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};
24 use rustc_data_structures::sync::Lrc;
25 use syntax::source_map;
27 use syntax_pos::{Span, DUMMY_SP};
29 use ty::query::Providers;
33 use hir::def_id::DefId;
34 use hir::intravisit::{self, Visitor, NestedVisitorMap};
35 use hir::{Block, Arm, Pat, PatKind, Stmt, Expr, Local};
36 use rustc_data_structures::indexed_vec::Idx;
37 use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
40 /// Scope represents a statically-describable scope that can be
41 /// used to bound the lifetime/region for values.
43 /// `Node(node_id)`: Any AST node that has any scope at all has the
44 /// `Node(node_id)` scope. Other variants represent special cases not
45 /// immediately derivable from the abstract syntax tree structure.
47 /// `DestructionScope(node_id)` represents the scope of destructors
48 /// implicitly-attached to `node_id` that run immediately after the
49 /// expression for `node_id` itself. Not every AST node carries a
50 /// `DestructionScope`, but those that are `terminating_scopes` do;
51 /// see discussion with `ScopeTree`.
53 /// `Remainder(BlockRemainder { block, statement_index })` represents
54 /// the scope of user code running immediately after the initializer
55 /// expression for the indexed statement, until the end of the block.
57 /// So: the following code can be broken down into the scopes beneath:
60 /// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y) } ) ;
64 /// +---------+ (R10.)
66 /// +----------+ (M8.)
67 /// +----------------------+ (R7.)
69 /// +----------+ (M5.)
70 /// +-----------------------------------+ (M4.)
71 /// +--------------------------------------------------+ (M3.)
73 /// +-----------------------------------------------------------+ (M1.)
75 /// (M1.): Node scope of the whole `let a = ...;` statement.
76 /// (M2.): Node scope of the `f()` expression.
77 /// (M3.): Node scope of the `f().g(..)` expression.
78 /// (M4.): Node scope of the block labeled `'b:`.
79 /// (M5.): Node scope of the `let x = d();` statement
80 /// (D6.): DestructionScope for temporaries created during M5.
81 /// (R7.): Remainder scope for block `'b:`, stmt 0 (let x = ...).
82 /// (M8.): Node scope of the `let y = d();` statement.
83 /// (D9.): DestructionScope for temporaries created during M8.
84 /// (R10.): Remainder scope for block `'b:`, stmt 1 (let y = ...).
85 /// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
86 /// (D12.): DestructionScope for temporaries created during M1 (e.g. f()).
89 /// Note that while the above picture shows the destruction scopes
90 /// as following their corresponding node scopes, in the internal
91 /// data structures of the compiler the destruction scopes are
92 /// represented as enclosing parents. This is sound because we use the
93 /// enclosing parent relationship just to ensure that referenced
94 /// values live long enough; phrased another way, the starting point
95 /// of each range is not really the important thing in the above
96 /// picture, but rather the ending point.
98 /// FIXME (pnkfelix): This currently derives `PartialOrd` and `Ord` to
99 /// placate the same deriving in `ty::FreeRegion`, but we may want to
100 /// actually attach a more meaningful ordering to scopes than the one
101 /// generated via deriving here.
102 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, RustcEncodable, RustcDecodable)]
104 pub(crate) id: hir::ItemLocalId,
105 pub(crate) data: ScopeData,
108 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, RustcEncodable, RustcDecodable)]
112 // Scope of the call-site for a function or closure
113 // (outlives the arguments as well as the body).
116 // Scope of arguments passed to a function or closure
117 // (they outlive its body).
120 // Scope of destructors for temporaries of node-id.
123 // Scope following a `let id = expr;` binding in a block.
124 Remainder(FirstStatementIndex)
127 /// Represents a subscope of `block` for a binding that is introduced
128 /// by `block.stmts[first_statement_index]`. Such subscopes represent
129 /// a suffix of the block. Note that each subscope does not include
130 /// the initializer expression, if any, for the statement indexed by
131 /// `first_statement_index`.
133 /// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
135 /// * the subscope with `first_statement_index == 0` is scope of both
136 /// `a` and `b`; it does not include EXPR_1, but does include
137 /// everything after that first `let`. (If you want a scope that
138 /// includes EXPR_1 as well, then do not use `Scope::Remainder`,
139 /// but instead another `Scope` that encompasses the whole block,
140 /// e.g. `Scope::Node`.
142 /// * the subscope with `first_statement_index == 1` is scope of `c`,
143 /// and thus does not include EXPR_2, but covers the `...`.
146 pub struct FirstStatementIndex { .. }
149 impl_stable_hash_for!(struct ::middle::region::FirstStatementIndex { private });
151 // compilation error if size of `ScopeData` is not the same as a `u32`
153 // only works on stage 1 when the rustc_layout_scalar_valid_range attribute actually exists
155 static ASSERT: () = [()][!(mem::size_of::<ScopeData>() == 4) as usize];
157 #[allow(non_snake_case)]
160 pub fn data(self) -> ScopeData {
165 pub fn new(id: hir::ItemLocalId, data: ScopeData) -> Self {
170 pub fn Node(id: hir::ItemLocalId) -> Self {
171 Self::new(id, ScopeData::Node)
175 pub fn CallSite(id: hir::ItemLocalId) -> Self {
176 Self::new(id, ScopeData::CallSite)
180 pub fn Arguments(id: hir::ItemLocalId) -> Self {
181 Self::new(id, ScopeData::Arguments)
185 pub fn Destruction(id: hir::ItemLocalId) -> Self {
186 Self::new(id, ScopeData::Destruction)
191 id: hir::ItemLocalId,
192 first: FirstStatementIndex,
194 Self::new(id, ScopeData::Remainder(first))
200 /// Returns a item-local id associated with this scope.
