix of the other,
481 // then the corresponding scope is a superscope of the other.
483 if a_ancestors[a_index] != b_ancestors[b_index] {
484 // In this case, the two regions belong to completely
485 // different functions. Compare those fn for lexical
486 // nesting. The reasoning behind this is subtle. See the
487 // "Modeling closures" section of the README in
488 // infer::region_inference for more details.
489 let a_root_scope = a_ancestors[a_index];
490 let b_root_scope = a_ancestors[a_index];
491 return match (a_root_scope, b_root_scope) {
492 (CodeExtent::DestructionScope(a_root_id),
493 CodeExtent::DestructionScope(b_root_id)) => {
494 if self.fn_is_enclosed_by(a_root_id, b_root_id) {
495 // `a` is enclosed by `b`, hence `b` is the ancestor of everything in `a`
497 } else if self.fn_is_enclosed_by(b_root_id, a_root_id) {
498 // `b` is enclosed by `a`, hence `a` is the ancestor of everything in `b`
501 // neither fn encloses the other
506 // root ids are always Misc right now
513 // Loop invariant: a_ancestors[a_index] == b_ancestors[b_index]
514 // for all indices between a_index and the end of the array
515 if a_index == 0 { return scope_a; }
516 if b_index == 0 { return scope_b; }
519 if a_ancestors[a_index] != b_ancestors[b_index] {
520 return a_ancestors[a_index + 1];
524 fn ancestors_of<'a, 'tcx>(scope_map: &FxHashMap<CodeExtent, CodeExtent>,
526 buf: &'a mut [CodeExtent; 32],
527 vec: &'a mut Vec<CodeExtent>)
528 -> &'a [CodeExtent] {
529 // debug!("ancestors_of(scope={:?})", scope);
530 let mut scope = scope;
535 match scope_map.get(&scope) {
536 Some(&superscope) => scope = superscope,
537 _ => return &buf[..i+1]
542 *vec = Vec::with_capacity(64);
543 vec.extend_from_slice(buf);
546 match scope_map.get(&scope) {
547 Some(&superscope) => scope = superscope,
554 /// Assuming that the provided region was defined within this `RegionMaps`,
555 /// returns the outermost `CodeExtent` that the region outlives.
556 pub fn early_free_extent<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
557 br: &ty::EarlyBoundRegion)
559 let param_owner = tcx.parent_def_id(br.def_id).unwrap();
561 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
562 let body_id = tcx.hir.maybe_body_owned_by(param_owner_id).unwrap_or_else(|| {
563 // The lifetime was defined on node that doesn't own a body,
564 // which in practice can only mean a trait or an impl, that
565 // is the parent of a method, and that is enforced below.
566 assert_eq!(Some(param_owner_id), self.root_parent,
567 "free_extent: {:?} not recognized by the region maps for {:?}",
569 self.root_body.map(|body| tcx.hir.body_owner_def_id(body)));
571 // The trait/impl lifetime is in scope for the method's body.
572 self.root_body.unwrap()
575 CodeExtent::CallSiteScope(body_id)
578 /// Assuming that the provided region was defined within this `RegionMaps`,
579 /// returns the outermost `CodeExtent` that the region outlives.
580 pub fn free_extent<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, fr: &ty::FreeRegion)
582 let param_owner = match fr.bound_region {
583 ty::BoundRegion::BrNamed(def_id, _) => {
584 tcx.parent_def_id(def_id).unwrap()
589 // Ensure that the named late-bound lifetimes were defined
590 // on the same function that they ended up being freed in.
