| //! 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 std::mem; |
| |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_hir as hir; |
| use rustc_hir::def::{CtorKind, DefKind, Res}; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::intravisit::{self, Visitor}; |
| use rustc_hir::{Arm, Block, Expr, LetStmt, Pat, PatKind, Stmt}; |
| use rustc_index::Idx; |
| use rustc_middle::middle::region::*; |
| use rustc_middle::ty::TyCtxt; |
| use rustc_session::lint; |
| use rustc_span::source_map; |
| use tracing::debug; |
| |
| #[derive(Debug, Copy, Clone)] |
| struct Context { |
| /// The scope that contains any new variables declared. |
| var_parent: Option<Scope>, |
| |
| /// Region parent of expressions, etc. |
| parent: Option<Scope>, |
| } |
| |
| struct ScopeResolutionVisitor<'tcx> { |
| tcx: TyCtxt<'tcx>, |
| |
| // The generated scope tree. |
| scope_tree: ScopeTree, |
| |
| cx: Context, |
| |
| extended_super_lets: FxHashMap<hir::ItemLocalId, Option<Scope>>, |
| } |
| |
| /// Records the lifetime of a local variable as `cx.var_parent` |
| fn record_var_lifetime(visitor: &mut ScopeResolutionVisitor<'_>, var_id: hir::ItemLocalId) { |
| 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 ScopeResolutionVisitor<'tcx>, |
| blk: &'tcx hir::Block<'tcx>, |
| terminating: bool, |
| ) { |
| 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, terminating); |
| 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::Let(LetStmt { els: Some(els), .. }) => { |
| // Let-else has a special lexical structure for variables. |
| // First we take a checkpoint of the current scope context here. |
| let mut prev_cx = visitor.cx; |
| |
| visitor.enter_scope(Scope { |
| local_id: blk.hir_id.local_id, |
| data: ScopeData::Remainder(FirstStatementIndex::new(i)), |
| }); |
| visitor.cx.var_parent = visitor.cx.parent; |
| visitor.visit_stmt(statement); |
| // We need to back out temporarily to the last enclosing scope |
| // for the `else` block, so that even the temporaries receiving |
| // extended lifetime will be dropped inside this block. |
| // We are visiting the `else` block in this order so that |
| // the sequence of visits agree with the order in the default |
| // `hir::intravisit` visitor. |
| mem::swap(&mut prev_cx, &mut visitor.cx); |
| resolve_block(visitor, els, true); |
| // From now on, we continue normally. |
| visitor.cx = prev_cx; |
| } |
| hir::StmtKind::Let(..) => { |
| // 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 { |
| local_id: blk.hir_id.local_id, |
| data: ScopeData::Remainder(FirstStatementIndex::new(i)), |
| }); |
| visitor.cx.var_parent = visitor.cx.parent; |
| visitor.visit_stmt(statement) |
| } |
| hir::StmtKind::Item(..) => { |
| // Don't create scopes for items, since they won't be |
| // lowered to THIR and MIR. |
| } |
| hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => visitor.visit_stmt(statement), |
| } |
| } |
| if let Some(tail_expr) = blk.expr { |
| let local_id = tail_expr.hir_id.local_id; |
| let edition = blk.span.edition(); |
| let terminating = edition.at_least_rust_2024(); |
| if !terminating |
| && !visitor |
| .tcx |
| .lints_that_dont_need_to_run(()) |
| .contains(&lint::LintId::of(lint::builtin::TAIL_EXPR_DROP_ORDER)) |
| { |
| // If this temporary scope will be changing once the codebase adopts Rust 2024, |
| // and we are linting about possible semantic changes that would result, |
| // then record this node-id in the field `backwards_incompatible_scope` |
| // for future reference. |
| visitor |
| .scope_tree |
| .backwards_incompatible_scope |
| .insert(local_id, Scope { local_id, data: ScopeData::Node }); |
| } |
| resolve_expr(visitor, tail_expr, terminating); |
| } |
| } |
| |
| visitor.cx = prev_cx; |
| } |
| |
| /// Resolve a condition from an `if` expression or match guard so that it is a terminating scope |
| /// if it doesn't contain `let` expressions. |
