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 //! Most of the documentation on regions can be found in
15 //! `middle/infer/region_constraints/README.md`
17 use ich::{StableHashingContext, NodeIdHashingMode};
18 use util::nodemap::{FxHashMap, FxHashSet};
26 use syntax_pos::{Span, DUMMY_SP};
28 use ty::maps::Providers;
31 use hir::def_id::DefId;
32 use hir::intravisit::{self, Visitor, NestedVisitorMap};
33 use hir::{Block, Arm, Pat, PatKind, Stmt, Expr, Local};
34 use rustc_data_structures::indexed_vec::Idx;
35 use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
38 /// Scope represents a statically-describable scope that can be
39 /// used to bound the lifetime/region for values.
41 /// `Node(node_id)`: Any AST node that has any scope at all has the
42 /// `Node(node_id)` scope. Other variants represent special cases not
43 /// immediately derivable from the abstract syntax tree structure.
45 /// `DestructionScope(node_id)` represents the scope of destructors
46 /// implicitly-attached to `node_id` that run immediately after the
47 /// expression for `node_id` itself. Not every AST node carries a
48 /// `DestructionScope`, but those that are `terminating_scopes` do;
49 /// see discussion with `ScopeTree`.
51 /// `Remainder(BlockRemainder { block, statement_index })` represents
52 /// the scope of user code running immediately after the initializer
53 /// expression for the indexed statement, until the end of the block.
55 /// So: the following code can be broken down into the scopes beneath:
58 /// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y) } ) ;
62 /// +---------+ (R10.)
64 /// +----------+ (M8.)
65 /// +----------------------+ (R7.)
67 /// +----------+ (M5.)
68 /// +-----------------------------------+ (M4.)
69 /// +--------------------------------------------------+ (M3.)
71 /// +-----------------------------------------------------------+ (M1.)
73 /// (M1.): Node scope of the whole `let a = ...;` statement.
74 /// (M2.): Node scope of the `f()` expression.
75 /// (M3.): Node scope of the `f().g(..)` expression.
76 /// (M4.): Node scope of the block labeled `'b:`.
77 /// (M5.): Node scope of the `let x = d();` statement
78 /// (D6.): DestructionScope for temporaries created during M5.
79 /// (R7.): Remainder scope for block `'b:`, stmt 0 (let x = ...).
80 /// (M8.): Node scope of the `let y = d();` statement.
81 /// (D9.): DestructionScope for temporaries created during M8.
82 /// (R10.): Remainder scope for block `'b:`, stmt 1 (let y = ...).
83 /// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
84 /// (D12.): DestructionScope for temporaries created during M1 (e.g. f()).
87 /// Note that while the above picture shows the destruction scopes
88 /// as following their corresponding node scopes, in the internal
89 /// data structures of the compiler the destruction scopes are
90 /// represented as enclosing parents. This is sound because we use the
91 /// enclosing parent relationship just to ensure that referenced
92 /// values live long enough; phrased another way, the starting point
93 /// of each range is not really the important thing in the above
94 /// picture, but rather the ending point.
96 /// FIXME (pnkfelix): This currently derives `PartialOrd` and `Ord` to
97 /// placate the same deriving in `ty::FreeRegion`, but we may want to
98 /// actually attach a more meaningful ordering to scopes than the one
99 /// generated via deriving here.
101 /// Scope is a bit-packed to save space - if `code` is SCOPE_DATA_REMAINDER_MAX
102 /// or less, it is a `ScopeData::Remainder`, otherwise it is a type specified
103 /// by the bitpacking.
104 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Copy, RustcEncodable, RustcDecodable)]
106 pub(crate) id: hir::ItemLocalId,
110 const SCOPE_DATA_NODE: u32 = !0;
111 const SCOPE_DATA_CALLSITE: u32 = !1;
112 const SCOPE_DATA_ARGUMENTS: u32 = !2;
113 const SCOPE_DATA_DESTRUCTION: u32 = !3;
114 const SCOPE_DATA_REMAINDER_MAX: u32 = !4;
116 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, RustcEncodable, RustcDecodable)]
118 Node(hir::ItemLocalId),
120 // Scope of the call-site for a function or closure
121 // (outlives the arguments as well as the body).
122 CallSite(hir::ItemLocalId),
124 // Scope of arguments passed to a function or closure
125 // (they outlive its body).
126 Arguments(hir::ItemLocalId),
128 // Scope of destructors for temporaries of node-id.
129 Destruction(hir::ItemLocalId),
131 // Scope following a `let id = expr;` binding in a block.
132 Remainder(BlockRemainder)
135 /// Represents a subscope of `block` for a binding that is introduced
136 /// by `block.stmts[first_statement_index]`. Such subscopes represent
137 /// a suffix of the block. Note that each subscope does not include
138 /// the initializer expression, if any, for the statement indexed by
139 /// `first_statement_index`.
141 /// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
143 /// * the subscope with `first_statement_index == 0` is scope of both
144 /// `a` and `b`; it does not include EXPR_1, but does include
145 /// everything after that first `let`. (If you want a scope that
146 /// includes EXPR_1 as well, then do not use `Scope::Remainder`,
147 /// but instead another `Scope` that encompasses the whole block,
148 /// e.g. `Scope::Node`.
150 /// * the subscope with `first_statement_index == 1` is scope of `c`,
151 /// and thus does not include EXPR_2, but covers the `...`.