202 /// NB: likely to be replaced as API is refined; e.g. pnkfelix
203 /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
204 pub fn item_local_id(&self) -> hir::ItemLocalId {
208 pub fn node_id(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> ast::NodeId {
209 match scope_tree.root_body {
211 tcx.hir.hir_to_node_id(hir::HirId {
213 local_id: self.item_local_id()
216 None => ast::DUMMY_NODE_ID
220 /// Returns the span of this Scope. Note that in general the
221 /// returned span may not correspond to the span of any node id in
223 pub fn span(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> Span {
224 let node_id = self.node_id(tcx, scope_tree);
225 if node_id == ast::DUMMY_NODE_ID {
228 let span = tcx.hir.span(node_id);
229 if let ScopeData::Remainder(first_statement_index) = self.data() {
230 if let Node::Block(ref blk) = tcx.hir.get(node_id) {
231 // Want span for scope starting after the
232 // indexed statement and ending at end of
233 // `blk`; reuse span of `blk` and shift `lo`
234 // forward to end of indexed statement.
236 // (This is the special case aluded to in the
237 // doc-comment for this method)
239 let stmt_span = blk.stmts[first_statement_index.index()].span;
241 // To avoid issues with macro-generated spans, the span
242 // of the statement must be nested in that of the block.
243 if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() {
244 return Span::new(stmt_span.lo(), span.hi(), span.ctxt());
252 pub type ScopeDepth = u32;
254 /// The region scope tree encodes information about region relationships.
255 #[derive(Default, Debug)]
256 pub struct ScopeTree {
257 /// If not empty, this body is the root of this region hierarchy.
258 root_body: Option<hir::HirId>,
260 /// The parent of the root body owner, if the latter is an
261 /// an associated const or method, as impls/traits can also
262 /// have lifetime parameters free in this body.
263 root_parent: Option<ast::NodeId>,
265 /// `parent_map` maps from a scope id to the enclosing scope id;
266 /// this is usually corresponding to the lexical nesting, though
267 /// in the case of closures the parent scope is the innermost
268 /// conditional expression or repeating block. (Note that the
269 /// enclosing scope id for the block associated with a closure is
270 /// the closure itself.)
271 parent_map: FxHashMap<Scope, (Scope, ScopeDepth)>,
273 /// `var_map` maps from a variable or binding id to the block in
274 /// which that variable is declared.
275 var_map: FxHashMap<hir::ItemLocalId, Scope>,
277 /// maps from a node-id to the associated destruction scope (if any)
278 destruction_scopes: FxHashMap<hir::ItemLocalId, Scope>,
280 /// `rvalue_scopes` includes entries for those expressions whose cleanup scope is
281 /// larger than the default. The map goes from the expression id
282 /// to the cleanup scope id. For rvalues not present in this
283 /// table, the appropriate cleanup scope is the innermost
284 /// enclosing statement, conditional expression, or repeating
285 /// block (see `terminating_scopes`).
286 /// In constants, None is used to indicate that certain expressions
287 /// escape into 'static and should have no local cleanup scope.
288 rvalue_scopes: FxHashMap<hir::ItemLocalId, Option<Scope>>,
290 /// Encodes the hierarchy of fn bodies. Every fn body (including
291 /// closures) forms its own distinct region hierarchy, rooted in
292 /// the block that is the fn body. This map points from the id of
293 /// that root block to the id of the root block for the enclosing
294 /// fn, if any. Thus the map structures the fn bodies into a
295 /// hierarchy based on their lexical mapping. This is used to
296 /// handle the relationships between regions in a fn and in a
297 /// closure defined by that fn. See the "Modeling closures"
298 /// section of the README in infer::region_constraints for
300 closure_tree: FxHashMap<hir::ItemLocalId, hir::ItemLocalId>,
302 /// If there are any `yield` nested within a scope, this map
303 /// stores the `Span` of the last one and its index in the
304 /// postorder of the Visitor traversal on the HIR.
306 /// HIR Visitor postorder indexes might seem like a peculiar
307 /// thing to care about. but it turns out that HIR bindings
308 /// and the temporary results of HIR expressions are never
309 /// storage-live at the end of HIR nodes with postorder indexes
310 /// lower than theirs, and therefore don't need to be suspended
311 /// at yield-points at these indexes.
313 /// For an example, suppose we have some code such as:
314 /// ```rust,ignore (example)
315 /// foo(f(), yield y, bar(g()))
318 /// With the HIR tree (calls numbered for expository purposes)
320 /// Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
323 /// Obviously, the result of `f()` was created before the yield
324 /// (and therefore needs to be kept valid over the yield) while
325 /// the result of `g()` occurs after the yield (and therefore
326 /// doesn't). If we want to infer that, we can look at the
327 /// postorder traversal:
329 /// `foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
332 /// In which we can easily see that `Call#1` occurs before the yield,
333 /// and `Call#3` after it.
335 /// To see that this method works, consider:
337 /// Let `D` be our binding/temporary and `U` be our other HIR node, with
338 /// `HIR-postorder(U) < HIR-postorder(D)` (in our example, U would be
339 /// the yield and D would be one of the calls). Let's show that
340 /// `D` is storage-dead at `U`.
342 /// Remember that storage-live/storage-dead refers to the state of
343 /// the *storage*, and does not consider moves/drop flags.
346 /// 1. From the ordering guarantee of HIR visitors (see
347 /// `rustc::hir::intravisit`), `D` does not dominate `U`.
348 /// 2. Therefore, `D` is *potentially* storage-dead at `U` (because
349 /// we might visit `U` without ever getting to `D`).
350 /// 3. However, we guarantee that at each HIR point, each
351 /// binding/temporary is always either always storage-live
352 /// or always storage-dead. This is what is being guaranteed
353 /// by `terminating_scopes` including all blocks where the
354 /// count of executions is not guaranteed.
