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rust/src/librustc/middle/region.rs

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// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! 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 guide].
//!
//! [rustc guide]: https://rust-lang-nursery.github.io/rustc-guide/mir-borrowck.html
use ich::{StableHashingContext, NodeIdHashingMode};
use util::nodemap::{FxHashMap, FxHashSet};
use ty;
use std::fmt;
use std::mem;
use rustc_data_structures::small_vec::SmallVec;
use rustc_data_structures::sync::Lrc;
use syntax::codemap;
use syntax::ast;
use syntax_pos::{Span, DUMMY_SP};
use ty::TyCtxt;
use ty::maps::Providers;
use hir;
use hir::def_id::DefId;
use hir::intravisit::{self, Visitor, NestedVisitorMap};
use hir::{Block, Arm, Pat, PatKind, Stmt, Expr, Local};
use rustc_data_structures::indexed_vec::Idx;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
StableHasherResult};
/// Scope represents a statically-describable scope that can be
/// used to bound the lifetime/region for values.
///
/// `Node(node_id)`: Any AST node that has any scope at all has the
/// `Node(node_id)` scope. Other variants represent special cases not
/// immediately derivable from the abstract syntax tree structure.
///
/// `DestructionScope(node_id)` represents the scope of destructors
/// implicitly-attached to `node_id` that run immediately after the
/// expression for `node_id` itself. Not every AST node carries a
/// `DestructionScope`, but those that are `terminating_scopes` do;
/// see discussion with `ScopeTree`.
///
/// `Remainder(BlockRemainder { block, statement_index })` represents
/// the scope of user code running immediately after the initializer
/// expression for the indexed statement, until the end of the block.
///
/// So: the following code can be broken down into the scopes beneath:
///
/// ```text
/// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y) } ) ;
///
/// +-+ (D12.)
/// +-+ (D11.)
/// +---------+ (R10.)
/// +-+ (D9.)
/// +----------+ (M8.)
/// +----------------------+ (R7.)
/// +-+ (D6.)
/// +----------+ (M5.)
/// +-----------------------------------+ (M4.)
/// +--------------------------------------------------+ (M3.)
/// +--+ (M2.)
/// +-----------------------------------------------------------+ (M1.)
///
/// (M1.): Node scope of the whole `let a = ...;` statement.
/// (M2.): Node scope of the `f()` expression.
/// (M3.): Node scope of the `f().g(..)` expression.
/// (M4.): Node scope of the block labeled `'b:`.
/// (M5.): Node scope of the `let x = d();` statement
/// (D6.): DestructionScope for temporaries created during M5.
/// (R7.): Remainder scope for block `'b:`, stmt 0 (let x = ...).
/// (M8.): Node scope of the `let y = d();` statement.
/// (D9.): DestructionScope for temporaries created during M8.
/// (R10.): Remainder scope for block `'b:`, stmt 1 (let y = ...).
/// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
/// (D12.): DestructionScope for temporaries created during M1 (e.g. f()).
/// ```
///
/// Note that while the above picture shows the destruction scopes
/// as following their corresponding node scopes, in the internal
/// data structures of the compiler the destruction scopes are
/// represented as enclosing parents. This is sound because we use the
/// enclosing parent relationship just to ensure that referenced
/// values live long enough; phrased another way, the starting point
/// of each range is not really the important thing in the above
/// picture, but rather the ending point.
///
/// FIXME (pnkfelix): This currently derives `PartialOrd` and `Ord` to
/// placate the same deriving in `ty::FreeRegion`, but we may want to
/// actually attach a more meaningful ordering to scopes than the one
/// generated via deriving here.
///
/// Scope is a bit-packed to save space - if `code` is SCOPE_DATA_REMAINDER_MAX
/// or less, it is a `ScopeData::Remainder`, otherwise it is a type specified
/// by the bitpacking.
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Copy, RustcEncodable, RustcDecodable)]
pub struct Scope {
pub(crate) id: hir::ItemLocalId,
pub(crate) code: u32
}
const SCOPE_DATA_NODE: u32 = !0;
const SCOPE_DATA_CALLSITE: u32 = !1;
const SCOPE_DATA_ARGUMENTS: u32 = !2;
const SCOPE_DATA_DESTRUCTION: u32 = !3;
const SCOPE_DATA_REMAINDER_MAX: u32 = !4;
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, RustcEncodable, RustcDecodable)]
pub enum ScopeData {
Node(hir::ItemLocalId),
// Scope of the call-site for a function or closure
// (outlives the arguments as well as the body).
CallSite(hir::ItemLocalId),
// Scope of arguments passed to a function or closure
// (they outlive its body).
Arguments(hir::ItemLocalId),
// Scope of destructors for temporaries of node-id.
