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,
163 pub struct FirstStatementIndex {
164 MAX = SCOPE_DATA_REMAINDER_MAX
168 impl_stable_hash_for!(struct ::middle::region::FirstStatementIndex { private });
170 impl From<ScopeData> for Scope {
172 fn from(scope_data: ScopeData) -> Self {
173 let (id, code) = match scope_data {
174 ScopeData::Node(id) => (id, SCOPE_DATA_NODE),
175 ScopeData::CallSite(id) => (id, SCOPE_DATA_CALLSITE),
176 ScopeData::Arguments(id) => (id, SCOPE_DATA_ARGUMENTS),
177 ScopeData::Destruction(id) => (id, SCOPE_DATA_DESTRUCTION),
178 ScopeData::Remainder(r) => (r.block, r.first_statement_index.index() as u32)
184 impl fmt::Debug for Scope {
185 fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
186 fmt::Debug::fmt(&self.data(), formatter)
190 #[allow(non_snake_case)]
193 pub fn data(self) -> ScopeData {
195 SCOPE_DATA_NODE => ScopeData::Node(self.id),
196 SCOPE_DATA_CALLSITE => ScopeData::CallSite(self.id),
197 SCOPE_DATA_ARGUMENTS => ScopeData::Arguments(self.id),
198 SCOPE_DATA_DESTRUCTION => ScopeData::Destruction(self.id),
199 idx => ScopeData::Remainder(BlockRemainder {
201 first_statement_index: FirstStatementIndex::new(idx as usize)
207 pub fn Node(id: hir::ItemLocalId) -> Self {
208 Self::from(ScopeData::Node(id))
212 pub fn CallSite(id: hir::ItemLocalId) -> Self {
213 Self::from(ScopeData::CallSite(id))
217 pub fn Arguments(id: hir::ItemLocalId) -> Self {
218 Self::from(ScopeData::Arguments(id))
222 pub fn Destruction(id: hir::ItemLocalId) -> Self {
223 Self::from(ScopeData::Destruction(id))
227 pub fn Remainder(r: BlockRemainder) -> Self {
228 Self::from(ScopeData::Remainder(r))
233 /// Returns a item-local id associated with this scope.
235 /// NB: likely to be replaced as API is refined; e.g. pnkfelix
236 /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
237 pub fn item_local_id(&self) -> hir::ItemLocalId {
241 pub fn node_id(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> ast::NodeId {
242 match scope_tree.root_body {
244 tcx.hir.hir_to_node_id(hir::HirId {
246 local_id: self.item_local_id()
249 None => ast::DUMMY_NODE_ID
253 /// Returns the span of this Scope. Note that in general the
254 /// returned span may not correspond to the span of any node id in
256 pub fn span(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> Span {
257 let node_id = self.node_id(tcx, scope_tree);
258 if node_id == ast::DUMMY_NODE_ID {
261 let span = tcx.hir.span(node_id);
262 if let ScopeData::Remainder(r) = self.data() {
263 if let Node::Block(ref blk) = tcx.hir.get(node_id) {
264 // Want span for scope starting after the
265 // indexed statement and ending at end of
266 // `blk`; reuse span of `blk` and shift `lo`
267 // forward to end of indexed statement.
269 // (This is the special case aluded to in the
270 // doc-comment for this method)
272 let stmt_span = blk.stmts[r.first_statement_index.index()].span;
274 // To avoid issues with macro-generated spans, the span
275 // of the statement must be nested in that of the block.
276 if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() {
277 return Span::new(stmt_span.lo(), span.hi(), span.ctxt());
285 pub type ScopeDepth = u32;
287 /// The region scope tree encodes information about region relationships.
288 #[derive(Default, Debug)]
289 pub struct ScopeTree {
290 /// If not empty, this body is the root of this region hierarchy.
291 root_body: Option<hir::HirId>,
293 /// The parent of the root body owner, if the latter is an
294 /// an associated const or method, as impls/traits can also
295 /// have lifetime parameters free in this body.
296 root_parent: Option<ast::NodeId>,
298 /// `parent_map` maps from a scope id to the enclosing scope id;
299 /// this is usually corresponding to the lexical nesting, though
300 /// in the case of closures the parent scope is the innermost
301 /// conditional expression or repeating block. (Note that the
302 /// enclosing scope id for the block associated with a closure is
303 /// the closure itself.)
304 parent_map: FxHashMap<Scope, (Scope, ScopeDepth)>,
306 /// `var_map` maps from a variable or binding id to the block in
307 /// which that variable is declared.
308 var_map: FxHashMap<hir::ItemLocalId, Scope>,
310 /// maps from a node-id to the associated destruction scope (if any)
311 destruction_scopes: FxHashMap<hir::ItemLocalId, Scope>,
313 /// `rvalue_scopes` includes entries for those expressions whose cleanup scope is
314 /// larger than the default. The map goes from the expression id
315 /// to the cleanup scope id. For rvalues not present in this
316 /// table, the appropriate cleanup scope is the innermost
317 /// enclosing statement, conditional expression, or repeating
318 /// block (see `terminating_scopes`).
319 /// In constants, None is used to indicate that certain expressions
320 /// escape into 'static and should have no local cleanup scope.
