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 builds up the `ScopeTree`, which describes
12 //! the parent links in the region hierarchy.
14 //! For more information about how MIR-based region-checking works,
15 //! see the [rustc guide].
17 //! [rustc guide]: https://rust-lang-nursery.github.io/rustc-guide/mir/borrowck.html
19 use ich::{StableHashingContext, NodeIdHashingMode};
20 use util::nodemap::{FxHashMap, FxHashSet};
25 use rustc_data_structures::sync::Lrc;
26 use syntax::source_map;
28 use syntax_pos::{Span, DUMMY_SP};
30 use ty::query::Providers;
34 use hir::def_id::DefId;
35 use hir::intravisit::{self, Visitor, NestedVisitorMap};
36 use hir::{Block, Arm, Pat, PatKind, Stmt, Expr, Local};
37 use rustc_data_structures::indexed_vec::Idx;
38 use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
41 /// Scope represents a statically-describable scope that can be
42 /// used to bound the lifetime/region for values.
44 /// `Node(node_id)`: Any AST node that has any scope at all has the
45 /// `Node(node_id)` scope. Other variants represent special cases not
46 /// immediately derivable from the abstract syntax tree structure.
48 /// `DestructionScope(node_id)` represents the scope of destructors
49 /// implicitly-attached to `node_id` that run immediately after the
50 /// expression for `node_id` itself. Not every AST node carries a
51 /// `DestructionScope`, but those that are `terminating_scopes` do;
52 /// see discussion with `ScopeTree`.
54 /// `Remainder(BlockRemainder { block, statement_index })` represents
55 /// the scope of user code running immediately after the initializer
56 /// expression for the indexed statement, until the end of the block.
58 /// So: the following code can be broken down into the scopes beneath:
61 /// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y) } ) ;
65 /// +---------+ (R10.)
67 /// +----------+ (M8.)
68 /// +----------------------+ (R7.)
70 /// +----------+ (M5.)
71 /// +-----------------------------------+ (M4.)
72 /// +--------------------------------------------------+ (M3.)
74 /// +-----------------------------------------------------------+ (M1.)
76 /// (M1.): Node scope of the whole `let a = ...;` statement.
77 /// (M2.): Node scope of the `f()` expression.
78 /// (M3.): Node scope of the `f().g(..)` expression.
79 /// (M4.): Node scope of the block labeled `'b:`.
80 /// (M5.): Node scope of the `let x = d();` statement
81 /// (D6.): DestructionScope for temporaries created during M5.
82 /// (R7.): Remainder scope for block `'b:`, stmt 0 (let x = ...).
83 /// (M8.): Node scope of the `let y = d();` statement.
84 /// (D9.): DestructionScope for temporaries created during M8.
85 /// (R10.): Remainder scope for block `'b:`, stmt 1 (let y = ...).
86 /// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
87 /// (D12.): DestructionScope for temporaries created during M1 (e.g. f()).
90 /// Note that while the above picture shows the destruction scopes
91 /// as following their corresponding node scopes, in the internal
92 /// data structures of the compiler the destruction scopes are
93 /// represented as enclosing parents. This is sound because we use the
94 /// enclosing parent relationship just to ensure that referenced
95 /// values live long enough; phrased another way, the starting point
96 /// of each range is not really the important thing in the above
97 /// picture, but rather the ending point.
99 /// FIXME (pnkfelix): This currently derives `PartialOrd` and `Ord` to
100 /// placate the same deriving in `ty::FreeRegion`, but we may want to
101 /// actually attach a more meaningful ordering to scopes than the one
102 /// generated via deriving here.
104 /// Scope is a bit-packed to save space - if `code` is SCOPE_DATA_REMAINDER_MAX
105 /// or less, it is a `ScopeData::Remainder`, otherwise it is a type specified
106 /// by the bitpacking.
107 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Copy, RustcEncodable, RustcDecodable)]
109 pub(crate) id: hir::ItemLocalId,
113 const SCOPE_DATA_NODE: u32 = !0;
114 const SCOPE_DATA_CALLSITE: u32 = !1;
115 const SCOPE_DATA_ARGUMENTS: u32 = !2;
116 const SCOPE_DATA_DESTRUCTION: u32 = !3;
117 const SCOPE_DATA_REMAINDER_MAX: u32 = !4;
119 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, RustcEncodable, RustcDecodable)]
121 Node(hir::ItemLocalId),
123 // Scope of the call-site for a function or closure
124 // (outlives the arguments as well as the body).
125 CallSite(hir::ItemLocalId),
127 // Scope of arguments passed to a function or closure
128 // (they outlive its body).
129 Arguments(hir::ItemLocalId),
131 // Scope of destructors for temporaries of node-id.
132 Destruction(hir::ItemLocalId),
134 // Scope following a `let id = expr;` binding in a block.
135 Remainder(BlockRemainder)
138 /// Represents a subscope of `block` for a binding that is introduced
139 /// by `block.stmts[first_statement_index]`. Such subscopes represent
140 /// a suffix of the block. Note that each subscope does not include
141 /// the initializer expression, if any, for the statement indexed by
142 /// `first_statement_index`.
144 /// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
146 /// * the subscope with `first_statement_index == 0` is scope of both
147 /// `a` and `b`; it does not include EXPR_1, but does include
148 /// everything after that first `let`. (If you want a scope that
149 /// includes EXPR_1 as well, then do not use `Scope::Remainder`,
150 /// but instead another `Scope` that encompasses the whole block,
151 /// e.g. `Scope::Node`.
153 /// * the subscope with `first_statement_index == 1` is scope of `c`,
154 /// and thus does not include EXPR_2, but covers the `...`.
