1 //! This file builds up the `ScopeTree`, which describes
2 //! the parent links in the region hierarchy.
4 //! For more information about how MIR-based region-checking works,
5 //! see the [rustc guide].
7 //! [rustc guide]: https://rust-lang.github.io/rustc-guide/mir/borrowck.html
9 use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
10 use rustc::middle::region::*;
11 use rustc::ty::query::Providers;
12 use rustc::ty::TyCtxt;
13 use rustc_data_structures::fx::FxHashSet;
15 use rustc_hir::def_id::DefId;
16 use rustc_hir::{Arm, Block, Expr, Local, Node, Pat, PatKind, Stmt};
17 use rustc_index::vec::Idx;
18 use rustc_span::source_map;
23 #[derive(Debug, Copy, Clone)]
25 /// The root of the current region tree. This is typically the id
26 /// of the innermost fn body. Each fn forms its own disjoint tree
27 /// in the region hierarchy. These fn bodies are themselves
28 /// arranged into a tree. See the "Modeling closures" section of
29 /// the README in `infer::region_constraints` for more
31 root_id: Option<hir::ItemLocalId>,
33 /// The scope that contains any new variables declared, plus its depth in
35 var_parent: Option<(Scope, ScopeDepth)>,
37 /// Region parent of expressions, etc., plus its depth in the scope tree.
38 parent: Option<(Scope, ScopeDepth)>,
41 struct RegionResolutionVisitor<'tcx> {
44 // The number of expressions and patterns visited in the current body.
45 expr_and_pat_count: usize,
46 // When this is `true`, we record the `Scopes` we encounter
47 // when processing a Yield expression. This allows us to fix
49 pessimistic_yield: bool,
50 // Stores scopes when `pessimistic_yield` is `true`.
51 fixup_scopes: Vec<Scope>,
52 // The generated scope tree.
53 scope_tree: ScopeTree,
57 /// `terminating_scopes` is a set containing the ids of each
58 /// statement, or conditional/repeating expression. These scopes
59 /// are calling "terminating scopes" because, when attempting to
60 /// find the scope of a temporary, by default we search up the
61 /// enclosing scopes until we encounter the terminating scope. A
62 /// conditional/repeating expression is one which is not
63 /// guaranteed to execute exactly once upon entering the parent
64 /// scope. This could be because the expression only executes
65 /// conditionally, such as the expression `b` in `a && b`, or
66 /// because the expression may execute many times, such as a loop
67 /// body. The reason that we distinguish such expressions is that,
68 /// upon exiting the parent scope, we cannot statically know how
69 /// many times the expression executed, and thus if the expression
70 /// creates temporaries we cannot know statically how many such
71 /// temporaries we would have to cleanup. Therefore, we ensure that
72 /// the temporaries never outlast the conditional/repeating
73 /// expression, preventing the need for dynamic checks and/or
74 /// arbitrary amounts of stack space. Terminating scopes end
75 /// up being contained in a DestructionScope that contains the
76 /// destructor's execution.
77 terminating_scopes: FxHashSet<hir::ItemLocalId>,
80 /// Records the lifetime of a local variable as `cx.var_parent`
81 fn record_var_lifetime(
82 visitor: &mut RegionResolutionVisitor<'_>,
83 var_id: hir::ItemLocalId,
86 match visitor.cx.var_parent {
88 // this can happen in extern fn declarations like
90 // extern fn isalnum(c: c_int) -> c_int
92 Some((parent_scope, _)) => visitor.scope_tree.record_var_scope(var_id, parent_scope),
96 fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx hir::Block<'tcx>) {
97 debug!("resolve_block(blk.hir_id={:?})", blk.hir_id);
99 let prev_cx = visitor.cx;
101 // We treat the tail expression in the block (if any) somewhat
102 // differently from the statements. The issue has to do with
103 // temporary lifetimes. Consider the following:
106 // let inner = ... (&bar()) ...;
108 // (... (&foo()) ...) // (the tail expression)
109 // }, other_argument());
111 // Each of the statements within the block is a terminating
112 // scope, and thus a temporary (e.g., the result of calling
113 // `bar()` in the initializer expression for `let inner = ...;`)
114 // will be cleaned up immediately after its corresponding
115 // statement (i.e., `let inner = ...;`) executes.