152 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
153 RustcDecodable, Debug, Copy)]
154 pub struct BlockRemainder {
155 pub block: hir::ItemLocalId,
156 pub first_statement_index: FirstStatementIndex,
159 newtype_index!(FirstStatementIndex
162 MAX = SCOPE_DATA_REMAINDER_MAX
165 impl From<ScopeData> for Scope {
167 fn from(scope_data: ScopeData) -> Self {
168 let (id, code) = match scope_data {
169 ScopeData::Node(id) => (id, SCOPE_DATA_NODE),
170 ScopeData::CallSite(id) => (id, SCOPE_DATA_CALLSITE),
171 ScopeData::Arguments(id) => (id, SCOPE_DATA_ARGUMENTS),
172 ScopeData::Destruction(id) => (id, SCOPE_DATA_DESTRUCTION),
173 ScopeData::Remainder(r) => (r.block, r.first_statement_index.index() as u32)
179 impl fmt::Debug for Scope {
180 fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
181 fmt::Debug::fmt(&self.data(), formatter)
185 #[allow(non_snake_case)]
188 pub fn data(self) -> ScopeData {
190 SCOPE_DATA_NODE => ScopeData::Node(self.id),
191 SCOPE_DATA_CALLSITE => ScopeData::CallSite(self.id),
192 SCOPE_DATA_ARGUMENTS => ScopeData::Arguments(self.id),
193 SCOPE_DATA_DESTRUCTION => ScopeData::Destruction(self.id),
194 idx => ScopeData::Remainder(BlockRemainder {
196 first_statement_index: FirstStatementIndex::new(idx as usize)
202 pub fn Node(id: hir::ItemLocalId) -> Self {
203 Self::from(ScopeData::Node(id))
207 pub fn CallSite(id: hir::ItemLocalId) -> Self {
208 Self::from(ScopeData::CallSite(id))
212 pub fn Arguments(id: hir::ItemLocalId) -> Self {
213 Self::from(ScopeData::Arguments(id))
217 pub fn Destruction(id: hir::ItemLocalId) -> Self {
218 Self::from(ScopeData::Destruction(id))
222 pub fn Remainder(r: BlockRemainder) -> Self {
223 Self::from(ScopeData::Remainder(r))
228 /// Returns a item-local id associated with this scope.
230 /// NB: likely to be replaced as API is refined; e.g. pnkfelix
231 /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
232 pub fn item_local_id(&self) -> hir::ItemLocalId {
236 pub fn node_id(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> ast::NodeId {
237 match scope_tree.root_body {
239 tcx.hir.hir_to_node_id(hir::HirId {
241 local_id: self.item_local_id()
244 None => ast::DUMMY_NODE_ID
248 /// Returns the span of this Scope. Note that in general the
249 /// returned span may not correspond to the span of any node id in
251 pub fn span(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> Span {
252 let node_id = self.node_id(tcx, scope_tree);
253 if node_id == ast::DUMMY_NODE_ID {
256 let span = tcx.hir.span(node_id);
257 if let ScopeData::Remainder(r) = self.data() {
258 if let hir::map::NodeBlock(ref blk) = tcx.hir.get(node_id) {
259 // Want span for scope starting after the
260 // indexed statement and ending at end of
261 // `blk`; reuse span of `blk` and shift `lo`
262 // forward to end of indexed statement.
264 // (This is the special case aluded to in the
265 // doc-comment for this method)
267 let stmt_span = blk.stmts[r.first_statement_index.index()].span;
269 // To avoid issues with macro-generated spans, the span
270 // of the statement must be nested in that of the block.
271 if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() {
272 return Span::new(stmt_span.lo(), span.hi(), span.ctxt());
280 /// The region scope tree encodes information about region relationships.
281 #[derive(Default, Debug)]
282 pub struct ScopeTree {
283 /// If not empty, this body is the root of this region hierarchy.
284 root_body: Option<hir::HirId>,
286 /// The parent of the root body owner, if the latter is an
287 /// an associated const or method, as impls/traits can also
288 /// have lifetime parameters free in this body.
289 root_parent: Option<ast::NodeId>,
291 /// `parent_map` maps from a scope id to the enclosing scope id;
292 /// this is usually corresponding to the lexical nesting, though
293 /// in the case of closures the parent scope is the innermost
294 /// conditional expression or repeating block. (Note that the
295 /// enclosing scope id for the block associated with a closure is
296 /// the closure itself.)
297 parent_map: FxHashMap<Scope, Scope>,
299 /// `var_map` maps from a variable or binding id to the block in
300 /// which that variable is declared.
301 var_map: FxHashMap<hir::ItemLocalId, Scope>,
303 /// maps from a node-id to the associated destruction scope (if any)
304 destruction_scopes: FxHashMap<hir::ItemLocalId, Scope>,
306 /// `rvalue_scopes` includes entries for those expressions whose cleanup scope is
307 /// larger than the default. The map goes from the expression id
308 /// to the cleanup scope id. For rvalues not present in this
309 /// table, the appropriate cleanup scope is the innermost
310 /// enclosing statement, conditional expression, or repeating
311 /// block (see `terminating_scopes`).
312 /// In constants, None is used to indicate that certain expressions
313 /// escape into 'static and should have no local cleanup scope.
314 rvalue_scopes: FxHashMap<hir::ItemLocalId, Option<Scope>>,
316 /// Encodes the hierarchy of fn bodies. Every fn body (including
317 /// closures) forms its own distinct region hierarchy, rooted in
318 /// the block that is the fn body. This map points from the id of
319 /// that root block to the id of the root block for the enclosing
320 /// fn, if any. Thus the map structures the fn bodies into a
321 /// hierarchy based on their lexical mapping. This is used to
322 /// handle the relationships between regions in a fn and in a
323 /// closure defined by that fn. See the "Modeling closures"
324 /// section of the README in infer::region_constraints for
326 closure_tree: FxHashMap<hir::ItemLocalId, hir::ItemLocalId>,
328 /// If there are any `yield` nested within a scope, this map
329 /// stores the `Span` of the last one and its index in the
330 /// postorder of the Visitor traversal on the HIR.
332 /// HIR Visitor postorder indexes might seem like a peculiar
333 /// thing to care about. but it turns out that HIR bindings
334 /// and the temporary results of HIR expressions are never
335 /// storage-live at the end of HIR nodes with postorder indexes
336 /// lower than theirs, and therefore don't need to be suspended
337 /// at yield-points at these indexes.
339 /// For an example, suppose we have some code such as:
340 /// ```rust,ignore (example)
341 /// foo(f(), yield y, bar(g()))
344 /// With the HIR tree (calls numbered for expository purposes)
346 /// Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
349 /// Obviously, the result of `f()` was created before the yield
350 /// (and therefore needs to be kept valid over the yield) while
351 /// the result of `g()` occurs after the yield (and therefore
352 /// doesn't). If we want to infer that, we can look at the
353 /// postorder traversal:
355 /// `foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
358 /// In which we can easily see that `Call#1` occurs before the yield,
359 /// and `Call#3` after it.