355 /// 4. By `2.` and `3.`, `D` is *statically* storage-dead at `U`,
358 /// I don't think this property relies on `3.` in an essential way - it
359 /// is probably still correct even if we have "unrestricted" terminating
360 /// scopes. However, why use the complicated proof when a simple one
363 /// A subtle thing: `box` expressions, such as `box (&x, yield 2, &y)`. It
364 /// might seem that a `box` expression creates a `Box<T>` temporary
365 /// when it *starts* executing, at `HIR-preorder(BOX-EXPR)`. That might
366 /// be true in the MIR desugaring, but it is not important in the semantics.
368 /// The reason is that semantically, until the `box` expression returns,
369 /// the values are still owned by their containing expressions. So
370 /// we'll see that `&x`.
371 yield_in_scope: FxHashMap<Scope, (Span, usize)>,
373 /// The number of visit_expr and visit_pat calls done in the body.
374 /// Used to sanity check visit_expr/visit_pat call count when
375 /// calculating generator interiors.
376 body_expr_count: FxHashMap<hir::BodyId, usize>,
379 #[derive(Debug, Copy, Clone)]
381 /// the root of the current region tree. This is typically the id
382 /// of the innermost fn body. Each fn forms its own disjoint tree
383 /// in the region hierarchy. These fn bodies are themselves
384 /// arranged into a tree. See the "Modeling closures" section of
385 /// the README in infer::region_constraints for more
387 root_id: Option<hir::ItemLocalId>,
389 /// The scope that contains any new variables declared, plus its depth in
391 var_parent: Option<(Scope, ScopeDepth)>,
393 /// Region parent of expressions, etc., plus its depth in the scope tree.
394 parent: Option<(Scope, ScopeDepth)>,
397 struct RegionResolutionVisitor<'a, 'tcx: 'a> {
398 tcx: TyCtxt<'a, 'tcx, 'tcx>,
400 // The number of expressions and patterns visited in the current body
401 expr_and_pat_count: usize,
403 // Generated scope tree:
404 scope_tree: ScopeTree,
408 /// `terminating_scopes` is a set containing the ids of each
409 /// statement, or conditional/repeating expression. These scopes
410 /// are calling "terminating scopes" because, when attempting to
411 /// find the scope of a temporary, by default we search up the
412 /// enclosing scopes until we encounter the terminating scope. A
413 /// conditional/repeating expression is one which is not
414 /// guaranteed to execute exactly once upon entering the parent
415 /// scope. This could be because the expression only executes
416 /// conditionally, such as the expression `b` in `a && b`, or
417 /// because the expression may execute many times, such as a loop
418 /// body. The reason that we distinguish such expressions is that,
419 /// upon exiting the parent scope, we cannot statically know how
420 /// many times the expression executed, and thus if the expression
421 /// creates temporaries we cannot know statically how many such
422 /// temporaries we would have to cleanup. Therefore we ensure that
423 /// the temporaries never outlast the conditional/repeating
424 /// expression, preventing the need for dynamic checks and/or
425 /// arbitrary amounts of stack space. Terminating scopes end
426 /// up being contained in a DestructionScope that contains the
427 /// destructor's execution.
428 terminating_scopes: FxHashSet<hir::ItemLocalId>,
431 struct ExprLocatorVisitor {
433 result: Option<usize>,
434 expr_and_pat_count: usize,
437 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor
438 // since `expr_count` is compared against the results there.
439 impl<'tcx> Visitor<'tcx> for ExprLocatorVisitor {
440 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
441 NestedVisitorMap::None
444 fn visit_pat(&mut self, pat: &'tcx Pat) {
445 intravisit::walk_pat(self, pat);
447 self.expr_and_pat_count += 1;
449 if pat.hir_id == self.hir_id {
450 self.result = Some(self.expr_and_pat_count);
454 fn visit_expr(&mut self, expr: &'tcx Expr) {
455 debug!("ExprLocatorVisitor - pre-increment {} expr = {:?}",
456 self.expr_and_pat_count,
459 intravisit::walk_expr(self, expr);
461 self.expr_and_pat_count += 1;
463 debug!("ExprLocatorVisitor - post-increment {} expr = {:?}",
464 self.expr_and_pat_count,
467 if expr.hir_id == self.hir_id {
468 self.result = Some(self.expr_and_pat_count);
473 impl<'tcx> ScopeTree {
474 pub fn record_scope_parent(&mut self, child: Scope, parent: Option<(Scope, ScopeDepth)>) {
475 debug!("{:?}.parent = {:?}", child, parent);
477 if let Some(p) = parent {
478 let prev = self.parent_map.insert(child, p);
479 assert!(prev.is_none());
482 // record the destruction scopes for later so we can query them
483 if let ScopeData::Destruction = child.data() {
484 self.destruction_scopes.insert(child.item_local_id(), child);
488 pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(Scope, Scope) {
489 for (&child, &parent) in &self.parent_map {
494 pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&hir::ItemLocalId, Scope) {
495 for (child, &parent) in self.var_map.iter() {
500 pub fn opt_destruction_scope(&self, n: hir::ItemLocalId) -> Option<Scope> {
501 self.destruction_scopes.get(&n).cloned()
504 /// Records that `sub_closure` is defined within `sup_closure`. These ids
505 /// should be the id of the block that is the fn body, which is
506 /// also the root of the region hierarchy for that fn.
507 fn record_closure_parent(&mut self,
508 sub_closure: hir::ItemLocalId,
509 sup_closure: hir::ItemLocalId) {
510 debug!("record_closure_parent(sub_closure={:?}, sup_closure={:?})",
511 sub_closure, sup_closure);
512 assert!(sub_closure != sup_closure);
513 let previous = self.closure_tree.insert(sub_closure, sup_closure);
514 assert!(previous.is_none());
517 fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) {
518 debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
519 assert!(var != lifetime.item_local_id());
520 self.var_map.insert(var, lifetime);
523 fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
524 debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
525 if let Some(lifetime) = lifetime {
526 assert!(var != lifetime.item_local_id());
528 self.rvalue_scopes.insert(var, lifetime);
531 pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> {
532 //! Returns the narrowest scope that encloses `id`, if any.
