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 dev guide].
7 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/borrow_check.html
9 use rustc_ast::walk_list;
10 use rustc_data_structures::fx::FxHashSet;
12 use rustc_hir::def_id::DefId;
13 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
14 use rustc_hir::{Arm, Block, Expr, Local, Node, Pat, PatKind, Stmt};
15 use rustc_index::vec::Idx;
16 use rustc_middle::middle::region::*;
17 use rustc_middle::ty::query::Providers;
18 use rustc_middle::ty::TyCtxt;
19 use rustc_span::source_map;
24 #[derive(Debug, Copy, Clone)]
26 /// The scope that contains any new variables declared, plus its depth in
28 var_parent: Option<(Scope, ScopeDepth)>,
30 /// Region parent of expressions, etc., plus its depth in the scope tree.
31 parent: Option<(Scope, ScopeDepth)>,
34 struct RegionResolutionVisitor<'tcx> {
37 // The number of expressions and patterns visited in the current body.
38 expr_and_pat_count: usize,
39 // When this is `true`, we record the `Scopes` we encounter
40 // when processing a Yield expression. This allows us to fix
42 pessimistic_yield: bool,
43 // Stores scopes when `pessimistic_yield` is `true`.
44 fixup_scopes: Vec<Scope>,
45 // The generated scope tree.
46 scope_tree: ScopeTree,
50 /// `terminating_scopes` is a set containing the ids of each
51 /// statement, or conditional/repeating expression. These scopes
52 /// are calling "terminating scopes" because, when attempting to
53 /// find the scope of a temporary, by default we search up the
54 /// enclosing scopes until we encounter the terminating scope. A
55 /// conditional/repeating expression is one which is not
56 /// guaranteed to execute exactly once upon entering the parent
57 /// scope. This could be because the expression only executes
58 /// conditionally, such as the expression `b` in `a && b`, or
59 /// because the expression may execute many times, such as a loop
60 /// body. The reason that we distinguish such expressions is that,
61 /// upon exiting the parent scope, we cannot statically know how
62 /// many times the expression executed, and thus if the expression
63 /// creates temporaries we cannot know statically how many such
64 /// temporaries we would have to cleanup. Therefore, we ensure that
65 /// the temporaries never outlast the conditional/repeating
66 /// expression, preventing the need for dynamic checks and/or
67 /// arbitrary amounts of stack space. Terminating scopes end
68 /// up being contained in a DestructionScope that contains the
69 /// destructor's execution.
70 terminating_scopes: FxHashSet<hir::ItemLocalId>,
73 /// Records the lifetime of a local variable as `cx.var_parent`
74 fn record_var_lifetime(
75 visitor: &mut RegionResolutionVisitor<'_>,
76 var_id: hir::ItemLocalId,
79 match visitor.cx.var_parent {
81 // this can happen in extern fn declarations like
83 // extern fn isalnum(c: c_int) -> c_int
85 Some((parent_scope, _)) => visitor.scope_tree.record_var_scope(var_id, parent_scope),
89 fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx hir::Block<'tcx>) {
90 debug!("resolve_block(blk.hir_id={:?})", blk.hir_id);
92 let prev_cx = visitor.cx;
94 // We treat the tail expression in the block (if any) somewhat
95 // differently from the statements. The issue has to do with
96 // temporary lifetimes. Consider the following:
99 // let inner = ... (&bar()) ...;
101 // (... (&foo()) ...) // (the tail expression)
102 // }, other_argument());
104 // Each of the statements within the block is a terminating
105 // scope, and thus a temporary (e.g., the result of calling
106 // `bar()` in the initializer expression for `let inner = ...;`)
107 // will be cleaned up immediately after its corresponding
108 // statement (i.e., `let inner = ...;`) executes.
110 // On the other hand, temporaries associated with evaluating the
111 // tail expression for the block are assigned lifetimes so that
112 // they will be cleaned up as part of the terminating scope
113 // *surrounding* the block expression. Here, the terminating
114 // scope for the block expression is the `quux(..)` call; so
115 // those temporaries will only be cleaned up *after* both
116 // `other_argument()` has run and also the call to `quux(..)`
117 // itself has returned.