| fn resolve_cond<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, cond: &'tcx hir::Expr<'tcx>) { |
| let terminate = match cond.kind { |
| // Temporaries for `let` expressions must live into the success branch. |
| hir::ExprKind::Let(_) => false, |
| // Logical operator chains are handled in `resolve_expr`. Since logical operator chains in |
| // conditions are lowered to control-flow rather than boolean temporaries, there's no |
| // temporary to drop for logical operators themselves. `resolve_expr` will also recursively |
| // wrap any operands in terminating scopes, other than `let` expressions (which we shouldn't |
| // terminate) and other logical operators (which don't need a terminating scope, since their |
| // operands will be terminated). Any temporaries that would need to be dropped will be |
| // dropped before we leave this operator's scope; terminating them here would be redundant. |
| hir::ExprKind::Binary( |
| source_map::Spanned { node: hir::BinOpKind::And | hir::BinOpKind::Or, .. }, |
| _, |
| _, |
| ) => false, |
| // Otherwise, conditions should always drop their temporaries. |
| _ => true, |
| }; |
| resolve_expr(visitor, cond, terminate); |
| } |
| |
| fn resolve_arm<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, arm: &'tcx hir::Arm<'tcx>) { |
| let prev_cx = visitor.cx; |
| |
| visitor.enter_node_scope_with_dtor(arm.hir_id.local_id, true); |
| visitor.cx.var_parent = visitor.cx.parent; |
| |
| resolve_pat(visitor, arm.pat); |
| if let Some(guard) = arm.guard { |
| // We introduce a new scope to contain bindings and temporaries from `if let` guards, to |
| // ensure they're dropped before the arm's pattern's bindings. This extends to the end of |
| // the arm body and is the scope of its locals as well. |
| visitor.enter_scope(Scope { local_id: arm.hir_id.local_id, data: ScopeData::MatchGuard }); |
| visitor.cx.var_parent = visitor.cx.parent; |
| resolve_cond(visitor, guard); |
| } |
| resolve_expr(visitor, arm.body, false); |
| |
| visitor.cx = prev_cx; |
| } |
| |
| #[tracing::instrument(level = "debug", skip(visitor))] |
| fn resolve_pat<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, pat: &'tcx hir::Pat<'tcx>) { |
| // 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); |
| } |
| |
| intravisit::walk_pat(visitor, pat); |
| } |
| |
| fn resolve_stmt<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, stmt: &'tcx hir::Stmt<'tcx>) { |
| let stmt_id = stmt.hir_id.local_id; |
| debug!("resolve_stmt(stmt.id={:?})", stmt_id); |
| |
| if let hir::StmtKind::Let(LetStmt { super_: Some(_), .. }) = stmt.kind { |
| // `super let` statement does not start a new scope, such that |
| // |
| // { super let x = identity(&temp()); &x }.method(); |
| // |
| // behaves exactly as |
| // |
| // (&identity(&temp()).method(); |
| intravisit::walk_stmt(visitor, stmt); |
| } else { |
| // 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. |
| |
| let prev_parent = visitor.cx.parent; |
| visitor.enter_node_scope_with_dtor(stmt_id, true); |
| |
| intravisit::walk_stmt(visitor, stmt); |
| |
| visitor.cx.parent = prev_parent; |
| } |
| } |
| |
| #[tracing::instrument(level = "debug", skip(visitor))] |
| fn resolve_expr<'tcx>( |
| visitor: &mut ScopeResolutionVisitor<'tcx>, |
| expr: &'tcx hir::Expr<'tcx>, |
| terminating: bool, |
| ) { |
| let prev_cx = visitor.cx; |
| visitor.enter_node_scope_with_dtor(expr.hir_id.local_id, terminating); |
| |
| 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 | hir::BinOpKind::Or, .. }, |
| left, |
| right, |
| ) => { |
| // expr is a short circuiting operator (|| or &&). As its |
| // functionality can't be overridden by traits, it always |
| // processes bool sub-expressions. bools are Copy and thus we |
| // can drop any temporaries in evaluation (read) order |
| // (with the exception of potentially failing let expressions). |
| // We achieve this by enclosing the operands in a terminating |
| // scope, both the LHS and the RHS. |
