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Diffstat (limited to 'compiler/rustc_typeck/src/check/region.rs')
| -rw-r--r-- | compiler/rustc_typeck/src/check/region.rs | 837 |
1 files changed, 837 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/check/region.rs b/compiler/rustc_typeck/src/check/region.rs new file mode 100644 index 000000000..0081e9049 --- /dev/null +++ b/compiler/rustc_typeck/src/check/region.rs @@ -0,0 +1,837 @@ +//! This file builds up the `ScopeTree`, which describes +//! the parent links in the region hierarchy. +//! +//! For more information about how MIR-based region-checking works, +//! see the [rustc dev guide]. +//! +//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/borrow_check.html + +use rustc_ast::walk_list; +use rustc_data_structures::fx::FxHashSet; +use rustc_hir as hir; +use rustc_hir::def_id::DefId; +use rustc_hir::intravisit::{self, Visitor}; +use rustc_hir::{Arm, Block, Expr, Local, Pat, PatKind, Stmt}; +use rustc_index::vec::Idx; +use rustc_middle::middle::region::*; +use rustc_middle::ty::TyCtxt; +use rustc_span::source_map; +use rustc_span::Span; + +use std::mem; + +#[derive(Debug, Copy, Clone)] +pub struct Context { + /// The scope that contains any new variables declared, plus its depth in + /// the scope tree. + var_parent: Option<(Scope, ScopeDepth)>, + + /// Region parent of expressions, etc., plus its depth in the scope tree. + parent: Option<(Scope, ScopeDepth)>, +} + +struct RegionResolutionVisitor<'tcx> { + tcx: TyCtxt<'tcx>, + + // The number of expressions and patterns visited in the current body. + expr_and_pat_count: usize, + // When this is `true`, we record the `Scopes` we encounter + // when processing a Yield expression. This allows us to fix + // up their indices. + pessimistic_yield: bool, + // Stores scopes when `pessimistic_yield` is `true`. + fixup_scopes: Vec<Scope>, + // The generated scope tree. + scope_tree: ScopeTree, + + cx: Context, + + /// `terminating_scopes` is a set containing the ids of each + /// statement, or conditional/repeating expression. These scopes + /// are calling "terminating scopes" because, when attempting to + /// find the scope of a temporary, by default we search up the + /// enclosing scopes until we encounter the terminating scope. A + /// conditional/repeating expression is one which is not + /// guaranteed to execute exactly once upon entering the parent + /// scope. This could be because the expression only executes + /// conditionally, such as the expression `b` in `a && b`, or + /// because the expression may execute many times, such as a loop + /// body. The reason that we distinguish such expressions is that, + /// upon exiting the parent scope, we cannot statically know how + /// many times the expression executed, and thus if the expression + /// creates temporaries we cannot know statically how many such + /// temporaries we would have to cleanup. Therefore, we ensure that + /// the temporaries never outlast the conditional/repeating + /// expression, preventing the need for dynamic checks and/or + /// arbitrary amounts of stack space. Terminating scopes end + /// up being contained in a DestructionScope that contains the + /// destructor's execution. + terminating_scopes: FxHashSet<hir::ItemLocalId>, +} + +/// Records the lifetime of a local variable as `cx.var_parent` +fn record_var_lifetime( + visitor: &mut RegionResolutionVisitor<'_>, + var_id: hir::ItemLocalId, + _sp: Span, +) { + match visitor.cx.var_parent { + None => { + // this can happen in extern fn declarations like + // + // extern fn isalnum(c: c_int) -> c_int + } + Some((parent_scope, _)) => visitor.scope_tree.record_var_scope(var_id, parent_scope), + } +} + +fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx hir::Block<'tcx>) { + debug!("resolve_block(blk.hir_id={:?