321 rvalue_scopes: FxHashMap<hir::ItemLocalId, Option<Scope>>,
323 /// Encodes the hierarchy of fn bodies. Every fn body (including
324 /// closures) forms its own distinct region hierarchy, rooted in
325 /// the block that is the fn body. This map points from the id of
326 /// that root block to the id of the root block for the enclosing
327 /// fn, if any. Thus the map structures the fn bodies into a
328 /// hierarchy based on their lexical mapping. This is used to
329 /// handle the relationships between regions in a fn and in a
330 /// closure defined by that fn. See the "Modeling closures"
331 /// section of the README in infer::region_constraints for
333 closure_tree: FxHashMap<hir::ItemLocalId, hir::ItemLocalId>,
335 /// If there are any `yield` nested within a scope, this map
336 /// stores the `Span` of the last one and its index in the
337 /// postorder of the Visitor traversal on the HIR.
339 /// HIR Visitor postorder indexes might seem like a peculiar
340 /// thing to care about. but it turns out that HIR bindings
341 /// and the temporary results of HIR expressions are never
342 /// storage-live at the end of HIR nodes with postorder indexes
343 /// lower than theirs, and therefore don't need to be suspended
344 /// at yield-points at these indexes.
346 /// For an example, suppose we have some code such as:
347 /// ```rust,ignore (example)
348 /// foo(f(), yield y, bar(g()))
351 /// With the HIR tree (calls numbered for expository purposes)
353 /// Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
356 /// Obviously, the result of `f()` was created before the yield
357 /// (and therefore needs to be kept valid over the yield) while
358 /// the result of `g()` occurs after the yield (and therefore
359 /// doesn't). If we want to infer that, we can look at the
360 /// postorder traversal:
362 /// `foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
365 /// In which we can easily see that `Call#1` occurs before the yield,
366 /// and `Call#3` after it.
368 /// To see that this method works, consider:
370 /// Let `D` be our binding/temporary and `U` be our other HIR node, with
371 /// `HIR-postorder(U) < HIR-postorder(D)` (in our example, U would be
372 /// the yield and D would be one of the calls). Let's show that
373 /// `D` is storage-dead at `U`.
375 /// Remember that storage-live/storage-dead refers to the state of
376 /// the *storage*, and does not consider moves/drop flags.
379 /// 1. From the ordering guarantee of HIR visitors (see
380 /// `rustc::hir::intravisit`), `D` does not dominate `U`.
381 /// 2. Therefore, `D` is *potentially* storage-dead at `U` (because
382 /// we might visit `U` without ever getting to `D`).
383 /// 3. However, we guarantee that at each HIR point, each
384 /// binding/temporary is always either always storage-live
385 /// or always storage-dead. This is what is being guaranteed
386 /// by `terminating_scopes` including all blocks where the
387 /// count of executions is not guaranteed.
388 /// 4. By `2.` and `3.`, `D` is *statically* storage-dead at `U`,
391 /// I don't think this property relies on `3.` in an essential way - it
392 /// is probably still correct even if we have "unrestricted" terminating
393 /// scopes. However, why use the complicated proof when a simple one
396 /// A subtle thing: `box` expressions, such as `box (&x, yield 2, &y)`. It
397 /// might seem that a `box` expression creates a `Box<T>` temporary
398 /// when it *starts* executing, at `HIR-preorder(BOX-EXPR)`. That might
399 /// be true in the MIR desugaring, but it is not important in the semantics.
401 /// The reason is that semantically, until the `box` expression returns,
402 /// the values are still owned by their containing expressions. So
403 /// we'll see that `&x`.
404 yield_in_scope: FxHashMap<Scope, (Span, usize)>,
406 /// The number of visit_expr and visit_pat calls done in the body.
407 /// Used to sanity check visit_expr/visit_pat call count when
408 /// calculating generator interiors.
409 body_expr_count: FxHashMap<hir::BodyId, usize>,
412 #[derive(Debug, Copy, Clone)]
414 /// the root of the current region tree. This is typically the id
415 /// of the innermost fn body. Each fn forms its own disjoint tree
416 /// in the region hierarchy. These fn bodies are themselves
417 /// arranged into a tree. See the "Modeling closures" section of
418 /// the README in infer::region_constraints for more
420 root_id: Option<hir::ItemLocalId>,
422 /// The scope that contains any new variables declared, plus its depth in
424 var_parent: Option<(Scope, ScopeDepth)>,
426 /// Region parent of expressions, etc., plus its depth in the scope tree.
427 parent: Option<(Scope, ScopeDepth)>,
430 struct RegionResolutionVisitor<'a, 'tcx: 'a> {
431 tcx: TyCtxt<'a, 'tcx, 'tcx>,
433 // The number of expressions and patterns visited in the current body
434 expr_and_pat_count: usize,
436 // Generated scope tree:
437 scope_tree: ScopeTree,
441 /// `terminating_scopes` is a set containing the ids of each
442 /// statement, or conditional/repeating expression. These scopes
443 /// are calling "terminating scopes" because, when attempting to
444 /// find the scope of a temporary, by default we search up the
445 /// enclosing scopes until we encounter the terminating scope. A
446 /// conditional/repeating expression is one which is not
447 /// guaranteed to execute exactly once upon entering the parent
448 /// scope. This could be because the expression only executes
449 /// conditionally, such as the expression `b` in `a && b`, or
450 /// because the expression may execute many times, such as a loop
451 /// body. The reason that we distinguish such expressions is that,
452 /// upon exiting the parent scope, we cannot statically know how
453 /// many times the expression executed, and thus if the expression
454 /// creates temporaries we cannot know statically how many such
455 /// temporaries we would have to cleanup. Therefore we ensure that
456 /// the temporaries never outlast the conditional/repeating
457 /// expression, preventing the need for dynamic checks and/or
458 /// arbitrary amounts of stack space. Terminating scopes end
459 /// up being contained in a DestructionScope that contains the
460 /// destructor's execution.