117 // On the other hand, temporaries associated with evaluating the
118 // tail expression for the block are assigned lifetimes so that
119 // they will be cleaned up as part of the terminating scope
120 // *surrounding* the block expression. Here, the terminating
121 // scope for the block expression is the `quux(..)` call; so
122 // those temporaries will only be cleaned up *after* both
123 // `other_argument()` has run and also the call to `quux(..)`
124 // itself has returned.
126 visitor.enter_node_scope_with_dtor(blk.hir_id.local_id);
127 visitor.cx.var_parent = visitor.cx.parent;
130 // This block should be kept approximately in sync with
131 // `intravisit::walk_block`. (We manually walk the block, rather
132 // than call `walk_block`, in order to maintain precise
133 // index information.)
135 for (i, statement) in blk.stmts.iter().enumerate() {
136 match statement.kind {
137 hir::StmtKind::Local(..) | hir::StmtKind::Item(..) => {
138 // Each declaration introduces a subscope for bindings
139 // introduced by the declaration; this subscope covers a
140 // suffix of the block. Each subscope in a block has the
141 // previous subscope in the block as a parent, except for
142 // the first such subscope, which has the block itself as a
144 visitor.enter_scope(Scope {
145 id: blk.hir_id.local_id,
146 data: ScopeData::Remainder(FirstStatementIndex::new(i)),
148 visitor.cx.var_parent = visitor.cx.parent;
150 hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => {}
152 visitor.visit_stmt(statement)
154 walk_list!(visitor, visit_expr, &blk.expr);
157 visitor.cx = prev_cx;
160 fn resolve_arm<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, arm: &'tcx hir::Arm<'tcx>) {
161 let prev_cx = visitor.cx;
163 visitor.enter_scope(Scope { id: arm.hir_id.local_id, data: ScopeData::Node });
164 visitor.cx.var_parent = visitor.cx.parent;
166 visitor.terminating_scopes.insert(arm.body.hir_id.local_id);
168 if let Some(hir::Guard::If(ref expr)) = arm.guard {
169 visitor.terminating_scopes.insert(expr.hir_id.local_id);
172 intravisit::walk_arm(visitor, arm);
174 visitor.cx = prev_cx;
177 fn resolve_pat<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, pat: &'tcx hir::Pat<'tcx>) {
178 visitor.record_child_scope(Scope { id: pat.hir_id.local_id, data: ScopeData::Node });
180 // If this is a binding then record the lifetime of that binding.
181 if let PatKind::Binding(..) = pat.kind {
182 record_var_lifetime(visitor, pat.hir_id.local_id, pat.span);
185 debug!("resolve_pat - pre-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
187 intravisit::walk_pat(visitor, pat);
189 visitor.expr_and_pat_count += 1;
191 debug!("resolve_pat - post-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
194 fn resolve_stmt<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, stmt: &'tcx hir::Stmt<'tcx>) {
195 let stmt_id = stmt.hir_id.local_id;
196 debug!("resolve_stmt(stmt.id={:?})", stmt_id);
198 // Every statement will clean up the temporaries created during
199 // execution of that statement. Therefore each statement has an
200 // associated destruction scope that represents the scope of the
201 // statement plus its destructors, and thus the scope for which
202 // regions referenced by the destructors need to survive.
203 visitor.terminating_scopes.insert(stmt_id);
205 let prev_parent = visitor.cx.parent;
206 visitor.enter_node_scope_with_dtor(stmt_id);
208 intravisit::walk_stmt(visitor, stmt);
210 visitor.cx.parent = prev_parent;
213 fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
214 debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
216 let prev_cx = visitor.cx;
217 visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);
220 let terminating_scopes = &mut visitor.terminating_scopes;
221 let mut terminating = |id: hir::ItemLocalId| {
222 terminating_scopes.insert(id);
225 // Conditional or repeating scopes are always terminating
226 // scopes, meaning that temporaries cannot outlive them.