Destruction(hir::ItemLocalId),
// Scope following a `let id = expr;` binding in a block.
Remainder(BlockRemainder)
}
/// Represents a subscope of `block` for a binding that is introduced
/// by `block.stmts[first_statement_index]`. Such subscopes represent
/// a suffix of the block. Note that each subscope does not include
/// the initializer expression, if any, for the statement indexed by
/// `first_statement_index`.
///
/// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
///
/// * the subscope with `first_statement_index == 0` is scope of both
/// `a` and `b`; it does not include EXPR_1, but does include
/// everything after that first `let`. (If you want a scope that
/// includes EXPR_1 as well, then do not use `Scope::Remainder`,
/// but instead another `Scope` that encompasses the whole block,
/// e.g. `Scope::Node`.
///
/// * the subscope with `first_statement_index == 1` is scope of `c`,
/// and thus does not include EXPR_2, but covers the `...`.
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
RustcDecodable, Debug, Copy)]
pub struct BlockRemainder {
pub block: hir::ItemLocalId,
pub first_statement_index: FirstStatementIndex,
}
newtype_index!(FirstStatementIndex
{
pub idx
MAX = SCOPE_DATA_REMAINDER_MAX
});
impl From<ScopeData> for Scope {
#[inline]
fn from(scope_data: ScopeData) -> Self {
let (id, code) = match scope_data {
ScopeData::Node(id) => (id, SCOPE_DATA_NODE),
ScopeData::CallSite(id) => (id, SCOPE_DATA_CALLSITE),
ScopeData::Arguments(id) => (id, SCOPE_DATA_ARGUMENTS),
ScopeData::Destruction(id) => (id, SCOPE_DATA_DESTRUCTION),
ScopeData::Remainder(r) => (r.block, r.first_statement_index.index() as u32)
};
Self { id, code }
}
}
impl fmt::Debug for Scope {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&self.data(), formatter)
}
}
#[allow(non_snake_case)]
impl Scope {
#[inline]
pub fn data(self) -> ScopeData {
match self.code {
SCOPE_DATA_NODE => ScopeData::Node(self.id),
SCOPE_DATA_CALLSITE => ScopeData::CallSite(self.id),
SCOPE_DATA_ARGUMENTS => ScopeData::Arguments(self.id),
SCOPE_DATA_DESTRUCTION => ScopeData::Destruction(self.id),
idx => ScopeData::Remainder(BlockRemainder {
block: self.id,
first_statement_index: FirstStatementIndex::new(idx as usize)
})
}
}
#[inline]
pub fn Node(id: hir::ItemLocalId) -> Self {
Self::from(ScopeData::Node(id))
}
#[inline]
pub fn CallSite(id: hir::ItemLocalId) -> Self {
Self::from(ScopeData::CallSite(id))
}
#[inline]
pub fn Arguments(id: hir::ItemLocalId) -> Self {
Self::from(ScopeData::Arguments(id))
}
#[inline]
pub fn Destruction(id: hir::ItemLocalId) -> Self {
Self::from(ScopeData::Destruction(id))
}
#[inline]
pub fn Remainder(r: BlockRemainder) -> Self {
Self::from(ScopeData::Remainder(r))
}
}
impl Scope {
/// Returns a item-local id associated with this scope.
///
/// NB: likely to be replaced as API is refined; e.g. pnkfelix
/// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
pub fn item_local_id(&self) -> hir::ItemLocalId {
self.id
}
pub fn node_id(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> ast::NodeId {
match scope_tree.root_body {
Some(hir_id) => {
tcx.hir.hir_to_node_id(hir::HirId {
owner: hir_id.owner,
local_id: self.item_local_id()
})
}
None => ast::DUMMY_NODE_ID
}
}
/// Returns the span of this Scope. Note that in general the
/// returned span may not correspond to the span of any node id in
/// the AST.
pub fn span(&self, tcx: TyCtxt, scope_tree: &ScopeTree) -> Span {
let node_id = self.node_id(tcx, scope_tree);
if node_id == ast::DUMMY_NODE_ID {
return DUMMY_SP;
}
let span = tcx.hir.span(node_id);
if let ScopeData::Remainder(r) = self.data() {
if let hir::map::NodeBlock(ref blk) = tcx.hir.get(node_id) {
// Want span for scope starting after the
// indexed statement and ending at end of
// `blk`; reuse span of `blk` and shift `lo`
// forward to end of indexed statement.
//
// (This is the special case aluded to in the
// doc-comment for this method)
let stmt_span = blk.stmts[r.first_statement_index.index()].span;
// To avoid issues with macro-generated spans, the span
// of the statement must be nested in that of the block.
if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() {
return Span::new(stmt_span.lo(), span.hi(), span.ctxt());
}
}
}
span
}
}
/// The region scope tree encodes information about region relationships.