461 terminating_scopes: FxHashSet<hir::ItemLocalId>,
464 struct ExprLocatorVisitor {
466 result: Option<usize>,
467 expr_and_pat_count: usize,
470 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor
471 // since `expr_count` is compared against the results there.
472 impl<'tcx> Visitor<'tcx> for ExprLocatorVisitor {
473 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
474 NestedVisitorMap::None
477 fn visit_pat(&mut self, pat: &'tcx Pat) {
478 intravisit::walk_pat(self, pat);
480 self.expr_and_pat_count += 1;
482 if pat.hir_id == self.hir_id {
483 self.result = Some(self.expr_and_pat_count);
487 fn visit_expr(&mut self, expr: &'tcx Expr) {
488 debug!("ExprLocatorVisitor - pre-increment {} expr = {:?}",
489 self.expr_and_pat_count,
492 intravisit::walk_expr(self, expr);
494 self.expr_and_pat_count += 1;
496 debug!("ExprLocatorVisitor - post-increment {} expr = {:?}",
497 self.expr_and_pat_count,
500 if expr.hir_id == self.hir_id {
501 self.result = Some(self.expr_and_pat_count);
506 impl<'tcx> ScopeTree {
507 pub fn record_scope_parent(&mut self, child: Scope, parent: Option<(Scope, ScopeDepth)>) {
508 debug!("{:?}.parent = {:?}", child, parent);
510 if let Some(p) = parent {
511 let prev = self.parent_map.insert(child, p);
512 assert!(prev.is_none());
515 // record the destruction scopes for later so we can query them
516 if let ScopeData::Destruction(n) = child.data() {
517 self.destruction_scopes.insert(n, child);
521 pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(Scope, Scope) {
522 for (&child, &parent) in &self.parent_map {
527 pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&hir::ItemLocalId, Scope) {
528 for (child, &parent) in self.var_map.iter() {
533 pub fn opt_destruction_scope(&self, n: hir::ItemLocalId) -> Option<Scope> {
534 self.destruction_scopes.get(&n).cloned()
537 /// Records that `sub_closure` is defined within `sup_closure`. These ids
538 /// should be the id of the block that is the fn body, which is
539 /// also the root of the region hierarchy for that fn.
540 fn record_closure_parent(&mut self,
541 sub_closure: hir::ItemLocalId,
542 sup_closure: hir::ItemLocalId) {
543 debug!("record_closure_parent(sub_closure={:?}, sup_closure={:?})",
544 sub_closure, sup_closure);
545 assert!(sub_closure != sup_closure);
546 let previous = self.closure_tree.insert(sub_closure, sup_closure);
547 assert!(previous.is_none());
550 fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) {
551 debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
552 assert!(var != lifetime.item_local_id());
553 self.var_map.insert(var, lifetime);
556 fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
557 debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
558 if let Some(lifetime) = lifetime {
559 assert!(var != lifetime.item_local_id());
561 self.rvalue_scopes.insert(var, lifetime);
564 pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> {
565 //! Returns the narrowest scope that encloses `id`, if any.
566 self.parent_map.get(&id).cloned().map(|(p, _)| p)
569 #[allow(dead_code)] // used in cfg
570 pub fn encl_scope(&self, id: Scope) -> Scope {
571 //! Returns the narrowest scope that encloses `id`, if any.
572 self.opt_encl_scope(id).unwrap()
575 /// Returns the lifetime of the local variable `var_id`
576 pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Scope {
577 match self.var_map.get(&var_id) {
579 None => { bug!("no enclosing scope for id {:?}", var_id); }
583 pub fn temporary_scope(&self, expr_id: hir::ItemLocalId) -> Option<Scope> {
584 //! Returns the scope when temp created by expr_id will be cleaned up
586 // check for a designated rvalue scope
587 if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
588 debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
592 // else, locate the innermost terminating scope
593 // if there's one. Static items, for instance, won't
594 // have an enclosing scope, hence no scope will be
596 let mut id = Scope::Node(expr_id);
598 while let Some(&(p, _)) = self.parent_map.get(&id) {
600 ScopeData::Destruction(..) => {
601 debug!("temporary_scope({:?}) = {:?} [enclosing]",
609 debug!("temporary_scope({:?}) = None", expr_id);
613 pub fn var_region(&self, id: hir::ItemLocalId) -> ty::RegionKind {
614 //! Returns the lifetime of the variable `id`.