227 // This ensures fixed size stacks.
228 hir::ExprKind::Binary(
229 source_map::Spanned { node: hir::BinOpKind::And, .. },
233 | hir::ExprKind::Binary(
234 source_map::Spanned { node: hir::BinOpKind::Or, .. },
238 // For shortcircuiting operators, mark the RHS as a terminating
239 // scope since it only executes conditionally.
240 terminating(r.hir_id.local_id);
243 hir::ExprKind::Loop(ref body, _, _) => {
244 terminating(body.hir_id.local_id);
247 hir::ExprKind::DropTemps(ref expr) => {
248 // `DropTemps(expr)` does not denote a conditional scope.
249 // Rather, we want to achieve the same behavior as `{ let _t = expr; _t }`.
250 terminating(expr.hir_id.local_id);
253 hir::ExprKind::AssignOp(..)
254 | hir::ExprKind::Index(..)
255 | hir::ExprKind::Unary(..)
256 | hir::ExprKind::Call(..)
257 | hir::ExprKind::MethodCall(..) => {
258 // FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls
260 // The lifetimes for a call or method call look as follows:
268 // The idea is that call.callee_id represents *the time when
269 // the invoked function is actually running* and call.id
270 // represents *the time to prepare the arguments and make the
271 // call*. See the section "Borrows in Calls" borrowck/README.md
272 // for an extended explanation of why this distinction is
275 // record_superlifetime(new_cx, expr.callee_id);
282 let prev_pessimistic = visitor.pessimistic_yield;
284 // Ordinarily, we can rely on the visit order of HIR intravisit
285 // to correspond to the actual execution order of statements.
286 // However, there's a weird corner case with compund assignment
287 // operators (e.g. `a += b`). The evaluation order depends on whether
288 // or not the operator is overloaded (e.g. whether or not a trait
289 // like AddAssign is implemented).
291 // For primitive types (which, despite having a trait impl, don't actually
292 // end up calling it), the evluation order is right-to-left. For example,
293 // the following code snippet:
296 // *{println!("LHS!"); y} += {println!("RHS!"); 1};
303 // However, if the operator is used on a non-primitive type,
304 // the evaluation order will be left-to-right, since the operator
305 // actually get desugared to a method call. For example, this
306 // nearly identical code snippet:
308 // let y = &mut String::new();
309 // *{println!("LHS String"); y} += {println!("RHS String"); "hi"};
315 // To determine the actual execution order, we need to perform
316 // trait resolution. Unfortunately, we need to be able to compute
317 // yield_in_scope before type checking is even done, as it gets
318 // used by AST borrowcheck.
320 // Fortunately, we don't need to know the actual execution order.
321 // It suffices to know the 'worst case' order with respect to yields.
322 // Specifically, we need to know the highest 'expr_and_pat_count'
323 // that we could assign to the yield expression. To do this,
324 // we pick the greater of the two values from the left-hand
325 // and right-hand expressions. This makes us overly conservative
326 // about what types could possibly live across yield points,
327 // but we will never fail to detect that a type does actually
328 // live across a yield point. The latter part is critical -
329 // we're already overly conservative about what types will live
330 // across yield points, as the generated MIR will determine
331 // when things are actually live. However, for typecheck to work
332 // properly, we can't miss any types.
335 // Manually recurse over closures, because they are the only
336 // case of nested bodies that share the parent environment.
337 hir::ExprKind::Closure(.., body, _, _) => {
338 let body = visitor.tcx.hir().body(body);
339 visitor.visit_body(body);
341 hir::ExprKind::AssignOp(_, ref left_expr, ref right_expr) => {
343 "resolve_expr - enabling pessimistic_yield, was previously {}",
347 let start_point = visitor.fixup_scopes.len();
348 visitor.pessimistic_yield = true;
350 // If the actual execution order turns out to be right-to-left,
351 // then we're fine. However, if the actual execution order is left-to-right,
352 // then we'll assign too low a count to any `yield` expressions
353 // we encounter in 'right_expression' - they should really occur after all of the
354 // expressions in 'left_expression'.