155 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
156 RustcDecodable, Debug, Copy)]
157 pub struct BlockRemainder {
158 pub block: hir::ItemLocalId,
159 pub first_statement_index: FirstStatementIndex,
162 newtype_index!(FirstStatementIndex
165 MAX = SCOPE_DATA_REMAINDER_MAX
168 impl From<ScopeData> for Scope {
170 fn from(scope_data: ScopeData) -> Self {
171 let (id, code) = match scope_data {
172 ScopeData::Node(id) => (id, SCOPE_DATA_NODE),
173 ScopeData::CallSite(id) => (id, SCOPE_DATA_CALLSITE),
174 ScopeData::Arguments(id) => (id, SCOPE_DATA_ARGUMENTS),
175 ScopeData::Destruction(id) => (id, SCOPE_DATA_DESTRUCTION),
176 ScopeData::Remainder(r) => (r.block, r.first_statement_index.index() as u32)
182 impl fmt::Debug for Scope {
183 fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
184 fmt::Debug::fmt(&self.data(), formatter)
188 #[allow(non_snake_case)]
191 pub fn data(self) -> ScopeData {
193 SCOPE_DATA_NODE => ScopeData::Node(self.id),
194 SCOPE_DATA_CALLSITE => ScopeData::CallSite(self.id),
195 SCOPE_DATA_ARGUMENTS => ScopeData::Arguments(self.id),
196 SCOPE_DATA_DESTRUCTION => ScopeData::Destruction(self.id),
197 idx => ScopeData::Remainder(BlockRemainder {
199 first_statement_index: FirstStatementIndex::new(idx as usize)
205 pub fn Node(id: hir::ItemLocalId) -> Self {
206 Self::from(ScopeData::Node(id))
210 pub fn CallSite(id: hir::ItemLocalId) -> Self {
211 Self::from(ScopeData::CallSite(id))
215 pub fn Arguments(id: hir::ItemLocalId) -> Self {
216 Self::from(ScopeData::Arguments(id))
220 pub fn Destruction(id: hir::ItemLocalId) -> Self {
221 Self::from(ScopeData::Destruction(id))
225 pub fn Remainder(r: BlockRemainder) -> Self {
226 Self::from(ScopeData::Remainder(r))
231 /// Returns a item-local id associated with this scope.
233 /// NB: likely to be replaced as API is refined; e.g. pnkfelix
234 /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
235 pub fn item_local_id(&self) -> hir::ItemLocalId {
239 pub fn node_id(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> ast::NodeId {
240 match scope_tree.root_body {
242 tcx.hir.hir_to_node_id(hir::HirId {
244 local_id: self.item_local_id()
247 None => ast::DUMMY_NODE_ID
251 /// Returns the span of this Scope. Note that in general the
252 /// returned span may not correspond to the span of any node id in
254 pub fn span(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> Span {
255 let node_id = self.node_id(tcx, scope_tree);
256 if node_id == ast::DUMMY_NODE_ID {
259 let span = tcx.hir.span(node_id);
260 if let ScopeData::Remainder(r) = self.data() {
261 if let Node::Block(ref blk) = tcx.hir.get(node_id) {
262 // Want span for scope starting after the
263 // indexed statement and ending at end of
264 // `blk`; reuse span of `blk` and shift `lo`
265 // forward to end of indexed statement.
267 // (This is the special case aluded to in the
268 // doc-comment for this method)
270 let stmt_span = blk.stmts[r.first_statement_index.index()].span;
272 // To avoid issues with macro-generated spans, the span
273 // of the statement must be nested in that of the block.
274 if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() {
275 return Span::new(stmt_span.lo(), span.hi(), span.ctxt());
283 pub type ScopeDepth = u32;
285 /// The region scope tree encodes information about region relationships.
286 #[derive(Default, Debug)]
287 pub struct ScopeTree {
288 /// If not empty, this body is the root of this region hierarchy.
289 root_body: Option<hir::HirId>,
291 /// The parent of the root body owner, if the latter is an
292 /// an associated const or method, as impls/traits can also
293 /// have lifetime parameters free in this body.
294 root_parent: Option<ast::NodeId>,
296 /// `parent_map` maps from a scope id to the enclosing scope id;
297 /// this is usually corresponding to the lexical nesting, though
298 /// in the case of closures the parent scope is the innermost
299 /// conditional expression or repeating block. (Note that the
300 /// enclosing scope id for the block associated with a closure is
301 /// the closure itself.)
302 parent_map: FxHashMap<Scope, (Scope, ScopeDepth)>,
304 /// `var_map` maps from a variable or binding id to the block in
305 /// which that variable is declared.
306 var_map: FxHashMap<hir::ItemLocalId, Scope>,
308 /// maps from a node-id to the associated destruction scope (if any)
309 destruction_scopes: FxHashMap<hir::ItemLocalId, Scope>,
311 /// `rvalue_scopes` includes entries for those expressions whose cleanup scope is
312 /// larger than the default. The map goes from the expression id
313 /// to the cleanup scope id. For rvalues not present in this
314 /// table, the appropriate cleanup scope is the innermost
315 /// enclosing statement, conditional expression, or repeating
316 /// block (see `terminating_scopes`).
317 /// In constants, None is used to indicate that certain expressions
318 /// escape into 'static and should have no local cleanup scope.
319 rvalue_scopes: FxHashMap<hir::ItemLocalId, Option<Scope>>,
321 /// Encodes the hierarchy of fn bodies. Every fn body (including
322 /// closures) forms its own distinct region hierarchy, rooted in
323 /// the block that is the fn body. This map points from the id of
324 /// that root block to the id of the root block for the enclosing
325 /// fn, if any. Thus the map structures the fn bodies into a
326 /// hierarchy based on their lexical mapping. This is used to
327 /// handle the relationships between regions in a fn and in a
328 /// closure defined by that fn. See the "Modeling closures"
329 /// section of the README in infer::region_constraints for
331 closure_tree: FxHashMap<hir::ItemLocalId, hir::ItemLocalId>,
333 /// If there are any `yield` nested within a scope, this map
334 /// stores the `Span` of the last one and its index in the
335 /// postorder of the Visitor traversal on the HIR.
337 /// HIR Visitor postorder indexes might seem like a peculiar
338 /// thing to care about. but it turns out that HIR bindings
339 /// and the temporary results of HIR expressions are never
340 /// storage-live at the end of HIR nodes with postorder indexes
341 /// lower than theirs, and therefore don't need to be suspended
342 /// at yield-points at these indexes.