361 /// To see that this method works, consider:
363 /// Let `D` be our binding/temporary and `U` be our other HIR node, with
364 /// `HIR-postorder(U) < HIR-postorder(D)` (in our example, U would be
365 /// the yield and D would be one of the calls). Let's show that
366 /// `D` is storage-dead at `U`.
368 /// Remember that storage-live/storage-dead refers to the state of
369 /// the *storage*, and does not consider moves/drop flags.
372 /// 1. From the ordering guarantee of HIR visitors (see
373 /// `rustc::hir::intravisit`), `D` does not dominate `U`.
374 /// 2. Therefore, `D` is *potentially* storage-dead at `U` (because
375 /// we might visit `U` without ever getting to `D`).
376 /// 3. However, we guarantee that at each HIR point, each
377 /// binding/temporary is always either always storage-live
378 /// or always storage-dead. This is what is being guaranteed
379 /// by `terminating_scopes` including all blocks where the
380 /// count of executions is not guaranteed.
381 /// 4. By `2.` and `3.`, `D` is *statically* storage-dead at `U`,
384 /// I don't think this property relies on `3.` in an essential way - it
385 /// is probably still correct even if we have "unrestricted" terminating
386 /// scopes. However, why use the complicated proof when a simple one
389 /// A subtle thing: `box` expressions, such as `box (&x, yield 2, &y)`. It
390 /// might seem that a `box` expression creates a `Box<T>` temporary
391 /// when it *starts* executing, at `HIR-preorder(BOX-EXPR)`. That might
392 /// be true in the MIR desugaring, but it is not important in the semantics.
394 /// The reason is that semantically, until the `box` expression returns,
395 /// the values are still owned by their containing expressions. So
396 /// we'll see that `&x`.
397 yield_in_scope: FxHashMap<Scope, (Span, usize)>,
399 /// The number of visit_expr and visit_pat calls done in the body.
400 /// Used to sanity check visit_expr/visit_pat call count when
401 /// calculating generator interiors.
402 body_expr_count: FxHashMap<hir::BodyId, usize>,
405 #[derive(Debug, Copy, Clone)]
407 /// the root of the current region tree. This is typically the id
408 /// of the innermost fn body. Each fn forms its own disjoint tree
409 /// in the region hierarchy. These fn bodies are themselves
410 /// arranged into a tree. See the "Modeling closures" section of
411 /// the README in infer::region_constraints for more
413 root_id: Option<hir::ItemLocalId>,
415 /// the scope that contains any new variables declared
416 var_parent: Option<Scope>,
418 /// region parent of expressions etc
419 parent: Option<Scope>,
422 struct RegionResolutionVisitor<'a, 'tcx: 'a> {
423 tcx: TyCtxt<'a, 'tcx, 'tcx>,
425 // The number of expressions and patterns visited in the current body
426 expr_and_pat_count: usize,
428 // Generated scope tree:
429 scope_tree: ScopeTree,
433 /// `terminating_scopes` is a set containing the ids of each
434 /// statement, or conditional/repeating expression. These scopes
435 /// are calling "terminating scopes" because, when attempting to
436 /// find the scope of a temporary, by default we search up the
437 /// enclosing scopes until we encounter the terminating scope. A
438 /// conditional/repeating expression is one which is not
439 /// guaranteed to execute exactly once upon entering the parent
440 /// scope. This could be because the expression only executes
441 /// conditionally, such as the expression `b` in `a && b`, or
442 /// because the expression may execute many times, such as a loop
443 /// body. The reason that we distinguish such expressions is that,
444 /// upon exiting the parent scope, we cannot statically know how
445 /// many times the expression executed, and thus if the expression
446 /// creates temporaries we cannot know statically how many such
447 /// temporaries we would have to cleanup. Therefore we ensure that
448 /// the temporaries never outlast the conditional/repeating
449 /// expression, preventing the need for dynamic checks and/or
450 /// arbitrary amounts of stack space. Terminating scopes end
451 /// up being contained in a DestructionScope that contains the
452 /// destructor's execution.
453 terminating_scopes: FxHashSet<hir::ItemLocalId>,
456 struct ExprLocatorVisitor {
458 result: Option<usize>,
459 expr_and_pat_count: usize,
462 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor
463 // since `expr_count` is compared against the results there.
464 impl<'tcx> Visitor<'tcx> for ExprLocatorVisitor {
465 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
466 NestedVisitorMap::None
469 fn visit_pat(&mut self, pat: &'tcx Pat) {
470 intravisit::walk_pat(self, pat);
472 self.expr_and_pat_count += 1;
474 if pat.id == self.id {
475 self.result = Some(self.expr_and_pat_count);
479 fn visit_expr(&mut self, expr: &'tcx Expr) {
480 debug!("ExprLocatorVisitor - pre-increment {} expr = {:?}",
481 self.expr_and_pat_count,
484 intravisit::walk_expr(self, expr);
486 self.expr_and_pat_count += 1;
488 debug!("ExprLocatorVisitor - post-increment {} expr = {:?}",
489 self.expr_and_pat_count,
492 if expr.id == self.id {
493 self.result = Some(self.expr_and_pat_count);
498 impl<'tcx> ScopeTree {
499 pub fn record_scope_parent(&mut self, child: Scope, parent: Option<Scope>) {
500 debug!("{:?}.parent = {:?}", child, parent);
502 if let Some(p) = parent {
503 let prev = self.parent_map.insert(child, p);
504 assert!(prev.is_none());
507 // record the destruction scopes for later so we can query them
508 if let ScopeData::Destruction(n) = child.data() {
509 self.destruction_scopes.insert(n, child);
513 pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(Scope, Scope) {
514 for (&child, &parent) in &self.parent_map {
519 pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&hir::ItemLocalId, Scope) {
520 for (child, &parent) in self.var_map.iter() {
525 pub fn opt_destruction_scope(&self, n: hir::ItemLocalId) -> Option<Scope> {
526 self.destruction_scopes.get(&n).cloned()
529 /// Records that `sub_closure` is defined within `sup_closure`. These ids
530 /// should be the id of the block that is the fn body, which is
531 /// also the root of the region hierarchy for that fn.