355 visitor.visit_expr(&right_expr);
356 visitor.pessimistic_yield = prev_pessimistic;
358 debug!("resolve_expr - restoring pessimistic_yield to {}", prev_pessimistic);
359 visitor.visit_expr(&left_expr);
360 debug!("resolve_expr - fixing up counts to {}", visitor.expr_and_pat_count);
362 // Remove and process any scopes pushed by the visitor
363 let target_scopes = visitor.fixup_scopes.drain(start_point..);
365 for scope in target_scopes {
366 let mut yield_data = visitor.scope_tree.yield_in_scope.get_mut(&scope).unwrap();
367 let count = yield_data.expr_and_pat_count;
368 let span = yield_data.span;
370 // expr_and_pat_count never decreases. Since we recorded counts in yield_in_scope
371 // before walking the left-hand side, it should be impossible for the recorded
372 // count to be greater than the left-hand side count.
373 if count > visitor.expr_and_pat_count {
375 "Encountered greater count {} at span {:?} - expected no greater than {}",
378 visitor.expr_and_pat_count
381 let new_count = visitor.expr_and_pat_count;
383 "resolve_expr - increasing count for scope {:?} from {} to {} at span {:?}",
384 scope, count, new_count, span
387 yield_data.expr_and_pat_count = new_count;
391 _ => intravisit::walk_expr(visitor, expr),
394 visitor.expr_and_pat_count += 1;
396 debug!("resolve_expr post-increment {}, expr = {:?}", visitor.expr_and_pat_count, expr);
398 if let hir::ExprKind::Yield(_, source) = &expr.kind {
399 // Mark this expr's scope and all parent scopes as containing `yield`.
400 let mut scope = Scope { id: expr.hir_id.local_id, data: ScopeData::Node };
402 let data = YieldData {
404 expr_and_pat_count: visitor.expr_and_pat_count,
407 visitor.scope_tree.yield_in_scope.insert(scope, data);
408 if visitor.pessimistic_yield {
409 debug!("resolve_expr in pessimistic_yield - marking scope {:?} for fixup", scope);
410 visitor.fixup_scopes.push(scope);
413 // Keep traversing up while we can.
414 match visitor.scope_tree.parent_map.get(&scope) {
415 // Don't cross from closure bodies to their parent.
416 Some(&(superscope, _)) => match superscope.data {
417 ScopeData::CallSite => break,
418 _ => scope = superscope,
425 visitor.cx = prev_cx;
428 fn resolve_local<'tcx>(
429 visitor: &mut RegionResolutionVisitor<'tcx>,
430 pat: Option<&'tcx hir::Pat<'tcx>>,
431 init: Option<&'tcx hir::Expr<'tcx>>,
433 debug!("resolve_local(pat={:?}, init={:?})", pat, init);
435 let blk_scope = visitor.cx.var_parent.map(|(p, _)| p);
437 // As an exception to the normal rules governing temporary
438 // lifetimes, initializers in a let have a temporary lifetime
439 // of the enclosing block. This means that e.g., a program
440 // like the following is legal:
442 // let ref x = HashMap::new();
444 // Because the hash map will be freed in the enclosing block.
446 // We express the rules more formally based on 3 grammars (defined
447 // fully in the helpers below that implement them):
449 // 1. `E&`, which matches expressions like `&<rvalue>` that
450 // own a pointer into the stack.
452 // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
453 // y)` that produce ref bindings into the value they are
454 // matched against or something (at least partially) owned by
455 // the value they are matched against. (By partially owned,
456 // I mean that creating a binding into a ref-counted or managed value
457 // would still count.)