344 /// For an example, suppose we have some code such as:
345 /// ```rust,ignore (example)
346 /// foo(f(), yield y, bar(g()))
349 /// With the HIR tree (calls numbered for expository purposes)
351 /// Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
354 /// Obviously, the result of `f()` was created before the yield
355 /// (and therefore needs to be kept valid over the yield) while
356 /// the result of `g()` occurs after the yield (and therefore
357 /// doesn't). If we want to infer that, we can look at the
358 /// postorder traversal:
360 /// `foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
363 /// In which we can easily see that `Call#1` occurs before the yield,
364 /// and `Call#3` after it.
366 /// To see that this method works, consider:
368 /// Let `D` be our binding/temporary and `U` be our other HIR node, with
369 /// `HIR-postorder(U) < HIR-postorder(D)` (in our example, U would be
370 /// the yield and D would be one of the calls). Let's show that
371 /// `D` is storage-dead at `U`.
373 /// Remember that storage-live/storage-dead refers to the state of
374 /// the *storage*, and does not consider moves/drop flags.
377 /// 1. From the ordering guarantee of HIR visitors (see
378 /// `rustc::hir::intravisit`), `D` does not dominate `U`.
379 /// 2. Therefore, `D` is *potentially* storage-dead at `U` (because
380 /// we might visit `U` without ever getting to `D`).
381 /// 3. However, we guarantee that at each HIR point, each
382 /// binding/temporary is always either always storage-live
383 /// or always storage-dead. This is what is being guaranteed
384 /// by `terminating_scopes` including all blocks where the
385 /// count of executions is not guaranteed.
386 /// 4. By `2.` and `3.`, `D` is *statically* storage-dead at `U`,
389 /// I don't think this property relies on `3.` in an essential way - it
390 /// is probably still correct even if we have "unrestricted" terminating
391 /// scopes. However, why use the complicated proof when a simple one
394 /// A subtle thing: `box` expressions, such as `box (&x, yield 2, &y)`. It
395 /// might seem that a `box` expression creates a `Box<T>` temporary
396 /// when it *starts* executing, at `HIR-preorder(BOX-EXPR)`. That might
397 /// be true in the MIR desugaring, but it is not important in the semantics.
399 /// The reason is that semantically, until the `box` expression returns,
400 /// the values are still owned by their containing expressions. So
401 /// we'll see that `&x`.
402 yield_in_scope: FxHashMap<Scope, (Span, usize)>,
404 /// The number of visit_expr and visit_pat calls done in the body.
405 /// Used to sanity check visit_expr/visit_pat call count when
406 /// calculating generator interiors.
407 body_expr_count: FxHashMap<hir::BodyId, usize>,
410 #[derive(Debug, Copy, Clone)]
412 /// the root of the current region tree. This is typically the id
413 /// of the innermost fn body. Each fn forms its own disjoint tree
414 /// in the region hierarchy. These fn bodies are themselves
415 /// arranged into a tree. See the "Modeling closures" section of
416 /// the README in infer::region_constraints for more
418 root_id: Option<hir::ItemLocalId>,
420 /// The scope that contains any new variables declared, plus its depth in
422 var_parent: Option<(Scope, ScopeDepth)>,
424 /// Region parent of expressions, etc., plus its depth in the scope tree.
425 parent: Option<(Scope, ScopeDepth)>,
428 struct RegionResolutionVisitor<'a, 'tcx: 'a> {
429 tcx: TyCtxt<'a, 'tcx, 'tcx>,
431 // The number of expressions and patterns visited in the current body
432 expr_and_pat_count: usize,
434 // Generated scope tree:
435 scope_tree: ScopeTree,
439 /// `terminating_scopes` is a set containing the ids of each
440 /// statement, or conditional/repeating expression. These scopes
441 /// are calling "terminating scopes" because, when attempting to
442 /// find the scope of a temporary, by default we search up the
443 /// enclosing scopes until we encounter the terminating scope. A
444 /// conditional/repeating expression is one which is not
445 /// guaranteed to execute exactly once upon entering the parent
446 /// scope. This could be because the expression only executes
447 /// conditionally, such as the expression `b` in `a && b`, or
448 /// because the expression may execute many times, such as a loop
449 /// body. The reason that we distinguish such expressions is that,
450 /// upon exiting the parent scope, we cannot statically know how
451 /// many times the expression executed, and thus if the expression
452 /// creates temporaries we cannot know statically how many such
453 /// temporaries we would have to cleanup. Therefore we ensure that
454 /// the temporaries never outlast the conditional/repeating
455 /// expression, preventing the need for dynamic checks and/or
456 /// arbitrary amounts of stack space. Terminating scopes end
457 /// up being contained in a DestructionScope that contains the
458 /// destructor's execution.
459 terminating_scopes: FxHashSet<hir::ItemLocalId>,
462 struct ExprLocatorVisitor {
464 result: Option<usize>,
465 expr_and_pat_count: usize,
468 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor
469 // since `expr_count` is compared against the results there.
470 impl<'tcx> Visitor<'tcx> for ExprLocatorVisitor {
471 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
472 NestedVisitorMap::None
475 fn visit_pat(&mut self, pat: &'tcx Pat) {
476 intravisit::walk_pat(self, pat);
478 self.expr_and_pat_count += 1;
480 if pat.hir_id == self.hir_id {
481 self.result = Some(self.expr_and_pat_count);
485 fn visit_expr(&mut self, expr: &'tcx Expr) {
486 debug!("ExprLocatorVisitor - pre-increment {} expr = {:?}",
487 self.expr_and_pat_count,
490 intravisit::walk_expr(self, expr);
492 self.expr_and_pat_count += 1;
494 debug!("ExprLocatorVisitor - post-increment {} expr = {:?}",
495 self.expr_and_pat_count,
498 if expr.hir_id == self.hir_id {
499 self.result = Some(self.expr_and_pat_count);
504 impl<'tcx> ScopeTree {
505 pub fn record_scope_parent(&mut self, child: Scope, parent: Option<(Scope, ScopeDepth)>) {
506 debug!("{:?}.parent = {:?}", child, parent);
508 if let Some(p) = parent {
509 let prev = self.parent_map.insert(child, p);
510 assert!(prev.is_none());
513 // record the destruction scopes for later so we can query them
514 if let ScopeData::Destruction(n) = child.data() {
515 self.destruction_scopes.insert(n, child);
519 pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(Scope, Scope) {
520 for (&child, &parent) in &self.parent_map {
525 pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&hir::ItemLocalId, Scope) {
526 for (child, &parent) in self.var_map.iter() {
531 pub fn opt_destruction_scope(&self, n: hir::ItemLocalId) -> Option<Scope> {
532 self.destruction_scopes.get(&n).cloned()
535 /// Records that `sub_closure` is defined within `sup_closure`. These ids
536 /// should be the id of the block that is the fn body, which is
537 /// also the root of the region hierarchy for that fn.