})", blk.hir_id); + + let prev_cx = visitor.cx; + + // We treat the tail expression in the block (if any) somewhat + // differently from the statements. The issue has to do with + // temporary lifetimes. Consider the following: + // + // quux({ + // let inner = ... (&bar()) ...; + // + // (... (&foo()) ...) // (the tail expression) + // }, other_argument()); + // + // Each of the statements within the block is a terminating + // scope, and thus a temporary (e.g., the result of calling + // `bar()` in the initializer expression for `let inner = ...;`) + // will be cleaned up immediately after its corresponding + // statement (i.e., `let inner = ...;`) executes. + // + // On the other hand, temporaries associated with evaluating the + // tail expression for the block are assigned lifetimes so that + // they will be cleaned up as part of the terminating scope + // *surrounding* the block expression. Here, the terminating + // scope for the block expression is the `quux(..)` call; so + // those temporaries will only be cleaned up *after* both + // `other_argument()` has run and also the call to `quux(..)` + // itself has returned. + + visitor.enter_node_scope_with_dtor(blk.hir_id.local_id); + visitor.cx.var_parent = visitor.cx.parent; + + { + // This block should be kept approximately in sync with + // `intravisit::walk_block`. (We manually walk the block, rather + // than call `walk_block`, in order to maintain precise + // index information.) + + for (i, statement) in blk.stmts.iter().enumerate() { + match statement.kind { + hir::StmtKind::Local(..) | hir::StmtKind::Item(..) => { + // Each declaration introduces a subscope for bindings + // introduced by the declaration; this subscope covers a + // suffix of the block. Each subscope in a block has the + // previous subscope in the block as a parent, except for + // the first such subscope, which has the block itself as a + // parent. + visitor.enter_scope(Scope { + id: blk.hir_id.local_id, + data: ScopeData::Remainder(FirstStatementIndex::new(i)), + }); + visitor.cx.var_parent = visitor.cx.parent; + } + hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => {} + } + visitor.visit_stmt(statement) + } + walk_list!(visitor, visit_expr, &blk.expr); + } + + visitor.cx = prev_cx; +} + +fn resolve_arm<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, arm: &'tcx hir::Arm<'tcx>) { + let prev_cx = visitor.cx; + + visitor.enter_scope(Scope { id: arm.hir_id.local_id, data: ScopeData::Node }); + visitor.cx.var_parent = visitor.cx.parent; + + visitor.terminating_scopes.insert(arm.body.hir_id.local_id); + + if let Some(hir::Guard::If(ref expr)) = arm.guard { + visitor.terminating_scopes.insert(expr.hir_id.local_id); + } + + intravisit::walk_arm(visitor, arm); + + visitor.cx = prev_cx; +} + +fn resolve_pat<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, pat: &'tcx hir::Pat<'tcx>) { + visitor.record_child_scope(Scope { id: pat.hir_id.local_id, data: ScopeData::Node }); + + // If this is a binding then record the lifetime of that binding. + if let PatKind::Binding(..) = pat.kind { + record_var_lifetime(visitor, pat.hir_id.local_id, pat.span); + } + + debug!("resolve_pat - pre-increment {} pat = {:?}", visitor.expr_and_pat_count, pat); + + intravisit::walk_pat(visitor, pat); + + visitor.expr_and_pat_count += 1; + + debug!("resolve_pat - post-increment {} pat = {:?}", visitor.expr_and_pat_count, pat); +} + +fn resolve_stmt<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, stmt: &'tcx hir::Stmt<'tcx>) { + let stmt_id = stmt.hir_id.local_id; + debug!("resolve_stmt(stmt.id={:?})", stmt_id); + + // Every statement will clean up the temporaries created during + // execution of that statement. Therefore each statement has an + // associated destruction scope that represents the scope of the + // statement plus its destructors, and thus the scope for which + // regions referenced by the destructors need to survive. + visitor.terminating_scopes.insert(stmt_id); + + let prev_parent = visitor.cx.parent; + visitor.enter_node_scope_with_dtor(stmt_id); + + intravisit::walk_stmt(visitor, stmt); + + visitor.cx.parent = prev_parent; +} + +fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx hir::Expr<'tcx>) { + debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr); + + let prev_cx = visitor.cx; + visitor.enter_node_scope_with_dtor(expr.hir_id.local_id); + + { + let terminating_scopes = &mut visitor.terminating_scopes; + let mut terminating = |id: hir::ItemLocalId| { + terminating_scopes.insert(id); + }; + match expr.kind { + // Conditional or repeating scopes are always terminating + // scopes, meaning that temporaries cannot outlive them. + // This ensures