#[derive(Default, Debug)]
pub struct ScopeTree {
/// If not empty, this body is the root of this region hierarchy.
root_body: Option<hir::HirId>,
/// The parent of the root body owner, if the latter is an
/// an associated const or method, as impls/traits can also
/// have lifetime parameters free in this body.
root_parent: Option<ast::NodeId>,
/// `parent_map` maps from a scope id to the enclosing scope id;
/// this is usually corresponding to the lexical nesting, though
/// in the case of closures the parent scope is the innermost
/// conditional expression or repeating block. (Note that the
/// enclosing scope id for the block associated with a closure is
/// the closure itself.)
parent_map: FxHashMap<Scope, Scope>,
/// `var_map` maps from a variable or binding id to the block in
/// which that variable is declared.
var_map: FxHashMap<hir::ItemLocalId, Scope>,
/// maps from a node-id to the associated destruction scope (if any)
destruction_scopes: FxHashMap<hir::ItemLocalId, Scope>,
/// `rvalue_scopes` includes entries for those expressions whose cleanup scope is
/// larger than the default. The map goes from the expression id
/// to the cleanup scope id. For rvalues not present in this
/// table, the appropriate cleanup scope is the innermost
/// enclosing statement, conditional expression, or repeating
/// block (see `terminating_scopes`).
/// In constants, None is used to indicate that certain expressions
/// escape into 'static and should have no local cleanup scope.
rvalue_scopes: FxHashMap<hir::ItemLocalId, Option<Scope>>,
/// Encodes the hierarchy of fn bodies. Every fn body (including
/// closures) forms its own distinct region hierarchy, rooted in
/// the block that is the fn body. This map points from the id of
/// that root block to the id of the root block for the enclosing
/// fn, if any. Thus the map structures the fn bodies into a
/// hierarchy based on their lexical mapping. This is used to
/// handle the relationships between regions in a fn and in a
/// closure defined by that fn. See the "Modeling closures"
/// section of the README in infer::region_constraints for
/// more details.
closure_tree: FxHashMap<hir::ItemLocalId, hir::ItemLocalId>,
/// If there are any `yield` nested within a scope, this map
/// stores the `Span` of the last one and its index in the
/// postorder of the Visitor traversal on the HIR.
///
/// HIR Visitor postorder indexes might seem like a peculiar
/// thing to care about. but it turns out that HIR bindings
/// and the temporary results of HIR expressions are never
/// storage-live at the end of HIR nodes with postorder indexes
/// lower than theirs, and therefore don't need to be suspended
/// at yield-points at these indexes.
///
/// For an example, suppose we have some code such as:
/// ```rust,ignore (example)
/// foo(f(), yield y, bar(g()))
/// ```
///
/// With the HIR tree (calls numbered for expository purposes)
/// ```
/// Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
/// ```
///
/// Obviously, the result of `f()` was created before the yield
/// (and therefore needs to be kept valid over the yield) while
/// the result of `g()` occurs after the yield (and therefore
/// doesn't). If we want to infer that, we can look at the
/// postorder traversal:
/// ```plain,ignore
/// `foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
/// ```
///
/// In which we can easily see that `Call#1` occurs before the yield,
/// and `Call#3` after it.
///
/// To see that this method works, consider:
///
/// Let `D` be our binding/temporary and `U` be our other HIR node, with
/// `HIR-postorder(U) < HIR-postorder(D)` (in our example, U would be
/// the yield and D would be one of the calls). Let's show that
/// `D` is storage-dead at `U`.
///
/// Remember that storage-live/storage-dead refers to the state of
/// the *storage*, and does not consider moves/drop flags.
///
/// Then:
/// 1. From the ordering guarantee of HIR visitors (see
/// `rustc::hir::intravisit`), `D` does not dominate `U`.
/// 2. Therefore, `D` is *potentially* storage-dead at `U` (because
/// we might visit `U` without ever getting to `D`).
/// 3. However, we guarantee that at each HIR point, each
/// binding/temporary is always either always storage-live
/// or always storage-dead. This is what is being guaranteed
/// by `terminating_scopes` including all blocks where the
/// count of executions is not guaranteed.
/// 4. By `2.` and `3.`, `D` is *statically* storage-dead at `U`,
/// QED.
///
/// I don't think this property relies on `3.` in an essential way - it
/// is probably still correct even if we have "unrestricted" terminating
/// scopes. However, why use the complicated proof when a simple one
/// works?
///
/// A subtle thing: `box` expressions, such as `box (&x, yield 2, &y)`. It
/// might seem that a `box` expression creates a `Box<T>` temporary
/// when it *starts* executing, at `HIR-preorder(BOX-EXPR)`. That might
/// be true in the MIR desugaring, but it is not important in the semantics.