538 fn record_closure_parent(&mut self,
539 sub_closure: hir::ItemLocalId,
540 sup_closure: hir::ItemLocalId) {
541 debug!("record_closure_parent(sub_closure={:?}, sup_closure={:?})",
542 sub_closure, sup_closure);
543 assert!(sub_closure != sup_closure);
544 let previous = self.closure_tree.insert(sub_closure, sup_closure);
545 assert!(previous.is_none());
548 fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) {
549 debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
550 assert!(var != lifetime.item_local_id());
551 self.var_map.insert(var, lifetime);
554 fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
555 debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
556 if let Some(lifetime) = lifetime {
557 assert!(var != lifetime.item_local_id());
559 self.rvalue_scopes.insert(var, lifetime);
562 pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> {
563 //! Returns the narrowest scope that encloses `id`, if any.
564 self.parent_map.get(&id).cloned().map(|(p, _)| p)
567 #[allow(dead_code)] // used in cfg
568 pub fn encl_scope(&self, id: Scope) -> Scope {
569 //! Returns the narrowest scope that encloses `id`, if any.
570 self.opt_encl_scope(id).unwrap()
573 /// Returns the lifetime of the local variable `var_id`
574 pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Scope {
575 match self.var_map.get(&var_id) {
577 None => { bug!("no enclosing scope for id {:?}", var_id); }
581 pub fn temporary_scope(&self, expr_id: hir::ItemLocalId) -> Option<Scope> {
582 //! Returns the scope when temp created by expr_id will be cleaned up
584 // check for a designated rvalue scope
585 if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
586 debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
590 // else, locate the innermost terminating scope
591 // if there's one. Static items, for instance, won't
592 // have an enclosing scope, hence no scope will be
594 let mut id = Scope::Node(expr_id);
596 while let Some(&(p, _)) = self.parent_map.get(&id) {
598 ScopeData::Destruction(..) => {
599 debug!("temporary_scope({:?}) = {:?} [enclosing]",
607 debug!("temporary_scope({:?}) = None", expr_id);
611 pub fn var_region(&self, id: hir::ItemLocalId) -> ty::RegionKind {
612 //! Returns the lifetime of the variable `id`.
614 let scope = ty::ReScope(self.var_scope(id));
615 debug!("var_region({:?}) = {:?}", id, scope);
619 pub fn scopes_intersect(&self, scope1: Scope, scope2: Scope)
621 self.is_subscope_of(scope1, scope2) ||
622 self.is_subscope_of(scope2, scope1)
625 /// Returns true if `subscope` is equal to or is lexically nested inside `superscope` and false
627 pub fn is_subscope_of(&self,
631 let mut s = subscope;
632 debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
633 while superscope != s {
634 match self.opt_encl_scope(s) {
636 debug!("is_subscope_of({:?}, {:?}, s={:?})=false",
637 subscope, superscope, s);
640 Some(scope) => s = scope
644 debug!("is_subscope_of({:?}, {:?})=true",
645 subscope, superscope);
650 /// Returns the id of the innermost containing body
651 pub fn containing_body(&self, mut scope: Scope)-> Option<hir::ItemLocalId> {
653 if let ScopeData::CallSite(id) = scope.data() {
657 match self.opt_encl_scope(scope) {
659 Some(parent) => scope = parent,
664 /// Finds the nearest common ancestor of two scopes. That is, finds the
665 /// smallest scope which is greater than or equal to both `scope_a` and
667 pub fn nearest_common_ancestor(&self, scope_a: Scope, scope_b: Scope) -> Scope {
668 if scope_a == scope_b { return scope_a; }
673 // Get the depth of each scope's parent. If either scope has no parent,
674 // it must be the root, which means we can stop immediately because the
675 // root must be the nearest common ancestor. (In practice, this is
676 // moderately common.)
677 let (parent_a, parent_a_depth) = match self.parent_map.get(&a) {
681 let (parent_b, parent_b_depth) = match self.parent_map.get(&b) {
686 if parent_a_depth > parent_b_depth {
687 // `a` is lower than `b`. Move `a` up until it's at the same depth
688 // as `b`. The first move up is trivial because we already found
689 // `parent_a` above; the loop does the remaining N-1 moves.
691 for _ in 0..(parent_a_depth - parent_b_depth - 1) {
692 a = self.parent_map.get(&a).unwrap().0;
694 } else if parent_b_depth > parent_a_depth {
695 // `b` is lower than `a`.
697 for _ in 0..(parent_b_depth - parent_a_depth - 1) {
698 b = self.parent_map.get(&b).unwrap().0;
701 // Both scopes are at the same depth, and we know they're not equal
702 // because that case was tested for at the top of this function. So
703 // we can trivially move them both up one level now.
704 assert!(parent_a_depth != 0);
709 // Now both scopes are at the same level. We move upwards in lockstep
710 // until they match. In practice, this loop is almost always executed
711 // zero times because `a` is almost always a direct ancestor of `b` or
714 a = self.parent_map.get(&a).unwrap().0;
715 b = self.parent_map.get(&b).unwrap().0;
721 /// Assuming that the provided region was defined within this `ScopeTree`,
722 /// returns the outermost `Scope` that the region outlives.