532 fn record_closure_parent(&mut self,
533 sub_closure: hir::ItemLocalId,
534 sup_closure: hir::ItemLocalId) {
535 debug!("record_closure_parent(sub_closure={:?}, sup_closure={:?})",
536 sub_closure, sup_closure);
537 assert!(sub_closure != sup_closure);
538 let previous = self.closure_tree.insert(sub_closure, sup_closure);
539 assert!(previous.is_none());
542 fn closure_is_enclosed_by(&self,
543 mut sub_closure: hir::ItemLocalId,
544 sup_closure: hir::ItemLocalId) -> bool {
546 if sub_closure == sup_closure { return true; }
547 match self.closure_tree.get(&sub_closure) {
548 Some(&s) => { sub_closure = s; }
549 None => { return false; }
554 fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) {
555 debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
556 assert!(var != lifetime.item_local_id());
557 self.var_map.insert(var, lifetime);
560 fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
561 debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
562 if let Some(lifetime) = lifetime {
563 assert!(var != lifetime.item_local_id());
565 self.rvalue_scopes.insert(var, lifetime);
568 pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> {
569 //! Returns the narrowest scope that encloses `id`, if any.
570 self.parent_map.get(&id).cloned()
573 #[allow(dead_code)] // used in cfg
574 pub fn encl_scope(&self, id: Scope) -> Scope {
575 //! Returns the narrowest scope that encloses `id`, if any.
576 self.opt_encl_scope(id).unwrap()
579 /// Returns the lifetime of the local variable `var_id`
580 pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Scope {
581 match self.var_map.get(&var_id) {
583 None => { bug!("no enclosing scope for id {:?}", var_id); }
587 pub fn temporary_scope(&self, expr_id: hir::ItemLocalId) -> Option<Scope> {
588 //! Returns the scope when temp created by expr_id will be cleaned up
590 // check for a designated rvalue scope
591 if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
592 debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
596 // else, locate the innermost terminating scope
597 // if there's one. Static items, for instance, won't
598 // have an enclosing scope, hence no scope will be
600 let mut id = Scope::Node(expr_id);
602 while let Some(&p) = self.parent_map.get(&id) {
604 ScopeData::Destruction(..) => {
605 debug!("temporary_scope({:?}) = {:?} [enclosing]",
613 debug!("temporary_scope({:?}) = None", expr_id);
617 pub fn var_region(&self, id: hir::ItemLocalId) -> ty::RegionKind {
618 //! Returns the lifetime of the variable `id`.
620 let scope = ty::ReScope(self.var_scope(id));
621 debug!("var_region({:?}) = {:?}", id, scope);
625 pub fn scopes_intersect(&self, scope1: Scope, scope2: Scope)
627 self.is_subscope_of(scope1, scope2) ||
628 self.is_subscope_of(scope2, scope1)
631 /// Returns true if `subscope` is equal to or is lexically nested inside `superscope` and false
633 pub fn is_subscope_of(&self,
637 let mut s = subscope;
638 debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
639 while superscope != s {
640 match self.opt_encl_scope(s) {
642 debug!("is_subscope_of({:?}, {:?}, s={:?})=false",
643 subscope, superscope, s);
646 Some(scope) => s = scope
650 debug!("is_subscope_of({:?}, {:?})=true",
651 subscope, superscope);
656 /// Returns the id of the innermost containing body
657 pub fn containing_body(&self, mut scope: Scope)-> Option<hir::ItemLocalId> {
659 if let ScopeData::CallSite(id) = scope.data() {
663 match self.opt_encl_scope(scope) {
665 Some(parent) => scope = parent,
670 /// Finds the nearest common ancestor (if any) of two scopes. That is, finds the smallest
671 /// scope which is greater than or equal to both `scope_a` and `scope_b`.
672 pub fn nearest_common_ancestor(&self,
676 if scope_a == scope_b { return scope_a; }
678 // [1] The initial values for `a_buf` and `b_buf` are not used.
679 // The `ancestors_of` function will return some prefix that
680 // is re-initialized with new values (or else fallback to a
681 // heap-allocated vector).
682 let mut a_buf: [Scope; 32] = [scope_a /* [1] */; 32];
683 let mut a_vec: Vec<Scope> = vec![];
684 let mut b_buf: [Scope; 32] = [scope_b /* [1] */; 32];
685 let mut b_vec: Vec<Scope> = vec![];
686 let parent_map = &self.parent_map;
687 let a_ancestors = ancestors_of(parent_map, scope_a, &mut a_buf, &mut a_vec);
688 let b_ancestors = ancestors_of(parent_map, scope_b, &mut b_buf, &mut b_vec);
689 let mut a_index = a_ancestors.len() - 1;
690 let mut b_index = b_ancestors.len() - 1;
692 // Here, [ab]_ancestors is a vector going from narrow to broad.
693 // The end of each vector will be the item where the scope is
694 // defined; if there are any common ancestors, then the tails of
695 // the vector will be the same. So basically we want to walk
696 // backwards from the tail of each vector and find the first point
697 // where they diverge. If one vector is a suffix of the other,
698 // then the corresponding scope is a superscope of the other.
700 if a_ancestors[a_index] != b_ancestors[b_index] {
701 // In this case, the two regions belong to completely
702 // different functions. Compare those fn for lexical
703 // nesting. The reasoning behind this is subtle. See the
704 // "Modeling closures" section of the README in
705 // infer::region_constraints for more details.
706 let a_root_scope = a_ancestors[a_index];
707 let b_root_scope = a_ancestors[a_index];
708 return match (a_root_scope.data(), b_root_scope.data()) {
709 (ScopeData::Destruction(a_root_id),
710 ScopeData::Destruction(b_root_id)) => {
711 if self.closure_is_enclosed_by(a_root_id, b_root_id) {
712 // `a` is enclosed by `b`, hence `b` is the ancestor of everything in `a`
714 } else if self.closure_is_enclosed_by(b_root_id, a_root_id) {
715 // `b` is enclosed by `a`, hence `a` is the ancestor of everything in `b`
718 // neither fn encloses the other
723 // root ids are always Node right now
730 // Loop invariant: a_ancestors[a_index] == b_ancestors[b_index]
731 // for all indices between a_index and the end of the array
732 if a_index == 0 { return scope_a; }
733 if b_index == 0 { return scope_b; }
736 if a_ancestors[a_index] != b_ancestors[b_index] {
737 return a_ancestors[a_index + 1];
741 fn ancestors_of<'a, 'tcx>(parent_map: &FxHashMap<Scope, Scope>,
743 buf: &'a mut [Scope; 32],
744 vec: &'a mut Vec<Scope>)
746 // debug!("ancestors_of(scope={:?})", scope);
747 let mut scope = scope;
752 match parent_map.get(&scope) {
753 Some(&superscope) => scope = superscope,
754 _ => return &buf[..i+1]
759 *vec = Vec::with_capacity(64);
760 vec.extend_from_slice(buf);
763 match parent_map.get(&scope) {
764 Some(&superscope) => scope = superscope,
771 /// Assuming that the provided region was defined within this `ScopeTree`,
772 /// returns the outermost `Scope` that the region outlives.