616 let scope = ty::ReScope(self.var_scope(id));
617 debug!("var_region({:?}) = {:?}", id, scope);
621 pub fn scopes_intersect(&self, scope1: Scope, scope2: Scope)
623 self.is_subscope_of(scope1, scope2) ||
624 self.is_subscope_of(scope2, scope1)
627 /// Returns true if `subscope` is equal to or is lexically nested inside `superscope` and false
629 pub fn is_subscope_of(&self,
633 let mut s = subscope;
634 debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
635 while superscope != s {
636 match self.opt_encl_scope(s) {
638 debug!("is_subscope_of({:?}, {:?}, s={:?})=false",
639 subscope, superscope, s);
642 Some(scope) => s = scope
646 debug!("is_subscope_of({:?}, {:?})=true",
647 subscope, superscope);
652 /// Returns the id of the innermost containing body
653 pub fn containing_body(&self, mut scope: Scope)-> Option<hir::ItemLocalId> {
655 if let ScopeData::CallSite(id) = scope.data() {
659 match self.opt_encl_scope(scope) {
661 Some(parent) => scope = parent,
666 /// Finds the nearest common ancestor of two scopes. That is, finds the
667 /// smallest scope which is greater than or equal to both `scope_a` and
669 pub fn nearest_common_ancestor(&self, scope_a: Scope, scope_b: Scope) -> Scope {
670 if scope_a == scope_b { return scope_a; }
675 // Get the depth of each scope's parent. If either scope has no parent,
676 // it must be the root, which means we can stop immediately because the
677 // root must be the nearest common ancestor. (In practice, this is
678 // moderately common.)
679 let (parent_a, parent_a_depth) = match self.parent_map.get(&a) {
683 let (parent_b, parent_b_depth) = match self.parent_map.get(&b) {
688 if parent_a_depth > parent_b_depth {
689 // `a` is lower than `b`. Move `a` up until it's at the same depth
690 // as `b`. The first move up is trivial because we already found
691 // `parent_a` above; the loop does the remaining N-1 moves.
693 for _ in 0..(parent_a_depth - parent_b_depth - 1) {
694 a = self.parent_map.get(&a).unwrap().0;
696 } else if parent_b_depth > parent_a_depth {
697 // `b` is lower than `a`.
699 for _ in 0..(parent_b_depth - parent_a_depth - 1) {
700 b = self.parent_map.get(&b).unwrap().0;
703 // Both scopes are at the same depth, and we know they're not equal
704 // because that case was tested for at the top of this function. So
705 // we can trivially move them both up one level now.
706 assert!(parent_a_depth != 0);
711 // Now both scopes are at the same level. We move upwards in lockstep
712 // until they match. In practice, this loop is almost always executed
713 // zero times because `a` is almost always a direct ancestor of `b` or
716 a = self.parent_map.get(&a).unwrap().0;
717 b = self.parent_map.get(&b).unwrap().0;
723 /// Assuming that the provided region was defined within this `ScopeTree`,
724 /// returns the outermost `Scope` that the region outlives.
725 pub fn early_free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
726 br: &ty::EarlyBoundRegion)
728 let param_owner = tcx.parent_def_id(br.def_id).unwrap();
730 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
731 let scope = tcx.hir.maybe_body_owned_by(param_owner_id).map(|body_id| {
732 tcx.hir.body(body_id).value.hir_id.local_id
733 }).unwrap_or_else(|| {
734 // The lifetime was defined on node that doesn't own a body,
735 // which in practice can only mean a trait or an impl, that
736 // is the parent of a method, and that is enforced below.
737 assert_eq!(Some(param_owner_id), self.root_parent,
738 "free_scope: {:?} not recognized by the \
739 region scope tree for {:?} / {:?}",
741 self.root_parent.map(|id| tcx.hir.local_def_id(id)),
742 self.root_body.map(|hir_id| DefId::local(hir_id.owner)));
744 // The trait/impl lifetime is in scope for the method's body.
745 self.root_body.unwrap().local_id
748 Scope::CallSite(scope)
751 /// Assuming that the provided region was defined within this `ScopeTree`,
752 /// returns the outermost `Scope` that the region outlives.
753 pub fn free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, fr: &ty::FreeRegion)
755 let param_owner = match fr.bound_region {
756 ty::BoundRegion::BrNamed(def_id, _) => {
757 tcx.parent_def_id(def_id).unwrap()
762 // Ensure that the named late-bound lifetimes were defined
763 // on the same function that they ended up being freed in.
764 assert_eq!(param_owner, fr.scope);
766 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
767 let body_id = tcx.hir.body_owned_by(param_owner_id);
768 Scope::CallSite(tcx.hir.body(body_id).value.hir_id.local_id)
771 /// Checks whether the given scope contains a `yield`. If so,
772 /// returns `Some((span, expr_count))` with the span of a yield we found and
773 /// the number of expressions and patterns appearing before the `yield` in the body + 1.
774 /// If there a are multiple yields in a scope, the one with the highest number is returned.
775 pub fn yield_in_scope(&self, scope: Scope) -> Option<(Span, usize)> {
776 self.yield_in_scope.get(&scope).cloned()
779 /// Checks whether the given scope contains a `yield` and if that yield could execute
780 /// after `expr`. If so, it returns the span of that `yield`.
781 /// `scope` must be inside the body.
782 pub fn yield_in_scope_for_expr(&self,
784 expr_hir_id: hir::HirId,
785 body: &'tcx hir::Body) -> Option<Span> {
786 self.yield_in_scope(scope).and_then(|(span, count)| {
787 let mut visitor = ExprLocatorVisitor {
790 expr_and_pat_count: 0,
792 visitor.visit_body(body);
793 if count >= visitor.result.unwrap() {
801 /// Gives the number of expressions visited in a body.
802 /// Used to sanity check visit_expr call count when
803 /// calculating generator interiors.
