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rust/src/librustc/middle/region.rs
Niko Matsakis 8a6118b748 move InlinedItem into librustc, where it belongs
2015-08-14 20:07:55 -04:00

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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 actually contains two passes related to regions. The first
//! pass builds up the `scope_map`, which describes the parent links in
//! the region hierarchy. The second pass infers which types must be
//! region parameterized.
//!
//! Most of the documentation on regions can be found in
//! `middle/typeck/infer/region_inference.rs`
use ast_map;
use metadata::inline::InlinedItem;
use middle::ty::{self, Ty};
use session::Session;
use util::nodemap::{FnvHashMap, FnvHashSet, NodeMap};
use std::cell::RefCell;
use syntax::codemap::{self, Span};
use syntax::{ast, visit};
use syntax::ast::{Block, Item, FnDecl, NodeId, Arm, Pat, Stmt, Expr, Local};
use syntax::ast_util::stmt_id;
use syntax::ptr::P;
use syntax::visit::{Visitor, FnKind};
/// CodeExtent represents a statically-describable extent that can be
/// used to bound the lifetime/region for values.
///
/// `Misc(node_id)`: Any AST node that has any extent at all has the
/// `Misc(node_id)` extent. Other variants represent special cases not
/// immediately derivable from the abstract syntax tree structure.
///
/// `DestructionScope(node_id)` represents the extent 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 `RegionMaps`.
///
/// `Remainder(BlockRemainder { block, statement_index })` represents
/// the extent 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 extents beneath:
/// ```
/// 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.): Misc extent of the whole `let a = ...;` statement.
/// (M2.): Misc extent of the `f()` expression.
/// (M3.): Misc extent of the `f().g(..)` expression.
/// (M4.): Misc extent of the block labelled `'b:`.
/// (M5.): Misc extent of the `let x = d();` statement
/// (D6.): DestructionScope for temporaries created during M5.
/// (R7.): Remainder extent for block `'b:`, stmt 0 (let x = ...).
/// (M8.): Misc Extent of the `let y = d();` statement.
/// (D9.): DestructionScope for temporaries created during M8.
/// (R10.): Remainder extent 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 misc extents, 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.
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
RustcDecodable, Debug, Copy)]
pub enum CodeExtent {
Misc(ast::NodeId),
// extent of parameters passed to a function or closure (they
// outlive its body)
ParameterScope { fn_id: ast::NodeId, body_id: ast::NodeId },
// extent of destructors for temporaries of node-id
DestructionScope(ast::NodeId),
// extent of code following a `let id = expr;` binding in a block
Remainder(BlockRemainder)
}
/// extent of destructors for temporaries of node-id
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
RustcDecodable, Debug, Copy)]
pub struct DestructionScopeData {
pub node_id: ast::NodeId
}
impl DestructionScopeData {
pub fn new(node_id: ast::NodeId) -> DestructionScopeData {
DestructionScopeData { node_id: node_id }
}
pub fn to_code_extent(&self) -> CodeExtent {
CodeExtent::DestructionScope(self.node_id)
}
}
/// 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 `CodeExtent::Remainder`,
/// but instead another `CodeExtent` that encompasses the whole block,
/// e.g. `CodeExtent::Misc`.
///
/// * 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: ast::NodeId,
pub first_statement_index: usize,
}
impl CodeExtent {
/// Creates a scope that represents the dynamic extent associated
/// with `node_id`.
pub fn from_node_id(node_id: ast::NodeId) -> CodeExtent {
CodeExtent::Misc(node_id)
}
/// Returns a node 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 node_id(&self) -> ast::NodeId {
match *self {
CodeExtent::Misc(node_id) => node_id,
// These cases all return rough approximations to the
// precise extent denoted by `self`.