773 pub fn early_free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
774 br: &ty::EarlyBoundRegion)
776 let param_owner = tcx.parent_def_id(br.def_id).unwrap();
778 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
779 let scope = tcx.hir.maybe_body_owned_by(param_owner_id).map(|body_id| {
780 tcx.hir.body(body_id).value.hir_id.local_id
781 }).unwrap_or_else(|| {
782 // The lifetime was defined on node that doesn't own a body,
783 // which in practice can only mean a trait or an impl, that
784 // is the parent of a method, and that is enforced below.
785 assert_eq!(Some(param_owner_id), self.root_parent,
786 "free_scope: {:?} not recognized by the \
787 region scope tree for {:?} / {:?}",
789 self.root_parent.map(|id| tcx.hir.local_def_id(id)),
790 self.root_body.map(|hir_id| DefId::local(hir_id.owner)));
792 // The trait/impl lifetime is in scope for the method's body.
793 self.root_body.unwrap().local_id
796 Scope::CallSite(scope)
799 /// Assuming that the provided region was defined within this `ScopeTree`,
800 /// returns the outermost `Scope` that the region outlives.
801 pub fn free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, fr: &ty::FreeRegion)
803 let param_owner = match fr.bound_region {
804 ty::BoundRegion::BrNamed(def_id, _) => {
805 tcx.parent_def_id(def_id).unwrap()
810 // Ensure that the named late-bound lifetimes were defined
811 // on the same function that they ended up being freed in.
812 assert_eq!(param_owner, fr.scope);
814 let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
815 let body_id = tcx.hir.body_owned_by(param_owner_id);
816 Scope::CallSite(tcx.hir.body(body_id).value.hir_id.local_id)
819 /// Checks whether the given scope contains a `yield`. If so,
820 /// returns `Some((span, expr_count))` with the span of a yield we found and
821 /// the number of expressions and patterns appearing before the `yield` in the body + 1.
822 /// If there a are multiple yields in a scope, the one with the highest number is returned.
823 pub fn yield_in_scope(&self, scope: Scope) -> Option<(Span, usize)> {
824 self.yield_in_scope.get(&scope).cloned()
827 /// Checks whether the given scope contains a `yield` and if that yield could execute
828 /// after `expr`. If so, it returns the span of that `yield`.
829 /// `scope` must be inside the body.
830 pub fn yield_in_scope_for_expr(&self,
833 body: &'tcx hir::Body) -> Option<Span> {
834 self.yield_in_scope(scope).and_then(|(span, count)| {
835 let mut visitor = ExprLocatorVisitor {
838 expr_and_pat_count: 0,
840 visitor.visit_body(body);
841 if count >= visitor.result.unwrap() {
849 /// Gives the number of expressions visited in a body.
850 /// Used to sanity check visit_expr call count when
851 /// calculating generator interiors.
852 pub fn body_expr_count(&self, body_id: hir::BodyId) -> Option<usize> {
853 self.body_expr_count.get(&body_id).map(|r| *r)
857 /// Records the lifetime of a local variable as `cx.var_parent`
858 fn record_var_lifetime(visitor: &mut RegionResolutionVisitor,
859 var_id: hir::ItemLocalId,
861 match visitor.cx.var_parent {
863 // this can happen in extern fn declarations like
865 // extern fn isalnum(c: c_int) -> c_int
867 Some(parent_scope) =>
868 visitor.scope_tree.record_var_scope(var_id, parent_scope),
872 fn resolve_block<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, blk: &'tcx hir::Block) {
873 debug!("resolve_block(blk.id={:?})", blk.id);
875 let prev_cx = visitor.cx;
877 // We treat the tail expression in the block (if any) somewhat
878 // differently from the statements. The issue has to do with
879 // temporary lifetimes. Consider the following:
882 // let inner = ... (&bar()) ...;
884 // (... (&foo()) ...) // (the tail expression)
885 // }, other_argument());
887 // Each of the statements within the block is a terminating
888 // scope, and thus a temporary (e.g. the result of calling
889 // `bar()` in the initalizer expression for `let inner = ...;`)
890 // will be cleaned up immediately after its corresponding
891 // statement (i.e. `let inner = ...;`) executes.
893 // On the other hand, temporaries associated with evaluating the
894 // tail expression for the block are assigned lifetimes so that
895 // they will be cleaned up as part of the terminating scope
896 // *surrounding* the block expression. Here, the terminating
897 // scope for the block expression is the `quux(..)` call; so
898 // those temporaries will only be cleaned up *after* both
899 // `other_argument()` has run and also the call to `quux(..)`
900 // itself has returned.
902 visitor.enter_node_scope_with_dtor(blk.hir_id.local_id);
903 visitor.cx.var_parent = visitor.cx.parent;
906 // This block should be kept approximately in sync with
907 // `intravisit::walk_block`. (We manually walk the block, rather
908 // than call `walk_block`, in order to maintain precise
909 // index information.)
911 for (i, statement) in blk.stmts.iter().enumerate() {
912 if let hir::StmtDecl(..) = statement.node {
913 // Each StmtDecl introduces a subscope for bindings
914 // introduced by the declaration; this subscope covers
915 // a suffix of the block . Each subscope in a block
916 // has the previous subscope in the block as a parent,
917 // except for the first such subscope, which has the
918 // block itself as a parent.