///
/// The reason is that semantically, until the `box` expression returns,
/// the values are still owned by their containing expressions. So
/// we'll see that `&x`.
yield_in_scope: FxHashMap<Scope, (Span, usize)>,
/// The number of visit_expr and visit_pat calls done in the body.
/// Used to sanity check visit_expr/visit_pat call count when
/// calculating generator interiors.
body_expr_count: FxHashMap<hir::BodyId, usize>,
}
#[derive(Debug, Copy, Clone)]
pub struct Context {
/// the root of the current region tree. This is typically the id
/// of the innermost fn body. Each fn forms its own disjoint tree
/// in the region hierarchy. These fn bodies are themselves
/// arranged into a tree. See the "Modeling closures" section of
/// the README in infer::region_constraints for more
/// details.
root_id: Option<hir::ItemLocalId>,
/// the scope that contains any new variables declared
var_parent: Option<Scope>,
/// region parent of expressions etc
parent: Option<Scope>,
}
struct RegionResolutionVisitor<'a, 'tcx: 'a> {
tcx: TyCtxt<'a, 'tcx, 'tcx>,
// The number of expressions and patterns visited in the current body
expr_and_pat_count: usize,
// 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>,
}
struct ExprLocatorVisitor {
id: ast::NodeId,
result: Option<usize>,
expr_and_pat_count: usize,
}
// This visitor has to have the same visit_expr calls as RegionResolutionVisitor
// since `expr_count` is compared against the results there.
impl<'tcx> Visitor<'tcx> for ExprLocatorVisitor {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
fn visit_pat(&mut self, pat: &'tcx Pat) {
intravisit::walk_pat(self, pat);
self.expr_and_pat_count += 1;
if pat.id == self.id {
self.result = Some(self.expr_and_pat_count);
}
}
fn visit_expr(&mut self, expr: &'tcx Expr) {
debug!("ExprLocatorVisitor - pre-increment {} expr = {:?}",
self.expr_and_pat_count,
expr);
intravisit::walk_expr(self, expr);
self.expr_and_pat_count += 1;
debug!("ExprLocatorVisitor - post-increment {} expr = {:?}",
self.expr_and_pat_count,
expr);
if expr.id == self.id {
self.result = Some(self.expr_and_pat_count);
}
}
}
impl<'tcx> ScopeTree {
pub fn record_scope_parent(&mut self, child: Scope, parent: Option<Scope>) {
debug!("{:?}.parent = {:?}", child, parent);
if let Some(p) = parent {
let prev = self.parent_map.insert(child, p);
assert!(prev.is_none());
}
// record the destruction scopes for later so we can query them
if let ScopeData::Destruction(n) = child.data() {
self.destruction_scopes.insert(n, child);
}
}
pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(Scope, Scope) {
for (&child, &parent) in &self.parent_map {
e(child, parent)
}
}
pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&hir::ItemLocalId, Scope) {
for (child, &parent) in self.var_map.iter() {
e(child, parent)
}
}
pub fn opt_destruction_scope(&self, n: hir::ItemLocalId) -> Option<Scope> {
self.destruction_scopes.get(&n).cloned()
}
/// Records that `sub_closure` is defined within `sup_closure`. These ids
/// should be the id of the block that is the fn body, which is
/// also the root of the region hierarchy for that fn.
fn record_closure_parent(&mut self,
sub_closure: hir::ItemLocalId,
sup_closure: hir::ItemLocalId) {
debug!("record_closure_parent(sub_closure={:?}, sup_closure={:?})",
sub_closure, sup_closure);
assert!(sub_closure != sup_closure);
let previous = self.closure_tree.insert(sub_closure, sup_closure);
assert!(previous.is_none());
}
fn closure_is_enclosed_by(&self,
mut sub_closure: hir::ItemLocalId,
sup_closure: hir::ItemLocalId) -> bool {
loop {
if sub_closure == sup_closure { return true; }
match self.closure_tree.get(&sub_closure) {
Some(&s) => { sub_closure = s; }
None => { return false; }
}
}
}
fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) {
debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
assert!(var != lifetime.item_local_id());
self.var_map.insert(var, lifetime);
}
fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
if let Some(lifetime) = lifetime {
assert!(var != lifetime.item_local_id());
}
self.rvalue_scopes.insert(var, lifetime);
}
pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> {
//! Returns the narrowest scope that encloses `id`, if any.
self.parent_map.get(&id).cloned()
}
#[allow(dead_code)] // used in cfg
pub fn encl_scope(&self, id: Scope) -> Scope {
//! Returns the narrowest scope that encloses `id`, if any.