CodeExtent::Remainder(br) => br.block,
CodeExtent::DestructionScope(node_id) => node_id,
CodeExtent::ParameterScope { fn_id: _, body_id } => body_id,
}
}
/// Maps this scope to a potentially new one according to the
/// NodeId transformer `f_id`.
pub fn map_id<F>(&self, mut f_id: F) -> CodeExtent where
F: FnMut(ast::NodeId) -> ast::NodeId,
{
match *self {
CodeExtent::Misc(node_id) => CodeExtent::Misc(f_id(node_id)),
CodeExtent::Remainder(br) =>
CodeExtent::Remainder(BlockRemainder {
block: f_id(br.block), first_statement_index: br.first_statement_index }),
CodeExtent::DestructionScope(node_id) =>
CodeExtent::DestructionScope(f_id(node_id)),
CodeExtent::ParameterScope { fn_id, body_id } =>
CodeExtent::ParameterScope { fn_id: f_id(fn_id), body_id: f_id(body_id) },
}
}
/// Returns the span of this CodeExtent. Note that in general the
/// returned span may not correspond to the span of any node id in
/// the AST.
pub fn span(&self, ast_map: &ast_map::Map) -> Option<Span> {
match ast_map.find(self.node_id()) {
Some(ast_map::NodeBlock(ref blk)) => {
match *self {
CodeExtent::ParameterScope { .. } |
CodeExtent::Misc(_) |
CodeExtent::DestructionScope(_) => Some(blk.span),
CodeExtent::Remainder(r) => {
assert_eq!(r.block, blk.id);
// Want span for extent 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].span;
Some(Span { lo: stmt_span.hi, ..blk.span })
}
}
}
Some(ast_map::NodeExpr(ref expr)) => Some(expr.span),
Some(ast_map::NodeStmt(ref stmt)) => Some(stmt.span),
Some(ast_map::NodeItem(ref item)) => Some(item.span),
Some(_) | None => None,
}
}
}
/// The region maps encode information about region relationships.
pub struct RegionMaps {
/// `scope_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.)
scope_map: RefCell<FnvHashMap<CodeExtent, CodeExtent>>,
/// `var_map` maps from a variable or binding id to the block in
/// which that variable is declared.
var_map: RefCell<NodeMap<CodeExtent>>,
/// `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`).
rvalue_scopes: RefCell<NodeMap<CodeExtent>>,
/// `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: RefCell<FnvHashSet<CodeExtent>>,
/// 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 middle::infer::region_inference for
/// more details.
fn_tree: RefCell<NodeMap<ast::NodeId>>,
}
/// Carries the node id for the innermost block or match expression,
/// for building up the `var_map` which maps ids to the blocks in
/// which they were declared.
#[derive(PartialEq, Eq, Debug, Copy, Clone)]
enum InnermostDeclaringBlock {
None,
Block(ast::NodeId),
Statement(DeclaringStatementContext),
Match(ast::NodeId),
FnDecl { fn_id: ast::NodeId, body_id: ast::NodeId },
}
impl InnermostDeclaringBlock {
fn to_code_extent(&self) -> Option<CodeExtent> {
let extent = match *self {
InnermostDeclaringBlock::None => {
return Option::None;
}
InnermostDeclaringBlock::FnDecl { fn_id, body_id } =>
CodeExtent::ParameterScope { fn_id: fn_id, body_id: body_id },
InnermostDeclaringBlock::Block(id) |
InnermostDeclaringBlock::Match(id) => CodeExtent::from_node_id(id),
InnermostDeclaringBlock::Statement(s) => s.to_code_extent(),
};
Option::Some(extent)
}
}
/// Contextual information for declarations introduced by a statement
/// (i.e. `let`). It carries node-id's for statement and enclosing
/// block both, as well as the statement's index within the block.