| |
| // We optimize this a little in the presence of chains. |
| // Chains like a && b && c get lowered to AND(AND(a, b), c). |
| // In here, b and c are RHS, while a is the only LHS operand in |
| // that chain. This holds true for longer chains as well: the |
| // leading operand is always the only LHS operand that is not a |
| // binop itself. Putting a binop like AND(a, b) into a |
| // terminating scope is not useful, thus we only put the LHS |
| // into a terminating scope if it is not a binop. |
| |
| let terminate_lhs = match left.kind { |
| // let expressions can create temporaries that live on |
| hir::ExprKind::Let(_) => false, |
| // binops already drop their temporaries, so there is no |
| // need to put them into a terminating scope. |
| // This is purely an optimization to reduce the number of |
| // terminating scopes. |
| hir::ExprKind::Binary( |
| source_map::Spanned { node: hir::BinOpKind::And | hir::BinOpKind::Or, .. }, |
| .., |
| ) => false, |
| // otherwise: mark it as terminating |
| _ => true, |
| }; |
| |
| // `Let` expressions (in a let-chain) shouldn't be terminating, as their temporaries |
| // should live beyond the immediate expression |
| let terminate_rhs = !matches!(right.kind, hir::ExprKind::Let(_)); |
| |
| resolve_expr(visitor, left, terminate_lhs); |
| resolve_expr(visitor, right, terminate_rhs); |
| } |
| // Manually recurse over closures, because they are nested bodies |
| // that share the parent environment. We handle const blocks in |
| // `visit_inline_const`. |
| hir::ExprKind::Closure(&hir::Closure { body, .. }) => { |
| let body = visitor.tcx.hir_body(body); |
| visitor.visit_body(body); |
| } |
| // 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. Fortunately, we don't need to know the actual execution order. |
| hir::ExprKind::AssignOp(_, left_expr, right_expr) => { |
| visitor.visit_expr(right_expr); |
| visitor.visit_expr(left_expr); |
| } |
| |
| hir::ExprKind::If(cond, then, Some(otherwise)) => { |
| let expr_cx = visitor.cx; |
| let data = if expr.span.at_least_rust_2024() { |
| ScopeData::IfThenRescope |
| } else { |
| ScopeData::IfThen |
| }; |
| visitor.enter_scope(Scope { local_id: then.hir_id.local_id, data }); |
| visitor.cx.var_parent = visitor.cx.parent; |
| resolve_cond(visitor, cond); |
| resolve_expr(visitor, then, true); |
| visitor.cx = expr_cx; |
| resolve_expr(visitor, otherwise, true); |
| } |
| |
| hir::ExprKind::If(cond, then, None) => { |
| let expr_cx = visitor.cx; |
| let data = if expr.span.at_least_rust_2024() { |
| ScopeData::IfThenRescope |
| } else { |
| ScopeData::IfThen |
| }; |
| visitor.enter_scope(Scope { local_id: then.hir_id.local_id, data }); |
| visitor.cx.var_parent = visitor.cx.parent; |
| resolve_cond(visitor, cond); |
| resolve_expr(visitor, then, true); |
| visitor.cx = expr_cx; |
| } |
| |
| hir::ExprKind::Loop(body, _, _, _) => { |
| resolve_block(visitor, body, true); |
| } |
| |
| hir::ExprKind::DropTemps(expr) => { |
| // `DropTemps(expr)` does not denote a conditional scope. |
| // Rather, we want to achieve the same behavior as `{ let _t = expr; _t }`. |
| resolve_expr(visitor, expr, true); |
| } |
| |
| _ => intravisit::walk_expr(visitor, expr), |
| } |
| |
| visitor.cx = prev_cx; |
| } |
| |
| #[derive(Copy, Clone, PartialEq, Eq, Debug)] |
| enum LetKind { |
| Regular, |
| Super, |
| } |
| |
| fn resolve_local<'tcx>( |
| visitor: &mut ScopeResolutionVisitor<'tcx>, |
| pat: Option<&'tcx hir::Pat<'tcx>>, |
| init: Option<&'tcx hir::Expr<'tcx>>, |
| let_kind: LetKind, |
| ) { |
| debug!("resolve_local(pat={:?}, init={:?}, let_kind={:?})", pat, init, let_kind); |
| |
| // 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_kind == LetKind::Super { |
| if let Some(scope) = visitor.extended_super_lets.remove(&pat.unwrap().hir_id.local_id) { |
| // This expression was lifetime-extended by a parent let binding. E.g. |
| // |
| // let a = { |