119 visitor.enter_node_scope_with_dtor(blk.hir_id.local_id);
120 visitor.cx.var_parent = visitor.cx.parent;
123 // This block should be kept approximately in sync with
124 // `intravisit::walk_block`. (We manually walk the block, rather
125 // than call `walk_block`, in order to maintain precise
126 // index information.)
128 for (i, statement) in blk.stmts.iter().enumerate() {
129 match statement.kind {
130 hir::StmtKind::Local(..) | hir::StmtKind::Item(..) => {
131 // Each declaration introduces a subscope for bindings
132 // introduced by the declaration; this subscope covers a
133 // suffix of the block. Each subscope in a block has the
134 // previous subscope in the block as a parent, except for
135 // the first such subscope, which has the block itself as a
137 visitor.enter_scope(Scope {
138 id: blk.hir_id.local_id,
139 data: ScopeData::Remainder(FirstStatementIndex::new(i)),
141 visitor.cx.var_parent = visitor.cx.parent;
143 hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => {}
145 visitor.visit_stmt(statement)
147 walk_list!(visitor, visit_expr, &blk.expr);
150 visitor.cx = prev_cx;
153 fn resolve_arm<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, arm: &'tcx hir::Arm<'tcx>) {
154 let prev_cx = visitor.cx;
156 visitor.enter_scope(Scope { id: arm.hir_id.local_id, data: ScopeData::Node });
157 visitor.cx.var_parent = visitor.cx.parent;
159 visitor.terminating_scopes.insert(arm.body.hir_id.local_id);
161 if let Some(hir::Guard::If(ref expr)) = arm.guard {
162 visitor.terminating_scopes.insert(expr.hir_id.local_id);
165 intravisit::walk_arm(visitor, arm);
167 visitor.cx = prev_cx;
170 fn resolve_pat<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, pat: &'tcx hir::Pat<'tcx>) {
171 visitor.record_child_scope(Scope { id: pat.hir_id.local_id, data: ScopeData::Node });
173 // If this is a binding then record the lifetime of that binding.
174 if let PatKind::Binding(..) = pat.kind {
175 record_var_lifetime(visitor, pat.hir_id.local_id, pat.span);
178 debug!("resolve_pat - pre-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
180 intravisit::walk_pat(visitor, pat);
182 visitor.expr_and_pat_count += 1;
184 debug!("resolve_pat - post-increment {} pat = {:?}", visitor.expr_and_pat_count, pat);
187 fn resolve_stmt<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, stmt: &'tcx hir::Stmt<'tcx>) {
188 let stmt_id = stmt.hir_id.local_id;
189 debug!("resolve_stmt(stmt.id={:?})", stmt_id);
191 // Every statement will clean up the temporaries created during
192 // execution of that statement. Therefore each statement has an
193 // associated destruction scope that represents the scope of the
194 // statement plus its destructors, and thus the scope for which
195 // regions referenced by the destructors need to survive.
196 visitor.terminating_scopes.insert(stmt_id);
198 let prev_parent = visitor.cx.parent;
199 visitor.enter_node_scope_with_dtor(stmt_id);
201 intravisit::walk_stmt(visitor, stmt);
203 visitor.cx.parent = prev_parent;
206 fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
207 debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
209 let prev_cx = visitor.cx;
210 visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);
213 let terminating_scopes = &mut visitor.terminating_scopes;
214 let mut terminating = |id: hir::ItemLocalId| {
215 terminating_scopes.insert(id);
218 // Conditional or repeating scopes are always terminating
219 // scopes, meaning that temporaries cannot outlive them.
220 // This ensures fixed size stacks.
221 hir::ExprKind::Binary(
222 source_map::Spanned { node: hir::BinOpKind::And, .. },
226 | hir::ExprKind::Binary(
227 source_map::Spanned { node: hir::BinOpKind::Or, .. },
231 // For shortcircuiting operators, mark the RHS as a terminating
232 // scope since it only executes conditionally.