#[derive(PartialEq, Eq, Debug, Copy, Clone)]
struct DeclaringStatementContext {
stmt_id: ast::NodeId,
block_id: ast::NodeId,
stmt_index: usize,
}
impl DeclaringStatementContext {
fn to_code_extent(&self) -> CodeExtent {
CodeExtent::Remainder(BlockRemainder {
block: self.block_id,
first_statement_index: self.stmt_index,
})
}
}
#[derive(PartialEq, Eq, Debug, Copy, Clone)]
enum InnermostEnclosingExpr {
None,
Some(ast::NodeId),
Statement(DeclaringStatementContext),
}
impl InnermostEnclosingExpr {
fn to_code_extent(&self) -> Option<CodeExtent> {
let extent = match *self {
InnermostEnclosingExpr::None => {
return Option::None;
}
InnermostEnclosingExpr::Statement(s) =>
s.to_code_extent(),
InnermostEnclosingExpr::Some(parent_id) =>
CodeExtent::from_node_id(parent_id),
};
Some(extent)
}
}
#[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 middle::infer::region_inference for more
/// details.
root_id: Option<ast::NodeId>,
/// the scope that contains any new variables declared
var_parent: InnermostDeclaringBlock,
/// region parent of expressions etc
parent: InnermostEnclosingExpr,
}
struct RegionResolutionVisitor<'a> {
sess: &'a Session,
// Generated maps:
region_maps: &'a RegionMaps,
cx: Context
}
impl RegionMaps {
pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(&CodeExtent, &CodeExtent) {
for (child, parent) in self.scope_map.borrow().iter() {
e(child, parent)
}
}
pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&ast::NodeId, &CodeExtent) {
for (child, parent) in self.var_map.borrow().iter() {
e(child, parent)
}
}
pub fn each_rvalue_scope<E>(&self, mut e:E) where E: FnMut(&ast::NodeId, &CodeExtent) {
for (child, parent) in self.rvalue_scopes.borrow().iter() {
e(child, parent)
}
}
pub fn each_terminating_scope<E>(&self, mut e:E) where E: FnMut(&CodeExtent) {
for scope in self.terminating_scopes.borrow().iter() {
e(scope)
}
}
/// Records that `sub_fn` is defined within `sup_fn`. 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_fn_parent(&self, sub_fn: ast::NodeId, sup_fn: ast::NodeId) {
debug!("record_fn_parent(sub_fn={:?}, sup_fn={:?})", sub_fn, sup_fn);
assert!(sub_fn != sup_fn);
let previous = self.fn_tree.borrow_mut().insert(sub_fn, sup_fn);
assert!(previous.is_none());
}
fn fn_is_enclosed_by(&self, mut sub_fn: ast::NodeId, sup_fn: ast::NodeId) -> bool {
let fn_tree = self.fn_tree.borrow();
loop {
if sub_fn == sup_fn { return true; }
match fn_tree.get(&sub_fn) {
Some(&s) => { sub_fn = s; }
None => { return false; }
}
}
}
pub fn record_encl_scope(&self, sub: CodeExtent, sup: CodeExtent) {
debug!("record_encl_scope(sub={:?}, sup={:?})", sub, sup);
assert!(sub != sup);
self.scope_map.borrow_mut().insert(sub, sup);
}
fn record_var_scope(&self, var: ast::NodeId, lifetime: CodeExtent) {
debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
assert!(var != lifetime.node_id());
self.var_map.borrow_mut().insert(var, lifetime);
}
fn record_rvalue_scope(&self, var: ast::NodeId, lifetime: CodeExtent) {
debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
assert!(var != lifetime.node_id());
self.rvalue_scopes.borrow_mut().insert(var, lifetime);
}
/// Records that a scope is a TERMINATING SCOPE. Whenever we create automatic temporaries --
/// e.g. by an expression like `a().f` -- they will be freed within the innermost terminating
/// scope.
fn mark_as_terminating_scope(&self, scope_id: CodeExtent) {
debug!("record_terminating_scope(scope_id={:?})", scope_id);
self.terminating_scopes.borrow_mut().insert(scope_id);
}
pub fn opt_encl_scope(&self, id: CodeExtent) -> Option<CodeExtent> {
//! Returns the narrowest scope that encloses `id`, if any.