| // super let b = temp(); |
| // &b |
| // }; |
| // |
| // (Which needs to behave exactly as: let a = &temp();) |
| // |
| // Processing of `let a` will have already decided to extend the lifetime of this |
| // `super let` to its own var_scope. We use that scope. |
| visitor.cx.var_parent = scope; |
| } else { |
| // This `super let` is not subject to lifetime extension from a parent let binding. E.g. |
| // |
| // identity({ super let x = temp(); &x }).method(); |
| // |
| // (Which needs to behave exactly as: identity(&temp()).method();) |
| // |
| // Iterate up to the enclosing destruction scope to find the same scope that will also |
| // be used for the result of the block itself. |
| while let Some(s) = visitor.cx.var_parent { |
| let parent = visitor.scope_tree.parent_map.get(&s).cloned(); |
| if let Some(Scope { data: ScopeData::Destruction, .. }) = parent { |
| break; |
| } |
| visitor.cx.var_parent = parent; |
| } |
| } |
| } |
| |
| if let Some(expr) = init { |
| record_rvalue_scope_if_borrow_expr(visitor, expr, visitor.cx.var_parent); |
| |
| if let Some(pat) = pat { |
| if is_binding_pat(pat) { |
| visitor.scope_tree.record_rvalue_candidate( |
| expr.hir_id, |
| RvalueCandidate { |
| target: expr.hir_id.local_id, |
| lifetime: visitor.cx.var_parent, |
| }, |
| ); |
| } |
| } |
| } |
| |
| // Make sure we visit the initializer first. |
| // The correct order, as shared between 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); |
| } |
| |
| /// Returns `true` if `pat` match the `P&` non-terminal. |
| /// |
| /// ```text |
| /// P& = ref X |
| /// | StructName { ..., P&, ... } |
| /// | VariantName(..., P&, ...) |
| /// | [ ..., P&, ... ] |
| /// | ( ..., P&, ... ) |
| /// | ... "|" P& "|" ... |
| /// | box P& |
| /// | P& if ... |
| /// ``` |
| 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::BindingMode(hir::ByRef::Yes(_), _), ..) => true, |
| |
| PatKind::Struct(_, field_pats, _) => field_pats.iter().any(|fp| is_binding_pat(fp.pat)), |
| |
| PatKind::Slice(pats1, pats2, 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(subpats) |
| | PatKind::TupleStruct(_, subpats, _) |
| | PatKind::Tuple(subpats, _) => subpats.iter().any(|p| is_binding_pat(p)), |
| |
| PatKind::Box(subpat) | PatKind::Deref(subpat) | PatKind::Guard(subpat, _) => { |
| is_binding_pat(subpat) |
| } |
| |
| PatKind::Ref(_, _) |
| | PatKind::Binding(hir::BindingMode(hir::ByRef::No, _), ..) |
| | PatKind::Missing |
| | PatKind::Wild |
| | PatKind::Never |
| | PatKind::Expr(_) |
| | PatKind::Range(_, _, _) |
| | PatKind::Err(_) => false, |
| } |
| } |
| |
| /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate: |
| /// |
| /// ```text |
| /// E& = & ET |
| /// | StructName { ..., f: E&, ... } |
| /// | [ ..., E&, ... ] |
| /// | ( ..., E&, ... ) |
| /// | {...; E&} |
| /// | { super let ... = E&; ... } |
| /// | if _ { ...; E& } else { ...; E& } |
| /// | match _ { ..., _ => E&, ... } |
| /// | box E& |
| /// | E& as ... |
| /// | ( E& ) |
| /// ``` |
| fn record_rvalue_scope_if_borrow_expr<'tcx>( |
| visitor: &mut ScopeResolutionVisitor<'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, |
| RvalueCandidate { 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(subexpr, _) => { |
| record_rvalue_scope_if_borrow_expr(visitor, subexpr, blk_id) |
| } |
| hir::ExprKind::Block(block, _) => { |
| if let Some(subexpr) = block.expr { |
| record_rvalue_scope_if_borrow_expr(visitor, subexpr, blk_id); |
| } |
| for stmt in block.stmts { |
| if let hir::StmtKind::Let(local) = stmt.kind |
| && let Some(_) = local.super_ |
| { |
| visitor.extended_super_lets.insert(local.pat.hir_id.local_id, blk_id); |
| } |
| } |
| } |
| hir::ExprKind::If(_, then_block, else_block) => { |
| record_rvalue_scope_if_borrow_expr(visitor, then_block, blk_id); |
| if let Some(else_block) = else_block { |
| record_rvalue_scope_if_borrow_expr(visitor, else_block, blk_id); |
| } |
| } |