233 terminating(r.hir_id.local_id);
236 hir::ExprKind::If(_, ref then, Some(ref otherwise)) => {
237 terminating(then.hir_id.local_id);
238 terminating(otherwise.hir_id.local_id);
241 hir::ExprKind::If(_, ref then, None) => {
242 terminating(then.hir_id.local_id);
245 hir::ExprKind::Loop(ref body, _, _, _) => {
246 terminating(body.hir_id.local_id);
249 hir::ExprKind::DropTemps(ref expr) => {
250 // `DropTemps(expr)` does not denote a conditional scope.
251 // Rather, we want to achieve the same behavior as `{ let _t = expr; _t }`.
252 terminating(expr.hir_id.local_id);
255 hir::ExprKind::AssignOp(..)
256 | hir::ExprKind::Index(..)
257 | hir::ExprKind::Unary(..)
258 | hir::ExprKind::Call(..)
259 | hir::ExprKind::MethodCall(..) => {
260 // FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls
262 // The lifetimes for a call or method call look as follows:
270 // The idea is that call.callee_id represents *the time when
271 // the invoked function is actually running* and call.id
272 // represents *the time to prepare the arguments and make the
273 // call*. See the section "Borrows in Calls" borrowck/README.md
274 // for an extended explanation of why this distinction is
277 // record_superlifetime(new_cx, expr.callee_id);
284 let prev_pessimistic = visitor.pessimistic_yield;
286 // Ordinarily, we can rely on the visit order of HIR intravisit
287 // to correspond to the actual execution order of statements.
288 // However, there's a weird corner case with compound assignment
289 // operators (e.g. `a += b`). The evaluation order depends on whether
290 // or not the operator is overloaded (e.g. whether or not a trait
291 // like AddAssign is implemented).
293 // For primitive types (which, despite having a trait impl, don't actually
294 // end up calling it), the evluation order is right-to-left. For example,
295 // the following code snippet:
298 // *{println!("LHS!"); y} += {println!("RHS!"); 1};
305 // However, if the operator is used on a non-primitive type,
306 // the evaluation order will be left-to-right, since the operator
307 // actually get desugared to a method call. For example, this
308 // nearly identical code snippet:
310 // let y = &mut String::new();
311 // *{println!("LHS String"); y} += {println!("RHS String"); "hi"};
317 // To determine the actual execution order, we need to perform
318 // trait resolution. Unfortunately, we need to be able to compute
319 // yield_in_scope before type checking is even done, as it gets
320 // used by AST borrowcheck.
322 // Fortunately, we don't need to know the actual execution order.
323 // It suffices to know the 'worst case' order with respect to yields.
324 // Specifically, we need to know the highest 'expr_and_pat_count'
325 // that we could assign to the yield expression. To do this,
326 // we pick the greater of the two values from the left-hand
327 // and right-hand expressions. This makes us overly conservative
328 // about what types could possibly live across yield points,
329 // but we will never fail to detect that a type does actually
330 // live across a yield point. The latter part is critical -
331 // we're already overly conservative about what types will live
332 // across yield points, as the generated MIR will determine
333 // when things are actually live. However, for typecheck to work
334 // properly, we can't miss any types.
337 // Manually recurse over closures and inline consts, because they are the only
338 // case of nested bodies that share the parent environment.
339 hir::ExprKind::Closure(.., body, _, _)
340 | hir::ExprKind::ConstBlock(hir::AnonConst { body, .. }) => {
341 let body = visitor.tcx.hir().body(body);
342 visitor.visit_body(body);
344 hir::ExprKind::AssignOp(_, ref left_expr, ref right_expr) => {
346 "resolve_expr - enabling pessimistic_yield, was previously {}",
350 let start_point = visitor.fixup_scopes.len();
351 visitor.pessimistic_yield = true;
353 // If the actual execution order turns out to be right-to-left,
354 // then we're fine. However, if the actual execution order is left-to-right,
355 // then we'll assign too low a count to any `yield` expressions
356 // we encounter in 'right_expression' - they should really occur after all of the
357 // expressions in 'left_expression'.