920 Scope::Remainder(BlockRemainder {
921 block: blk.hir_id.local_id,
922 first_statement_index: FirstStatementIndex::new(i)
925 visitor.cx.var_parent = visitor.cx.parent;
927 visitor.visit_stmt(statement)
929 walk_list!(visitor, visit_expr, &blk.expr);
932 visitor.cx = prev_cx;
935 fn resolve_arm<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, arm: &'tcx hir::Arm) {
936 visitor.terminating_scopes.insert(arm.body.hir_id.local_id);
938 if let Some(ref expr) = arm.guard {
939 visitor.terminating_scopes.insert(expr.hir_id.local_id);
942 intravisit::walk_arm(visitor, arm);
945 fn resolve_pat<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, pat: &'tcx hir::Pat) {
946 visitor.record_child_scope(Scope::Node(pat.hir_id.local_id));
948 // If this is a binding then record the lifetime of that binding.
949 if let PatKind::Binding(..) = pat.node {
950 record_var_lifetime(visitor, pat.hir_id.local_id, pat.span);
953 debug!("resolve_pat - pre-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
955 intravisit::walk_pat(visitor, pat);
957 visitor.expr_and_pat_count += 1;
959 debug!("resolve_pat - post-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
962 fn resolve_stmt<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, stmt: &'tcx hir::Stmt) {
963 let stmt_id = visitor.tcx.hir.node_to_hir_id(stmt.node.id()).local_id;
964 debug!("resolve_stmt(stmt.id={:?})", stmt_id);
966 // Every statement will clean up the temporaries created during
967 // execution of that statement. Therefore each statement has an
968 // associated destruction scope that represents the scope of the
969 // statement plus its destructors, and thus the scope for which
970 // regions referenced by the destructors need to survive.
971 visitor.terminating_scopes.insert(stmt_id);
973 let prev_parent = visitor.cx.parent;
974 visitor.enter_node_scope_with_dtor(stmt_id);
976 intravisit::walk_stmt(visitor, stmt);
978 visitor.cx.parent = prev_parent;
981 fn resolve_expr<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, expr: &'tcx hir::Expr) {
982 debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
984 let prev_cx = visitor.cx;
985 visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);
988 let terminating_scopes = &mut visitor.terminating_scopes;
989 let mut terminating = |id: hir::ItemLocalId| {
990 terminating_scopes.insert(id);
993 // Conditional or repeating scopes are always terminating
994 // scopes, meaning that temporaries cannot outlive them.
995 // This ensures fixed size stacks.
997 hir::ExprBinary(codemap::Spanned { node: hir::BiAnd, .. }, _, ref r) |
998 hir::ExprBinary(codemap::Spanned { node: hir::BiOr, .. }, _, ref r) => {
999 // For shortcircuiting operators, mark the RHS as a terminating
1000 // scope since it only executes conditionally.
1001 terminating(r.hir_id.local_id);
1004 hir::ExprIf(ref expr, ref then, Some(ref otherwise)) => {
1005 terminating(expr.hir_id.local_id);
1006 terminating(then.hir_id.local_id);
1007 terminating(otherwise.hir_id.local_id);
1010 hir::ExprIf(ref expr, ref then, None) => {
1011 terminating(expr.hir_id.local_id);
1012 terminating(then.hir_id.local_id);
1015 hir::ExprLoop(ref body, _, _) => {
1016 terminating(body.hir_id.local_id);
1019 hir::ExprWhile(ref expr, ref body, _) => {
1020 terminating(expr.hir_id.local_id);
1021 terminating(body.hir_id.local_id);
1024 hir::ExprMatch(..) => {
1025 visitor.cx.var_parent = visitor.cx.parent;
1028 hir::ExprAssignOp(..) | hir::ExprIndex(..) |
1029 hir::ExprUnary(..) | hir::ExprCall(..) | hir::ExprMethodCall(..) => {
1030 // FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls
1032 // The lifetimes for a call or method call look as follows:
1040 // The idea is that call.callee_id represents *the time when
1041 // the invoked function is actually running* and call.id
1042 // represents *the time to prepare the arguments and make the
1043 // call*. See the section "Borrows in Calls" borrowck/README.md
1044 // for an extended explanation of why this distinction is
1047 // record_superlifetime(new_cx, expr.callee_id);
1055 // Manually recurse over closures, because they are the only
1056 // case of nested bodies that share the parent environment.
1057 hir::ExprClosure(.., body, _, _) => {
1058 let body = visitor.tcx.hir.body(body);
1059 visitor.visit_body(body);
1062 _ => intravisit::walk_expr(visitor, expr)
1065 visitor.expr_and_pat_count += 1;
1067 debug!("resolve_expr post-increment {}, expr = {:?}", visitor.expr_and_pat_count, expr);
1069 if let hir::ExprYield(..) = expr.node {
1070 // Mark this expr's scope and all parent scopes as containing `yield`.
1071 let mut scope = Scope::Node(expr.hir_id.local_id);
1073 visitor.scope_tree.yield_in_scope.insert(scope,
1074 (expr.span, visitor.expr_and_pat_count));
1076 // Keep traversing up while we can.
1077 match visitor.scope_tree.parent_map.get(&scope) {
1078 // Don't cross from closure bodies to their parent.
1079 Some(&superscope) => match superscope.data() {
1080 ScopeData::CallSite(_) => break,
1081 _ => scope = superscope
1088 visitor.cx = prev_cx;
1091 fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1092 pat: Option<&'tcx hir::Pat>,
1093 init: Option<&'tcx hir::Expr>) {
1094 debug!("resolve_local(pat={:?}, init={:?})", pat, init);
1096 let blk_scope = visitor.cx.var_parent;
1098 // As an exception to the normal rules governing temporary
1099 // lifetimes, initializers in a let have a temporary lifetime
1100 // of the enclosing block. This means that e.g. a program
1101 // like the following is legal:
1103 // let ref x = HashMap::new();
1105 // Because the hash map will be freed in the enclosing block.
1107 // We express the rules more formally based on 3 grammars (defined
1108 // fully in the helpers below that implement them):
1110 // 1. `E&`, which matches expressions like `&<rvalue>` that
1111 // own a pointer into the stack.
1113 // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
1114 // y)` that produce ref bindings into the value they are
1115 // matched against or something (at least partially) owned by
1116 // the value they are matched against. (By partially owned,
1117 // I mean that creating a binding into a ref-counted or managed value
1118 // would still count.)
1120 // 3. `ET`, which matches both rvalues like `foo()` as well as places
1121 // based on rvalues like `foo().x[2].y`.