| hir::ExprKind::Match(_, arms, _) => { |
| for arm in arms { |
| record_rvalue_scope_if_borrow_expr(visitor, arm.body, blk_id); |
| } |
| } |
| hir::ExprKind::Call(func, args) => { |
| // Recurse into tuple constructors, such as `Some(&temp())`. |
| // |
| // That way, there is no difference between `Some(..)` and `Some { 0: .. }`, |
| // even though the former is syntactically a function call. |
| if let hir::ExprKind::Path(path) = &func.kind |
| && let hir::QPath::Resolved(None, path) = path |
| && let Res::SelfCtor(_) | Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) = path.res |
| { |
| for arg in args { |
| record_rvalue_scope_if_borrow_expr(visitor, arg, blk_id); |
| } |
| } |
| } |
| _ => {} |
| } |
| } |
| } |
| |
| impl<'tcx> ScopeResolutionVisitor<'tcx> { |
| /// Records the current parent (if any) as the parent of `child_scope`. |
| fn record_child_scope(&mut self, child_scope: Scope) { |
| let parent = self.cx.parent; |
| self.scope_tree.record_scope_parent(child_scope, parent); |
| } |
| |
| /// 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) { |
| self.record_child_scope(child_scope); |
| self.cx.parent = Some(child_scope); |
| } |
| |
| fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId, terminating: bool) { |
| // If node was previously marked as a terminating scope during the |
| // recursive visit of its parent node in the HIR, then we need to |
| // account for the destruction scope representing the scope of |
| // the destructors that run immediately after it completes. |
| if terminating { |
| self.enter_scope(Scope { local_id: id, data: ScopeData::Destruction }); |
| } |
| self.enter_scope(Scope { local_id: id, data: ScopeData::Node }); |
| } |
| |
| fn enter_body(&mut self, hir_id: hir::HirId, f: impl FnOnce(&mut Self)) { |
| let outer_cx = self.cx; |
| |
| self.enter_scope(Scope { local_id: hir_id.local_id, data: ScopeData::CallSite }); |
| self.enter_scope(Scope { local_id: hir_id.local_id, data: ScopeData::Arguments }); |
| |
| f(self); |
| |
| // Restore context we had at the start. |
| self.cx = outer_cx; |
| } |
| } |
| |
| impl<'tcx> Visitor<'tcx> for ScopeResolutionVisitor<'tcx> { |
| fn visit_block(&mut self, b: &'tcx Block<'tcx>) { |
| resolve_block(self, b, false); |
| } |
| |
| fn visit_body(&mut self, body: &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 |
| ); |
| |
| self.enter_body(body.value.hir_id, |this| { |
| if this.tcx.hir_body_owner_kind(owner_id).is_fn_or_closure() { |
| // The arguments and `self` are parented to the fn. |
| this.cx.var_parent = this.cx.parent; |
| for param in body.params { |
| this.visit_pat(param.pat); |
| } |
| |
| // The body of the every fn is a root scope. |
| resolve_expr(this, body.value, true); |
| } 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. |
| this.cx.var_parent = None; |
| this.enter_scope(Scope { |
| local_id: body.value.hir_id.local_id, |
| data: ScopeData::Destruction, |
| }); |
| resolve_local(this, None, Some(body.value), LetKind::Regular); |
| } |
| }) |
| } |
| |
| 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, false); |
| } |
| fn visit_local(&mut self, l: &'tcx LetStmt<'tcx>) { |
| let let_kind = match l.super_ { |
| Some(_) => LetKind::Super, |
| None => LetKind::Regular, |
| }; |
| resolve_local(self, Some(l.pat), l.init, let_kind); |
| } |
| fn visit_inline_const(&mut self, c: &'tcx hir::ConstBlock) { |
| let body = self.tcx.hir_body(c.body); |
| self.visit_body(body); |
| } |
| } |
| |
| /// 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(crate) 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) = tcx.hir_maybe_body_owned_by(def_id.expect_local()) { |
| let mut visitor = ScopeResolutionVisitor { |
| tcx, |
| scope_tree: ScopeTree::default(), |
| cx: Context { parent: None, var_parent: None }, |
| extended_super_lets: Default::default(), |
| }; |
| |
| 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) |
| } |