fixed size stacks. + hir::ExprKind::Binary( + source_map::Spanned { node: hir::BinOpKind::And, .. }, + _, + ref r, + ) + | hir::ExprKind::Binary( + source_map::Spanned { node: hir::BinOpKind::Or, .. }, + _, + ref r, + ) => { + // For shortcircuiting operators, mark the RHS as a terminating + // scope since it only executes conditionally. + terminating(r.hir_id.local_id); + } + + hir::ExprKind::If(_, ref then, Some(ref otherwise)) => { + terminating(then.hir_id.local_id); + terminating(otherwise.hir_id.local_id); + } + + hir::ExprKind::If(_, ref then, None) => { + terminating(then.hir_id.local_id); + } + + hir::ExprKind::Loop(ref body, _, _, _) => { + terminating(body.hir_id.local_id); + } + + hir::ExprKind::DropTemps(ref expr) => { + // `DropTemps(expr)` does not denote a conditional scope. + // Rather, we want to achieve the same behavior as `{ let _t = expr; _t }`. + terminating(expr.hir_id.local_id); + } + + hir::ExprKind::AssignOp(..) + | hir::ExprKind::Index(..) + | hir::ExprKind::Unary(..) + | hir::ExprKind::Call(..) + | hir::ExprKind::MethodCall(..) => { + // FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls + // + // The lifetimes for a call or method call look as follows: + // + // call.id + // - arg0.id + // - ... + // - argN.id + // - call.callee_id + // + // The idea is that call.callee_id represents *the time when + // the invoked function is actually running* and call.id + // represents *the time to prepare the arguments and make the + // call*. See the section "Borrows in Calls" borrowck/README.md + // for an extended explanation of why this distinction is + // important. + // + // record_superlifetime(new_cx, expr.callee_id); + } + + _ => {} + } + } + + let prev_pessimistic = visitor.pessimistic_yield; + + // Ordinarily, we can rely on the visit order of HIR intravisit + // to correspond to the actual execution order of statements. + // However, there's a weird corner case with compound assignment + // operators (e.g. `a += b`). The evaluation order depends on whether + // or not the operator is overloaded (e.g. whether or not a trait + // like AddAssign is implemented). + + // For primitive types (which, despite having a trait impl, don't actually + // end up calling it), the evaluation order is right-to-left. For example, + // the following code snippet: + // + // let y = &mut 0; + // *{println!("LHS!"); y} += {println!("RHS!"); 1}; + // + // will print: + // + // RHS! + // LHS! + // + // However, if the operator is used on a non-primitive type, + // the evaluation order will be left-to-right, since the operator + // actually get desugared to a method call. For example, this + // nearly identical code snippet: + // + // let y = &mut String::new(); + // *{println!("LHS String"); y} += {println!("RHS String"); "hi"}; + // + // will print: + // LHS String + // RHS String + // + // To determine the actual execution order, we need to perform + // trait resolution. Unfortunately, we need to be able to compute + // yield_in_scope before type checking is even done, as it gets + // used by AST borrowcheck. + // + // Fortunately, we don't need to know the actual execution order. + // It suffices to know the 'worst case' order with respect to yields. + // Specifically, we need to know the highest 'expr_and_pat_count' + // that we could assign to the yield expression. To do this, + // we pick the greater of the two values from the left-hand + // and right-hand expressions. This makes us overly conservative + // about what types could possibly live across yield points, + // but we will never fail to detect that a type does actually + // live across a yield point. The latter part is critical - + // we're already overly conservative about what types will live + // across yield points, as the generated MIR will determine + // when things are actually live. However, for typecheck to work + // properly, we can't miss any types. + + match expr.kind { + // Manually recurse over closures and inline consts, because they are the only + // case of nested bodies that share the parent environment. + hir::ExprKind::Closure(&hir::Closure { body, .. }) + | hir::ExprKind::ConstBlock(hir::AnonConst { body, .. }) => { + let body = visitor.tcx.hir().body(body); + visitor.visit_body(body); + } + hir::ExprKind::AssignOp(_, ref left_expr, ref right_expr) => { + debug!