[drop tracking] Use parent expression for scope

Previously we were just using the parent node as the scope for a
temporary value, but it turns out this is too narrow. For example, in
an expression like

    Foo {
        b: &42,
        a: async { 0 }.await,
    }

the scope for the &42 was set to the ExprField node for `b: &42`, when
we actually want to use the Foo struct expression.

We fix this by recursively searching through parent nodes until we find
a Node::Expr. It may be that we don't find one, and if so that's okay,
we will just fall back on the enclosing temporary scope which is always
sufficient.

Author: eholk

compiler/rustc_typeck/src/check/generator_interior.rs

@@ -387,6 +387,18 @@ impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
             ty.needs_drop(self.fcx.tcx, self.fcx.param_env)
         };
 
+        let find_parent_expr = |mut hir_id| {
+            let hir = self.fcx.tcx.hir();
+            hir_id = hir.find_parent_node(hir_id)?;
+            loop {
+                if let hir::Node::Expr(_) = self.fcx.tcx.hir().find(hir_id)? {
+                    return Some(hir_id);
+                } else {
+                    hir_id = hir.find_parent_node(hir_id)?;
+                }
+            }
+        };
+
         // Typically, the value produced by an expression is consumed by its parent in some way,
         // so we only have to check if the parent contains a yield (note that the parent may, for
         // example, store the value into a local variable, but then we already consider local
@@ -409,8 +421,9 @@ impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
             }) {
             self.rvalue_scopes.temporary_scope(self.region_scope_tree, expr.hir_id.local_id)
         } else {
-            debug!("parent_node: {:?}", self.fcx.tcx.hir().find_parent_node(expr.hir_id));
-            match self.fcx.tcx.hir().find_parent_node(expr.hir_id) {
+            let parent_expr = find_parent_expr(expr.hir_id);
+            debug!("parent_expr: {:?}", parent_expr);
+            match parent_expr {
                 Some(parent) => Some(Scope { id: parent.local_id, data: ScopeData::Node }),
                 None => {
                     self.rvalue_scopes.temporary_scope(self.region_scope_tree, expr.hir_id.local_id)

compiler/rustc_typeck/src/check/generator_interior/drop_ranges/record_consumed_borrow.rs

@@ -159,8 +159,8 @@ impl<'tcx> expr_use_visitor::Delegate<'tcx> for ExprUseDelegate<'tcx> {
         bk: rustc_middle::ty::BorrowKind,
     ) {
         debug!(
-            "borrow: place_with_id = {place_with_id:?}, diag_expr_id={diag_expr_id:?}, \
-            borrow_kind={bk:?}"
+            "borrow: place_with_id = {place_with_id:#?}, diag_expr_id={diag_expr_id:#?}, \
+            borrow_kind={bk:#?}"
         );
 
         self.borrow_place(place_with_id);

src/test/ui/async-await/issue-73137.rs

@@ -2,6 +2,9 @@
 
 // run-pass
 // edition:2018
+// revisions: normal drop-tracking
+// [normal]compile-flags: -Zdrop-tracking=no
+// [drop-tracking]compile-flags: -Zdrop-tracking
 
 #![allow(dead_code)]
 use std::future::Future;