self.scope_map.borrow().get(&id).cloned()
}
#[allow(dead_code)] // used in middle::cfg
pub fn encl_scope(&self, id: CodeExtent) -> CodeExtent {
//! Returns the narrowest scope that encloses `id`, if any.
match self.scope_map.borrow().get(&id) {
Some(&r) => r,
None => { panic!("no enclosing scope for id {:?}", id); }
}
}
/// Returns the lifetime of the local variable `var_id`
pub fn var_scope(&self, var_id: ast::NodeId) -> CodeExtent {
match self.var_map.borrow().get(&var_id) {
Some(&r) => r,
None => { panic!("no enclosing scope for id {:?}", var_id); }
}
}
pub fn temporary_scope(&self, expr_id: ast::NodeId) -> Option<CodeExtent> {
//! Returns the scope when temp created by expr_id will be cleaned up
// check for a designated rvalue scope
match self.rvalue_scopes.borrow().get(&expr_id) {
Some(&s) => {
debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
return Some(s);
}
None => { }
}
// 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 = match self.opt_encl_scope(CodeExtent::from_node_id(expr_id)) {
Some(i) => i,
None => { return None; }
};
while !self.terminating_scopes.borrow().contains(&id) {
match self.opt_encl_scope(id) {
Some(p) => {
id = p;
}
None => {
debug!("temporary_scope({:?}) = None", expr_id);
return None;
}
}
}
debug!("temporary_scope({:?}) = {:?} [enclosing]", expr_id, id);
return Some(id);
}
pub fn var_region(&self, id: ast::NodeId) -> ty::Region {
//! 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: CodeExtent, scope2: CodeExtent)
-> 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: CodeExtent,
superscope: CodeExtent)
-> bool {
let mut s = subscope;
while superscope != s {
match self.scope_map.borrow().get(&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;
}
/// 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: CodeExtent,
scope_b: CodeExtent)
-> CodeExtent {
if scope_a == scope_b { return scope_a; }
let a_ancestors = ancestors_of(self, scope_a);
let b_ancestors = ancestors_of(self, scope_b);
let mut a_index = a_ancestors.len() - 1;
let mut b_index = b_ancestors.len() - 1;
// Here, [ab]_ancestors is a vector going from narrow to broad.
// The end of each vector will be the item where the scope is
// defined; if there are any common ancestors, then the tails of
// the vector will be the same. So basically we want to walk
// backwards from the tail of each vector and find the first point
// where they diverge. If one vector is a suffix of the other,
// then the corresponding scope is a superscope of the other.
if a_ancestors[a_index] != b_ancestors[b_index] {
// In this 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
// middle::infer::region_inference for more details.
let a_root_scope = a_ancestors[a_index];
let b_root_scope = a_ancestors[a_index];
return match (a_root_scope, b_root_scope) {
(CodeExtent::DestructionScope(a_root_id),
CodeExtent::DestructionScope(b_root_id)) => {
if self.fn_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.fn_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
unreachable!()
}
}
_ => {
// root ids are always Misc right now
unreachable!()
}
};
}
loop {
// Loop invariant: a_ancestors[a_index] == b_ancestors[b_index]
// for all indices between a_index and the end of the array
if a_index == 0 { return scope_a; }
if b_index == 0 { return scope_b; }
a_index -= 1;
b_index -= 1;
if a_ancestors[a_index] != b_ancestors[b_index] {
return a_ancestors[a_index + 1];
}
}
fn ancestors_of(this: &RegionMaps, scope: CodeExtent) -> Vec<CodeExtent> {
// debug!("ancestors_of(scope={:?})", scope);
let mut result = vec!(scope);
let mut scope = scope;
loop {
match this.scope_map.borrow().get(&scope) {
None => return result,
Some(&superscope) => {
result.push(superscope);
scope = superscope;
}
}
// debug!("ancestors_of_loop(scope={:?})", scope);
}
}
}
}
/// Records the current parent (if any) as the parent of `child_scope`.