723 pub fn early_free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
724 br: &ty::EarlyBoundRegion)
726 let param_owner = tcx.parent_def_id(br.def_id).unwrap();
728 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
729 let scope = tcx.hir.maybe_body_owned_by(param_owner_id).map(|body_id| {
730 tcx.hir.body(body_id).value.hir_id.local_id
731 }).unwrap_or_else(|| {
732 // The lifetime was defined on node that doesn't own a body,
733 // which in practice can only mean a trait or an impl, that
734 // is the parent of a method, and that is enforced below.
735 assert_eq!(Some(param_owner_id), self.root_parent,
736 "free_scope: {:?} not recognized by the \
737 region scope tree for {:?} / {:?}",
739 self.root_parent.map(|id| tcx.hir.local_def_id(id)),
740 self.root_body.map(|hir_id| DefId::local(hir_id.owner)));
742 // The trait/impl lifetime is in scope for the method's body.
743 self.root_body.unwrap().local_id
746 Scope::CallSite(scope)
749 /// Assuming that the provided region was defined within this `ScopeTree`,
750 /// returns the outermost `Scope` that the region outlives.
751 pub fn free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, fr: &ty::FreeRegion)
753 let param_owner = match fr.bound_region {
754 ty::BoundRegion::BrNamed(def_id, _) => {
755 tcx.parent_def_id(def_id).unwrap()
760 // Ensure that the named late-bound lifetimes were defined
761 // on the same function that they ended up being freed in.
762 assert_eq!(param_owner, fr.scope);
764 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
765 let body_id = tcx.hir.body_owned_by(param_owner_id);
766 Scope::CallSite(tcx.hir.body(body_id).value.hir_id.local_id)
769 /// Checks whether the given scope contains a `yield`. If so,
770 /// returns `Some((span, expr_count))` with the span of a yield we found and
771 /// the number of expressions and patterns appearing before the `yield` in the body + 1.
772 /// If there a are multiple yields in a scope, the one with the highest number is returned.
773 pub fn yield_in_scope(&self, scope: Scope) -> Option<(Span, usize)> {
774 self.yield_in_scope.get(&scope).cloned()
777 /// Checks whether the given scope contains a `yield` and if that yield could execute
778 /// after `expr`. If so, it returns the span of that `yield`.
779 /// `scope` must be inside the body.
780 pub fn yield_in_scope_for_expr(&self,
782 expr_hir_id: hir::HirId,
783 body: &'tcx hir::Body) -> Option<Span> {
784 self.yield_in_scope(scope).and_then(|(span, count)| {
785 let mut visitor = ExprLocatorVisitor {
788 expr_and_pat_count: 0,
790 visitor.visit_body(body);
791 if count >= visitor.result.unwrap() {
799 /// Gives the number of expressions visited in a body.
800 /// Used to sanity check visit_expr call count when
801 /// calculating generator interiors.
802 pub fn body_expr_count(&self, body_id: hir::BodyId) -> Option<usize> {
803 self.body_expr_count.get(&body_id).map(|r| *r)
807 /// Records the lifetime of a local variable as `cx.var_parent`
808 fn record_var_lifetime(visitor: &mut RegionResolutionVisitor,
809 var_id: hir::ItemLocalId,
811 match visitor.cx.var_parent {
813 // this can happen in extern fn declarations like
815 // extern fn isalnum(c: c_int) -> c_int
817 Some((parent_scope, _)) =>
818 visitor.scope_tree.record_var_scope(var_id, parent_scope),
822 fn resolve_block<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, blk: &'tcx hir::Block) {
823 debug!("resolve_block(blk.id={:?})", blk.id);
825 let prev_cx = visitor.cx;
827 // We treat the tail expression in the block (if any) somewhat
828 // differently from the statements. The issue has to do with
829 // temporary lifetimes. Consider the following:
832 // let inner = ... (&bar()) ...;
834 // (... (&foo()) ...) // (the tail expression)
835 // }, other_argument());
837 // Each of the statements within the block is a terminating
838 // scope, and thus a temporary (e.g. the result of calling
839 // `bar()` in the initializer expression for `let inner = ...;`)
840 // will be cleaned up immediately after its corresponding
841 // statement (i.e. `let inner = ...;`) executes.
843 // On the other hand, temporaries associated with evaluating the
844 // tail expression for the block are assigned lifetimes so that
845 // they will be cleaned up as part of the terminating scope
846 // *surrounding* the block expression. Here, the terminating
847 // scope for the block expression is the `quux(..)` call; so
848 // those temporaries will only be cleaned up *after* both
849 // `other_argument()` has run and also the call to `quux(..)`
850 // itself has returned.
852 visitor.enter_node_scope_with_dtor(blk.hir_id.local_id);
853 visitor.cx.var_parent = visitor.cx.parent;
856 // This block should be kept approximately in sync with
857 // `intravisit::walk_block`. (We manually walk the block, rather
858 // than call `walk_block`, in order to maintain precise
859 // index information.)
861 for (i, statement) in blk.stmts.iter().enumerate() {
862 if let hir::StmtKind::Decl(..) = statement.node {
863 // Each StmtKind::Decl introduces a subscope for bindings
864 // introduced by the declaration; this subscope covers
865 // a suffix of the block . Each subscope in a block
866 // has the previous subscope in the block as a parent,
867 // except for the first such subscope, which has the
868 // block itself as a parent.
870 Scope::Remainder(BlockRemainder {
871 block: blk.hir_id.local_id,
872 first_statement_index: FirstStatementIndex::new(i)
875 visitor.cx.var_parent = visitor.cx.parent;
877 visitor.visit_stmt(statement)
879 walk_list!(visitor, visit_expr, &blk.expr);
882 visitor.cx = prev_cx;
885 fn resolve_arm<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, arm: &'tcx hir::Arm) {
886 visitor.terminating_scopes.insert(arm.body.hir_id.local_id);
888 if let Some(ref expr) = arm.guard {
889 visitor.terminating_scopes.insert(expr.hir_id.local_id);
892 intravisit::walk_arm(visitor, arm);
895 fn resolve_pat<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, pat: &'tcx hir::Pat) {
896 visitor.record_child_scope(Scope::Node(pat.hir_id.local_id));
898 // If this is a binding then record the lifetime of that binding.