591 assert_eq!(param_owner, fr.scope);
593 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
594 CodeExtent::CallSiteScope(tcx.hir.body_owned_by(param_owner_id))
598 /// Records the lifetime of a local variable as `cx.var_parent`
599 fn record_var_lifetime(visitor: &mut RegionResolutionVisitor,
602 match visitor.cx.var_parent {
604 // this can happen in extern fn declarations like
606 // extern fn isalnum(c: c_int) -> c_int
608 Some(parent_scope) =>
609 visitor.region_maps.record_var_scope(var_id, parent_scope),
613 fn resolve_block<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, blk: &'tcx hir::Block) {
614 debug!("resolve_block(blk.id={:?})", blk.id);
616 let prev_cx = visitor.cx;
618 // We treat the tail expression in the block (if any) somewhat
619 // differently from the statements. The issue has to do with
620 // temporary lifetimes. Consider the following:
623 // let inner = ... (&bar()) ...;
625 // (... (&foo()) ...) // (the tail expression)
626 // }, other_argument());
628 // Each of the statements within the block is a terminating
629 // scope, and thus a temporary (e.g. the result of calling
630 // `bar()` in the initalizer expression for `let inner = ...;`)
631 // will be cleaned up immediately after its corresponding
632 // statement (i.e. `let inner = ...;`) executes.
634 // On the other hand, temporaries associated with evaluating the
635 // tail expression for the block are assigned lifetimes so that
636 // they will be cleaned up as part of the terminating scope
637 // *surrounding* the block expression. Here, the terminating
638 // scope for the block expression is the `quux(..)` call; so
639 // those temporaries will only be cleaned up *after* both
640 // `other_argument()` has run and also the call to `quux(..)`
641 // itself has returned.
643 visitor.enter_node_extent_with_dtor(blk.id);
644 visitor.cx.var_parent = visitor.cx.parent;
647 // This block should be kept approximately in sync with
648 // `intravisit::walk_block`. (We manually walk the block, rather
649 // than call `walk_block`, in order to maintain precise
650 // index information.)
652 for (i, statement) in blk.stmts.iter().enumerate() {
653 if let hir::StmtDecl(..) = statement.node {
654 // Each StmtDecl introduces a subscope for bindings
655 // introduced by the declaration; this subscope covers
656 // a suffix of the block . Each subscope in a block
657 // has the previous subscope in the block as a parent,
658 // except for the first such subscope, which has the
659 // block itself as a parent.
660 visitor.enter_code_extent(
661 CodeExtent::Remainder(BlockRemainder {
663 first_statement_index: i as u32
666 visitor.cx.var_parent = visitor.cx.parent;
668 visitor.visit_stmt(statement)
670 walk_list!(visitor, visit_expr, &blk.expr);
673 visitor.cx = prev_cx;
676 fn resolve_arm<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, arm: &'tcx hir::Arm) {
677 visitor.terminating_scopes.insert(arm.body.id);
679 if let Some(ref expr) = arm.guard {
680 visitor.terminating_scopes.insert(expr.id);
683 intravisit::walk_arm(visitor, arm);
686 fn resolve_pat<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, pat: &'tcx hir::Pat) {
687 visitor.record_code_extent(CodeExtent::Misc(pat.id));
689 // If this is a binding then record the lifetime of that binding.
690 if let PatKind::Binding(..) = pat.node {
691 record_var_lifetime(visitor, pat.id, pat.span);
694 intravisit::walk_pat(visitor, pat);
697 fn resolve_stmt<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, stmt: &'tcx hir::Stmt) {
698 let stmt_id = stmt.node.id();
699 debug!("resolve_stmt(stmt.id={:?})", stmt_id);
701 // Every statement will clean up the temporaries created during
702 // execution of that statement. Therefore each statement has an
703 // associated destruction scope that represents the extent of the
704 // statement plus its destructors, and thus the extent for which
705 // regions referenced by the destructors need to survive.
706 visitor.terminating_scopes.insert(stmt_id);
708 let prev_parent = visitor.cx.parent;
709 visitor.enter_node_extent_with_dtor(stmt_id);
711 intravisit::walk_stmt(visitor, stmt);
713 visitor.cx.parent = prev_parent;
716 fn resolve_expr<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, expr: &'tcx hir::Expr) {
717 debug!("resolve_expr(expr.id={:?})", expr.id);
719 let prev_cx = visitor.cx;
720 visitor.enter_node_extent_with_dtor(expr.id);
723 let terminating_scopes = &mut visitor.terminating_scopes;
724 let mut terminating = |id: ast::NodeId| {
725 terminating_scopes.insert(id);
728 // Conditional or repeating scopes are always terminating
729 // scopes, meaning that temporaries cannot outlive them.