533 self.parent_map.get(&id).cloned().map(|(p, _)| p)
536 #[allow(dead_code)] // used in cfg
537 pub fn encl_scope(&self, id: Scope) -> Scope {
538 //! Returns the narrowest scope that encloses `id`, if any.
539 self.opt_encl_scope(id).unwrap()
542 /// Returns the lifetime of the local variable `var_id`
543 pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Scope {
544 match self.var_map.get(&var_id) {
546 None => { bug!("no enclosing scope for id {:?}", var_id); }
550 pub fn temporary_scope(&self, expr_id: hir::ItemLocalId) -> Option<Scope> {
551 //! Returns the scope when temp created by expr_id will be cleaned up
553 // check for a designated rvalue scope
554 if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
555 debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
559 // else, locate the innermost terminating scope
560 // if there's one. Static items, for instance, won't
561 // have an enclosing scope, hence no scope will be
563 let mut id = Scope::Node(expr_id);
565 while let Some(&(p, _)) = self.parent_map.get(&id) {
567 ScopeData::Destruction => {
568 debug!("temporary_scope({:?}) = {:?} [enclosing]",
576 debug!("temporary_scope({:?}) = None", expr_id);
580 pub fn var_region(&self, id: hir::ItemLocalId) -> ty::RegionKind {
581 //! Returns the lifetime of the variable `id`.
583 let scope = ty::ReScope(self.var_scope(id));
584 debug!("var_region({:?}) = {:?}", id, scope);
588 pub fn scopes_intersect(&self, scope1: Scope, scope2: Scope)
590 self.is_subscope_of(scope1, scope2) ||
591 self.is_subscope_of(scope2, scope1)
594 /// Returns true if `subscope` is equal to or is lexically nested inside `superscope` and false
596 pub fn is_subscope_of(&self,
600 let mut s = subscope;
601 debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
602 while superscope != s {
603 match self.opt_encl_scope(s) {
605 debug!("is_subscope_of({:?}, {:?}, s={:?})=false",
606 subscope, superscope, s);
609 Some(scope) => s = scope
613 debug!("is_subscope_of({:?}, {:?})=true",
614 subscope, superscope);
619 /// Returns the id of the innermost containing body
620 pub fn containing_body(&self, mut scope: Scope)-> Option<hir::ItemLocalId> {
622 if let ScopeData::CallSite = scope.data() {
623 return Some(scope.item_local_id());
626 match self.opt_encl_scope(scope) {
628 Some(parent) => scope = parent,
633 /// Finds the nearest common ancestor of two scopes. That is, finds the
634 /// smallest scope which is greater than or equal to both `scope_a` and
636 pub fn nearest_common_ancestor(&self, scope_a: Scope, scope_b: Scope) -> Scope {
637 if scope_a == scope_b { return scope_a; }
642 // Get the depth of each scope's parent. If either scope has no parent,
643 // it must be the root, which means we can stop immediately because the
644 // root must be the nearest common ancestor. (In practice, this is
645 // moderately common.)
646 let (parent_a, parent_a_depth) = match self.parent_map.get(&a) {
650 let (parent_b, parent_b_depth) = match self.parent_map.get(&b) {
655 if parent_a_depth > parent_b_depth {
656 // `a` is lower than `b`. Move `a` up until it's at the same depth
657 // as `b`. The first move up is trivial because we already found
658 // `parent_a` above; the loop does the remaining N-1 moves.
660 for _ in 0..(parent_a_depth - parent_b_depth - 1) {
661 a = self.parent_map.get(&a).unwrap().0;
663 } else if parent_b_depth > parent_a_depth {
664 // `b` is lower than `a`.
666 for _ in 0..(parent_b_depth - parent_a_depth - 1) {
667 b = self.parent_map.get(&b).unwrap().0;
670 // Both scopes are at the same depth, and we know they're not equal
671 // because that case was tested for at the top of this function. So
672 // we can trivially move them both up one level now.
673 assert!(parent_a_depth != 0);
678 // Now both scopes are at the same level. We move upwards in lockstep
679 // until they match. In practice, this loop is almost always executed
680 // zero times because `a` is almost always a direct ancestor of `b` or
683 a = self.parent_map.get(&a).unwrap().0;
684 b = self.parent_map.get(&b).unwrap().0;
690 /// Assuming that the provided region was defined within this `ScopeTree`,
691 /// returns the outermost `Scope` that the region outlives.
692 pub fn early_free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
693 br: &ty::EarlyBoundRegion)
695 let param_owner = tcx.parent_def_id(br.def_id).unwrap();
697 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
698 let scope = tcx.hir.maybe_body_owned_by(param_owner_id).map(|body_id| {
699 tcx.hir.body(body_id).value.hir_id.local_id
700 }).unwrap_or_else(|| {
701 // The lifetime was defined on node that doesn't own a body,
702 // which in practice can only mean a trait or an impl, that
703 // is the parent of a method, and that is enforced below.
704 assert_eq!(Some(param_owner_id), self.root_parent,
705 "free_scope: {:?} not recognized by the \
706 region scope tree for {:?} / {:?}",
708 self.root_parent.map(|id| tcx.hir.local_def_id(id)),
709 self.root_body.map(|hir_id| DefId::local(hir_id.owner)));
711 // The trait/impl lifetime is in scope for the method's body.
712 self.root_body.unwrap().local_id
715 Scope::CallSite(scope)
718 /// Assuming that the provided region was defined within this `ScopeTree`,
719 /// returns the outermost `Scope` that the region outlives.