899 if let PatKind::Binding(..) = pat.node {
900 record_var_lifetime(visitor, pat.hir_id.local_id, pat.span);
903 debug!("resolve_pat - pre-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
905 intravisit::walk_pat(visitor, pat);
907 visitor.expr_and_pat_count += 1;
909 debug!("resolve_pat - post-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
912 fn resolve_stmt<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, stmt: &'tcx hir::Stmt) {
913 let stmt_id = visitor.tcx.hir.node_to_hir_id(stmt.node.id()).local_id;
914 debug!("resolve_stmt(stmt.id={:?})", stmt_id);
916 // Every statement will clean up the temporaries created during
917 // execution of that statement. Therefore each statement has an
918 // associated destruction scope that represents the scope of the
919 // statement plus its destructors, and thus the scope for which
920 // regions referenced by the destructors need to survive.
921 visitor.terminating_scopes.insert(stmt_id);
923 let prev_parent = visitor.cx.parent;
924 visitor.enter_node_scope_with_dtor(stmt_id);
926 intravisit::walk_stmt(visitor, stmt);
928 visitor.cx.parent = prev_parent;
931 fn resolve_expr<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, expr: &'tcx hir::Expr) {
932 debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
934 let prev_cx = visitor.cx;
935 visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);
938 let terminating_scopes = &mut visitor.terminating_scopes;
939 let mut terminating = |id: hir::ItemLocalId| {
940 terminating_scopes.insert(id);
943 // Conditional or repeating scopes are always terminating
944 // scopes, meaning that temporaries cannot outlive them.
945 // This ensures fixed size stacks.
947 hir::ExprKind::Binary(
948 source_map::Spanned { node: hir::BinOpKind::And, .. },
950 hir::ExprKind::Binary(
951 source_map::Spanned { node: hir::BinOpKind::Or, .. },
953 // For shortcircuiting operators, mark the RHS as a terminating
954 // scope since it only executes conditionally.
955 terminating(r.hir_id.local_id);
958 hir::ExprKind::If(ref expr, ref then, Some(ref otherwise)) => {
959 terminating(expr.hir_id.local_id);
960 terminating(then.hir_id.local_id);
961 terminating(otherwise.hir_id.local_id);
964 hir::ExprKind::If(ref expr, ref then, None) => {
965 terminating(expr.hir_id.local_id);
966 terminating(then.hir_id.local_id);
969 hir::ExprKind::Loop(ref body, _, _) => {
970 terminating(body.hir_id.local_id);
973 hir::ExprKind::While(ref expr, ref body, _) => {
974 terminating(expr.hir_id.local_id);
975 terminating(body.hir_id.local_id);
978 hir::ExprKind::Match(..) => {
979 visitor.cx.var_parent = visitor.cx.parent;
982 hir::ExprKind::AssignOp(..) | hir::ExprKind::Index(..) |
983 hir::ExprKind::Unary(..) | hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) => {
984 // FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls
986 // The lifetimes for a call or method call look as follows:
994 // The idea is that call.callee_id represents *the time when
995 // the invoked function is actually running* and call.id
996 // represents *the time to prepare the arguments and make the
997 // call*. See the section "Borrows in Calls" borrowck/README.md
998 // for an extended explanation of why this distinction is
1001 // record_superlifetime(new_cx, expr.callee_id);
1009 // Manually recurse over closures, because they are the only
1010 // case of nested bodies that share the parent environment.
1011 hir::ExprKind::Closure(.., body, _, _) => {
1012 let body = visitor.tcx.hir.body(body);
1013 visitor.visit_body(body);
1016 _ => intravisit::walk_expr(visitor, expr)
1019 visitor.expr_and_pat_count += 1;
1021 debug!("resolve_expr post-increment {}, expr = {:?}", visitor.expr_and_pat_count, expr);
1023 if let hir::ExprKind::Yield(..) = expr.node {
1024 // Mark this expr's scope and all parent scopes as containing `yield`.
1025 let mut scope = Scope::Node(expr.hir_id.local_id);
1027 visitor.scope_tree.yield_in_scope.insert(scope,
1028 (expr.span, visitor.expr_and_pat_count));
1030 // Keep traversing up while we can.
1031 match visitor.scope_tree.parent_map.get(&scope) {
1032 // Don't cross from closure bodies to their parent.
1033 Some(&(superscope, _)) => match superscope.data() {
1034 ScopeData::CallSite(_) => break,
1035 _ => scope = superscope
1042 visitor.cx = prev_cx;
1045 fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1046 pat: Option<&'tcx hir::Pat>,
1047 init: Option<&'tcx hir::Expr>) {
1048 debug!("resolve_local(pat={:?}, init={:?})", pat, init);
1050 let blk_scope = visitor.cx.var_parent.map(|(p, _)| p);
1052 // As an exception to the normal rules governing temporary
1053 // lifetimes, initializers in a let have a temporary lifetime
1054 // of the enclosing block. This means that e.g. a program
1055 // like the following is legal:
1057 // let ref x = HashMap::new();
1059 // Because the hash map will be freed in the enclosing block.
1061 // We express the rules more formally based on 3 grammars (defined
1062 // fully in the helpers below that implement them):
1064 // 1. `E&`, which matches expressions like `&<rvalue>` that
1065 // own a pointer into the stack.
1067 // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
1068 // y)` that produce ref bindings into the value they are
1069 // matched against or something (at least partially) owned by
1070 // the value they are matched against. (By partially owned,
1071 // I mean that creating a binding into a ref-counted or managed value
1072 // would still count.)
1074 // 3. `ET`, which matches both rvalues like `foo()` as well as places
1075 // based on rvalues like `foo().x[2].y`.
1077 // A subexpression `<rvalue>` that appears in a let initializer
1078 // `let pat [: ty] = expr` has an extended temporary lifetime if
1079 // any of the following conditions are met:
1081 // A. `pat` matches `P&` and `expr` matches `ET`
1082 // (covers cases where `pat` creates ref bindings into an rvalue
1083 // produced by `expr`)
1084 // B. `ty` is a borrowed pointer and `expr` matches `ET`
1085 // (covers cases where coercion creates a borrow)
1086 // C. `expr` matches `E&`
1087 // (covers cases `expr` borrows an rvalue that is then assigned
1088 // to memory (at least partially) owned by the binding)
1090 // Here are some examples hopefully giving an intuition where each
1091 // rule comes into play and why:
1093 // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
1094 // would have an extended lifetime, but not `foo()`.