358 visitor.visit_expr(&right_expr);
359 visitor.pessimistic_yield = prev_pessimistic;
361 debug!("resolve_expr - restoring pessimistic_yield to {}", prev_pessimistic);
362 visitor.visit_expr(&left_expr);
363 debug!("resolve_expr - fixing up counts to {}", visitor.expr_and_pat_count);
365 // Remove and process any scopes pushed by the visitor
366 let target_scopes = visitor.fixup_scopes.drain(start_point..);
368 for scope in target_scopes {
369 let mut yield_data = visitor.scope_tree.yield_in_scope.get_mut(&scope).unwrap();
370 let count = yield_data.expr_and_pat_count;
371 let span = yield_data.span;
373 // expr_and_pat_count never decreases. Since we recorded counts in yield_in_scope
374 // before walking the left-hand side, it should be impossible for the recorded
375 // count to be greater than the left-hand side count.
376 if count > visitor.expr_and_pat_count {
378 "Encountered greater count {} at span {:?} - expected no greater than {}",
381 visitor.expr_and_pat_count
384 let new_count = visitor.expr_and_pat_count;
386 "resolve_expr - increasing count for scope {:?} from {} to {} at span {:?}",
387 scope, count, new_count, span
390 yield_data.expr_and_pat_count = new_count;
394 hir::ExprKind::If(ref cond, ref then, Some(ref otherwise)) => {
395 let expr_cx = visitor.cx;
396 visitor.enter_scope(Scope { id: then.hir_id.local_id, data: ScopeData::IfThen });
397 visitor.cx.var_parent = visitor.cx.parent;
398 visitor.visit_expr(cond);
399 visitor.visit_expr(then);
400 visitor.cx = expr_cx;
401 visitor.visit_expr(otherwise);
404 hir::ExprKind::If(ref cond, ref then, None) => {
405 let expr_cx = visitor.cx;
406 visitor.enter_scope(Scope { id: then.hir_id.local_id, data: ScopeData::IfThen });
407 visitor.cx.var_parent = visitor.cx.parent;
408 visitor.visit_expr(cond);
409 visitor.visit_expr(then);
410 visitor.cx = expr_cx;
413 _ => intravisit::walk_expr(visitor, expr),
416 visitor.expr_and_pat_count += 1;
418 debug!("resolve_expr post-increment {}, expr = {:?}", visitor.expr_and_pat_count, expr);
420 if let hir::ExprKind::Yield(_, source) = &expr.kind {
421 // Mark this expr's scope and all parent scopes as containing `yield`.
422 let mut scope = Scope { id: expr.hir_id.local_id, data: ScopeData::Node };
424 let data = YieldData {
426 expr_and_pat_count: visitor.expr_and_pat_count,
429 visitor.scope_tree.yield_in_scope.insert(scope, data);
430 if visitor.pessimistic_yield {
431 debug!("resolve_expr in pessimistic_yield - marking scope {:?} for fixup", scope);
432 visitor.fixup_scopes.push(scope);
435 // Keep traversing up while we can.
436 match visitor.scope_tree.parent_map.get(&scope) {
437 // Don't cross from closure bodies to their parent.
438 Some(&(superscope, _)) => match superscope.data {
439 ScopeData::CallSite => break,
440 _ => scope = superscope,
447 visitor.cx = prev_cx;
450 fn resolve_local<'tcx>(
451 visitor: &mut RegionResolutionVisitor<'tcx>,
452 pat: Option<&'tcx hir::Pat<'tcx>>,
453 init: Option<&'tcx hir::Expr<'tcx>>,
455 debug!("resolve_local(pat={:?}, init={:?})", pat, init);
457 let blk_scope = visitor.cx.var_parent.map(|(p, _)| p);
459 // As an exception to the normal rules governing temporary
460 // lifetimes, initializers in a let have a temporary lifetime
461 // of the enclosing block. This means that e.g., a program
462 // like the following is legal:
464 // let ref x = HashMap::new();
466 // Because the hash map will be freed in the enclosing block.
468 // We express the rules more formally based on 3 grammars (defined
469 // fully in the helpers below that implement them):
471 // 1. `E&`, which matches expressions like `&<rvalue>` that
472 // own a pointer into the stack.
