1 files changed, 57 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/rvalue_scopes.rs b/compiler/rustc_middle/src/ty/rvalue_scopes.rs
new file mode 100644
index 000000000..e86dafae3
--- /dev/null
+++ b/compiler/rustc_middle/src/ty/rvalue_scopes.rs
@@ -0,0 +1,57 @@
+use crate::middle::region::{Scope, ScopeData, ScopeTree};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_hir as hir;
+
+/// `RvalueScopes` is a mapping from sub-expressions to _extended_ lifetime as determined by
+/// rules laid out in `rustc_typeck::check::rvalue_scopes`.
+#[derive(TyEncodable, TyDecodable, Clone, Debug, Default, Eq, PartialEq, HashStable)]
+pub struct RvalueScopes {
+    map: FxHashMap<hir::ItemLocalId, 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.
+    pub fn temporary_scope(
+        &self,
+        region_scope_tree: &ScopeTree,
+        expr_id: hir::ItemLocalId,
+    ) -> 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;
+        }
+
+        // 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 { id: expr_id, data: ScopeData::Node };
+
+        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);
+                }
+                _ => id = p,
+            }
+        }
+
+        debug!("temporary_scope({expr_id:?}) = None");
+        None
+    }
+
+    /// 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.item_local_id());
+        }
+        self.map.insert(var, lifetime);
+    }
+}