720 pub fn free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, fr: &ty::FreeRegion)
722 let param_owner = match fr.bound_region {
723 ty::BoundRegion::BrNamed(def_id, _) => {
724 tcx.parent_def_id(def_id).unwrap()
729 // Ensure that the named late-bound lifetimes were defined
730 // on the same function that they ended up being freed in.
731 assert_eq!(param_owner, fr.scope);
733 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
734 let body_id = tcx.hir.body_owned_by(param_owner_id);
735 Scope::CallSite(tcx.hir.body(body_id).value.hir_id.local_id)
738 /// Checks whether the given scope contains a `yield`. If so,
739 /// returns `Some((span, expr_count))` with the span of a yield we found and
740 /// the number of expressions and patterns appearing before the `yield` in the body + 1.
741 /// If there a are multiple yields in a scope, the one with the highest number is returned.
742 pub fn yield_in_scope(&self, scope: Scope) -> Option<(Span, usize)> {
743 self.yield_in_scope.get(&scope).cloned()
746 /// Checks whether the given scope contains a `yield` and if that yield could execute
747 /// after `expr`. If so, it returns the span of that `yield`.
748 /// `scope` must be inside the body.
749 pub fn yield_in_scope_for_expr(&self,
751 expr_hir_id: hir::HirId,
752 body: &'tcx hir::Body) -> Option<Span> {
753 self.yield_in_scope(scope).and_then(|(span, count)| {
754 let mut visitor = ExprLocatorVisitor {
757 expr_and_pat_count: 0,
759 visitor.visit_body(body);
760 if count >= visitor.result.unwrap() {
768 /// Gives the number of expressions visited in a body.
769 /// Used to sanity check visit_expr call count when
770 /// calculating generator interiors.
771 pub fn body_expr_count(&self, body_id: hir::BodyId) -> Option<usize> {
772 self.body_expr_count.get(&body_id).map(|r| *r)
776 /// Records the lifetime of a local variable as `cx.var_parent`
777 fn record_var_lifetime(visitor: &mut RegionResolutionVisitor,
778 var_id: hir::ItemLocalId,
780 match visitor.cx.var_parent {
782 // this can happen in extern fn declarations like
784 // extern fn isalnum(c: c_int) -> c_int
786 Some((parent_scope, _)) =>
787 visitor.scope_tree.record_var_scope(var_id, parent_scope),
791 fn resolve_block<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, blk: &'tcx hir::Block) {
792 debug!("resolve_block(blk.id={:?})", blk.id);
794 let prev_cx = visitor.cx;
796 // We treat the tail expression in the block (if any) somewhat
797 // differently from the statements. The issue has to do with
798 // temporary lifetimes. Consider the following:
801 // let inner = ... (&bar()) ...;
803 // (... (&foo()) ...) // (the tail expression)
804 // }, other_argument());
806 // Each of the statements within the block is a terminating
807 // scope, and thus a temporary (e.g. the result of calling
808 // `bar()` in the initializer expression for `let inner = ...;`)
809 // will be cleaned up immediately after its corresponding
810 // statement (i.e. `let inner = ...;`) executes.
812 // On the other hand, temporaries associated with evaluating the
813 // tail expression for the block are assigned lifetimes so that
814 // they will be cleaned up as part of the terminating scope
815 // *surrounding* the block expression. Here, the terminating
816 // scope for the block expression is the `quux(..)` call; so
817 // those temporaries will only be cleaned up *after* both
818 // `other_argument()` has run and also the call to `quux(..)`
819 // itself has returned.
821 visitor.enter_node_scope_with_dtor(blk.hir_id.local_id);
822 visitor.cx.var_parent = visitor.cx.parent;
825 // This block should be kept approximately in sync with
826 // `intravisit::walk_block`. (We manually walk the block, rather
827 // than call `walk_block`, in order to maintain precise
828 // index information.)
830 for (i, statement) in blk.stmts.iter().enumerate() {
831 if let hir::StmtKind::Decl(..) = statement.node {
832 // Each StmtKind::Decl introduces a subscope for bindings
833 // introduced by the declaration; this subscope covers
834 // a suffix of the block . Each subscope in a block
835 // has the previous subscope in the block as a parent,
836 // except for the first such subscope, which has the
837 // block itself as a parent.
839 Scope::Remainder(blk.hir_id.local_id, FirstStatementIndex::new(i))
841 visitor.cx.var_parent = visitor.cx.parent;
843 visitor.visit_stmt(statement)
845 walk_list!(visitor, visit_expr, &blk.expr);
848 visitor.cx = prev_cx;
851 fn resolve_arm<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, arm: &'tcx hir::Arm) {
852 visitor.terminating_scopes.insert(arm.body.hir_id.local_id);
854 if let Some(ref g) = arm.guard {
856 hir::Guard::If(ref expr) => visitor.terminating_scopes.insert(expr.hir_id.local_id),
860 intravisit::walk_arm(visitor, arm);
863 fn resolve_pat<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, pat: &'tcx hir::Pat) {
864 visitor.record_child_scope(Scope::Node(pat.hir_id.local_id));
866 // If this is a binding then record the lifetime of that binding.
867 if let PatKind::Binding(..) = pat.node {
868 record_var_lifetime(visitor, pat.hir_id.local_id, pat.span);
871 debug!("resolve_pat - pre-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
873 intravisit::walk_pat(visitor, pat);
875 visitor.expr_and_pat_count += 1;
877 debug!("resolve_pat - post-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
880 fn resolve_stmt<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, stmt: &'tcx hir::Stmt) {
881 let stmt_id = visitor.tcx.hir.node_to_hir_id(stmt.node.id()).local_id;
882 debug!("resolve_stmt(stmt.id={:?})", stmt_id);
884 // Every statement will clean up the temporaries created during
885 // execution of that statement. Therefore each statement has an
886 // associated destruction scope that represents the scope of the
887 // statement plus its destructors, and thus the scope for which
888 // regions referenced by the destructors need to survive.