474 // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
475 // y)` that produce ref bindings into the value they are
476 // matched against or something (at least partially) owned by
477 // the value they are matched against. (By partially owned,
478 // I mean that creating a binding into a ref-counted or managed value
479 // would still count.)
481 // 3. `ET`, which matches both rvalues like `foo()` as well as places
482 // based on rvalues like `foo().x[2].y`.
484 // A subexpression `<rvalue>` that appears in a let initializer
485 // `let pat [: ty] = expr` has an extended temporary lifetime if
486 // any of the following conditions are met:
488 // A. `pat` matches `P&` and `expr` matches `ET`
489 // (covers cases where `pat` creates ref bindings into an rvalue
490 // produced by `expr`)
491 // B. `ty` is a borrowed pointer and `expr` matches `ET`
492 // (covers cases where coercion creates a borrow)
493 // C. `expr` matches `E&`
494 // (covers cases `expr` borrows an rvalue that is then assigned
495 // to memory (at least partially) owned by the binding)
497 // Here are some examples hopefully giving an intuition where each
498 // rule comes into play and why:
500 // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
501 // would have an extended lifetime, but not `foo()`.
503 // Rule B. `let x = &foo().x`. The rvalue `foo()` would have extended
506 // In some cases, multiple rules may apply (though not to the same
507 // rvalue). For example:
509 // let ref x = [&a(), &b()];
511 // Here, the expression `[...]` has an extended lifetime due to rule
512 // A, but the inner rvalues `a()` and `b()` have an extended lifetime
515 if let Some(expr) = init {
516 record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
518 if let Some(pat) = pat {
519 if is_binding_pat(pat) {
520 record_rvalue_scope(visitor, &expr, blk_scope);
525 // Make sure we visit the initializer first, so expr_and_pat_count remains correct
526 if let Some(expr) = init {
527 visitor.visit_expr(expr);
529 if let Some(pat) = pat {
530 visitor.visit_pat(pat);
533 /// Returns `true` if `pat` match the `P&` non-terminal.
537 /// | StructName { ..., P&, ... }
538 /// | VariantName(..., P&, ...)
539 /// | [ ..., P&, ... ]
540 /// | ( ..., P&, ... )
541 /// | ... "|" P& "|" ...
544 fn is_binding_pat(pat: &hir::Pat<'_>) -> bool {
545 // Note that the code below looks for *explicit* refs only, that is, it won't
546 // know about *implicit* refs as introduced in #42640.
548 // This is not a problem. For example, consider
550 // let (ref x, ref y) = (Foo { .. }, Bar { .. });
552 // Due to the explicit refs on the left hand side, the below code would signal
553 // that the temporary value on the right hand side should live until the end of
554 // the enclosing block (as opposed to being dropped after the let is complete).
556 // To create an implicit ref, however, you must have a borrowed value on the RHS
557 // already, as in this example (which won't compile before #42640):
559 // let Foo { x, .. } = &Foo { x: ..., ... };
563 // let Foo { ref x, .. } = Foo { ... };
565 // In the former case (the implicit ref version), the temporary is created by the
566 // & expression, and its lifetime would be extended to the end of the block (due
567 // to a different rule, not the below code).