( + "resolve_expr - enabling pessimistic_yield, was previously {}", + prev_pessimistic + ); + + let start_point = visitor.fixup_scopes.len(); + visitor.pessimistic_yield = true; + + // If the actual execution order turns out to be right-to-left, + // then we're fine. However, if the actual execution order is left-to-right, + // then we'll assign too low a count to any `yield` expressions + // we encounter in 'right_expression' - they should really occur after all of the + // expressions in 'left_expression'. + visitor.visit_expr(&right_expr); + visitor.pessimistic_yield = prev_pessimistic; + + debug!("resolve_expr - restoring pessimistic_yield to {}", prev_pessimistic); + visitor.visit_expr(&left_expr); + debug!("resolve_expr - fixing up counts to {}", visitor.expr_and_pat_count); + + // Remove and process any scopes pushed by the visitor + let target_scopes = visitor.fixup_scopes.drain(start_point..); + + for scope in target_scopes { + let mut yield_data = + visitor.scope_tree.yield_in_scope.get_mut(&scope).unwrap().last_mut().unwrap(); + let count = yield_data.expr_and_pat_count; + let span = yield_data.span; + + // expr_and_pat_count never decreases. Since we recorded counts in yield_in_scope + // before walking the left-hand side, it should be impossible for the recorded + // count to be greater than the left-hand side count. + if count > visitor.expr_and_pat_count { + bug!( + "Encountered greater count {} at span {:?} - expected no greater than {}", + count, + span, + visitor.expr_and_pat_count + ); + } + let new_count = visitor.expr_and_pat_count; + debug!( + "resolve_expr - increasing count for scope {:?} from {} to {} at span {:?}", + scope, count, new_count, span + ); + + yield_data.expr_and_pat_count = new_count; + } + } + + hir::ExprKind::If(ref cond, ref then, Some(ref otherwise)) => { + let expr_cx = visitor.cx; + visitor.enter_scope(Scope { id: then.hir_id.local_id, data: ScopeData::IfThen }); + visitor.cx.var_parent = visitor.cx.parent; + visitor.visit_expr(cond); + visitor.visit_expr(then); + visitor.cx = expr_cx; + visitor.visit_expr(otherwise); + } + + hir::ExprKind::If(ref cond, ref then, None) => { + let expr_cx = visitor.cx; + visitor.enter_scope(Scope { id: then.hir_id.local_id, data: ScopeData::IfThen }); + visitor.cx.var_parent = visitor.cx.parent; + visitor.visit_expr(cond); + visitor.visit_expr(then); + visitor.cx = expr_cx; + } + + _ => intravisit::walk_expr(visitor, expr), + } + + visitor.expr_and_pat_count += 1; + + debug!("resolve_expr post-increment {}, expr = {:?}", visitor.expr_and_pat_count, expr); + + if let hir::ExprKind::Yield(_, source) = &expr.kind { + // Mark this expr's scope and all parent scopes as containing `yield`. + let mut scope = Scope { id: expr.hir_id.local_id, data: ScopeData::Node }; + loop { + let span = match expr.kind { + hir::ExprKind::Yield(expr, hir::YieldSource::Await { .. }) => { + expr.span.shrink_to_hi().to(expr.span) + } + _ => expr.span, + }; + let data = + YieldData { span, expr_and_pat_count: visitor.expr_and_pat_count, source: *source }; + match visitor.scope_tree.yield_in_scope.get_mut(&scope) { + Some(yields) => yields.push(data), + None => { + visitor.scope_tree.yield_in_scope.insert(scope, vec![data]); + } + } + + if visitor.pessimistic_yield { + debug!("resolve_expr in pessimistic_yield - marking scope {:?} for fixup", scope); + visitor.fixup_scopes.push(scope); + } + + // Keep traversing up while we can. + match visitor.scope_tree.parent_map.get(&scope) { + // Don't cross from closure bodies to their parent. + Some(&(superscope, _)) => match superscope.data { + ScopeData::CallSite => break, + _ => scope = superscope, + }, + None => break, + } + } + } + + visitor.cx = prev_cx; +} + +fn resolve_local<'tcx>( + visitor: &mut RegionResolutionVisitor<'tcx>, + pat: Option<&'tcx hir::Pat<'tcx>>, + init: Option<&'tcx hir::Expr<'tcx>>, + els: Option<&'tcx hir::Block<'tcx>>, +) { + debug!("resolve_local(pat={:?}, init={:?