self.opt_encl_scope(id).unwrap()
}
/// Returns the lifetime of the local variable `var_id`
pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Scope {
match self.var_map.get(&var_id) {
Some(&r) => r,
None => { bug!("no enclosing scope for id {:?}", var_id); }
}
}
pub fn temporary_scope(&self, expr_id: hir::ItemLocalId) -> Option<Scope> {
//! Returns the scope when temp created by expr_id will be cleaned up
// check for a designated rvalue scope
if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
return s;
}
// else, locate the innermost terminating scope
// if there's one. Static items, for instance, won't
// have an enclosing scope, hence no scope will be
// returned.
let mut id = Scope::Node(expr_id);
while let Some(&p) = self.parent_map.get(&id) {
match p.data() {
ScopeData::Destruction(..) => {
debug!("temporary_scope({:?}) = {:?} [enclosing]",
expr_id, id);
return Some(id);
}
_ => id = p
}
}
debug!("temporary_scope({:?}) = None", expr_id);
return None;
}
pub fn var_region(&self, id: hir::ItemLocalId) -> ty::RegionKind {
//! Returns the lifetime of the variable `id`.
let scope = ty::ReScope(self.var_scope(id));
debug!("var_region({:?}) = {:?}", id, scope);
scope
}
pub fn scopes_intersect(&self, scope1: Scope, scope2: Scope)
-> bool {
self.is_subscope_of(scope1, scope2) ||
self.is_subscope_of(scope2, scope1)
}
/// Returns true if `subscope` is equal to or is lexically nested inside `superscope` and false
/// otherwise.
pub fn is_subscope_of(&self,
subscope: Scope,
superscope: Scope)
-> bool {
let mut s = subscope;
debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
while superscope != s {
match self.opt_encl_scope(s) {
None => {
debug!("is_subscope_of({:?}, {:?}, s={:?})=false",
subscope, superscope, s);
return false;
}
Some(scope) => s = scope
}
}
debug!("is_subscope_of({:?}, {:?})=true",
subscope, superscope);
return true;
}
/// Returns the id of the innermost containing body
pub fn containing_body(&self, mut scope: Scope)-> Option<hir::ItemLocalId> {
loop {
if let ScopeData::CallSite(id) = scope.data() {
return Some(id);
}
match self.opt_encl_scope(scope) {
None => return None,
Some(parent) => scope = parent,
}
}
}
/// Finds the nearest common ancestor (if any) of two scopes. That is, finds the smallest
/// scope which is greater than or equal to both `scope_a` and `scope_b`.
pub fn nearest_common_ancestor(&self,
scope_a: Scope,
scope_b: Scope)
-> Scope {
if scope_a == scope_b { return scope_a; }
// Process the lists in tandem from the innermost scope, recording the
// scopes seen so far. The first scope that comes up for a second time
// is the nearest common ancestor.
//
// Note: another way to compute the nearest common ancestor is to get
// the full scope chain for both scopes and then compare the chains to
// find the first scope in a common tail. But getting a parent scope
// requires a hash table lookup, and we often have very long scope
// chains (10s or 100s of scopes) that only differ by a few elements at
// the start. So this algorithm is faster.
let mut ma = Some(scope_a);
let mut mb = Some(scope_b);
let mut seen_a: SmallVec<[Scope; 32]> = SmallVec::new();
let mut seen_b: SmallVec<[Scope; 32]> = SmallVec::new();
loop {
if let Some(a) = ma {
if seen_b.iter().position(|s| *s == a).is_some() {
return a;
}
seen_a.push(a);
ma = self.parent_map.get(&a).map(|s| *s);
}
if let Some(b) = mb {
if seen_a.iter().position(|s| *s == b).is_some() {
return b;
}
seen_b.push(b);
mb = self.parent_map.get(&b).map(|s| *s);
}
if ma.is_none() && mb.is_none() {
break;
}
};
fn outermost_scope(parent_map: &FxHashMap<Scope, Scope>, scope: Scope) -> Scope {
let mut scope = scope;
loop {
match parent_map.get(&scope) {
Some(&superscope) => scope = superscope,
None => break scope,
}
}
}
// In this (rare) case, the two regions belong to completely different
// functions. Compare those fn for lexical nesting. The reasoning
// behind this is subtle. See the "Modeling closures" section of the
// README in infer::region_constraints for more details.
let a_root_scope = outermost_scope(&self.parent_map, scope_a);
let b_root_scope = outermost_scope(&self.parent_map, scope_b);
match (a_root_scope.data(), b_root_scope.data()) {
(ScopeData::Destruction(a_root_id),
ScopeData::Destruction(b_root_id)) => {
if self.closure_is_enclosed_by(a_root_id, b_root_id) {
// `a` is enclosed by `b`, hence `b` is the ancestor of everything in `a`
scope_b
} else if self.closure_is_enclosed_by(b_root_id, a_root_id) {
// `b` is enclosed by `a`, hence `a` is the ancestor of everything in `b`
scope_a
} else {
// neither fn encloses the other
bug!()
}
}
_ => {
// root ids are always Node right now
bug!()
}
}
}
/// Assuming that the provided region was defined within this `ScopeTree`,
/// returns the outermost `Scope` that the region outlives.
