--- /dev/null
+//! 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::Local { 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 {
+ 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);
+ visitor.terminating_scopes.insert(els.hir_id.local_id);
+ visitor.visit_block(els);
+ // From now on, we continue normally.
+ visitor.cx = prev_cx;
+ }
+ 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;
+ visitor.visit_stmt(statement)
+ }
+ 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.
+
+ // `Let` expressions (in a let-chain) shouldn't be terminating, as their temporaries
+ // should live beyond the immediate expression
+ if !matches!(r.kind, hir::ExprKind::Let(_)) {
+ 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>>,
+) {
+ 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);
+ }
+
+ /// 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(hir::ByRef::Yes, _), ..) => 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(hir::ByRef::No, _), ..)
+ | 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));
+ }
+
+ 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)
+ }
+}
+
+/// 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)
+}
projects / rustc.git / blobdiff