459 // 3. `ET`, which matches both rvalues like `foo()` as well as places
460 // based on rvalues like `foo().x[2].y`.
462 // A subexpression `<rvalue>` that appears in a let initializer
463 // `let pat [: ty] = expr` has an extended temporary lifetime if
464 // any of the following conditions are met:
466 // A. `pat` matches `P&` and `expr` matches `ET`
467 // (covers cases where `pat` creates ref bindings into an rvalue
468 // produced by `expr`)
469 // B. `ty` is a borrowed pointer and `expr` matches `ET`
470 // (covers cases where coercion creates a borrow)
471 // C. `expr` matches `E&`
472 // (covers cases `expr` borrows an rvalue that is then assigned
473 // to memory (at least partially) owned by the binding)
475 // Here are some examples hopefully giving an intuition where each
476 // rule comes into play and why:
478 // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
479 // would have an extended lifetime, but not `foo()`.
481 // Rule B. `let x = &foo().x`. The rvalue `foo()` would have extended
484 // In some cases, multiple rules may apply (though not to the same
485 // rvalue). For example:
487 // let ref x = [&a(), &b()];
489 // Here, the expression `[...]` has an extended lifetime due to rule
490 // A, but the inner rvalues `a()` and `b()` have an extended lifetime
493 if let Some(expr) = init {
494 record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
496 if let Some(pat) = pat {
497 if is_binding_pat(pat) {
498 record_rvalue_scope(visitor, &expr, blk_scope);
503 // Make sure we visit the initializer first, so expr_and_pat_count remains correct
504 if let Some(expr) = init {
505 visitor.visit_expr(expr);
507 if let Some(pat) = pat {
508 visitor.visit_pat(pat);
511 /// Returns `true` if `pat` match the `P&` non-terminal.
515 /// | StructName { ..., P&, ... }
516 /// | VariantName(..., P&, ...)
517 /// | [ ..., P&, ... ]
518 /// | ( ..., P&, ... )
519 /// | ... "|" P& "|" ...
522 fn is_binding_pat(pat: &hir::Pat<'_>) -> bool {
523 // Note that the code below looks for *explicit* refs only, that is, it won't
524 // know about *implicit* refs as introduced in #42640.
526 // This is not a problem. For example, consider
528 // let (ref x, ref y) = (Foo { .. }, Bar { .. });
530 // Due to the explicit refs on the left hand side, the below code would signal
531 // that the temporary value on the right hand side should live until the end of
532 // the enclosing block (as opposed to being dropped after the let is complete).
534 // To create an implicit ref, however, you must have a borrowed value on the RHS
535 // already, as in this example (which won't compile before #42640):
537 // let Foo { x, .. } = &Foo { x: ..., ... };
541 // let Foo { ref x, .. } = Foo { ... };
543 // In the former case (the implicit ref version), the temporary is created by the
544 // & expression, and its lifetime would be extended to the end of the block (due
545 // to a different rule, not the below code).
547 PatKind::Binding(hir::BindingAnnotation::Ref, ..)
548 | PatKind::Binding(hir::BindingAnnotation::RefMut, ..) => true,
550 PatKind::Struct(_, ref field_pats, _) => {
551 field_pats.iter().any(|fp| is_binding_pat(&fp.pat))
554 PatKind::Slice(ref pats1, ref pats2, ref pats3) => {
555 pats1.iter().any(|p| is_binding_pat(&p))
556 || pats2.iter().any(|p| is_binding_pat(&p))
557 || pats3.iter().any(|p| is_binding_pat(&p))
560 PatKind::Or(ref subpats)
561 | PatKind::TupleStruct(_, ref subpats, _)
562 | PatKind::Tuple(ref subpats, _) => subpats.iter().any(|p| is_binding_pat(&p)),
564 PatKind::Box(ref subpat) => is_binding_pat(&subpat),
567 | PatKind::Binding(hir::BindingAnnotation::Unannotated, ..)
568 | PatKind::Binding(hir::BindingAnnotation::Mutable, ..)