804 pub fn body_expr_count(&self, body_id: hir::BodyId) -> Option<usize> {
805 self.body_expr_count.get(&body_id).map(|r| *r)
809 /// Records the lifetime of a local variable as `cx.var_parent`
810 fn record_var_lifetime(visitor: &mut RegionResolutionVisitor,
811 var_id: hir::ItemLocalId,
813 match visitor.cx.var_parent {
815 // this can happen in extern fn declarations like
817 // extern fn isalnum(c: c_int) -> c_int
819 Some((parent_scope, _)) =>
820 visitor.scope_tree.record_var_scope(var_id, parent_scope),
824 fn resolve_block<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, blk: &'tcx hir::Block) {
825 debug!("resolve_block(blk.id={:?})", blk.id);
827 let prev_cx = visitor.cx;
829 // We treat the tail expression in the block (if any) somewhat
830 // differently from the statements. The issue has to do with
831 // temporary lifetimes. Consider the following:
834 // let inner = ... (&bar()) ...;
836 // (... (&foo()) ...) // (the tail expression)
837 // }, other_argument());
839 // Each of the statements within the block is a terminating
840 // scope, and thus a temporary (e.g. the result of calling
841 // `bar()` in the initializer expression for `let inner = ...;`)
842 // will be cleaned up immediately after its corresponding
843 // statement (i.e. `let inner = ...;`) executes.
845 // On the other hand, temporaries associated with evaluating the
846 // tail expression for the block are assigned lifetimes so that
847 // they will be cleaned up as part of the terminating scope
848 // *surrounding* the block expression. Here, the terminating
849 // scope for the block expression is the `quux(..)` call; so
850 // those temporaries will only be cleaned up *after* both
851 // `other_argument()` has run and also the call to `quux(..)`
852 // itself has returned.
854 visitor.enter_node_scope_with_dtor(blk.hir_id.local_id);
855 visitor.cx.var_parent = visitor.cx.parent;
858 // This block should be kept approximately in sync with
859 // `intravisit::walk_block`. (We manually walk the block, rather
860 // than call `walk_block`, in order to maintain precise
861 // index information.)
863 for (i, statement) in blk.stmts.iter().enumerate() {
864 if let hir::StmtKind::Decl(..) = statement.node {
865 // Each StmtKind::Decl introduces a subscope for bindings
866 // introduced by the declaration; this subscope covers
867 // a suffix of the block . Each subscope in a block
868 // has the previous subscope in the block as a parent,
869 // except for the first such subscope, which has the
870 // block itself as a parent.
872 Scope::Remainder(BlockRemainder {
873 block: blk.hir_id.local_id,
874 first_statement_index: FirstStatementIndex::new(i)
877 visitor.cx.var_parent = visitor.cx.parent;
879 visitor.visit_stmt(statement)
881 walk_list!(visitor, visit_expr, &blk.expr);
884 visitor.cx = prev_cx;
887 fn resolve_arm<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, arm: &'tcx hir::Arm) {
888 visitor.terminating_scopes.insert(arm.body.hir_id.local_id);
890 if let Some(ref g) = arm.guard {
892 hir::Guard::If(ref expr) => visitor.terminating_scopes.insert(expr.hir_id.local_id),
896 intravisit::walk_arm(visitor, arm);
899 fn resolve_pat<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, pat: &'tcx hir::Pat) {
900 visitor.record_child_scope(Scope::Node(pat.hir_id.local_id));
902 // If this is a binding then record the lifetime of that binding.
903 if let PatKind::Binding(..) = pat.node {
904 record_var_lifetime(visitor, pat.hir_id.local_id, pat.span);
907 debug!("resolve_pat - pre-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
909 intravisit::walk_pat(visitor, pat);
911 visitor.expr_and_pat_count += 1;
913 debug!("resolve_pat - post-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
916 fn resolve_stmt<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, stmt: &'tcx hir::Stmt) {
917 let stmt_id = visitor.tcx.hir.node_to_hir_id(stmt.node.id()).local_id;
918 debug!("resolve_stmt(stmt.id={:?})", stmt_id);
920 // Every statement will clean up the temporaries created during
921 // execution of that statement. Therefore each statement has an
922 // associated destruction scope that represents the scope of the
923 // statement plus its destructors, and thus the scope for which
924 // regions referenced by the destructors need to survive.
925 visitor.terminating_scopes.insert(stmt_id);
927 let prev_parent = visitor.cx.parent;
928 visitor.enter_node_scope_with_dtor(stmt_id);
930 intravisit::walk_stmt(visitor, stmt);
932 visitor.cx.parent = prev_parent;
935 fn resolve_expr<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, expr: &'tcx hir::Expr) {
936 debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
938 let prev_cx = visitor.cx;
939 visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);
942 let terminating_scopes = &mut visitor.terminating_scopes;
943 let mut terminating = |id: hir::ItemLocalId| {
944 terminating_scopes.insert(id);
947 // Conditional or repeating scopes are always terminating
948 // scopes, meaning that temporaries cannot outlive them.
949 // This ensures fixed size stacks.
951 hir::ExprKind::Binary(
952 source_map::Spanned { node: hir::BinOpKind::And, .. },
954 hir::ExprKind::Binary(
955 source_map::Spanned { node: hir::BinOpKind::Or, .. },
957 // For shortcircuiting operators, mark the RHS as a terminating
958 // scope since it only executes conditionally.