889 visitor.terminating_scopes.insert(stmt_id);
891 let prev_parent = visitor.cx.parent;
892 visitor.enter_node_scope_with_dtor(stmt_id);
894 intravisit::walk_stmt(visitor, stmt);
896 visitor.cx.parent = prev_parent;
899 fn resolve_expr<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, expr: &'tcx hir::Expr) {
900 debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
902 let prev_cx = visitor.cx;
903 visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);
906 let terminating_scopes = &mut visitor.terminating_scopes;
907 let mut terminating = |id: hir::ItemLocalId| {
908 terminating_scopes.insert(id);
911 // Conditional or repeating scopes are always terminating
912 // scopes, meaning that temporaries cannot outlive them.
913 // This ensures fixed size stacks.
915 hir::ExprKind::Binary(
916 source_map::Spanned { node: hir::BinOpKind::And, .. },
918 hir::ExprKind::Binary(
919 source_map::Spanned { node: hir::BinOpKind::Or, .. },
921 // For shortcircuiting operators, mark the RHS as a terminating
922 // scope since it only executes conditionally.
923 terminating(r.hir_id.local_id);
926 hir::ExprKind::If(ref expr, ref then, Some(ref otherwise)) => {
927 terminating(expr.hir_id.local_id);
928 terminating(then.hir_id.local_id);
929 terminating(otherwise.hir_id.local_id);
932 hir::ExprKind::If(ref expr, ref then, None) => {
933 terminating(expr.hir_id.local_id);
934 terminating(then.hir_id.local_id);
937 hir::ExprKind::Loop(ref body, _, _) => {
938 terminating(body.hir_id.local_id);
941 hir::ExprKind::While(ref expr, ref body, _) => {
942 terminating(expr.hir_id.local_id);
943 terminating(body.hir_id.local_id);
946 hir::ExprKind::Match(..) => {
947 visitor.cx.var_parent = visitor.cx.parent;
950 hir::ExprKind::AssignOp(..) | hir::ExprKind::Index(..) |
951 hir::ExprKind::Unary(..) | hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) => {
952 // FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls
954 // The lifetimes for a call or method call look as follows:
962 // The idea is that call.callee_id represents *the time when
963 // the invoked function is actually running* and call.id
964 // represents *the time to prepare the arguments and make the
965 // call*. See the section "Borrows in Calls" borrowck/README.md
966 // for an extended explanation of why this distinction is
969 // record_superlifetime(new_cx, expr.callee_id);
977 // Manually recurse over closures, because they are the only
978 // case of nested bodies that share the parent environment.
979 hir::ExprKind::Closure(.., body, _, _) => {
980 let body = visitor.tcx.hir.body(body);
981 visitor.visit_body(body);
984 _ => intravisit::walk_expr(visitor, expr)
987 visitor.expr_and_pat_count += 1;
989 debug!("resolve_expr post-increment {}, expr = {:?}", visitor.expr_and_pat_count, expr);
991 if let hir::ExprKind::Yield(..) = expr.node {
992 // Mark this expr's scope and all parent scopes as containing `yield`.
993 let mut scope = Scope::Node(expr.hir_id.local_id);
995 visitor.scope_tree.yield_in_scope.insert(scope,
996 (expr.span, visitor.expr_and_pat_count));
998 // Keep traversing up while we can.
999 match visitor.scope_tree.parent_map.get(&scope) {
1000 // Don't cross from closure bodies to their parent.
1001 Some(&(superscope, _)) => match superscope.data() {
1002 ScopeData::CallSite => break,
1003 _ => scope = superscope
1010 visitor.cx = prev_cx;
1013 fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1014 pat: Option<&'tcx hir::Pat>,
1015 init: Option<&'tcx hir::Expr>) {
1016 debug!("resolve_local(pat={:?}, init={:?})", pat, init);
1018 let blk_scope = visitor.cx.var_parent.map(|(p, _)| p);
1020 // As an exception to the normal rules governing temporary
1021 // lifetimes, initializers in a let have a temporary lifetime
1022 // of the enclosing block. This means that e.g. a program
1023 // like the following is legal:
1025 // let ref x = HashMap::new();
1027 // Because the hash map will be freed in the enclosing block.
1029 // We express the rules more formally based on 3 grammars (defined
1030 // fully in the helpers below that implement them):
1032 // 1. `E&`, which matches expressions like `&<rvalue>` that
1033 // own a pointer into the stack.
1035 // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
1036 // y)` that produce ref bindings into the value they are
1037 // matched against or something (at least partially) owned by
1038 // the value they are matched against. (By partially owned,
1039 // I mean that creating a binding into a ref-counted or managed value
1040 // would still count.)
1042 // 3. `ET`, which matches both rvalues like `foo()` as well as places
1043 // based on rvalues like `foo().x[2].y`.
1045 // A subexpression `<rvalue>` that appears in a let initializer
1046 // `let pat [: ty] = expr` has an extended temporary lifetime if
1047 // any of the following conditions are met:
1049 // A. `pat` matches `P&` and `expr` matches `ET`
1050 // (covers cases where `pat` creates ref bindings into an rvalue
1051 // produced by `expr`)
1052 // B. `ty` is a borrowed pointer and `expr` matches `ET`
1053 // (covers cases where coercion creates a borrow)
1054 // C. `expr` matches `E&`
1055 // (covers cases `expr` borrows an rvalue that is then assigned
1056 // to memory (at least partially) owned by the binding)
1058 // Here are some examples hopefully giving an intuition where each
1059 // rule comes into play and why:
1061 // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
1062 // would have an extended lifetime, but not `foo()`.