1123 // A subexpression `<rvalue>` that appears in a let initializer
1124 // `let pat [: ty] = expr` has an extended temporary lifetime if
1125 // any of the following conditions are met:
1127 // A. `pat` matches `P&` and `expr` matches `ET`
1128 // (covers cases where `pat` creates ref bindings into an rvalue
1129 // produced by `expr`)
1130 // B. `ty` is a borrowed pointer and `expr` matches `ET`
1131 // (covers cases where coercion creates a borrow)
1132 // C. `expr` matches `E&`
1133 // (covers cases `expr` borrows an rvalue that is then assigned
1134 // to memory (at least partially) owned by the binding)
1136 // Here are some examples hopefully giving an intuition where each
1137 // rule comes into play and why:
1139 // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
1140 // would have an extended lifetime, but not `foo()`.
1142 // Rule B. `let x = &foo().x`. The rvalue ``foo()` would have extended
1145 // In some cases, multiple rules may apply (though not to the same
1146 // rvalue). For example:
1148 // let ref x = [&a(), &b()];
1150 // Here, the expression `[...]` has an extended lifetime due to rule
1151 // A, but the inner rvalues `a()` and `b()` have an extended lifetime
1154 if let Some(expr) = init {
1155 record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
1157 if let Some(pat) = pat {
1158 if is_binding_pat(pat) {
1159 record_rvalue_scope(visitor, &expr, blk_scope);
1164 // Make sure we visit the initializer first, so expr_and_pat_count remains correct
1165 if let Some(expr) = init {
1166 visitor.visit_expr(expr);
1168 if let Some(pat) = pat {
1169 visitor.visit_pat(pat);
1172 /// True if `pat` match the `P&` nonterminal:
1175 /// | StructName { ..., P&, ... }
1176 /// | VariantName(..., P&, ...)
1177 /// | [ ..., P&, ... ]
1178 /// | ( ..., P&, ... )
1180 fn is_binding_pat(pat: &hir::Pat) -> bool {
1181 // Note that the code below looks for *explicit* refs only, that is, it won't
1182 // know about *implicit* refs as introduced in #42640.
1184 // This is not a problem. For example, consider
1186 // let (ref x, ref y) = (Foo { .. }, Bar { .. });
1188 // Due to the explicit refs on the left hand side, the below code would signal
1189 // that the temporary value on the right hand side should live until the end of
1190 // the enclosing block (as opposed to being dropped after the let is complete).
1192 // To create an implicit ref, however, you must have a borrowed value on the RHS
1193 // already, as in this example (which won't compile before #42640):
1195 // let Foo { x, .. } = &Foo { x: ..., ... };
1199 // let Foo { ref x, .. } = Foo { ... };
1201 // In the former case (the implicit ref version), the temporary is created by the
1202 // & expression, and its lifetime would be extended to the end of the block (due
1203 // to a different rule, not the below code).
1205 PatKind::Binding(hir::BindingAnnotation::Ref, ..) |
1206 PatKind::Binding(hir::BindingAnnotation::RefMut, ..) => true,
1208 PatKind::Struct(_, ref field_pats, _) => {
1209 field_pats.iter().any(|fp| is_binding_pat(&fp.node.pat))
1212 PatKind::Slice(ref pats1, ref pats2, ref pats3) => {
1213 pats1.iter().any(|p| is_binding_pat(&p)) ||
1214 pats2.iter().any(|p| is_binding_pat(&p)) ||
1215 pats3.iter().any(|p| is_binding_pat(&p))
1218 PatKind::TupleStruct(_, ref subpats, _) |
1219 PatKind::Tuple(ref subpats, _) => {
1220 subpats.iter().any(|p| is_binding_pat(&p))
1223 PatKind::Box(ref subpat) => {
1224 is_binding_pat(&subpat)
1231 /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
1234 /// | StructName { ..., f: E&, ... }
1235 /// | [ ..., E&, ... ]
1236 /// | ( ..., E&, ... )
1241 fn record_rvalue_scope_if_borrow_expr<'a, 'tcx>(
1242 visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1244 blk_id: Option<Scope>)
1247 hir::ExprAddrOf(_, ref subexpr) => {
1248 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
1249 record_rvalue_scope(visitor, &subexpr, blk_id);
1251 hir::ExprStruct(_, ref fields, _) => {
1252 for field in fields {
1253 record_rvalue_scope_if_borrow_expr(
1254 visitor, &field.expr, blk_id);
1257 hir::ExprArray(ref subexprs) |
1258 hir::ExprTup(ref subexprs) => {
1259 for subexpr in subexprs {
1260 record_rvalue_scope_if_borrow_expr(
1261 visitor, &subexpr, blk_id);
1264 hir::ExprCast(ref subexpr, _) => {
1265 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
1267 hir::ExprBlock(ref block) => {
1268 if let Some(ref subexpr) = block.expr {
1269 record_rvalue_scope_if_borrow_expr(
1270 visitor, &subexpr, blk_id);
1277 /// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
1278 /// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
1279 /// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
1282 /// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
1283 /// `<rvalue>` as `blk_id`:
1291 /// Note: ET is intended to match "rvalues or places based on rvalues".
1292 fn record_rvalue_scope<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
1294 blk_scope: Option<Scope>) {
1295 let mut expr = expr;
1297 // Note: give all the expressions matching `ET` with the
1298 // extended temporary lifetime, not just the innermost rvalue,
1299 // because in trans if we must compile e.g. `*rvalue()`
1300 // into a temporary, we request the temporary scope of the
1301 // outer expression.
1302 visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
1305 hir::ExprAddrOf(_, ref subexpr) |
1306 hir::ExprUnary(hir::UnDeref, ref subexpr) |
1307 hir::ExprField(ref subexpr, _) |
1308 hir::ExprTupField(ref subexpr, _) |
1309 hir::ExprIndex(ref subexpr, _) => {
1320 impl<'a, 'tcx> RegionResolutionVisitor<'a, 'tcx> {
1321 /// Records the current parent (if any) as the parent of `child_scope`.
1322 fn record_child_scope(&mut self, child_scope: Scope) {
1323 let parent = self.cx.parent;
1324 self.scope_tree.record_scope_parent(child_scope, parent);
1327 /// Records the current parent (if any) as the parent of `child_scope`,
1328 /// and sets `child_scope` as the new current parent.