569 PatKind::Binding(hir::BindingAnnotation::Ref, ..)
570 | PatKind::Binding(hir::BindingAnnotation::RefMut, ..) => true,
572 PatKind::Struct(_, ref field_pats, _) => {
573 field_pats.iter().any(|fp| is_binding_pat(&fp.pat))
576 PatKind::Slice(ref pats1, ref pats2, ref pats3) => {
577 pats1.iter().any(|p| is_binding_pat(&p))
578 || pats2.iter().any(|p| is_binding_pat(&p))
579 || pats3.iter().any(|p| is_binding_pat(&p))
582 PatKind::Or(ref subpats)
583 | PatKind::TupleStruct(_, ref subpats, _)
584 | PatKind::Tuple(ref subpats, _) => subpats.iter().any(|p| is_binding_pat(&p)),
586 PatKind::Box(ref subpat) => is_binding_pat(&subpat),
590 hir::BindingAnnotation::Unannotated | hir::BindingAnnotation::Mutable,
596 | PatKind::Range(_, _, _) => false,
600 /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
604 /// | StructName { ..., f: E&, ... }
605 /// | [ ..., E&, ... ]
606 /// | ( ..., E&, ... )
612 fn record_rvalue_scope_if_borrow_expr<'tcx>(
613 visitor: &mut RegionResolutionVisitor<'tcx>,
614 expr: &hir::Expr<'_>,
615 blk_id: Option<Scope>,
618 hir::ExprKind::AddrOf(_, _, ref subexpr) => {
619 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
620 record_rvalue_scope(visitor, &subexpr, blk_id);
622 hir::ExprKind::Struct(_, fields, _) => {
623 for field in fields {
624 record_rvalue_scope_if_borrow_expr(visitor, &field.expr, blk_id);
627 hir::ExprKind::Array(subexprs) | hir::ExprKind::Tup(subexprs) => {
628 for subexpr in subexprs {
629 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
632 hir::ExprKind::Cast(ref subexpr, _) => {
633 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
635 hir::ExprKind::Block(ref block, _) => {
636 if let Some(ref subexpr) = block.expr {
637 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
644 /// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
645 /// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
646 /// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
649 /// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
650 /// `<rvalue>` as `blk_id`:
660 /// Note: ET is intended to match "rvalues or places based on rvalues".
661 fn record_rvalue_scope<'tcx>(
662 visitor: &mut RegionResolutionVisitor<'tcx>,
663 expr: &hir::Expr<'_>,
664 blk_scope: Option<Scope>,
668 // Note: give all the expressions matching `ET` with the
669 // extended temporary lifetime, not just the innermost rvalue,
670 // because in codegen if we must compile e.g., `*rvalue()`
671 // into a temporary, we request the temporary scope of the
673 visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
676 hir::ExprKind::AddrOf(_, _, ref subexpr)
677 | hir::ExprKind::Unary(hir::UnOp::Deref, ref subexpr)
678 | hir::ExprKind::Field(ref subexpr, _)
679 | hir::ExprKind::Index(ref subexpr, _) => {
690 impl<'tcx> RegionResolutionVisitor<'tcx> {
691 /// Records the current parent (if any) as the parent of `child_scope`.
692 /// Returns the depth of `child_scope`.
693 fn record_child_scope(&mut self, child_scope: Scope) -> ScopeDepth {
694 let parent = self.cx.parent;
695 self.scope_tree.record_scope_parent(child_scope, parent);
696 // If `child_scope` has no parent, it must be the root node, and so has
697 // a depth of 1. Otherwise, its depth is one more than its parent's.
698 parent.map_or(1, |(_p, d)| d + 1)
701 /// Records the current parent (if any) as the parent of `child_scope`,
702 /// and sets `child_scope` as the new current parent.
703 fn enter_scope(&mut self, child_scope: Scope) {
704 let child_depth = self.record_child_scope(child_scope);
705 self.cx.parent = Some((child_scope, child_depth));
708 fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) {
709 // If node was previously marked as a terminating scope during the
710 // recursive visit of its parent node in the AST, then we need to
711 // account for the destruction scope representing the scope of
712 // the destructors that run immediately after it completes.
713 if self.terminating_scopes.contains(&id) {
714 self.enter_scope(Scope { id, data: ScopeData::Destruction });
716 self.enter_scope(Scope { id, data: ScopeData::Node });
720 impl<'tcx> Visitor<'tcx> for RegionResolutionVisitor<'tcx> {
721 type Map = intravisit::ErasedMap<'tcx>;
723 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
724 NestedVisitorMap::None
727 fn visit_block(&mut self, b: &'tcx Block<'tcx>) {
728 resolve_block(self, b);
731 fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) {
732 let body_id = body.id();
733 let owner_id = self.tcx.hir().body_owner(body_id);
736 "visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
738 self.tcx.sess.source_map().span_to_diagnostic_string(body.value.span),
743 // Save all state that is specific to the outer function
744 // body. These will be restored once down below, once we've
746 let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
747 let outer_cx = self.cx;
748 let outer_ts = mem::take(&mut self.terminating_scopes);
749 // The 'pessimistic yield' flag is set to true when we are
750 // processing a `+=` statement and have to make pessimistic
751 // control flow assumptions. This doesn't apply to nested
752 // bodies within the `+=` statements. See #69307.