pub fn early_free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
br: &ty::EarlyBoundRegion)
-> Scope {
let param_owner = tcx.parent_def_id(br.def_id).unwrap();
let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
let scope = tcx.hir.maybe_body_owned_by(param_owner_id).map(|body_id| {
tcx.hir.body(body_id).value.hir_id.local_id
}).unwrap_or_else(|| {
// The lifetime was defined on node that doesn't own a body,
// which in practice can only mean a trait or an impl, that
// is the parent of a method, and that is enforced below.
assert_eq!(Some(param_owner_id), self.root_parent,
"free_scope: {:?} not recognized by the \
region scope tree for {:?} / {:?}",
param_owner,
self.root_parent.map(|id| tcx.hir.local_def_id(id)),
self.root_body.map(|hir_id| DefId::local(hir_id.owner)));
// The trait/impl lifetime is in scope for the method's body.
self.root_body.unwrap().local_id
});
Scope::CallSite(scope)
}
/// Assuming that the provided region was defined within this `ScopeTree`,
/// returns the outermost `Scope` that the region outlives.
pub fn free_scope<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, fr: &ty::FreeRegion)
-> Scope {
let param_owner = match fr.bound_region {
ty::BoundRegion::BrNamed(def_id, _) => {
tcx.parent_def_id(def_id).unwrap()
}
_ => fr.scope
};
// Ensure that the named late-bound lifetimes were defined
// on the same function that they ended up being freed in.
assert_eq!(param_owner, fr.scope);
let param_owner_id = tcx.hir.as_local_node_id(param_owner).unwrap();
let body_id = tcx.hir.body_owned_by(param_owner_id);
Scope::CallSite(tcx.hir.body(body_id).value.hir_id.local_id)
}
/// Checks whether the given scope contains a `yield`. If so,
/// returns `Some((span, expr_count))` with the span of a yield we found and
/// the number of expressions and patterns appearing before the `yield` in the body + 1.
/// If there a are multiple yields in a scope, the one with the highest number is returned.
pub fn yield_in_scope(&self, scope: Scope) -> Option<(Span, usize)> {
self.yield_in_scope.get(&scope).cloned()
}
/// Checks whether the given scope contains a `yield` and if that yield could execute
/// after `expr`. If so, it returns the span of that `yield`.
/// `scope` must be inside the body.
pub fn yield_in_scope_for_expr(&self,
scope: Scope,
expr: ast::NodeId,
body: &'tcx hir::Body) -> Option<Span> {
self.yield_in_scope(scope).and_then(|(span, count)| {
let mut visitor = ExprLocatorVisitor {
id: expr,
result: None,
expr_and_pat_count: 0,
};
visitor.visit_body(body);
if count >= visitor.result.unwrap() {
Some(span)
} else {
None
}
})
}
/// Gives the number of expressions visited in a body.
/// Used to sanity check visit_expr call count when
/// calculating generator interiors.
pub fn body_expr_count(&self, body_id: hir::BodyId) -> Option<usize> {
self.body_expr_count.get(&body_id).map(|r| *r)
}
}
/// 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<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, blk: &'tcx hir::Block) {
debug!("resolve_block(blk.id={:?})", blk.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() {
if let hir::StmtDecl(..) = statement.node {
// Each StmtDecl 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::Remainder(BlockRemainder {
block: blk.hir_id.local_id,
first_statement_index: FirstStatementIndex::new(i)
})
);
visitor.cx.var_parent = visitor.cx.parent;
}
visitor.visit_stmt(statement)
}
walk_list!(visitor, visit_expr, &blk.expr);
}
visitor.cx = prev_cx;
}
fn resolve_arm<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, arm: &'tcx hir::Arm) {
visitor.terminating_scopes.insert(arm.body.hir_id.local_id);
if let Some(ref expr) = arm.guard {
visitor.terminating_scopes.insert(expr.hir_id.local_id);
}
intravisit::walk_arm(visitor, arm);
}
fn resolve_pat<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, pat: &'tcx hir::Pat) {
visitor.record_child_scope(Scope::Node(pat.hir_id.local_id));
// If this is a binding then record the lifetime of that binding.
if let PatKind::Binding(..) = pat.node {
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<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, stmt: &'tcx hir::Stmt) {
let stmt_id = visitor.tcx.hir.node_to_hir_id(stmt.node.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<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>, expr: &'tcx hir::Expr) {
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.node {
// Conditional or repeating scopes are always terminating
// scopes, meaning that temporaries cannot outlive them.