fn record_superlifetime(visitor: &mut RegionResolutionVisitor,
child_scope: CodeExtent,
_sp: Span) {
match visitor.cx.parent.to_code_extent() {
Some(parent_scope) =>
visitor.region_maps.record_encl_scope(child_scope, parent_scope),
None => {}
}
}
/// Records the lifetime of a local variable as `cx.var_parent`
fn record_var_lifetime(visitor: &mut RegionResolutionVisitor,
var_id: ast::NodeId,
_sp: Span) {
match visitor.cx.var_parent.to_code_extent() {
Some(parent_scope) =>
visitor.region_maps.record_var_scope(var_id, parent_scope),
None => {
// this can happen in extern fn declarations like
//
// extern fn isalnum(c: c_int) -> c_int
}
}
}
fn resolve_block(visitor: &mut RegionResolutionVisitor, blk: &ast::Block) {
debug!("resolve_block(blk.id={:?})", blk.id);
let prev_cx = visitor.cx;
let blk_scope = CodeExtent::Misc(blk.id);
// If block 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 extent of
// the destructors that run immediately after the the block itself
// completes.
if visitor.region_maps.terminating_scopes.borrow().contains(&blk_scope) {
let dtor_scope = CodeExtent::DestructionScope(blk.id);
record_superlifetime(visitor, dtor_scope, blk.span);
visitor.region_maps.record_encl_scope(blk_scope, dtor_scope);
} else {
record_superlifetime(visitor, blk_scope, blk.span);
}
// 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 initalizer 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.cx = Context {
root_id: prev_cx.root_id,
var_parent: InnermostDeclaringBlock::Block(blk.id),
parent: InnermostEnclosingExpr::Some(blk.id),
};
{
// This block should be kept approximately in sync with
// `visit::walk_block`. (We manually walk the block, rather
// than call `walk_block`, in order to maintain precise
// `InnermostDeclaringBlock` information.)
for (i, statement) in blk.stmts.iter().enumerate() {
if let ast::StmtDecl(_, stmt_id) = 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.
let declaring = DeclaringStatementContext {
stmt_id: stmt_id,
block_id: blk.id,
stmt_index: i,
};
record_superlifetime(
visitor, declaring.to_code_extent(), statement.span);
visitor.cx = Context {
root_id: prev_cx.root_id,
var_parent: InnermostDeclaringBlock::Statement(declaring),
parent: InnermostEnclosingExpr::Statement(declaring),
};
}
visitor.visit_stmt(&**statement)
}
visit::walk_expr_opt(visitor, &blk.expr)
}
visitor.cx = prev_cx;
}
fn resolve_arm(visitor: &mut RegionResolutionVisitor, arm: &ast::Arm) {
let arm_body_scope = CodeExtent::from_node_id(arm.body.id);
visitor.region_maps.mark_as_terminating_scope(arm_body_scope);
match arm.guard {
Some(ref expr) => {
let guard_scope = CodeExtent::from_node_id(expr.id);
visitor.region_maps.mark_as_terminating_scope(guard_scope);
}
None => { }
}
visit::walk_arm(visitor, arm);
}
fn resolve_pat(visitor: &mut RegionResolutionVisitor, pat: &ast::Pat) {
record_superlifetime(visitor, CodeExtent::from_node_id(pat.id), pat.span);
// If this is a binding (or maybe a binding, I'm too lazy to check
// the def map) then record the lifetime of that binding.
match pat.node {
ast::PatIdent(..) => {
record_var_lifetime(visitor, pat.id, pat.span);
}
_ => { }
}
visit::walk_pat(visitor, pat);
}
fn resolve_stmt(visitor: &mut RegionResolutionVisitor, stmt: &ast::Stmt) {
let stmt_id = stmt_id(stmt);
debug!("resolve_stmt(stmt.id={:?})", stmt_id);
let stmt_scope = CodeExtent::from_node_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 extent of the
// statement plus its destructors, and thus the extent for which
// regions referenced by the destructors need to survive.