})", pat, init); + + let blk_scope = visitor.cx.var_parent.map(|(p, _)| p); + + // As an exception to the normal rules governing temporary + // lifetimes, initializers in a let have a temporary lifetime + // of the enclosing block. This means that e.g., a program + // like the following is legal: + // + // let ref x = HashMap::new(); + // + // Because the hash map will be freed in the enclosing block. + // + // We express the rules more formally based on 3 grammars (defined + // fully in the helpers below that implement them): + // + // 1. `E&`, which matches expressions like `&<rvalue>` that + // own a pointer into the stack. + // + // 2. `P&`, which matches patterns like `ref x` or `(ref x, ref + // y)` that produce ref bindings into the value they are + // matched against or something (at least partially) owned by + // the value they are matched against. (By partially owned, + // I mean that creating a binding into a ref-counted or managed value + // would still count.) + // + // 3. `ET`, which matches both rvalues like `foo()` as well as places + // based on rvalues like `foo().x[2].y`. + // + // A subexpression `<rvalue>` that appears in a let initializer + // `let pat [: ty] = expr` has an extended temporary lifetime if + // any of the following conditions are met: + // + // A. `pat` matches `P&` and `expr` matches `ET` + // (covers cases where `pat` creates ref bindings into an rvalue + // produced by `expr`) + // B. `ty` is a borrowed pointer and `expr` matches `ET` + // (covers cases where coercion creates a borrow) + // C. `expr` matches `E&` + // (covers cases `expr` borrows an rvalue that is then assigned + // to memory (at least partially) owned by the binding) + // + // Here are some examples hopefully giving an intuition where each + // rule comes into play and why: + // + // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)` + // would have an extended lifetime, but not `foo()`. + // + // Rule B. `let x = &foo().x`. The rvalue `foo()` would have extended + // lifetime. + // + // In some cases, multiple rules may apply (though not to the same + // rvalue). For example: + // + // let ref x = [&a(), &b()]; + // + // Here, the expression `[...]` has an extended lifetime due to rule + // A, but the inner rvalues `a()` and `b()` have an extended lifetime + // due to rule C. + + if let Some(expr) = init { + record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope); + + if let Some(pat) = pat { + if is_binding_pat(pat) { + visitor.scope_tree.record_rvalue_candidate( + expr.hir_id, + RvalueCandidateType::Pattern { + target: expr.hir_id.local_id, + lifetime: blk_scope, + }, + ); + } + } + } + + // Make sure we visit the initializer first, so expr_and_pat_count remains correct. + // The correct order, as shared between generator_interior, drop_ranges and intravisitor, + // is to walk initializer, followed by pattern bindings, finally followed by the `else` block. + if let Some(expr) = init { + visitor.visit_expr(expr); + } + if let Some(pat) = pat { + visitor.visit_pat(pat); + } + if let Some(els) = els { + visitor.visit_block(els); + } + + /// Returns `true` if `pat` match the `P&` non-terminal. + /// + /// ```text + /// P& = ref X + /// | StructName { ..., P&, ... } + /// | VariantName(..., P&, ...) + /// | [ ..., P&, ... ] + /// | ( ..., P&, ... ) + /// | ... "|" P& "|" ... + /// | box P& + /// ``` + fn is_binding_pat(pat: &hir::Pat<'_>) -> bool { + // Note that the code below looks for *explicit* refs only, that is, it won't + // know about *implicit* refs as introduced in #42640. + // + // This is not a problem. For example, consider + // + // let (ref x, ref y) = (Foo { .. }, Bar { .. }); + // + // Due to the explicit refs on the left hand side, the below code would signal + // that the temporary value on the right hand side should live until the end of + // the enclosing block (as opposed to being dropped after the let is complete). + // + // To create an implicit ref, however, you must have a borrowed value on the RHS + // already, as in this example (which won't compile before #42640): + // + // let Foo { x, .. } = &Foo { x: ..., ... }; + // + // in place of + // + // let Foo { ref x, .. } = Foo { ... }; + // + // In the former case (the implicit ref version), the temporary is created by the + // & expression, and its lifetime would be extended to the end of the block (due + // to a different rule, not the below code). + match pat.kind { + PatKind::Binding(hir::BindingAnnotation::Ref, ..) + | PatKind::Binding(hir::BindingAnnotation::RefMut, ..) => true, + + PatKind::Struct(_, ref field_pats, _) => { + field_pats.iter().any(|fp| is_binding_pat(&fp.pat)) + } + + PatKind::Slice(ref pats1, ref pats2, ref pats3) => { + pats1.iter().any(|p| is_binding_pat(&p)) + || pats2.iter().any(|p| is_binding_pat(&p)) + || pats3.iter().any(|p| is_binding_pat(&p)) + } + + PatKind::Or(ref subpats) + | PatKind::TupleStruct(_, ref subpats, _) + | PatKind::Tuple(ref subpats, _) => subpats.iter().any(|p| is_binding_pat(&p)), + + PatKind::Box(ref subpat) => is_binding_pat(&subpat), + + PatKind::Ref(_, _) + | PatKind::Binding( + hir::BindingAnnotation::Unannotated | hir::BindingAnnotation::Mutable, + .., + ) + | PatKind::Wild + | PatKind::Path(_) + | PatKind::Lit(_) + | PatKind::Range(_, _, _) => false, + } + } + + /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate: + /// + /// ```text + /// E& = & ET + /// | StructName { ..., f: E&, ... } + /// | [ ..., E&, ... ] + /// | ( ..., E&, ... ) + /// | {...; E&} + /// | box E& + /// | E& as ... + /// | ( E& ) + /// ``` + fn record_rvalue_scope_if_borrow_expr<'tcx>( + visitor: &mut RegionResolutionVisitor<'tcx>, + expr: &hir::Expr<'_>, + blk_id: Option<Scope>, + ) { + match expr.kind { + hir::ExprKind::AddrOf(_, _, subexpr) => { + record_rvalue_scope_if_borrow_expr(visitor, subexpr, blk_id); + visitor.scope_tree.record_rvalue_candidate( + subexpr.hir_id, + RvalueCandidateType::Borrow { + target: subexpr.hir_id.local_id, + lifetime: blk_id, + }, + ); + } + hir::ExprKind::Struct(_, fields, _) => { + for field in fields { + record_rvalue_scope_if_borrow_expr(visitor, &field.expr, blk_id); + } + } + hir::ExprKind::Array(subexprs) | hir::ExprKind::Tup(subexprs) => { + for subexpr in subexprs { + record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id); + } + } + hir::ExprKind::Cast(ref subexpr, _) => { + record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id) + } + hir::ExprKind::Block(ref block, _) => { + if let Some(ref subexpr) = block.expr { + record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id); + } + } + hir::ExprKind::Call(..) | hir::ExprKind::MethodCall(..) => { + // FIXME(@dingxiangfei2009): choose call arguments here + // for candidacy for extended parameter rule application + } + hir::ExprKind::Index(..) => { + // FIXME(@dingxiangfei2009): select the indices + // as candidate for rvalue scope rules + } + _ => {} + } + } +} + +impl<'tcx> RegionResolutionVisitor<'tcx> { + /// Records the current parent (if any) as the parent of `child_scope`. + /// Returns the depth of `child_scope`. + fn record_child_scope(&mut self, child_scope: Scope) -> ScopeDepth { + let parent = self.cx.parent; + self.scope_tree.record_scope_parent(child_scope, parent); + // If `child_scope` has no parent, it must be the root node, and so has + // a depth of 1. Otherwise, its depth is one more than its parent's. + parent.map_or(1, |(_p, d)| d + 1) + } + + /// Records the current parent (if any) as the parent of `child_scope`, + /// and sets `child_scope` as the new current parent. + fn enter_scope(&mut self, child_scope: Scope) { + let child_depth = self.record_child_scope(child_scope); + self.cx.parent = Some((child_scope, child_depth)); + } + + fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) { + // If node was previously marked as a terminating scope during the + // recursive visit of its parent node in the AST, then we need to + // account for the destruction scope representing the scope of + // the destructors that run immediately after it completes. + if self.terminating_scopes.contains(&id) { + self.enter_scope(Scope { id, data: ScopeData::Destruction }); + } + self.enter_scope(Scope { id, data: ScopeData::Node }); + } +} + +impl<'tcx> Visitor<'tcx> for RegionResolutionVisitor<'tcx> { + fn visit_block(&mut self, b: &'tcx Block<'tcx>) { + resolve_block(self, b); + } + + fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) { + let body_id = body.id(); + let owner_id = self.tcx.hir().body_owner_def_id(body_id); + + debug!