730 // This ensures fixed size stacks.
732 hir::ExprBinary(codemap::Spanned { node: hir::BiAnd, .. }, _, ref r) |
733 hir::ExprBinary(codemap::Spanned { node: hir::BiOr, .. }, _, ref r) => {
734 // For shortcircuiting operators, mark the RHS as a terminating
735 // scope since it only executes conditionally.
739 hir::ExprIf(ref expr, ref then, Some(ref otherwise)) => {
740 terminating(expr.id);
741 terminating(then.id);
742 terminating(otherwise.id);
745 hir::ExprIf(ref expr, ref then, None) => {
746 terminating(expr.id);
747 terminating(then.id);
750 hir::ExprLoop(ref body, _, _) => {
751 terminating(body.id);
754 hir::ExprWhile(ref expr, ref body, _) => {
755 terminating(expr.id);
756 terminating(body.id);
759 hir::ExprMatch(..) => {
760 visitor.cx.var_parent = visitor.cx.parent;
763 hir::ExprAssignOp(..) | hir::ExprIndex(..) |
764 hir::ExprUnary(..) | hir::ExprCall(..) | hir::ExprMethodCall(..) => {
765 // FIXME(#6268) Nested method calls
767 // The lifetimes for a call or method call look as follows:
775 // The idea is that call.callee_id represents *the time when
776 // the invoked function is actually running* and call.id
777 // represents *the time to prepare the arguments and make the
778 // call*. See the section "Borrows in Calls" borrowck/README.md
779 // for an extended explanation of why this distinction is
782 // record_superlifetime(new_cx, expr.callee_id);
790 // Manually recurse over closures, because they are the only
791 // case of nested bodies that share the parent environment.
792 hir::ExprClosure(.., body, _) => {
793 let body = visitor.tcx.hir.body(body);
794 visitor.visit_body(body);
797 _ => intravisit::walk_expr(visitor, expr)
800 visitor.cx = prev_cx;
803 fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
804 local: &'tcx hir::Local) {
805 debug!("resolve_local(local.id={:?},local.init={:?})",
806 local.id,local.init.is_some());
808 // For convenience in trans, associate with the local-id the var
809 // scope that will be used for any bindings declared in this
811 let blk_scope = visitor.cx.var_parent;
812 let blk_scope = blk_scope.expect("locals must be within a block");
813 visitor.region_maps.record_var_scope(local.id, blk_scope);
815 // As an exception to the normal rules governing temporary
816 // lifetimes, initializers in a let have a temporary lifetime
817 // of the enclosing block. This means that e.g. a program
818 // like the following is legal:
820 // let ref x = HashMap::new();
822 // Because the hash map will be freed in the enclosing block.
824 // We express the rules more formally based on 3 grammars (defined
825 // fully in the helpers below that implement them):
827 // 1. `E&`, which matches expressions like `&<rvalue>` that
828 // own a pointer into the stack.
830 // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
831 // y)` that produce ref bindings into the value they are
832 // matched against or something (at least partially) owned by
833 // the value they are matched against. (By partially owned,
834 // I mean that creating a binding into a ref-counted or managed value
835 // would still count.)
837 // 3. `ET`, which matches both rvalues like `foo()` as well as lvalues
838 // based on rvalues like `foo().x[2].y`.
840 // A subexpression `<rvalue>` that appears in a let initializer
841 // `let pat [: ty] = expr` has an extended temporary lifetime if
842 // any of the following conditions are met:
844 // A. `pat` matches `P&` and `expr` matches `ET`
845 // (covers cases where `pat` creates ref bindings into an rvalue
846 // produced by `expr`)
847 // B. `ty` is a borrowed pointer and `expr` matches `ET`
848 // (covers cases where coercion creates a borrow)
849 // C. `expr` matches `E&`
850 // (covers cases `expr` borrows an rvalue that is then assigned
851 // to memory (at least partially) owned by the binding)
853 // Here are some examples hopefully giving an intuition where each
854 // rule comes into play and why:
856 // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
857 // would have an extended lifetime, but not `foo()`.