// This ensures fixed size stacks.
hir::ExprBinary(codemap::Spanned { node: hir::BiAnd, .. }, _, ref r) |
hir::ExprBinary(codemap::Spanned { node: hir::BiOr, .. }, _, ref r) => {
// For shortcircuiting operators, mark the RHS as a terminating
// scope since it only executes conditionally.
terminating(r.hir_id.local_id);
}
hir::ExprIf(ref expr, ref then, Some(ref otherwise)) => {
terminating(expr.hir_id.local_id);
terminating(then.hir_id.local_id);
terminating(otherwise.hir_id.local_id);
}
hir::ExprIf(ref expr, ref then, None) => {
terminating(expr.hir_id.local_id);
terminating(then.hir_id.local_id);
}
hir::ExprLoop(ref body, _, _) => {
terminating(body.hir_id.local_id);
}
hir::ExprWhile(ref expr, ref body, _) => {
terminating(expr.hir_id.local_id);
terminating(body.hir_id.local_id);
}
hir::ExprMatch(..) => {
visitor.cx.var_parent = visitor.cx.parent;
}
hir::ExprAssignOp(..) | hir::ExprIndex(..) |
hir::ExprUnary(..) | hir::ExprCall(..) | hir::ExprMethodCall(..) => {
// 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);
}
_ => {}
}
}
match expr.node {
// Manually recurse over closures, because they are the only
// case of nested bodies that share the parent environment.
hir::ExprClosure(.., body, _, _) => {
let body = visitor.tcx.hir.body(body);
visitor.visit_body(body);
}
_ => 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::ExprYield(..) = expr.node {
// Mark this expr's scope and all parent scopes as containing `yield`.
let mut scope = Scope::Node(expr.hir_id.local_id);
loop {
visitor.scope_tree.yield_in_scope.insert(scope,
(expr.span, visitor.expr_and_pat_count));
// 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<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
pat: Option<&'tcx hir::Pat>,
init: Option<&'tcx hir::Expr>) {
debug!("resolve_local(pat={:?}, init={:?})", pat, init);
let blk_scope = visitor.cx.var_parent;
// 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) {
record_rvalue_scope(visitor, &expr, blk_scope);
}
}
}
// Make sure we visit the initializer first, so expr_and_pat_count remains correct
if let Some(expr) = init {
visitor.visit_expr(expr);
}
if let Some(pat) = pat {
visitor.visit_pat(pat);
}
/// True if `pat` match the `P&` nonterminal:
///
/// P& = ref X
/// | StructName { ..., P&, ... }
/// | VariantName(..., 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.node {
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.node.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::TupleStruct(_, ref subpats, _) |
PatKind::Tuple(ref subpats, _) => {
subpats.iter().any(|p| is_binding_pat(&p))
}
PatKind::Box(ref subpat) => {
is_binding_pat(&subpat)
}
_ => false,
}
}
/// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
///
/// E& = & ET
/// | StructName { ..., f: E&, ... }
/// | [ ..., E&, ... ]
/// | ( ..., E&, ... )
/// | {...; E&}
/// | box E&
/// | E& as ...
/// | ( E& )
fn record_rvalue_scope_if_borrow_expr<'a, 'tcx>(
visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
expr: &hir::Expr,
blk_id: Option<Scope>)
{
match expr.node {
hir::ExprAddrOf(_, ref subexpr) => {
record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
record_rvalue_scope(visitor, &subexpr, blk_id);
}
hir::ExprStruct(_, ref fields, _) => {
for field in fields {
record_rvalue_scope_if_borrow_expr(
visitor, &field.expr, blk_id);
}
}
hir::ExprArray(ref subexprs) |
hir::ExprTup(ref subexprs) => {
for subexpr in subexprs {
record_rvalue_scope_if_borrow_expr(
visitor, &subexpr, blk_id);
}
}
hir::ExprCast(ref subexpr, _) => {
record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
}
hir::ExprBlock(ref block, _) => {
if let Some(ref subexpr) = block.expr {
record_rvalue_scope_if_borrow_expr(
visitor, &subexpr, blk_id);
}
}
_ => {}
}
}
/// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
/// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
/// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
/// statement.
///
/// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
/// `<rvalue>` as `blk_id`:
///
/// ET = *ET
/// | ET[...]