572 | PatKind::Range(_, _, _) => false,
576 /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
580 /// | StructName { ..., f: E&, ... }
581 /// | [ ..., E&, ... ]
582 /// | ( ..., E&, ... )
588 fn record_rvalue_scope_if_borrow_expr<'tcx>(
589 visitor: &mut RegionResolutionVisitor<'tcx>,
590 expr: &hir::Expr<'_>,
591 blk_id: Option<Scope>,
594 hir::ExprKind::AddrOf(_, _, ref subexpr) => {
595 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
596 record_rvalue_scope(visitor, &subexpr, blk_id);
598 hir::ExprKind::Struct(_, fields, _) => {
599 for field in fields {
600 record_rvalue_scope_if_borrow_expr(visitor, &field.expr, blk_id);
603 hir::ExprKind::Array(subexprs) | hir::ExprKind::Tup(subexprs) => {
604 for subexpr in subexprs {
605 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
608 hir::ExprKind::Cast(ref subexpr, _) => {
609 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
611 hir::ExprKind::Block(ref block, _) => {
612 if let Some(ref subexpr) = block.expr {
613 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
620 /// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
621 /// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
622 /// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
625 /// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
626 /// `<rvalue>` as `blk_id`:
636 /// Note: ET is intended to match "rvalues or places based on rvalues".
637 fn record_rvalue_scope<'tcx>(
638 visitor: &mut RegionResolutionVisitor<'tcx>,
639 expr: &hir::Expr<'_>,
640 blk_scope: Option<Scope>,
644 // Note: give all the expressions matching `ET` with the
645 // extended temporary lifetime, not just the innermost rvalue,
646 // because in codegen if we must compile e.g., `*rvalue()`
647 // into a temporary, we request the temporary scope of the
649 visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
652 hir::ExprKind::AddrOf(_, _, ref subexpr)
653 | hir::ExprKind::Unary(hir::UnOp::UnDeref, ref subexpr)
654 | hir::ExprKind::Field(ref subexpr, _)
655 | hir::ExprKind::Index(ref subexpr, _) => {
666 impl<'tcx> RegionResolutionVisitor<'tcx> {
667 /// Records the current parent (if any) as the parent of `child_scope`.
668 /// Returns the depth of `child_scope`.
669 fn record_child_scope(&mut self, child_scope: Scope) -> ScopeDepth {
670 let parent = self.cx.parent;
671 self.scope_tree.record_scope_parent(child_scope, parent);
672 // If `child_scope` has no parent, it must be the root node, and so has
673 // a depth of 1. Otherwise, its depth is one more than its parent's.
674 parent.map_or(1, |(_p, d)| d + 1)
677 /// Records the current parent (if any) as the parent of `child_scope`,
678 /// and sets `child_scope` as the new current parent.
679 fn enter_scope(&mut self, child_scope: Scope) {
680 let child_depth = self.record_child_scope(child_scope);
681 self.cx.parent = Some((child_scope, child_depth));
684 fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) {
685 // If node was previously marked as a terminating scope during the
686 // recursive visit of its parent node in the AST, then we need to
687 // account for the destruction scope representing the scope of
688 // the destructors that run immediately after it completes.
689 if self.terminating_scopes.contains(&id) {
690 self.enter_scope(Scope { id, data: ScopeData::Destruction });
692 self.enter_scope(Scope { id, data: ScopeData::Node });
696 impl<'tcx> Visitor<'tcx> for RegionResolutionVisitor<'tcx> {
697 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
698 NestedVisitorMap::None
701 fn visit_block(&mut self, b: &'tcx Block<'tcx>) {
702 resolve_block(self, b);
705 fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) {
706 let body_id = body.id();
707 let owner_id = self.tcx.hir().body_owner(body_id);
710 "visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
712 self.tcx.sess.source_map().span_to_string(body.value.span),
717 let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
718 let outer_cx = self.cx;
719 let outer_ts = mem::take(&mut self.terminating_scopes);
720 self.terminating_scopes.insert(body.value.hir_id.local_id);
722 if let Some(root_id) = self.cx.root_id {
723 self.scope_tree.record_closure_parent(body.value.hir_id.local_id, root_id);
725 self.cx.root_id = Some(body.value.hir_id.local_id);
727 self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::CallSite });
728 self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::Arguments });
730 // The arguments and `self` are parented to the fn.