( + "visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})", + owner_id, + self.tcx.sess.source_map().span_to_diagnostic_string(body.value.span), + body_id, + self.cx.parent + ); + + // Save all state that is specific to the outer function + // body. These will be restored once down below, once we've + // visited the body. + let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0); + let outer_cx = self.cx; + let outer_ts = mem::take(&mut self.terminating_scopes); + // The 'pessimistic yield' flag is set to true when we are + // processing a `+=` statement and have to make pessimistic + // control flow assumptions. This doesn't apply to nested + // bodies within the `+=` statements. See #69307. + let outer_pessimistic_yield = mem::replace(&mut self.pessimistic_yield, false); + self.terminating_scopes.insert(body.value.hir_id.local_id); + + self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::CallSite }); + self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::Arguments }); + + // The arguments and `self` are parented to the fn. + self.cx.var_parent = self.cx.parent.take(); + for param in body.params { + self.visit_pat(¶m.pat); + } + + // The body of the every fn is a root scope. + self.cx.parent = self.cx.var_parent; + if self.tcx.hir().body_owner_kind(owner_id).is_fn_or_closure() { + self.visit_expr(&body.value) + } else { + // Only functions have an outer terminating (drop) scope, while + // temporaries in constant initializers may be 'static, but only + // according to rvalue lifetime semantics, using the same + // syntactical rules used for let initializers. + // + // e.g., in `let x = &f();`, the temporary holding the result from + // the `f()` call lives for the entirety of the surrounding block. + // + // Similarly, `const X: ... = &f();` would have the result of `f()` + // live for `'static`, implying (if Drop restrictions on constants + // ever get lifted) that the value *could* have a destructor, but + // it'd get leaked instead of the destructor running during the + // evaluation of `X` (if at all allowed by CTFE). + // + // However, `const Y: ... = g(&f());`, like `let y = g(&f());`, + // would *not* let the `f()` temporary escape into an outer scope + // (i.e., `'static`), which means that after `g` returns, it drops, + // and all the associated destruction scope rules apply. + self.cx.var_parent = None; + resolve_local(self, None, Some(&body.value), None); + } + + if body.generator_kind.is_some() { + self.scope_tree.body_expr_count.insert(body_id, self.expr_and_pat_count); + } + + // Restore context we had at the start. + self.expr_and_pat_count = outer_ec; + self.cx = outer_cx; + self.terminating_scopes = outer_ts; + self.pessimistic_yield = outer_pessimistic_yield; + } + + fn visit_arm(&mut self, a: &'tcx Arm<'tcx>) { + resolve_arm(self, a); + } + fn visit_pat(&mut self, p: &'tcx Pat<'tcx>) { + resolve_pat(self, p); + } + fn visit_stmt(&mut self, s: &'tcx Stmt<'tcx>) { + resolve_stmt(self, s); + } + fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) { + resolve_expr(self, ex); + } + fn visit_local(&mut self, l: &'tcx Local<'tcx>) { + resolve_local(self, Some(&l.pat), l.init, l.els) + } +} + +/// Per-body `region::ScopeTree`. The `DefId` should be the owner `DefId` for the body; +/// in the case of closures, this will be redirected to the enclosing function. +/// +/// Performance: This is a query rather than a simple function to enable +/// re-use in incremental scenarios. We may sometimes need to rerun the +/// type checker even when the HIR hasn't changed, and in those cases +/// we can avoid reconstructing the region scope tree. +pub fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree { + let typeck_root_def_id = tcx.typeck_root_def_id(def_id); + if typeck_root_def_id != def_id { + return tcx.region_scope_tree(typeck_root_def_id); + } + + let scope_tree = if let Some(body_id) = tcx.hir().maybe_body_owned_by(def_id.expect_local()) { + let mut visitor = RegionResolutionVisitor { + tcx, + scope_tree: ScopeTree::default(), + expr_and_pat_count: 0, + cx: Context { parent: None, var_parent: None }, + terminating_scopes: Default::default(), + pessimistic_yield: false, + fixup_scopes: vec![], + }; + + let body = tcx.hir().body(body_id); + visitor.scope_tree.root_body = Some(body.value.hir_id); + visitor.visit_body(body); + visitor.scope_tree + } else { + ScopeTree::default() + }; + + tcx.arena.alloc(scope_tree) +} |