859 // Rule B. `let x = &foo().x`. The rvalue ``foo()` would have extended
862 // In some cases, multiple rules may apply (though not to the same
863 // rvalue). For example:
865 // let ref x = [&a(), &b()];
867 // Here, the expression `[...]` has an extended lifetime due to rule
868 // A, but the inner rvalues `a()` and `b()` have an extended lifetime
871 // FIXME(#6308) -- Note that `[]` patterns work more smoothly post-DST.
873 if let Some(ref expr) = local.init {
874 record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
876 if is_binding_pat(&local.pat) {
877 record_rvalue_scope(visitor, &expr, blk_scope);
881 intravisit::walk_local(visitor, local);
883 /// True if `pat` match the `P&` nonterminal:
886 /// | StructName { ..., P&, ... }
887 /// | VariantName(..., P&, ...)
888 /// | [ ..., P&, ... ]
889 /// | ( ..., P&, ... )
891 fn is_binding_pat(pat: &hir::Pat) -> bool {
893 PatKind::Binding(hir::BindByRef(_), ..) => true,
895 PatKind::Struct(_, ref field_pats, _) => {
896 field_pats.iter().any(|fp| is_binding_pat(&fp.node.pat))
899 PatKind::Slice(ref pats1, ref pats2, ref pats3) => {
900 pats1.iter().any(|p| is_binding_pat(&p)) ||
901 pats2.iter().any(|p| is_binding_pat(&p)) ||
902 pats3.iter().any(|p| is_binding_pat(&p))
905 PatKind::TupleStruct(_, ref subpats, _) |
906 PatKind::Tuple(ref subpats, _) => {
907 subpats.iter().any(|p| is_binding_pat(&p))
910 PatKind::Box(ref subpat) => {
911 is_binding_pat(&subpat)
918 /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
921 /// | StructName { ..., f: E&, ... }
922 /// | [ ..., E&, ... ]
923 /// | ( ..., E&, ... )
928 fn record_rvalue_scope_if_borrow_expr<'a, 'tcx>(
929 visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
934 hir::ExprAddrOf(_, ref subexpr) => {
935 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
936 record_rvalue_scope(visitor, &subexpr, blk_id);
938 hir::ExprStruct(_, ref fields, _) => {
939 for field in fields {
940 record_rvalue_scope_if_borrow_expr(
941 visitor, &field.expr, blk_id);
944 hir::ExprArray(ref subexprs) |
945 hir::ExprTup(ref subexprs) => {
946 for subexpr in subexprs {
947 record_rvalue_scope_if_borrow_expr(
948 visitor, &subexpr, blk_id);
951 hir::ExprCast(ref subexpr, _) => {
952 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
954 hir::ExprBlock(ref block) => {
955 if let Some(ref subexpr) = block.expr {
956 record_rvalue_scope_if_borrow_expr(
957 visitor, &subexpr, blk_id);
964 /// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
965 /// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
966 /// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
969 /// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
970 /// `<rvalue>` as `blk_id`:
978 /// Note: ET is intended to match "rvalues or lvalues based on rvalues".
979 fn record_rvalue_scope<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
981 blk_scope: CodeExtent) {
984 // Note: give all the expressions matching `ET` with the
985 // extended temporary lifetime, not just the innermost rvalue,
986 // because in trans if we must compile e.g. `*rvalue()`
987 // into a temporary, we request the temporary scope of the
989 visitor.region_maps.record_rvalue_scope(expr.id, blk_scope);
992 hir::ExprAddrOf(_, ref subexpr) |
993 hir::ExprUnary(hir::UnDeref, ref subexpr) |
994 hir::ExprField(ref subexpr, _) |
995 hir::ExprTupField(ref subexpr, _) |
996 hir::ExprIndex(ref subexpr, _) => {
1007 impl<'a, 'tcx> RegionResolutionVisitor<'a, 'tcx> {
1008 /// Records the current parent (if any) as the parent of `child_scope`.
1009 fn record_code_extent(&mut self, child_scope: CodeExtent) {
1010 let parent = self.cx.parent;
1011 self.region_maps.record_code_extent(child_scope, parent);
1014 /// Records the current parent (if any) as the parent of `child_scope`,
1015 /// and sets `child_scope` as the new current parent.