1096 // Rule B. `let x = &foo().x`. The rvalue ``foo()` would have extended
1099 // In some cases, multiple rules may apply (though not to the same
1100 // rvalue). For example:
1102 // let ref x = [&a(), &b()];
1104 // Here, the expression `[...]` has an extended lifetime due to rule
1105 // A, but the inner rvalues `a()` and `b()` have an extended lifetime
1108 if let Some(expr) = init {
1109 record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
1111 if let Some(pat) = pat {
1112 if is_binding_pat(pat) {
1113 record_rvalue_scope(visitor, &expr, blk_scope);
1118 // Make sure we visit the initializer first, so expr_and_pat_count remains correct
1119 if let Some(expr) = init {
1120 visitor.visit_expr(expr);
1122 if let Some(pat) = pat {
1123 visitor.visit_pat(pat);
1126 /// True if `pat` match the `P&` nonterminal:
1129 /// | StructName { ..., P&, ... }
1130 /// | VariantName(..., P&, ...)
1131 /// | [ ..., P&, ... ]
1132 /// | ( ..., P&, ... )
1134 fn is_binding_pat(pat: &hir::Pat) -> bool {
1135 // Note that the code below looks for *explicit* refs only, that is, it won't
1136 // know about *implicit* refs as introduced in #42640.
1138 // This is not a problem. For example, consider
1140 // let (ref x, ref y) = (Foo { .. }, Bar { .. });
1142 // Due to the explicit refs on the left hand side, the below code would signal
1143 // that the temporary value on the right hand side should live until the end of
1144 // the enclosing block (as opposed to being dropped after the let is complete).
1146 // To create an implicit ref, however, you must have a borrowed value on the RHS
1147 // already, as in this example (which won't compile before #42640):
1149 // let Foo { x, .. } = &Foo { x: ..., ... };
1153 // let Foo { ref x, .. } = Foo { ... };
1155 // In the former case (the implicit ref version), the temporary is created by the
1156 // & expression, and its lifetime would be extended to the end of the block (due
1157 // to a different rule, not the below code).
1159 PatKind::Binding(hir::BindingAnnotation::Ref, ..) |
1160 PatKind::Binding(hir::BindingAnnotation::RefMut, ..) => true,
1162 PatKind::Struct(_, ref field_pats, _) => {
1163 field_pats.iter().any(|fp| is_binding_pat(&fp.node.pat))
1166 PatKind::Slice(ref pats1, ref pats2, ref pats3) => {
1167 pats1.iter().any(|p| is_binding_pat(&p)) ||
1168 pats2.iter().any(|p| is_binding_pat(&p)) ||
1169 pats3.iter().any(|p| is_binding_pat(&p))
1172 PatKind::TupleStruct(_, ref subpats, _) |
1173 PatKind::Tuple(ref subpats, _) => {
1174 subpats.iter().any(|p| is_binding_pat(&p))
1177 PatKind::Box(ref subpat) => {
1178 is_binding_pat(&subpat)
1185 /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
1188 /// | StructName { ..., f: E&, ... }
1189 /// | [ ..., E&, ... ]
1190 /// | ( ..., E&, ... )
1195 fn record_rvalue_scope_if_borrow_expr<'a, 'tcx>(
1196 visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1198 blk_id: Option<Scope>)
1201 hir::ExprKind::AddrOf(_, ref subexpr) => {
1202 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
1203 record_rvalue_scope(visitor, &subexpr, blk_id);
1205 hir::ExprKind::Struct(_, ref fields, _) => {
1206 for field in fields {
1207 record_rvalue_scope_if_borrow_expr(
1208 visitor, &field.expr, blk_id);
1211 hir::ExprKind::Array(ref subexprs) |
1212 hir::ExprKind::Tup(ref subexprs) => {
1213 for subexpr in subexprs {
1214 record_rvalue_scope_if_borrow_expr(
1215 visitor, &subexpr, blk_id);
1218 hir::ExprKind::Cast(ref subexpr, _) => {
1219 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
1221 hir::ExprKind::Block(ref block, _) => {
1222 if let Some(ref subexpr) = block.expr {
1223 record_rvalue_scope_if_borrow_expr(
1224 visitor, &subexpr, blk_id);
1231 /// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
1232 /// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
1233 /// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
1236 /// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
1237 /// `<rvalue>` as `blk_id`:
1245 /// Note: ET is intended to match "rvalues or places based on rvalues".
1246 fn record_rvalue_scope<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1248 blk_scope: Option<Scope>) {
1249 let mut expr = expr;
1251 // Note: give all the expressions matching `ET` with the
1252 // extended temporary lifetime, not just the innermost rvalue,
1253 // because in codegen if we must compile e.g. `*rvalue()`
1254 // into a temporary, we request the temporary scope of the
1255 // outer expression.
1256 visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
1259 hir::ExprKind::AddrOf(_, ref subexpr) |
1260 hir::ExprKind::Unary(hir::UnDeref, ref subexpr) |
1261 hir::ExprKind::Field(ref subexpr, _) |
1262 hir::ExprKind::Index(ref subexpr, _) => {
1273 impl<'a, 'tcx> RegionResolutionVisitor<'a, 'tcx> {
1274 /// Records the current parent (if any) as the parent of `child_scope`.
1275 /// Returns the depth of `child_scope`.
1276 fn record_child_scope(&mut self, child_scope: Scope) -> ScopeDepth {
1277 let parent = self.cx.parent;
1278 self.scope_tree.record_scope_parent(child_scope, parent);
1279 // If `child_scope` has no parent, it must be the root node, and so has
1280 // a depth of 1. Otherwise, its depth is one more than its parent's.
1281 parent.map_or(1, |(_p, d)| d + 1)
1284 /// Records the current parent (if any) as the parent of `child_scope`,
1285 /// and sets `child_scope` as the new current parent.
