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use rustc_hir as hir;
use rustc_hir::ItemLocalMap;
use rustc_macros::{HashStable, TyDecodable, TyEncodable};
use tracing::debug;
use crate::middle::region::{Scope, ScopeData, ScopeTree};
/// `RvalueScopes` is a mapping from sub-expressions to _extended_ lifetime as determined by
/// rules laid out in `rustc_hir_analysis::check::rvalue_scopes`.
#[derive(TyEncodable, TyDecodable, Clone, Debug, Default, Eq, PartialEq, HashStable)]
pub struct RvalueScopes {
map: ItemLocalMap<Option<Scope>>,
}
impl RvalueScopes {
pub fn new() -> Self {
Self { map: <_>::default() }
}
/// Returns the scope when the temp created by `expr_id` will be cleaned up.
/// It also emits a lint on potential backwards incompatible change to the temporary scope
/// which is *for now* always shortening.
pub fn temporary_scope(
&self,
region_scope_tree: &ScopeTree,
expr_id: hir::ItemLocalId,
) -> (Option<Scope>, Option<Scope>) {
// Check for a designated rvalue scope.
if let Some(&s) = self.map.get(&expr_id) {
debug!("temporary_scope({expr_id:?}) = {s:?} [custom]");
return (s, None);
}
// Otherwise, 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 { local_id: expr_id, data: ScopeData::Node };
let mut backwards_incompatible = None;
while let Some(&p) = region_scope_tree.parent_map.get(&id) {
match p.data {
ScopeData::Destruction => {
debug!("temporary_scope({expr_id:?}) = {id:?} [enclosing]");
return (Some(id), backwards_incompatible);
}
ScopeData::IfThenRescope | ScopeData::MatchGuard => {
debug!("temporary_scope({expr_id:?}) = {p:?} [enclosing]");
return (Some(p), backwards_incompatible);
}
ScopeData::Node
| ScopeData::CallSite
| ScopeData::Arguments
| ScopeData::IfThen
| ScopeData::Remainder(_) => {
// If we haven't already passed through a backwards-incompatible node,
// then check if we are passing through one now and record it if so.
// This is for now only working for cases where a temporary lifetime is
// *shortened*.
if backwards_incompatible.is_none() {
backwards_incompatible = region_scope_tree
.backwards_incompatible_scope
.get(&p.local_id)
.copied();
}
id = p
}
}
}
debug!("temporary_scope({expr_id:?}) = None");
(None, backwards_incompatible)
}
/// Make an association between a sub-expression and an extended lifetime
pub fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
debug!("record_rvalue_scope(var={var:?}, lifetime={lifetime:?})");
if let Some(lifetime) = lifetime {
assert!(var != lifetime.local_id);
}
self.map.insert(var, lifetime);
}
}
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