visitor.region_maps.mark_as_terminating_scope(stmt_scope);
let dtor_scope = CodeExtent::DestructionScope(stmt_id);
visitor.region_maps.record_encl_scope(stmt_scope, dtor_scope);
record_superlifetime(visitor, dtor_scope, stmt.span);
let prev_parent = visitor.cx.parent;
visitor.cx.parent = InnermostEnclosingExpr::Some(stmt_id);
visit::walk_stmt(visitor, stmt);
visitor.cx.parent = prev_parent;
}
fn resolve_expr(visitor: &mut RegionResolutionVisitor, expr: &ast::Expr) {
debug!("resolve_expr(expr.id={:?})", expr.id);
let expr_scope = CodeExtent::Misc(expr.id);
// If expr 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 extent of
// the destructors that run immediately after the the expression
// itself completes.
if visitor.region_maps.terminating_scopes.borrow().contains(&expr_scope) {
let dtor_scope = CodeExtent::DestructionScope(expr.id);
record_superlifetime(visitor, dtor_scope, expr.span);
visitor.region_maps.record_encl_scope(expr_scope, dtor_scope);
} else {
record_superlifetime(visitor, expr_scope, expr.span);
}
let prev_cx = visitor.cx;
visitor.cx.parent = InnermostEnclosingExpr::Some(expr.id);
{
let region_maps = &mut visitor.region_maps;
let terminating = |e: &P<ast::Expr>| {
let scope = CodeExtent::from_node_id(e.id);
region_maps.mark_as_terminating_scope(scope)
};
let terminating_block = |b: &P<ast::Block>| {
let scope = CodeExtent::from_node_id(b.id);
region_maps.mark_as_terminating_scope(scope)
};
match expr.node {
// Conditional or repeating scopes are always terminating
// scopes, meaning that temporaries cannot outlive them.
// This ensures fixed size stacks.
ast::ExprBinary(codemap::Spanned { node: ast::BiAnd, .. }, _, ref r) |
ast::ExprBinary(codemap::Spanned { node: ast::BiOr, .. }, _, ref r) => {
// For shortcircuiting operators, mark the RHS as a terminating
// scope since it only executes conditionally.
terminating(r);
}
ast::ExprIf(_, ref then, Some(ref otherwise)) => {
terminating_block(then);
terminating(otherwise);
}
ast::ExprIf(ref expr, ref then, None) => {
terminating(expr);
terminating_block(then);
}
ast::ExprLoop(ref body, _) => {
terminating_block(body);
}
ast::ExprWhile(ref expr, ref body, _) => {
terminating(expr);
terminating_block(body);
}
ast::ExprMatch(..) => {
visitor.cx.var_parent = InnermostDeclaringBlock::Match(expr.id);
}
ast::ExprAssignOp(..) | ast::ExprIndex(..) |
ast::ExprUnary(..) | ast::ExprCall(..) | ast::ExprMethodCall(..) => {
// FIXME(#6268) 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);
}
_ => {}
}
}
visit::walk_expr(visitor, expr);
visitor.cx = prev_cx;
}
fn resolve_local(visitor: &mut RegionResolutionVisitor, local: &ast::Local) {
debug!("resolve_local(local.id={:?},local.init={:?})",
local.id,local.init.is_some());
// For convenience in trans, associate with the local-id the var
// scope that will be used for any bindings declared in this
// pattern.
let blk_scope = visitor.cx.var_parent.to_code_extent()
.unwrap_or_else(|| visitor.sess.span_bug(
local.span, "local without enclosing block"));
visitor.region_maps.record_var_scope(local.id, blk_scope);
// 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 lvalues
// 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().x]`
// would have an extended lifetime, but not `foo()`.
//
// Rule C. `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.