1286 fn enter_scope(&mut self, child_scope: Scope) {
1287 let child_depth = self.record_child_scope(child_scope);
1288 self.cx.parent = Some((child_scope, child_depth));
1291 fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) {
1292 // If node was previously marked as a terminating scope during the
1293 // recursive visit of its parent node in the AST, then we need to
1294 // account for the destruction scope representing the scope of
1295 // the destructors that run immediately after it completes.
1296 if self.terminating_scopes.contains(&id) {
1297 self.enter_scope(Scope::Destruction(id));
1299 self.enter_scope(Scope::Node(id));
1303 impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
1304 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1305 NestedVisitorMap::None
1308 fn visit_block(&mut self, b: &'tcx Block) {
1309 resolve_block(self, b);
1312 fn visit_body(&mut self, body: &'tcx hir::Body) {
1313 let body_id = body.id();
1314 let owner_id = self.tcx.hir.body_owner(body_id);
1316 debug!("visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
1318 self.tcx.sess.source_map().span_to_string(body.value.span),
1322 let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
1323 let outer_cx = self.cx;
1324 let outer_ts = mem::replace(&mut self.terminating_scopes, FxHashSet());
1325 self.terminating_scopes.insert(body.value.hir_id.local_id);
1327 if let Some(root_id) = self.cx.root_id {
1328 self.scope_tree.record_closure_parent(body.value.hir_id.local_id, root_id);
1330 self.cx.root_id = Some(body.value.hir_id.local_id);
1332 self.enter_scope(Scope::CallSite(body.value.hir_id.local_id));
1333 self.enter_scope(Scope::Arguments(body.value.hir_id.local_id));
1335 // The arguments and `self` are parented to the fn.
1336 self.cx.var_parent = self.cx.parent.take();
1337 for argument in &body.arguments {
1338 self.visit_pat(&argument.pat);
1341 // The body of the every fn is a root scope.
1342 self.cx.parent = self.cx.var_parent;
1343 if let hir::BodyOwnerKind::Fn = self.tcx.hir.body_owner_kind(owner_id) {
1344 self.visit_expr(&body.value);
1346 // Only functions have an outer terminating (drop) scope, while
1347 // temporaries in constant initializers may be 'static, but only
1348 // according to rvalue lifetime semantics, using the same
1349 // syntactical rules used for let initializers.
1351 // E.g. in `let x = &f();`, the temporary holding the result from
1352 // the `f()` call lives for the entirety of the surrounding block.
1354 // Similarly, `const X: ... = &f();` would have the result of `f()`
1355 // live for `'static`, implying (if Drop restrictions on constants
1356 // ever get lifted) that the value *could* have a destructor, but
1357 // it'd get leaked instead of the destructor running during the
1358 // evaluation of `X` (if at all allowed by CTFE).
1360 // However, `const Y: ... = g(&f());`, like `let y = g(&f());`,
1361 // would *not* let the `f()` temporary escape into an outer scope
1362 // (i.e. `'static`), which means that after `g` returns, it drops,
1363 // and all the associated destruction scope rules apply.
1364 self.cx.var_parent = None;
1365 resolve_local(self, None, Some(&body.value));
1368 if body.is_generator {
1369 self.scope_tree.body_expr_count.insert(body_id, self.expr_and_pat_count);
1372 // Restore context we had at the start.
1373 self.expr_and_pat_count = outer_ec;
1375 self.terminating_scopes = outer_ts;
1378 fn visit_arm(&mut self, a: &'tcx Arm) {
1379 resolve_arm(self, a);
1381 fn visit_pat(&mut self, p: &'tcx Pat) {
1382 resolve_pat(self, p);
1384 fn visit_stmt(&mut self, s: &'tcx Stmt) {
1385 resolve_stmt(self, s);
1387 fn visit_expr(&mut self, ex: &'tcx Expr) {
1388 resolve_expr(self, ex);
1390 fn visit_local(&mut self, l: &'tcx Local) {
1391 resolve_local(self, Some(&l.pat), l.init.as_ref().map(|e| &**e));
1395 fn region_scope_tree<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
1398 let closure_base_def_id = tcx.closure_base_def_id(def_id);
1399 if closure_base_def_id != def_id {
1400 return tcx.region_scope_tree(closure_base_def_id);
1403 let id = tcx.hir.as_local_node_id(def_id).unwrap();
1404 let scope_tree = if let Some(body_id) = tcx.hir.maybe_body_owned_by(id) {
1405 let mut visitor = RegionResolutionVisitor {
1407 scope_tree: ScopeTree::default(),
1408 expr_and_pat_count: 0,
1414 terminating_scopes: FxHashSet(),
1417 let body = tcx.hir.body(body_id);
1418 visitor.scope_tree.root_body = Some(body.value.hir_id);
1420 // If the item is an associated const or a method,
1421 // record its impl/trait parent, as it can also have
1422 // lifetime parameters free in this body.
1423 match tcx.hir.get(id) {
1425 Node::TraitItem(_) => {
1426 visitor.scope_tree.root_parent = Some(tcx.hir.get_parent(id));
1431 visitor.visit_body(body);
1435 ScopeTree::default()
1438 Lrc::new(scope_tree)
1441 pub fn provide(providers: &mut Providers) {
1442 *providers = Providers {
1448 impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
1449 fn hash_stable<W: StableHasherResult>(&self,
1450 hcx: &mut StableHashingContext<'a>,
1451 hasher: &mut StableHasher<W>) {
1455 ref body_expr_count,
1458 ref destruction_scopes,
1464 hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
1465 root_body.hash_stable(hcx, hasher);
1466 root_parent.hash_stable(hcx, hasher);
1469 body_expr_count.hash_stable(hcx, hasher);
1470 parent_map.hash_stable(hcx, hasher);
1471 var_map.hash_stable(hcx, hasher);
1472 destruction_scopes.hash_stable(hcx, hasher);
1473 rvalue_scopes.hash_stable(hcx, hasher);
1474 closure_tree.hash_stable(hcx, hasher);
1475 yield_in_scope.hash_stable(hcx, hasher);