1016 fn enter_code_extent(&mut self, child_scope: CodeExtent) {
1017 self.record_code_extent(child_scope);
1018 self.cx.parent = Some(child_scope);
1021 fn enter_node_extent_with_dtor(&mut self, id: ast::NodeId) {
1022 // If node was previously marked as a terminating scope during the
1023 // recursive visit of its parent node in the AST, then we need to
1024 // account for the destruction scope representing the extent of
1025 // the destructors that run immediately after it completes.
1026 if self.terminating_scopes.contains(&id) {
1027 self.enter_code_extent(CodeExtent::DestructionScope(id));
1029 self.enter_code_extent(CodeExtent::Misc(id));
1033 impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
1034 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1035 NestedVisitorMap::None
1038 fn visit_block(&mut self, b: &'tcx Block) {
1039 resolve_block(self, b);
1042 fn visit_body(&mut self, body: &'tcx hir::Body) {
1043 let body_id = body.id();
1044 let owner_id = self.tcx.hir.body_owner(body_id);
1046 debug!("visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
1048 self.tcx.sess.codemap().span_to_string(body.value.span),
1052 let outer_cx = self.cx;
1053 let outer_ts = mem::replace(&mut self.terminating_scopes, NodeSet());
1055 // Only functions have an outer terminating (drop) scope,
1056 // while temporaries in constant initializers are 'static.
1057 if let MirSource::Fn(_) = MirSource::from_node(self.tcx, owner_id) {
1058 self.terminating_scopes.insert(body_id.node_id);
1061 if let Some(root_id) = self.cx.root_id {
1062 self.region_maps.record_fn_parent(body_id.node_id, root_id);
1064 self.cx.root_id = Some(body_id.node_id);
1066 self.enter_code_extent(CodeExtent::CallSiteScope(body_id));
1067 self.enter_code_extent(CodeExtent::ParameterScope(body_id));
1069 // The arguments and `self` are parented to the fn.
1070 self.cx.var_parent = self.cx.parent.take();
1071 for argument in &body.arguments {
1072 self.visit_pat(&argument.pat);
1075 // The body of the every fn is a root scope.
1076 self.cx.parent = self.cx.var_parent;
1077 self.visit_expr(&body.value);
1079 // Restore context we had at the start.
1081 self.terminating_scopes = outer_ts;
1084 fn visit_arm(&mut self, a: &'tcx Arm) {
1085 resolve_arm(self, a);
1087 fn visit_pat(&mut self, p: &'tcx Pat) {
1088 resolve_pat(self, p);
1090 fn visit_stmt(&mut self, s: &'tcx Stmt) {
1091 resolve_stmt(self, s);
1093 fn visit_expr(&mut self, ex: &'tcx Expr) {
1094 resolve_expr(self, ex);
1096 fn visit_local(&mut self, l: &'tcx Local) {
1097 resolve_local(self, l);
1101 fn region_maps<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
1104 let closure_base_def_id = tcx.closure_base_def_id(def_id);
1105 if closure_base_def_id != def_id {
1106 return tcx.region_maps(closure_base_def_id);
1109 let id = tcx.hir.as_local_node_id(def_id).unwrap();
1110 let maps = if let Some(body) = tcx.hir.maybe_body_owned_by(id) {
1111 let mut visitor = RegionResolutionVisitor {
1113 region_maps: RegionMaps::new(),
1119 terminating_scopes: NodeSet(),
1122 visitor.region_maps.root_body = Some(body);
1124 // If the item is an associated const or a method,
1125 // record its impl/trait parent, as it can also have
1126 // lifetime parameters free in this body.
1127 match tcx.hir.get(id) {
1128 hir::map::NodeImplItem(_) |
1129 hir::map::NodeTraitItem(_) => {
1130 visitor.region_maps.root_parent = Some(tcx.hir.get_parent(id));
1135 visitor.visit_body(tcx.hir.body(body));
1145 pub fn provide(providers: &mut Providers) {
1146 *providers = Providers {