959 terminating(r.hir_id.local_id);
962 hir::ExprKind::If(ref expr, ref then, Some(ref otherwise)) => {
963 terminating(expr.hir_id.local_id);
964 terminating(then.hir_id.local_id);
965 terminating(otherwise.hir_id.local_id);
968 hir::ExprKind::If(ref expr, ref then, None) => {
969 terminating(expr.hir_id.local_id);
970 terminating(then.hir_id.local_id);
973 hir::ExprKind::Loop(ref body, _, _) => {
974 terminating(body.hir_id.local_id);
977 hir::ExprKind::While(ref expr, ref body, _) => {
978 terminating(expr.hir_id.local_id);
979 terminating(body.hir_id.local_id);
982 hir::ExprKind::Match(..) => {
983 visitor.cx.var_parent = visitor.cx.parent;
986 hir::ExprKind::AssignOp(..) | hir::ExprKind::Index(..) |
987 hir::ExprKind::Unary(..) | hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) => {
988 // FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls
990 // The lifetimes for a call or method call look as follows:
998 // The idea is that call.callee_id represents *the time when
999 // the invoked function is actually running* and call.id
1000 // represents *the time to prepare the arguments and make the
1001 // call*. See the section "Borrows in Calls" borrowck/README.md
1002 // for an extended explanation of why this distinction is
1005 // record_superlifetime(new_cx, expr.callee_id);
1013 // Manually recurse over closures, because they are the only
1014 // case of nested bodies that share the parent environment.
1015 hir::ExprKind::Closure(.., body, _, _) => {
1016 let body = visitor.tcx.hir.body(body);
1017 visitor.visit_body(body);
1020 _ => intravisit::walk_expr(visitor, expr)
1023 visitor.expr_and_pat_count += 1;
1025 debug!("resolve_expr post-increment {}, expr = {:?}", visitor.expr_and_pat_count, expr);
1027 if let hir::ExprKind::Yield(..) = expr.node {
1028 // Mark this expr's scope and all parent scopes as containing `yield`.
1029 let mut scope = Scope::Node(expr.hir_id.local_id);
1031 visitor.scope_tree.yield_in_scope.insert(scope,
1032 (expr.span, visitor.expr_and_pat_count));
1034 // Keep traversing up while we can.
1035 match visitor.scope_tree.parent_map.get(&scope) {
1036 // Don't cross from closure bodies to their parent.
1037 Some(&(superscope, _)) => match superscope.data() {
1038 ScopeData::CallSite(_) => break,
1039 _ => scope = superscope
1046 visitor.cx = prev_cx;
1049 fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1050 pat: Option<&'tcx hir::Pat>,
1051 init: Option<&'tcx hir::Expr>) {
1052 debug!("resolve_local(pat={:?}, init={:?})", pat, init);
1054 let blk_scope = visitor.cx.var_parent.map(|(p, _)| p);
1056 // As an exception to the normal rules governing temporary
1057 // lifetimes, initializers in a let have a temporary lifetime
1058 // of the enclosing block. This means that e.g. a program
1059 // like the following is legal:
1061 // let ref x = HashMap::new();
1063 // Because the hash map will be freed in the enclosing block.
1065 // We express the rules more formally based on 3 grammars (defined
1066 // fully in the helpers below that implement them):
1068 // 1. `E&`, which matches expressions like `&<rvalue>` that
1069 // own a pointer into the stack.
1071 // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
1072 // y)` that produce ref bindings into the value they are
1073 // matched against or something (at least partially) owned by
1074 // the value they are matched against. (By partially owned,
1075 // I mean that creating a binding into a ref-counted or managed value
1076 // would still count.)
1078 // 3. `ET`, which matches both rvalues like `foo()` as well as places
1079 // based on rvalues like `foo().x[2].y`.
1081 // A subexpression `<rvalue>` that appears in a let initializer
1082 // `let pat [: ty] = expr` has an extended temporary lifetime if
1083 // any of the following conditions are met:
1085 // A. `pat` matches `P&` and `expr` matches `ET`
1086 // (covers cases where `pat` creates ref bindings into an rvalue
1087 // produced by `expr`)
1088 // B. `ty` is a borrowed pointer and `expr` matches `ET`
1089 // (covers cases where coercion creates a borrow)
1090 // C. `expr` matches `E&`
1091 // (covers cases `expr` borrows an rvalue that is then assigned
1092 // to memory (at least partially) owned by the binding)
1094 // Here are some examples hopefully giving an intuition where each
1095 // rule comes into play and why:
1097 // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
1098 // would have an extended lifetime, but not `foo()`.
1100 // Rule B. `let x = &foo().x`. The rvalue ``foo()` would have extended
1103 // In some cases, multiple rules may apply (though not to the same
1104 // rvalue). For example:
1106 // let ref x = [&a(), &b()];
1108 // Here, the expression `[...]` has an extended lifetime due to rule
1109 // A, but the inner rvalues `a()` and `b()` have an extended lifetime
1112 if let Some(expr) = init {
1113 record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
1115 if let Some(pat) = pat {
1116 if is_binding_pat(pat) {
1117 record_rvalue_scope(visitor, &expr, blk_scope);
1122 // Make sure we visit the initializer first, so expr_and_pat_count remains correct
1123 if let Some(expr) = init {
1124 visitor.visit_expr(expr);
1126 if let Some(pat) = pat {
1127 visitor.visit_pat(pat);
1130 /// True if `pat` match the `P&` nonterminal:
1133 /// | StructName { ..., P&, ... }
1134 /// | VariantName(..., P&, ...)