1064 // Rule B. `let x = &foo().x`. The rvalue ``foo()` would have extended
1067 // In some cases, multiple rules may apply (though not to the same
1068 // rvalue). For example:
1070 // let ref x = [&a(), &b()];
1072 // Here, the expression `[...]` has an extended lifetime due to rule
1073 // A, but the inner rvalues `a()` and `b()` have an extended lifetime
1076 if let Some(expr) = init {
1077 record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
1079 if let Some(pat) = pat {
1080 if is_binding_pat(pat) {
1081 record_rvalue_scope(visitor, &expr, blk_scope);
1086 // Make sure we visit the initializer first, so expr_and_pat_count remains correct
1087 if let Some(expr) = init {
1088 visitor.visit_expr(expr);
1090 if let Some(pat) = pat {
1091 visitor.visit_pat(pat);
1094 /// True if `pat` match the `P&` nonterminal:
1097 /// | StructName { ..., P&, ... }
1098 /// | VariantName(..., P&, ...)
1099 /// | [ ..., P&, ... ]
1100 /// | ( ..., P&, ... )
1102 fn is_binding_pat(pat: &hir::Pat) -> bool {
1103 // Note that the code below looks for *explicit* refs only, that is, it won't
1104 // know about *implicit* refs as introduced in #42640.
1106 // This is not a problem. For example, consider
1108 // let (ref x, ref y) = (Foo { .. }, Bar { .. });
1110 // Due to the explicit refs on the left hand side, the below code would signal
1111 // that the temporary value on the right hand side should live until the end of
1112 // the enclosing block (as opposed to being dropped after the let is complete).
1114 // To create an implicit ref, however, you must have a borrowed value on the RHS
1115 // already, as in this example (which won't compile before #42640):
1117 // let Foo { x, .. } = &Foo { x: ..., ... };
1121 // let Foo { ref x, .. } = Foo { ... };
1123 // In the former case (the implicit ref version), the temporary is created by the
1124 // & expression, and its lifetime would be extended to the end of the block (due
1125 // to a different rule, not the below code).
1127 PatKind::Binding(hir::BindingAnnotation::Ref, ..) |
1128 PatKind::Binding(hir::BindingAnnotation::RefMut, ..) => true,
1130 PatKind::Struct(_, ref field_pats, _) => {
1131 field_pats.iter().any(|fp| is_binding_pat(&fp.node.pat))
1134 PatKind::Slice(ref pats1, ref pats2, ref pats3) => {
1135 pats1.iter().any(|p| is_binding_pat(&p)) ||
1136 pats2.iter().any(|p| is_binding_pat(&p)) ||
1137 pats3.iter().any(|p| is_binding_pat(&p))
1140 PatKind::TupleStruct(_, ref subpats, _) |
1141 PatKind::Tuple(ref subpats, _) => {
1142 subpats.iter().any(|p| is_binding_pat(&p))
1145 PatKind::Box(ref subpat) => {
1146 is_binding_pat(&subpat)
1153 /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
1156 /// | StructName { ..., f: E&, ... }
1157 /// | [ ..., E&, ... ]
1158 /// | ( ..., E&, ... )
1163 fn record_rvalue_scope_if_borrow_expr<'a, 'tcx>(
1164 visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1166 blk_id: Option<Scope>)
1169 hir::ExprKind::AddrOf(_, ref subexpr) => {
1170 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
1171 record_rvalue_scope(visitor, &subexpr, blk_id);
1173 hir::ExprKind::Struct(_, ref fields, _) => {
1174 for field in fields {
1175 record_rvalue_scope_if_borrow_expr(
1176 visitor, &field.expr, blk_id);
1179 hir::ExprKind::Array(ref subexprs) |
1180 hir::ExprKind::Tup(ref subexprs) => {
1181 for subexpr in subexprs {
1182 record_rvalue_scope_if_borrow_expr(
1183 visitor, &subexpr, blk_id);
1186 hir::ExprKind::Cast(ref subexpr, _) => {
1187 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
1189 hir::ExprKind::Block(ref block, _) => {
1190 if let Some(ref subexpr) = block.expr {
1191 record_rvalue_scope_if_borrow_expr(
1192 visitor, &subexpr, blk_id);
1199 /// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
1200 /// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
1201 /// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
1204 /// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
1205 /// `<rvalue>` as `blk_id`:
1213 /// Note: ET is intended to match "rvalues or places based on rvalues".
1214 fn record_rvalue_scope<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1216 blk_scope: Option<Scope>) {
1217 let mut expr = expr;
1219 // Note: give all the expressions matching `ET` with the
1220 // extended temporary lifetime, not just the innermost rvalue,
1221 // because in codegen if we must compile e.g. `*rvalue()`
1222 // into a temporary, we request the temporary scope of the
1223 // outer expression.
1224 visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
1227 hir::ExprKind::AddrOf(_, ref subexpr) |
1228 hir::ExprKind::Unary(hir::UnDeref, ref subexpr) |
1229 hir::ExprKind::Field(ref subexpr, _) |
1230 hir::ExprKind::Index(ref subexpr, _) => {
1241 impl<'a, 'tcx> RegionResolutionVisitor<'a, 'tcx> {
1242 /// Records the current parent (if any) as the parent of `child_scope`.
1243 /// Returns the depth of `child_scope`.
1244 fn record_child_scope(&mut self, child_scope: Scope) -> ScopeDepth {
1245 let parent = self.cx.parent;
1246 self.scope_tree.record_scope_parent(child_scope, parent);
1247 // If `child_scope` has no parent, it must be the root node, and so has
1248 // a depth of 1. Otherwise, its depth is one more than its parent's.
1249 parent.map_or(1, |(_p, d)| d + 1)
1252 /// Records the current parent (if any) as the parent of `child_scope`,
1253 /// and sets `child_scope` as the new current parent.
1254 fn enter_scope(&mut self, child_scope: Scope) {
1255 let child_depth = self.record_child_scope(child_scope);
1256 self.cx.parent = Some((child_scope, child_depth));
1259 fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) {
1260 // If node was previously marked as a terminating scope during the
1261 // recursive visit of its parent node in the AST, then we need to
1262 // account for the destruction scope representing the scope of
1263 // the destructors that run immediately after it completes.