753 let outer_pessimistic_yield = mem::replace(&mut self.pessimistic_yield, false);
754 self.terminating_scopes.insert(body.value.hir_id.local_id);
756 self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::CallSite });
757 self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::Arguments });
759 // The arguments and `self` are parented to the fn.
760 self.cx.var_parent = self.cx.parent.take();
761 for param in body.params {
762 self.visit_pat(¶m.pat);
765 // The body of the every fn is a root scope.
766 self.cx.parent = self.cx.var_parent;
767 if self.tcx.hir().body_owner_kind(owner_id).is_fn_or_closure() {
768 self.visit_expr(&body.value)
770 // Only functions have an outer terminating (drop) scope, while
771 // temporaries in constant initializers may be 'static, but only
772 // according to rvalue lifetime semantics, using the same
773 // syntactical rules used for let initializers.
775 // e.g., in `let x = &f();`, the temporary holding the result from
776 // the `f()` call lives for the entirety of the surrounding block.
778 // Similarly, `const X: ... = &f();` would have the result of `f()`
779 // live for `'static`, implying (if Drop restrictions on constants
780 // ever get lifted) that the value *could* have a destructor, but
781 // it'd get leaked instead of the destructor running during the
782 // evaluation of `X` (if at all allowed by CTFE).
784 // However, `const Y: ... = g(&f());`, like `let y = g(&f());`,
785 // would *not* let the `f()` temporary escape into an outer scope
786 // (i.e., `'static`), which means that after `g` returns, it drops,
787 // and all the associated destruction scope rules apply.
788 self.cx.var_parent = None;
789 resolve_local(self, None, Some(&body.value));
792 if body.generator_kind.is_some() {
793 self.scope_tree.body_expr_count.insert(body_id, self.expr_and_pat_count);
796 // Restore context we had at the start.
797 self.expr_and_pat_count = outer_ec;
799 self.terminating_scopes = outer_ts;
800 self.pessimistic_yield = outer_pessimistic_yield;
803 fn visit_arm(&mut self, a: &'tcx Arm<'tcx>) {
804 resolve_arm(self, a);
806 fn visit_pat(&mut self, p: &'tcx Pat<'tcx>) {
807 resolve_pat(self, p);
809 fn visit_stmt(&mut self, s: &'tcx Stmt<'tcx>) {
810 resolve_stmt(self, s);
812 fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
813 resolve_expr(self, ex);
815 fn visit_local(&mut self, l: &'tcx Local<'tcx>) {
816 resolve_local(self, Some(&l.pat), l.init);
820 fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree {
821 let typeck_root_def_id = tcx.typeck_root_def_id(def_id);
822 if typeck_root_def_id != def_id {
823 return tcx.region_scope_tree(typeck_root_def_id);
826 let id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
827 let scope_tree = if let Some(body_id) = tcx.hir().maybe_body_owned_by(id) {
828 let mut visitor = RegionResolutionVisitor {
830 scope_tree: ScopeTree::default(),
831 expr_and_pat_count: 0,
832 cx: Context { parent: None, var_parent: None },
833 terminating_scopes: Default::default(),
834 pessimistic_yield: false,
835 fixup_scopes: vec![],
838 let body = tcx.hir().body(body_id);
839 visitor.scope_tree.root_body = Some(body.value.hir_id);
841 // If the item is an associated const or a method,
842 // record its impl/trait parent, as it can also have
843 // lifetime parameters free in this body.
844 match tcx.hir().get(id) {
845 Node::ImplItem(_) | Node::TraitItem(_) => {
846 visitor.scope_tree.root_parent = Some(tcx.hir().get_parent_item(id));
851 visitor.visit_body(body);
858 tcx.arena.alloc(scope_tree)
861 pub fn provide(providers: &mut Providers) {
862 *providers = Providers { region_scope_tree, ..*providers };