//
// FIXME(#6308) -- Note that `[]` patterns work more smoothly post-DST.
match local.init {
Some(ref expr) => {
record_rvalue_scope_if_borrow_expr(visitor, &**expr, blk_scope);
let is_borrow =
if let Some(ref ty) = local.ty { is_borrowed_ty(&**ty) } else { false };
if is_binding_pat(&*local.pat) || is_borrow {
record_rvalue_scope(visitor, &**expr, blk_scope);
}
}
None => { }
}
visit::walk_local(visitor, local);
/// True if `pat` match the `P&` nonterminal:
///
/// P& = ref X
/// | StructName { ..., P&, ... }
/// | VariantName(..., P&, ...)
/// | [ ..., P&, ... ]
/// | ( ..., P&, ... )
/// | box P&
fn is_binding_pat(pat: &ast::Pat) -> bool {
match pat.node {
ast::PatIdent(ast::BindByRef(_), _, _) => true,
ast::PatStruct(_, ref field_pats, _) => {
field_pats.iter().any(|fp| is_binding_pat(&*fp.node.pat))
}
ast::PatVec(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))
}
ast::PatEnum(_, Some(ref subpats)) |
ast::PatTup(ref subpats) => {
subpats.iter().any(|p| is_binding_pat(&**p))
}
ast::PatBox(ref subpat) => {
is_binding_pat(&**subpat)
}
_ => false,
}
}
/// True if `ty` is a borrowed pointer type like `&int` or `&[...]`.
fn is_borrowed_ty(ty: &ast::Ty) -> bool {
match ty.node {
ast::TyRptr(..) => true,
_ => 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(visitor: &mut RegionResolutionVisitor,
expr: &ast::Expr,
blk_id: CodeExtent) {
match expr.node {
ast::ExprAddrOf(_, ref subexpr) => {
record_rvalue_scope_if_borrow_expr(visitor, &**subexpr, blk_id);
record_rvalue_scope(visitor, &**subexpr, blk_id);
}
ast::ExprStruct(_, ref fields, _) => {
for field in fields {
record_rvalue_scope_if_borrow_expr(
visitor, &*field.expr, blk_id);
}
}
ast::ExprVec(ref subexprs) |
ast::ExprTup(ref subexprs) => {
for subexpr in subexprs {
record_rvalue_scope_if_borrow_expr(
visitor, &**subexpr, blk_id);
}
}
ast::ExprUnary(ast::UnUniq, ref subexpr) => {
record_rvalue_scope_if_borrow_expr(visitor, &**subexpr, blk_id);
}
ast::ExprCast(ref subexpr, _) |
ast::ExprParen(ref subexpr) => {
record_rvalue_scope_if_borrow_expr(visitor, &**subexpr, blk_id)
}
ast::ExprBlock(ref block) => {
match block.expr {
Some(ref subexpr) => {
record_rvalue_scope_if_borrow_expr(
visitor, &**subexpr, blk_id);
}
None => { }
}
}
_ => {
}
}
}
/// 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 lvalues based on rvalues".
fn record_rvalue_scope<'a>(visitor: &mut RegionResolutionVisitor,
expr: &'a ast::Expr,
blk_scope: CodeExtent) {
let mut expr = expr;
loop {
// Note: give all the expressions matching `ET` with the
// extended temporary lifetime, not just the innermost rvalue,
// because in trans if we must compile e.g. `*rvalue()`
// into a temporary, we request the temporary scope of the
// outer expression.
visitor.region_maps.record_rvalue_scope(expr.id, blk_scope);
match expr.node {
ast::ExprAddrOf(_, ref subexpr) |
ast::ExprUnary(ast::UnDeref, ref subexpr) |
ast::ExprField(ref subexpr, _) |
ast::ExprTupField(ref subexpr, _) |
ast::ExprIndex(ref subexpr, _) |
ast::ExprParen(ref subexpr) => {
expr = &**subexpr;
}
_ => {
return;
}
}
}
}
}
fn resolve_item(visitor: &mut RegionResolutionVisitor, item: &ast::Item) {
// Items create a new outer block scope as far as we're concerned.