1264 if self.terminating_scopes.contains(&id) {
1265 self.enter_scope(Scope::Destruction(id));
1267 self.enter_scope(Scope::Node(id));
1271 impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
1272 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1273 NestedVisitorMap::None
1276 fn visit_block(&mut self, b: &'tcx Block) {
1277 resolve_block(self, b);
1280 fn visit_body(&mut self, body: &'tcx hir::Body) {
1281 let body_id = body.id();
1282 let owner_id = self.tcx.hir.body_owner(body_id);
1284 debug!("visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
1286 self.tcx.sess.source_map().span_to_string(body.value.span),
1290 let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
1291 let outer_cx = self.cx;
1292 let outer_ts = mem::replace(&mut self.terminating_scopes, FxHashSet());
1293 self.terminating_scopes.insert(body.value.hir_id.local_id);
1295 if let Some(root_id) = self.cx.root_id {
1296 self.scope_tree.record_closure_parent(body.value.hir_id.local_id, root_id);
1298 self.cx.root_id = Some(body.value.hir_id.local_id);
1300 self.enter_scope(Scope::CallSite(body.value.hir_id.local_id));
1301 self.enter_scope(Scope::Arguments(body.value.hir_id.local_id));
1303 // The arguments and `self` are parented to the fn.
1304 self.cx.var_parent = self.cx.parent.take();
1305 for argument in &body.arguments {
1306 self.visit_pat(&argument.pat);
1309 // The body of the every fn is a root scope.
1310 self.cx.parent = self.cx.var_parent;
1311 if let hir::BodyOwnerKind::Fn = self.tcx.hir.body_owner_kind(owner_id) {
1312 self.visit_expr(&body.value);
1314 // Only functions have an outer terminating (drop) scope, while
1315 // temporaries in constant initializers may be 'static, but only
1316 // according to rvalue lifetime semantics, using the same
1317 // syntactical rules used for let initializers.
1319 // E.g. in `let x = &f();`, the temporary holding the result from
1320 // the `f()` call lives for the entirety of the surrounding block.
1322 // Similarly, `const X: ... = &f();` would have the result of `f()`
1323 // live for `'static`, implying (if Drop restrictions on constants
1324 // ever get lifted) that the value *could* have a destructor, but
1325 // it'd get leaked instead of the destructor running during the
1326 // evaluation of `X` (if at all allowed by CTFE).
1328 // However, `const Y: ... = g(&f());`, like `let y = g(&f());`,
1329 // would *not* let the `f()` temporary escape into an outer scope
1330 // (i.e. `'static`), which means that after `g` returns, it drops,
1331 // and all the associated destruction scope rules apply.
1332 self.cx.var_parent = None;
1333 resolve_local(self, None, Some(&body.value));
1336 if body.is_generator {
1337 self.scope_tree.body_expr_count.insert(body_id, self.expr_and_pat_count);
1340 // Restore context we had at the start.
1341 self.expr_and_pat_count = outer_ec;
1343 self.terminating_scopes = outer_ts;
1346 fn visit_arm(&mut self, a: &'tcx Arm) {
1347 resolve_arm(self, a);
1349 fn visit_pat(&mut self, p: &'tcx Pat) {
1350 resolve_pat(self, p);
1352 fn visit_stmt(&mut self, s: &'tcx Stmt) {
1353 resolve_stmt(self, s);
1355 fn visit_expr(&mut self, ex: &'tcx Expr) {
1356 resolve_expr(self, ex);
1358 fn visit_local(&mut self, l: &'tcx Local) {
1359 resolve_local(self, Some(&l.pat), l.init.as_ref().map(|e| &**e));
1363 fn region_scope_tree<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
1366 let closure_base_def_id = tcx.closure_base_def_id(def_id);
1367 if closure_base_def_id != def_id {
1368 return tcx.region_scope_tree(closure_base_def_id);
1371 let id = tcx.hir.as_local_node_id(def_id).unwrap();
1372 let scope_tree = if let Some(body_id) = tcx.hir.maybe_body_owned_by(id) {
1373 let mut visitor = RegionResolutionVisitor {
1375 scope_tree: ScopeTree::default(),
1376 expr_and_pat_count: 0,
1382 terminating_scopes: FxHashSet(),
1385 let body = tcx.hir.body(body_id);
1386 visitor.scope_tree.root_body = Some(body.value.hir_id);
1388 // If the item is an associated const or a method,
1389 // record its impl/trait parent, as it can also have
1390 // lifetime parameters free in this body.
1391 match tcx.hir.get(id) {
1393 Node::TraitItem(_) => {
1394 visitor.scope_tree.root_parent = Some(tcx.hir.get_parent(id));
1399 visitor.visit_body(body);
1403 ScopeTree::default()
1406 Lrc::new(scope_tree)
1409 pub fn provide(providers: &mut Providers) {
1410 *providers = Providers {
1416 impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
1417 fn hash_stable<W: StableHasherResult>(&self,
1418 hcx: &mut StableHashingContext<'a>,
1419 hasher: &mut StableHasher<W>) {
1423 ref body_expr_count,
1426 ref destruction_scopes,
1432 hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
1433 root_body.hash_stable(hcx, hasher);
1434 root_parent.hash_stable(hcx, hasher);
1437 body_expr_count.hash_stable(hcx, hasher);
1438 parent_map.hash_stable(hcx, hasher);
1439 var_map.hash_stable(hcx, hasher);
1440 destruction_scopes.hash_stable(hcx, hasher);
1441 rvalue_scopes.hash_stable(hcx, hasher);
1442 closure_tree.hash_stable(hcx, hasher);
1443 yield_in_scope.hash_stable(hcx, hasher);