1135 /// | [ ..., P&, ... ]
1136 /// | ( ..., P&, ... )
1138 fn is_binding_pat(pat: &hir::Pat) -> bool {
1139 // Note that the code below looks for *explicit* refs only, that is, it won't
1140 // know about *implicit* refs as introduced in #42640.
1142 // This is not a problem. For example, consider
1144 // let (ref x, ref y) = (Foo { .. }, Bar { .. });
1146 // Due to the explicit refs on the left hand side, the below code would signal
1147 // that the temporary value on the right hand side should live until the end of
1148 // the enclosing block (as opposed to being dropped after the let is complete).
1150 // To create an implicit ref, however, you must have a borrowed value on the RHS
1151 // already, as in this example (which won't compile before #42640):
1153 // let Foo { x, .. } = &Foo { x: ..., ... };
1157 // let Foo { ref x, .. } = Foo { ... };
1159 // In the former case (the implicit ref version), the temporary is created by the
1160 // & expression, and its lifetime would be extended to the end of the block (due
1161 // to a different rule, not the below code).
1163 PatKind::Binding(hir::BindingAnnotation::Ref, ..) |
1164 PatKind::Binding(hir::BindingAnnotation::RefMut, ..) => true,
1166 PatKind::Struct(_, ref field_pats, _) => {
1167 field_pats.iter().any(|fp| is_binding_pat(&fp.node.pat))
1170 PatKind::Slice(ref pats1, ref pats2, ref pats3) => {
1171 pats1.iter().any(|p| is_binding_pat(&p)) ||
1172 pats2.iter().any(|p| is_binding_pat(&p)) ||
1173 pats3.iter().any(|p| is_binding_pat(&p))
1176 PatKind::TupleStruct(_, ref subpats, _) |
1177 PatKind::Tuple(ref subpats, _) => {
1178 subpats.iter().any(|p| is_binding_pat(&p))
1181 PatKind::Box(ref subpat) => {
1182 is_binding_pat(&subpat)
1189 /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
1192 /// | StructName { ..., f: E&, ... }
1193 /// | [ ..., E&, ... ]
1194 /// | ( ..., E&, ... )
1199 fn record_rvalue_scope_if_borrow_expr<'a, 'tcx>(
1200 visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1202 blk_id: Option<Scope>)
1205 hir::ExprKind::AddrOf(_, ref subexpr) => {
1206 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
1207 record_rvalue_scope(visitor, &subexpr, blk_id);
1209 hir::ExprKind::Struct(_, ref fields, _) => {
1210 for field in fields {
1211 record_rvalue_scope_if_borrow_expr(
1212 visitor, &field.expr, blk_id);
1215 hir::ExprKind::Array(ref subexprs) |
1216 hir::ExprKind::Tup(ref subexprs) => {
1217 for subexpr in subexprs {
1218 record_rvalue_scope_if_borrow_expr(
1219 visitor, &subexpr, blk_id);
1222 hir::ExprKind::Cast(ref subexpr, _) => {
1223 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
1225 hir::ExprKind::Block(ref block, _) => {
1226 if let Some(ref subexpr) = block.expr {
1227 record_rvalue_scope_if_borrow_expr(
1228 visitor, &subexpr, blk_id);
1235 /// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
1236 /// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
1237 /// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
1240 /// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
1241 /// `<rvalue>` as `blk_id`:
1249 /// Note: ET is intended to match "rvalues or places based on rvalues".
1250 fn record_rvalue_scope<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1252 blk_scope: Option<Scope>) {
1253 let mut expr = expr;
1255 // Note: give all the expressions matching `ET` with the
1256 // extended temporary lifetime, not just the innermost rvalue,
1257 // because in codegen if we must compile e.g. `*rvalue()`
1258 // into a temporary, we request the temporary scope of the
1259 // outer expression.
1260 visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
1263 hir::ExprKind::AddrOf(_, ref subexpr) |
1264 hir::ExprKind::Unary(hir::UnDeref, ref subexpr) |
1265 hir::ExprKind::Field(ref subexpr, _) |
1266 hir::ExprKind::Index(ref subexpr, _) => {
1277 impl<'a, 'tcx> RegionResolutionVisitor<'a, 'tcx> {
1278 /// Records the current parent (if any) as the parent of `child_scope`.
1279 /// Returns the depth of `child_scope`.
1280 fn record_child_scope(&mut self, child_scope: Scope) -> ScopeDepth {
1281 let parent = self.cx.parent;
1282 self.scope_tree.record_scope_parent(child_scope, parent);
1283 // If `child_scope` has no parent, it must be the root node, and so has
1284 // a depth of 1. Otherwise, its depth is one more than its parent's.
1285 parent.map_or(1, |(_p, d)| d + 1)
1288 /// Records the current parent (if any) as the parent of `child_scope`,
1289 /// and sets `child_scope` as the new current parent.
1290 fn enter_scope(&mut self, child_scope: Scope) {
1291 let child_depth = self.record_child_scope(child_scope);
1292 self.cx.parent = Some((child_scope, child_depth));
1295 fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) {
1296 // If node was previously marked as a terminating scope during the
1297 // recursive visit of its parent node in the AST, then we need to
1298 // account for the destruction scope representing the scope of
1299 // the destructors that run immediately after it completes.