let prev_cx = visitor.cx;
visitor.cx = Context {
root_id: None,
var_parent: InnermostDeclaringBlock::None,
parent: InnermostEnclosingExpr::None
};
visit::walk_item(visitor, item);
visitor.cx = prev_cx;
}
fn resolve_fn(visitor: &mut RegionResolutionVisitor,
_: FnKind,
decl: &ast::FnDecl,
body: &ast::Block,
sp: Span,
id: ast::NodeId) {
debug!("region::resolve_fn(id={:?}, \
span={:?}, \
body.id={:?}, \
cx.parent={:?})",
id,
visitor.sess.codemap().span_to_string(sp),
body.id,
visitor.cx.parent);
// This scope covers the function body, which includes the
// bindings introduced by let statements as well as temporaries
// created by the fn's tail expression (if any). It does *not*
// include the fn parameters (see below).
let body_scope = CodeExtent::from_node_id(body.id);
visitor.region_maps.mark_as_terminating_scope(body_scope);
let dtor_scope = CodeExtent::DestructionScope(body.id);
visitor.region_maps.record_encl_scope(body_scope, dtor_scope);
let fn_decl_scope = CodeExtent::ParameterScope { fn_id: id, body_id: body.id };
visitor.region_maps.record_encl_scope(dtor_scope, fn_decl_scope);
record_superlifetime(visitor, fn_decl_scope, body.span);
if let Some(root_id) = visitor.cx.root_id {
visitor.region_maps.record_fn_parent(body.id, root_id);
}
let outer_cx = visitor.cx;
// The arguments and `self` are parented to the fn.
visitor.cx = Context {
root_id: Some(body.id),
parent: InnermostEnclosingExpr::None,
var_parent: InnermostDeclaringBlock::FnDecl {
fn_id: id, body_id: body.id
},
};
visit::walk_fn_decl(visitor, decl);
// The body of the every fn is a root scope.
visitor.cx = Context {
root_id: Some(body.id),
parent: InnermostEnclosingExpr::None,
var_parent: InnermostDeclaringBlock::None
};
visitor.visit_block(body);
// Restore context we had at the start.
visitor.cx = outer_cx;
}
impl<'a, 'v> Visitor<'v> for RegionResolutionVisitor<'a> {
fn visit_block(&mut self, b: &Block) {
resolve_block(self, b);
}
fn visit_item(&mut self, i: &Item) {
resolve_item(self, i);
}
fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v FnDecl,
b: &'v Block, s: Span, n: NodeId) {
resolve_fn(self, fk, fd, b, s, n);
}
fn visit_arm(&mut self, a: &Arm) {
resolve_arm(self, a);
}
fn visit_pat(&mut self, p: &Pat) {
resolve_pat(self, p);
}
fn visit_stmt(&mut self, s: &Stmt) {
resolve_stmt(self, s);
}
fn visit_expr(&mut self, ex: &Expr) {
resolve_expr(self, ex);
}
fn visit_local(&mut self, l: &Local) {
resolve_local(self, l);
}
}
pub fn resolve_crate(sess: &Session, krate: &ast::Crate) -> RegionMaps {
let maps = RegionMaps {
scope_map: RefCell::new(FnvHashMap()),
var_map: RefCell::new(NodeMap()),
rvalue_scopes: RefCell::new(NodeMap()),
terminating_scopes: RefCell::new(FnvHashSet()),
fn_tree: RefCell::new(NodeMap()),
};
{
let mut visitor = RegionResolutionVisitor {
sess: sess,
region_maps: &maps,
cx: Context {
root_id: None,
parent: InnermostEnclosingExpr::None,
var_parent: InnermostDeclaringBlock::None,
}
};
visit::walk_crate(&mut visitor, krate);
}
return maps;
}
pub fn resolve_inlined_item(sess: &Session,
region_maps: &RegionMaps,
item: &InlinedItem) {
let mut visitor = RegionResolutionVisitor {
sess: sess,
region_maps: region_maps,
cx: Context {
root_id: None,
parent: InnermostEnclosingExpr::None,
var_parent: InnermostDeclaringBlock::None
}
};
item.visit(&mut visitor);
}
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