/// | ET.f
/// | (ET)
/// | <rvalue>
///
/// Note: ET is intended to match "rvalues or places based on rvalues".
fn record_rvalue_scope<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
expr: &hir::Expr,
blk_scope: Option<Scope>) {
let mut expr = expr;
loop {
// Note: give all the expressions matching `ET` with the
// extended temporary lifetime, not just the innermost rvalue,
// because in codegen if we must compile e.g. `*rvalue()`
// into a temporary, we request the temporary scope of the
// outer expression.
visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
match expr.node {
hir::ExprAddrOf(_, ref subexpr) |
hir::ExprUnary(hir::UnDeref, ref subexpr) |
hir::ExprField(ref subexpr, _) |
hir::ExprIndex(ref subexpr, _) => {
expr = &subexpr;
}
_ => {
return;
}
}
}
}
}
impl<'a, 'tcx> RegionResolutionVisitor<'a, '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) {
// 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::Destruction(id));
}
self.enter_scope(Scope::Node(id));
}
}
impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
fn visit_block(&mut self, b: &'tcx Block) {
resolve_block(self, b);
}
fn visit_body(&mut self, body: &'tcx hir::Body) {
let body_id = body.id();
let owner_id = self.tcx.hir.body_owner(body_id);
debug!("visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
owner_id,
self.tcx.sess.codemap().span_to_string(body.value.span),
body_id,
self.cx.parent);
let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
let outer_cx = self.cx;
let outer_ts = mem::replace(&mut self.terminating_scopes, FxHashSet());
self.terminating_scopes.insert(body.value.hir_id.local_id);
if let Some(root_id) = self.cx.root_id {
self.scope_tree.record_closure_parent(body.value.hir_id.local_id, root_id);
}
self.cx.root_id = Some(body.value.hir_id.local_id);
self.enter_scope(Scope::CallSite(body.value.hir_id.local_id));
self.enter_scope(Scope::Arguments(body.value.hir_id.local_id));
// The arguments and `self` are parented to the fn.
self.cx.var_parent = self.cx.parent.take();
for argument in &body.arguments {
self.visit_pat(&argument.pat);
}
// The body of the every fn is a root scope.
self.cx.parent = self.cx.var_parent;
if let hir::BodyOwnerKind::Fn = self.tcx.hir.body_owner_kind(owner_id) {
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.is_generator {
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;
}
fn visit_arm(&mut self, a: &'tcx Arm) {
resolve_arm(self, a);
}
fn visit_pat(&mut self, p: &'tcx Pat) {
resolve_pat(self, p);
}
fn visit_stmt(&mut self, s: &'tcx Stmt) {
resolve_stmt(self, s);
}
fn visit_expr(&mut self, ex: &'tcx Expr) {
resolve_expr(self, ex);
}
fn visit_local(&mut self, l: &'tcx Local) {
resolve_local(self, Some(&l.pat), l.init.as_ref().map(|e| &**e));
}
}
fn region_scope_tree<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
-> Lrc<ScopeTree>
{
let closure_base_def_id = tcx.closure_base_def_id(def_id);
if closure_base_def_id != def_id {
return tcx.region_scope_tree(closure_base_def_id);
}
let id = tcx.hir.as_local_node_id(def_id).unwrap();
let scope_tree = if let Some(body_id) = tcx.hir.maybe_body_owned_by(id) {
let mut visitor = RegionResolutionVisitor {
tcx,
scope_tree: ScopeTree::default(),
expr_and_pat_count: 0,
cx: Context {
root_id: None,
parent: None,
var_parent: None,
},
terminating_scopes: FxHashSet(),
};
let body = tcx.hir.body(body_id);
visitor.scope_tree.root_body = Some(body.value.hir_id);
// If the item is an associated const or a method,
// record its impl/trait parent, as it can also have
// lifetime parameters free in this body.
match tcx.hir.get(id) {
hir::map::NodeImplItem(_) |
hir::map::NodeTraitItem(_) => {
visitor.scope_tree.root_parent = Some(tcx.hir.get_parent(id));
}
_ => {}
}
visitor.visit_body(body);
visitor.scope_tree
} else {
ScopeTree::default()
};
Lrc::new(scope_tree)
}
pub fn provide(providers: &mut Providers) {
*providers = Providers {
region_scope_tree,
..*providers
};
}
impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
fn hash_stable<W: StableHasherResult>(&self,
hcx: &mut StableHashingContext<'a>,
hasher: &mut StableHasher<W>) {
let ScopeTree {
root_body,
root_parent,
ref body_expr_count,
ref parent_map,
ref var_map,
ref destruction_scopes,
ref rvalue_scopes,
ref closure_tree,
ref yield_in_scope,
} = *self;
hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
root_body.hash_stable(hcx, hasher);
root_parent.hash_stable(hcx, hasher);
});
body_expr_count.hash_stable(hcx, hasher);
parent_map.hash_stable(hcx, hasher);
var_map.hash_stable(hcx, hasher);
destruction_scopes.hash_stable(hcx, hasher);
rvalue_scopes.hash_stable(hcx, hasher);
closure_tree.hash_stable(hcx, hasher);
yield_in_scope.hash_stable(hcx, hasher);
}
}
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