1329 fn enter_scope(&mut self, child_scope: Scope) {
1330 self.record_child_scope(child_scope);
1331 self.cx.parent = Some(child_scope);
1334 fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) {
1335 // If node was previously marked as a terminating scope during the
1336 // recursive visit of its parent node in the AST, then we need to
1337 // account for the destruction scope representing the scope of
1338 // the destructors that run immediately after it completes.
1339 if self.terminating_scopes.contains(&id) {
1340 self.enter_scope(Scope::Destruction(id));
1342 self.enter_scope(Scope::Node(id));
1346 impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
1347 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1348 NestedVisitorMap::None
1351 fn visit_block(&mut self, b: &'tcx Block) {
1352 resolve_block(self, b);
1355 fn visit_body(&mut self, body: &'tcx hir::Body) {
1356 let body_id = body.id();
1357 let owner_id = self.tcx.hir.body_owner(body_id);
1359 debug!("visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
1361 self.tcx.sess.codemap().span_to_string(body.value.span),
1365 let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
1366 let outer_cx = self.cx;
1367 let outer_ts = mem::replace(&mut self.terminating_scopes, FxHashSet());
1368 self.terminating_scopes.insert(body.value.hir_id.local_id);
1370 if let Some(root_id) = self.cx.root_id {
1371 self.scope_tree.record_closure_parent(body.value.hir_id.local_id, root_id);
1373 self.cx.root_id = Some(body.value.hir_id.local_id);
1375 self.enter_scope(Scope::CallSite(body.value.hir_id.local_id));
1376 self.enter_scope(Scope::Arguments(body.value.hir_id.local_id));
1378 // The arguments and `self` are parented to the fn.
1379 self.cx.var_parent = self.cx.parent.take();
1380 for argument in &body.arguments {
1381 self.visit_pat(&argument.pat);
1384 // The body of the every fn is a root scope.
1385 self.cx.parent = self.cx.var_parent;
1386 if let hir::BodyOwnerKind::Fn = self.tcx.hir.body_owner_kind(owner_id) {
1387 self.visit_expr(&body.value);
1389 // Only functions have an outer terminating (drop) scope, while
1390 // temporaries in constant initializers may be 'static, but only
1391 // according to rvalue lifetime semantics, using the same
1392 // syntactical rules used for let initializers.
1394 // E.g. in `let x = &f();`, the temporary holding the result from
1395 // the `f()` call lives for the entirety of the surrounding block.
1397 // Similarly, `const X: ... = &f();` would have the result of `f()`
1398 // live for `'static`, implying (if Drop restrictions on constants
1399 // ever get lifted) that the value *could* have a destructor, but
1400 // it'd get leaked instead of the destructor running during the
1401 // evaluation of `X` (if at all allowed by CTFE).
1403 // However, `const Y: ... = g(&f());`, like `let y = g(&f());`,
1404 // would *not* let the `f()` temporary escape into an outer scope
1405 // (i.e. `'static`), which means that after `g` returns, it drops,
1406 // and all the associated destruction scope rules apply.
1407 self.cx.var_parent = None;
1408 resolve_local(self, None, Some(&body.value));
1411 if body.is_generator {
1412 self.scope_tree.body_expr_count.insert(body_id, self.expr_and_pat_count);
1415 // Restore context we had at the start.
1416 self.expr_and_pat_count = outer_ec;
1418 self.terminating_scopes = outer_ts;
1421 fn visit_arm(&mut self, a: &'tcx Arm) {
1422 resolve_arm(self, a);
1424 fn visit_pat(&mut self, p: &'tcx Pat) {
1425 resolve_pat(self, p);
1427 fn visit_stmt(&mut self, s: &'tcx Stmt) {
1428 resolve_stmt(self, s);
1430 fn visit_expr(&mut self, ex: &'tcx Expr) {
1431 resolve_expr(self, ex);
1433 fn visit_local(&mut self, l: &'tcx Local) {
1434 resolve_local(self, Some(&l.pat), l.init.as_ref().map(|e| &**e));
1438 fn region_scope_tree<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
1441 let closure_base_def_id = tcx.closure_base_def_id(def_id);
1442 if closure_base_def_id != def_id {
1443 return tcx.region_scope_tree(closure_base_def_id);
1446 let id = tcx.hir.as_local_node_id(def_id).unwrap();
1447 let scope_tree = if let Some(body_id) = tcx.hir.maybe_body_owned_by(id) {
1448 let mut visitor = RegionResolutionVisitor {
1450 scope_tree: ScopeTree::default(),
1451 expr_and_pat_count: 0,
1457 terminating_scopes: FxHashSet(),
1460 let body = tcx.hir.body(body_id);
1461 visitor.scope_tree.root_body = Some(body.value.hir_id);
1463 // If the item is an associated const or a method,
1464 // record its impl/trait parent, as it can also have
1465 // lifetime parameters free in this body.
1466 match tcx.hir.get(id) {
1467 hir::map::NodeImplItem(_) |
1468 hir::map::NodeTraitItem(_) => {
1469 visitor.scope_tree.root_parent = Some(tcx.hir.get_parent(id));
1474 visitor.visit_body(body);
1478 ScopeTree::default()
1484 pub fn provide(providers: &mut Providers) {
1485 *providers = Providers {
1491 impl<'gcx> HashStable<StableHashingContext<'gcx>> for ScopeTree {
1492 fn hash_stable<W: StableHasherResult>(&self,
1493 hcx: &mut StableHashingContext<'gcx>,
1494 hasher: &mut StableHasher<W>) {
1498 ref body_expr_count,
1501 ref destruction_scopes,
1507 hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
1508 root_body.hash_stable(hcx, hasher);
1509 root_parent.hash_stable(hcx, hasher);
1512 body_expr_count.hash_stable(hcx, hasher);
1513 parent_map.hash_stable(hcx, hasher);
1514 var_map.hash_stable(hcx, hasher);
1515 destruction_scopes.hash_stable(hcx, hasher);
1516 rvalue_scopes.hash_stable(hcx, hasher);
1517 closure_tree.hash_stable(hcx, hasher);
1518 yield_in_scope.hash_stable(hcx, hasher);