731 self.cx.var_parent = self.cx.parent.take();
732 for param in body.params {
733 self.visit_pat(¶m.pat);
736 // The body of the every fn is a root scope.
737 self.cx.parent = self.cx.var_parent;
738 if self.tcx.hir().body_owner_kind(owner_id).is_fn_or_closure() {
739 self.visit_expr(&body.value)
741 // Only functions have an outer terminating (drop) scope, while
742 // temporaries in constant initializers may be 'static, but only
743 // according to rvalue lifetime semantics, using the same
744 // syntactical rules used for let initializers.
746 // e.g., in `let x = &f();`, the temporary holding the result from
747 // the `f()` call lives for the entirety of the surrounding block.
749 // Similarly, `const X: ... = &f();` would have the result of `f()`
750 // live for `'static`, implying (if Drop restrictions on constants
751 // ever get lifted) that the value *could* have a destructor, but
752 // it'd get leaked instead of the destructor running during the
753 // evaluation of `X` (if at all allowed by CTFE).
755 // However, `const Y: ... = g(&f());`, like `let y = g(&f());`,
756 // would *not* let the `f()` temporary escape into an outer scope
757 // (i.e., `'static`), which means that after `g` returns, it drops,
758 // and all the associated destruction scope rules apply.
759 self.cx.var_parent = None;
760 resolve_local(self, None, Some(&body.value));
763 if body.generator_kind.is_some() {
764 self.scope_tree.body_expr_count.insert(body_id, self.expr_and_pat_count);
767 // Restore context we had at the start.
768 self.expr_and_pat_count = outer_ec;
770 self.terminating_scopes = outer_ts;
773 fn visit_arm(&mut self, a: &'tcx Arm<'tcx>) {
774 resolve_arm(self, a);
776 fn visit_pat(&mut self, p: &'tcx Pat<'tcx>) {
777 resolve_pat(self, p);
779 fn visit_stmt(&mut self, s: &'tcx Stmt<'tcx>) {
780 resolve_stmt(self, s);
782 fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
783 resolve_expr(self, ex);
785 fn visit_local(&mut self, l: &'tcx Local<'tcx>) {
786 resolve_local(self, Some(&l.pat), l.init.as_ref().map(|e| &**e));
790 fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree {
791 let closure_base_def_id = tcx.closure_base_def_id(def_id);
792 if closure_base_def_id != def_id {
793 return tcx.region_scope_tree(closure_base_def_id);
796 let id = tcx.hir().as_local_hir_id(def_id).unwrap();
797 let scope_tree = if let Some(body_id) = tcx.hir().maybe_body_owned_by(id) {
798 let mut visitor = RegionResolutionVisitor {
800 scope_tree: ScopeTree::default(),
801 expr_and_pat_count: 0,
802 cx: Context { root_id: None, parent: None, var_parent: None },
803 terminating_scopes: Default::default(),
804 pessimistic_yield: false,
805 fixup_scopes: vec![],
808 let body = tcx.hir().body(body_id);
809 visitor.scope_tree.root_body = Some(body.value.hir_id);
811 // If the item is an associated const or a method,
812 // record its impl/trait parent, as it can also have
813 // lifetime parameters free in this body.
814 match tcx.hir().get(id) {
815 Node::ImplItem(_) | Node::TraitItem(_) => {
816 visitor.scope_tree.root_parent = Some(tcx.hir().get_parent_item(id));
821 visitor.visit_body(body);
828 tcx.arena.alloc(scope_tree)
831 pub fn provide(providers: &mut Providers<'_>) {
832 *providers = Providers { region_scope_tree, ..*providers };