1300 if self.terminating_scopes.contains(&id) {
1301 self.enter_scope(Scope::Destruction(id));
1303 self.enter_scope(Scope::Node(id));
1307 impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
1308 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1309 NestedVisitorMap::None
1312 fn visit_block(&mut self, b: &'tcx Block) {
1313 resolve_block(self, b);
1316 fn visit_body(&mut self, body: &'tcx hir::Body) {
1317 let body_id = body.id();
1318 let owner_id = self.tcx.hir.body_owner(body_id);
1320 debug!("visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
1322 self.tcx.sess.source_map().span_to_string(body.value.span),
1326 let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
1327 let outer_cx = self.cx;
1328 let outer_ts = mem::replace(&mut self.terminating_scopes, FxHashSet());
1329 self.terminating_scopes.insert(body.value.hir_id.local_id);
1331 if let Some(root_id) = self.cx.root_id {
1332 self.scope_tree.record_closure_parent(body.value.hir_id.local_id, root_id);
1334 self.cx.root_id = Some(body.value.hir_id.local_id);
1336 self.enter_scope(Scope::CallSite(body.value.hir_id.local_id));
1337 self.enter_scope(Scope::Arguments(body.value.hir_id.local_id));
1339 // The arguments and `self` are parented to the fn.
1340 self.cx.var_parent = self.cx.parent.take();
1341 for argument in &body.arguments {
1342 self.visit_pat(&argument.pat);
1345 // The body of the every fn is a root scope.
1346 self.cx.parent = self.cx.var_parent;
1347 if let hir::BodyOwnerKind::Fn = self.tcx.hir.body_owner_kind(owner_id) {
1348 self.visit_expr(&body.value);
1350 // Only functions have an outer terminating (drop) scope, while
1351 // temporaries in constant initializers may be 'static, but only
1352 // according to rvalue lifetime semantics, using the same
1353 // syntactical rules used for let initializers.
1355 // E.g. in `let x = &f();`, the temporary holding the result from
1356 // the `f()` call lives for the entirety of the surrounding block.
1358 // Similarly, `const X: ... = &f();` would have the result of `f()`
1359 // live for `'static`, implying (if Drop restrictions on constants
1360 // ever get lifted) that the value *could* have a destructor, but
1361 // it'd get leaked instead of the destructor running during the
1362 // evaluation of `X` (if at all allowed by CTFE).
1364 // However, `const Y: ... = g(&f());`, like `let y = g(&f());`,
1365 // would *not* let the `f()` temporary escape into an outer scope
1366 // (i.e. `'static`), which means that after `g` returns, it drops,
1367 // and all the associated destruction scope rules apply.
1368 self.cx.var_parent = None;
1369 resolve_local(self, None, Some(&body.value));
1372 if body.is_generator {
1373 self.scope_tree.body_expr_count.insert(body_id, self.expr_and_pat_count);
1376 // Restore context we had at the start.
1377 self.expr_and_pat_count = outer_ec;
1379 self.terminating_scopes = outer_ts;
1382 fn visit_arm(&mut self, a: &'tcx Arm) {
1383 resolve_arm(self, a);
1385 fn visit_pat(&mut self, p: &'tcx Pat) {
1386 resolve_pat(self, p);
1388 fn visit_stmt(&mut self, s: &'tcx Stmt) {
1389 resolve_stmt(self, s);
1391 fn visit_expr(&mut self, ex: &'tcx Expr) {
1392 resolve_expr(self, ex);
1394 fn visit_local(&mut self, l: &'tcx Local) {
1395 resolve_local(self, Some(&l.pat), l.init.as_ref().map(|e| &**e));
1399 fn region_scope_tree<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
1402 let closure_base_def_id = tcx.closure_base_def_id(def_id);
1403 if closure_base_def_id != def_id {
1404 return tcx.region_scope_tree(closure_base_def_id);
1407 let id = tcx.hir.as_local_node_id(def_id).unwrap();
1408 let scope_tree = if let Some(body_id) = tcx.hir.maybe_body_owned_by(id) {
1409 let mut visitor = RegionResolutionVisitor {
1411 scope_tree: ScopeTree::default(),
1412 expr_and_pat_count: 0,
1418 terminating_scopes: FxHashSet(),
1421 let body = tcx.hir.body(body_id);
1422 visitor.scope_tree.root_body = Some(body.value.hir_id);
1424 // If the item is an associated const or a method,
1425 // record its impl/trait parent, as it can also have
1426 // lifetime parameters free in this body.
1427 match tcx.hir.get(id) {
1429 Node::TraitItem(_) => {
1430 visitor.scope_tree.root_parent = Some(tcx.hir.get_parent(id));
1435 visitor.visit_body(body);
1439 ScopeTree::default()
1442 Lrc::new(scope_tree)
1445 pub fn provide(providers: &mut Providers) {
1446 *providers = Providers {
1452 impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
1453 fn hash_stable<W: StableHasherResult>(&self,
1454 hcx: &mut StableHashingContext<'a>,
1455 hasher: &mut StableHasher<W>) {
1459 ref body_expr_count,
1462 ref destruction_scopes,
1468 hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
1469 root_body.hash_stable(hcx, hasher);
1470 root_parent.hash_stable(hcx, hasher);
1473 body_expr_count.hash_stable(hcx, hasher);
1474 parent_map.hash_stable(hcx, hasher);
1475 var_map.hash_stable(hcx, hasher);
1476 destruction_scopes.hash_stable(hcx, hasher);
1477 rvalue_scopes.hash_stable(hcx, hasher);
1478 closure_tree.hash_stable(hcx, hasher);
1479 yield_in_scope.hash_stable(hcx, hasher);